Analysis of Access Delay in Ad Hoc Wireless Networks for Multimedia Applications

Analysis of Access Delay in Ad Hoc Wireless Networks for Multimedia Applications

Arundhati Arjaria (Rajiv Gandhi Proudyogiki Vishwavidyalaya, India)
Copyright: © 2019 |Pages: 15
DOI: 10.4018/978-1-5225-9096-5.ch006

Abstract

Mobile ad hoc networks are infrastructure-less wireless networks; all nodes can quickly share information without using any fixed infrastructure like base station or access point. Wireless ad hoc networks are characterized by frequent topology changes, unreliable wireless channel, network congestion, and resource contention. Multimedia applications usually are bandwidth hungry with stringent delay, jitter, and loss requirements. Designing ad hoc networks which support multimedia applications, hence, is considered a hard task. The hidden and exposed terminal problems are the main which consequently reduces the network capacity. Hidden and exposed nodes reduce the performance of the wireless ad hoc networks. Access delay is the major parameter that is to be taken under consideration. Due to hidden and exposed terminal problems, the network suffers from a serious unfairness problem.
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Introduction

In wireless ad hoc networks, the well-known hidden terminal and exposed terminal problems may degrade the performance of the network in terms of lesser throughput and unfairness problems. Medium Access Control (MAC) protocol is a contention based protocol which has been simulated and implemented widely for various reasons. MAC has a critical role in the performance computation in Wireless Ad hoc Networks. The main aim to design this protocol is to increase the channel utilization. Where multiple contending terminals are there to access the same medium, MAC protocol is used for association of the all the nodes for channel utilization.

To achieve this goal MAC scheme has to minimize the chances of collisions and at the same time maximize the Spatial reuse Ad hoc networks are continuously becoming popular because of their characteristics such as lesser cost, easy to install and no need of any fixed and pre-installed infrastructure. An ad hoc network is known because of its self-organized behavior. Ad hoc network plays very important role in various applications includes a fety operations, catastrophic recovery, ad hoc formation of networks in conferences, connecting wirelessly in rustic places where any stable infrastructure is not available. Such a network is expected to work in the lack of any infrastructure by independently creating multi-hop paths for carriage of the packets. Multimedia has a significant function in the development of wireless networks supporting high bandwidth applications with QoS.

An ad hoc network is a set of wireless mobile nodes where there is no need of interference of incorporated access points or base stations that form a dynamic autonomous network. Ad hoc networks are different from traditional wireless networks, which do not need any fixed network infrastructure and can be deployed as multi-hop packet networks rapidly and with relatively low price. Such networks can be very useful in the environment where natural condition or time restraints makes it impossible to have infrastructure pre-deployed or in emergency cases. Ad hoc networks are useful in military, emergency services, meetings, and home or official instruments.

Ad hoc wireless networks are becoming popular because of their advantages such as less costly, easy to deploy and no need of any stable and pre-deployed infrastructure. An ad hoc network is characterized by its self-organized behavior.

To achieve high utilization of a channel in a medium, Medium Access Control protocol also needs to enhance the spatial reuse level. To achieve this goal exposed terminal problem should get resolved. Exposed terminal problem is a factor that affects the spatial reuse. An exposed terminal senses the transmission at the transmitter end & does not interfere with the reception at the receiver end.

The introduction towards hidden and exposed terminal problem is as follows:

Consider the scenario with three mobile nodes. The transmission area of node A can sense node B, but not node C (the detection range does not reach C either). The transmission range of node C can sense node B, but not node A. Finally, the transmission range of node B can sense node A and node C, i.e., node A cannot detect node C and vice versa. A starts sending to B, C does not receive this transmission. C also wants to send something to B and senses the medium. The medium appears to be free, the carrier sense fails. C also starts sending causing a collision at B. But A cannot detect this collision at B and continues with its transmission. A is hidden for C and vice versa. While hidden terminals may cause collisions, the next effect only causes unnecessary delay. Now consider the situation that B sends something to A and C wants to transmit data to some other mobile phone outside the interference ranges of A and B. C senses the carrier and detects that the carrier is busy (B’s signal). C postpones its transmission until it detects the medium as being idle again. But as A is outside the interference range of C, waiting is not necessary. Causing a ‘collision’ at B does not matter because the collision is too weak to propagate to A. In this situation, C is exposed to B.

Figure1.

Hidden and exposed node problem

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