Research On Multi-channel MAC Protocol And Bandwidth Adaptation In Wireless Networks

The prevailing of the wireless broadband services calls for a significantimprovement of the wireless network performance, and it is difficult to satisfy theincreasing demand under the limited available bandwidth. Because wireless media isopen and shared by neighbor nodes, the traditional single channel media access control(MAC) protocols work inefficiently while taking all available wireless media as onechannel. However, by dividing the wireless media into several orthogonal channels,multi-channel MAC and bandwidth adaptation can improve the wireless networkperformance in utilization efficiency of wireless media, which motivates thedevelopment of new protocols designed for wireless networks. To increase thebandwidth efficiency and improve the network capacity, in this dissertation, we willinvestigate the issues of multi-channel MAC and bandwidth adaptation protocols designin wireless networks. The main contribution of this disertaiton is as follows:Firstly, we propose a simple multi-channel MAC protocol for infrastructure-basedwireless LANs. The classical IEEE802.11DCF mechanism designed for single channelWLAN is analysed by employing Bianchi’s model and the results indicate that thesingle channel MAC protocol can not work well in the heavy traffic load and high speednetworks because of the high collision rate and excessive overhead respectively. Basedon above analysis, we propose a simple multi-channel MAC protocol forinfrastructure-based WLANs to improve the throughput performance without anymodification on the physical layer. The basic idea is that the contending nodes randomlyselect one channel from all available sub-channels to communicate with AP, whichleads both the alleviation of the channel contention by reducing the number ofcontending nodes and the decrease of the protocol overhead by reducing thetransmission rate. Furthermore, an extended analysis model based on Bianchi’s isproposed to quantitatively analyse the proposed multi-channel MAC protocol, revealingthe influence of the transmission rate and number of channels on the protocolperformance. Both the analysis and network simulation results validate the advantage ofour proposed protocol.Secondly, a self-adaptive multi-channel MAC protocol based on windowoptimization is proposed for distributed networks. Because of the distributedcoordination and the potential multi-channel hidden terminal and deafness problems, thedesign of multi-channel MAC protocol is more complicated than single-channel MACprotocol. In this research, we design a novel split-phase approach multi-channel MACprotocol, which dynamically designates the optimal size of control window and datawindow. The main idea is that each node measures the real-time network states bycarrier sensing and estimates the state in the following period depending on the previous measurements via utilizing a Kalman filter with change detector. Based on theestimation on the network state, the optimal sizes of control and data window arecomputed, which leads to an improvement of bandwidth utilization efficiency.Finally, a novel multi-channel random access and bandwidth adaptation protocolfor the SC-FDMA-based network is proposed. SC-FDMA mechanism enables differentnodes to transmit data parallelly without interference, and has been employed as themultiplexing access standard by WiMAX and3GPP LTE. This provides a practicalapplication platform for the research on the multi-channel access and bandwidthadaptation. This research proposes a novel multi-channel random access protocol for thewireless network based on SC-FDMA, which enables contending nodes to utilizemultiple subcarriers blocks to reserve a certain bandwidth. By using proportion-fairprincipal for bandwidth adaptation, orthogonal subcarrier blocks are assigned to eachnode, which improve the fairness among contending nodes and thus improve thebandwidth utilization.