Space-time Block Coded MIMO Systems Research Articles

Evaluation of the Performance of a Reed Solomon Coded STBC MIMO System Concatenated with MPSK and MQAM in Different Channels

Background & Objective: Wireless technologies like Wi-Fi, WiMAX, and LTE are using Multiple Input, Multiple Output (MIMO) communications that play an important role in achieving high data rates. Bit Error Rate (BER) is one of the most important performance parameters in multipath channels for data communication. Methods: This research proposes a new method based on Reed Solomon (RS) coding to improve the efficacy of a Space-Time Block Coded (STBC) MIMO System concatenated with M-ary Phase Shift Keying (MPSK) and M-ary Quadrature Amplitude Modulation (MQAM) in reducing BER in Rayleigh, Rician and Nakagami channels. It is based on the error detection and correction properties intrinsic to RS coding processes. Binary data is coded using an RS encoder and the modulated signal STBC encoded and transmitted through Rayleigh, Rician and Nakagami channels. Signals received by two antennas are STBC decoded, demodulated, RS decoded and tested for BER. Results & Conclusion: Results show lower BER rates for RS Coded systems as compared for uncoded systems in all three channels. In addition, it was found that reduction in BER is greater for high Signal to Noise Ratio (SNR) but deteriorates for low SNR. Furthermore, this research observed that RS coding gives 63% to 98% improvement in BER in the Rayleigh as compared to Rician and Nakagami channels. This research has been able to successfully incorporate the BER reduction of STBC MIMO to further enhance the efficacy of an STBC MIMO system.

Analysis of Image Transmission using MIMO-Alamouti Space-Time Encoding

Rapid increase in requirements of high speed transmission of multi-media information resulted in development of MIMO systems. MIMO systems have emerged as the most efficient methodology for the high speed robust data transmission. In this paper, the performance of Alamouti Space-time block coded MIMO system is analysed using the metric of efficient image transmission over the Rayleigh fading channel. The transmitted image is modulated using M-PSK modulation technique, and its reconstructed version is plotted as an output function. Zero-forcing equalization is done for the detection of the original symbols from the received symbols which are influenced by the multipath fading and the channel noise. The results for image transmission using 2í—1 and 2í—2 Alamouti STBC are evaluated for different SNR values. The inverse relationship between the SNR and BER in the results depict that the high value of SNR and receiver antenna leads to enhanced system efficiency with reduced BER and distortion less recovery of image. It is very evident from the analysis of the received images that as we increase the SNR or the number of the antennas at the receiving side, the quality of the received image improves for the same channel environment. During the analysis, it is also found that increasing the number of bits forming one symbol in M-PSK modulation increase the BER which is undesirable. Thus, trade-off between the number of antenna, SNR and the M value of PSK is an essential requirement for achieving enhanced performance.

A Distributionally Robust Linear Receiver Design for Multi-Access Space-Time Block Coded MIMO Systems

A receiver design problem for multi-access space-time block coded multiple-input multiple-output systems is considered. To hedge the mismatch between the true and the estimated channel state information (CSI), several robust receivers have been developed in the past decades. Among these receivers, the Gaussian robust receiver has been shown to be superior in performance. This receiver is designed based on the assumption that the CSI mismatch has Gaussian distribution. However, in real-world applications, the assumption of Guassianity might not hold. Motivated by this fact, a more general distributionally robust receiver is proposed in this paper, where only the mean and the variance of the CSI mismatch distribution are required in the receiver design. A tractable semi-definite programming (SDP) reformulation of the robust receiver design is developed. To suppress the self-interferences, a more advanced distributionally robust receiver is proposed. A tight convex approximation is given and the corresponding tractable SDP reformulation is developed. Moreover, for the sake of easy implementation, we present a simplified distributionally robust receiver. Simulations results are provided to show the effectiveness of our design by comparing with some existing well-known receivers.

Performance of cross-layer design for orthogonal space-time block coded MIMO systems with imperfect CSI in Ricean fading channels

A cross-layer design (CLD) scheme for orthogonal space-time block coded MIMO systems with imperfect channel state information is presented by combining adaptive modulation and automatic repeat request, and the corresponding system performance is investigated over Ricean fading channel. The fading gain value is partitioned into a number of regions by which the modulation is adapted in terms of the region the fading gain falls in. The fading gain switching thresholds subject to a target packet error rate (PER) constraint are derived. According to these results, and using the generalized Marcum Q-function, we derive the theoretical formulae of average PER and spectrum efficiency (SE) of the system with CLD for both perfect and imperfect estimation in detail. As a result, closed-form expressions for average PER and SE are obtained. These expressions include some existing expressions in Rayleigh channel as special cases. With these expressions, the system performance in Ricean channel with perfect and imperfect estimation information can be evaluated effectively. Computer simulation for average PER and SE show that the theoretical analysis and simulation are consistent. The results show that the system performance will be effectively improved as Ricean factor increases, but it will be degraded as estimation errors increases.

Power Control for Space-Time Block Coded MIMO System with Beamforming and Imperfect Channel State Information

In this paper, an optimal power control for minimizing bit error rate (BER) subject to a power constraint for space-time block coded MIMO systems with beamforming over Rayleigh fading channels under imperfect channel state information (CSI) is presented. The optimal power control procedure is developed. It is shown that the Lagrange multiplier for the constrained optimization does exist and is unique. To simplify the power control procedure, a closed-form suboptimal power control scheme is drived based on the asymptotic performance analysis of the optimal power control and Taylor's series expansion. The calculation of the suboptimal power control is straightforward with low computational complexity. Moreover, the suboptimal scheme can provide the BER performance close to that of the optimal power control and is lower than that of the existing suboptimal scheme. Simulation results show that the proposed two power control schemes can provide BER lower than that of the equal power allocation and the existing suboptimal scheme under imperfect CSI.

High-Rate Space–Time Coded Large-MIMO Systems: Low-Complexity Detection and Channel Estimation

In this paper, we present a low-complexity algorithm for detection in high-rate, non-orthogonal space-time block coded (STBC) large-MIMO systems that achieve high spectral efficiencies of the order of tens of bps/Hz. We also present a training-based iterative detection/channel estimation scheme for such large STBC MIMO systems. Our simulation results show that excellent bit error rate and nearness-to-capacity performance are achieved by the proposed multistage likelihood ascent search (M-LAS) detector in conjunction with the proposed iterative detection/channel estimation scheme at low complexities. The fact that we could show such good results for large STBCs like 16x16 and 32x32 STBCs from Cyclic Division Algebras (CDA) operating at spectral efficiencies in excess of 20 bps/Hz (even after accounting for the overheads meant for pilot based training for channel estimation and turbo coding) establishes the effectiveness of the proposed detector and channel estimator. We decode perfect codes of large dimensions using the proposed detector. With the feasibility of such a low-complexity detection/channel estimation scheme, large-MIMO systems with tens of antennas operating at several tens of bps/Hz spectral efficiencies can become practical, enabling interesting high data rate wireless applications.

Multiaccess Interference Suppression in Orthogonal Space–Time Block Coded MIMO Systems by Adaptive Projected Subgradient Method

This paper introduces adaptive filters that are effective to suppress multiple access interference (MAI) in orthogonal space-time block coded/ multiple-input multiple-output (OSTBC-MIMO) systems. We define an optimal linear filter that minimizes the mean-square error between the filter output and a scaled version of the desired output under a constraint defined by the available channel state information (CSI). The adaptive filters refine a given estimate of the optimal filter by suppressing a sequence of closed convex functions with the adaptive projected subgradient method (APSM) at each iteration. To provide robustness against imperfect CSI, the adaptive filters use not only the available CSI but also estimates of previously transmitted symbols, which usually belong to a small finite set in digital communication systems. The resulting algorithms employ computationally efficient projections onto hyperplanes or hyperslabs and do not require any matrix inversion. An efficient recursive scheme based on such an algorithm is also presented. Convergence analysis and simulation results show the excellent performance of the proposed schemes.

Exact error probability for space–time block-coded MIMO systems over Rayleigh fading channels

Existing analysis on the error performance of space-time block codes has focused on deriving error-rate upper bounds for a general system or exact error probabilities for some special cases. The authors introduce a general method to calculate the exact error probability for orthogonal space-time block codes in multiple-input multiple-output systems which employ coherent and differentially coherent phase shift keying (PSK) modulation over flat Rayleigh fading channels. These results enable one to evaluate the performance of space-time block-coded systems with different coding rates and an arbitrary number of transmit and receive antennas.