PhD Alumni Detail

Name: Md. Ruhul Amin
Supervisor: Dr. Md. Shohrab Hossain
Abstract: Wireless networking is expanding fast and becoming popular rapidly among the people as a means of communication. The demands for high speed data rates are growing and the traditional in-band half-duplex (IB-HD) wireless has become unable to satiate such demands with the available scarce bandwidth owing to the conventional belief that an IB-HD radio transceiver cannot transmit and receive simultaneously in the same radio channel. In-band full-duplex (IB-FD) wireless is a promising next generation communication technology which can double the spectral efficiency with respect to the conventional IB-HD radio. Therefore, the fundamental re-design of the wireless system is required not only at the physical layer but also at the medium access control (MAC) layer of the TCP/IP protocol stack to fully exploit the potential benefits of IB-FD radio. Unlike half-duplex wireless local area networks, MAC protocols for IB-FD wireless networks have to deal with several unique issues and challenges which have been identified and explored in this dissertation. Hidden station and inter-station interference are the two dominant impediments in achieving two folds spectral efficiency for the higher layers using IB-FD wireless. Hidden stations degrade the performances of any practical wireless networks, but unlike IB-HD, hidden station scenarios are diverse in IB-FD wireless networks. This dissertation presents a CSMA based MAC protocol exploiting the network allocation vector of the IEEE 802.11 RTS-CTS access scheme, whereby mitigating the hidden station problem. No other work has been proposed in literature which derives an analytical model to unveil the impact of the distance between a primary-secondary transceiver pair in order to select a secondary receiver to initiate a successful relay like IB-FD wireless link, thereby diminishing the adverse effect of the inter-station interference. The proposed analytical model shows that, in the presence of hidden stations, the number of IB-FD transmission link increases if the secondary transmitter uses adaptive transmission power. The performance of the proposed protocol has been evaluated through detailed simulations using a modified version of network simulator-3 (NS-3) in which the wireless module has been re-designed to accommodate the concept of IB-FD radio. Simulation results show that the proposed MAC protocol achieves at least 1.61 times higher throughput and consumes 1.58 times lower energy than the IEEE 802.11 RTS-CTS access scheme. The IEEE 802.11 distributed coordination function (DCF), a slotted binary exponential back-off scheme, has been used extensively as the fundamental contention resolution technique in IB-HD wireless networks. Unlike IB-HD, an IB-FD network can contain two simultaneously active transmission links within a single collision domain. In addition, from the perspective of MAC sub layer, an IB-FD wireless transceiver being in transmit mode can detect collision. These phenomena invalidate the applicability of the existing models to compute the performance (i.e., saturation throughput) of the IEEE 802.11 DCF accurately in IB-FD wireless networks. A simple discrete time markov chain (DTMC) based probabilistic model has been formulated to evaluate the performance of the IEEE 802.11 DCF in the context of IB-FD wireless networks. This dissertation also presents two MAC protocols for two types of network scenarios taking early collision detection capability of a transceiver into consideration. Exploiting the concept of primary-secondary transmission link along with the effect of inter-station interference free parameter (?), the probability that a station transmits either as primary or secondary in a random time-slot has been derived thoroughly taking the secondary transmitter's back-off counter into account. The analytical results show that, the proposed protocol, when applied to network without hidden stations, has obtained 1.68 times higher throughput than that of the IEEE 802.11 basic access scheme. Increased throughput gain has been realized with hidden stations, thanks to the busytone frame and the ?. Extensive simulations using NS-3 have been carried out on network topology with varying number of stations. It is observed that simulation results closely conform to those of the analytical results.