MIMO space frequency block coded system for double-selective wireless channels

Abstract

This thesis considers the performance evaluation of various multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) systems. In particular, the thesis focuses on 2 × 2 space time block code (STBC) and 2 × 2 space frequency block code (SFBC) systems. The performance of STBC and SFBC systems is evaluated analytically and via Monte Carlo simulation over various static and mobile wireless channels. The results obtained revealed that STBC system suffers from severe bit error rate (BER) degradation over wireless channels with high mobility level due to the inter-carrier interference (ICI) introduced by the Doppler spread. Consequently, SFBC systems are proposed to combat the time variation of the channel because the SFBC blocks are transmitted simultaneously over multiple adjacent subcarriers. However, in mobile frequency-selective channels, the channel response at adjacent subcarriers could vary drastically and cause severe BER degradation. This thesis presents a new SFBC system that resolves the BER degradation of SFBC systems in mobile frequency-selective channels. The proposed system, denoted as Channel Matrix Shaping (CMS) system, guarantees that the channel frequency responses over each SFBC block of two adjacent subcarriers are identical, i.e., the channel becomes piecewise flat regardless of the frequency selectivity of the channel. The proposed system is based on a simple 2 ×2 Walsh Hadamard Transform (WHT) unitary matrix. The BER performance of the proposed system is evaluated analytically and via Monte Carlo simulation over various static and mobile wireless channels. The simulation results demonstrated that the proposed system outperforms the STBC and SFBC systems in mobile frequency-selective channels. As a benchmark, the performance of the proposed system and 2×2 version of WHT-STBC system introduced in [1] is verified using Monte Carlo simulation over various static and mobile wireless channels. Simulation results confirmed the robustness of the proposed system and demonstrated that it substantially outperforms the WHT-STBC system over severe fading channels with high mobility levels. On the other hand, WHT-STBC system outperforms the proposed system in static and extremely low mobile frequency-selective channels. In addition, a complexity comparison between the proposed and WHT-STBC system is conducted in terms of number of mathematical operations. Results have shown that the proposed system has low complexity compared to WHT-STBC system because it is based on short block length Walsh Hadamard Transform (WHT), and it requires onlyhalf of the channel coefficients to equalize the entire set of subcarriers. The main constraint of the proposed system is that its optimal performance is achieved with binary phase shift keying (BPSK ) modulation. However, it is worth noting that BPSK is included as a modulation option in most state-of-the-art adaptive standards such as WiMAX, LTE-Advanced, IEEE 802.11p and IEEE 802.15.

Date of Award	2013
Original language	American English
Supervisor	Arafat Aldweik (Supervisor)