Researches On Guarantee Mechanisms Of QoS In Ad Hoc Networks

The mobile Ad Hoc network is a wireless system without a fixed (wired or wireless)infrastructure. There are no base stations or mobile switching centers in Ad Hoc networks.Consequently, all protocols used in it must operate in a distributed manner. As it can provide aflexible and convenient support for mobility and keep a continuous and seamless multimediacommunication, the mobile Ad Hoc networks have increasingly become the hot spot of personalcommunications and Internet recently.Different from fixed wired network and conventional cellular network, it is difficult toprovide QoS support in Ad Hoc networks with characteristics as dynamical changes of networktopology, limited wireless bandwidth, power limitation etc. Because of leaving out ofconsideration of the characteristics above, the traditional QoS frameworks and guaranteemechanisms in Internet can not be applied to Ad Hoc networks directly. As a result, it is requiredto design the novel QoS guarantee mechanisms and offer the corresponding QoS support for avariety of packets in Ad Hoc networks.Much attention has been paid on researches on Guarantee Mechanisms of QoS in Ad HocNetworks. Based on the analysis of QoS guarantee mechanisms applying to Ad Hoc networks,this paper executes a detailed research of cross-layer framework for supporting QoS.Subsequently, for eliminating drawbacks of QoS guarantee in the MAC layer, a novelmulti-channel MAC algorithm, which can improve TCP throughput and provide basic QoSsupport as bandwidth reservation and packets division, is proposed for Ad Hoc networks,.Furthermore, in order to testify the capability of our work, the mathematical model fortheoretical analysis and NS-2 for validation of the function and investigation of the performanceare used. The main research works and results are listed as follows:1. Put forward a cross-layer framework to support QoS in Ad Hoc networks.Nowadays, most of researches on Guarantee Mechanisms framework of QoS are based ondelamination, however, the delaminated QoS guarantee mechanisms cause the problem that eachlayer of network has optimized independently while the whole system can not get optimize.Therefore, integrated with the wireless channel prediction mechanism based on MARKOV chain,a cross-layer framework to support QoS is proposed. In this framework, the central controllerwhich consists of predictor, compensator and coordinator passes and coordinates stateinformation between the adaptive mechanisms,so as to improve the quality of service of Ad Hocnetworks.2. Implement the detailed performance analysis between existing multi-channel MACprotocols in Ad Hoc networks.Based on the exhaustive analysis of hidden terminal problem and exposed terminal problemwhich are the intrinsic problems of Ad Hoc networks, the conclusion that the problems abovecan be solved well under multi-channel MAC model is given. Subsequently, the thesis classifiesthe multi-channel MAC protocols into four categories which are dedicated control channel,common hopping, split phase and multiple rendezvous, and executes theoretic analysis andperformance comparison based on mathematical models and NS-2 simulation. The results ofanalysis show, the multi-channel MAC protocols based on dedicated control channel haveabsolute preponderance in improving Ad Hoc networks' performance, and have been chosen asthe foundation of the enhanced algorithm below.3. Put forward a novel bidirectional multi-channel MAC protocol (NBMC protocol) for AdHoc networks on the basis of increasing the TCP throughput.The protocol reduces the link-layer contention using two key ideas: (1) It utilizes multipletransmission channels at the link layer to decrease the contention time between flows. (2) Itextends the RTS/CTS handshake to do bidirectional channel reservations, which reducescontention between TCP data and ACK packets. The theoretic analysis and simulation resultsshow, compared with IEEE 802.11DCF algorithm, the TCP performance of NBMC is improvedobviously, especially in the TCP throughput and fairness of TCP flows. Furthermore, in order tosolve the hidden terminal and exposed terminal problems, the EX control packet used fordenoting the exposed terminals and the HIDE control packet used for preventing the hiddenterminals from receiving CTS packet successfully,are also introduced into the protocol.4. Put forward a QoS enhanced algorithm with Piggyback Reservations.Aiming at the limitation of NBMC protocol in dividing packets and reserving bandwidth, aQoS enhanced algorithm is proposed. For the data packets, the algorithm utilizes the originalNBMC protocol which provides high TCP throughout. For the real-time traffic with higherpriority, the system introduces piggyback reservations for ensuring the advantage of real-timetraffic while competing data channel. The NS-2 simulation results are satisfactory especially inthe effect of real-time packet latency and lossy.