Wireless communications over fast fading channels are challenging, requiring either frequent channel tracking or complicated signaling schemes such as orthogonal time frequency space (OTFS) modulation. In this paper, we propose low-complexity frequency domain equalizations to combat fast fading, based on novel discrete delay-time and frequency-Doppler channel models. Exploiting the circular stripe diagonal nature of the frequency-Doppler channel matrix, we introduce low-complexity frequency domain minimum mean square error (MMSE) equalization for OTFS systems with fully resolvable Doppler spreads. We also demonstrate that the proposed MMSE equalization is applicable to conventional orthogonal frequency division multiplexing (OFDM) and single carrier frequency domain equalization (SC-FDE) systems with short signal frames and partially resolvable Doppler spreads. After generalizing the input-output data symbol relationship, we analyze the equalization performance via channel matrix eigenvalue decomposition and derive a closed-form expression for the theoretical bit-error-rate. Simulation results for OTFS, OFDM, and SC-FDE modulations verify that the proposed low-complexity frequency domain equalization methods can effectively exploit the time diversity over fast fading channels. Even with partially resolvable Doppler spread, the conventional SC-FDE can achieve performance close to OTFS, especially in fast fading channels with a dominating line-of-sight path.
翻译:在快速淡化的频道上,无线通信具有挑战性,需要频繁的频道跟踪或复杂的信号计划,如时频空间调制。在本文中,我们提出低复杂频率域域均分,以基于新颖的离散延迟时间和频率多普勒频道模型来应对快速淡化。利用频率-多普勒频道矩阵的圆形条形斜形特性,我们引入低兼容性频域域最小平均正方差(MMSE),以具有完全可溶离离散的多普勒空间。我们还表明,拟议的MMSE均衡性适用于常规或超离调频率多功能分分化(OFDM)和单承运人域域均分(SC-FDE)系统,其信号框架短,部分可再解解脱脱脱脱。在对输入输出数据符号进行总体分析后,我们通过可透析的频道基模值解方差变平均分法(MMSE)系统,并为理论的位分解分流线生成一种封闭式表达式表达方式。在OTF-DME平流快速平流轨道上,将快速平流、平流、平流、平流、平流、平流、平流、平流、平流、平流、平流、平流、平流、平流、平流、平流、平流、平流、平流、平流、平流、平流、平流、平流、平流、平流、平流、平流、平流、平流、平流、平流、平流、平流、平流、平流、平流、平流、平流、平流、平流、平流、平流、平流、平流、平流、平流、平流、平流、平流、平流、平流、平流、平流、平流、平流、平流、平流、平流、平流、平流、平流、平流、平流、平流、平流、平流、平流、平流、平流、平流、平流、平流、平流、平流、平流、平流、平流、平流、平流、平流、平流、平流、平流、平流、平流、平流、