Quality-of-Service Of Wireless Ad Hoc Networks At MAC Layer

A mobile wireless ad hoc network (MANET) comprises of a cluster of mobile nodes without any fixed infrastructure of base station. Due to the transmission range constraint of transceivers, two mobile nodes may communicate with each other either directly, if they are close enough, or indirectly, by having other intermediate mobile nodes to forward their packets. MANET has become the one of the most significant hotspots in the fields of computer networks and wireless communications over the last two decades. Since MANET can be rapidly deployed, it has important merit for military applications such as armies in march, battle fields, fleets in oceans and other hostile scenarios. Because of the existing bit error rate in shared wireless channel and dynamic topology, it imposes big challenge on Quality-of-Service (QoS) supportting for multimedia communications over wireless ad hoc networks.The media access control (MAC) protocol, which lies at the low layer of the protocol stack for MANET, has significant influence on the performance of the network. The most important MAC protocol for MANET is IEEE 802.11 Distributed Coordination Function (DCF). DCF is a career sense multiple access with collision avoidance (CSMA/CA) protocol with binary exponential backoff. By modeling of IEEE 802.11 DCF, this dissertation focuses on providing service differentiation and statistical QoS gurantee in original IEEE 802.11 ad hoc networks. Furthermore, the tranditional single channel 802.11 MAC protocol is extended for the case that multiple transceivers and multiple channels available for a node in MANET. The main contributions in this thesis are organized as follows.(1)Performance analysis of IEEE 802.11 DCF in non-saturated traffic conditionsOn the assumption that each station can buffer just one date packet, a bi-dimensional Markov chain model is developed for modeling of 802.11 DCF in non-saturated conditions. The analytical model is quite simple but highly accurate. It's shown that basic access mechanism can achieve almost the same maximum throughput as that of RTS/CTS mechanism in non-saturated conditions, at the same time, the average packet delay as well as its standard deviation is much lower than that in saturated conditions.(2)Performance analysis of IEEE 802.11e service differentiation mechniams in non-saturated conditionsBy extending the Markov chain model for 802.11 station in non-saturated conditions, this thesis further analyazes the QoS differentiation performance of IEEE 802.11e EDCA in non-saturated conditions. Unfortunately, IEEE 802.11e just can achieve relative service differentiation in saturated conditions. When the total load is less than the optimal point, 802.11e can hardly achieve significant serice differentiation.(3)On packet size and arrival rate diversity in IEEE 802.11 ad hoc networksPacket size and arrival rate diversity is very typical for practical traffics over 802.11 wireless links. The analytical model is useful for addressing the question of fairness between competing flows over IEEE 802.11 wireless links. When the total load is less than the optimal value, the throughput of each station is approximate to its load and the packet delay is much lower than that in saturated cases despite the packet size and arrival rate diversity. The results also indicate a MAC-independent scheme for 802.11 DCF to achieve not only throughput differentiation but also statistical QoS guarantee including throughput and packet delay.(4)Accurate queuing analysis of IEEE 802.11 MAC layerIn this thesis, the author develops a unified analytical model for IEEE 802.11 DCF with arbitrary buffer size in unsaturated conditions. The model comprises of a generalized Markov chain model and an M/G/1/K queuing model which enabling the thorough and accurate queuing analysis of IEEE 802.11 MAC layer. The performance metrics of queuing system include throughput, average queuing delay, and packet blocking probability, the average MAC service delay as well as its standard deviation.(5)Performance optimization and statistical QoS provisioning for IEEE 802.11 DCF in non-saturated conditionsIt's shown that for practical 802.11 wireless ad hoc networks (i.e., buffer size larger than one and number of stations comparatively large) under the optimal offered load, the total throughput is maximized, the packet blocking probability (due to limited buffer size) and the average queuing delay tends to zero, the average MAC service delay as well as its standard deviation, which is much lower than that in saturated conditions, has its upper bound, furthermore, the optimal load is very close to the maximum achievable throughput regardless of the number of stations or buffer size. Hence the original IEEE 802.11 DCF protocol can accurately providing statistical QoS guarantee under optimal load.(6)Multi-transceiver multiple access (MTMA) protocol for mobile wireless ad hoc networksIn this thesis, the author proposes a multi-transceiver multiple access (MTMA) protocol for ad hoc networks in which each node has multiple sub-nodes equipped with independent wireless transceiver which can be tuned over all the available wireless frequency bands defined by IEEE 802.11 standard. Every sub-node dynamically reserves an idle traffic channel by RTS/CTS dialogue on the common channel that enable a node to perform parallel communications with other nodes. The MTMA protocol, which is suitable for vehicular based tactical ad hoc networks, greatly outperforms the single-transceiver RTS/CTS protocols with single channel or multi-channel.