MIMO Spatial Multiplexing Systems Research Articles

Near-Optimal Performance With Low-Complexity ML-Based Detector for MIMO Spatial Multiplexing

In Spatial Multiplexing MIMO systems, many powerful non-linear detection techniques as sphere decoding have emerged to overcome the performance limitations of linear detection techniques. However, these non-linear techniques suffer from high complexity that increases dramatically with the number of antennas and the modulation order. Hence, they cannot be implemented on highly parallel hardware architecture and are thus not suitable for real-time high data rate transmission. In this letter, a new detection technique is proposed to approach the optimal performance obtained by Maximum Likelihood (ML) detector without increasing the complexity significantly. This detector is denoted by OSIC-ML since it combines two techniques: the Ordered Successive Interference Cancellation (OSIC) and the ML. The proposed OSIC-ML detector shows a near-optimal performance at very low complexity even with large scale MIMO and imperfect channel estimation, where this complexity can be efficiently controlled to achieve the desired complexity-performance tradeoff.

Novel MIMO Technique for Wireless Terabits Systems in Sub-THz Band

In this paper, a generalized MIMO Spatial Multiplexing (SMX) system with a new Index Modulation (IM) domain called filter IM domain is proposed. This filter domain generalizes the time and frequency IM domains. In particular, a Filter Shape IM (FSIM) is used to virtually transmit a part of the information bitstream by indexing the filter shape varying at the symbol rate. This scheme permits to achieve high Spectral Efficiency (SE) since it uses all the available time, frequency, and spatial resources. The proposed transceiver can be easily reconfigured to operate as a conventional MIMO SMX transceiver. Compared to the existing systems, the proposed system achieves the highest SE gain with the help of IM and MIMO multiplexing gain. The theoretical lower bound is derived to characterize the SMX FSIM system performance. The results reveal that SMX FSIM with 2 filter shapes only outperforms by 3.5 dB up to more than 12 dB the equivalent SMX QAM system at the same SE. Furthermore, a complete analysis in the sub-THz indoor environment with RF impairments is provided for the proposed system, SMX QAM, and Generalized Spatial Modulation. Finally, the results show that SMX FSIM with a linear receiver has better performance and robustness to phase noise, lower transceiver cost, higher SE/energy efficiency gain, and lower power consumption.

Incremental Antenna Selection Based on Lattice-Reduction for Spatial Multiplexing MIMO Systems

Antenna selection is a method to enhance the performance of spatial multiplexing multiple-input multiple-output (MIMO) systems, which can achieve the diversity order of the full MIMO systems. Although various selection criteria have been studied in the literature, they should be adjusted to the detection operation implemented at the receiver. In this paper, antenna selection methods that optimize the post-processing signal-to-noise ratio (SNR) and eigenvalue are considered for the lattice reduction (LR)-based receiver. To develop a complexity-efficient antenna selection algorithm, the incremental selection strategy is adopted. Moreover, for improvement of performance, an additional iterative selection method is presented in combination with an incremental strategy.

Performance of OQAM/GFDM in Spatial Multiplexing MIMO Systems

Generalized frequency division multiplexing (GFDM) is a prominent candidate to be used by the mobile Fifth Generation (5G) physical layer. Nevertheless, the integration of GFDM with Spatial Multiplexing (SM) MIMO system is essential to fulfill the data rate requirements. SM detection of MIMO-GFDM becomes a more challenging topic because of ICI and ISI due to the non-orthogonal nature of GFDM, along with IAI. In this article, the authors propose a system that combines the Offset-Quadrature Amplitude Modulation (OQAM) with GFDM to mitigate self-induced interference, by using a simple Matched Filter (MF) detector and minimum additional processing at the receiver. Simulation results show a considerable achieved improvement in BER by the proposed OQAM/GFDM compared to QAM/GFDM when using MMSE-based Ordered Successive Interference Cancellation (OSIC) detector. Furthermore, this system is unaffected by the roll-off factor variations of used pulse-shaping filters.

Performance Analysis of Matched-Filter Detector for MIMO Spatial Multiplexing Over Rayleigh Fading Channels With Imperfect Channel Estimation

The matched-filter (MF) detector is the lowest complexity linear detector in practical MIMO spatial multiplexing systems. Its performance is significantly affected by the number of available antennas and an operating channel SNR. In this paper, we analyze the exact performance of the MF detector without any restrictions on the numbers of the transmit and receive antennas. To this end, we first develop the exact, closed-form expression of the MF detector output over uncorrelated Rayleigh fading channels with an arbitrary number of antennas. Based on this result, we derive the exact closed-form bit error rate expressions for uncoded BPSK, QPSK, and $M$ -ary QAM signaling, which can be seen as the generalized forms of the conventional receiver diversity based on maximum ratio combining. We also elucidate the conditions on the numbers of antennas and channel SNR, where the use of MF detector should become effective. Furthermore, in the case of coded MIMO systems, we develop the optimal metric derived from the exact MF output. The corresponding mutual information justifies the simulated performance of LDPC-encoded MIMO spatial multiplexing with the MF detector over ideally interleaved Rayleigh fading channels. Finally, we extend our analysis to more practical systems with imperfect channel estimation.

FPGA Implementation of Sphere Detector for Spatial Multiplexing MIMO System

Multiple Input Multiple Output (MIMO (techniquesuse multiple antennas at both transmitter and receiver forincreasing the channel reliability and enhancing the spectralefficiency of wireless communication system.MIMO Spatial Multiplexing (SM) is a technology that can increase the channelcapacity without additional spectral resources. The implementation of MIMO detection techniques become a difficult missionas the computational complexity increases with the number of transmitting antenna and constellation size. So designing detection techniques that can recover transmitted signals from SpatialMultiplexing (SM) MIMO with reduced complexity and highperformance is challenging. In this survey, the general model ofMIMO communication system is presented in addition to multipleMIMO Spatial Multiplexing (SM) detection techniques. These detection techniques are divided into different categories, such as linear detection, Non-linear detection and tree-search detection. Detailed discussions on the advantages and disadvantages of each detection algorithm are introduced. Hardware implementation of Sphere Decoder (SD) algorithm using VHDL/FPGA is also presented

Low‐complexity transmit antenna selection algorithm exploiting null space in spatial multiplexing UWB MIMO systems

In this paper, a new transmit antenna selection algorithm for spatial multiplexing ultra‐wideband multiple‐input multiple‐output systems is proposed. It utilizes the null space of the channel matrix spatially and temporally combined for available transmit antennas. A selection strategy is used to successively find and remove the transmit antennas having the largest contribution to the null space. Its error performance is shown to be close to that of the optimal antenna selection algorithm with low complexity. © 2017 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

MIMO Interference Channel Between Spatial Multiplexing and Spatial Modulation

In this paper, two major multiple-input-multiple-output (MIMO) transmission techniques such as spatial modulation (SM) and spatial multiplexing (SMX) are considered. In particular, the focus is on an interference scenario, where an SM MIMO system interferes with a conventional SMX MIMO system. The interference caused by SM has a peculiar behavior. In SMX MIMO networks, the interference subspace is fixed in a given coherence time interval. It can be estimated accurately, and interference suppression techniques can be applied accordingly. However, the interference caused by an SM system has no fixed interference subspace, and it changes in every single channel use. Therefore, SM interference could pose some unique challenges to SMX MIMO systems in some scenarios. In this paper, the effect of SM interference on SMX MIMO systems and methods to overcome/reduce the adverse effects caused by SM interference are studied. Furthermore, the effect of SMX interference on SM MIMO systems is also studied.

Remarks on the Performance of the Linear Detectors in MIMO Spatial Multiplexing Systems

Linear minimum mean square error (MMSE) detector has been shown to alleviate the noise amplification problem associated with the conventional zero-forcing (ZF) detector. In this paper, we analyze the performance improvement by the MMSE detector in terms of the condition number of its filtering matrix, the post-processing signal to noise ratio (SNR) improvement, and the variance of the postprocessing SNRs. To this end, we derive explicit formulas for the condition numbers of the filtering matrices and the post-processing SNRs. Analytical and simulation results demonstrate that the improvement achieved by the MMSE detector over the ZF detector does not only depend on the noise variance and the condition number of the channel matrix, but also on how close the smallest singular values are to the noise variance. This conjecture is also proven correct via analyzing the post-processing SNR of both detectors.

A Performance Study of Semidefinite Relaxation Detector in Spatially Correlated and Rank Deficient Large MIMO Systems

Large MIMO detection has gained significant attention in the recent past with computational complexity as the research focus. However, they assume the channel to be i.i.d and uncorrelated, which is not a valid assumption in practice due to the fixed physical space constraints in large MIMO. Nevertheless, there is a little work carried out in these lines. In this paper, we consider the problem of detection in large spatial multiplexing MIMO systems and we investigate the semidefinite relaxation (SDR) approach to solve this problem. We investigate the applicability of SDR approach in large MIMO setting and study its performance in spatially correlated and rank deficient channel conditions. Through the simulation results, we demonstrate the superior performance of semidefinite relaxation detector over other existing methods in uncorrelated and correlated large MIMO systems especially in low SNR regime. The performance of SDR detector is noteworthy with large number of antennas despite the system being rank deficient and the average running time also scales up well for large systems.

A low-latency high-throughput soft-output signal detector for spatial multiplexing MIMO systems

This paper presents a low latency, high throughput soft-output signal detector for a 4×4 64-QAM spatial-multiplexing MIMO system. To achieve high data-level parallelism and accurate soft information, the detector adopts a channel-adaptive node perturbation technique to generate a list of candidate vectors around an initial linear estimation. The detection algorithm provides a large range and convenient performance-complexity trade-off by adjusting the node perturbation parameter. A partial-parallel pipelined VLSI architecture is developed to implement the algorithm with high throughput, low processing latency, while offering the flexibility to support run-time performance tuning. Moreover, a fast and hardware-friendly node enumeration scheme is developed to further reduce the processing delay by exploiting the geometric property of the quadrature amplitude modulation (QAM) constellation. The detector was synthesized using Synopsys Design Compiler with a 65nm CMOS standard cell library. The core area is 0.58mm2 with 290K gates. The peak throughput is 3Gb/s at 500MHz clock frequency with a latency of 20ns. Compared to other reported soft-output MIMO detectors, this is a latency reduction of 71%. The corresponding energy consumption is 33pJ per bit detection.

X-Structured Precoder Designs for Spatial-Multiplexing MIMO and MIMO Relay Systems

In multiple-input-multiple-output (MIMO) transmission, precoding has been considered a promising technique to improve the system performance. In general, the criterion of precoder design depends on the detector used at the receiver. For the maximum-likelihood (ML) detector, the criterion is to maximize the minimum distance of the received signal constellation. Unfortunately, the derivation of the optimum solution is known to be difficult, and suboptimum solutions have then been developed. One promising approach confines the precoder having an X-structure. Several methods have been developed to solve the X-structured precoder. However, most of them use numerical searches to find their solutions and require lookup tables during run time. In this paper, we propose a systematic design method to solve the problems. The proposed precoder has a simple closed-form expression, and no numerical searches and lookup tables are required. Simulation results show that the proposed method can yield almost the same performance as the existing methods. We also consider the problem of joint source/relay precoder design in a two-hop amplify-and-forward MIMO relay system. Since the problem is much more involved and a closed-form solution is intractable to find, we then extend the use of the proposed X-structured precoder so that the problem can be reformulated as a simple scalar-valued optimization problem. Simulations show that the proposed method can significantly outperform existing joint design methods.

Fast codeword selection for limited feedback beamforming multiple‐input–multiple‐output systems using breadth‐first tree search

Codebooks with constant modulus entries are being considered for the limited feedback beamforming multiple-input-multiple-output (MIMO) system to improve the power amplifier efficiency at the transmitter. Assume that one such codebook is known to both the transmitter and receiver. The receiver must determine a target codeword from this codebook and send its index back to the transmitter. A receiver can be implemented with low cost if fast codeword selection algorithm is executed. In this study, the authors utilise the properties possessed by three such codebooks and propose a novel tree search algorithm for fast codeword selection. Compared with two previously reported codeword selection algorithms, our algorithm is of fixed complexity and does find the target codeword. Furthermore, our algorithm for codeword selection is similar to the tree search for MIMO detection. These two similar tree search algorithms for both codeword selection and MIMO detection can be implemented by the same hardware architecture. A baseband receiver with small chip area for the dual-mode (the spatial multiplexing and beamforming transmission modes) MIMO system is possible.

A VLSI Architecture for the V-BLAST Algorithm in Spatial-Multiplexing MIMO Systems

This paper presents a VLSI architecture for the suboptimal hard-output Vertical-Bell Laboratories Layered Space-Time (V-BLAST) algorithm in the context of Spatial Multiplexing Multiple-Input Multiple-Output (SM-MIMO) systems immersed in Rayleigh fading channels. The design and implementation of its corresponding data-path and control-path components over FPGA devices are considered. Results on synthesis, bit error rate performance, and data throughput are reported.

Analysis and design of coding and interleaving in a MIMO-OFDM communication system

Use of Wireless communications for Metropolitan Area Network (MAN) in consumer electronics has increased significantly in the recent past. This paper, presents the performance analysis of four different channel coding and interleaving schemes for MIMO-OFDM communications systems. A comparison is done based on the BER, hardware implementation resources requirement, and power dissipation. It also presents a memory-efficient and low-latency interleaver implementation technique for the MIMO-OFDM communication system. It is shown that among the four coding and interleaving schemes studied, the cross-antenna coding and per-antenna interleaving performs the best under all SNR conditions and for all modulation schemes. It is also the best scheme as far as the hardware resource implication and power dissipation are concerned, which are particularly important in the context of consumer electronics. Next, using the proposed interleaver, a MIMO-OFDM based transmitter employing a double data stream 2×2 MIMO spatial multiplexing system is built.

Minimum Euclidean Distance-Based Precoding for Three-Dimensional Multiple Input Multiple Output Spatial Multiplexing Systems

Through a feedback link, the channel state information acquired at the receiver is known at the transmitter and MIMO precoding techniques can be applied according to various criteria. In this paper, an efficient linear precoder based on the maximization of the minimum Euclidean distance between two received data vectors for three data-stream MIMO spatial multiplexing systems is proposed. By using a singular value decomposition, the precoding matrix can be parameterized as the product of a power allocation matrix and an input shaper matrix. According to this representation, the optimal precoders are proposed for the case of three independent data-streams. Simulation results over Rayleigh fading channels show considerable bit-error-rate improvement with the proposed solution in comparison with other precoding strategies.

Performance Evaluation of Spatial Multiplexing MIMO Systems with Various Detection Schemes

Performance Evaluation of Spatial Multiplexing MIMO Systems with Various Detection Schemes

Improved FCLSD algorithm based on LTE/LTE-A system

In order to meet the high data rate, large capacity and low latency in LTE, advanced MIMO technology has been introduced in LTE system, which becomes one of the core technologies in physical layer. In a variety of MIMO detection algorithms, the ZF and MMSE linear detection algorithms are the most simple, but the performance is poor. MLD algorithm can achieve optimal detection performance, but it’s too complexity to be applied in practice. CLSD algorithm has similar detection performance and lower complexity with the MLD algorithm, but the uncertainty of complexity will bring hardware difficulties. FCLSD algorithm can maximize the advantages of CLSD algorithm and solve difficult problems in practice. Based on advanced FCLSD algorithm and combined with LTE / LTE-A practical system applications, this article designed two improved algorithms. The two improved algorithms can be flexibly and adaptively used in various antenna configurations and modulation scene in LTE / LTE-A spatial multiplexing MIMO system. The Simulation results show that the improved algorithm can achieve an approximate performance to the original FCLSD algorithm; in addition, it has a fixed complexity and could be carried out by parallel processing.

Adaptive Reduced-Rank Equalization Algorithms Based on Alternating Optimization Design Techniques for MIMO Systems

This paper presents a novel adaptive reduced-rank multiple-input-multiple-output (MIMO) equalization scheme and algorithms based on alternating optimization design techniques for MIMO spatial multiplexing systems. The proposed reduced-rank equalization structure consists of a joint iterative optimization of the following two equalization stages: 1) a transformation matrix that performs dimensionality reduction and 2) a reduced-rank estimator that retrieves the desired transmitted symbol. The proposed reduced-rank architecture is incorporated into an equalization structure that allows both decision feedback and linear schemes to mitigate the interantenna (IAI) and intersymbol interference (ISI). We develop alternating least squares (LS) expressions for the design of the transformation matrix and the reduced-rank estimator along with computationally efficient alternating recursive least squares (RLS) adaptive estimation algorithms. We then present an algorithm that automatically adjusts the model order of the proposed scheme. An analysis of the LS algorithms is carried out along with sufficient conditions for convergence and a proof of convergence of the proposed algorithms to the reduced-rank Wiener filter. Simulations show that the proposed equalization algorithms outperform the existing reduced- and full- algorithms while requiring a comparable computational cost.

Minimum BER Bit Allocations for MIMO Spatial Multiplexing Systems

该文基于最小误比特率(BER)准则，提出了多输入多输出(MIMO)空间复用系统的贪婪比特分配算法和基于二分法的比特分配算法。在总比特速率和每个发射天线分配相等功率的约束条件下，通过比特分配优化每个发射天线的调制方式，改善了系统的BER性能。仿真结果表明，与传统的MIMO系统相比，比特分配的MIMO系统可获得显著的信噪比(SNR)增益；与功率分配相比，比特分配在性能损失很小的情况下减少了每个发射天线的功率放大器的动态范围。