This paper presents precoded space-time-frequency (STF) 4 × 1 and 4 × 2 orthogonal frequency-division multiplexing (OFDM) systems in frequency-selective fading channels. First, a regular 2 × 1 space-time (ST) block code OFDM system is presented as the baseline. Second, further developing this 2 × 1 ST OFDM, both novel 4 × 1 and 4 × 2 STF OFDM architectures and computing algorithms are developed, specifically at a code rate 3/4. Third, four orthogonal transforms, Walsh-Hadamard, Slant, Harley, and Haar, are employed as the precoder to form four different 4 × 1 and 4 × 2 precoded STF OFDM systems, respectively. All four precoded systems improve the bit error rate (BER) without expanding power or bandwidth in comparing with the regular 4 × 1 and 4 × 2 STF OFDM schemes. Simulations indicate that the precoded 4 × 2 STF OFDM system has the best BER; the 4 × 2 STF OFDM system, the precoded 4 × 1 STF OFDM system, the 4 × 1 STF OFDM system, and the 2 × 1 ST OFDM system follow in order due to the achieved diversity order in fading channels. All systems are well-matched with the current OFDM system. They may serve as basic modules in the fourth-generation (4G) and future planned 5G multiple input multiple output (MIMO) OFDM systems.

中文翻译：

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在选频衰落信道中设计预编码的空时频4×1和4×2 OFDM架构

本文提出了频率选择性衰落信道中的预编码空时频（STF）4×1和4×2正交频分复用（OFDM）系统。首先，将常规的2×1空时（ST）分组码OFDM系统作为基线。其次，进一步开发此2×1 ST OFDM，同时开发了新颖的4×1和4×2 STF OFDM架构以及计算算法，特别是在3/4的编码速率下。第三，采用四个正交变换Walsh-Hadamard，Slant，Harley和Haar作为预编码器，分别形成四个不同的4×1和4×2预编码STF OFDM系统。与常规的4×1和4×2 STF OFDM方案相比，所有四个预编码系统均在不扩展功率或带宽的情况下提高了误码率（BER）。仿真表明，预编码的4×2 STF OFDM系统具有最佳的BER。4×2 STF OFDM系统，预编码4×1 STF OFDM系统，4×1 STF OFDM系统和2×1 ST OFDM系统按照衰落信道中实现的分集顺序依次排列。所有系统都与当前的OFDM系统完全匹配。它们可以用作第四代（4G）和未来计划的5G多输入多输出（MIMO）OFDM系统的基本模块。