To solve the problem of information being intercepted by illegal users during wireless communication, a secure transmission strategy based on optimal relay selection was proposed. Firstly, the pre-designed artificial noise and useful information were integrated at the source node, and the best relay selection algorithm was used to select the best relay to forward the received information. Secondly, the secrecy capacity, outage probability and interpret probability of the system were derived. Finally, the optimal number of relays were determined by the comprehensive performance of security and reliability. Theoretical analysis and experimental simulation results show that compared with the traditional system model without artificial noise, the performance of the proposed system can be significantly improved by adding relay nodes.

To overcome the severe performance loss of conventional coded cooperation schemes under dynamic channel conditions in mobility scenarios, a novel adaptive coded cooperation scheme was proposed by using rate-compatible Low-Density Parity Check (LDPC) codes in combination with a Hybrid Automatic Repeat reQuest (HARQ) protocol. It was assumed that channel state information changed during each transmission. By automatic retransmission of unequal length incremental redundancy, the equivalent code rates at the cooperative and destination nodes could be nonlinearly adjusted with channel conditions. The expressions for outage probability and throughput were derived for evaluating the system performance of the proposed scheme, and theoretical analysis and simulation results were presented. These results show that, compared with conventional schemes and equal-length retransmission schemes, the proposed scheme with properly designed compatible rates can effectively reduce the system outage probability, increase the throughput, and improve the transmission reliability of cooperative communications in mobility scenarios.