Spatial Multiplexing MIMO Research Articles

Fast Receive Antenna Selection for Spatial Multiplexing MIMO over Correlated Rayleigh Fading Channels

It is well known that the capacity of spatial multiplexing multiple-input multiple-output (SM-MIMO) system employing optimal antenna selection can significantly outperform a system without selection for same number of costly radio frequency chains. However, it requires an exhaustive search for the optimal selection (OS) that grows exponentially with the available number of transmit (u) and receive (m) antennas. In this paper, a novel low complexity receive antenna selection (RAS) technique is proposed for SM-MIMO to maximize the channel capacity over correlated Rayleigh fading environment. It is based on the Euclidean norms of channel matrix rows and the corresponding phase differences due to their direct impact on the capacity. Extensive analysis and simulations have shown near optimal performance for any signal-to-noise-ratio and correlation values with low complexity of $${\mathcal{O} \left({u^{2}m}\right)}$$ vector calculations. This technique provides fast RAS to capture most of the capacity gain promised by multiple antenna systems over different channel conditions. Furthermore, it enables efficient spectrum utilization for next generation wireless communications.

Analysis of WiMAX Physical Layer using Spatial Diversity

Broadband Wireless Access (BWA) has emerged as a promising solution for providing last mile internet access technology to provide high speed internet access to the users in the residential as well as in the small and medium sized enterprise sectors. IEEE 802.16e is one of the most promising and attractive candidate among the emerging technologies for broadband wireless access. The emergence of WiMAX protocol has attracted various interests from almost all the fields of wireless communications. MIMO systems which are created according to the IEEE 802.16-2005 standard (WiMAX) under different fading channels can be implemented to get the benefits of both the MIMO and WiMAX technologies. In this paper analysis of higher level of modulations (i.e. M-PSK and M-QAM for different values of M) with different code rates and on WiMAX-MIMO system is presented for Rayleigh channel by focusing on spatial multiplexing MIMO technique. Signal-to Noise Ratio (SNR) vs Bit Error Rate (BER) analysis has been done.

Analysis of WiMAX Physical Layer Using Spatial Multiplexing

Broadband Wireless Access (BWA) has emerged as a promising solution for providing last mile internet access technology to provide high speed internet access to the users in the residential as well as in the small and medium sized enterprise sectors. IEEE 802.16e is one of the most promising and attractive candidate among the emerging technologies for broadband wireless access. The emergence of WiMAX protocol has attracted various interests from almost all the fields of wireless communications. MIMO systems which are created according to the IEEE 802.16-2005 standard (WiMAX) under different fading channels can be implemented to get the benefits of both the MIMO and WiMAX technologies. In this paper analysis of higher level of modulations (i.e. M-PSK and M-QAM for different values of M) with different code rates and on WiMAX-MIMO system is presented for Rayleigh channel by focusing on spatial multiplexing MIMO technique. Signal-to Noise Ratio (SNR) vs Bit Error Rate (BER) analysis has been done.

Modified Waterfilling Algorithms for MIMO Spatial Multiplexing with Asymmetric CSI

This paper studies the transmit power-multiplexing tradeoff in MIMO systems when two users with different priorities are to be accommodated simultaneously. In the general problem formulation, a minimum information rate must be guaranteed for a prioritized user whose channel state information (CSI) is known, while the data rate for the other user with completely unknown CSI is "best-effort." The drawbacks of the classic spatial water-filling algorithm are discussed, and two modified water-filling algorithms are proposed that either balance the required transmit power with the number of spatial dimensions available for each user, or minimize the number of transmit spatial dimensions allocated for the prioritized user. We then specialize to applications in the MIMO wiretap channel, the MIMO multiuser downlink channel, and spectrum underlay in MIMO cognitive radio networks, where existing methods are not applicable under the asymmetric CSI scenario. Numerical results verify the performance advantages of the proposed transmission schemes for each of these case studies.

Low-Complexity Likelihood Information Generation for Spatial-Multiplexing MIMO Signal Detection

Signal detection algorithms providing likelihood information for coded spatial-multiplexing multiple-input-multiple-output (MIMO) wireless communication systems pose a critical design challenge due to their prohibitively high computational complexity. In this paper, we present a low-complexity soft-output detection algorithm by adopting four implementation-friendly algorithm-level improvements to the fixed-complexity sphere decoder. More specifically, we introduce a reliability-dependent tree expansion approach and an on-demand list-size reduction scheme for low-cost candidate list generation. In terms of performance improvement, we apply an early bit-flipping strategy and utilize the l1-norm distance representation. The algorithm is evaluated by computer simulations performed over Rayleigh flat fading channels and computational complexity analysis. Compared with the soft-output K-Best algorithm, the proposed algorithm saves at least 60% of the computations for detecting 4 × 4 64-quadrature amplitude modulation (QAM) MIMO signal and, at the same time, provides better detection performance, making it a promising detection scheme for real-life hardware implementation.

Performance Analysis of MMSE-Based Amplify and Forward Spatial Multiplexing MIMO Relaying Systems

In this paper, we propose a general framework to quantify the average error probability of the minimum mean squared error based precoding schemes in amplify-and-forward relay networks where all nodes are equipped with multiple antennas. Especially, we investigate spatial multiplexing schemes which transmit multiple data streams simultaneously. Due to difficulty in finding an exact expression of the average error rate, we exploit the high signal-to-noise-ratio (SNR) based approach which allows a simple and accurate characterization of the performance. Then, we derive new closed form expressions for bit error rate performance of both the optimal source-relay joint precoding schemes and the optimal relay only precoding schemes in terms of a coding gain as well as a diversity gain. Taking a different pathloss in each hop into consideration, we evaluate the performance in a generalized environment. Through our analysis, we discuss several interesting observations and provide a helpful guideline for designing MMSE-based relaying systems. Monte-Carlo simulations show that our analytical work accurately predicts numerical results.

Grassmannian Subspace Prediction for Precoded Spatial Multiplexing MIMO With Delayed Feedback

In unitary precoded multi-antenna systems with delayed feedback, the quantized channel state information (CSI) may become outdated before its actual use at the transmitter. In this letter, by exploiting the geometric properties of the Grassmannian manifold, we invoke the use of Grassmannian subspace predictive coding (GSPC) to overcome this problem. Under the framework of GSPC, a novel limited feedback strategy is proposed which consists of a two-stage optimization process at the receiver. The first stage quantizes the estimated CSI by accounting for the feedback delay; while the second stage optimizes the prediction on the Grassmannian manifold.

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.

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。

A Low-power and Low-complexity Baseband Processor for MIMO-OFDM WLAN Systems

This paper presents an energy-efficient design and the implementation results of a high speed two transmitter--two receiver multi-input multi-output orthogonal frequency division multiplexing (MIMO-OFDM) wireless LAN baseband processor. The proposed processor includes a bit-parallel processing physical layer convergence procedure (PLCP) processor which lowers system clock frequency. A cost-efficient MIMO spatial multiplexing (SM) symbol detector is also proposed in a physical medium dependent (PMD) processor. The proposed symbol detection algorithm is based on a sorted QR decomposition (SQRD) scheme followed by a maximum-likelihood (ML) test. The proposed algorithm shows enhanced performance compared to the conventional algorithms such as SQRD and ordered successive interference cancellation (OSIC) algorithms. The proposed baseband processor supports a maximum data rate of 130 Mbps at a 40 MHz operation frequency. The power consumptions of the PLCP processor are 27 mW and 93 mW for TX and RX modes, respectively, which are reduced by 70% compared with that of a common bit-serial architecture. The complexity of the symbol detector in the PMD processor is reduced by 18% compared with that of the conventional hardware architecture.

Enhanced Groupwise Detection with a New Receive Combiner for Spatial Multiplexing MIMO Systems

In this letter, we propose a new groupwise receive combiner design for multiple-input multiple-output spatial multiplexing systems. The conventional group detection (GD) suffers from a considerable performance loss since the noise components are not taken into account. The output signal-to-interference-plus-noise ratio (SINR) is defined in each subgroup in order to consider both the desired signal and noise statistics. Adopting the real-valued representation, we provide an optimal receive combiner which maximizes the SINR with a general group size. The simulation results show that the proposed scheme achieves a large performance gain over the conventional GD in coded systems. Also, when combining with near-optimal detection algorithms such as sphere decoder, the proposed GD scheme offers a comparable performance with significant reduced complexity.

A 74.8 mW Soft-Output Detector IC for 8$\,\times\,$8 Spatial-Multiplexing MIMO Communications

In this paper, VLSI implementation of a configurable, soft-output MIMO detector is presented. The proposed chip can support up to 8 × 8 64-QAM spatial multiplexing MIMO communications, which surpasses all reported MIMO detector ICs in antenna number and modulation order. Moreover, this chip provides configurable antenna number from 2 × 2 up to 8 × 8 and modulation order from QPSK to 64-QAM. Its outputs include bit-wise log likelihood ratios (LLRs) and a candidate list, making it compatible with powerful soft-input channel decoders and iterative decoding system. The MIMO detector adopts a novel sphere decoding algorithm with high decoding efficiency and superior error rate performance, called modified best-first with fast descent (MBF-FD). Moreover, a low-power pipelined quad-dual-heap (quad-DEAP) circuit for efficient node pool management and several circuit techniques are implemented in this chip. When this chip is configured as 4 × 4 64-QAM and 8 × 8 64-QAM soft-output MIMO detectors, it achieves average throughputs of 431.8 Mbps and 428.8 Mbps with only 58.2 mW and 74.8 mW respective power consumption and reaches 10-5 coded bit error rate (BER) at signal-to-noise ratio (SNR) of 24.2 dB and 22.6 dB, respectively.

Joint admission control and antenna assignment for multiclass QoS in spatial multiplexing MIMO wireless networks

We consider the problem of quality-of-service (QoS) provisioning for multiple traffic classes in a MIMO wireless network. This QoS provisioning is posed as a radio resource management (RRM) problem at a wireless node (e.g., a wireless mesh router) with multiple antennas. We decompose this RRM problem into two tractable subproblems, namely, the antenna assignment and the admission control problems. The objective of antenna assignment is to minimize the weighted packet dropping probability for the different traffic classes under constrained packet delay. The objective of admission control is to maximize the revenue of the wireless node gained from the ongoing connections for different traffic classes under constrained connection blocking probability and average per-connection throughput. The decision of antenna assignment is made in a short-term basis (e.g., for every packet transmission interval) while that of admission control is made in a long-term basis (i.e., when a connection arrives). Constrained Markov decision process (CMDP) models are formulated to obtain the optimal decisions on antenna assignment and admission control. To provide efficient channel utilization, the RRM framework considers adaptive modulation at the physical layer which exploits channel state information. Performance evaluation results show that this joint antenna assignment and admission control framework can provide class-based service differentiation while satisfying both the connection-level and packet-level QoS requirements.

Mobile Station Spatio-Temporal Multipath Clustering of an Estimated Wideband MIMO Double-Directional Channel of a Small Urban 4.5 GHz Macrocell

Multipath clusters in a wireless channel could act as additional channels for spatial multiplexing MIMO systems. However, identifying them in order to come up with better cluster channel models has been a hurdle due to how they are defined. This paper considers the identification of these clusters at themobile station through a middle ground approach--combining a globally optimized automatic clustering approach and manual clustering of the physical scatterers. By including the scattering verification in the cluster identification, better insight into their behavior in wireless channels would be known, especially the physical realism and eventually a more satisfactorily accurate cluster channel model could be proposed. The results show that overlapping clusters make up the majority of the observed channel, which stems from automatic clustering, whereas only a few clusters have clear delineation of their dispersion. In addition, it is difficult to judge the physical realism of overlapping clusters. This further points to a need for the physical interpretation and verification of clustering results, which is an initial step taken in this paper. From the identification results, scattering mechanisms of the clusters are presented and also their selected first and second order statistics.

Ordered Eigenvalues of a General Class of Hermitian Random Matrices With Application to the Performance Analysis of MIMO Systems

In this paper, we present a general formulation that unifies the probabilistic characterization of Hermitian random matrices with a specific structure. Based on a general expression for the joint pdf of the ordered eigenvalues, we obtain i) the joint cdf; ii) the marginal cdfs; and iii) the marginal pdfs of the ordered eigenvalues, where ii) and iii) follow as simple particularizations of i). Our formulation is shown to include the distribution of some common MIMO channel models such as the uncorrelated, semicorrelated, and double-correlated Rayleigh MIMO fading channel and the uncorrelated Rician MIMO fading channel, although it is not restricted only to these. Hence, the proposed formulation and derived results provide a solid framework for the simultaneous analytical performance analysis of MIMO systems under different channel models. As an illustrative application, we obtain the exact outage probability of a spatial multiplexing MIMO system transmitting through the strongest channel eigenmodes.

Tree Based Approximate Optimal Signal Detectors for MIMO Spatial Multiplexing Systems

In multiple antenna systems that use spatial multiplexing to raise transmission rates, it is preferable to use maximum likelihood (ML) detection to exploit the full receive diversity and minimize the error probability. In this paper, we present two tree based approximate ML detectors that use new two ordering criteria in conjunction with efficient search strategies. Unlike conventional tree detectors, the new detectors closely approximate the error performance of the exact ML detector while achieving a dramatic reduction in complexity. Moreover, they ensure a fixed detection delay and high level of parallelization in the tree search.

Theoretical Analysis of Capacities in Dynamic Spatial Multiplexing MIMO Systems

Theoretical Analysis of Capacities in Dynamic Spatial Multiplexing MIMO Systems

Measurement-Based Performance Evaluation of Coded MIMO-OFDM Spatial Multiplexing with MMSE Spatial Filtering in an Indoor Line-of-Sight Environment

The MIMO system can meet the growing demand for higher capacity in wireless communication fields. So far, the authors have reported that, based on channel measurements, uncoded performance of narrowband MIMO spatial multiplexing in indoor line-of-sight (LOS) environments generally outperforms that in non-LOS (NLOS) ones under the same transmit power condition. In space-frequency coded MIMO-OFDM spatial multiplexing, however, we cannot expect high space-frequency diversity gain in LOS environments because of high fading correlations and low frequency selectivity of channels so that the performance may degrade unlike uncoiled cases. In this letter, we present the practical performance of coded MIMO-OFDM spatial multiplexing based on indoor channel measurements. The results show that an LOS environment tends to provide lower space-frequency diversity effect whereas the MIMO-OFDM spatial multiplexing performance is still better in the environment compared with an NLOS environment.

Performance Evaluation of MIMO in IEEE802.16e/WiMAX

The methodology used to evaluate the performance of the various MIMO schemes in orthogonal frequency division multiplexing (OFDM) WiMAXWiMAX stands for Worldwide Interoperability for Microwave Access. systems is described. The per-tone signal-to-noise plus interference ratio (SINR) of a MIMO OFDM system is derived in a multi user, multicell and multisector communication system. The sector average spectral efficiency for a coded MIMO OFDM system is evaluated under a single frequency reuse deployment scenario. It is shown that the second antenna at the subscriber station receiver provides significant gains over single transmit single receive antenna (SISO) systems. The rate 2 spatial multiplexing MIMO scheme on the downlink improves the sector spectral efficiency by 10% over single transmit and two receive antenna (SIMO) system in a single frequency reuse deployment. It is also shown that in a time-division duplex (TDD) WiMAX system, the gain in downlink spectral efficiency from beamforming can be very large if the delay between the uplink channel estimate and the downlink beamforming is small compared to the coherence time of the channel. On the uplink, it is shown that the collaborative spatial multiplexing increases the spectral efficiency by 9% over a SIMO system with the same number of receive antennas at the base station (BS). Significant gains in uplink spectral efficiency are seen with more antennas at the BS and by using uplink beamforming as compared to SISO.

Overcoming interference in spatial multiplexing MIMO cellular networks

Multi-antenna transmission and reception (known as MIMO) is widely touted as the key technology for enabling wireless broadband services, whose widespread success will require 10 times higher spectral efficiency than current cellular systems, at 10 times lower cost per bit. Spectrally efficient, inexpensive cellular systems are by definition densely populated and interference-limited. But spatial multiplexing MIMO systems- whose principal merit is a supposed dramatic increase in spectral efficiency- lose much of their effectiveness in high levels of interference. This article overviews several approaches to handling interference in multicell MIMO systems. The discussion is applicable to any multi-antenna cellular network, including 802.16e/WiMAX, 3GPP (HSDPA and 3GPP LTE), and 3GPP2 (lxEVDO). We argue that many of the traditional interference management techniques have limited usefulness (or are even counterproductive) when viewed in concert with MIMO. The problem of interference in MIMO systems is too large in scope to be handled with a single technique: in practice a combination of complementary countermeasures will be needed. We overview emerging system-level interference-reducing strategies based on cooperation, which will be important for overcoming interference in future spatial multiplexing cellular systems.