M. Torabi

On the BER Performance of Space-Frequency Block Coded OFDM Systems in Fading MIMO Channels

Closed-form expressions for the bit error rate (BER) performance of space-frequency block coded OFDM (SFBC-OFDM) systems are derived and evaluated for frequency-selective fading channels. In the performance analysis, both M-ary phase shift keying (MPSK) and M-ary quadrature amplitude modulation (MQAM) are considered, and the effects of channel estimation errors on the BER performance are studied. Numerical results and comparisons are provided for several forms of SFBC-OFDM. It is shown that the results obtained from the closed-form formulae are very close to the ones using the exact expressions and to simulation results of the SFBC-OFDM model. The BER deterioration that results from channel estimation errors in the SFBC-OFDM systems is also illustrated. Using the provided results, the amount of degradation can be quantified.

Space-time-frequency COFDM with power allocation for broadband wireless communications

A scheme consisting of a combination of orthogonal transmit diversity (OTD) and OFDM with power allocation is presented. The proposed scheme is a new approach to space-time-frequency coded OFDM (COFDM) that combines OFDM with orthogonal transmit diversity, power control and turbo codes so that the diversity in frequency, time and space is exploited to provide high quality of transmission for wireless communications over frequency selective fading channels with enhanced performance in terms of spectral and power efficiency.

Variable-rate OFDM systems with selective antenna diversity and adaptive modulation

In this article, a new scheme consisting of a combination of adaptive modulation, orthogonal frequency division multiplexing (OFDM), high order space-frequency block coding (SFBC), and antenna selection is presented. The proposed scheme, exploits the benefits of space-frequency block codes, OFDM and adaptive modulation to provide high quality of transmission for wireless communications over frequency selective fading channels. We examine the spectral efficiency and coding gain advantages of the proposed system. It is shown that antenna selection with adaptive modulation can greatly improve the performance of the conventional SFBC-OFDM systems.

MIMO-OFDM Systems with Imperfect Channel Information: Capacity, Outage and BER Performance

In this paper, a study of the effect of channel estimation error on the capacity, outage probability, and bit error rate (BER) performance of multiple-input multiple-output OFDM (MIMO-OFDM) systems, is provided. First, a lower bound for the mutual information of MIMO-OFDM in the presence of channel estimation error is derived. Then, we derive an outage probability expression under imperfect channel information for MIMO-OFDM systems in general and for space-frequency block coded OFDM (SFBC-OFDM) in particular. Furthermore, we consider SFBC-OFDM used in conjunction with adaptive modulation, and evaluate the spectral efficiency of the adaptive SFBC-OFDM system under imperfect channel information at the transmitter. Simulation results are provided to analyze the performance of the MIMO-OFDM systems under study, and quantify the amount of degradation that imperfect channel information yields on the channel capacity, BER, outage probability and system throughput.

Performance evaluation of space-frequency coded OFDM systems over frequency selective fading channels

In this paper, closed-form expressions of bit error rate (BER) performance of space-frequency block coded OFDM (SFBC-OFDM) systems are derived and evaluated over frequency selective fading channels. In the performance evaluation both M-ary phase shift keying (MPSK) and M-ary quadrature amplitude modulation (MQAM) are considered. Numerical results are provided for analysis and simulations. In addition performance of several forms of SFBC-OFDM system are also evaluated and compared.

Adaptive modulation for OFDM systems using space-frequency block codes

This paper presents a new approach to adaptive modulation for OFDM using Space-Frequency Block Codes. In the proposed scheme, the benefits of adaptive modulation, space-frequency block codes (SFBC) and OFDM are exploited to provide high quality of data transmission over multipath fading channels. When the channel state information is known at the transmitter, a large gain over non-adaptive system can be obtained. The performance of the proposed system is eval- uated and compared with non-adaptive systems. We show that the proposed adaptive modulated SFBC-OFDM, has superior performance compared to non-adaptive systems.

On the performance of MIMO-OFDM systems with imperfect channel information

In this paper, we consider a multiple-input multiple-output OFDM (MIMO-OFDM) system and study the effects of MMSE channel estimation error on the channel capacity and BER performance of MIMO-OFDM systems, in particular, for space-frequency block coded OFDM (SFBC-OFDM). We assume that the channel is imperfectly known at the receiver within some mean-square error. It is shown that channel estimation errors decrease the channel capacity and BER performance of the MIMO-OFDM systems.

A new space-frequency-time block coded OFDM scheme for broadband wireless communications

In this paper, a new scheme for space-frequency-time block coded OFDM system is presented. In the proposed scheme, we considered a combination of high order space-time code with OFDM utilizing joint diversity of space-frequency-time over frequency selective fading channels to provide high quality of transmission for broadband wireless communications. Numerical results are provided for evaluating the performance of several forms of the proposed system.

COFDM with orthogonal transmit diversity and power control for broadband wireless communications

A new approach to space-time-frequency coded OFDM (COFDM) employing turbo product codes (TPC) is proposed. The proposed scheme combines OFDM with orthogonal transmit diversity with power control and turbo codes so that the diversity in frequency, time and space is exploited to provide high quality of transmission for multimedia wireless communications over frequency selective multipath channels with enhanced performance in terms of spectral and power efficiency. The system performance over both flat fading and frequency selective multipath fading channels are investigated and compared with other schemes. The proposed scheme can be considered as a promising technique for high data rate wireless transmission over frequency selective multipath fading channels and for broadband wireless communications.

Adaptive OFDM with space-time coding and antenna selection for broadband wireless communications

This paper presents a new scheme of adaptive OFDM, combined with space-time coding and antenna selection. Coding gain and spectral efficiency advantages of the proposed system are examined. It is shown that antenna selection with adaptive modulation can greatly improve the performance of the conventional SFBC-OFDM systems.