Design and Implementation of TDMA-Based Cooperative MAC Protocol
|School||National University of Defense Science and Technology|
|Keywords||Cooperative communication Cooperative MAC protocol TDMA Slot assignment Cooperative strategy|
As one of the hotspots in communication filed, cooperative communication technology servers to cope with wireless channel fading,enhance communication reliability and increase system throughput. By employing the broadcast nature of the wireless signal, cooperative communication chose one or more cooperative nodes retransmit the overhearing data to achieve cooperative diversity gain. Many researches have been done and many achievements have been acquired in physical layer and MAC layer. However, there are also many problems to be solved before employ in practical applications. Consider the need of the practical project, this paper focus on the study of design and realization of a cooperative MAC protocol.Firstly,this paper introduces several factors that affect the design and the effect of the MAC protocol. With the physical layer and the system requirement considered, a layered distributed network structure and a TDMA based access strategy are proposed, and the time frame and the packet form also have been designed, so the QoS and efficiency assured with the stable of the network.Secondly, the importance of the synchronization is emphasized. The synchronization of the slot is base of TDMA access and the also necessary for DSTC. With the thought of exchange frame to achieve time synchronization in NTP and take the MAC flow in consider, a slot synchronization scheme is proposed. The scheme achieves the synchronization of super frame , frame and slot by open loop synchronization scheme, and then achieves clock count synchronization by close loop synchronization scheme. The validity of the scheme is proved by analysis and the implement.Thirdly, researches are done on the two major factors that affect the efficiency of the MAC protocol. By analyzing the advantage and the disadvantage of fixed allocation and dynamically, a hybrid allocation scheme that combined fixed allocation and allocation is proposed. The scheme makes the frame length dynamically and adjusts to the network topology, and can support QoS under high efficiency. A cooperative MAC protocol is designed with the careful design of transmit model and cooperative node choose. The protocol can cope with the performance decline under the fading channel with makes use of idle slots and good condition cooperative node.At last, by describing the MAC flow and parameter choice from network model,node model and process model, a MAC protocol model is build up. The simulation is done one the model, and the results show the slot allocation scheme and the cooperative MAC protocol works well.