Research On Combination Transmission Techniques Of Space-Time Block Fountain Codes Based On Underwater Acoustic Channel Prediction

The effectiveness and reliability of underwater acoustic communication are seriously affected by multipath effect,and high transmission loss of underwater acoustic channel.In order to overcome the frequency selective fading and multi-path benefit of underwater acoustic channel and improve the error control capability of the system,In this paper,a combination transmission system model based on space-time block fountain code is constructed in the underwater acoustic sensor network,and focus on the BER performance of the system under different conditions.The main innovation points are as follows:1. In underwater acoustic sensor networks based on leach algorithm,adopt the virtual multi-antenna technology to build a virtual MIMO system,in order to solved the problem which is traditional single antenna structure of relay node in the network can't obtain diversity gain,we design a combined transmission system model with STBC-OFDM/SC-FDE technology,at the same time adopt combined design can better develop the advantages of anti-multipath fading.In this system model,the uplink adopts the STBC-SCFDE system model,while the downlink adopts the STBC-OFDM system model,and the complex FFT/IFFT function module is deployed on the side of the energy unrestricted node,will further reducing the hardware complexity and power consumption of the sensor node.The simulation results show that the BER performance of the system can be effectively improved by the transmission diversity and receiver diversity,and the BER performance of the system does not decrease significantly when some collaborative communication nodes fail which is used as virtual antennas.In addition on the basis of channel prediction,an improved STBC-SCFDE system based on clustering algorithm is studied.The simulation results show that the BER of the system is improved under the condition of low SNR.In order to further improve the transmission performance of the system,a kind of underwater acoustic QOSTBC-SCFDE system was studied,which can reach full diversity and full rate.The simulation results show that the gain of the system is at least 2d B higher than that of the underwater acoustic STBC-SCFDE system at the same transmission rate and BER.2. Aiming at the characteristics of large delay of underwater acoustic channel,in order to improve the bit error performance of the system,we design the combined transmission system based on space-time block fountain codes,by serially concatenated encoding with LT codes or Raptor code which has the ability to forward correct errors and rateless characteristics in STBC-SCFDE system,that can solve the problem of high BER of underwater acoustic STBC-SCFDE system in uplink,and realize the reliable transmission of information.The simulation results show that when the decoding overhead increases to 1.25 times,the bit error rate of serial concatenated codes system can also be quickly reduced to less than10^-4 even in the condition of low SNR,especially,the BER performance of STBC-SCFDE system is more better with multiple antennas.Under the same decoding overhead and SNR conditions,the BER of serial concatenated codes system based on Raptor code is at least one order of magnitude lower than the serial concatenated codes system based on LT code.