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Medium Access Control (MAC)
forWireless Body Area Network (WBAN):
Superframe structure, multiple access
technique, taxonomy, andchallenges
Fasee Ullah1,2, Abdul Hanan Abdullah1, Omprakash Kaiwartya3* , Sushil Kumar4 and Marina Md. Arshad1
Introduction
Google search trend verifies the fact that ‘health monitoring’ is in the limelight now-
adays [1]. Health monitoring has achieved a higher ranking as compared to ‘environ-
ment monitoring’ using sensors. is is due to the significant reduction in healthcare
cost by using the technological advancements in health monitoring. e department of
economic and social affairs of the United Nations has a report on the vilest health condi-
tions of elderly aged people [2]. e report states that elderly aged people will be 761 mil-
lion at the age of 60 plus of the total population of world in 2025, which is approximately
Abstract
Health monitoring using biomedical sensors has witnessed significant attention in
recent past due to the evolution of a new research area in sensor network known as
Wireless Body Area Networks (WBANs). In WBANs, a number of implantable, wearable,
and off-body biomedical sensors are utilized to monitor various vital signs of patient’s
body for early detection, and medication of grave diseases. In literature, a number of
Medium Access Control (MAC) protocols for WBANs have been suggested for address-
ing the unique challenges related to reliability, delay, collision and energy in the new
research area. The design of MAC protocols is based on multiple access techniques.
Understanding the basis of MAC protocol designs for identifying their design objec-
tives in broader perspective, is a quite challenging task. In this context, this paper quali-
tatively reviews MAC protocols for WBANs. Firstly, 802.15.4 and 802.15.6 based MAC
Superframe structures are investigated focusing on design objectives. Secondly, dif-
ferent multiple access techniques such as TDMA, CSMA/CA, Slotted Aloha and Hybrid
are explored in terms of design goals. Thirdly, a two-layered taxonomy is presented for
MAC protocols. First layer classification is based on multiple access techniques, whereas
second layer classification is based on design objectives and characteristics of MAC
protocols. Critical and qualitative analysis is carried out for each considered MAC proto-
col. Comparative study of different MAC protocols is also performed. Finally, some open
research challenges in the area are identified with initial research directions.
Keywords: WBAN, MAC Superframe structure, Nature of patient’s data, Scheduling
access schemes, Reliability, Energy
Open Access
© The Author(s) 2017. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License
(http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium,
provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and
indicate if changes were made.
REVIEW
Ullah et al. Hum. Cent. Comput. Inf. Sci. (2017) 7:34
DOI 10.1186/s13673-017-0115-4
*Correspondence:
omprakash.kaiwartya@
northumbria.ac.uk
3 Department of Computer
and Information Sciences,
Northumbria University,
Newcastle upon Tyne NE2
1XE, UK
Full list of author information
is available at the end of the
article
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Ullah et al. Hum. Cent. Comput. Inf. Sci. (2017) 7:34
15% of the whole world’s population. Since, the elderly aged people require more medi-
cal checkup, as they are more in a life threatening situation of various health diseases
[3]. ese regular health checkup and monitoring of real time health conditions incur
higher cost, which is a challenging problem specifically for lower income and developing
countries. e report suggests the usage of technological advancements for health moni-
toring which results in early detection of diseases, and thus, reduction of medical cost.
In health domain, Wireless Body Area Network (WBAN) has got a significant atten-
tion in research and applications development, due to the considerable impact on
patient-care or patient monitoring via biomedical sensors (BMSs) [4]. e real time
health monitoring of patients significantly improves the rate of successful diagnosis in
case of life threatening diseases. It also reduces the cost incurred in diagnosis, due to the
early detection of diseases [5]. WBAN comprises of small BMSs that are wirelessly con-
nected to a Body Area Network Coordinator (BANC) [6]. BMSs can be broadly divided
into three categories, namely; in-body, on-body and off-body sensors [7]. In-body sen-
sors are implanted inside the patient’s body, whereas on-body sensors are sewed to the
shirt or attached on the skin of a patient’s body, and off-body sensors are kept away few
centimeters from a patient’s body [8]. An operation framework of WBANs with these
sensors is presented in Fig.1. BMSs are deployed to monitor different vital signs of a
patient’s body in Tier 1. BMSs forward the monitored data of vital signs to BANC. e
BANC transmits these data to Tier 2. Tier 2 comprises of a Base Station (BS), and it for-
wards the outcomes of vital signs to Tier 3 over the dedicated internet communication
links. Tier 3 includes a computer server, medical staff and transportation facilities [9].
rough this way, the patient’s vital signs are examined by medical staffs, and advice a
treatment. e vital signs monitored via BMSs includes heartbeat rate, respiratory rate,
EEG, ECG, blood pressure, temperature and glucose level [10]. Each category of vital
sign is represented by a specific type of medical data, and is completely different from
other categories of vital signs. erefore, BMSs data is heterogeneous and have different
processing requirements by the medical team, which is based on the category of data.
e responsibility of a BANC is to allocate slots or channels to the monitored vital signs
based on the category of data. Efficient slot allocation is a challenging task due to the
resource constraint involved in sensor network such as limited energy, processing power,
storage and transmission capability [11].
Public Switch
Telephone
Network
(PSTN)
Tier 1
Tier 2
Tier 3
BANC
Implantable Senso
r
Wearable Sensor
Off-Body Sensor
Wirele ss Link
Fig. 1 An overview of communication tiers in WBANs
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Ullah et al. Hum. Cent. Comput. Inf. Sci. (2017) 7:34
Various MAC protocols have been suggested for WBANs to address the slot alloca-
tion problems. ere are two major design decisions have been made in MAC protocols
namely, Superframe structure and multiple access (MA) scheme. e first design deci-
sion, MAC Superframe structure is based on two IEEE standards namely, IEEE 802.15.4
and IEEE 802.15.6. e Superframe structures have different classification of data, frame
format and MA schemes. e second design decision, MA schemes consist of stand-
ard schemes and their combinations, which include Aloha, Slotted Aloha, Time Divi-
sion Multiple Access (TDMA), Frequency Division Multiple Access (FDMA) and carrier
sense multiple access with collision avoidance (CSMA/CA). MAC protocols based on
these MA schemes utilize different approaches for slot allocation such as predefined,
predefined and prediction, contention, non-contention and urgency, probability, alert
and permission. MA scheduling schemes are also known as scheduling access schemes
in WBANs which is interchangeably used in the rest of the paper. e allocation of slots
to emergency and non-emergency data increases collision in CAP channel accessing.
e slot allocation is not an appropriate solution for emergency data. It reduces the per-
formance of MAC protocol in term of insufficient slots for patient’s data, delay, retrans-
mission of collided data packets, frequent invocation of beacon interval (BI), minimum
duration of Superframe and slots, and higher energy consumption. e recent develop-
ments in MAC protocols for WBANs are focusing on these issues.
In this context, this paper qualitatively reviews recent developments on MAC protocol
designs for WBANs. e critical investigation focuses on Superframe structure, multi-
ple access scheme, and taxonomy for MAC protocols. e broad picture of the paper is
summarized below as major contributions of the work:
•Firstly, MAC Superframe structure is classified into two categories, namely, IEEE
802.15.4 and IEEE 802.15.6. Each category has been qualitatively investigated focus-
ing on frame format, classification of a patient’s data, and MA scheduling schemes.
•Secondly, MA schemes are classically explored considering slot allocation and the
impact of slot allocation on the various performance parameters.
•irdly, a two-layered taxonomy for MAC protocols in WBANs is presented. First
layer classification is based on MA techniques, whereas second layer classification is
based on design objectives and characteristics of MAC protocols. Comparative study
of different MAC protocols is also performed.
•Finally, some open research challenges in the area are identified, and the directions of
their solutions are explored.
e rest of the paper is organized as follows. “Related literature reviews” section dis-
cusses various survey papers in WBAN focusing on MAC protocols. “MAC Superframe
structure” section presents a classification of MAC Superframe structure. “Multiple
access scheduling schemes for MAC in WBANs” section discusses MA schemes with
their impact on slot allocation. “Taxonomy of MAC protocols for WBANs” section
reviews MAC protocols following a taxonomy. “Performance evaluation” section dis-
cusses simulation results for performance evaluation. Open research challenges are
identified in “Future challenges” section, followed by conclusion made in “Conclusion”
section.
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Ullah et al. Hum. Cent. Comput. Inf. Sci. (2017) 7:34
Related literature reviews
A survey on WBANs have focused on three layers including routing, MAC and PHY
layers considering IEEE 802.15.6 standard [4, 18]. It has described the communica-
tion range between BMSs for on and in-body with different considerations. However,
the limitations of Superframe structure of IEEE 802.15.4 and PHY layer have not been
identified. In [5, 12], authors have discuss applications of WBAN using different sensors
for in and on body monitoring of a person. IEEE 802.15.4 MAC Superframe structure
has discussed in with using TelOS. It has considered beacon interval (BI), durations of
a slot, and Superframe structure. e selection of these metrics has been investigated
for energy consumption of BMSs in terms of reliability and delay. A survey on channel
interferences, energy, and scheduling access schemes has been conducted considering
IEEE 802.15.4 and IEEE 802.15.6 [8]. ese performance metrics have been considered
based on the importance of the patient’s life. e issues on the design and development
of low-powered BMSs have been in explored, for monitoring of in and out vital signs of
a person in different applications [13]. e issues have been investigated due to the dif-
ferent data rates to transmit the sensory information of a patient for each BMS. Further,
the provision of quality of service has been discussed for MAC and PHY layers consider-
ing IEEE 802.15.4 and IEEE 802.15.6. A similar survey has been presented focusing on
low-powered BMSs [14]. e Superframe structure has been classified into low power
listening, contention and TDMA considering MAC protocols studies. Most of the MAC
protocols have designed for wireless sensor networks (WSNs). However, the require-
ments of WBAN are different due to the heterogeneous nature of a patient’s data, as
compared to the homogeneous nature of data in WSNs.
e frame structure, frequency modulation techniques, and the security authentica-
tion have been focused for MAC and PHY layers in IEEE 802.15.6 [15]. e Narrowband
(NB), Ultra-wideband (UWB), and Human Body Communications (HBC) are the Super-
frame structures, have been considered for human beings to animals using Slotted Aloha
and CSMA/CA. e application, transport, network, MAC and PHY layers have been
considered for Superframe structures of IEEE 802.15.4 and IEEE 802.15.6 in WBAN
[16]. ese layers have been investigated to establish an association between Superframe
structure using Slotted Aloha, CSMA/CA and TDMA. e simulations have been con-
ducted for Superframe structures of Bluetooth, IEEE 802.15.4, and IEEE 802.15.6 in [17].
e performance has been tested on data payload transmission, delay, throughput, and
energy consumption using CSMA/CA and Slotted Aloha. Clearly, it has been investi-
gated from simulations that IEEE 802.15.4 has performed better against IEEE 802.15.6
and Bluetooth. Most of the aforementioned surveys on WBAN have been considering
multiple layers including physical, MAC, and routing. Contrary to theses generalized
surveys, we focus on recent developments in MAC protocols considering Superframe
structure, multiple access scheme, and two-layered taxonomy.
MAC Superframe structure
is section classifies MAC Superframe structures into IEEE 802.15.4 [19] and IEEE
802.15.6 [20] as shown in Fig.2. Each classification is investigated in terms of the Super-
frame format, classification of a patient’s data and MA scheduling access schemes.
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Ullah et al. Hum. Cent. Comput. Inf. Sci. (2017) 7:34
IEEE 802.15.4 based Superframe structure
e BMSs are implanted or attached on the surface of a patient’s body for monitor-
ing of various vital signs of a patient. ese BMSs are connected to a BANC in the star
topology [13]. e patient data are classified into normal, periodic and emergency data.
e normal data comprises of a temperature. e periodic data contains the reading of
glucose and blood pressure. e emergency data contains a life threatening vital signs
information such as low or high threshold value of a heartbeat. Further, the Superframe
structure of IEEE 802.15.4 MAC comprises of a beacon, contention access period (CAP),
contention free period (CFP) and LPL as depicted in Fig.3. In IEEE 802.15.4 MAC, all
BMSs use CSMA/CA access scheme and the CSM/CA-based BMSs perform contention
to access channel in CAP period. During contention, each BMS performs many backoffs
and clear channel assessment (CCA) to access channel [14, 21]. e TDMA scheduling
access scheme is grouped in CFP period and the CFP period allocates the guaranteed
MAC Super-frame structure
IEEE 802.15.4 IEEE 802.15.6
Beacon
CAP
CFP
Inactive Period
Normal
Periodic
Emergency
Enabled Beacon
MAC Superframe
Non-beacon Without
Superframe
Non-beacon
MAC Superframe
Beacon
Type I/II
EAP 1
RAP 1
Type I/II
EAP 2
RAP 2
CAP
CSMA/CA
Slotted Aloha
Normal
Emergency
Type I/II CSMA/CA
Slotted Aloha
Normal
Emergency
16 slots Predefined
Contention
Hybrid
Non-Emergency
Flexible Slot
TDMA and FDMA
Structure Multiple Access Schemes
CSMA/CA and Slotted Aloha
Patient Data Classification
Structure Multiple Access Schemes Patient
Data Classification
Structure Multiple Access Schemes Patient
Data Classification
Type I/II CSMA/CA
Slotted Aloha
Emergency
Structure Multiple Access Schemes
Patient
Data Classification
Fig. 2 Classification of MAC Superframe structures
Beacon CAPCFP Beacon
Inactive Period
0
91011 12 13 14 15
2345678
1
GTS
Fig. 3 IEEE 802.15.4 MAC Superframe structure
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Ullah et al. Hum. Cent. Comput. Inf. Sci. (2017) 7:34
time slots to transmit the patient’s data [22]. However, the BANC allocates the CFP slots
to those BMSs who obtain a channel access in CAP period.
At the beginning of communication, the BANC broadcasts a beacon to all BMSs in the
network which contains information of synchronization, the logical address of BANC,
and the next announcement of the beacon interval (BI). In synchronization, BMSs trans-
mit the request for channel association and dissociation to a BANC. e address of the
BANC is broadcasted to BMSs for remembering it as the head/coordinator for allocating
of channels and data transmission. e BI is the time period whereas each BMS con-
tends and transmits sensory data in the specified amount of time. e inactive period
(IP) is used for saving energy when a BMS is not busy for transmitting sensory data. e
followings are the limitations of the Superframe structure of IEEE 802.15.4 MAC [23] as
follows:
•IEEE 802.15.4 provides limited 16 (0–15) channels.
•All BMSs perform contention to access channel in CAP period.
•Allocation of CFP channels only to those BMSs who obtains a channel access in CAP
period.
•During contention for accessing channel, there is no priority-based slot allocated to
emergency data and is no differentiation between normal, periodic, and emergency
data to assign the first slot on the priority-basis during in the life critical situations.
•No priority based a dedicated slots are occupied for emergency data.
•Due to contention, BMSs consume a higher amount of energy.
•In TDMA, each BMS transmits sensory data in the fixed length of time and drops
data if it has a large amount of data (frame).
•Emergency data face a higher delay due to collision, retransmission of the lost pack-
ets, and limited time period of a BI.
ese limitations severely reduce the performance of a MAC Superframe structure in
terms of lower data reliability, collision and a higher amount of energy consumption.
Moreover, the standard MAC Superframe structure does not support heterogeneous
nature of patient’s data which is not appropriate for emergency data. Numerous research
contributions have been made that are [24–26]. ese papers have modified the Super-
frame structure of IEEE 802.15.4 MAC according to the need of a patient’s data.
IEEE 802.15.6 MAC Superframe structure
ere are two types of communication possible for data transmission in WBAN that is
one-hop and two-hop with the support of star and mesh topologies, respectively [15]. In
one-hop communication, the BANC or hub is a centralized device which is responsible
for allocating of slots to BMSs. In two-hop communication, the relay sensors (interme-
diates sensors) are used to exchange the frames between the sender sensor and BANC
when they are far away from access of each other. Since, the use of the intermediate sen-
sors consume a higher amount of energy during transmission of the patient’s packet
which create overheads in terms of a higher delay and is not feasible during in the life
critical situation of a patient. Hence, IEEE 802.15 Task Group 6 (TG6) was decided to
design low power sensors to monitor the patient’s vital signs and the health conditions
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Ullah et al. Hum. Cent. Comput. Inf. Sci. (2017) 7:34
of a sportsman in different sports activities. e first draft version of IEEE 802.15.6 for
MAC and PHY layers was publicized in 2012 [16]. is draft version describes IEEE
802.15.6 which divides the whole Superframe structure into different channels and bea-
cons. Each channel is assigned an equal time frame to transmit the patient’s data. Fig-
ure4 (re-drawn from [15, 27]) shows an overview of IEEE 802.15.6 MAC Superframe
structure.
e Superframe structure of IEEE 802.15.6 MAC comprises of three main modules
that are MAC header, MAC variable length and frame check sequences (FCS). e MAC
header reserves 7 bytes, the variable length reserves 0–255 bytes and FCS reserves 2
bytes as depicted in Fig.4. e MAC frame body is further categorized into three sub-
headers that are (a) Data Freshness which occupies 1 byte to protect data from the reply
attack, (b) Message Integrity Code (MIC) occupies 4 bytes to authenticate the frame and
maintains the integrity check of a frame, and (c) Data Payload contains data with MIC
headers in the frame. Moreover, IEEE 802.15.6 MAC header is categorized into 4 sub-
headers. First, the Frame Control occupies 4 bytes and uses to distinguish between con-
trol frame and data frame along with an acknowledgment. e second and third headers
are the addresses of the receiver and sender sensors, respectively. Each sensor uses 1
byte to store the address. e BANC header is the final header which occupies 1 byte
to store the address. e slot allocation to the nature of a patient’s data in both IEEE
802.15.4 and IEEE 802.15.6 MACs is the responsibility of a BANC. erefore, the draft
version of IEEE 802.15.6 MAC defines three ways for transmitting the patient’s data [4,
15] which are discussed in the following subsections.
Enabled‑beacon MAC Superframe structure
e enabled-Beacon MAC Superframe structure comprises of a beacon, exclusive access
phase (EAP-I-II), random access phase (RAP-I-II), Type (I–II) and CAP periods as
shown in Fig.5 (re-drawn from [4, 15]). e beacon is used to synchronize BMSs with a
BANC. e channel allocation policy to BMSs is based on CSMA/CA or Slotted Aloha
Frame Control Recipient ID Sender ID BAN ID
MAC Header MAC frame body variable length: 0 -255 byte sFCS
Octets:2
70-255
MHRFTR
Octets:
4111
Fig. 4 802.15.6 MAC Superframe structure
Beacon
EAP1 RAP1
Type I/II EAP2 RAP2 CAP
Beacon
Type I/II
Enabled-Beacon MAC Superframe Structure
Fig. 5 Enabled-Beacon Mode MAC Superframe
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Ullah et al. Hum. Cent. Comput. Inf. Sci. (2017) 7:34
schedule access scheme which are implemented on EAP, RAP and CAP periods. e
EAP-I and EAP-II are reserved for life critical a patient’s data and these critical data are
represented by Type-I in Enabled-beacon MAC. Further, the RAP-I, RAP-II, and CAP
periods are reserved for normal and regular monitoring of the health conditions of a
patient which is represented as Type-II. e enabled-beacon MAC provides only dedi-
cated slots to emergency and non-emergency data as compared to IEEE 802.15.4 MAC.
However, the limitations of IEEE 802.15.6 MAC Superframe structure are the same as
aforementioned in IEEE 802.15.4 MAC as challenging problems.
Non‑beacon MAC Superframe structure
Figure 6 (re-drawn from [4]) shows the structure of non-beacon MAC Superframe
structure. e non-beacon MAC allocates the entire channels (slots) of the Superframe
to Type-I or Type-II category of a patient’s data. During data transmission, the non-bea-
con based BMSs do not require synchronization with a BANC. With this advantage, the
energy consumption of such BMSs is very minimum. e disadvantage is that the BANC
cannot transmit data directly to BMSs but it must first transmit an activation alert signal
to the recipient BMS. e second disadvantage is that the non-beacon MAC allocates
slots to one type of a patient’s data at one time which is not an acceptable during life
critical situations of a patient.
Non‑beacon withoutSuperframe structure
is type of structure of Superframe does not use the predefined periods to transmit
all types of a patient’s data but it is designed for scenario of Type-II. In this Superframe
structure, the slot allocation to BMSs is based on contention or post-contention. e
advantage of this structure is that the non-emergency based BMSs do not interrupt con-
tention of emergency-based BMSs. However, the predefined allocation of slots to one
type of sensory data is the wastage of slots.
Comparative analysis ofMAC Superframe structures
IEEE 802.11, IEEE 802.15, and IEEE 802.15.1 [17] are not capable to monitor and detect
early abnormal conditions of a patient. However, IEEE 802.15.4 has the capabilities to
monitor and detects abnormal conditions and transmit the sensory data to a BANC with
the higher data reliability [28]. Lots of researchers have been modified the Superframe
structure of IEEE 802.15.4 MAC and used for WBAN. Table1 presents characteristics of
IEEE 802.15.4 MAC and compares with IEEE 802.15.6 MAC [29].
Patient traffic types
Type I or Type II
Superframe (Beacon period)
Fig. 6 Non-beacon MAC Superframe
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Ullah et al. Hum. Cent. Comput. Inf. Sci. (2017) 7:34
Multiple access scheduling schemes forMAC inWBANs
e slots allocation activities to BMSs in MAC Superframe structure of IEEE 802.15.4
are carried out with the support of different multiple access (MA) scheduling schemes.
e scheduling access schemes can reduce collision, delay, avoids retransmission of the
lost packets and energy consumption. us, the existing MA schemes in MAC proto-
cols classifies the scheduling access schemes into three main categories; namely, res-
ervation-based, contention-based and hybrid [12, 14]. ese three scheduling access
schemes assist to allocate slots to heterogeneous nature of a patient’s data. e nature
of patient’s data is divided into three classes as aforementioned. However, the classifica-
tions of a patient’s data into three classes are not justifiable because these classifications
do not discuss low and high threshold values of vital signs and delay-sensitive data. In
fact, the existing literature classifies the patient’s data into four to five classes [25, 30].
e patient’s data are transmitted to the BANC using various scheduling access schemes
as discussed in the following sub-sections.
Reservation‑based slots allocation
e TDMA scheduling access is the reservation-based slots allocation mechanism and
this scheduling access is used for slots of the CFP period of MAC IEEE 802.15.4 Super-
frame structure [18, 31] as aforementioned in Fig.3. e body coordinator divides the
time frames of CFP period into different predefined time frames. Each BMS waits and
transmits sensory data in the allocated predefined time frame as shown in Fig.7. For
example, the nodes 1 and 2 are normal data whereas they transmit in the allocated pre-
defined time frames. e node 3 detects an emergency data (i.e. low or high threshold
value) at the same time during data transmission of nodes 1 and 2. In this life-critical
situation, the node 3 must wait and transmit emergency data in the predefined allocated
Table 1 Comparison ofIEEE 802.15.4 and802.15.6 based onSuperframe
Characteristics IEEE 802.15.4 IEEE 802.15.6
Domain-specific task Sensors applications to monitor and
detect an events from environ-
ments like home temperature
monitoring, pipeline leakage
detection, and battlefield, etc
Specially designed for healthcare
related domains
Nature of data Homogenous Heterogeneous
Network deployment range 10–100 m 3–6 m
Network coverage Scalable Medium
Support of min-to-max sensors 10–65,000 3–256
Energy consumption 20–35 mW 0.01–40 mW
Frequency band ISM ISM and other approved by medical
authorities for in/on-body such as
UWB PHY
Data transmission medium Air Air, on-body, in-body
Data transmission rate 20 kb/s to max 250 kb/s 50 kb/s to Max 10 mb/s
Safety precautions for deployed
environment Varies situation to situation but uses
SAR in WBAN Yes, use SAR for measuring of tem-
perature in/out organs of a patient
Scheduling access scheme CSMA/CA, TDMA, FDMA, Aloha CSMA/CA, TDMA, FDMA, Aloha
Controls overhead Low Average
Channel allocation mechanism to
end-devices Contention, polling and alert based Contention and post-allocation
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Ullah et al. Hum. Cent. Comput. Inf. Sci. (2017) 7:34
time frame. Hence, the predefined-based time frame allocation is not suitable for emer-
gency data due to the long waiting period which degrades the performance of MAC
Superframe structure as well as ruins the patient’s life.
Contention‑based slots allocation
e most widely adopted scheduling access scheme is the CSMA/CA due to its sim-
plicity, and infrastructure-free for data transmission [18]. e slot allocation policy of
CSMA/CA access scheme to BMSs is based on first come first serve (FCFS) mechanism
[32] and it is implemented on CAP period of IEEE 802.15.4 MAC Superframe struc-
ture. During contention, each BMS performs contention to access slot (channel) in CAP
period and all BMSs have the equal probability of accessing CAP slots [33]. Further, the
body coordinator allocates the CFP slots to those BMSs who obtain a channel access
in CAP period. Due to this challenging problem, the contention-based slot allocation
to emergency data is not suitable because of collisions, retransmits the lost packets, a
higher delay with lower data reliability and BMSs consume a higher energy [34].
FDMA‑based ofTDMA slots allocation
e TDMA are the guaranteed timeslots for sending of a patient’s data to the medical
doctor. Some research articles such as [35] has changed the contention of the BMSs for
accessing channel in the CAP period and is using the frequency division multiple access
(FDMA) for contention. e FDMA divides channels into different frequencies and
timeslots whereas each BMS contends and transmits data within a specific amount of
time without a higher of collisions of data packets and delay.
Hybrid‑based slots allocation
e hybrid-based slots allocations to BMSs are the combination of TDMA and CSMA/
CA scheduling access schemes. e TDMA-based slots are used for emergency-based
BMSs whereas these types of BMSs transmit alert signals to the body coordinator dur-
ing detection of low or high threshold values of vital signs. e non-emergency based
BMSs perform contention with the support of a CSMA/CA access scheme for access-
ing channel in CAP period. e existing studies [25, 30] divide the CFP slots into emer-
gency transfer slots (ETSs), data transfer slots (DTSs) and emergency beacon (EB). e
patient’s data are divided into Critical data Packet (CP), Reliability data Packet (RP),
Delay data Packet (DP) and, Ordinary data Packet (OP) [30, 36]. e CP and RP are
the emergency data while DP and OP are non-emergency data. e body coordinator
Node 1
Time Frame
Node 2
Time Frame
Node 3
Time Frame
Body Coordinato
r
Node 1
Node 2
Node 3
Fig. 7 TDMA-based slots allocation to BMSs
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Ullah et al. Hum. Cent. Comput. Inf. Sci. (2017) 7:34
reserves the DTS slots for non-emergency data and allocates to those non-emergency
based BMSs who obtains a channel access in CAP period. In a similar way, the emer-
gency-based BMSs transmit alert signals using EB slots during detection of emergency
data. e decision of slots allocation on the priority basis depends on the criticality level
of sensory data as described as
Priority
=
Sensory_Data
G∗S
. Where the Priority is assigned to
four types of a patient’s data, Sensory_data is the detected data of different vital signs,
G is the data generation rate, and S is the size of a vital sign in bytes. However, the pro-
posed protocol does not low and high threshold values of vital signs which is the limita-
tion of this protocol.
Comparative analysis ofMA scheduling schemes
In wireless communication, the data transmission between BMSs and the body coor-
dinator is scheduled with the support of scheduling access schemes [37]. It has been
noticed that most of the MAC schemes use TDMA with CSMA/CA scheduling access
schemes for allocating of slots in CFP and CAP periods, respectively. e high energy
consumption, a higher delay, low throughput and data collision are the most challenging
problems during contention for BMSs for accessing channel which degrades the perfor-
mance of MAC protocol. In a similar way, TDMA-based BMSs wait and transmit data in
their predefined time slots. us, both scheduling accessing schemes are not suitable for
emergency-based BMSs due to contention and the long waiting period. Table2 [38, 39]
presents and compares different functionalities of both scheduling schemes in terms of
power, bandwidth, traffic, network, packet delivery and synchronization. However, the
energy consumption of CSMA/CA access scheme is higher as compared to TDMA. In
fact, we can enhance the performance of both scheduling access schemes with the sup-
port of network simulator 2 (NS2) [40].
Taxonomy ofMAC protocols forWBANs
In this section, MAC protocols for WBANs have been investigated on the basis of the
taxonomy presented in Fig.8. In this taxonomy, MAC protocol designs are classified
in two levels. e first level of classification contains seven categorizes of MAC proto-
col designs which is based on MA schemes. e second level of classification is further
divided into one, two and three sub-categories which are based on the specific slot allo-
cation approach followed in the category. Each of the MAC protocols studied under tax-
onomy are investigated considering Superframe structure, MA schemes, classification
of the patient’s data, slot allocation process based on the classification of data and their
Table 2 Comparison ofTDMA andCSMA/CA functionalities
Function TDMA CSMA/CA
Power consumption Low High
Bandwidth utilization Maximum Low
Preferred Traffic level High Low
Dynamic network Average Good
Effect of packet failure Latency Low
Synchronization Essential N/A
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Ullah et al. Hum. Cent. Comput. Inf. Sci. (2017) 7:34
impact on performance parameters such as data reliability, delay, throughput, collision
and energy consumption.
TDMA based MAC protocols
e TDMA based MAC protocols are divided into predefined and predefined with pre-
diction based slot allocation to a patient’s data. Each BMS waits for transmitting data
in the predefined time slot. During the wait period, a BMS drops data and consumes a
higher energy which degrades the performance of MAC protocol. e predefined slot
allocation process is not acceptable for emergency data in terms of the lower data reli-
ability with a higher delay. Lots of research contributions have been made to resolve the
addressed problems and are discussed different MAC protocols in the followings.
e TDMA based changeable Superframe structure comprises the Control data and
Sensing data as depicted in Fig.9 (re-drawn from [34]). e Control data contains a syn-
chronization, broadcast, power detection, neighboring information upload and schedul-
ing assignment slots. e Sensing data is used for synchronizing clocks of BMSs with the
body coordinator before data transmission. Since, the body coordinator broadcasts the
control schedule data to all BMSs for occupying different slots. ese slots are ‘power
MACProtocols in WBAN
TDMA basedMAC
EP-MAC[35]
TPL-MAC[29]
AN-MAC[15]
CA-MAC[46]
A-MAC[48]
F-MAC[49]
RF-MAC[51]
AN-MAC[15]
PNP-MAC[20]
ATLAS[21]
A-MAC[48]
CSMA/CA with
TDMA basedMAC
Contention Non-Contention &
Urgency HybridPredefined slot Allocation Predefined &Predictionbased
slot Allocation
E-MAC[34]
PE-MAC [40]
EL-MAC[41]
EF-MAC [42]
AE-MAC [43]
I-MAC [44]
HD-MAC [45]
EP-MAC[35]
CSMA/CA with
AlohaMAC
Contention Predefined Probability
U-MAC[52]
AC-MAC [53]
U-MAC[52]
AC-MAC[53]
SlottedAloha MAC
Contention
A-MAC[55]
Permission based
HR-MAC [54]
MS-MAC [56]
Hybrid Approaches
basedMAC
TDMA with FDMA
MAC
Contention Alertbased Hybrid
PE-MAC [19] PE-MAC [19] CO-MAC [59]
TDMA with Frame
Slotted Aloha MAC
Pre-Allocated &Alert
based Hybrid
UW-MAC [26]
LPDQ [57]
PG-MAC [58]
HEH-BMAC[60]
WMAC [61]
TAD-MAC[62]
EDSA [63]
ULW-MAC[64]
TAF[65]
TRRS [66]
ART-GAS [32]
BodyMAC [47]
PTA[50]
BodyMAC[47]
Fig. 8 Taxonomy of MAC protocols for WBANs
Data Slots
Sensing Data
Control Data
Schedule
Assignment
UploadPower De tection
Synchron ization
Broadcast
12N + 2N + 3 2N + 2 2N + 5 3N + 4
Fig. 9 Energy efficient Superframe structure
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Ullah et al. Hum. Cent. Comput. Inf. Sci. (2017) 7:34
detection’, ‘information uploading’ and ‘schedule assignment’. During data transmission,
the body coordinator uses neighboring upload slot field for calculating the path and slot
schedule which are transmitted to BMSs with the support of schedule assignment field.
In this way, each node transmits data in the assigned timeslots with transmission power.
However, the suggested scheme [34] uses many control fields which creates overheads
for BMSs to execute all fields. e another limitation is that each sensor waits for its turn
for transmitting data in the pre-allocated timeslot which is not suitable for emergency
data due to a higher delay in the life-critical condition.
e suggested protocol in [41] reduces energy by using state transition with the sup-
port of wake-up radio and main radio. e wakeup radio comprises of the sleep and
wakeup states. e main radio contains idle (ready) state, Tx and Rx states. e default
state of nodes is the sleep state. Both wake-up radio and main radio use wake-up state
for periodic data (normal data) and random data (emergency data) transmission, respec-
tively. e limitation of [41] is that each BMS either normal or emergency-based BMS
waits and transmits data in the predefined time slot. With the waiting period degrades
the performance of MAC protocol in terms of collisions, a higher delay with lower data
reliability and higher energy consumption which is not appropriate for emergency data.
e second limitation is that the suggested protocol does not differentiate between low
and high threshold values of vital signs.
e suggested Superframe structure of MAC comprises of Control data and Sensing
data as depicted in Fig.10 (re-drawn from [42]). e control data contains a beacon,
broadcast, information exchange, upload information, and schedule assignment. e
sensing data field contains data slots whereas each node sends or receives data in the
predefined time slot. In the beginning of communication, the beacon and broadcast are
transmitted by the body coordinator to all nodes in the network for synchronization and
information exchange, uploading data and schedule assignment, respectively. Since, each
node calculates the transmission timeslots and sends back to the body coordinator. e
calculation step is processed in the information exchange phase and upload information.
In the upload information session, at a time one sensor can upload data and the body
coordinator stops other sensors for sending data. However, this scheme [42] consumes a
higher energy of sensors due to the outnumbers of control overheads which are used in
the data transmission. e blockage of other sensors suffers the patient’s life which is not
acceptable for real time health domain and also reduces the performance of MAC proto-
col in terms of a higher delay with lower data reliability.
Table3 presents the analysis of different MAC protocols in terms of data reliability and
energy consumption of nodes during the long waiting period and data transmission. e
predefined-based slot allocation to nodes is reducing data reliability in terms of a higher
Data Slots
Sensing Data
Control Data
Schedule
Assignment
Upload
Broadcast
Info Exchange
12N + 1 2N + 1 2N + 4 3N + 3
N + 2
Beacon
Fig. 10 Energy Efficient MAC Superframe Structure
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Ullah et al. Hum. Cent. Comput. Inf. Sci. (2017) 7:34
delay which drops patient’s data and consumes a higher energy consumption of nodes.
erefore, the predefined scheduling schemes are suitable for non-emergency data and
are not suitable for emergency data.
Predened andprediction based slot allocation
e Medical MAC (MedMAC) protocol [43] is using TDMA scheduling access scheme
and classifies the patient’s data into 0, 1 and 2 classes. e class-0 comprises of a low-
grade data such as temperature and respiratory rate. e class-1 comprises of a medium-
grade data such as ECG, EEG and blood pressure while class-2 contains a high-grade
data such as EMG, and capsule endoscope. e beacon period of the proposed MAC is
used to allocate a dedicated channel to emergency data when a node detects an unpre-
dictable data. During data transmission, each node transmits the request of synchroni-
zation to the body coordinator. However, the synchronization, the contention and does
not considering the differences between low and high threshold values of two vital signs
reduce the performance of MAC protocol in terms of a higher collision, and delay with
low data reliability.
e allocation of a slot to nodes is based on first come first serve (FCFS) and each node
requires a synchronization with the master node (MN) for data transmission [44]. Since,
the monitoring node (MN) forwards the collected data of vital signs to the monitoring
system (MS). e slot allocation to nodes on the FCFS approach, the emergency-based
sensor drops and it is retransmitted in the extra slot (ES). is protocol [44] consumes
a high amount of energy of sensor nodes during retransmission of the collided data and
also does not differentiate between low and high threshold values of vital signs. us,
these parameters reduce the performance of MAC protocol in terms of collision and
higher delay with low data reliability.
e Superframe structure of MAC [45] comprises of Exclusive Access Periods (EAP-I/
II), and Random Access Periods (RAP-I/II) using Traffic types Type-I and Type-II. e
EAP-I and EAP-II are used to transmit emergency data with the support of TYPE-
I. e RAP-I and RAP-II are used to transmit normal/periodic data with the support
Table 3 Analysis ofthe predened based slots allocation
MAC protocol Data reliability Energy consumption Remarks
E-MAC [34]Low High Each sensor waits and transmits data in the pre-
defined time slot. For data transmission, sensors
change the format of Superframe according to
the needs of a patient’s data. With these changes,
sensors consume a higher energy during which
create overhead to execute all fields of Superframe
structure
PE-MAC [41] Medium High Sensors consume more energy in the wakeup radio
and main radio state transitions. The waiting
based transmission of emergency data in the
pre-allocated time increases a chance of dropping
data. The Low and high threshold values are not
considered in this scheme
EL-MAC [42]Low High Sensor consumes a high energy due to outnumbers
of the control overheads and faces a higher delay
which is not appropriate for a life critical patient’s
data
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of TYPE-II. Both Types (I, II) inform the master node to allocate the slots when each
node transmits data in the pre-allocated time slot. However, the master node blocks
other slave nodes during data transmission of the one node in the pre-allocated time slot
which consumes a higher amount of energy of other nodes in waiting. Another draw-
back is that one node can upload information at a time which degrades the performance
of the suggested MAC in terms of a higher delay with the higher packets drop.
e heartbeat rhythm MAC (H-MAC) protocol [46] is suggested whereas the body
coordinator does not broadcast a beacon but it uses heartbeat rhythm for clock synchro-
nization. e purpose of this process is to avoid periodic synchronization and achieves
the minimum energy consumption without turn-on the radio signals. Moreover, the
activation of radio signals is based on the heartbeat peak values (high threshold values)
and valley (low threshold values) values of a patient which are associated with a blood
circulation of the human body. If the blood circulation increases or decreases, the bio-
sensor broadcasts a threshold value and activates the body coordinator to allocate a slot.
However, this scheme [46] does not investigate the decision of slots allocation between
two sensors if both sensors detect low and/or high threshold values of two vital signs at
the same time and transmit to the body coordinator. is challenging problem reduces
the performance of MAC protocol in terms of a higher delay and higher energy con-
sumption which is not suitable in the life threatening conditions. Table4 presents MAC
protocols which are analyzing the predefined and prediction based slot allocation to
BMSs. is type of slot allocation is suitable for non-emergency based BMSs because the
BMSs consume minimum energy with higher data reliability. However, the main draw-
back of these types of MAC protocols is that they cannot decide to allocate the slot on
the priority basis between two vital signs if both sensors detect low and high threshold
values and transmit to the body coordinator at the same time. Due to this challenging
Table 4 Analysis ofpredened andprediction based slot allocation
MAC protocol Data reli‑
ability Energy consump‑
tion Remarks
EF-MAC [43]Low High Higher delay and lower data reliability have been
noticed during contention of multiple nodes to
access channel. This scheme is not suitable to
transmit emergency data of more than one sensor
at a time. In addition, it does not focus on low and
high threshold values of vital signs
AE-MAC [44]Low High Retransmission of the lost packets degrades data reli-
ability. Sensors consume more energy in the wait-
ing state for a beacon to receive from MN which is
not suitable for emergency data
I-MAC [45]Low High Nodes consume a higher energy during the waiting
period to transmit data in their own turns because
the master node locks the services of other slave
nodes which are not suitable in case of emergency
data
HD-MAC [46] Average Low Allocation of the slot is based on the heartbeat in the
predefined time unit. This protocol is not suitable
for life-threatening vital signs due to the long wait-
ing period whereas the body coordinator cannot
decide the slot allocation process between two
vital signs
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problem, the BMSs consume a higher amount of energy and drop sensory data due to
long waiting period.
CSMA/CA withTDMA based MAC protocols
is section explains CSMA/CA with TDMA based MAC protocols in WBAN. As dis-
cussed the challenging problems of IEEE 802.15.4 MAC, the [36] modifies the Super-
frame structure of MAC and classifies the patient’s data into Emergency Data (ED),
Periodic Data (PD), and Normal Data (ND). During contention of sensors if the channel
is busy then ND-based sensor waits for a random amount of time and performs many
backoffs. e PD-based sensor uses TDMA access scheme to transmit data. Further, this
study uses an equation that is
Priority
=
Data type
t∗Psize
which calculates the criticality levels
of sensory data and differentiates between ND and PD for declaring it as ED as repre-
sented by data type. e λt is the generation rate of the packet and Psize is the length of
the generated data. However, the CSMA/CA and TDMA scheduling schemes reduce the
performance of MAC protocol in terms of contention for emergency-based sensors due
to the long waiting period during slots allocation process which is not an appropriate
practice. Another limitation of this protocol does not differentiate between low and high
threshold values of vital signs and also does not resolve the conflict of slots allocation if
two sensors transmit the same types of data at the same time to the body coordinator.
e Priority-based Load Adaptive MAC (PLA-MAC) [29] protocol classifies the
patient’s data into Critical data Packet (CP), Reliability data Packet (RP), Delay data
Packet (DP) and Ordinary Packet (OP). e CP is the first highest critical data and needs
to allocate the first available channel. e RP is second the priority of data for allocat-
ing channel without loss of the packet. e DP is the third priority of data which must
be delivered on time. e OP is the fourth priority of patient’s data that can delay. e
suggested Superframe comprises of a beacon, CAP, notification, CFP, and LPL. e CFP
period is further divided into Emergency Data Transfer Slots (ETSs) and Data Transfer
Slots (DTSs). At the beginning of channel allocation, all nodes perform contention to
access channel in CAP period. e body coordinator allocates ETS slots to those emer-
gency-based sensors who obtain a channel access in CAP period. e non-emergency
based sensors can occupy ETS slots but they must perform a CCA to ensure collision-
free data transmission. However, the suggested protocol [29] consumes a higher energy
of sensors during contention period and does not different between low and high thresh-
old values of vital signs. e contention reduces the performance of MAC in terms of a
higher delay with low data reliability which is not suitable for emergency data.
e preemptive and non-preemptive MAC (PNP-MAC) protocol [25] classifies the
patient’s data into emergency alarm, medical continuous, medical routine, non-medi-
cal continuous and file transfer. e suggested MAC Superframe structure comprises
of an advertisement, Beacon, DTS and ETS. e DTS and ETS slots are grouped into
CFP period. Each node performs contention to access channel in the CAP period. e
body coordinator allocates DTS slots to those sensors who achieve a channel access in
CAP period. Moreover, the body coordinator preempts the low-priority data, i.e. the
non-medical continuous from the DTS slots and assigns the slots of DTS on the arrival
of the high priority data if there is no empty slot available in DTS. In this moment, the
body coordinator transmits a request message to all nodes to de-allocate the slots of the
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DTS and updates their status. e allocation of ETS slots in the life critical conditions
if all slots in DTS are not empty. e limitation of this scheme is the preemption of the
non-critical data from DTS slots on the arrival of critical data which is the drawback of
this scheme in terms of the preempted nodes drop data. e energy consumption of the
nodes is higher due to contention and does not differentiate between critical and non-
critical data to allocate a separate channel without performing of contention.
e Superframe structure of Low-delay Traffic-adaptive Medium Access Control
(LTDA-MAC) [15] comprises of a beacon, fixed CAP, CFP, extended dynamic CFP and
inactive sleep state. At the beginning of communication, the body coordinator broad-
casts a beacon to all nodes in the network for clocks synchronization. During a channel
allocation period, each node competes for a slot in the fixed CAP period along with the
requesting of dynamic CFP slot from a body coordinator. e body coordinator allocates
the fixed CFP and extended CFP slots to those nodes who gets a channel access in the
fixed CAP slot. e limitation of this scheme is that the body coordinator transmits a
notification alert to all nodes for stopping data transmission. With this stopping of data,
the throughput of the MAC is reduced in the terms of a higher dropping of a patient’s
data, a higher delay, and re-transmission of the dropped packet which consumes a
higher energy of nodes. us, these issues badly reduce the performance of MAC proto-
col which cannot allocate the slots to emergency data in an appropriate time.
e MAC Superframe structure of A-Traffic Load Aware Sensor (ATLAS) [26] com-
prises of a beacon, CAP, CFP and IP. e sensory data is transmitted from sensors to
cluster-head (S-to-CH) and cluster-head to the gateway (CH-to-G) using multi-hops.
e CH synchronizes the clock with nodes during slots allocation process. e alloca-
tion of slots to sensory data is based on the traffic load which is divided into low, mod-
erate, high and overload traffic load. e CAP slots and IP of the Superframe structure
are assigned to low load traffic. e gateway assigns CAP, IP and CFP slots to moderate
traffic load. For high load data, the gateway assigns CFP and IP. While the CFP slots
are assigned to overload data. In fact, the drawback of this protocol [26] is the higher
delay in transmitting data to sensor-to-cluster and cluster-to-gateway which consumes
a higher energy of the nodes and is not suitable in the life critical situations of a patient.
e Adaptive and Real-Time GTS Allocation Scheme (ART-GAS) [32] provides ‘ser-
vice differentiation’ and ‘GTS’ slot allocation. Since, the ‘service differentiation’ offers
two types of services that are ‘data-based priority’ and ‘rate-based priority’. e ‘data-
based priority’ devices contain emergency data and these types of emergency data allo-
cate slots on the priority basis. e rate-based priority means data is generated recently
with a high rate and needs a higher attention to transmit it. In this suggested protocol,
each device is configured with different priorities such as CSMA/CA hit-miss and GTS
hit-miss. ese two priorities are used to avoid the wastage of the GTS slots. However,
the contention consumes more energy of emergency-based sensors and reduces the per-
formance of MAC protocol with lower data reliability in terms of collision, delay and
retransmission of the collided packets.
e suggested Superframe structure comprises of a beacon, Emergency-TDMA
(ETDMA), Medical Contention Access Period (MCAP), Normal-TDMA (NTDMA),
CAP, and Emergency Slot (ES) [47]. e ETDMA slots are reserved for emergency data
during an alarming situation. In a similar way, the MCAP slots are used for allocating
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channels when outnumbers of nodes are the alarming situations. For periodic and nor-
mal data, the NTDMA slots are occupied. e following steps are used for allocating of a
slot to emergency data as follows:
1. e emergency-based node tries during contention to transmit emergency data in
CAP slots. However, the successful rate of emergency data transmission in CAP slot
is comparatively very low because the normal-based nodes also perform contention.
2. In the case of failure, the particular node informs the hub in ES slot about an alarm-
ing situation. e collision may also occur in ES slot due to the multiple requests
transmitted by other nodes.
3. In these situations, the nodes drop the packets if data transmission counter is reached
to the maximum threshold values.
e drawback of this protocol [46] is high energy consumption during contention to
access channel whereas the dropping ratio of packets of nodes exceed. Another limi-
tation is that the proposed protocol changes the order of fields of the proposed MAC
Superframe structure which creates overheads for emergency data.
e suggested BodyMAC protocol [47] comprises of a beacon, downlink and uplink.
e downlink is used for a unicast, broadcast message, and control command. e
uplink is used for CAP and CFP slots for sending data to the gateway. e suggested pro-
tocol maintains ‘control-bandwidth’ and ‘data-bandwidth’ requests. e ‘control-band-
width’ request is used by a node when a node contains more than one control packets
and wants to transmit to the gateway. Similarly, the ‘data-bandwidth’ request generates
by the sender node and transmits it to the gateway. e bandwidth of slots is divided
into’ burst bandwidth’, ‘periodic bandwidth’, and ‘adjust-bandwidth’. e ‘adjust-band-
width’ is assigned to nodes on-demands while other types of bandwidth are assigned to
nodes on the temporary basis. However, this protocol [47] consumes a higher energy
during contention to access channel which is not suitable for a patient’s data due to per-
mission-based transmission and reception. e overall performance is not satisfactory
in terms of a high energy consumption and low data reliability.
e suggested MAC Superframe structure of an Adaptive MAC (A-MAC) [48] con-
tains a beacon/synchronization, CFP, CAP, guard-band, and time slot [48]. e suggested
protocol uses data and control packets. e data packets contain the patient’s data and
the control packets contain the channel packet, Time Slot Request (TSR), TSR Reply
(TSRR), Synchronization Acknowledgment (SYN-ACK), Data Request (DR) packet, and
ACK (acknowledgment). During data transmission, the nodes transmit the TSR packet
to the coordinator node (CN) for the allocation of slots. On the successful allocation
of slots, the CN replies with a TSRR to nodes. Further, the node transmits a request of
SYN-ACK for allocating of slots if a node needs a slot before the predefined timeslot. e
DR assists in transmitting on-demand data. However, the suggested A-MAC does not
allocate dedicated slots to emergency data and consumes a higher energy of BMSs dur-
ing contention to access channel. e control packet creates overheads and degrades the
performance of MAC in terms of collision and delay with lower data reliability.
e Fuzzy Control Medium Access (FCMA) [49] implements acquisition, fuzzy
logic control, and implementation phases for handling the non-real time data, normal
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real-time data, abnormal data, and emergency data of a patient body. e data acquisi-
tion phase is used to collect data from the deployed sensors. When a body coordinator
receives the patient’s data then it uses the fuzzy rules to decide whether to assign CAP
or CFP slots. is activity is performed under the fuzzy logic control phase. In the CAP
period, the fuzzy rules manage the Contention Window Size for priority data and data
rate. e priority data represents the patient’s data such as normal, abnormal and emer-
gency. While data rate represents the severity of a patient’s data such as low, medium
and high. e suggested mechanism is suitable for emergency data, but sensors con-
sume a higher amount of energy during contention to access channel. e sensory data
is delayed during the decision making for allocating of slots to sensors.
e Priority-based adaptive Timeslots Allocation (PTA) protocol [48] divides the CAP
slots into phase-1, phase-2, and phase-3 timeslots. e phase-1 slot is assigned to emer-
gency data and is represented by C1 (critical). e phase-2 slot is assigned to contin-
uous and discontinuous data and is represented by C2. In the same way, the phase-3
slot is assigned to an audio/video data and is represented by C3. e allocation of CAP
timeslots to the phase-2 and phase-3 based traffic depends on contention of nodes. e
phase-1 slot is occupied for emergency traffic and cannot occupy by any other type of
traffic. e drawback of this protocol is higher energy consumption during contention
of nodes for accessing channel which is not suitable for emergency data in terms of a
higher delay with lower data reliability.
e Radio Frequency Identification (RFID) based MAC (R-MAC) protocol classifies
the patient’s data into emergency and routine data [51]. e emergency and routine-
based sensors perform contention to access channel using CSMA/CA access scheme.
Moreover, the suggested MAC Superframe structure comprises of a Configurable CAP
(CCAP) slot, CFP guaranteed slots, and IP or LPL. During emergency data, the sensor
will perform contention and will wait for a clear channel access. Since, the body coor-
dinator allocates CFP slots to those nodes who gets a channel access in CCAP period.
However, there is no slot allocate during alarming situations and each sensor contends
to access channel. In these situations, the performance of the suggested protocol is
reduced in terms of a higher delay with higher energy consumption.
Table5 investigates the techniques used for slot allocation to sensors that are con-
tention, non-contention, and urgency. e patient’s data are categorized into different
classes and each type of a patient’s data performs contention for accessing channel in
CAP period. e body coordinator allocates slots of the CFP period to those nodes who
obtains a channel access in CAP period. With this contention, the energy consumption
of nodes is high which reduce data reliability. In TDMA-based approach, each node
waits for transmitting data in the predefined time slot. Both types of scheduling access
schemes are not optimal solutions for emergency data. Hence, the optimal solution is
that the emergency-based node should transmit an alert signal in the guaranteed time
slot for allocating of slot without contention. With this type of data transmission avoids
the conflict of the priority-based slot allocation between two vital signs.
CSMA/CA withAloha based MAC protocols
is section describes the hybrid scheduling access schemes which are the combination
of CSMA/CA and Aloha. An Urgency-based MAC (U-MAC) protocol [53] is used to
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Table 5 Analysis ofCSMA/CA withTDMA based slot allocation MAC protocols
MAC protocol Data reliability Energy consumption Remarks
EP-MAC [36]Low High Sensors consume a high energy during
contention. The high delay is noticed
due to the clock synchronization which
is not suitable for emergency data.
Another limitation of not differentiating
between low and high threshold values
of vital signs
TPL-MAC [30]Low High All sensors perform contention for
accessing channel in CAP period which
effects data reliability and consumes a
higher energy of nodes which is not an
appropriate solution in the life critical
situation
PNP-MAC [25]Low High Sensors consume a high energy when
they contend for slots in CAP. Preempts
other data on the arrival of high priority
data from the allocated slots which
reduces the performance of data reli-
ability due to preemption and sensors
consume more energy
AN-MAC (LTDA-MAC) [23]Low High Nodes consume a high energy during
contention to access channel. Notify
other nodes to terminate data transmis-
sion if there is no empty slot available
in CFP which is not an appropriate
solution for emergency data
ATLAS [26]Low High Allocation of slots depends on the traf-
fic load. The higher delay is faced to
transmit data from sensors-to-cluster
and cluster-to-gateway. This process
consumes a high amount of energy
which is not suitable for emergency
data in terms of outnumbers of emer-
gency data
ART-GAS [32]Low High The different classification of a patient’s
data is represented by low, middle, and
high. The suggested MAC does not
define the priority to allocate dedicated
slots in the alarming situations. With
this shortcoming, the performance of
the suggested MAC is reduced
CA-MAC [47]Low High High energy consumption is noticed due
to contention and data collision which
affects the performance of slots alloca-
tion to emergency data in the alarming
situation
Body-MAC [49] N/A High Sensors consume a high energy during
contention to access channel and is
not suitable for the nature of a patient’s
data due to permission-based slots allo-
cation and data transmission. Gateway
is always ACTIVE which also consumes
a high energy
A-MAC [50]Low High There is no slot allocated for emergency-
based sensors which consume more
energy during contention to access
channel. The control packets create
overheads and reduce the data reli-
ability
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Ullah et al. Hum. Cent. Comput. Inf. Sci. (2017) 7:34
assign priority-based slots to the critical data as compared to non-critical data. e Slot-
ted Aloha channel access method is used with the support of an enabled-beacon con-
trol. At the beginning of data transfer, each node allocates a timeslot whereas a node can
transmit critical and non-critical data. erefore, ‘G’ is the total number of packets which
are ready for transmission at the initial time slot as described as
G
=
x=X
x=1
n=r
x
n=0
C
n
x
[53]. Where ‘x’ is the traffic index, ‘n’ is the retransmission of the lost traffic and its range
is from 1, 2, 3 to rx. e Cx
n is the number of critical and non-critical patient’s data in the
packet. e X (capital) is the supported traffic classes of the
Cn
x
whereas G is the success-
ful packet delivery transmission which must be equal to 1. However, each node transmits
critical and non-critical data in the pre-allocated time slots which reduce data reliability
with higher data collision. Another limitation is nodes consume a higher energy during
contention and reduces the performance of MAC protocol.
A cross-layer based IEEE 802.15.6 Superframe structure is employed for transmit-
ting the patient’s data on the reliable and an efficient path [54]. e proposed protocol
is developed for extended star topology and divides the patient’s data into Emergency
data (EM), Delay Sensitive packets (DS) and General Monitoring packets (GM). e
body coordinator allocates the slots EAPI and EAPII to EM and DS-based sensors dur-
ing data transmission, respectively. GM-based sensors employ RAP (I,II) and CAP slots
for data transmission. e slot allocation priority to EM is highly preferred as compared
to other two types of data which consume minimum energy. However, the data deliv-
ery reliability for EM suddenly goes down when all BMSs continuously transmit data.
Another limitation is that this protocol [54] does not discuss threshold values of vital
signs. Table6 presents the analysis of CSMA/CA with aloha based slot allocation to sen-
sory data. e contention and predefined based slot allocation reduce data reliability and
consume a higher amount of energy of nodes due to collision and a long wait, respec-
tively. However, the probability based slot allocation reduces contention and avoids pre-
defined time slots. With this optimal solution, the energy consumption is reduced, but
it does not solve the conflict of slots between two emergency-based nodes. Hence, the
Table 5 continued
MAC protocol Data reliability Energy consumption Remarks
F-MAC [51]Low High Sensors consume more energy during
contention to access channel. The rules
based assignment of the GTS slots
produces a higher delay during the
verification of different conditions
PTA [48]Low High The reserved slots for emergency-based
BMSs cannot assign to non-emergency
based BMSs if these are empty. This
limitation wastes resources in terms
of higher number of collisions of the
packets, delay with lower data reliability
and BMSs consume more energy
RF-MAC [52]Low High Nodes perform contention to access
channels in CAP period. With these
contentions of nodes reduce the
performance of MAC protocol in terms
of a higher delay and higher energy
consumption
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recommended solution is to allocate dedicated slots to low and high threshold values of
vital signs without interrupting the contention of other nodes.
Slotted Aloha based MAC protocols
An urgency based Distributed Queuing Body Area Network (DQBAN) MAC protocol
[55] is suggested with Collision Resolution Queue (CRQ) and Data Transmission Queue
(DTQ). e CRQ provides a channel access to those sensors which has emergency data
of vital signs. While DTQ is employed to allocate collision-free channels to emergency
sensors. e suggested protocol uses fuzzy logic rules in helping to specify the criticality
level of vital signs and residual energy of a node. e drawback of [55] is that it cannot
decide to allocate slots between two sensors if both detect the same types of emergency
data at the same time.
e suggested Superframe structure of MAC protocol comprises of a beacon, emer-
gency access period (EAP), normal access period (NAP), guaranteed access period
(GAP) and acknowledgement [56]. e EAP period is associated with uplink and down-
link. e uplink is employed to transmit data from BMSs to the body coordinator. e
downlink is employed to transmit data between the body coordinator and BMSs. During
an emergency situation, the BMSs transmit a message to EAP period using contention
and the coordinator replies back with the allocation of GAP slots. However, the energy
consumption of this scheme [56] increases if more BMSs are added to the network
which affects the data reliability in terms of higher data delay and collision.
e Discrete Time Markov Chain mode is employed together with Slotted Aloha slots
in the non-saturated conditions which can access finite number of BMSs (users) [57].
e slot allocation to the higher priority BMSs is given a higher ranking as represented
by CPmax [57]. e data reliability degrades with higher data collision if more BMSs con-
tend to access a slot. However, this scheme does not concentrate on the patient’s data
and energy consumption of BMSs is high during contention. Most of the MAC schemes
allocate slots on the basis of contention as depicted in Table7. e slot allocation conflict
is the same challenging problem as noticed in this analysis. us, the permission-based
slot allocation is an optimal solution to reduce the energy consumption and supports to
increase data reliability.
Table 6 Analysis ofCSMA/CA withAloha based slot allocation MAC protocols
MAC protocol Data reliability Energy consumption Remarks
U-MAC [53]Low High The slot allocation is based on the contention and
predefined time slot. The energy consumption is
high which degrades the data reliability in terms
of a higher delay with collision and does not
acceptable for critical data
AC-MAC [54] High Low The patient’s data are distributed to different
channels, but GM data cannot access the chan-
nel which has reserved for EM. This restriction
improves the performance of MAC in terms of
lower energy consumption with higher data
reliability
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TDMA withFrame Slotted Aloha based MAC protocols
e following contributions design the MAC protocol in WBAN which are based on
TDMA with Frame Slotted Aloha (FSA) scheduling access schemes. e Traffic adaptive
MAC (TaMAC) protocol [28] is suggested to handle normal data, emergency and on-
demand data. e suggested Superframe structure comprises of CCAP and CFP periods.
e CCAP provides Mini-slots to transmit data in the short duration. In the TaMAC
protocol, the wake-up of traffic-pattern is employed for non-emergency data. While
wake-up radio is employed for emergency and on-demand traffic. In an emergency situ-
ation, the sensor transmits an alert signal to the body coordinator and the body coordi-
nator replies with allocation of a channel. e energy consumption is low but sensors
wait to transmit data in their predefined time slot which is the drawback of this protocol
[28] due to outnumber of states in the state-transaction diagram. Another limitation is
that the predefined based slot allocation to normal and emergency data is not acceptable
due to the long wait where sensors drop data.
e Low-Power Distributed Queue (LPDQ) [58] scheme uses LPL, Distributed Queue
(DQ) and Channel Hopping (CH) for ensuring the collision-free transmission, minimize
the delay and reduce energy consumption. e suggested protocol comprises of net-
work synchronization and data transmission phases [58]. In the network synchroniza-
tion phase, all nodes are in LPL state whereas they periodically wake up and turn-on
their radios to assure activities in the network. e DQ and CH are employed in the data
transmission phase. e data transmission phase provides a fixed time structure where
all nodes must transmit their packets by using an access request period (ARP). However,
each sensor transmits an ARP message and waits to occupy channel which reduces the
performance of MAC in terms of higher delay, ACK, retransmission of the lost packets,
and high energy consumption. Another limitation of this scheme does not concentrate
on a patient’s data.
e MAC Superframe structure of [59] comprises of active and inactive parts whereas
body coordinator divides channels into application-specific control and traffic-specific
data channels. e active part is further divided into a beacon, timeslot-has reserved for
periodic traffic (TSRP), timeslot-has reserved for bursty traffic (TSRB), control channel
access (AC) AC1 and AC2 as shown in Fig.11 (re-drawn from [59]). e uplink chan-
nels AC1 and AC2 are used to transmit medical and consumer electronics (CE) data,
respectively using slotted-Aloha access scheme. In the life-critical situation, the body
Table 7 Analysis ofSlotted Aloha based slot allocation MAC protocols
MAC protocol Data reliability Energy consumption Remarks
HR-MAC [55] High Average The energy consumption is minimum and allocates
error-free slots to BMSs. The drawback is that it
cannot decide a slot allocation if the same types
of two emergency data occurred at the same time
A-MAC [56]Low High The contention-based slot allocation and does not
specify the patient’s data in this scheme. The data
reliability is reduced if more BMSs are added to
network
MS-MAC [57]Low High The suggested protocol does not discuss patient’s
data and consumes a higher energy of BMSs dur-
ing contention to access slot. The data reliability
decreases if more BMSs contend to access a slot
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Ullah et al. Hum. Cent. Comput. Inf. Sci. (2017) 7:34
coordinator assigns AC1 channel to the high priority data. For contention-based slot
allocation, the body coordinator calculates how many nodes are performing contention
as described in
N=min{NLf,N
}
[59]. Where N is the total available nodes, λ is the
traffic average arrival rate, and Lf is the waiting duration for the next announcement of
Superframe. However, the suggested MAC protocol [59] consumes a higher amount of
energy of sensors during maintaining the sessions of control ad data channels which cre-
ates overheads. e second limitation is that this scheme does not define low and high
threshold values of vital signs.
e long waits of BMSs in the predefined timeslots drop the patient’s data and BMSs
consume more energy in this period as described in Table8. ese types of BMSs are
instructed to wake up periodically and verify events in the network. However, the desir-
able solution is to transmit an alert command to the body coordinator during emergency
situation where this process assists to resolve the conflict of slot allocation between two
vital signs.
TDMA withFDMA based MAC protocols
is section presents different MAC protocols with combination TDMA and FDMA
scheduling access schemes. e table-based wakeup for normal data and the radio-chip
based wakeup for emergency data are introduced [24]. e patient’s traffic is classified
into normal, on-demand and emergency data. With radio-chip wake up of on-demand
and emergency sensors transmit request for slots allocation with few conditions. First,
the body coordinator transmits a wake-up authentication code (WAC) packet to emer-
gency and on-demand traffic sensors, respectively. Second, the particular sensor com-
pares the received WAC packet with its own generated WAC packet. ird, if the data
packets of both are matched, then data communication link is established and updates
the counter. Fourth, if WAC code does not match or sensors do not have enough energy
TSRP AC1AC2 TSRB Inactiv e
Beacon CFP1 CAPCFP2
Fig. 11 Priority based Superframe structure
Table 8 Analysis ofTDMA withFrame Slotted Aloha based Slot allocation
MAC protocol Data reliability Energy consumption Remarks
UW-MACs [28] Average Low Does not different between low and high threshold
values and drops emergency data if other types of
sensors occupy slots. Each node waits to transmit
data in its predefined time slot
LPDQ [58]Low High Each sensor transmits an ARP and waits for the chan-
nel which increases delay. The sensors re-transmit
the packet, and wakes up periodically to verify any
activity in the network which consumes a higher
energy
PG-MAC [59]Low High The sensors follow the control header and then data
channels which consume a higher energy of BMSs.
No priority is defined for low and high threshold
of vital signs
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Ullah et al. Hum. Cent. Comput. Inf. Sci. (2017) 7:34
to transmit their data, then both on-demand and emergency-based sensors drop data.
However, this authentication process is the expensive practice in the life-critical alarm-
ing situations whereas sensors consume a higher energy and drop the life-threatening
data.
e suggested MAC [35] uses TDMA with FDMA and provides two channels during
data transmission from BMSs to the body coordinator. e TDMA scheduling access
scheme is implemented on the distributed algorithm and provides control and data sec-
tions. e body coordinator uses a control section which supports a beacon to transmit
in the network for synchronization. With this synchronization, the body coordinator
allocates slots to BMSs. e BMSs transmit data in the data section when they receive a
slot allocation message from the body coordinator. e FDMA divides slots into differ-
ent frequencies and time-slots for data transmission. e suggested protocol [35] does
not consider the patient’s data but energy consumption is minimized with collision-free
data transmission. Table9 shows that non-emergency based nodes use contention and
emergency-based nodes transmit alert commands for informing the body coordina-
tor in the life-threatening conditions. e energy consumption and data reliability are
achieved with these processes because the patient’s data are categorized and each type of
data is transmitted in the required slot. Further, an alert based data transmission avoids
contention and consumes minimum energy but it does not resolve the slot conflict dur-
ing allocation to emergency data if both types of a patient’s data are the same status. For
example, if a node H detects low threshold values of a heartbeat and a node R detects
the high threshold value of the respiratory rate. In this situation, both nodes inform the
body coordinator at the same time and the body coordinator cannot decide which of
them should give a higher and lower priority to allocate slots.
Hybrid approaches based MAC protocols
e hybrid based MAC protocols design new scheduling access schemes for allocating
slots to different types of a patient’s data. is section explains each hybrid approach in
the following subsections.
Polling andcontention‑based slot allocation
e Human Energy Harvesting Medium Access Control (HEH-BMAC) protocol is sug-
gested with objectives to re-charge the batteries of wireless nodes from the harvesting
Table 9 Analysis ofTDMA withFDMA based slot allocation MAC protocols
MAC protocol Data reli‑
ability Energy consump‑
tion Remarks
PE-MAC [24] High Low The energy consumption of BMSs is low and provides
a higher data reliability due to distribution and
allocation of the separated channels to each type of
a patient’s data
CO-MAC [35] High Low Each type of a patient’s data is allocated a separated
channel during contention and transmission. By this
process, the energy consumption is reduced and
increases the chance of data transmission higher in
terms of data reliability
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Ullah et al. Hum. Cent. Comput. Inf. Sci. (2017) 7:34
energy of a human, uses ID-polling timeslot for emergency data and the probabilistic
contention (PC) for normal data [60]. e body coordinator node is placed in the center
and assigns the Monitoring Interval (MITID-BN) to each body node (BN) in assisting to
calculate the packet Inter-Arrival Time (IATBN) and constant energy harvesting rate
(KEH). e body coordinator inserts an offset in MITID-BN for avoiding a collision in the
packet inter-arrival time with increasing or decreasing the polling time of a node. In PC
mode, the body coordinator broadcasts the ‘Control Packet’ (CP) to nodes whereas the
nodes define their threshold values (Xi) for data packet transmission. Further, the node
transmits data and gets an acknowledgment reply from the body coordinator if Xi<CP.
If the node does not receive the CP’s packet, then the body coordinator waits for the
predefined interval and sends it back with changing the threshold values. However, the
packet collision occurs if more than one node have the same threshold values for data
transmission, whereas the energy consumption of the nodes become high.
e [60] protocol does not predict in advance which node detects an emergency and
non-emergency data to allocate slots for data transmission accordingly. During data col-
lision, the body coordinator adjusts the threshold values of the sender sensors to build
a gap between their timing and data transmission. With this process, the data reliability
of MAC protocol becomes degraded in terms of delay and consumes a higher energy
of nodes. However, this protocol does not define low and threshold values of vital signs
which is not suitable for emergency data.
Polling based slot allocation
e suggested BodyQoS protocol comprises of an Admission Control, QoS scheduler
and Virtual MAC (VMAC) [61]. e functionalities of admission control and QoS sched-
uler are implemented on the master node (aggregator) and slave nodes (sensors). e
admission control and scheduler for a master node are handled by the aggregator. For
a slave node, the admission and scheduler are handled by sensor nodes. e benefits of
admission control are: (i) the node transmits the request for new QoS channel reserva-
tion which can be accepted or rejected. e acceptance or rejection is based on the avail-
ability of bandwidth, (ii) polling of individual sensor to access channel, and (iii) measures
the criticality level of a patient’s data. In the QoS scheduler, there are three types of traf-
fic considered that are aggregator to a sensor, Sensor to the aggregator and best effort
delivery. e VMAC is used to connect the transport layer with MAC layer. e sug-
gested protocol [61] consumes a higher amount of energy of sensors because most of
the activities are performed on sensors. Another limitation of this protocol is that each
sensor waits for verifying the availability of slots to transmit data which reduces the per-
formance of the suggested MAC in terms of collision with a higher delay.
Preamble based slot allocation
e Traffic-Aware Dynamic MAC (TAD-MAC) protocol [62] is suggested for in-body
and on-body traffic communication. e suggested protocol uses ‘Before convergence’
and ‘After convergence’ phases. In the ‘Before convergence’ phase, each node cannot
transmit data and must wait for a beacon signal from the body coordinator. e body
coordinator learns various wakeup states of nodes from a beacon signal and uses the
wake-up interval (WUInt) under the convergence phase. e WUInt and the node traffic
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Ullah et al. Hum. Cent. Comput. Inf. Sci. (2017) 7:34
information are maintained in Traffic Status Register (TSR) bank. On the successful
delivery of data, the recipient node replies with ‘1’. Otherwise, it replies with ‘0’ which
indicates the failure of data to sender node. is scheme [62] faces a higher delay in
transmitting data and consumes a higher amount of energy of the node during the wait
period for a beacon which is not acceptable in emergency situation.
Node ID based slot allocation
An Efficient Dynamic Scheduling Approach (EDSA) is suggested and compares with
Time Division Beacon Scheduling (TDBS) [63]. e comparison of both schemes is based
on the allocation of dynamic slots and assignments of addresses to nodes. e TDBS
scheme assigns addresses and slots to nodes in the predefined time interval whereas each
node waits for a long period of time. While EDSA scheme uses static and dynamic algo-
rithms to assign addresses and slots to nodes. e addresses and time slots allocation are
assigned to each node using static algorithm in the predefined schedule. Both slot alloca-
tion processes are verified from the table which is maintained under the supervision of
a personal area network coordinator (PANC). e advantage of the dynamic algorithm
is collision-free processing without delay and achieves a higher data reliability. Moreo-
ver, the slot allocation procedure in the dynamic algorithm is based on the first come
first serve but the static algorithm assigns slots to each node in sequence and each node
waits for its predefined time. As compared static algorithm to a dynamic algorithm, the
dynamic algorithm outperforms and allocates collision-free slots without the verifica-
tion of sequence of nodes. In the static algorithm, the nodes consume a higher amount
of energy during the waiting period for allocation of slots. Another limitation is that this
scheme does not differentiate between low and high threshold values of vital signs.
Slot allocation based onthe criticality level ofa patient’s data
An ultra-light weight and low power complexity MAC protocol is suggested with the
support of three-way handshakes between a body coordinator and nodes [64]. e
CSMA/CA access scheme can avoid data collision but this scheme creates overheads
and increases a higher delay during data transmission due to RTS, CTS, DATA and
acknowledgment (ACK). us, the suggested protocol [64] replaces the functionalities of
CSMA/CA access scheme with ‘Data Request’ (DR), DATA and ACK. e DR maintains
the address of each node whereas a node waits for DR message from the body coordina-
tor before data transmission. During data transmission of a node-1 to the body coordi-
nator, all nodes turn-off their radio signals and change their states to the sleep states.
Since, the body coordinator replies back with piggybacking message (ACK+DR2) to a
node-1 when the body coordinator receives DATA. e [64] tries to change the control
signal messages of the CSMA/CA scheme access but each node waits for a DR message
before data transmission. Hence, the energy consumption of the suggested scheme is
enhanced but the allocation of slots to nodes is based on the contention which reduces
data reliability of sensory data in terms of a higher delay which is not acceptable for
emergency data.
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Urgency based slot allocation
e table-based, aggregation and fuzzy logic based proposed approaches are used to find
the criticality levels of respiratory rate (RR), heartbeat rate (HR), and mental status (MS)
[65]. e RR and HR are further classified into low_critical, high_critical and normal
values. e MS is represented by responsiveness (means ok) and non-responsiveness.
e lower threshold value of a vital sign is more in life-critical situation as compared to
high threshold value. e reason is that the low threshold value approaches towards zero
value while the high critical threshold value is far away from the ranges of low thresh-
old values. Hence, the first priority of a slot allocation is given to low threshold values.
e table approach represents the tabular representation and assigns the priority on the
basis of criticality level of threshold values. e aggregation based approach calculates
the average of three vital signs and takes decision as described in Cagg=
C
RR
+C
HR
+CMS
3
.
e fuzzy logic is the third approach and uses member functions for representing vital
signs. e purpose of the member function is to extract the knowledge from threshold
values. However, this scheme does not consider other vital signs of a patient, energy con-
sumption and data reliability in the resource constraints environment of WBAN.
Permission based slot allocation
e master node uses Transmit Slot (TX), Receive Slot (RX), Receive to Synchronize (RXS)
and Stand By slot (SB) [66] to transmit the patient’s data as shown in Fig.12 (re-drawn
from [66]). All nodes in the network are in SB or RXS. During SB state, the node hears
the transmission of the sender node and becomes active to receive the packets if the
intended packets are coming to it. However, the suggested protocol allocates slots to
nodes in the predefined pattern and each node transmits data in the predefined time
slot. e master node blocks data transmission of other nodes when one node is busy for
data transmission. Due to this blockage problem, the nodes consume a higher amount of
energy and reduce data reliability which is not appropriate for emergency data.
Performance evaluation
e simulation is performed using NS2 and compares the performance of the MAC
protocols in terms of average packet delivery delay, the average delay for delay-driven
packets, throughput and energy consumption of BMSs. Table10 shows the simulation
parameters list of LTDA-MAC [15], PNP-MAC [20], PLA-MAC [20], and IEEE 802.15.4
MAC [12] protocols. e number of available slots in the MAC Superframe structure
of LTDA-MAC is 32, IEEE 802.15.4 provides 16 slots, and PNP-MAC and PLA-MAC
both provide 128 slots. e common parameters list of simulation is provided which
have used in the four MAC protocols as aforementioned. e operating frequency is
2.4GHz and the channel sending rate is 250 kbps. Moreover, all twelve BMSs are static
SB Slot TX Slot RX Slot SB Slot TX Slot SB Slot TX Slot RX Slot SB Slot
RXS Slot TX Slot SB Slot RX Slot TX Slot SB Slot TX Slot SB Slot RX Slot
RXS Slot TX Slot SB Slot RX Slot SB Slot
Master Node
Node 1
Node 2
1
23
4
5
Fig. 12 The Master and Slave Nodes data exchange scenario
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Ullah et al. Hum. Cent. Comput. Inf. Sci. (2017) 7:34
and connected with a body coordinator in the star topology. e simulation area is 3×2
m and simulation runs for 200s.
e average packet delivery delay of PLA-MAC, PNP-MAC, LTD-MAC and IEEE
802.15.4 MAC are compared as shown in Fig.13. ese four MAC protocols allocate
slots to all nature of a patient’s body based contention in the CAP period. us, the body
coordinator allocates the guaranteed timeslots of the CFP period to those BMSs who
obtain a channel in the CAP period. Each BMS is allocated a certain amount of time in
which the BMS contends and transmits data. e contention and transmission of data
Table 10 Simulation parameters list
Common parameters list Common parameters list
Parameter Value Parameter Value
Operating frequency 2.4 GHz LTDA-MAC [15]
Channel rate 250 kbps Total no. of slots in Superframe 32
CCA time 8 symbols Slots in CAP 6
Max frame retries 4 Transmit power 36.5 mW
Traffic type CBR Receive 41.4 mW
Turnaroundtime 12 symbols PLA-MAC [29]
UnitBackoffPeriod 20 symbols Total no. of slots in Superframe 128
macAckWaitDuration 54 Slots in CAP 20
Topology Star BO 6
PNP-MAC [20]IEEE 802.15.4 MAC [12]
Total no. of slots in Superframe 128 Total no. of slots in Superframe 16
BO 6 BO 6
SO 3 SO 3
Slot size 7.68 ms Slot size 7.68 ms
CAP 8 slots CAP 8 slots
CFP (PNP) 116 slots CFP 7 slots
MACMinBE 3 MACMinBE 3
MACMaxBE 5 MACMaxBE 5
MACMaxCSMACABackoffs 4 MACMaxCSMACABackoffs 4
Fig. 13 Average packet delivery delay VS number of BMS
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depend on the values of beacon order (BO) and Superframe order (SO). e BO is the
interval between two successive beacons of the MAC Superframe structure whereas
SO is the time duration of the active slots of the MAC Superframe structure. Since,
the beacon order BO=6 and SO=3 are configured for IEEE 802.15.4 MAC Super-
frame structure. e allocated channels for contention in IEEE 802.15.4 MAC are 8 in
the CAP period. As more BMSs contend for accessing channel in CAP period of IEEE
802.15.4 MAC, the packet delivery delay is increased due to contention as more BMSs
contend. is is because of the limited channels, retransmission of the lost packets,
and limited time of Superframe duration which is 1.536s and a slot duration is 0.012s.
Another reason is that all BMSs cannot contend and transmit data in the same beacon
interval (BI) but they wait for the next announcement of BI. As compared IEEE 802.15.4
MAC, the LTDA-MAC outperforms in terms of reduced delay of the packets but the
delay increases when the traffic loads exceed the number of available slot in LTDA-MAC
Superframe structure. e PNP-MAC classifies the patient’s data into five classes and
each class has assigned a unique priority. With this unique priority is denoted for allo-
cating of slots on the priority-basis during contention for accessing channel. e packet
delivery delay is reduced by PNP-MAC and outperforms as compared to IEEE 802.15.4
MAC and LTDA-MAC because the BI provides 128 slots, dedicated slots to different
types of a patient’s data and a sufficient timing for BMSs for accessing channel in CAP
period which is BI=19.668s. However, the packet delivery delay increases of PNP-MAC
due to preemption of the non-emergency data from allocated slots on the arrival of the
emergency data. e PLA-MAC uses the same configuration as used in PNP-MAC but
it does not perform preemption techniques as addressed in PNP-MAC. e PLA-MAC
outperforms as compared all MAC protocols discussed. e PLA-MAC protocol classi-
fies the patient’s data into four types which fulfills the needs of a patient. With this clas-
sification, each patient’s data have assigned dedicated slots and the allocation of slots is
based on the criticality level of a patient which reduce the packet delivery delay.
e average delivery delay for delay-driven packets is compared of PLA-MAC with
PNP-MAC as shown in Fig.14. Both MAC protocols provide 128 slots with allocating
Fig. 14 Average delivery delay for delivery-driven packets VS number of BMS
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of dedicated slots for non-emergency and life-critical emergency data. However, the
contention-based slot allocation to BMSs reduces the performance of MAC in terms of
collision, retransmission of the lost packets with a higher delay which is not acceptable
for life-critical patient’s data. ese problems have noticed in PNP-MAC because this
MAC first removes the non-critical data from the allocated slots and then assigns these
slots to emergency data. During preemption of the non-emergency data from slots, the
life-critical data based BMSs face a higher delay because of contention of other BMSs
and in this way the delay increases as the traffic load exceeds. As compared PLA-MAC
to PNP-MAC, the PLA-MAC outperforms by allocating separate and dedicated slots for
non-emergency and emergency data in the CFP period. Further, this PLA-MAC is not
practicing the preemption technique due to which the life-critical data are not delayed
as shown in Fig.14.
Figure15 presents the throughput of the existing MAC Superframe structures. e
throughput of IEEE 802.15.4 MAC reduces when the data packets sending of BMSs
are increased. e reason for this reduction is because of the limited channels in MAC
Superframe structure, contention-based channel allocation, a higher number of colli-
sions, and retransmission of the collided packets with a higher delay. e second rea-
son is the waiting period whereas BMSs cannot transmit data in the same BI and they
wait for the announcement of next BI. e throughput of LTDA-MAC is better as com-
pared to IEEE 802.15.4 MAC but the throughput reduces of LTDA-MAC as more BMSs
contend and transmit data to the body coordinator. is LTDA-MAC has the same
problems as highlighted in IEEE 802.15.4. Further, the reduction of throughput of PNP-
MAC is due to preemption of sensory data of one BMS on the arrival of sensory data of
another BMSs. However, the PNP-MAC outperforms in allocating of slots and transmis-
sion of sensory data of BMSs as compared to LTDA-MAC and IEEE 802.15.4. e final
PLA-MAC allocates dedicated slots to emergency and non-emergency data whereas
each type of BMS transmits data in those dedicated slots. With these advantages, the
throughput of PLA-MAC is the highest as compared to the rest of MAC protocols as
shown in Fig.15.
Fig. 15 Throughput VS number of BMS
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Ullah et al. Hum. Cent. Comput. Inf. Sci. (2017) 7:34
e high energy consumption of BMSs in the MAC protocols is IEEE 802.15.4 MAC
and LTDA-MAC as more BMSs transmit data to the body coordinator as shown in
Fig.16. Both protocols allocate channels to BMSs with the assistance of contention, the
limited channels with no separate and dedicated channels for emergency and non-emer-
gency data, and all BMSs cannot contend for accessing CAP period and transmit the
patient’s data in the same BI. As more BMSs generate more traffic, the chances of the
preemption of data increase which consume more energy of BMSs as noticed in PNP-
MAC. However, the minimum energy consumption of BMSs has been noticed in PLA-
MAC as compared to the remaining MAC protocols as shown in Fig.16. e reason for
the minimum energy consumption of BMSs is dedicated slots to emergency and non-
emergency data without interrupting the contention process of each other.
Figure17 evaluates the energy consumption of the body coordinators of their respec-
tive MAC Superframe structures. IEEE 802.15.4 provides fixed 7 slots in the CAP
period whereas all types of BMSs whether emergency or non-emergency based BMSs
perform contention to access channel. BMSs drop the patients’ data when the conten-
tion reaches to the highest peak because of the limited 16 slots. With this higher col-
lision of the patient’s data, all BMSs wait for contending and transmitting data in the
next announcement of BI which consume a higher energy of the body coordinator. e
energy consumption of the body coordinator in the LTDA-MAC increases gradually due
to limited slots in CAP period, high traffic load, and the body coordinator announces
a new BI after 98s. e PNP-MAC and PLA-MAC provide 128 slots and their energy
consumption are low as compared to the aforementioned MAC protocols. However, the
energy consumption of PNP-MAC is higher due to the preemption of sensory data from
allocated slots for coming sensory data of other BMSs, and provides limited 8 slots in
CAP period. With these changing of the order of the patient’s data, the body coordina-
tor is actively involved for such types of activities. While PLA-MAC provides 20 slots in
CAP period which are sufficient for BMSs to contend and transmit data without actively
involving of the body coordinator.
Fig. 16 Energy Consumption VS BMSs
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Ullah et al. Hum. Cent. Comput. Inf. Sci. (2017) 7:34
Future challenges
e WBAN is the medical application of WSN and it needs to design an efficient MAC
protocol due to their unique requirements and specific characteristics [67]. is paper
classifies the challenging and open issues in WBAN in two classes. e first class gives
an explanation of different scheduling access schemes which are used in MAC layer for
a patient’s data. e second class of classification highlights the different routing issues.
MAC layer issues
Suering ofheterogeneous nature ofa patient’s data inWBAN
ere are different types of BMSs used to monitor different vital signs such as heartbeat
rate, respiratory rate, EEG, ECG, glucose, temperature, blood pressure. e BMSs trans-
mit the patient’s data in different data rates and frequencies which require high process-
ing power, high storage and high energy to transmit to the body coordinator [68]. Hence,
the researchers ought to design MAC protocol that fulfills the requirements of the dedi-
cated data rates for BMSs.
Waiting period based slot allocation
e waiting period based slot allocation is performed with the support of TDMA sched-
uling access scheme whereas the nodes require synchronization before data transmis-
sion in the pre-allocated time slots [29]. e emergency-based nodes require a higher
care to transmit their data without waiting and synchronization to the body coordinator
in the life-critical situations. us, the waiting of nodes suffers the patient’s life and tech-
nologically the nodes consume a higher energy with lower data reliability.
Unconditional contention‑based slot allocation
It has been noticed in the existing studies that MAC schemes use CSMA/CA sched-
uling scheme in which all types of nodes perform contention to access channel in the
CAP period [48]. During contention, the non-emergency based nodes do not care of
emergency-based nodes to give priority in the allocation of slots which is not acceptable
Fig. 17 The body coordinator Energy Consumption VS BMSs
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Ullah et al. Hum. Cent. Comput. Inf. Sci. (2017) 7:34
medically for emergency data and technologically the nodes consume a higher amount
of energy, higher collision, and re-transmission of the lost packets [57].
Channel access design complexity
e FDMA provides collision-free data transmission but designing of hardware is the
most crucial and challenging problem during establishing the communication links
between nodes [59].
Threshold values based slot allocation
e existing studies do not decide for allocating of slots on the priority basis to two vital
signs if two vital signs are detected with low-to-high or high-to-low threshold values at
the same time. As stated in [65] that low threshold of a vital sign is in more life-critical
conditions as compared to the high threshold value of a vital sign. Hence to resolve such
challenging problem, the MAC Superframe structure needs to add an individual slot for
each type of emergency data.
Alert‑based slot allocation
e dedicated slot is used to receive an alert signal from the particular BMS and allocate
slots in emergency situation. In fact, the node requires three-way handshaking process
to establish a communication session with the body coordinator and transmits data [26].
is approach drops the patient’s data due to the long waiting period of allocating a slot.
Permission‑based slot allocation
e permission-based slot allocation to nodes consume a higher energy with higher
delay which degrades the performance of MAC protocol in terms of lower data reli-
ability [66]. ese challenging issues are not appropriate for emergency-based nodes
whereas they wait for beacons to transmit and receive data.
Preemptive andnon‑preemptive based slot allocation
On the arrival of emergency data, the body coordinator preempts the non-emergency
data from allocated slots and assigns to emergency data [20]. e blockage and removing
of non-emergency data from the allocated slots reduces the performance of MAC proto-
col in terms of lower data reliability with higher dropping of a patient’s data, and BMSs
consume more energy on the re-transmission of the lost packets.
Hybrid based slot allocation
Most of the existing MAC schemes use TDMA and CSMA/CA scheduling access
scheme as hybrid scheduling schemes [36]. Both scheduling schemes are an optimal
solution to allocate slots to non-emergency data. However, the contention and prede-
fined access based slots allocation to emergency-based nodes reduces data reliability in
terms of a higher data collision, higher re-transmit of the lost packets, and nodes con-
sume a higher amount of energy.
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Ullah et al. Hum. Cent. Comput. Inf. Sci. (2017) 7:34
Priority based slot allocation toemergency data inWBAN
e patient’s data is classified into emergency, periodic and non-emergency data. e
emergency data comprises of low and high threshold values of vital signs such as the
heartbeat-based BMS detects a low threshold value and the respiratory rate-based BMS
detects a high threshold value [69]. e periodic data is used for on-demand service that
is the body coordinator which retrieves data from any BMS and transmits the outcomes
to the medical doctor. e non-emergency data comprises of temperature, blood pres-
sure and glucose level. Hence, the emergency data requires a higher attention to giv-
ing the first channel access as compared to periodic and non-emergency data [70]. e
emergency data are in a life-threatening situation and may suffer the patient’s life if it
does not allocate the first channel [65]. e researchers ought to re-design MAC and
routing protocols with efficient scheduling access schemes in order to transmit emer-
gency data without contention.
General research issues ofWBANs
Radiation absorption andoverheating inWBAN
e radio frequency (RF), the radiation of biosensors’ antenna and the circuitry of sen-
sor node are the three sources of temperature-rise which heat up BMSs during moni-
toring of vital signs and data transmission to the body coordinator. With this heat up,
BMSs damage tissues and skin of a patient’s body [71]. Due to these challenging prob-
lems, some new routing protocols should need to design for keeping safe the tissues and
skin from overheating.
Quality ofService (QoS) inWBAN
e patient’s data are classified into critical data, delay sensitive data, reliability-sensitive
data and ordinary data [72]. ese types of data require a dedicated and guaranteed QoS
to transmit without delay and packet loss. e researchers need to suggest and design an
efficient QoS for delay sensitive data of WBAN as compared to WSN data.
Path loss inWBAN andWSN
BMSs are implanted inside the patient’s body and/or attached on the skin for monitor-
ing of various vital signs. e path loss occurs in WBAN due to fat and various postural
movements of a patient’s body such as LYING-DOWN, SIT, SIT-RECLINING, STAND,
WALK and RUN [73]. e data transmission in WSN is in free space where it has mini-
mum path loss as compared to WBAN. e researchers ought to improve the existing
MAC and routing protocols for WBAN to minimize the path loss problems.
Data protection inWBAN andWSN
Both WBAN and WSN transmit data in free space which faces problems of data integ-
rity. e existing security techniques are difficult to apply on the tiny BMSs due to lim-
ited memory, storage, energy and processing power [74]. erefore, it is suggested to
develop new and light weight security techniques for protecting the patient’s data from
an unauthorized access.
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Ullah et al. Hum. Cent. Comput. Inf. Sci. (2017) 7:34
High energy consumption
Most of the energy of BMSs is consumed due to contention-based slot allocation, pre-
defined based slot allocation and permission. In order to minimize the energy consump-
tion, the alert based slot allocation to BMS is the appropriate solution for extending the
network life time.
Limited resources
e low data storage, low processing power and high energy consumption are the chal-
lenging problems of WSN’s sensor and these sensors are used in WBAN to monitor
the sensitive organs of humans [75]. e manufacturers and designers are suggested to
enhance the performance of sensors in terms to minimize the energy consumption, pro-
vide high data storage and high processing power.
Conclusion
In this paper, a qualitative review of MAC protocols for WBAN has been carried out by
analyzing the designs of Superframe structure, describing multiple access schemes, and
presenting a taxonomy based qualitative analysis of the MAC protocols. e design of
Superframe structure and multiple access schemes are the two most significant design
decisions, from where the optimal prioritization of the patient’s data can be obtained for
a MAC protocol in WBANs. e optimality in prioritization of a patient’s data deter-
mines the efficiency of MAC protocol in terms of slot allocation, energy consumption
during contention, and reliability of data. It has been observed that the classification of
the patient’s data in four categories, namely, Critical data Packet (CP), Reliability data
Packet (RP), Delay data Packet (DP) and Ordinary data Packet (OP) is the most appro-
priate classification. e classification consider the requirements including low and high
threshold values, on-demand access to a specific vital sign, and normal, emergency and
non-emergency data. CSMA/CA scheduling is more appropriate for normal and non-
emergency data due to the absence of time constraint, in case of these types of data
where contentions are performed for slot allocation. TDMA scheduling schemes are
more appropriate for emergency data, where without performing contention, the emer-
gency-based sensor transmits an alert signal to body coordinator for slot allocation. e
contention based sensors perform backoffs to access channels, which creates overheads
resulting in higher collision, delay, retransition of lost packets, and lower reliability of
data.
Authors’ contributions
This research is a group work, and each author has significant contributions. FU carried out the technical review with
suggestions from AHA and OK. SK and MMA helped in carrying out revisions of the paper. All authors read, and approved
the final manuscript.
Author details
1 Faculty of Computing, Universiti Teknologi Malaysia (UTM), Room No: L4.04.01, PCRG, N28a, Johor Bahru 81310, Malay-
sia. 2 Department of Computer, Sarhad University of Science and Information Technology, Peshawar, Pakistan. 3 Depart-
ment of Computer and Information Sciences, Northumbria University, Newcastle upon Tyne NE2 1XE, UK. 4 School
of Computer & Systems Sciences, Jawaharlal Nehru University, New Delhi 110067, India.
Competing interests
The authors declare that they have no competing interests.
Acknowledgements
The research is supported by Ministry of Education Malaysia (MOE) and conducted in collaboration with Research Man-
agement Center (RMC) at University Teknologi Malaysia (UTM) under VOT NUMBER: RJ130000.7828.4F708.
Page 37 of 39
Ullah et al. Hum. Cent. Comput. Inf. Sci. (2017) 7:34
Publisher’s Note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Received: 5 August 2016 Accepted: 3 September 2017
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