Performance Evaluation of High-Rate Stbc Communication System Using Imperfect CSI Working Under Time-Selective Flat-Fading Channel

Abstract

Multi-input-multi-output (MIMO) system employs multiple antennas at both sides of the link, which enhances transmit diversity and provides better reliability. An orthogonal-space-time-block-coding (O-STBC) scheme has been first proposed by Alamouti, for achieving maximum diversity gain for two transmitting antennas. It also attains the full rate as well as full diversity gain. In addition to this, O-STBC scheme was proposed for more than two transmitting antennas to attain full diversity gain (Tarokh et al., 1999). However, the scheme could not achieve the full rate. To overcome this, a quasi-orthogonal-space-time-block-coding (QO-STBC) scheme was proposed by Jafarkhani (Jafarkhani, 2001). In practical scenario, channel coefficients in the wireless transmission varies due to Doppler spread and local oscillator frequency mismatch between transmitter and receiver, i.e., carrier-frequency-offset (CFO). To analyze the time-selective channels, these are modelled as an autoregressive (AR) process. This work discusses high-rate transmission scheme under time-selective fading channel in terms of symbol-error-rate (SER) and the effective throughput performance under the perfect channel state information (CSI). As, it is not practically possible for channel estimator to estimate the channel without errors, so the proposed schemes has also been analyzed under the imperfect CSI at the receiver side. This analysis uses Rayleigh flat-fading channel. Here, we evaluate the performance of high-rate (5/4) space-time-block-coding (STBC) system working under time-selective flat-fading channel in the presence of channel estimation errors. For the performance evaluation of high-rate (9/8) STBC system, we have considered time-nonselective flat-fading channel in the presence of channel estimation errors. The STBC high-rate (5/4) and (9/8) are achieved using two transmitter and four transmitter antennas respectively. Both the schemes use selective power scaling in combination with quadrature-phase-shift-keying (QPSK) modulation technique. The main focus is on the impact of CFO and Doppler spread on the SER and effective throughput performance of the underlying STBC system. Simulation results are presented to illustrate that the proposed high-rate (5/4) and (9/8) STBC systems perform well only under the high signal-to-noise-ratio (SNR) and low channel estimation errors. Thus, the presented system outperforms the conventional system under these conditions. The performance of high-rate (5/4) STBC and Liu rate-one (Liu et al., 2002) are compared using simulation results under perfect and imperfect CSI in time-selective environment. Also, the performance evaluation of high-rate (9/8) STBC and Alamouti rate-one (Alamouti, 1998) are compared under perfect and imperfect CSI in time-nonselective environment. It focuses on the adverse effects of imperfect CSI at the receiver on SER and effective throughput performances. The proposed high-rate STBC systems outperform the conventional rate-one STBC systems in the presence of Doppler spread and CFO under prevalent conditions.