This work proposes a novel interleave-division multiple access (IDMA) system based on cyclic shift keying (CSK) modulation, named CSK-IDMA, for multiuser underwater acoustic (UWA) communications. The CSK modulation uses a circular cyclic shift of the spreading sequence to represent the information, which can be viewed as a special $M$-ary spread spectrum modulation. Compared with conventional direct-sequence spread spectrum (DSSS) technique, CSK overcomes the spreading gain versus data rate limitations. The proposed scheme adopts the IDMA technique to reduce the cochannel interference. At the receiver, we employ passive time reversal (PTR) technique to compress the channels and improve the signal-to-interference-noise ratio (SINR) at first. In order to perfectly incorporate with the IDMA receive structure, we propose a soft CSK demodulation which can iteratively exchange extrinsic information with a soft channel decoder to form a turbo equalization. Simulation results show the proposed CSK-IDMA scheme can offer significantly improved performance. The data processing results from a lake experiment show that the proposed scheme can support 8 users and 10 users with zero error bits for 2.3 km transmission and 2.7 km transmission, respectively. The corresponding bit error rate (BER) for 16 users are $\text{8.4} \times \text{10}^{-4}$ and $\text{9.7} \times \text{10}^{-4}$, respectively. The data rate is 62.5 bit/s per user within 4 kHz bandwidth and spreading sequences of 256 chips. To the best of our knowledge, this is the first work which can support more than 8 users for multiuser UWA communications with a high bandwidth efficiency.

中文翻译：

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一种用于多用户水声通信的基于CSK调制的新型IDMA系统

这项工作提出了一种基于循环移位键控 (CSK) 调制的新型交织-分多址 (IDMA) 系统，称为 CSK-IDMA，用于多用户水声 (UWA) 通信。CSK 调制使用扩频序列的循环循环移位来表示信息，可以看作是一种特殊的百万美元-ary 扩频调制。与传统的直接序列扩频 (DSSS) 技术相比，CSK 克服了扩频增益与数据速率的限制。所提出的方案采用IDMA技术来减少同信道干扰。在接收端，我们首先采用无源时间反转 (PTR) 技术来压缩信道并提高信干噪比 (SINR)。为了与 IDMA 接收结构完美结合，我们提出了一种软 CSK 解调，它可以与软信道解码器迭代交换外部信息以形成涡轮均衡。仿真结果表明，所提出的 CSK-IDMA 方案可以显着提高性能。湖实验的数据处理结果表明，所提出的方案可以分别支持8个用户和10个用户的2.3公里传输和2.7公里传输零误码。16个用户对应的误码率（BER）为$\text{8.4} \times \text{10}^{-4}$ 和 $\text{9.7} \times \text{10}^{-4}$， 分别。在 4 kHz 带宽和 256 个码片的扩展序列内，数据速率为每用户 62.5 比特/秒。据我们所知，这是第一个可以支持超过 8 个用户进行高带宽效率的多用户 UWA 通信的工作。