IEEE 802.11-based wireless ad hoc networks are well suited for critical scenarios such as rescue operations during natural calamities, military applications on battle fields and so on where the existing infrastructure fails. In these networks, since nodes have limited battery power, the reduction in packet collision is very important, otherwise the nodes have to spend more energy for packet transmission. In these wireless networks, the packet transmission procedure plays a pivotal role in performance. Several packet transmission procedures represented with Markov chain models have been suggested by the authors to improve the network performance. However, these procedures have not been suitable for dense networks due to the high collision rate. A new packet transmission procedure for the IEEE 802.11 distributed coordination function (DCF) protocol is proposed to reduce the number of collisions and enhance the throughput of wireless networks. A mathematical framework is carried out for transmission probability and performance analysis is presented showing that the new procedure greatly enhances the network performance and as a result can be applied in the design and performance optimisation of wireless network protocols.Introduction: Distributed coordination function (DCF) is the basic medium access control technique used in all IEEE 802.11-based wireless local area networks. Basic access and request-to-send/clear-to-send (RTS/CTS) access are the two techniques described in the DCF protocol for data transmission. A DCF uses carrier sense multiple access with collision avoidance scheme with the binary exponential backoff (BEB) algorithm.Several packet transmission procedures have been suggested by researchers for the DCF protocol and are represented by a two-state Markov chain model. Many researchers concentrated on the performance evaluation of DCF assuming ideal channel conditions. Bianchi [1] was the pioneer of the model which includes the exponential backoff process intrinsic to 802.11 as a two-dimensional Markov chain in order to analyse the saturated throughput of 802.11 and demonstrate that the Markov analysis works fairly. 'Busy-medium' conditions are cogitated in the model to improve the accuracy of the results [2]. Here, the channel errors are not considered and the throughput is analysed under saturated traffic conditions. Bianchi's model was extended by Malone et al.[3] to assess the throughput in non-saturated conditions bearing in mind various traffic arrival rates. The throughput is analysed taking into consideration the capture effects and transmission errors over Rayleigh fading channel conditions in [4]. However, these models cannot evaluate the performance of DCF accurately. Besides, the currently existing models experience high packet collisions causing degradation of throughput, predominantly under congested environments. In our previous research, we have modified the DCF protocol called the collision alleviating DCF (CAD) protocol and proved that the model predicts the performance of the networ...
The IEEE has standardized the 802.11 protocol for Wireless Local Area Networks. The primary medium access control (MAC) technique of 802.11 is called distributed coordination function (DCF). DCF is a carrier sense multiple access with collision avoidance (CSM A/CA) scheme with binary exponential backoff algorithm (BEB). DCF describes two techniques to employ for packet transmission: the two-way handshaking technique called basic access mechanism and an optional four way handshaking technique, known as request-tosend/clear-to-send (RTS/CTS) mechanism. In wireless networks, the energy consumed to transmit bits across a wireless link, is a critical design parameter. The Constant backoff Window Algorithm (CWA) is the modification of the IEEE 802.11 BEB algorithm, which is used to control the contention window in the case of collisions, in order to provide a better Throughput and Energy efficiency. The new algorithm has been tested against the legacy IEEE 802.11 through matlab simulation. The tests have shown significant improvements in performance in throughput and energy efficiency using CWA compared to the original BEB algorithm.
The increasing rate of users and network capacity creates a necessity to address the challenges in Wireless Ad-hoc Networks. Secrecy of information in wireless ad hoc networks also plays a vital role. Physical layer security is an essential technology to achieve secure information transmission in Wireless Ad hoc networks. Several algorithms are developed to transfer the data between legitimate users with zero information to the eavesdropper appearing with uniform distribution only. In this paper, Opinion Trust Algorithm was developed to improve the transmission rate in Wireless Ad hoc networks considering eavesdropper appearing with uniform distribution as well as random distribution. The performance metrics throughput, packet loss and delay are improved even considering random distribution.
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