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Receiver Initiated Multi-channel Medium Access
Control Protocol for Cognitive Radio Network
Amran Hossain, Sahelee Sultana and Md. Obaidur Rahman
Department of Computer Science and Engineering , Dhaka University of Engineering & Technology(DUET), Gazipur
Gazipur-1700, Bangladesh
amran_duet38@duet.ac.bd, sahelee.cse@gmail.com, orahman@duet.ac.bd
Abstract— At present Cognitive Radio Network (CRN) is one of
the contemporary research area in order to improve efficiency as
well as improve spectrum utilization factor of wireless
communication. The impression of profitable CRN (i.e.,
simultaneous presence of primary and secondary users in
licensed bands) is increasing popularity in wireless
communication research. In fact fixed unlicensed band is used by
wireless users in different networks to complete data
communication. However, in practical number of wireless users
are increasing day by day and guides this limited bandwidth to a
saturation state. In CRN as at the absence of primary user, the
secondary users access the channels of licensed bands; thereby
the Medium Access Control (MAC) protocol for CRN faces many
challenges. The challenges include throughput maximization,
channel rendezvous amongst the secondary users, minimize
delay, and to keep continuing data transmission without
interfering the primary users. A large number of sender initiated
MAC protocols have been proposed for CRN to solve these
challenging issues. However we argue that efficient channel
rendezvous in many scenarios still a major concern in accordance
with the rest of the mentioned challenges. In this paper, we have
come up with a Receiver Initiated Multi-channel (RIM) Medium
Access Control (MAC) protocol named as RIM-MAC exploiting
the pseudorandom number channel sequence and hopping
method for multi-channel rendezvous amongst the secondary
users of CRN. This protocol is efficient scheme for channel
rendezvous success rate. We have analyzed and implemented our
proposed RIM-MAC protocol, and found that it provides better
performance in terms of throughput, rendezvous rate and delay.
Keywords—Cognitive radio, psedurandom number channel
sequence, channel rendezvous, primary user, secondary user.
I. INTRODUCTION
Cognitive Radio Network (CRN) gains popularity in the
research area because it enables the current fixed spectrum
channel assigned by FCC to be utilized by the new users [1]. It
is noteworthy that most of the spectrums assigned to television
channels, radio channels dividends a huge amount of
bandwidth and are kept idle most of the time; whereas
wireless network users (i.e., WLAN and Wi-fi users) share a
small range of spectrum. In practical, when there are many
wireless users at a time, the network gets congested because of
the limited number of channels with less bandwidth. Hence, it
is predictable that bandwidth would not be sufficient to
provide better support for the wireless users in terms of quality
of service (QoS), throughput and delay. So, the ultimate
solution is to find out some alternative. CRN is one of the
possible solutions to overcome this problem. Cognitive radio
(CR) is an intelligent transceiver, adaptive and network
technology, which can be configured with dynamism property.
It has ability to automatically detect free or available channels
from wireless spectrum and change its transmission
parameters enabling more communications to run
concurrently. In point of fact, CRN is structured with both the
secondary user (SU) and primary user (PU) in which, SUs
consist CR-enabled radios and the PUs whose radios need not
be CR-enabled [2]. Cognitive capability means to the ability to
sense opportunities in spectrum where and when channels are
not employed by PUs [3].
In view of the fact that, the SUs operate separately on
dissimilar channels based on availability (i.e., during the
absence of primary users), channel rendezvous seems to be the
most challenging issue in CRN. Fig. 1, illustrates that nodes A
and Y, W, C and X, B and Z; the pairs of SUs opportunistically
make channel rendezvous on channel 1, channel 3, and
channel 5 respectively, where no PU exists. Note that channel
2 and 4 are occupied by the PUs. Hence, SU do not have any
activity on these channels. It is observed that, there are
different approaches exist for channel rendezvous between
two SUs in CRN. Firstly, the common control channel (CCC)
approach for channel rendezvous [4] creates bottleneck
situation on the common control channel.
Figure 1: Basic communication manner in CRN
Furthermore, rendezvous scheduling complexity may arise.
Secondly, the channel hopping approach [5-6] can be used by
the SUs to discover each other on a channel while hopping
different channels. This approach uses pseudorandom
sequence according to available channel list. When PU is
occupied channel(s) gradually, then decrease channel
rendezvous rate as well as increase channel rendezvous delay.
Conversely, if two SUs follow reciprocally exclusive
sequence, still after lots of iterations, those may not succeed in
978-1-4673-9257-0/15/$31.00 ©2015 IEEE
2015 International Conference on Electrical Information and Communication Technology (EICT)
350
discovering each other [7]. Finally, in synchronization
approach [8], nodes are needed to be synchronized; hence
synchronous overhead becomes the main concern for a large
network.
Considering the above mentioned limitations on different
channel rendezvous approaches, we have motivated to design
an efficient channel rendezvous technique using
pseudorandom number channel sequence for making channel
rendezvous between SUs considering all channels.
The rest of the paper is organized as follows: in Section II
the background study and problems domains are presented.
Section III describes the proposed RIM-MAC protocol design.
Analysis and performance evaluation are described in Section
IV and V respectively, and Section VI concludes the paper.
II. RELATED WORK AND PROBLEM STATEMENT
Till date, a number of MAC protocols have been proposed
for CRN to solve the channel rendezvous problem, where the
protocols either use any one approach of the followings or
make the combinations amongst those; such as- common
control channel approach [9-12], channel hopping approach
[6], and synchronization approach [8].
A. Common Control Channel Approach
In this approach selects one channel that serves as a
rendezvous channel and all the essential control information is
exchanged among the SUs on this channel [9-12]. When a SU
wishes to communicate with its potential receiver (i.e., another
SU), at first it switches to the CCC during control interval and
attempts to negotiate with its potential receiver using a control
packet. When negotiation is complete on CCC, the SU
switches to negotiation channel [5] which is available or
common to both and then data communication can be
accomplished during the data exchange interval through
available channel. In addition, bottleneck situation may occur
in the CCC when multiple nodes negotiate for rendezvous in a
single channel.
B. Channel Hopping Approach
In the channel hopping approach [6], each SU generates a
pseudorandom sequence using its own available channels.
According to predefined hopping sequence SU switches/hops
from one channel to another until finds its neighbor. When
two SUs meet on a channel which is common between them,
they need to exchange the necessary control information as
well as complete their data communication. Hence, we
conclude that a large number of iterations are required for
channel rendezvous using pseudorandom channel hopping
sequence as well as, even after lots of iterations; neighbor
discovery of SUs may not be successful if SUs follow
mutually exclusive pseudorandom sequence [7].
C. Synchronization Approach
In this approach [8] time is divided into N number of equal
time slots of fixed duration. Each time slot is dedicated to one
channel for control signal exchange. At the end of the network
initialization state, all nodes are synchronized and every node
has the information about its neighbors and their respective
channel sets. To exchange the control signals it chooses one of
the channels common between itself and its neighbor during at
the beginning of specified time slot. Therefore, nodes are
needed to be synchronized; hence, synchronization overhead
occurs in this approach and increase the rendezvous delay.
Considering the above mentioned limitations of different
channel rendezvous approaches, in this paper we have
proposed a RIM-MAC protocol for SUs. The proposed
method makes a pseudorandom number channel sequence
according to total number of channels for rendezvous among
the SUs.
III. PROPOSED RIM-MAC PROTOCOL DESIGN
A. Protocol Overview
RIM-MAC is a multichannel asynchronous duty-cycling
MAC protocol. It does not require nodes to synchronize. It
also does not use common control channel behavior. In this
protocol design a beacon packet (i.e., Hello Packet) is
considered to exchange all the control information of a SU
node. Each SU has a prediction state (i.e., initial state) to
learn about receiver’s available channel set, beacon sending
time and pseudorandom number channel sequence.
In RIM-MAC protocol, a node avoids choosing channels
that are occupied by PU. When a node wakes up on a channel
according to pseudorandom number channel sequence to send
a beacon, it uses a CCA (Clear Channel Assessment)
technique to check and make sure the channel is idle/free
before beginning its transmission. If the channel is idle/free,
the node sends the beacon and complete data transmission
with their potential sender node. If the channel is occupied by
PU, the receiver node skips the channel and goes to sleep; and
wait on that channel till a cycle time, denoted by TC (i.e.,
mentioned later). Additionally, after waiting the nodes switch
to next pseudo randomly chosen channel and repeat the CCA
technique and beacon sending method.
B. Network Model
Fig. 2 is shown as simple cognitive radio network model.
In this model SUs are mentioned as S (i.e., Sender Node) and
R (i.e., Receiver Node). We know that in IEEE 802.11b
standard protocol uses only 16 channels. SU can occupy any
channel among the standard channel list of ISM band. Here,
for simple explanation we have assumed only 5 channels. The
PUs is mentioned as PS in sender side and PR in receiver side
respectively.
Figure 2: Simple CRN model
351
In sender range PUs occupied channel(s) are (2, 3) and in
receiver range PUs occupied channel(s) are (3, 4). So the
available channel(s) set of S is {1, 4, 5} and available
channel(s) set of R is {1, 2, 5}. In the next sections we have
used these available channel(s) list for explanation.
C. Protocol Operation
RIM-MAC is a multichannel asynchronous duty-cycling
MAC protocol. The design of RIM-MAC is mainly
encouraged by the multi-channel EM-MAC [13] protocol for
WSN. RIM-MAC protocol operation is categorized into three
phases such as-Network Initialization State, Stable Phase and
Adaptive Phase which are described in the following sections.
1) Network Initialization State
Each SU node equipped with a single radio multi-channel
transceiver and can act as a sender or a receiver and maintains
a common communication characteristic. Initially it is
considered that a node has a packet to send to a receiver but
does not have the receiver’s prediction state (i.e., receiver’s
available channel list, beacon time and pseudorandom number
channel sequence). Hence, at the initialization the node having
data (i.e., the sender S) starts sensing the first available
channel of its own pseudorandom number channel sequence.
Firstly, the sender checks that if the channel is occupied by
any PU, it switches to the next channel of pseudorandom
number channel sequence; otherwise, it enlists the channel in
its available channel list and waits for receiver’s beacon on
that channel. If the sender does not receive beacon from the
receiver during its waiting time interval on that channel, then
the sender switch to another channel and so on. After
receiving the beacon from the receiver, the sender sets a flag
in the header of the data packet sent to the receiver, requesting
the receiver to embed its prediction state in the following
beacon. Thus, the node gets aware of the receiver’s beacon
time offset on respective available channels and maintains the
same for future data communication. So the receiver beacon
should be sufficient to ensure that the receiver will visit the
channel at least once during this time. Let TC be the cycle
time interval of a node and the node wakes-up on different
channels using the pseudorandom number channel sequence
using the TC cycle time interval. However, if the next
channel(s) of the pseudorandom number channel sequence is
occupied by the PU the node stays on its current channel and
after elapsing appropriate TC cycle time interval(s) it switches
to the next available channel. It should be sufficient to ensure
that receiver will visit the available channel at least once
during this time. So the maximum waiting time of a sender on
a channel would be
CWait ch TNT×= (1)
Where, TC is the cycle time, and Nch is the total number of
channels. Fig. 3 illustrates the initialization state of protocol.
Based on the overlapping principle [14] it is expected that S
would receive the beacon from R and subsequently sends the
data packets and complete communication. If the sender does
not receive a beacon from the receiver after waiting TWait, the
sender switches to the next channel and repeats the waiting
procedure. If the sender is unable to rendezvous with the
receiver after waiting on all channels, the sender assume that
Figure 3: Network initialization state
the receiver is unreachable. In contrast, the same node, when
acts as a receiver, then it sends the beacon to its potential
sender(s) posterior to the waiting time (TWait) for its own
receiver’s beacon.
2) Stable Phase
Every SU node independently decides and maintains its
own pseudorandom number channel sequence switching
behavior, wake-up offsets and available channel list. A sender
rendezvous with a receiver on a particular channel by
predicting the receiver’s wake-up channel, wake-up offset and
available channels. We denote that a SU Sender as node S and
a SU Receiver as node R. Fig. 4 illustrates an example of the
operation of proposed RIM-MAC, with time progressing from
left to right. As RIM-MAC is a receiver initiated multichannel
MAC protocol, a receiver node R first sends a beacon on an
available channel (i.e., no primary user is on that channel)
according to its generated pseudorandom number channel
sequence. On the contrary, it is assumed that the sender S is
well aware of receiver’s channel sequence, available channel
list and beacon time offset on different channels. Hence, the
sender S proactively remains on the receiver’s available
channel to receive the beacon from node R and consequently
sends data to R. As shown in Fig. 4, sender S has channel {1,
4, 5} as its available channel list. Now receiver R first scans
the channels according to its pseudorandom number channel
sequence. Thus, on a particular time offset/interval receiver R
sends a beacon B to sender S and initiates a communication on
available channel 2 during cycle time TC, but on that time
sender S is not stayed on that channel because channel 2 is
occupied by PU for S. So R does not get any data from sender
S. Now R switches to next channel(s) and so on. Here,
channels 3 and 4 are occupied by PU so receiver skips these
channels and switches to next channel. The channel 1 is
available to R, so R sends a beacon to sender S on this channel.
After receiving the beacon B from R, node S sends the data
packet D to R. In reply, R sends an acknowledgement beacon
B to S to acknowledge the data packet receipt. Moreover, the
acknowledgement beacon B works as a request for another
data packet to be sent to R by S or another sender. In the
providing example no other data packet is available so S and R
352
Figure 4: RIM-MAC protocol operation scenario.
quickly go back to sleep. After Cycle time TC, R wakes up for
the second time on another available channel such as 5 and
complete data packet transmission with S and so on. Hence,
sender S has prediction state of R, so S wakes up shortly
before predicted time on predicted channel(s) before data
transmission.
3) Adaptive phase
In adaptive phase, we have assumed that after sometimes
or next cycle, when available channel list of R is updated with
few additional channels due to non-occupation of PUs. In such
case, receiver R follows its own pseudorandom number
channel sequence for sending beacon in the newly added
channel(s). In contrast, it is expected that S will be updated
about the changes in available channel list in R through the
earlier/later beacons. Thus it can perform data transmission
with R in the newly added channel(s). When, available
channel list of R is updated with fewer channel(s) due to
channel occupation of PUs.
In such case, receiver R follows its own pseudorandom
number channel sequence for sending beacon in the available
channel(s) only. Here as well S will be updated or presume
about the changes in available channel list in R. Thus it can
perform data transmission with R in the newly added
channel(s). Let, after few seconds previous sender S now acts
as a new receiver R, and its available channel(s) list is {1, 4,
5} and its pseudorandom number channel sequence is 31542.
Therefore, new receiver R follows its own pseudorandom
number channel sequence and completes the data transmission
with another sender S according to stable phase. Fig. 5
illustrates new adaptive operation in this case.
IV. RENDEZVOUS DELAY ANALYSIS
For channel rendezvous delay analysis, we have
considered three cases as follows: worst case rendezvous
delay analysis, best case rendezvous delay analysis and
average case rendezvous delay analysis.
Case 1: Worst case rendezvous delay analysis
If a sender S has no prediction state of R, then S first waits
on an available channel until getting the receiver beacon. Let
TC be the cycle time interval of a node and the node wakes-up
on different channels using the pseudorandom number channel
sequence using the TC cycle time interval. However, if the next
channel(s) of the pseudorandom number sequence is occupied
by the PU the S stays on its current channel and after elapsing
appropriate TC cycle time interval(s) it switches to the next
available channel. It should be sufficient to ensure that
receiver will visit the available channel at least once during
this time. So worst case rendezvous delay would be calculated
as follows:
C
Worst
Wait ch TTN×= (2)
Here, TC = Cycle time, Nch is the total number of channels.
Case 2: Best case rendezvous delay analysis
In the best case sender S would get the beacon exactly on
its first available channel without wait. So the best case
rendezvous delay would be calculated as follows:
;0
Best
Wait WhereT
δδ
=→
(3)
Case 3: Average case rendezvous delay analysis
Average case rendezvous delay would be calculated as:
2
;
Average ch C
Wait
NT
Twhere
δδ
×
=→
(4)
Figure 5: RIM-MAC protocol operation in adaptive phase
353
V. PERFORMANCE EVALUATION
We have demonstrated the performance evaluation of our
proposed RIM-MAC protocol and compare the results with
that of a CCC-MAC protocol and SYN-MAC protocol. We
have used our own simulation model developed in Java
Platform (NetBeans IDE 7.0) and we have implemented our
proposed RIM-MAC, CCC-MAC and SYN-MAC protocols
and compare the results with among them. In this simulation
environment, 10 channels are used for modeling licensed
channels for PUs and randomly some of the channels made
free/unlicensed and set available to the SUs. Maximum 20
nodes are deployed in 500 x 500 m2 area to make variation in
number of PU and SU. 10 nodes are chosen randomly as the
sources and the other 10 nodes as destinations. The
transmission range of each node is set to 250m. In this
simulation, 10 simulation cycles are considered, each having a
cycle period of 10 seconds. Hence, total simulation time is 100
seconds. Each data packet is considered to cost 1 Joule for
single transmission, which is used to calculate energy
consumption of each node. In case of data packet transmission
failure, 1 Unit (i.e., Second) is assumed, which is used to
calculate delay of each node. In our simulation, for evaluation
the performance of Proposed RIM-MAC, SYN-MAC and
CCC-MAC, we have considered five performance metrics
such as- Throughput, Rendezvous Success Rate, Rendezvous
Delay, Packet Transmission Success Rate, and Energy
Consumption.
A. Throughput Performance
Fig. 6 shows the aggregated throughput of proposed RIM-
MAC with the SYN-MAC and CCC-MAC protocols as the
network traffic is increased. The throughput of RIM-MAC is
significantly higher than SYN-MAC and CCC-MAC. The
main cause for this behavior is that a CCC among all the
nodes is not always available and so many times a connection
is not established. Hence, due to these failures the throughput
is significantly lower in CCC-MAC. In SYN-MAC when
nodes are increased, then synchronization overhead is
increased so connection problem and problem of message
collaboration among the nodes are increased. So throughput is
comparatively lower than the RIM-MAC. In RIM-MAC, there
is no control signal shared with among all nodes and hence,
nodes are communicated any time any available channel(s).
Therefore, RIM-MAC has the better throughput from the
SYN-MAC and CCC-MAC protocols.
0 102030405060708090100
0
200
400
600
800
1000
1200
1400
Aggregated Throughput (kbps)
Average Flow Rate (Packets/sec)
Proposed RIM-MAC
SYN-MAC
CCC-MAC
Figure 6: Average throughput Vs flow rate
B. Rendezvous Success Rate
Fig. 7 demonstrates the results of rendezvous success rate
in percent with respect to simulation time for channel
rendezvous. As shown in figure, in 1st cycle, rendezvous
success rate among the SUs in RIM-MAC is 100%, in SYN-
MAC is 100% and in CCC-MAC is 70%, and so on. After 10th
cycle of simulation, it is observed that the rendezvous success
rate in RIM-MAC is 60% and steady, and SYN-MAC and
CCC-MAC are abrupt. So, it can be concluded that proposed
RIM-MAC protocol provides higher rendezvous success rate
than the SYN-MAC and CCC-MAC approaches.
C. Rendezvous Delay Rate
Fig. 8 demonstrates the outcome of rendezvous delay in
second with respect to simulation time for channel
rendezvous. As shown in figure, in 1st cycle, rendezvous delay
among the SUs in RIM-MAC is 0 (i.e., no delay), in SYN-
MAC is 1 and in CCC-MAC is 3, in 2nd cycle; rendezvous
delay among the SUs in RIM-MAC is 0 in SYN-MAC is 1
and in CCC-MAC is 4 and so on. Finally at 10th cycle of
simulation, it is observed that the rendezvous delay in RIM-
MAC is 4 and steady, and SYN-MAC and CCC-MAC are
increased. So, it can be concluded that proposed RIM-MAC
protocol provides lower rendezvous delay than the SYN-MAC
and CCC-MAC approaches.
D. Packet Transmission Rate
Fig. 9 exhibits the results of packet transmission success
rate in percentage with respect to simulation time. In figure, in
1st cycle, packet transmission rate among the SUs in RIM-
MAC is 100%, in SYN-MAC is 90% and in CCC-MAC is
70% and so on. It is also observed that in 10th cycle, the packet
0 102030405060708090100110
0
10
20
30
40
50
60
70
80
90
100
110
Rendezvous Success Rate (%)
Simulaton Time (Second)
RIM-MAC(SU=20, PU=10)
SYNC-MAC (SU=20, PU=10)
CCC-MAC (SU=20, PU=10)
Figure 7: Rendezvous success rate with respect to simulation time
0 102030405060708090100110
0
1
2
3
4
5
6
7
8
9
10
11
Rendezvous Delay (Second)
Simulaton Ti me (Second)
RIM-MAC(SU=20, PU=10)
SYNC-MAC (SU=20, PU=10)
CCC-MAC (SU=20, PU=10)
Figure 8: Rendezvous delay with respect to simulation time
354
0 102030405060708090100110
0
10
20
30
40
50
60
70
80
90
100
110
Packet Transmission Success Rate (%)
Simulaton Time (Second)
RIM-MAC(SU=20, PU=10)
SYNC-MAC (SU=20, PU=10)
CCC-MAC (SU=20, PU=10)
Figure 9: Packet transmission success rate with respect to simulation time
0 102030405060708090100110
0
1
2
3
4
5
6
7
8
9
10
11
Energy Consumption (Joule)
Simulaton Time (Second)
RIM-MAC(SU=20, PU=10)
SYNC-MAC (SU=20, PU=10)
CCC-MAC (SU=20, PU=10)
Figure 10: Energy consumption with respect to simulation time
transmission success rate in RIM-MAC is 30%, and 20% in
SYN-MAC and CCC-MAC respectively. So we can say that
RIM-MAC protocol provides higher packet transmission
success rate than the SYN-MAC and CCC-MAC protocols
E. Energy Consumption
Fig. 10 illustrates the outcome of energy consumption in
second with respect to simulation time. It is observed in RIM-
MAC rendezvous success rate and packet transmission success
rate is higher than the SYN-MAC and CCC-MAC which are
shown in Fig. 7 and 9 respectively. So it is concluded that the
energy consumption in proposed RIM-MAC is higher than the
SYN-MAC and CCC-MAC.
VI. CONCLUSION
In this paper we have presented a new CRN MAC protocol
and channel rendezvous scheme using pseudorandom number
channel sequence based mechanism for SUs considering all
the channels of the list. Proposed RIM-MAC protocol
algorithm ensures that maximum number of SUs can make
channel rendezvous and successfully complete their data
transmission with each other. This protocol automatically
eliminates the control channel saturation problem and
synchronization overhead. In addition, this protocol increases
throughput, maximize channel rendezvous success rate,
maximize packet transmission rate and reduces delay.
ACKNOWLEDGMENT
This work is supported by the “Research Development
Fund” of Dhaka University of Engineering & Technology
(DUET), Gazipur and Dr. M. O. Rahman is the corresponding
author.
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