Search

Recent advances in wireless communications promised the realisation of a revolutionary technique, called full-duplex (FD), which allows communication in both directions at the same time and over the same channel. However, the viability of FD in the physical layer requires the support of the MAC layer to fully spread the advantages of this technology to the whole wireless network. In this study, the authors introduce a distributed MAC protocol, termed distributed-access FD MAC, suitable for multi-hop communications whereby nodes are FD enabled. Using this protocol, a data packet can be forwarded by a number of nodes along a multi-hop path with un-contented access to the channel at each hop except for the head node. After detailing the specifications of this protocol, they establish a finite-state discrete-time Markov model to evaluate its performance. Using probabilistic mathematical methods, they derive important quantitative metrics such as path delay and throughput. Numerical results are provided and demonstrate the considerable improvement in network performance that the proposed protocol achieves compared with CSMA/CA half-duplex access mechanism.

In this paper, we present a novel analytical model for the service delay in IEEE 802.11 networks. This model is capable of closely tracking service delay's behavior in real wireless local area networks. We find a compact closed-form expression for the probability-generating function (PGF) of service delay using which all higher-order moments are achievable. We begin with finding the service-delay PGF; then we determine the probability density (mass) function of the delay metric by taking the inverse z-transform using numerical methods. At last, by comparing the first two statistical moments of this PGF with the mean delay and standard deviation from simulation results, the accuracy of the proposed analytical model is proved.

A cognition scheme, whereby nodes are enabled with the full-duplex technology at the PHY layer in conjunction with packet fragmentation at the MAC layer, is proposed to increase the performance of cognitive radio networks. As full-duplex allows doubling the throughput by equipping secondary users (SUs) with the capability to sense and transmit simultaneously, it also enables them to inflict considerably less interference to primary users (PUs), and to discover spectrum holes for transmission opportunities more efficiently. On the other hand, fragmentation technique at the MAC layer provides better quality-of-service for the SUs by empowering the information forwarding in the unpredictable PUs' channels in a progressive manner. Selecting the effective data transfer, the successful packet transmission time and the energy efficiency as metrics, we assess the performance of this cognition scheme and demonstrate its overall merits in cognitive radio networks, in comparison with conventional schemes that use half-duplex and no packet fragmentation.

IEEE 802.11 WLAN utilizes a distributed function at its MAC layer, namely, DCF to access the wireless medium. Due to its distributed nature, DCF is able to guarantee working stability in a wireless medium while maintaining the assembling and maintenance cost in a low level. However, DCF is inefficient in dealing with real-time traffics due to its incapability on providing QoS. IEEE 802.11e was introduced as a supplementary standard to cope with this problem. This standard introduces an Enhanced Distributed Coordination Function (EDCF) that works based on diff-Serve model and can serve multiple classes of traffics (by using different prioritizations schemes). With the emergence of new time-sensitive applications, EDCF has proved to be yet inefficient in dealing with these kinds of traffics because it could not provide network with well-differentiated QoS. In this study, we propose a novel prioritization scheme to improve QoS level in IEEE 802.11e network. In this scheme, we replace Uniform PDF with Gamma PDF, which has salient differentiating properties. We investigate the suitability and superiority of this scheme on furnishing network with well-differentiated QoS using probabilistic analysis. We strengthen our claims by extensive simulation runs.