Coverage and capacity enhancement in multiuser MIMO systems with scheduling

In this paper, we present a performance analysis of the user scheduling for the multiuser MIMO systems exploiting the multiuser and antenna diversities while maintaining the fairness among the users. We present different scheduling schemes including absolute throughput-based scheduling, normalized throughput-based scheduling, absolute SNR-based scheduling, and normalized SNR-based scheduling schemes. We use an antenna selection scheme to overcome the drawback of channel hardening in multiuser MIMO systems. This also improves the system performance and reduces the system complexity. Using mathematical analysis and numerical simulations, we compare the presented schemes and show their significant advantages.

It is well known that accurate direction of arrival (DOA) estimation can help to improve the performance of MIMO systems. However, when large scale MIMO systems are considered, the DOA estimation becomes very difficult due to the large dimension of DOAs. Based on the observation that correlation exists between the neighboring antennas due to the limited size of the antenna array, we propose a correlation based DOA estimation method for the large scale multi-user (MU) MIMO system in this paper. It is verified that the proposed DOA estimation method can obtain a better performance than the existing methods with a much lower computational complexity.

Introduction: One of the main advantages of multiple antenna systems is the support of multi-user connections, simultaneouslytransmitting parallel data streams. This can significantly increase the overall system throughput. However, the spectral efficiency can be additionally increased through the usage of various dynamic strategies which take into account the current state of the system.Here we propose a method to evaluate the effectiveness of such strategies with the help of appropriate mathematical models. Purpose:Development of mathematical models for a multi-user MIMO system which would allow you to evaluate the average delay of a filetransfer. Results: Mathematical models of the MIMO system are presented in the form of discrete/continuous time queuing systemsfor three user service strategies. We provide formulas for estimating the average file transfer delay in a closed form, which simplifynumerical analysis as compared to the well-known methods using mathematical models in continuous time. This method allows you tofind the most effective strategy with less computational complexity. Another advantage of the constructed models is the opportunityof further research on the effect of file length distributions on the file transfer delay. The conclusions we made about the effectivenessof each strategy are consistent with our earlier work, which is confirmed by a numerical example. Practical relevance: The developedmathematical models for a multi-user MIMO system can be used to set the operating parameters of a real wireless MIMO system.

In this paper, we present a performance analysis for the user scheduling for the multiuser MRC MIMO systems exploiting the user and antenna diversities. We consider two scheduling schemes including absolute SNR-based scheduling and normalized SNR-based scheduling schemes. We propose the utilization of an antenna selection scheme to overcome the drawback of channel hardening in multiuser MIMO systems and to improve the system performance. We derive new closedform expressions for the average bit error rate of the presented schemes for two scenarios: Heterogeneous (independent nonidentically distributed SNRs- i.ni.d.) and Homogeneous (independent identically distributed SNRs- i.i.d.) cases. Using mathematical analysis and numerical simulations, we compare the presented schemes.

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.

The performance of a cellular multiuser MIMO system depends on various parameters, e.g. the system structure, the transmitter and receiver strategy, the channel state information at the transmitter and the receiver and the channel properties. Recently, the main focus of research was on single-user MIMO systems and its capacity and its error performance with space-time coding. In general, the performance of the cellular multiuser MIMO system is limited by additive white Gaussian noise, intracell interference from other users within the cell and by intercell interference from users outside the considered cell. In our analysis, the base applies a MMSE receiver. Therefore, we choose the normalised MSE as the performance metric of the wireless system. We study one point-to-point link, on which interference act. The interference models the different system scenarios and various parameters. Therefore, we consider three scenarios in which the noise is subject to different constraints. A general trace constraint is used in the first scenario. The noise covariance matrix eigenvalues are kept fixed in the second scenario and in the third scenario the entries on the diagonal of the noise covariance matrix are kept fix. We assume that the receiver as well as the transmitter have perfect channel state information. We solve the corresponding minimax programming problems and characterise the worst case noise and the optimal transmit strategy. In all scenarios the normalised MSE of the MIMO system with worst case noise is equal to the MSE of some MIMO system in which either the channels are orthogonal or the transmit antennas are not allowed to cooperate or in which no channel state information is available at the transmitter. Furthermore, the minimax expressions fulfill a saddle point property. All theoretical results are illustrated by examples and numerical simulations

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.

For the poor transmission reliability of data, this paper focuses on the precoding techniques of the multi-user MIMO system in the broadcast phase in, and the single-user MIMO and multi-user MIMO precoding techniques have been studied. In the multi-user MIMO system, BD-MMSE-VP coding algorithm is proposed to improve the BER performance of the system by using the MMSE criterion to optimize the perturbation vector, and the system uses QR technique to decompose BD channel matrix. Simulation results verify the effective of the proposed precoding algorithm.

This chapter implements detection processes for spatial multiplexing MIMO systems. It compares the performances of MIMO system with various detection methods. The chapter investigates the performances of MIMO system with different system parameters. MIMO systems may be broadly classified into two categories: spatial diversity (SD) systems and spatial multiplexing (SM) systems. SM MIMO systems exploit the multiple transmit and receive antennas to transmit multiple data streams simultaneously in the same frequency band to increase the spectral efficiency. Some of the existing literature defines only SM MIMO systems as MIMO systems. The user-defined MATLAB function zf_bpsk( ) implements zero forcing (ZF) detection for BPSK MIMO systems. It takes the received signal vector r and channel matrix H as its inputs. The chapter is designed to help teach and understand communication systems using a classroom-tested, active learning approach.

A multi-user MIMO (MU-MIMO) system configures orthogonal MIMO channels for active mobile users by use of multiple antennas of the base station (BS). Because different grouping of users can introduce different channel properties in MU-MIMO, user groupinging can minimize BS transmit power in order to satisfy an essential requirement for BS energy savings. In this paper, we discuss how such user groupinging can vary transmit power consumption in a hybrid spatial and time diversity access (SDMA/TDMA) downstream. Then, we proposed an energy efficient user grouping algorithm for applications in MU-MIMO systems which finds a solution close to optimal by swapping users between different groups and comparing the transmit powers. The proposed greedy-swapping algorithm achieves 37% transmit power saving, which is close to the optimal for the exhaustive search, compared to the traditional capacity optimal scheduling algorithm PU2RC with 6% of the computational time for the optimal exhaustive search.

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.

Communication systems with low-resolution analog-to-digital-converters (ADCs) can exploit channel state information at the transmitter and receiver. This paper presents codebook designs and performance analyses for limited feedback MIMO systems with finite-bit ADCs. A point-to-point single-user channel is firstly considered. When the received signal is sliced by 1-bit ADCs, the absolute phase at the receiver is important to align the phase of the received signals. A new codebook design for beamforming, which separately quantizes the channel direction and the residual phase, is therefore proposed. For the multi-bit case where the optimal transmission method is unknown, suboptimal Gaussian signaling and eigenvector beamforming is assumed to obtain a lower bound of the achievable rate. It is found that to limit the rate loss, more feedback bits are needed in the medium SNR regime than the low and high SNR regimes, which is quite different from the conventional infinite-bit ADC case. Second, a multi-user system where a multiple-antenna transmitter sends signals to multiple single-antenna receivers with finite-bit ADCs is considered. Based on the derived performance loss due to finite-bit ADCs and finite-bit CSI feedback, the number of bits per feedback should increase linearly with the ADC resolution in order to restrict the rate loss.

The performance of a downlink multi-user MIMO system seriously degrades in time-varying environments because MIMO channels change during the time interval between transmission parameter determination and actual MIMO transmission. Channel prediction techniques have been proposed to improve the performance in dynamic environments. In this paper, based on indoor measurement data, we show the effect of the linear channel extrapolation, and evaluate the bit error rate performance of the multi-user MIMO system with the channel prediction technique.

By combining adaptive modulation (AM) and automatic repeat request (ARQ) protocol, cross-layer design (CLD) scheme of multiuser MIMO system with antenna selection (AS) is presented. By means of exact expression of packet error rate (PER), the switching thresholds (STs) of fading gain subject to a target PER constraint are derived, which is more accurate than the conventional STs based on approximate PER expression. According to these results, and using mathematical manipulation, we obtain the tightly closed-form expressions of the average spectral efficiency (SE) and average PER. Simulation results show that the multiuser MIMO system with CLD-AS scheme using the derived STs provides higher SE than that using existing approximate STs while meeting the PER requirement. Besides, simulations for average SE and PER are in good agreement with the derived theoretical expressions, which demonstrates the validity of the theoretical analysis.

Covariance shaping least squares estimator is a new kind of linear estimator based on covariance shaping in quantum signal processing (QSP) framework, it is a biased estimator directed at improving the performance of traditional leastsquares (LS) estimator. In this paper, we discuss the covariance shaping least squares (CSLS) estimator, and apply it in multi-user detection that leads to a new detection algorithm, and then we employ it in the detection of MIMO systems. The numerical results in synchronous DS-CDMA communications system show that the performance of covariance shaping multi-user detection which depends only on the users' signatures is better than that of traditional MF and decorrelation detection, and is an approach to the MMSE detection method. The results in MIMO systems also show that the performance of system is better than that of detection algorithm with Zero-forcing and MMSE solutions.