Research On MAC Layer Protocols For Wireless Cooperative Networks

In recent years, cooperative communications is an enhanced method, which can overcome negative multi-path effects, effectively increase the spectrum efficiency and robustness of wireless systems. Meanwhile, cooperative communication technology can improve the channel situation, promote the practical application of MIMO technology and solve the contradiction between high-speed transmission and network coverage, which caused widespread concern from academe and enterprises, has been recognized as a candidacy of the future mobile communication system.This dissertation studies on MAC layer key technologies of multi-user cooperative transmission in future wireless networks. My research focuses on cooperative protocol design for uplink transmission and reliable MAC layer cooperative broadcast mechanism for downlink transmission.Firstly, to adapt to variable wireless channel and dynamic network topology, I investigate cooperative choice and partner selection mechanism, and propose an adaptive cooperative MAC ptotocol, called ACoopMAC, based on channel state information (CSI) feedback. In ACoopMAC protocl, the station selects transmission mode based on the instantaneous channel measurements and will determine again whether it directly transmits to the receiver or forwards through a helper station, which can enhance the robust of cooperative protocol. Meanwhile, a new network allocation vector (NAV) mechanism is introduced to reduce access delay of stations caused by collision, which is beneficial to throughput improvement. Simulation results show that ACoopMAC is superior to the existing cooperative MAC protocols when it comes to saturated throughput, access delay, mean energy consumption, and node mobility.Sencondly, the existing cooperative MAC protocols change more or less the frame formats of legacy RTS/CTS in order to support the cooprative communications among multi-users, which causes the control signalings of cooperative transmission is not comptabile with those of directly transmission. By fully utilizing the reserved bits in the head of control frame, the information of CSI is piggybacked in control signalings and a cooperation flag is introduced to indicate whether coopertive transmission is adopted. Thus, the adaptive cooperative MAC protocol is completely compatible with the legacy 802.11 DCF.Thirdly, in order to overcome absence of efficent analysis model of cooperation at MAC layer and complexity of typical 2-dimensional Markov chains analysis model for MAC protocols, I investigate performance analysis of cooperative MAC protocl. A simple analytical model based on elementary conditional probability and geometrical probability is proposed to evaluate performance of cooperative MAC protocol and closed-form solutions of throughput and average delay are given. On the basis of this, we develop an efficent system level simulation platform for cooperative MAC protocols and verify its scientificalness by simulation.Lastly, in order to greatly decrease the probability of collisions and improve system efficiency caused by uncertain hops, dynamic network topology and variable wireless channel, I propose a rate-adaptive cooperative broadcast mechanism based on node clustering. Furthermore, I investigate an analysis model based on elementary conditional probability and 1-dimensional Markov chains to model cooperative broadcast MAC scheme and evaluate its performance.The main works of this dissertation are investigating MAC layer protocols for cooperative wireless networks, an adaptive cooperative MAC protocols for uplink transmission and a reliable cooperative broadcast MAC scheme for downlink broadcast services are proposed. The research is helpful for study on cooperative communication from theroy to practice and has forward-looking in theroy and practicability in reality.