Studies Of Cooperative Transmission And Networking Protocol In Near Space Platform Networks

Near space platform communications systems have many advantages, includingsmall path loss of line-of-sight, low transmission delay, low cost of system construction,easy update and flexible maintenance. So it becomes a new hot spot in the field ofwireless communications. However, the downlink channel of low elevation coveragearea in a single platform is often in a deep fade condition, which will make a seriousimpact on the communication performance. Forming overlapping coverage throughmultiple platforms in low elevation coverage area, we could utilize cooperativetransmission and networking technology to improve the communication performance inthis region effectively.This dissertation focuses on improving the communication performance of the nearspace platform communications systems in the low elevation overlapping coverage area,by utilizing cooperative transmitting and networking. The main contributions are asfollows：Firstly, we analyze the channel propagation properties in near space platformcommunications systems, and then establish the channel model for the near spaceplatform communications systems. Based on this channel model, we propose to usecooperative communication technology to improve the downlink communicationperformance over low elevation areas in the near space platform communicationssystems. And we further compare the two key cooperative communication technologies,i.e., cooperative space-time coding technology and cooperative beam formingtechnology. The simulation results show that comparing to cooperative space-timecoding technology, cooperative beam forming technology can obtain additional arrayprocessing gain, and thus resulting in a lower bit error rate.Secondly, we mainly study two cooperative beam forming schemes that areefficiently applied in the near space communications systems. In order to obtaindownlink channel state information (CSI) for the near space platform, we mainlyresearch the channel prediction technology and the limited feedback technology. Forcooperative beam forming scheme based on channel prediction, a Kalman filter basedchannel predictor is proposed to predict the current CSI. The simulation results showthat the prediction of CSI is necessary for ensuring cooperative beam formingperformance. For cooperative beam forming scheme based on limited feedbacktechnology, we use joint scalar quantization and vector quantization algorithm toquantify CSI. Through the simulation experiments, we obtain the best bit allocationscheme for channel feedback bits.Finally, in order to guarantee good performance for cooperative beam formingscheme at the physical layer, we propose a dual-platform cooperative protocol in MAC layer. The protocol takes advantage of idle slots on the near space platform and exploitsthe advantages of beam forming technology well. Through building OPNET simulationplatform, the proposed protocol is validated. The simulation results show that it canenhance the network performance in terms of throughput, end-to-end delay and packetloss rate.