MIMO antenna selection with lattice-reduction-aided linear receivers

A method to improve the performance of multiple-input-multiple-output systems is to employ a large number of antennas and select the optimal subset depending on the specific channel realization. A simple antenna-selection criterion is to choose the antenna subset that maximizes the mutual information. However, when the receiver has finite complexity decoders, this criterion does not necessarily minimize the error rate (ER). Therefore, different selection criteria should be tailored to the specific receiver implementation. In this paper, we develop new antenna-selection criteria to minimize the ER in spatial multiplexing systems with lattice-reduction-aided receivers. We also adapt other known selection criteria, such as maximum mutual information, to this specific receiver. Moreover, we consider adaptive antenna-selection algorithms when the channel is not perfectly known at the receiver but can only be estimated. We present simulation examples to show the ER of the different selection criteria and the convergence of the adaptive algorithms. We also discuss the difference in complexity and performance among them.     

Receive antenna selection for MIMO spatial multiplexing: theory and algorithms

This paper discusses the problem of receive antenna subset selection in multiple-input multiple-output spatial multiplexing (MIMO-SM) systems. We develop selection algorithms for maximizing the channel capacity. One algorithm in particular allows tractable statistical analysis of performance. We leverage this to prove that the capacity of the system through receive antenna selection is statistically lower bounded by the capacity of a set of parallel independent single input multiple output (SIMO) channels, each with selection diversity. This provides the crucial step in proving the next main result: The diversity order achievable through antenna selection is the same as that of the full system. The result sets up strong motivation for introducing receive selection in MIMO-SM systems. The remainder of the paper discusses selection algorithms for two popular MIMO-SM systems, namely, ordered successive interference cancellation with independently encoded layers and minimum mean square error (MMSE) receiver with joint encoding of data streams. Extensive Monte Carlo simulations are presented to validate and demonstrate performance.     

Compact polarisation and spatial multiplexing antenna for MIMO applications

A compact size, polarisation and spatial multiplexing slot antenna utilising the Spatial Multiplexing of Local Elements (SMILE) technique, is proposed. The antenna is used to explore diversity gain with a single RF channel in the applications of a multiple-input multiple-output (MIMO) wireless communication system.     

Detection techniques for MIMO spatial multiplexing systems

We discuss and compare the most important detection techniques for MIMO spatial multiplexing wireless systems, focusing on their performance and computational complexity. Our analysis shows that the limited performance of conventional suboptimal detection techniques is primarily caused by their inability to cope with poorly conditioned channels. The recently proposed sphere projection algorithm is better suited to these channels and can achieve near-optimal performance.     

Antenna selection for spatial multiplexing systems with linearreceivers

Future cellular systems will employ spatial multiplexing with multiple antennas at both the transmitter and receiver to take advantage of large capacity gains. In such systems it will be desirable to select a subset of available transmit antennas for link initialization, maintenance or handoff. We present a criterion for selecting the optimal antenna subset when linear, coherent receivers are used over a slowly varying channel. We propose use of the post-processing SNRs (signal to noise ratios) of the multiplexed streams whereby the antenna subset that induces the largest minimum SNR is chosen. Simulations demonstrate that our selection algorithm also provides diversity advantage thus making linear receivers useful over fading channels     

Joint antenna subset selection for spatial multiplexing systems based on statistical and instantaneous selection criteria

While the joint transmit/receive (Tx/Rx) AnSS with exhaustive search is the best solution for error rate minimization, its complexity makes it difficult for implementation on practical systems. To overcome this disadvantage, we propose a two-stage AnSS algorithm for the spatial multiplexing (SM) in the multiple input multiple output (MIMO) system, which employs both the statistical (i.e., average Euclidean distance, AED) and instantaneous selection criteria (i.e., modified instantaneous Euclidean distance, M-IED). The proposed algorithm reduces the computational complexity by decoupling the joint Tx/Rx selection into two separate selections of the numbers of Tx/Rx antennas and antenna subset, respectively. We show that the proposed AED criterion can be implemented through a simple look up table (LUT), thereby significantly reducing the computational complexity. Simulation results and computational complexity comparisons, prove that the proposed two-stage AnSS algorithm for the SM scheme reduces the hardware and computational complexity without any loss of the signal-to-noise ratio (SNR) and the diversity order, compared to the exhaustive search method.     

Maximising capacity of MIMO systems with receive antenna subarray formation

Antenna subarray formation is a novel RF pre-processing technique that reduces hardware complexity of multiple-input multiple-output systems while alleviating the performance degradation of conventional antenna selection techniques. With this method, each RF chain is allocated to a linear combination of the responses of a subset of the available antenna elements, which is performed in the radio frequency domain. A novel, analytical, suboptimal algorithm is introduced for receive antenna subarray formation based on instantaneous channel information that maximises the effective channel capacity.     

BER criterion and codebook construction for finite-rate precoded spatial multiplexing with linear receivers

Precoded spatial multiplexing systems with rate-limited feedback have been studied recently based on various precoder selection criteria. Instead of those based on indirect performance indicators, we in this paper propose a new criterion directly based on the exact bit error rate (BER) that is applicable to systems with linear receivers and rectangular/square quadrature-amplitude-modulation constellations. The BER criterion outperforms any other alternative in terms of optimizing the BER performance for an uncoded system with linear receivers. We then develop a precoder codebook construction method based on the generalized Lloyd algorithm from the vector quantization literature. This construction is not directly based on the BER criterion. Hence, it is suboptimal in the BER sense. However, relative to those currently available, our newfound codebooks improve considerably various minimum distances between any pair of codewords of the codebook. Finally, we analyze the BER-optimal precoder in the asymptotic case with infinite-rate feedback that amounts to perfect channel knowledge at the transmitter. The infinite-rate optimal precoder based on the BER criterion is drastically different from the counterparts with other criteria, and it leads to a benchmark performance for finite-rate precoded spatial multiplexing systems. We observe from numerical results that the BER performance of finite-rate feedback with suboptimal codebooks approaches quickly the benchmark performance of infinite-rate feedback. This suggests that i) the number of feedback bits in practical systems need not be large and ii) the room for performance improvement via further codebook optimization shrinks quickly as the codebook size increases.     

Spatial multiplexing with transmit antenna and constellation selection for correlated MIMO fading channels

We consider spatial multiplexing systems in correlated multiple-input multiple-output (MIMO) fading channels with equal power allocated to each transmit antenna. Under this constraint, the number and subset of transmit antennas together with the transmit symbol constellations are determined assuming knowledge of the channel correlation matrices. We first consider a fixed data rate system and vary the number of transmit antennas and constellation such that the minimum margin in the signal-to-noise ratio (SNR) is maximized for linear and Vertical Bell Laboratories Layered Space-Time (V-BLAST) receivers. We also derive transmit antenna and constellation selection criteria for a successive interference cancellation receiver (SCR) with a fixed detection order and a variable number of bits transmitted on each substream. Compared with a system using all available antennas, performance results show significant gains using a subset of transmit antennas, even for independent fading channels. Finally, we select a subset of transmit antennas to maximize data rate given a minimum SNR margin. A lower bound on the maximum outage data rate is derived. The maximum outage data rate of the SCR receiver is seen to be close to the outage channel capacity.     

Efficient capacity-based antenna selection for MIMO systems

The achieved capacity of the multiple-input-multiple-output wireless channel is typically dependent on the array configurations at the transmitter and receiver. Maximizing system capacity or throughput therefore requires that the arrays adapt to changing channel conditions, which may be accomplished by selecting an appropriate subset of available antenna elements for connection to the electronic transmit and receive modules. This work presents algorithms, derived using relatively straightforward information theoretic considerations, for efficiently and effectively selecting the antenna elements. Computational examples using a realistic channel model for indoor environments illustrate the performance of the techniques.     

Optimal minimum distance-based precoder for MIMO spatial multiplexing systems

We describe a new precoder based on optimization of the minimum Euclidean distance d/sub min/ between signal points at the receiver side and for use in multiple-input multiple-output (MIMO) spatial multiplexing systems. Assuming that channel state information (CSI) can be made available at the transmitter, the three steps ( noise whitening, channel diagonalization and dimension reduction), which are currently used in investigations on MIMO systems, are performed. Thanks to this representation, an optimal d/sub min/ precoder is derived in the case of two different transmitted data streams. For quadrature phase-shift keying (QPSK) modulation, a numerical approach shows that the precoder design depends on the channel characteristics. Comparisons with maximum signal-to-noise ratio (SNR) strategy and other precoders based on criteria, such as water-filling (WF), minimum mean square error (MMSE), and maximization of the minimum singular value of the global channel matrix, are performed to illustrate the significant bit-error-rate (BER) improvement of the proposed precoder.     

自适应MIMO系统中的支持选择功能的四单元天线

天线选择是自适应MIMO系统中实现可重构多天线的一种有效方法.提出了一种支持选择功能的四单元天线.通过在馈电网络中增加PIN二极管,该天线具备选择任意一组天线单元的功能,同时未被选择的天线单元终端加载匹配的集总负载以维持方向图的稳定.测量结果表明:在任意一种天线单元组合下,该天线都可以覆盖UMTS频段并保持较低的互耦;同时天线单元的方向图具有稳定性.     

Combined transmit antenna selection and detection over spatial correlated MIMO systems

In this paper a method that combines transmit antenna selection and reduced-constellation detection in spatially correlated Multi-Input Multi-Output (MIMO) fading channels is presented. To mitigate the performance degradation caused by the use of antenna selection that is based on correlation among columns, an iterative receiver scheme that uses only a subset of the constellation points close to the expected symbol value estimated in the previous iteration is proposed. The size of the subset can adapt to the maximum correlation of the sub-matrix after the simple antenna selection. Furthermore, the error rate performance of the scheme under linear Minimum Mean Square Error (MMSE) or Ordered Successive Interference Cancellation (OSIC) for the first run detection and different interleaver lengths is investigated while the transmit antenna selection is considered. The simulation results show a sig- nificant advantage both for implementation complexity and for error rate performance under a fixed data rate.     

Receive antenna selection for MIMO-SM systems with linear MMSE receivers in the presence of unknown interference

In this paper, a novel receive antenna subset selection technique is proposed for multiple input multiple output spatial multiplexing (MIMO-SM) systems with linear minimum mean square error (MMSE) receivers in the presence of unknown co-channel interference. This antenna selection technique is directly implemented based on training sample sequence by utilizing backward greedy algorithm (BGA) under the least squares (LS) criterion. In the case of practical implementation. Diagonal loading (DL) technique is incorporated into the selection process to insure robustness of antenna selection given limited training sample support. Simulation results show that the proposed antenna selection technique is able to retain the diversity order of a full complexity system in the presence of unknown multiple access interference (MAI)     

Transmit selection in spatial multiplexing systems

In this letter we solve the transmit antenna selection problem for a zero forcing spatial multiplexing system with knowledge of the channel statistics at the transmitter. We show through Wishart matrix analysis that the signal-to-noise ratio on the kth stream is a weighted Chi-squared variable with the weight equal to-the kth diagonal entry of the inverted transmit correlation matrix. We use this result to develop selection algorithms for two cases-maximizing ergodic capacity and minimizing the average probability of error. Monte Carlo simulations illustrate potential performance improvements.     

Transmit antenna selection for partial linear precoding MIMO schemes

A novel transmit antenna selection technique is proposed, specifically designed to maximise the benefit of partial precoding on narrowband downlink multiuser multiple input multiple output (MU-MIMO) systems employing antenna redundancy. The partial precoding utilises the constructive part of the existing interference between the MIMO sub-channels by applying partial sub-channel orthogonalisation and thus improves the signal-to-noise ratio at the receiver. In addition, a customised antenna selection criterion is employed at the transmitter, that maximises the constructive interference among the active antennas and optimises the benefits of partial precoding.     

结合发射天线重分组和接收天线选择的双空时发射分集系统的实现方案

对线性接收双空时发射分集系统提出一种新的接收天线选择方案,通信系统在增加较小的实现复杂度的情况下可以有效的改善系统的信道状态,抑制不同子数据流间的干扰,降低系统的误码率(BER).结合发射天线重分组(TAs)方案,不同子数据流间的干扰可以得到更好的抑制,系统性能得到进一步的提高.仿真表明,在增加较少的反馈信息冗余及系统硬件实现复杂度的情况下,系统的性能得到了很大的改善.     

Optimal precoding for orthogonalized spatial multiplexing in closed-loop MIMO systems

In this paper, we propose a new precoding algorithm for orthogonalized spatial multiplexing (OSM) systems over flat-fading multiple-input multiple-output (MIMO) channels. The OSM scheme was recently introduced for closed-loop MIMO systems which allows single symbol decodable maximum likelihood detection. To further improve the performance of the OSM system, we propose a new precoding method by maximizing the minimum Euclidean distance between constellation points in the effective channel. In order to efficiently identify the parameters of a precoder which maximizes the minimum distance, we introduce a partitioning approach. Through analysis, it is shown that one real value parameter and two bits are required for feedback information for precoding in 16-QAM systems. Simulation results demonstrate that our algorithm provides 9 dB and 7.5 dB gains at a bit error rate (BER) of 10^-4 over the conventional OSM systems for 4-QAM and 16-QAM, respectively. We also confirm that the performance of the proposed scheme is the same as that of the optimum closed-loop MIMO systems in terms of the minimum distance. Consequently, our precoding algorithm significantly improves the system performance with a small increase of feedback amount.     

Transmit antenna selection in linear receivers: geometrical approach

Transmit antenna subset selection in spatial multiplexing systems is considered. In particular, selection algorithms aiming to minimise the error rate when linear detectors are used at the receiver are proposed. Previous work on antenna selection has considered capacity and post-processing SNR selection criteria. However, a geometrical interpretation of the decoding process which also permits development of a suboptimal algorithm that yields a considerable complexity reduction with only a small loss in performance, is considered.     

Dual code Tx diversity with antenna selection for spatial multiplexing in MIMO-WCDMA networks

This letter investigates the performance of a mixed diversity-spatial multiplexing transmission strategy for multiple input-multiple output (MIMO) networks based on dual code transmission with antenna selection. The wideband code division multiple access (WCDMA) physical layer protocol has been used to demonstrate that for eight transmit and four receive antennas per user, 2.4Mbps more capacity is provided compared to single code spatial multiplexing transmission and 100% code allocation gain, compared to diversity combining and four codes per user.