Design Precoded Space-Time-Frequency 4 × 1 and 4 × 2 OFDM Architectures in Frequency-Selective Fading Channels

Abstract

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.