The Study Of The Link Adaptation And Relay Selection In The DF Cooperative Communication Networks

The technology of cooperative communication is the further use of MIMO (multiple-input multiple-output). This technology can gets the especial gain of MIMO with single antenna in one terminal. The basic idea is that the terminals with single antenna can share each others antennas with some modes to create a virtual MIMO system and further to get gain in a multi-user environment. The link adaptation is an effective method to improve the spectrum efficiency under the premise of guaranteeing the performance of the bit error rate. In the non-cooperative networks, this technology has been highlighted and applied in many areas. This thesis investigates the performance of the link adaptation in common decode-and-forward (DF) cooperative communication network and security DF cooperative communication network respectively. The main contributions are as follows:(1) By introducing the channel type judgment into the common cooperative networks, the channel type fitting with the realistic channel conditions is determined. Where the channel type is known the signal to noise (SNR) intervals which are suitable to different modulation techniques are obtained. The selection between the fast link adaptation and the slow link adaptation depends on the speed of the destination node. Thereafter, a kind of relay selection method in the adaptive cooperative network is proposed. Simulation results show that using the channel type judgment and fast and slow fused link adaptation can promote the system outage performance effectively. Although fast and slow fused link adaptation has a slightly lower spectrum effectiveness, compared with the fast link adaptation, it reduces the complexity of system obviously.(2) In the security cooperative communication network, aiming at the physical layer information security in the wireless environments, this paper proposes a secure relay selection method based on the fast and slow fused link adaptive transmission. In this method, the fast or slow link adaptive transmission depends on the mobile velocity. Whether using jamming node or not depends on the "positive" or "negative" effect that the jamming node will play on the secure capacity of the system. On this basis, the relay forwarding the data to the destination is selected through maximizing the secure capacity. Performance analysis for the proposed method, in terms of the outage probability, is given and validated by simulation. More simulation results show that our proposed method has the lower bit error rate and outage probability and the lager secure capacity, compared to the methods in the literatures.