IDMA水声多用户下行通信链路迭代接收算法

水声通信网络的快速发展对多用户水声物理层通信技术提出了迫切的需求。本文主要针对水声多用户下行通信链路中存在严重码间干扰和多址干扰的问题，提出了一种交织多址（IDMA）水声多用户下行通信链路迭代接收算法，能够根据译码器输出的软信息对估计的信道进行迭代更新，同时根据信道估计结果重建各用户对当前用户的多址干扰（MAI），并使用干扰抵消器予以抵消，通过在均衡器、译码器和干扰抵消器之间的迭代逐次提高当前用户信息的输出信噪比，最终实现正确解调。其中，信道估计算法采用LMMSE初始化的分簇OMP稀疏信道估计算法，多普勒估计采用时频二维搜索结合自相关相位估计的方法，计算机仿真结果表明该接收机具有与已知信道时接近或相当的性能。进行了多用户水声通信海上试验，在4.5km、6km和7km三个距离实现了对2个用户、3个用户和4个用户的同时通信，每个用户的通信净速率约为500bps，证明了本文所提出的方法能够有效应用在多用户水声通信中，为水声通信网络的发展提供了一种重要的物理层通信技术手段。 

An IDMA receiver for multi-user underwater acoustic communication

A downlink interleave division multiple access (IDMA) receiver, employing sparse channel estimation and interference canceller (IC), is proposed for multi-user underwater communications. To eliminate inter-symbol interference (ISI) and multiple access interference (MAI), an equalizer, a decoder and an interference canceller are implemented in the receiver. The equalizer is used to eliminate ISI. The channel parameters used in the equalizer are estimated by a modified OMP sparse channel estimation algorithm. The performance of channel estimation is further improved using the decoder soft output information during the receiver iteration. MAI, reconstructed by the decoder output and channel parameters, can be eliminated in IC section of other users. The receiver’s performance is verified in shallow water acoustic channels during a sea-trail in the South China Sea. Three different ranges between the transmitter and the receiver, i.e. 4.5km,6km and 7km, were investigated with a maximum of four users at the data rate of 500bps per user. The results demonstrated that the proposed IDMA receiver provides good performance with low bit error rate (BER). Furthermore, the receiver has been applied in a real-time underwater communication network.