Coded Multiple-input Multiple-output Systems Research Articles

Gallager Exponent Analysis of Coherent MIMO FSO Systems over Gamma-Gamma Turbulence Channels.

This paper studies the Gallager’s exponent for coherent multiple-input multiple-output (MIMO) free space optical (FSO) communication systems over gamma–gamma turbulence channels. We assume that the perfect channel state information (CSI) is known at the receiver, while the transmitter has no CSI and equal power is allocated to all of the transmit apertures. Through the use of Hadamard inequality, the upper bound of the random coding exponent, the ergodic capacity and the expurgated exponent are derived over gamma–gamma fading channels. In the high signal-to-noise ratio (SNR) regime, simpler closed-form upper bound expressions are presented to obtain further insights into the effects of the system parameters. In particular, we found that the effects of small and large-scale fading are decoupled for the ergodic capacity upper bound in the high SNR regime. Finally, a detailed analysis of Gallager’s exponents for space-time block code (STBC) MIMO systems is discussed. Monte Carlo simulation results are provided to verify the tightness of the proposed bounds.

Design and implementation of a novel unequal error protection scheme for coded MIMO systems

Mobile and wireless technologies such as Wi-Fi, WiMAX, 3G, 4G/LTE and the emerging 5G require communication of high quality videos with the limited available bandwidth. H.264/AVC and High Efficiency Video Coding (HEVC) or H.265 multimedia standards are implemented in these technologies to fulfill this requirement. Moreover, these standards achieve high error performance over wireless channels and large compression efficiency thereby optimizing channel bandwidth. Multimedia standards employ multi-class bitstreams where unequal levels of importance are assigned to the multimedia content. Consequently, the multi-class bit streams employ Unequal Error Protection (UEP) techniques to achieve optimal redundancy as well as better multimedia error performance and coding gains over wireless channels.Recently, coded Multiple-Input Multiple-Output (MIMO) systems employing Orthogonal Space-Time Block Codes (OSTBCs) have been adopted in mobile and wireless networks with the aim of maximizing spatial diversity gain without sacrificing the channel bandwidth. The problem of establishing reliable wireless communication links with high spatial diversity and coding gains for recent and future networks is a big challenge for researchers. A thorough literature survey reveals that the transmission of HEVC multi-class coded data streams over wireless channels employing coded MIMO systems to achieve both spatial diversity and coding gains has not been explicitly explored. To this end we propose, in this paper, to evaluate the error performance of Multiple-Input Multiple-Output (MIMO) systems employing Orthogonal Space-Time Block Codes (OSTBC) and Hierarchical 4/MQAM Modulation to promote unequal error protection of the coded data. The approach adopted provides excellent unequal error protection capabilities through the hierarchically modulated symbol and both diversity as well as coding gains are achieved. The proposed MIMO systems are designed and implemented in MATLAB Simulink® 2017 and error performances are evaluated through simulations. Experimental results show at a Bit Error Probability (BEP) of 10−4 a coding gain of around 10 dB can be observed between the base and refinement sub-channels with the 2x2 Alamouti code.

QOSTBC coded MIMO system with reduced complexity and optimised decoding for rank deficient channels

In multiple-input multiple-output (MIMO) systems, rank deficient channels are the most common and key areas of research. In these channels, the number of transmit antennas (M Tx) is higher than receive antennas (M Rx) and subsequently the unknown variables are more than the number of equations. In such situations, the conventional sphere decoder (SD) fails due to the presence of zero diagonal elements in Cholesky decomposition. This study analyses the quasi-orthogonal space-time block code (QOSTBC) of symbol rate-2 for M Tx = 4 with modified double-layer SD detection to overcome rank deficiency problem. The first half of transmitted symbols is detected using two partially dependent SDs with optimised search radii. The remaining half is detected by employing single symbol maximum likelihood detection. Simulation and analytical results indicate that the proposed detection scheme reduces bit error rate and complexity compared to existing techniques.

MINIMUM PEARSON DISTANCE BASED DETECTION FOR MIMO SYSTEMS

Abstract The wireless fading channel creates unknown impairments on the transmitted signal. Multiple antenna systems have been well studied for providing diversity and/or coding gain over fading channels. In this paper, a new simpler form of signaling scheme is developed for Multiple Input Multiple Output(MIMO) channels. At the receiver, minimum Pearson distance based detector (MPD) is employed with Slepian’s algorithm, which uses a unique codebook design to estimate the transmitted code word with lesser computations. The scheme is developed for BPSK/QPSK 2x2 and 4x4 MIMO systems over time invariant Rayleigh fading channel. Simulations show significant gains in terms of Bit Error Rate (BER) performance and computational complexity when compared with conventional space time block coded MIMO systems.

Fast Symbol Detection for Massive G-STBC MIMO Systems

In this paper, a group-based fast symbol detection scheme is proposed for massive Group-wise Space–Time Block Code Multiple-Input Multiple-Output systems. The proposed scheme first chooses a number G, (e.g. $$G=4,6,8$$ ) as the size of each group and then conducts the Minimum Mean Square Error (MMSE) detectors to facilitate symbol detection group by group. In particular, instead of directly using huge computational complexity to compute the MMSE detectors, the proposed scheme recursively finds the corresponding assistant matrices to determine the groups and calculate the MMSE detectors. As a result, the transmitted symbols can be recursively estimated group by group. Finally, simulation results and complexity analysis show the proposed scheme performs very close to the existing methods, while using lower computational complexity.

TESTBED IMPLEMENTATION OF ENERGY EFFICIENT MULTI ANTENNA SYSTEM AND ITS PERFORMANCE EVALUATION

With the recent development and requirement for high-speed wireless communications, the demand of energy has increased exponentially in order to support required quality of service (QoS). Multiple Input Multiple Output (MIMO) technique gaining more popularity in current communication network, since it provides advantages in terms of higher data rates and maximum capacity with the cost of more energy consumption. In this paper, QAM modulation scheme is analyzed as the best modulation scheme for the total energy required to transmit the given number of bits is reduced. A SDR testbed has been built to implement Almouti coded MIMO system using LABVIEW and Universal Software Radio Peripheral (USRP) platform. The analysis was then extended to evaluate the energy consumption of the system where it was observed that by minimizing the transmission power the energy requirement of the system gets reduced. Then the system efficiency in terms of transmit power was evaluated using USRP. It has been observed that by adjusting carrier frequency transmit power of the system gets reduced up to 25%.Finally the performance of the system is evaluated by demonstrating the effect of transmission distance, symbol rate, spectral efficiency and circuit power on energy consumption of the system using LABVIEW math script.

Two Decades of MIMO Design Tradeoffs and Reduced-Complexity MIMO Detection in Near-Capacity Systems

A pair of salient tradeoffs have driven the multiple-input multiple-output (MIMO) systems developments. More explicitly, the early era of MIMO developments was predominantly motivated by the multiplexing-diversity tradeoff between the Bell Laboratories layered space-time and space-time block coding. Later, the linear dispersion code concept was introduced to strike a flexible tradeoff. The more recent MIMO system designs were motivated by the performance-complexity tradeoff, where the spatial modulation and space-time shift keying concepts eliminate the problem of inter-antenna interference and perform well with the aid of low-complexity linear receivers without imposing a substantial performance loss on generic maximum-likelihood/max a posteriori -aided MIMO detection. Against the background of the MIMO design tradeoffs in both uncoded and coded MIMO systems, in this treatise, we offer a comprehensive survey of MIMO detectors ranging from hard decision to soft decision. The soft-decision MIMO detectors play a pivotal role in approaching to the full-performance potential promised by the MIMO capacity theorem. In the near-capacity system design, the soft-decision MIMO detection dominates the total complexity, because all the MIMO signal combinations have to be examined, when both the channel’s output signal and the a priori log-likelihood ratios gleaned from the channel decoder are taken into account. Against this background, we provide reduced-complexity design guidelines, which are conceived for a wide-range of soft-decision MIMO detectors.

Enhancing the Performance of the Quasi-ML Receiver (Detector Plus Decoder) for Coded MIMO Systems Via Statistical Information

We propose a statistical information-based approach to enhance the performance of the noniterative quasi-maximum-likelihood (QML) receiver (detector plus decoder) recorded at the output of the channel decoder for coded multiple-input–multiple-output (MIMO) systems. As an illustrative example, the QR decomposition with an $M$ -algorithm (QRD-M)-based noniterative QML receiver is employed in this paper. We first illustrate that there is a large discrepancy between the amplitude of the raw log-likelihood ratio (LLR) generated by the complexity-constrained QRD-M detector and its reliability, particularly for LLRs with high amplitudes. The discrepancy is shown to be the main underlying cause of degraded performance in coded MIMO systems. Then, we propose a reliability-aware transformation technique, which exploits the statistical relationship between the raw LLR's amplitude and its reliability to adjust the raw LLR's amplitude to a level commensurate with its reliability. By using the proposed statistical knowledge-based technique, the performance of the receiver (detector plus decoder) recorded at the output of the channel decoder is significantly enhanced for high-order modulations. The extension of the proposed method to other QML receivers such as the list sequential (LISS) detector and list sphere detector (LSD)-based receivers is straightforward.

Error Resilient SPIHT Coded Grayscale Image transmission over MIMO System

In this paper, we propose Error Resilient SPIHT coded MIMO system to address the issue of image transmission and reception over noisy Rayleigh Fading channel. Set Partitioning in Hierarchical Trees (SPIHT) is chosen as the compression algorithm since it offers the lossless compression and excellent rate distortion in noiseless environment. SPIHT encoded data is modulated in the manner that it will provide Unequal Error Protection (UEP) to achieve error resilience. In proposed method, SPIHT encoded data is divided into the low priority stream (LP) and the high priority stream (HP) to achieve UEP and as a result it yields high PSNR value. These streams are modulated using MQAM modulation scheme and transmitted over Multiple Input Multiple Output (MIMO) system to achieve better diversity. The adaptive value of M is determined by the proposed algorithm. Simulation results depicts that PSNR of received images are better as compared to that reported by Fowdur et al. [12].

Performance Comparison of Space Time Block Coding with Code Rate ½ and ¾ for Turbo Coded Multiple Input Multiple Output System

This paper compares the performance of Space Time Block Coding with code rate ½ and ¾ for a Turbo Coded Multiple Input Multiple Output (MIMO) system and uncoded MIMO system. Turbo encoder encodes the input information bits and sends to a QPSK or 16 QAM or 64 QAM modulator. Modulated symbols are mapped by STBC. Outputs of STBC split into n streams which are simultaneously transmitted using n transmit antennas. The Rayleigh fading effected received signal at receiver is a linear superposition of the transmitted signals. It is observed that t here is around 7-11 db coding gain for using code rate ½ compared to code rate ¾ of a TC coded MIMO system and there is around 8-10 db coding gain for using code rate ½ compared to code rate ¾ of a uncoded MIMO system.

A Binary Space-Time Code for Additional Diversity Gains

In this paper, we introduce a bit-interleaved binary space-time code (B-STC) for a coded multiple-input multiple-output (MIMO) system to obtain an additional diversity gain over the full-rate spatial multiplexing (SM) transmission. By applying the B-STC scheme, codeword bits from each stream are transmitted effectively through N_t or (N_t - 1) layers in N_r x N_t MIMO systems. At the receiver, the iterative decoding is performed. The extrinsic information provided by the soft-in/soft-out (SISO) decoder is applied as an improved priori information after the B-STC decoding at the next iteration. Since a priori information can be extracted from multiple layers independently by the B-STC scheme, codeword bits have an improved diversity gain of (N_t - 1). In order to verify the proposed scheme, we derive the asymptotic bit error probability, which can be achieved after convergence of the iterative decoder. Because the proposed B-STC scheme is a binary code for coded MIMO systems, different types of channel codes and various space-time codes can be also concatenated.

Probability-Distribution-Based Node Pruning for Sphere Decoding

Node pruning strategies based on probability distributions are developed for maximum-likelihood (ML) detection for spatial-multiplexing multiple-input–multiple-output (MIMO) systems. Uniform pruning, geometric pruning, threshold pruning, hybrid pruning, and depth-dependent pruning are thus developed in detail. By considering the symbol error probability in the high signal-to-noise ratio (SNR) region, the desirable diversity order of uniform pruning and the threshold level for threshold pruning are derived. Simulation results show that threshold pruning saves complexity compared with popular sphere decoder (SD) algorithms, such as the $K$ -best SD, the fixed-complexity SD (FSD), and the probabilistic tree pruning SD (PTP-SD), particularly for high SNRs and large-antenna MIMO systems. Furthermore, our proposed node pruning strategies may also be applied to other systems, including coded MIMO systems and relay networks.

Discrete‐rate adaptive modulation with optimum switching thresholds for space‐time coded multiple‐input multiple‐output system with imperfect channel state information

The performance analysis of a space-time coded multiple-input multiple-output (MIMO) system with variable-rate adaptive modulation over flat Rayleigh fading channels for both perfect and imperfect channel state information (CSI) is presented. In this study, the optimum fading gain switching thresholds for attaining maximum spectrum efficiency (SE) subject to an average bit error rate (BER) constraint are derived. The existence and uniqueness of the Lagrange multiplier in the constrained SE optimisation is studied. It is shown that the Lagrange multiplier does exist and is unique for imperfect CSI. On the other hand, the Lagrange multiplier will be unique if the existence condition for MIMO under perfect CSI is satisfied. A practical iterative algorithm based on Newton's method for finding the Lagrange multiplier is proposed. By the switching thresholds, closed-form expressions of the SE and average BER are obtained. Simulation results for SE and BER are in good agreement with the theoretical analysis. The results show that the space-time block coded MIMO system using adaptive modulation (AM-STBC-MIMO) with average BER constraint provides SE better than AM-STBC-MIMO with fixed thresholds, and AM-STBC-MIMO using a BER upper bound, but it has performance degradation in SE for imperfect CSI.

Study and Simulation of Quasi and Rotated Quasi Space Time Block Codes in MIMO systems using Dent Channel model

Multiple Input Multiple Output (MIMO) has become one of the most exciting field in modern engineering.It has become one of the key technologiesfor wideband wireless communication systems .It is mainly used to increase capacity and data rate of any wireless systems .In this paper,we exploit the space and time diversity to decode the quasi and rotated quasi space time block codes (QOSTBC) based on dent channel model.For doppler shifting and rayleigh distribution we make use of dent channel model. A general Quasi and rotated quasi Space -Time Block Coded (STBC) MIMO structure is presented in this paper. BER analysis is presented in terms of code rate and diversity achieved using Quasi and Rotated quasi STBC methods. Furthermore, simulations are carr ied out using above two OSTBC methods with various modulation schemes in quasi staticdent channel model and then optimum coding method is suggested for 4×2 quasi and rotated quasi Space time block coded MIMO systems .This provide fast decoding and gives better performance of communication system. BER analysis is presented in terms of diversity and code rate.

Improved K-Best Sphere Detection for Uncoded and Coded MIMO Systems

The conventional K-best sphere decoder (KSD) keeps the best K nodes at each level of the search tree. In addition to retaining the best K nodes, we also consider all the nodes whose costs are within a certain margin of the cost of the Kth best node. The resulting algorithm is called improved K-best sphere decoder (IKSD). Three IKSD variants are considered in this letter, which are fixed threshold, normalized threshold and adaptive threshold IKSD. The proposed IKSD requires a smaller K (indicating lower complexity) while still achieving a better and near optimal performance compared to the conventional KSD. These gains are confirmed by the simulation results. For example, for the fixed threshold IKSD in a 4 x 4 16-QAM multiple-input multiple-output (MIMO) system, with K=2, it achieves the same performance as the conventional KSD (K=16), yielding about 80% complexity savings. For coded MIMO systems, the IKSD is also extended as a list sphere decoder for joint iterative detection and decoding.

Peak-to-Average Power Ratio Analysis for Golden Coded MIMO Systems

combination of the orthogonal frequency-division multiplexing (OFDM) technique and the multiple-input multiple-output (MIMO) architecture has emerged as a promising candidate for future wireless communications. The Space-time block coding (STBC) technique permits to fully take advantage of MIMO-OFDM systems and to effectively improve the channel capacity and the spatial diversity. The Golden Code (GC) is a full-rate and full-diversity, space-time code for 2 × 2 MIMO systems. Thanks to its algebraic construction, the GC achieves Diversity-Multiplexing gain trade-off and preserves the mutual information. However, it is well known that STBC-MIMO-OFDM systems are sensitive to the high Peak-to-Average-Power Ratio (PAPR) of the transmitted signals. The purpose of this paper is to analyze the PAPR of golden coded MIMO-OFDM systems. We investigate the effect of the roll-off factor on the PAPR characteristics and analyze the system performances. KeywordsOFDM, PAPR, Golden Code.

Enhancing the Performance of the SIC-MMSE Iterative Receiver for Coded MIMO Systems via Companding

Iterative detection and decoding (IDD) method based on soft interference cancellation and minimum-mean squared-error filtering (SIC-MMSE) has received considerable attention in recent years due to its good performance-complexity tradeoff for coded multiple-input multiple-output (MIMO) systems. The Gaussianity of the a priori and a posteriori log-likelihood ratios (LLRs) computed at the constitute stages of the SIC-MMSE iterative receiver is a presumption for IDD to work. In this letter, the Gaussianity assumption is first shown to be not tight for high rate coded MIMO systems and thus leads to poor performance (for high rate coded MIMO systems). Then a non-linear companding based transformation method is incorporated into the SIC-MMSE iterative receiver to alleviate the non-Gaussianity of the a priori and a posteriori LLRs due to the imperfection of the (high-rate) code and per-stream approximation. Analytical and numerical results show that the proposed transformed SIC-MMSE iterative receiver achieves significant performances gains over the conventional one for coded MIMO systems, in particular, high rate coded ones with even lower computational complexity.

Link Performance Estimation Techniques for MIMO-OFDM Systems with Maximum Likelihood Receiver

Link adaptation allows a communication system to adapt its transmission modes according to channel conditions. Although a maximum likelihood (ML) receiver for multiple-input multiple-output (MIMO) systems provides optimal performance, estimating its link performance has been a difficult problem. In this paper, we propose a new link performance abstraction technique for MIMO orthogonal frequency-division multiplexing systems with the ML receiver. The performance of ML detection (MLD) is estimated by employing capacity bounds of two simple linear receivers. Then, we give a simple parametrization to compute the desired per-stream signal-to-noise ratio (SNR) values, which can be applied for both vertically and horizontally coded MIMO systems. Based on the derived per-stream SNR estimates, the block error rate is obtained using the received-bit information rate metrics. We also examine the effect of imperfect channel estimation as well as spatial correlations among antennas. Finally, extensive simulation results show that the proposed method provides superior estimation accuracy in the MIMO-MLD link evaluation with very low computational complexity.

Codebook-Based Lattice-Reduction-Aided Precoding for Limited-Feedback Coded MIMO Systems

Lattice-reduction-aided precoding (LRP) provides near-capacity rates with the use of low-complexity linear receivers for coded multiple-input multiple-output (MIMO) systems. However, a large amount of feedback in the feedback for an integer or binary precoding matrix has been a bottleneck in its implementation. In this paper, we propose a codebook-based LRP scheme for limited-feedback coded MIMO systems. The proposed LRP scheme follows the fundamentals of the previous LRP scheme that employed multilevel binary coset coding so that the precoding matrix is binary. In the proposed LRP scheme, the conventional precoding matrix obtained from the Lenstra-Lenstra-Lovasz algorithm is modified to specific forms that are predefined in a codebook set. The new precoding matrix is selected such that the lower bound on the capacity is maximized for a given codebook set, while the codebook set is designed offline such that the upper bound of the average capacity loss induced by the limitation on the codebook size is minimized. The simulation results show that the proposed LRP scheme nearly achieves the achievable rate of the conventional LRP scheme with a greatly reduced amount of feedback.

Reduced complexity sphere decoding

ABSTRACTIn multiple‐input multiple‐output (MIMO) systems, sphere decoding (SD) can achieve a performance equivalent to a full‐search maximum likelihood decoding, with reduced complexity. Several researchers reported techniques that reduce the complexity of SD further. In this paper, a new technique that decreases the computational complexity of SD substantially, without sacrificing performance, is introduced. The reduction is accomplished by deconstructing the decoding metric to decrease the number of computations and by exploiting the structure of a lattice representation. Furthermore, an application of SD employing a proposed smart implementation with very low computational complexity is introduced. This application calculates the soft bit metrics of a bit‐interleaved convolutional‐coded MIMO system in an efficient manner. On the basis of the reduced complexity SD, the proposed smart implementation employs the initial radius acquired by zero‐forcing decision feedback equalization, which ensures no empty spheres. Other than that, a technique of a particular data structure is also incorporated to efficiently reduce the number of executions carried out by SD. Simulation results show that these approaches achieve substantial gains in terms of the computational complexity for both uncoded and coded MIMO systems. Copyright © 2011 John Wiley & Sons, Ltd.