Uplink Multiuser MIMO Research Articles

On the Spectral Efficiency of Multi-User Holographic MIMO Uplink Transmission

On the Spectral Efficiency of Multi-User Holographic MIMO Uplink Transmission

Enhancing Wideband Multiuser MIMO Uplink Using Superimposed Pilots: Joint Receiver Design

Enhancing Wideband Multiuser MIMO Uplink Using Superimposed Pilots: Joint Receiver Design

Improving Signal Detector by Precoding in Uplink Multiuser MIMO System

Improving Signal Detector by Precoding in Uplink Multiuser MIMO System

Practical Uplink Multi-User MIMO Scheduling Based on Iterative Heuristic Search

Practical Uplink Multi-User MIMO Scheduling Based on Iterative Heuristic Search

Matched-Filter Detector With Quadrature Interference Cancellation for Coded Uplink Multiuser MIMO Systems With Massive IoT Devices

Matched-Filter Detector With Quadrature Interference Cancellation for Coded Uplink Multiuser MIMO Systems With Massive IoT Devices

Uplink NOMA-MIMO Systems with Rayleigh Power Distribution

The article is devoted to multiple-input multiple-output antenna systems, also called MIMO systems, which are widely used in wireless communication systems. In this article we consider a case when the MIMO system works in overloaded mode. In this mode MIMO systems can be considered as a system with non-orthogonal multiple access NOMA. The main goal of this article is to analyze this interesting case using statistical computer simulation. Based on the analysis of the capacity of a discrete-continuous multiuser MIMO uplink channel, the possibility of such systems functioning in overload mode is proved.

Energy efficient data detection with low complexity for an uplink multi-user massive MIMO system

The current development of the Internet of Things (IoT) network in sixth-generation (6G) communication opens up various opportunities. When IoT devices with edge platforms connect to the telecommunication network, mobility, interferences, and intelligent device capacity issues might occur. The challenge with uplink MU-MIMO systems is data detection owing to noise, frequency allocations, and dense deployment of intelligent devices. The exponential complexity of extensive wireless networks makes optimal maximum likelihood detection impossible. Using MATLAB simulation-based analysis, we suggested an iterative data detection strategy based on a coordinate descent method (CDM) to reduce computing complexity while preserving an acceptable bit error rate (BER). Linear systems demand low co-channel interference (CCI) MU-MIMO uplink communications (CCI). A superior mean square error or BER performance is achieved using Maximum ratio combining with CDM. The proposed system outperforms the Richardson Method (RM), approximation message passing (AMP), and linear minimum mean square error (LMMSE) algorithms in terms of BER and complexity.

Outage Performance Analysis of Widely Linear Receivers in Uplink Multi-User MIMO Systems

This paper considers the application of widely linear (WL) receivers in an uplink multi-user system using real-valued modulation schemes, where the cellular base station (BS) with multiple antennas provides connectivity for randomly deployed single-antenna users. The targeted use case is massive machine type communication (mMTC) with grant-free access in the uplink, where the network is required to host a large number of low data rate devices transmitting in an uncoordinated fashion. Four types of WL receivers are investigated, namely the WL zero-forcing (ZF) and the WL minimum mean-squared error (MMSE) receivers, along with their enhanced versions employing successive interference cancellation (SIC) with channel-dependent ordering, i.e., the WL-ZF-SIC and WL-MMSE-SIC receivers. The outage performances of these receivers are analytically characterized in the high signal-to-noise ratio (SNR) regime and compared to those of conventional linear (CL) receivers using complex-valued modulation schemes. For the non-SIC receivers, we show that, when compared to the CL counterparts, the WL receivers yield a higher diversity gain when decoding the same number of users and have the same diversity gain but a decreased coding gain when the number of users is nearly doubled. The outage performance analysis of WL-SIC receivers is facilitated by the marginal distribution of ordered eigenvalues of a real-valued Wishart matrix. It is shown that the SIC operation with channel-dependent ordering brings no additional diversity gain to the WL receivers but instead increases the coding gain. Moreover, the coding gain of WL-SIC receivers grows as the number of users increases and even exceeds that of CL-SIC receivers under suitable conditions. For the mMTC scenario with grant-free transmission, it is demonstrated that the WL receivers outperform their CL counterparts in terms of offering a lower outage (and packet drop) probability and a higher system throughput for a given packet drop probability.

A Design Framework for All-Digital mmWave Massive MIMO With per-Antenna Nonlinearities

Millimeter wave MIMO combines the benefits of compact antenna arrays with a large number of elements and massive bandwidths, so that fully digital beamforming has the potential of supporting a large number of simultaneous users with <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">per user</i> data rates of multiple gigabits/sec (Gbps). In this paper, we develop an analytical model for the impact of nonlinearities in such a system, and illustrate its utility in providing hardware design guidelines regarding two key challenges: the low available precision of analog-to-digital conversion at high sampling rates, and nonlinearities in ultra-high speed radio frequency (RF) and baseband circuits. We consider linear minimum mean square error (LMMSE) reception for a multiuser MIMO uplink, and provide performance guarantees based on two key concepts: (a) summarization of the impact of per-antenna nonlinearities via a quantity that we term the “intrinsic SNR”, (b) using linear MMSE performance in an ideal system without nonlinearities to bound that in our non-ideal system. For our numerical results, we employ nominal parameters corresponding to outdoor picocells operating at a carrier frequency of 140 GHz, with a data rate of 10 Gbps per user.

Spectral efficiency analysis and optimal power allocation for uplink multi-user cell-free massive MIMO networks employing STBCs

Massive MIMO is a key technique in the fifth generation (5G) of wireless networks. This technique, by increasing base station (BS) antennas and exploiting spatial diversity, improves system performance in terms of common criteria such as spectral efficiency. Cell free massive MIMO is considered for 6G mobile communications to overcome the shortcomings associated with the cellular design. In this system, BS antennas are distributed across the system environment and provide uniform service to all users. Also, space time block codes (STBCs) can be used to improve the diversity gain and reliability of the system. In this paper, a cell free massive MIMO system is investigated in the uplink considering effects of channel estimation errors. Users are equipped with two antennas and employ STBC. Lower bound of spectral efficiency is derived for the zero forcing (ZF) and maximal ratio combining (MRC) decoders. Furthermore, spectral efficiency is compared for dual and single antenna users. Moreover, two power control problems are defined based on minimizing the total transmit power and maximizing the minimum rate of the users. Also, an algorithm is proposed for removing the inefficient BSs in the network. The proposed theoretical ideas are evaluated via numerical simulations.

G-MultiSphere: Generalizing Massively Parallel Detection for Non-Orthogonal Signal Transmissions

The increasing demand for connectivity and throughput, despite the spectrum limitations, has triggered a paradigm shift towards non-orthogonal signal transmissions. However, the complexity requirements of near-optimal detection methods for such systems becomes impractical, due to the large number of mutually interfering streams and to the rank-deficient or ill-determined nature of the corresponding interference matrix. This work introduces g-MultiSphere; a generic massively parallel and near-optimal sphere-decoding-based approach that, in contrast to prior work, applies to both well- and ill-determined non-orthogonal systems. We show that g-MultiSphere is the first approach that can support large uplink multi-user MIMO systems with numbers of concurrently transmitting users that exceed the number of receive antennas by a factor of two or more, while attaining throughput gains of up to 60% and with reduced complexity requirements in comparison to known approaches. By eliminating the need for sparse signal transmissions for non-orthogonal multiple access (NOMA) schemes, g-MultiSphere can support more users than existing systems with better detection performance and practical complexity requirements. In comparison to state-of-the-art detectors for NOMA schemes and non-orthogonal signal waveforms (e.g., SEFDM) g-MultiSphere can be up to an order of magnitude less complex, and can provide throughput gains of up to 60%.

A Noncoherent Massive MIMO System Employing Beamspace Techniques

Noncoherent detection schemes are an appealing and low-complexity alternative in multi-user massive MIMO uplink systems compared to classical coherent detection algorithms, since no actual channel knowledge is required at the receiver. For noncoherent multi-user detection to function, the induced power at the base station is utilized to separate the different users. However, spatial separation is impossible when the users are located in the far-field of the receiving antenna array. Consequently, noncoherent detection fails in such scenarios. To this end, beamspace techniques can be applied, focusing the energy of the incident wave to a smaller subset of the receive antennas and enabling again the noncoherent detection scheme. This paper analyzes the beamspace capabilities of a dielectric lens and an analog beamforming network applied at the receiver. Furthermore, a sub-array architecture is proposed, relaxing the design requirements for practical implementation. It is shown that noncoherent detection in combination with beamspace techniques performs comparably to channel-estimation-based detection. In addition, the sub-array architecture revealed a significant performance enhancement accompanied by a reduced user separability.

Dynamic Group-Based Antenna Selection for Uplink Multi-User MIMO in Distributed Antenna System

Dynamic Group-Based Antenna Selection for Uplink Multi-User MIMO in Distributed Antenna System

Uplink Multiuser MIMO Access with Probe Packets in Distributed Wireless Networks

Uplink Multiuser MIMO Access with Probe Packets in Distributed Wireless Networks

Comments on “Energy-Efficient Uplink Multiuser MIMO”

In the paper “Energy-efficient Uplink Multi-user MIMO,” it was mentioned that the employed linear receiver does not change the variance of the elements of the noise vector. Then, the performance was calculated based on this proposition. In this note, we show that this proposition does not hold by providing the counter examples. In addition, we analyze how the performance will be affected by fixing this proposition.

ΔSNR-MAC: A priority-based multi-round contention scheme for MU-MIMO WLANs

The performance of uplink multiuser MIMO (MU-MIMO) transmissions heavily depends on which users to transmit together. In WLANs where each user independently determines when to transmit by random access, the performance degradation occurs when a set of users for concurrent transmissions are not chosen properly. In this paper, we address this problem and propose ΔSNR-MAC protocol to enhance the uplink throughput in MU-MIMO WLANs. In ΔSNR-MAC, a set of users transmitting together are determined one after another through a multi-round contention where the number of rounds equals the number of antennas at the AP. In each round, given winning users that are already transmitting, each user calculates its SNR reduction amount due to the winning users. ΔSNR-MAC gives a higher priority to users with less SNR reduction amounts. To achieve this, each round consists of multiple stages where earlier stages are reserved for users with less SNR reduction amounts. In this way, users with the strong channel orthogonality can transmit together in a fully distributed manner. We theoretically analyze the throughput of ΔSNR-MAC and propose a parameter selection method to maximize the throughput. Our evaluation results confirm that ΔSNR-MAC improves the uplink throughput over existing schemes both in two- and three-antenna AP cases and achieves temporal fairness in mobile environments.

A Novel Low-Complexity Joint User-Relay Selection and Association for Multi-User Multi-Relay MIMO Uplink

In this work, we study joint user-relay selection and association in multi-user multi-relay cooperative wireless relay uplinks with multi-antenna nodes. For non-regenerative and altruistic relays we propose a low-complexity joint scheme, which simultaneously selects multiple relays and users for cooperation as well as assigns the selected users to different selected relays for service. The proposed scheme is sub-optimal and utilizes only the channel gains between the nodes, which leads to reduced feedback and overhead in comparison to schemes that require full channel knowledge. Furthermore, the complexity of the scheme scales linearly as the product of the total number of relays, the total number of users and the number of selected users. Simulation results demonstrate the superiority of the proposed joint scheme compared to a scheme with neither user-relay selection nor user-relay association and another scheme with user-relay association, but no user-relay selection. The favorable performance and low-complexity of the proposed scheme make it very attractive for possible implementation in emerging broadband wireless relay networks (e.g., LTE-Advanced).

상향 링크 다중 사용자 환경에서 공간 변조의 BER 성능

본 논문에서는 다중 안테나 시스템(Multiple Input Multiple Output: MIMO)를 사용하는 상향 링크 다중 사용자 환경에서 공간 변조(Spatial Modulation: SM) 기법을 사용하고, 변조된 신호를 수신 신호와 모든 송신 신호 후보를 비교하는 최대 우도(Maximum Likelihood: ML) 기법으로 복조하는 방법을 사용하여 시스템의 성능을 평가한다. 같은 데이터 율(date rate)로 전송하였을 때 공간 변조 기법이 기존에 제안된 다중 사용자 환경에서의 공간편이 방식(Space Shift Keying: SSK)보다 비트오류율(Bit Error Rate: BER) 성능이 좋아졌다. In this paper, we evaluate the performance of up-link multi-user MIMO systems with SM. The receiver demodulates the received signal using ML method determines the signal which seems to be the most probable after comparing the received signal and all transmitted signal candidates. When transmitting with the same data rate, the SM method shows better performance of bit error rate(BER) than that of the space shift keying(SSK) of the previously proposed multi-user system.

A New Low Complexity Uplink Multiuser MIMO Detecting Algorithm

In multiuser MIMO uplink communications, it is necessary to design linear schemes that are able to suppress co-channel interferences (CCIs). In this paper, we propose a linear block QR decomposition (BQRD) which transforms the multiuser channel to a block upper triangular structure based on Gram-Schmidt orthonormalization and can obtain more diversity gain than traditional BD. And a optimal ordering criterion is proposed at last to do full study of BQRD scheme. Simulation results show that the BQRD with the optimal ordering proposed achieves much better performance than the non-ordering one.

Distributed user selection scheme for uplink multiuser MIMO systems in a multicell environment

Abstract We propose an interference-aware user selection scheme for uplink multiuser multiple-input multiple-output systems in a multicell environment. The proposed scheme works in a distributed manner. Each mobile station determines its transmit beamforming vector based on the locally available channel state information, and informs the associated base station (BS) of the amount of potential interference caused to adjacent cells along with the resulting beamforming vector. Then, the BS selects a set of users to be served simultaneously with consideration of intercell interference. The user selection scheme is devised either to maximize the sum rate or to achieve proportional fairness among users. For each case, we derive an optimal user selection criterion and propose a suboptimal distributed user selection algorithm with low complexity. Simulation results confirm that the proposed scheme offers significant throughput enhancement due to reduction of the intercell interference in a multicell environment.