Sign Of Short-Wave Ofdm System Based On Cooperative Communication

Short-wave or high frequency (HF) communications occupies a crucial position in the wireless communications field, and is transferring towards the Ad hoc network with the development of modern communications. Applying cooperative transmission into shortwave system, which has important research value, can eliminate the HF channel’s severe doubly-selective fading effectively.We study the HF communication and the space-time coding in cooperative technique. In this paper, a integrated HF cooperative communication system is proposed, which using the analysis of HF basic transmission forms and the space-time code scheme. In the system, HF communication form of different cooperation phases and coding scheme of each node are determined. Moreover, the system parameters are designed, according to the typical shortwave channel parameters.In this paper, we propose variable length space-time block coding scheme combined with orthogonal frequency division multiplexing (VLSTBC-OFDM) specific to HF time and frequency selective fading channel, to realize the cooperative transmission in HF communication. Furthermore, randomized coding is introduced into the scheme to adapt to the randomness of relay nodes. We compare VLSTBC-OFDM with fixed length space-time block coding through simulation, and observe that VLSTBC-OFDM shows the best performance and cooperative communication can effectively improve the performance of the HF communication.Synchronization technology affects the performance of cooperative communication system seriously. While OFDM is introduced into existing synchronization algorithm to resist the timing offset in a certain extent. The multipath delay in HF band reduces the timing accuracy of synchronization algorithm. In this paper, a new training sequence structure and a novel synchronization algorithm have been proposed. First, we complete the signal reach forecast by the relevant operations. Then we can get the precise scope of synchronization operations by the relevant operations results. And then we make the accurate relevant operations in the precise scope. At last a simulation of the proposed algorithm is made, and the results of which proves that the proposed algorithm has better performance than the existing algorithm.