In this paper, we propose a multi-user downlink system for two users based on the orthogonal time frequency space (OTFS) modulation scheme. The design leverages the generalized singular value decomposition (GSVD) of the channels between the base station and the two users, applying precoding and detection matrices based on the right and left singular vectors, respectively. We derive the analytical expressions for three scenarios and present the corresponding simulation results. These results demonstrate that, in terms of bit error rate (BER), the proposed system outperforms the conventional multi-user OTFS system in two scenarios when using minimum mean square error (MMSE) equalizers or precoder, both for perfect channel state information and for a scenario with channel estimation errors. In the third scenario, the design is equivalent to zero-forcing (ZF) precoding at the transmitter.

翻译：本文提出了一种基于正交时频空间（OTFS）调制方案的双用户多用户下行链路系统。该设计利用基站与两个用户之间信道的广义奇异值分解（GSVD），分别基于右奇异向量和左奇异向量应用预编码和检测矩阵。我们推导了三种场景下的解析表达式，并给出了相应的仿真结果。结果表明，在误码率（BER）方面，无论是对于理想信道状态信息还是存在信道估计误差的场景，所提出的系统在使用最小均方误差（MMSE）均衡器或预编码器的两种场景下均优于传统的多用户OTFS系统。在第三种场景中，该设计等效于发射端的迫零（ZF）预编码。