A traditional direct sequence CDMA (DS-CDMA) system works based on spreading codes, which should have good auto-correlation and cross-correlation properties to eliminate multiple access interference (MAI) and multipath interference (MI). However, to find a large number of good spreading codes is extremely difficult, and thus the capacity of a DS-CDMA system is limited strictly by the number of available spreading codes. This work proposes a downlink DS-CDMA design to enable multiple access using only one spreading code, namely identical code cyclic shift (ICCS) code, where in-phase and quadrature channels are used to transmit data and pilot, respectively. In particular, the ICCS code is used at a transmitter to perform DS modulation for user data, which is then sent to the in-phase channel. At the same time, the pilots are sent over the quadrature channel in a time-division multiplex (TDM) mode to construct a correlation matrix of ICCS code. At a receiver, MAI is removed by so-designed pilots plus a matched filter-bank. Simulation results show that the proposed ICCS multiple access (ICCSMA) can achieve a better performance than a traditional DS-CDMA system in a high signal to noise ratio region. ICCSMA serves as a bridge to turn CDMA to NOMA to enable massive connectivity in 5 G and beyond communications.

中文翻译：

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同码循环移位多址 - CDMA 和 NOMA 之间的桥梁

传统的直接序列CDMA（DS-CDMA）系统基于扩频码工作，扩频码应具有良好的自相关和互相关特性，以消除多址干扰（MAI）和多径干扰（MI）。然而，要找到大量好的扩频码是极其困难的，因此DS-CDMA系统的容量受到可用扩频码数量的严格限制。这项工作提出了一种下行链路 DS-CDMA 设计，以仅使用一个扩频码即相同码循环移位 (ICCS) 码实现多址接入，其中同相和正交信道分别用于传输数据和导频。特别地，ICCS码在发射机处用于对用户数据执行DS调制，然后将其发送到同相信道。同时，导频以时分复用（TDM）模式通过正交信道发送，以构建ICCS码的相关矩阵。在接收器处，MAI 被如此设计的导频加上匹配的滤波器组去除。仿真结果表明，所提出的ICCS多址（ICCSMA）在高信噪比区域可以实现比传统DS-CDMA系统更好的性能。ICCSMA 充当了将 CDMA 转变为 NOMA 的桥梁，以在 5G 及以后的通信中实现大规模连接。仿真结果表明，所提出的ICCS多址（ICCSMA）在高信噪比区域可以实现比传统DS-CDMA系统更好的性能。ICCSMA 充当了将 CDMA 转变为 NOMA 的桥梁，以在 5G 及以后的通信中实现大规模连接。仿真结果表明，所提出的ICCS多址（ICCSMA）在高信噪比区域可以实现比传统DS-CDMA系统更好的性能。ICCSMA 充当了将 CDMA 转变为 NOMA 的桥梁，以在 5G 及以后的通信中实现大规模连接。