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International Journal of Applied Engineering Research
ISSN 0973-4562 Volume 10, Number 8 (2015) pp. 21199-21214
© Research India Publications
http://www.ripublication.com
Comparative Study Between Static Dynamic and Hybrid
Channel Assignment Techniques In Multi Channel and
Multi Radio In Wireless Mesh Network
Abstract
A major challenge in multichannel multiradio wireless mesh network is the
allocation of channels that optimizes both packet delay and network
throughput. We propose a hybrid multichannel multiradio wireless mesh
network where each router works on two interfaces, one interface from each
router works on statically allocated channel, while the other interfaces works
on dynamically allocated channel. The hybrid architecture is implemented by
two protocol, they are Adaptive Dynamic Channel Allocation protocol
(ADCA) and Interference and Congestion Aware Routing protocol (ICAR).
The Adaptive Dynamic Channel Allocation protocol reduces the packet delay
in the network without degrading the network throughput and it is suitable for
more number of routers while, Interference and Congestion Aware Routing
protocol (ICAR) reduces the interference and packet loss by proper utilization
of the channels in the network. The hybrid architecture shows much better
adaptively to changing traffic and counteracts router failure more efficiently
than purely static architecture and dynamic architecture without remarkable
increase in overhead .In addition we also examine the quality of service and
fairness parameters of hybrid multichannel multiradio wireless mesh network.
Keywords: Wireless Mesh Network, Static, Dynamic, Hybrid, Interference
and Congestion Aware Routing protocol, Adaptive Dynamic Channel
Allocation protocol.
Mrs. B. Sathyasri
Assistant Professor/ECE Department
Veltech , Chennai -62
sathayasri.me@gmail.com
Dr. E. N. Ganesh
Dean Research
Rajalakshmi Institute of Technology, Chennai -124
enganesh50@yahoo.co.in
Dr. P. Senthil Kumar
Professor / CSE Department,
SKR Engineering College, Chennai
drsenthilkumar2010@gmail.com
21200 B. Sathyasri
Introduction
Now a day’s wireless network is foremost used. It should provide better service to all
its users. Around a number of application domains such as the mobile networks, ad
hoc networks, ubiquitously and pervasive computing, sensor networks and so on. To
provide better service Wireless mesh networks (WMNs) is used. WMN are
dynamically self-organized and self-configured, with the nodes in the network [1]. A
wireless mesh network (WMN) is a mesh network created through the connection of
wireless access points installed at each network user's point. Each network user is also
a provider, forwarding data to the next node. Another issue is Channel assignment
problem in wireless mesh networks. The major task of channel assignment is
assigning frequency channels to the users satisfying the interference constraints and
using as small bandwidth as possible is known as the Channel Assignment Problem
(CAP). Channel assignment schemes are finding a proper mapping between the
available channels and the radios at each node such that the network performance is
optimized. Channel assignment methods can be categorized according to the
frequency of channel assignment. We distinguish different categories: Centralized,
Distributed, Static, Dynamic and Hybrid.
Figure 1: Wireless Mesh Networks
Classification of Channel Assignment Methods In Multi Channel
Mutli Radio Wmns
In Channel assignment methods we have (i) Static (ii) Dynamic (iii) Hybrid (iv)
Centralized (v) Distributed
Static Channel Assignment Method:
In Static Channel Assignment we have two types i) Fixed Assignment Scheme ii)
Varying Channel Assignment Scheme.
Fixed assignment schemes assign channels to interfaces either enduringly or for
long time period with respect to the interface switching time. Common Channel
Comparative Study Between Static Dynamic and Hybrid Channel Assignment et.al. 21201
Assignment is the simplest scheme. In this case the radio interfaces of each node are
all assigned the same set of channels. [2]
Varying Channel Assignment scheme, interfaces of different nodes may be
assigned different sets of channels. The assignment of channels may lead to network
partitions and topology changes that may increase the length of routes between the
mesh nodes and assignment needs to be carried out carefully. [2]
Dynamic Channel Assignment Method:
Dynamic assignment allows any interface to be assigned any channel, and interfaces
can often switch from one channel to another. When nodes need to communicate with
any other node, a synchronization mechanism has to make sure they are on a common
channel.
The key issue is to involve channel switching delays and the need for
synchronization mechanisms for channel switching between nodes. [2]
Hybrid Channel Assignment Method:
Hybrid channel assignment strategy combines together static and dynamic assignment
properties. Some of the interfaces are assigned for Static and remaining interfaces is
assigned for Dynamic. [2]
Centralized Channel Assignment Method:
Presumptuous the availability of complete information at a central point, the
centralized Channel Assignment approaches are introduced before their distributed
counterparts.
The centralized approaches are classified into three categories according to their
problem formulations: the graph-based approaches, the network flows approaches,
and the network partitioning approaches. [5]
Disturbed Channel Assignment Method:
Distributed CA approaches involve communication and coordination among multiple
parties; they are more difficult to design than their centralized counterparts.[5]
Figure 2: Classification of Channel Assignment
21202 B. Sathyasri
Key Design Issues of Channel Assignment in Multi Channel Mutli
Radio WMNs
In Channel assignment we should follow some of major issues while assigning the
channel to the users.
Main design issues are as follows.
a) Interference
b) Connectivity
c) Stability
d) Throughput/Delay
e) Routing
f) Fault Tolerance
g) Fairness
Interference
Interference is one of the important issues that causes in channel assignment in
WMNs. When two close by nodes assigning similar frequency, they cannot transmit
data at the same time. Interference is the prime factor that degrades the network
performance. [7]
There are two models:
a) Protocol Model
b) Physical Model
Protocol Model: Each radio has an interference range and a transmission range For
example a transmission from radio 1 to radio 2 is successful. If 2 is in the
transmission range of 1 and not in the interference range of radios other than 1 that are
currently transmitting.
Physical Model: If transmission is active the Signal to Interference and Noise
Ratio (SINR) of the transmitter’s signal at the receiver is best and the interference and
noise power at the receiver consists of the noises generated by other ongoing
transmissions and the ambient noise in the network.
Connectivity
The difference between the single-channel and multi-channel networks is that
Channel assignment can change the network topology.
Connectivity is defined on graphs, which are used to model computer networks.
Two graph concepts are Unit Disk Graph and Network topology. [3]
D
B
A C
(a) Unit Disk Graph
D
B
A C
(b) Network Topology
with discrepancy (1)
[2] [1]
[1, 2]
[2, 3] D
B
A C
(c) Network Topology
with discrepancy (2)
[2] [1]
[1, 2]
[1, 2]
Figure 3: Two Kinds of Discrepancies Between Unit Disk Graph And Topology
Comparative Study Between Static Dynamic and Hybrid Channel Assignment et.al. 21203
Stability
In channel assignment the stability of the network is depend upon two things i) Ripple
effect ii) Channel Oscillation.
Ripple Effect: A stretching effect or series of consequences caused by a single
action or event. [3]
Channel Oscillation: The channel assignment does not converge and changes back
and forth among several choices.
Throughput/ Delay
Throughput: Rate of successful message delivery over a communication channel.
Channels should be treated differently when assigning channels.
Delay: The delay of a network specify how long it takes for a bit of data to travel
across the network from one to another. [3]
Routing
Routing is the process of selecting best paths in a network. Forwarding network traffic
among networks or simply forwarding.
Fault Tolerance
Fault tolerance enables a network to continue working correctly in the event of the
failure also.
Fairness
A basic fairness criterion for Channel Assignment is the capability to avoid that the
traffic of some nodes only has access to crowded channels shared by many links.
Implementation of Static, Dynamic And Hybrid Architecture
Static Architecture
In Static Channel Assignment schemes, a set of channels is permanently allocated to
each node in the network.
Entire number of available channels in the system S is divided into sets; the
minimum number of channel sets N required serving the entire coverage area.
Static Channel Assignment schemes are often not able to maintain high quality of
service and capacity attainable with static traffic demands.
Dynamic Architecture
In Dynamic Channel Assignment schemes, all channels are kept in a central pool and
are assigned dynamically to new nodes as they arrive in the system.
After each node task is completed, the channel is return to the central pool. It is
fairly easy to select the most appropriate channel for any node based simply on
current allocation and current traffic, with intend of minimizing the interference.
Dynamic Channel Assignment scheme can overcome the problem of static
Channel Assignment scheme.
21204 B. Sathyasri
Hybrid Architecture
Hybrid Channel Assignment schemes are the combination of both Static Channel
Assignment and Dynamic Channel Assignment techniques.
The hybrid architecture is designed in such a way that each dynamic interface
maintains multiple queues in the link layer with one queue for each neighbor and
static interface has a single queue for each neighboring nodes. The data to be sent to
each neighbor are buffered in the corresponding queue.
Dynamic interface has data to transmit, it selects a neighbor that it wants to
communicate and try to negotiate a common channel with the neighbor.
When there exist a static channel between the source and destination node then the
node can transmit some packet through the static channel and the rest through the
dynamic channel in order to reduce the delay and to overcome the node failure
problem.
Figure 4: Hybrid Node Architecture
When a node needs to transmit data in a hybrid network then each node informs its
neighbors of its fixed channels by broadcasting a message to all the channels of its
neighbors. A node needs to transmit some packets to a neighbor; it first switches one
of its switchable interfaces to a channel, with the fixed interface of the receiving node,
and then sends the packets through the switchable interface. This approach maintains
good adaptivity to changing traffic.
There are many criteria for selecting neighbors. If throughput is the only concern,
we may select the neighbor with the longest queue. This strategy may cause
undernourishment. We enhance it with some fairness considerations, that is, we
estimate a neighbor priority by considering both its queue length and how long the
queue has not been served. A pair of nodes that have already negotiated a channel,
then node which sends data in that channel is the sending node, and the other node as
getting node. The node has not succeeded in negotiating a channel with any other
node is denoted as pending node. [4]
Adaptive Dynamic Channel Allocation
The adaptive dynamic channel allocation performs a hybrid channel allocation
protocol in multi channel multi radio wireless mesh network. In this hybrid network
each router have two interfaces, one interface from each router uses the static channel
allocation, while the other uses dynamic channel allocation. The static channel
allocation provides a fixed channel between the neighboring nodes and improves the
Comparative Study Between Static Dynamic and Hybrid Channel Assignment et.al. 21205
network throughput. The dynamic channel allocation maintains a switching channel
that switches between the neighboring nodes periodically this switching mechanism
reduces the overall packet delay and suitable for varying traffic pattern in the network.
The hybrid architecture is also capable of adapting to the changing traffic quite faster,
because the dynamic interfaces renegotiate channels every 100ms. Thus the hybrid
architecture provides a combined architecture of static and dynamic channel
allocation and is capable of improving the network throughput and dramatically
reduces the packet delay. [4]
In adaptive dynamic channel allocation when there are N nodes limited channel
negotiation is enough that the source node can directly transfer data to the destination
node hence this hybrid channel allocation dramatically reduces delay in the network
the below Fig 5 shows that node A and node B had already negotiated a common
channel between them and node D and node E also had negotiated a channel hence
when node A needs to transmit data to node E then it enough that node B and node D
negotiates to a common channel then node A transmits data through this route hence
reduces delay and improves the performance of the network. [4]
This does not have any effect with network having few number of nodes but when
the number of nodes increases then channel negotiation between all the node has to be
done and only then the data transfer can take place this causes huge delay and
interference in the network.
Figure 5: Adaptive Dynamic Channel Allocation
Assigning Interfaces To Channel
Fixed Interface:
In wireless mesh network when there are K interface, then M interface has to be
assigned statically between the nodes.
Switchable Interface:
The remaining K-M interfaces are dynamically assigned to any of the remaining K
interface, based on data traffic and is made to switch between the remaining interface.
21206 B. Sathyasri
The Fig.6 shows the basic hybrid channel allocation, where all the nodes are
connected through one static channel and multiple dynamic channels with the
neighbouring nodes.
Figure 6: Hybrid Channel Allocation
Channel Negotiation Algorithm
The channel negotiation algorithm provide a procedure to the nodes for negotiating a
common channel the node that had not negotiated a common channel with any other
node is the pending node. The node that has a common channel and sends data to that
channel is the sending node and the node that receives the data is the receiving node.
[4]
Pending Node:
It broadcast PNODE REQ message to notify its neighbors that it is a pending node
and if receives SWITCH CHNL then switch to channel c indicated in the message and
ends the connection.
Sending Node:
If its queue length for the receives node < QT then it broadcast SNODE REQ message
to notify its neighbours that it is a sending node and the traffic load is below
saturation. If it receives SWITCH CHNL and the receiving node (r) is not negotiating
with any other sending nodes then switch to channel c indicated in the message.
Notify r to switch to channel c and ends the connection establishment.
Receiving node:
If the queue length of the sending node < QT and if receives PNODE REQ then it
sends SWITCH CHNL message to the pending node including its own channel c and
ends the connection else if it receives SNODE REQ then it send SWITCH CHNL
message to the sending node including its own channel c and ends the connection.
Advantages of Adaptive Dynamic Channel Allocation Protocol
There are quite a few reward of using this hybrid channel allocation.
If purely static channel allocation strategies are used, the connectivity will be
degrading. By using one dynamic interface in each mesh node, the connectivity of the
network can be improved.
Comparative Study Between Static Dynamic and Hybrid Channel Assignment et.al. 21207
Purely static channel allocation strategies cannot adapt to the frequently changing
network traffic. The use of one or more dynamic links is able to direct traffic around
the congested areas and therefore achieve better load balance in the network.
The hybrid channel allocation provides improved network throughput and capable
of counteracting node failure and loss of packet it improves the fairness of the
network and provides better quality of service.
Interference and Congestion Aware Routing Protocol
The multi channel multi radio wireless mesh network consist of more than one
channel assigned to each routers hence interference and congestion is the major
parameter which determines the performance of the network. In order improve the
throughput and to reduce the packet loss in the network the interfering links and
congestion occurrence must be considered while selecting the route to the destination
router.[4]
The dynamic routing protocols, routes based on the shortest path and switching
channel and does not considers the interfering links and proper utilization of
bandwidth therefore the congestion and interference in the network is more this
eventually reduces the throughput and fairness of the network.
In order to improve the channel consumption and network throughput in the multi
channel multi radio wireless mesh network it is very important that the routes of
different flows to be selected efficiently such that channel usage is balanced at each
node and links are selected for routing based on the probability of interference.
Steps In Interference And Congestion Aware Routing Protocol.
The routing in interference and congestion aware routing is performed by
Route discovery.
Route maintenance.
Interference and congestion based routing.
Rediscovery and switching of channel.
Route Discovery
The route discovery is the process involved for finding the routes for an efficient data
transmission which provides better quality of service and bandwidth usage. Route
discovery process is initiated by source router which broadcast a Route Request
(RREQ) packet. All the routers looks into its routing table and send route reply
message (RREP) the ICAR protocol selects the best route which provides better
utilization of network bandwidth and reduces the interference and congestion in the
network.
Route Maintanance
The route maintenance is the process involved to check and maintain the performance
of the link in the network. It periodically checks and evaluates the bandwidth
utilization and state of congestion in the network to perform channel switching to
21208 B. Sathyasri
reduce the interference. In case of congestion or interference in the network the
routing protocol selects a different route.
Interference and Congestion Aware Routing
The interference and congestion aware routing performs evaluation of congestion
occurrence in the network and when there is a possibility of congestion occurrence the
ICAR protocol selects a new route that provides congestion less and interference free
route with low bandwidth utilization.
Rediscovery and Switching of Channel
The ICAR protocol performs switching of link to another router based on rediscovery
of routes with minimum consideration of congestion less and interference less route
with queue length less than queue threshold.
Interference Reduction In Wireless Mesh Network
The interference and congestion aware routing protocol aims to reduce interference by
proper selection of channels based on the state of congestion occurrence in the links.
In order to determine the state of congestion each link is categorized into three states
they are,
Congested state.
Low congestion state.
Median congestion state.
Congested state is the state of a link where the transmission through that link had
already resulted in congestion and therefore it is not the desirable route for
transmission of data. Median congested state is where the link has considerable
amount of load but still it is able to transmit considerable amount of data based on the
data rate. Low congested state is the state where the link has very low load and the
link is more suitable for heavy load hence preferred for additional traffic.
The ICAR protocol considers the congestion state and bandwidth availability for
routing where the number of links connected to each router is taken into account to
define the occurrence of interference and performs two determinations they are, [4]
Determining of the links states.
Determination of interfering links.
The link state can be inferred from the queue length and the interfering links can
be determined from the number of interfaces working on that router and based on the
congestion state and bandwidth the link is selected for routing.
The total bandwidth consumed for routing in a network of routing path R with a
data rate of d and link l belongs to the path R and interfering links be IE(l) and ETX(l)
be the expected transmission count of link l. is calculated by, [4]
Total Bandwidth = ∑ [IE (l)] * ETX (l)*d , where l € R.
Where,
l – Links in the network.
R – Routing path.
ETX (l) – expected transmission hop count.
IE (l) – interfering links.
Comparative Study Between Static Dynamic and Hybrid Channel Assignment et.al. 21209
The bandwidth metric reflects the resource consumed by routing the flow through
the network. In order to support as many as flows in the network as possible the
routing of each flow must consider the bandwidth and congestion occurrence with
interference in the network. In order to provide better quality of service and fairness
the ICAR protocol routes to suitable links which considers efficient utilization of the
bandwidth and selects channel based on the occurrence of congestion and interference
in the network.
Advantages of Interference And Congestion Aware Routing Protocol
It improves the network throughput and reduces the packet delay in the network.
It reduces switching latency and packet loss in the hybrid multi channel multi radio
wireless mesh network.
It provides proper utilization of channel and bandwidth of the network thereby
improves the quality of service and fairness of the network.
Performance Evaluation
The parameters are to be found are
Network Throughput
Packet Delay
Fairness
Quality of Service
Network Throughput
It can be seen from the Fig 7 that the throughput of the dynamic channel allocation
increases as the data rate increases and when the data rate reaches 5Mbps the network
throughput increases slowly and on further increases in data rate results in decreases
of network throughput. But in static channel allocation the network throughput
increases with data rate and can support data rate up to 25Mbps with unnoticeable
change in the performance of network.
It can be seen from the Fig 7 that in hybrid channel allocation protocol the network
throughput increases as the data rate increases up to 15Mbps beyond which constant
network throughput occurs and provides better throughput performance.
21210 B. Sathyasri
Figure 7: Throughput In Static, Dynamic And Hybrid Architecture
It can be seen from the Fig 8 that the throughput performance of the hybrid
architecture is better than static and dynamic channel allocation.
Figure 8: Bar graph for Network Throughput
Packet Delay
It can be seen from the Fig 9 that the average packet delay in the dynamic channel
allocation increases steeply as the data rate increases and between the data rate of
3Mbps to 4Mbps the delay is almost constant beyond 10Mbps the delay increases
slowly and the static channel allocation provides unnoticeable change in delay up to
25Mbps. In static channel allocation average packet delay is high for 1Mbps and
increases as the data rate increases.
It can be seen the Fig 9 that the hybrid channel allocation provides an optimized
delay and throughput and improves the performance of the network better than static
and dynamic channel allocation. A delay increase up to 4 Mb further increases in data
rate does not have a noticeable change in the average packet delay in the network.
Comparative Study Between Static Dynamic and Hybrid Channel Assignment et.al. 21211
Figure 9: Packet delay in Static, Dynamic and Hybrid architecture
It can be seen from the Fig 10 that the hybrid architecture reduces the average
packet delay in the network than static and dynamic channel allocation.
Figure 10: Bar graph for average packet delay
Fairness
The fairness of the network is examined where we vary the data rate and focus on the
rate of packet loss in the network. It can be seen from the Fig 11 that the lossless
packet delivery ratio in the dynamic channel allocation is better than the static channel
allocation.
From the Fig 11 it can be seen that the amount of packet loss in hybrid architecture
is less compared with the static and dynamic channel allocation and hence the fairness
of the hybrid architecture is better than the static and dynamic channel allocation.
Often to improve the throughput and reduce the delay in the network the fairness of
the network is sacrificed but in hybrid architecture the fairness is also considered and
improved.
21212 B. Sathyasri
Figure 11: Fairness in Static, Dynamic and Hybrid architecture.
It can be seen from the Fig 12 that the fairness of the hybrid architecture is
optimized, counteracting average packet delay and network throughput better than
static and dynamic channel allocation.
Figure 12: Bar Graph For Fairness
Quality of Service
The quality of service is a priority based approach where each specific service is
prioritized differently and the network provides different service to the flow.
Comparative Study Between Static Dynamic and Hybrid Channel Assignment et.al. 21213
Quality of Service Performance on Throughput
Figure 13: Quality of Service performance on throughput when number of user varies
Quality of Service Performance With Packet Delay
The packet delay is moderate for number of users between 10 and 18 and as the
number of user’s increases the bandwidth is utilized at the maximum and hence the
network is entirely utilized and hence the delay in the network is increased beyond 20
users, as shown in Fig 14.
Figure 14: Quality of Service Performance on Delay When Number of Users Varies
21214 B. Sathyasri
Conclusion and Future Enhancement
The main aim is to increase the overall network throughput and average packet delay
in the multichannel multiradio wireless network. Here performance of the hybrid
channel allocation strategy and interference and congestion aware routing protocol for
reducing congestion and interference in the network thus improving the overall
network throughput and reduces the packet delay in the network more effectively and
efficiently than the static and dynamic channel allocation. Along with the network
throughput and packet delay analysis in the network, we also examined the fairness
and quality of service provided by the hybrid architecture and it can be seen that the
fairness performance of the hybrid architecture is better than the existing method and
the hybrid architecture provides a varying throughput and packet delay processing for
varying number of user in the network since the bandwidth is equally shared between
the different flows and to different number of users in the network.
In future the same performance analyzing strategy on hybrid architecture can be
extended by including the parameter such as the energy used by each node and the
power consuming efficiency of the hybrid multichannel multiradio wireless mesh
network can be used for providing better and efficient quality of service and fairness.
References
[1] I.F. Akyildiz and X. Wang, “Wireless Mesh Networks: A
Survey,”Computer Networks, vol. 47, pp. 445-487, 2005.
[2] Tinku Rasheed and Massimiliano Slongo. “Channel Assignment in
Wireless Mesh Networks” CREATE-NET TECHNICAL REPORT CN-
TR-200800022. 2008.
[3] WEISHENG SI and SELVADURAI SELVAKENNEDY “A Survey on
Channel Assignment Approaches for Multi- Radio Multi-Channel
Wireless Mesh Networks” August 2007.
[4] Y. Ding, K. Pongaliur, and L. Xiao, “Hybrid Multichannel Multiradio
Wireless mesh network “,(icnp) , 2009.
[5] K.N. Ramachandran, E.M. Belding, K.C. Almeroth, and M.M. Buddhikot,
“Interference-Aware Channel Assignment in Multi-Radio Wireless Mesh
Networks,” Proc. IEEE INFOCOM, 2006.
[6] P. Kyasanur and N. Vaidya,” Routing in Multi-Radio Multi-Hop Wireless
Mesh Networks” (ispan), 2006.
[7] GUPTA, P. and KUMAR, P.R. 2000. The capacity of wireless networks.
Information Theory, IEEE Transactions on 46 (2), 388-404.
Biographies
B.Sathyasri is currently working as Assistant Professor in VELTECH Avadi, Chennai. I
received M.E (Embedded Systems) in 2007 from Anna University, Chennai. I have 10
years of teaching experience in various engineering colleges. Am doing research in Anna
University, Chennai. Am very much interested in Wireless Communication and networking.
I published 4 papers in national conferences.
Dr.Senthil Kumar Ponnusamy is currently working as Professor and Head of the Department
of Information Technology, SKR Engineering College, and Chennai. He received his ME in
2002 from Arulmigu Kalasalingam college of engineering, Krishnankovil and PhD in 2010
from Bharath University, India. He has 13 years of experience in various engineering college.
He has published 26 papers in various national and International journal and conferences. His
area of research is network.
Dr.E.N.Ganesh is currently working as Dean (Research and Innovation) at Rajalakshmi
Institute of Technology . He received M.Tech., degree in Electrical Engineering from IIT
Madras, Ph.D. from JNTU Hyderabad. He has over 20 years of academic experience in
various engineering college. His area of interests is Nanoelectronics, Robotics and Hyper
spectral Image Processing.
