Design 4x1 Space-Time Conjugate Two-Path Full-Rate OFDM Systems

Secured and robust wireless communication systems are critical in rapidly changing mobile fading channels. Further developing the 2x1 conjugate cancellation (CC), we proposed a 4x1 space-time (ST) orthogonal frequency division multiplexing (OFDM) system in conjunction with CC as a block coded two-path transmission scheme. This full-rate 4x1 STCCOFDM system alleviates the effect of inter-carrier interference (ICI) in mobile channels with an outstanding BER performance due to the high diversity order and two-path CC block coding scheme which offers high signal-to-ICI ratio. Both Walsh–Hadamard transform (WHT) and Zadoff-Chu transform (ZCT) are used as the orthogonal pre-coder to further improve bit error rate (BER) performance. Employing the unique pre-coder at the transmitter, the security is achieved at the user’s receiver terminal since the user must perform the inverse operation via a prior known pre-coder. By employing the same order M-ary modulation in transmission, this 4x1 pre-coded full-rate STCCOFDM systems offer an outstanding BER than that of the 4x1 pre-coded half-rate ST OFDM system in mobile channels with the same bandwidth efficiency. By using a higher order M-ary modulation in transmission, the 4x1 full-rate STCCOFDM systems offer an outstanding BER over the full-rate 4x1 ST OFDM in mobile environments with the same bandwidth efficiency. Simulations prove that this full-rate 4x1 STCCOFDM systems are robust to mobile channels and the architecture can be generalized to multiple receiver antennas in the fifth generation (5G) systems.