The Research Of Adaptive Transmission And Power Allocation In Cooperative Wireless Networks

In cooperative system, all nodes with a single antenna share resources and form a virtual multiple antennas transmission environment to help source node to transmit information to destination node in the network. It not only overcomes difficulties to fix multiple antennas on the portable mobile device due to the volume and energy restriction, but also can fully achieve the diversity gain of traditional multiple input multiple output technology and improve the performance of cooperative system. Adaptive techniques through transmitting higher rate speed information in good channel state condition and lower rate speed information in poor channel state condition can make full use of the time-varying characteristics of wireless channels, which improves the throughput performance of cooperative system. At the same time, as the transmitting power of communication system is limited, proposing new algorithm of allocating the limited power to each node to improve the performance of system is of great importance.Recently, cooperative communication technology has become one of the hotspots in the field of wireless communication. Most research about adaptive rate transmission is based on amplify-and-forward cooperative protocol at present, but amplify-and-forward protocol will bring the noise propagation effects, and need the destination node to know all the channel instantaneous state information, which greatly increases overhead to the system. This paper proposes a new adaptive M-QAM algorithm based on channel statistical state information in a multi-relay cooperative system with decode and forward protocol. The algorithm firstly deduces a tight closed upper bound of system symbol error rate, and then based on the closed expression, proposes an adaptive rate control scheme qualifying a given system SER. The simulation results show that the derived upper bound approximates the practical SER and the proposed adaptive rate scheme greatly decreases the overhead of system with very small performance loss compared with the adaptive rate algorithm based on the channel instantaneous state information.On the other hand, power allocation in cooperative communication system has been extensively studied both at home and abroad. But existed power allocation algorithms are restricted to the network with a single relay node or require the destination node to obtain all channel instantaneous state information. This paper proposed a new suboptimal power allocation algorithm based on channel statistic state information in a multi-relay cooperative system with decode-and-forward protocol .The algorithm first deduces an optimal model to minimize the derived closed upper bound of system symbol error rate, and then uses Lagrange multiplier method to obtain the power allocation factors. The simulation results show that the proposed suboptimal power allocation algorithm achieves performance gain.