Multiuser massive MIMO uplink performance with mutual coupling effects

This work focuses on the multi-cell multi-user distributed massive MIMO (DM-MIMO) systems, of which each user is equipped with single antenna and the base stations (BSs) consists of distributed antenna units. We first investigate the arbitrary BS antenna topology scenario. The derivation indicates that in this case the achievable uplink rate of an arbitrary user in central cell depends on both the number of BS's antennas and the users' access distance to each distributed antenna unit (DAU). As a result, the performance analysis based on the derivations is difficult. To overcome this issue and achieve clearer insight, we then consider a circularly distributed BS antenna array and obtain the asymptotic uplink rate of an arbitrary user by considering the asymptotic case where the number of antennas of BSs tends to infinity. It is achieved that the asymptotic uplink rate only depends on the distance from users' position to the center of reference cell. The presented numerical results show clearly that the distributed massive MIMO systems outperform the centralized ones. Moreover, it is also achieved that the interference from the adjacent cells imposes great impact on system performance. Besides this, in numerical analysis the average asymptotic uplink rate of a user is presented, which is free of the users' position and only depends on the radius of circular antenna arrays. It is achieved the maximum average uplink rate would be achieved when the radius of circularly distributed antenna array goes to its optimization location.

In this paper, we develop the weighted sum-rate maximization (WSRM) problem for the cooperative multicell multiuser massive MIMO (C4M) system with the limited cooperative scheme where each base station (BS) has user data of all the users in a system. It is shown that by the simple domain change technique, the WSRM problem can be exploited for hidden mono-tonicity and turn out to be a monotonic optimization problem. We propose a robust algorithm for discretized approximation of the Pareto boundary of achievable rate region. Using this algorithm, the normal boundary intersection (NBI) problem is solved. We solve the WSRM problem by using the outer polyblock approximation (OPA) algorithm. Through simulation results, we show that our proposed method has high accuracy as well as a fast convergence rate.

To fully utilize the spatial multiplexing gains or array gains of massive MIMO, the channel state information must be obtained at the transmitter side (CSIT). However, conventional CSIT estimation approaches are not suitable for FDD massive MIMO systems because of the overwhelming training and feedback overhead. In this paper, we consider multi-user massive MIMO systems and deploy the compressive sensing (CS) technique to reduce the training as well as the feedback overhead in the CSIT estimation. The multi-user massive MIMO systems exhibits a hidden joint sparsity structure in the user channel matrices due to the shared local scatterers in the physical propagation environment. As such, instead of naively applying the conventional CS to the CSIT estimation, we propose a distributed compressive CSIT estimation scheme so that the compressed measurements are observed at the users locally, while the CSIT recovery is performed at the base station jointly. A joint orthogonal matching pursuit recovery algorithm is proposed to perform the CSIT recovery, with the capability of exploiting the hidden joint sparsity in the user channel matrices. We analyze the obtained CSIT quality in terms of the normalized mean absolute error, and through the closed-form expressions, we obtain simple insights into how the joint channel sparsity can be exploited to improve the CSIT recovery performance.

Hybrid precoding has been recognized as a promising technology for millimeter wave-based massive MIMO systems. As an improved scheme for conventional hybrid precoding structures, the adaptively-connected structure requires low hardware cost and has attractive system performance. In this paper, we propose an adaptive hybrid precoding (AHP) scheme for multi-user massive MIMO systems. The hybrid precoder design is formulated as minimizing the difference between the hybrid precoder and the full digital precoder, and a rough design and revision based AHP (RDR-AHP) algorithm is developed to seek for a near-optimal solution. The proposed RDR-AHP algorithm is achieved by a three-step process including rough design of baseband precoder based on singular value unification, stepwise design of radio frequency precoder and baseband precoder revision. Simulation results demonstrate that the proposed scheme achieves higher spectral efficiency than existing schemes with same hardware cost in millimeter wave channel.

This paper reports the performance of a downlink of a multiuser MIMO system which uses a successive beamforming broadcasting scheme. The investigations take into account the effects of mutual coupling that is present in receiving antennas. It is shown that that the mutual coupling changes the received signals statistic properties and impacts the co-channel interference component. The overall mutual coupling effect on the system performance as measured in terms of sum rate capacity depends on the inter-element spacing. Simulation results show that the mutual coupling increases the sum rate capacity when an inter-antenna spacing is smaller than 0.5 wavelength.

The design procedure of hybrid beamforming is investigated considering multi-user MIMO communication systems taking into account the number of independent data streams for each user. Hybrid precoding and combining are utilized at the transmitter and receiver sides of millimeter-wave multi-user massive MIMO. The obtained results indicate the trade-off in performance based on the ratio of the number of antennas to the number of data streams at the transmitter as well as the receiver. The optimization of the number of parallel data streams per user allows the increase of transmitted data rate while keeping the levels of error vector magnitude (EVM) at acceptable levels.

This paper characterizes the performance of massive multiuser spatial modulation MIMO systems, when a regularized form of the least-squares method is used for detection. For a generic distortion function and right unitarily invariant channel matrices, the per-antenna transmit rate and the asymptotic distortion achieved by this class of detectors are derived. Invoking an asymptotic characterization, we address two particular applications. Namely, we derive the error rate achieved by the computationally-intractable optimal Bayesian detector, and we propose an efficient approach to tune LASSO-type detectors. We further validate our derivations through various numerical experiments.

Noncoherent multi-user detection schemes in combination with subspace projection were shown to be an attractive approach in multi-user massive MIMO systems. Up to now, the subspace projection has been performed via a singular value decomposition (SVD) of the receive matrix and nulling the non-signal dimensions. In this paper, we employ an alternative approach to the subspace estimation step, namely the signed URV (SURV) decomposition. We compare the two schemes in terms of complexity and performance in noncoherent massive MIMO systems. Numerical results cover the complexity reduction achieved by a suited choice of the parameters in the SURV strategy.

In multiuser massive MIMO systems, it is not clear whether users should feed back the channel or the precoder when they can exchange the channel state information (CSI). This paper compares the precoder feedback scheme with the channel feedback scheme. It is found that when there are sufficient number of bits for CSI exchange, the precoder feedback scheme can reduce the interference leakage to 1 /(K − 1) of the channel feedback scheme, where K is the number of users. Moreover, the interference leakage under the precoder feedback scheme decreases faster than the channel feedback scheme when the number of feedback bits increases.

All-digital basestation (BS) architectures enable superior spectral efficiency compared to hybrid solutions in massive multi-user MIMO systems. However, supporting large bandwidths with all-digital architectures at mmWave frequencies is challenging as traditional baseband processing would result in excessively high power consumption and large silicon area. The recently-proposed concept of finite-alphabet equalization is able to address both of these issues by using equalization matrices that contain low-resolution entries to lower the power and complexity of high-throughput matrix-vector products in hardware. In this brief, we explore two different finite-alphabet equalization hardware implementations that tightly integrate the memory and processing elements: (i) a parallel array of multiply-accumulate (MAC) units and (ii) a bit-serial processing-in-memory (PIM) architecture. Our all-digital VLSI implementation results in 28nm CMOS show that the bit-serial PIM architecture reduces the area and power consumption up to a factor of 2× and 3×, respectively, when compared to a parallel MAC array that operates at the same throughput.

In this paper, a hybrid multi-user massive MIMO system operating on the mmWave frequency is considered. To reduce the heavy beam training overhead for such a massive MIMO system, we propose a 3D beam training algorithm, which estimates the azimuth and elevation of the angle of arrival (AoA) and departure (AoD) between the base station (BS) and the mobile stations (MSs). The proposed algorithm first executes a hierarchical search to acquire the range of azimuth and elevation, then applies an exhaustive search within this range for a more precise matching. Through this two-stage approach, the beam training overhead can be substantially reduced.

The 5th and 6th (5G and 6G) generation wireless communications exploit large antenna arrays to serve a large number of users over large distances. In 6G sky communication, large antenna arrays will be used for communications with unmanned aerial vehicles (UAV), satellites and high altitude platforms (HAP) along with terrestrial infrastructures. The manuscript at hand dispenses an organized technical survey of the effects of mutual coupling in massive MIMO (mMIMO) (multiple input multiple output) systems, subsuming the effects on te direction-of-arrival (DoA) of the signals and digital beamforming, which substantiate the performance of the design of smart antenna (SA). The mutual coupling distorts the wave front of the incoming signal, resulting in an erroneous DoA estimation and majorly degrading other performances of the antenna array in an mMIMO system. An assortment of compensation techniques is elucidated since it is unfeasible to completely eliminate the mutual coupling. Further, some investigated results of isotropic antennas and dipole arrays are explicated, screening the mutual coupling effects. For practical antenna array design, compensation for the effect of mutual coupling is necessary, especially for densely populated arrays in an mMIMO system. Investigations on various methods of compensation of mutual coupling in antenna array design are surveyed.

The performance of an antenna array is considerably affected by mutual coupling effects between antenna elements. When a large number of antenna elements are located close to each other, mutual coupling becomes more significant. In this study, by using a new mutual impedance matrix, a decoupling methodology for compensating mutual coupling effects in a practical very high frequency (VHF)/ultra high frequency (UHF) Yagi‐Uda antenna array is introduced. No previous publications have studied VHF/UHF Yagi‐Uda antenna arrays in this context. In the proposed scheme, extreme care has been taken to account for both self‐ and mutual impedance related to mutual coupling effects. Experimental and simulation results show that using the proposed method, a perfect decoupling is achieved. The application of high‐resolution direction of arrival (DOA) estimation algorithms in decoupled experimental data leads to excellent performance of DOA estimation, in terms of accuracy and resolution. In addition, it is concluded (from experimental and simulation results) that mutual coupling effects between array elements as well as the root‐mean‐square error of estimated parameters depend on the direction of arrival. It is also deduced that in the presence of mutual coupling, estimation of signal parameter via rotation invariance techniques algorithm performs better than other subspace‐based algorithms.

This paper deals with antenna selection for multi-user massive MIMO systems with the aim of maximising energy efficiency. Massive MIMO technology, by employing a large number of antennas at base station, provides huge improvements in throughput and energy efficiency. The increased number of antennas leads to additional energy consumption due to RF chains and signal processing circuit. The main purpose of the paper is to determine the optimal subset of antennas at the base station that should be activated to serve a given number of active user equipment. This idea is implemented using artificial bee colony algorithm which has proven it efficiency by specifying the best control parameters.

The uplink of full-duplex multi-cell massive MEMO systems is analyzed in this paper. Besides the interference due to multi-user transmissions as in half duplex massive MIMO system-s, interference from other base stations (BSs) and self-interference coming from the base station's downlink transmission would occur, which complicates the analysis on the uplink achievable rate. To be practical, both antenna correlation and line-of-sight (LoS) path are considered in the BS-to-BS channel model. A deterministic approximation of the uplink achievable rate is derived based on random matrix theory. It is then proved that the BS-to-BS interference and self interference would asymptotically vanish. It means the asymptotic achievable rate is exactly the double of that of half-duplex transmission. With finite number of antennas per-BS, however, the BS-to-BS interference and self interference would limit the performance of full duplex. To ensure full duplex to outperform half duplex in the uplink, the number of antennas per-BS should be larger than a threshold which is also derived explicitly. Finally the accuracy of the analytical results is validated by computer simulations.