Spatial Multiplexing MIMO Research Articles

ArguteDUB: Deep Learning Based Distributed Uplink Beamforming in 6G-Based IoV

In the last decade, MIMO spatial multiplexing and distributed beamforming play a significant role in improving data throughput through cooperative transmission. It has been widely used in wireless communication, especially in 6 G. However, the distributed uplink beamforming is still an open problem in highly dynamic environments. However, the proposed 6 G technology represents the further integration of deep learning and wireless communication. In this paper, we propose Argute Distributed Uplink Beamforming (ArguteDUB), which uses a feedback algorithm with an offline-trained deep learning model to implement highly dynamic distributed uplink beamforming for the Internet of Vehicles (IoV) in 6 G. Specifically, each vehicle enables the base station (BS)/access point (AP) to separate different channel state information (CSI) by inserting orthogonal sequences into the sending data. The BS adopts deep learning to filter the noise and predict the beamforming weight to achieve phase synchronization. Unlike traditional distributed uplink beamforming, ArguteDUB can be adapted to the highly dynamic time-varying channels. The simple network structure ensures the fast response of ArguteDUB. In addition, we make ArguteDUB Orthogonal Frequency Division Multiplexing (OFDM) compatible so that it can be easily deployed in 6 G networks. Our evaluation shows that ArguteDUB has an signal-to-noise ratio (SNR) gain of about 5 dB to 5.3 dB over the single vehicle transmission mode.

Overloaded MIMO spatial multiplexing independent of antenna setups

Overloaded MIMO spatial multiplexing independent of antenna setups

Achievable Spectral Efficiency of Line-of-Sight MIMO Fixed Links with Compact Planar Antenna Arrays and Power Amplifier Limitations

Fixed Point-to-Point microwave wireless systems with high spectral efficiency are needed to meet the pervasive and increasing demand for capacity in back-haul networks of mobile radio systems. In this context, spatially multiplexed LoS-MIMO (Line-of-Sight Multiple Input Multiple Output) systems have been studied for about twenty years, particularly in the millimeter wave frequency bands (above 15 GHz). However, their deployment in real networks has been really limited, to the authors’ knowledge. This has been due to several factors, i.e. the practical possibility of using extremely high-level modulation formats (nowadays up to 8192-QAM), the joint use of co-channel dual polarization, and the availability of wider channel bands in the new high frequency ranges (e.g. E-Band). In addition, a crucial reason has been the difficulty of installing multiple antennas spaced apart in order to maximize the MIMO spatial multiplexing so providing the maximum capacity gain. This optimal antenna separation, even for the classical MIMO M×N\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$M \ imes N$$\\end{document} with M = 2 antennas at the receiver and N = 2 antennas at the transmitter, can be several meters, e.g. 5.71 m at 23 GHz on a 5 km link. In this article, we analyze the performance of LoS-MIMO systems where antenna separation is highly sub-optimal, for limiting the array size, and a satisfactory performance is made possible by the exploitation of specific bit loading and power allocation strategies and the setting of the working region of the RF transmitter power amplifiers to operate at a given Signal-to-Inter Modulation Distortion Ratio (SIMDR). The result is an overview of the advantages and drawbacks of compact LoS-MIMO from a wider perspective than in the existing literature, including fundamental aspects for the practical implementation of these systems. Performance is discussed in many cases of interest and compared with the state of the art SISO (Single Input Single Output) system.

Sub-Terahertz MIMO Spatial Multiplexing in Indoor Propagation Environments

Sub-Terahertz MIMO Spatial Multiplexing in Indoor Propagation Environments

Linearized Model for MIMO-MFSK Systems With Energy Detection

For user terminals, energy-detection based multiple-input-multiple-output (MIMO) has the advantages of low complexity and anti-Doppler capability. However, the energy detector makes it difficult to linearly separate the signals in spatial multiplexing. In this letter, the linearized model is introduced in <inline-formula> <tex-math notation="LaTeX">$2\times 2$ </tex-math></inline-formula> M-ary frequency-shifted keying (MFSK) V-BLAST system with energy detection. To avoid rank deficiency of the model, we propose nonlinear virtual antennas (NVA) to increases both the dimension and receive diversity gain of MIMO system. Then the full-rank condition is discussed. In multiple-antenna systems, NVA is further generalized by spatial index modulation with dual antennas selection. By simulations, linear detectors are verified to be feasible for non-coherent spatial-multiplexing MIMO, and its diversity gain is obviously increased by the proposed NVA.

Experimental demonstration on long-range time-reversal multiple-input/multiple-output underwater acoustic communication over tens of kbps in 12.5 km range

In this paper, the adaptive time reversal (ATR) technique combined with a single channel decision feedback equalizer (DFE) is applied to an at-sea experiment of the underwater acoustic multiple-input/multiple-output (MIMO) communication utilizing the signal bandwidth of 4.5–8.5 kHz over the distance of 12.5 km. This paper focuses on the demonstration of the effectiveness of the spatial division multiplexing MIMO using ATR-DFE schemes in time-varying real sea environment, and how much the communication rate could be achieved, with changing the signal parameters. We report that the communication quality is dependent on the duration from the channel probing for ATR process to signal reception, and we found that the output signal-to-noise ratio of the demodulated results highly correlated to the temporal coherence of the acoustic channel. Finally, the relationship between the effective data rate and the bit error rate is evaluated. As a result, the achievable data rate in the experiment of this study would be a remarkable considering the distance of the communication.

Robust Vehicular Communications Using the Fast-Frequency-Hopping-OFDM Technology and the MIMO Spatial Multiplexing

Vehicle-to-Vehicle communication is one of the more emerging technologies in the 21st century from either the comfortable transportation or safer transportation point of view. Vehicle-to-Vehicle communication has one crucial factor, which is the huge information to be shared among vehicles, such as the position, the road data. In such situation, the accurate information sharing process is the most important factor in order to make the vehicles operating in the most feasible way. This work proposes a more robust vehicle communication system to make the existing vehicle transportation system more efficient. In this paper, we propose a fast frequency hopping orthogonal frequency division multiplexing to mitigate the Doppler spread effect on our previously published clustering benchmark. This benchmark contains both of a clustering weighting factor based stage and a multiparallel processing stage. This is in addition to modify the PHY layer of the existing IEEE 802.11p standard in order to impose Multiple Input Multiple Output for higher throughput purposes.The results show a noticeable stability compared to our previously published work. Furthermore, the results are almost exceeds the achieved results from the Lower-ID Distributed Clustering Algorithm (DCA) from both of the speed and communication range.

UAV Swarm Position Optimization for High Capacity MIMO Backhaul

A swarm of cooperating UAVs communicating with a distant multiantenna ground station can leverage MIMO spatial multiplexing to scale the capacity. Due to the line-of-sight propagation between the swarm and the ground station, the MIMO channel is highly correlated, leading to limited multiplexing gains. In this paper, we optimize the UAV positions to attain the maximum MIMO capacity given by the single user bound. An infinite set of UAV placements that attains the capacity bound is first derived. Given an initial swarm placement, we formulate the problem of minimizing the distance traveled by the UAVs to reach a placement within the capacity maximizing set of positions. An offline centralized solution to the problem using block coordinate descent is developed assuming known initial positions of UAVs. We also propose an online distributed algorithm, where the UAVs iteratively adjust their positions to maximize the capacity. Our proposed approaches are shown to significantly increase the capacity at the expense of a bounded translation from the initial UAV placements. This capacity increase persists when using a massive MIMO ground station. Using numerical simulations, we show the robustness of our approaches in a Rician channel under UAV motion disturbances.

Performance evaluation of MIMO broadcast systems for advanced digital terrestrial TV

The transmission performance of spatial multiplexing cross-polarized MIMO is studied to determine how to increase the capacity of digital terrestrial broadcasting and make it more robust. In this paper, the performance was evaluated in laboratory experiments and large-scale field experiments in central Tokyo under three deployment scenarios. The results showed that the required received power can be improved by 7.3 dB when MIMO is introduced to enhance transmission robustness, i.e., maintaining the same transmission capacity as SISO. Alternatively, the transmission capacity can be doubled by introducing MIMO for the same robustness as SISO, requiring a slight increase in received power of 0.9 dB compared with SISO. The field experiments were performed by using a prototype transmission system for advanced digital terrestrial TV broadcasting in Japan, but the results obtained are also valid for 5G broadcasting. Regarding the feasibility of the advanced terrestrial broadcasting system operating at a target bit rate of about 60 Mbps to distribute a VVC-based 8 K program within a 6-MHz channel bandwidth, an increased received power of 3.7 dB compared with SISO was required for MIMO to achieve a higher transmission capacity in the worst case for 28 reception points evaluated in urban areas.

Near-Optimal Performance With Low-Complexity ML-Based Detector for MIMO Spatial Multiplexing

In Spatial Multiplexing MIMO systems, many powerful non-linear detection techniques as sphere decoding have emerged to overcome the performance limitations of linear detection techniques. However, these non-linear techniques suffer from high complexity that increases dramatically with the number of antennas and the modulation order. Hence, they cannot be implemented on highly parallel hardware architecture and are thus not suitable for real-time high data rate transmission. In this letter, a new detection technique is proposed to approach the optimal performance obtained by Maximum Likelihood (ML) detector without increasing the complexity significantly. This detector is denoted by OSIC-ML since it combines two techniques: the Ordered Successive Interference Cancellation (OSIC) and the ML. The proposed OSIC-ML detector shows a near-optimal performance at very low complexity even with large scale MIMO and imperfect channel estimation, where this complexity can be efficiently controlled to achieve the desired complexity-performance tradeoff.

Novel MIMO Technique for Wireless Terabits Systems in Sub-THz Band

In this paper, a generalized MIMO Spatial Multiplexing (SMX) system with a new Index Modulation (IM) domain called filter IM domain is proposed. This filter domain generalizes the time and frequency IM domains. In particular, a Filter Shape IM (FSIM) is used to virtually transmit a part of the information bitstream by indexing the filter shape varying at the symbol rate. This scheme permits to achieve high Spectral Efficiency (SE) since it uses all the available time, frequency, and spatial resources. The proposed transceiver can be easily reconfigured to operate as a conventional MIMO SMX transceiver. Compared to the existing systems, the proposed system achieves the highest SE gain with the help of IM and MIMO multiplexing gain. The theoretical lower bound is derived to characterize the SMX FSIM system performance. The results reveal that SMX FSIM with 2 filter shapes only outperforms by 3.5 dB up to more than 12 dB the equivalent SMX QAM system at the same SE. Furthermore, a complete analysis in the sub-THz indoor environment with RF impairments is provided for the proposed system, SMX QAM, and Generalized Spatial Modulation. Finally, the results show that SMX FSIM with a linear receiver has better performance and robustness to phase noise, lower transceiver cost, higher SE/energy efficiency gain, and lower power consumption.

Spatial Multiplexing MIMO Visible Light Communications With Densely Distributed LEDs and PDs

Multiple-input multiple-output visible light communications (MIMO-VLC) have been considered as an advanced technique owing to the enhancement of communication capacity and reliability. However, the performance of MIMO-VLC highly depends on channel correlation, which means that the system performs worse when the channels are more highly correlated. Some studies have developed techniques to alleviate channel correlation and improve the performance of spatial multiplexing MIMO-VLC systems. However, these works have not considered situations where all LEDs and PDs are integrated into a compact structure. In this paper, a single-user spatial multiplexing MIMO-VLC system with densely distributed LEDs (light emitting diodes) and PDs (photodiodes) is proposed. Designs of optimal signal vectors and system structures are introduced, to fulfill multiplexing gains when LEDs and PDs are set close to each other respectively. Numerical simulations are carried out and the results illustrate that the proposed system can realize multiplexing gains over the system where LEDs and PDs are distributed densely, and also outperforms the traditional repetition coding (RC) technique.

Incremental Antenna Selection Based on Lattice-Reduction for Spatial Multiplexing MIMO Systems

Antenna selection is a method to enhance the performance of spatial multiplexing multiple-input multiple-output (MIMO) systems, which can achieve the diversity order of the full MIMO systems. Although various selection criteria have been studied in the literature, they should be adjusted to the detection operation implemented at the receiver. In this paper, antenna selection methods that optimize the post-processing signal-to-noise ratio (SNR) and eigenvalue are considered for the lattice reduction (LR)-based receiver. To develop a complexity-efficient antenna selection algorithm, the incremental selection strategy is adopted. Moreover, for improvement of performance, an additional iterative selection method is presented in combination with an incremental strategy.

Performance of OQAM/GFDM in Spatial Multiplexing MIMO Systems

Generalized frequency division multiplexing (GFDM) is a prominent candidate to be used by the mobile Fifth Generation (5G) physical layer. Nevertheless, the integration of GFDM with Spatial Multiplexing (SM) MIMO system is essential to fulfill the data rate requirements. SM detection of MIMO-GFDM becomes a more challenging topic because of ICI and ISI due to the non-orthogonal nature of GFDM, along with IAI. In this article, the authors propose a system that combines the Offset-Quadrature Amplitude Modulation (OQAM) with GFDM to mitigate self-induced interference, by using a simple Matched Filter (MF) detector and minimum additional processing at the receiver. Simulation results show a considerable achieved improvement in BER by the proposed OQAM/GFDM compared to QAM/GFDM when using MMSE-based Ordered Successive Interference Cancellation (OSIC) detector. Furthermore, this system is unaffected by the roll-off factor variations of used pulse-shaping filters.

Capacity Maximized Linear Precoder Design for Spatial-Multiplexing MIMO VLC Systems

This paper proposes a novel linear precoder design based on the singular value decomposition (SVD) for multi-input multi-output visible light communications (MIMO VLC). We provide an analytical expression on power allocation subject to the function of maximizing the lower bound of capacity according to the optical wireless communication channel model. The expression is rather different from the radio frequency (RF) communications due to the non-negativity of the transmitted signals in VLC. Furthermore, we design an adaptive bit loading scheme for sub-streams with consideration of the tremendous gain difference among subchannels. Performances of the proposed adaptive power and bits allocation strategy are evaluated in two traditional MIMO VLC scenarios, i.e., a practical $2\times 2$ indoor scenario and a classical $4\times 4$ system that is generated according to the MIMO model. In simulations, the techniques of unipolar M -level pulse amplitude modulation ( M -PAM) and spatial-multiplexing (SMP) are employed, and the performance comparison with other SVD-based linear precoders is also given. Simulation results show that the proposed approach can effectively improve the spectral efficiency and guarantee the bit error rate (BER) performance under the same constraints of aggregate optical power budget and non-negativity included by the intensity modulation. It indicates that the strategy of uneven bits and power allocation with full consideration of the ill-conditioned characteristics of subchannels performs better than that based on equal bits transmission in VLC systems.

New Efficient Transmission Technique for HetNets With Massive MIMO Wireless Backhaul

In order to cope with the rapid increase in power consumption of heterogeneous cellular networks, this article proposes a new efficient transmission technique for heterogeneous networks with massive MIMO wireless backhaul with the objective of minimizing power consumption cost. We assume that transmissions on the backhaul link and the access link occur simultaneously on the same frequency band (in-band) thanks to MIMO spatial multiplexing. On the other hand, we consider that uplink and downlink transmissions are separated in time. In order to prevent multi-user and inter-tier interference, block diagonalization beamforming is considered at the macro base station (MBS) and the signal from the small base station (SBS) to the MBS is transmitted orthogonally to the channel of the SBS's users. The problem of minimizing the transmit power of base stations under users’ minimum-rate constraints is formulated. We first derive analytically the optimal time splitting parameter and the allocated transmit power considering that the inter-SBS interference is generated by fixed power. Next, we solve the power allocation problem when the generated inter-SBS interference is no longer considered fixed by proposing an efficient iterative power allocation algorithm. A heuristic user scheduling algorithm is devised in order to deal with the feasibility problem. Finally, simulations validate our analysis and show that the proposed transmission technique outperforms the conventional reverse time division duplex with bandwidth splitting (out-band) in terms of total power consumption.

Multi-Hop Cooperative MIMO Transmission in Wireless Sensor Networks

This article presents a multihop spatial multiplexing cooperative MIMO (SM-CMIMO) transmission scheme. The SM-CMIMO scheme employs a novel configuration on MIMO system which works in a cooperative manner, to achieve a least energy consuming path, with reduced rate of bit error and higher data rate. In this approach, list of relay nodes located in equal distance at any route towards destination selected. The source selects a set of relay nodes and cooperative nodes to frame a cooperative MIMO System. The cooperative nodes are selected using NSA (Node Selection Algorithm) with no channel state, bit error rate and data rate constraints. Each hop is evaluated for suitable replacement with V-MIMO configurations. To reduce the depletion of energy at MIMO cooperative network, at the middle of these hops, relay nodes are selected and evaluated for possible replacement of long-hop with two smaller MIMO transmission hops. We show that proposed SM-CMIMO transmission offers significant energy efficiency improvement compared with SISO transmission. The performance of the system degrades indirectly with the channel correlation.

Performance Analysis of Matched-Filter Detector for MIMO Spatial Multiplexing Over Rayleigh Fading Channels With Imperfect Channel Estimation

The matched-filter (MF) detector is the lowest complexity linear detector in practical MIMO spatial multiplexing systems. Its performance is significantly affected by the number of available antennas and an operating channel SNR. In this paper, we analyze the exact performance of the MF detector without any restrictions on the numbers of the transmit and receive antennas. To this end, we first develop the exact, closed-form expression of the MF detector output over uncorrelated Rayleigh fading channels with an arbitrary number of antennas. Based on this result, we derive the exact closed-form bit error rate expressions for uncoded BPSK, QPSK, and $M$ -ary QAM signaling, which can be seen as the generalized forms of the conventional receiver diversity based on maximum ratio combining. We also elucidate the conditions on the numbers of antennas and channel SNR, where the use of MF detector should become effective. Furthermore, in the case of coded MIMO systems, we develop the optimal metric derived from the exact MF output. The corresponding mutual information justifies the simulated performance of LDPC-encoded MIMO spatial multiplexing with the MF detector over ideally interleaved Rayleigh fading channels. Finally, we extend our analysis to more practical systems with imperfect channel estimation.

A Millimeter-Wave Partially Overlapped Beamforming-MIMO Receiver: Theory, Design, and Implementation

This paper presents an analysis and design of a partially overlapped beamforming-multiple-input multiple-output (MIMO) architecture capable of achieving higher beamforming and spatial multiplexing gains with lower number of elements compared to conventional architectures. As a proof of concept, a four-element beamforming-MIMO receiver (RX) covering 64-67-GHz frequency band (the FCC’s newly allocated 64–71-GHz frequency band for high-speed wireless links between small cells) enabling two-stream concurrent reception is designed and measured. By partitioning the RX elements into two clusters and partially overlapping these clusters to create two three-element beamformers, both phased array (coherent beamforming) as well as MIMO (spatial multiplexing) features are simultaneously acquired. 6-bit phase shifters with 360° phase control and 5-bit VGAs with 11-dB range are designed to enable steering of the two RX clusters toward two arbitrary angular locations corresponding to two users. Fabricated in a 130-nm SiGe BiCMOS process, the RX achieves a 30.15-dB maximum direct conversion gain and a 9.8-dB minimum noise figure across 548-MHz IF bandwidth. S-parameter-based array factor measurements verify spatial filtering of the interference and spatial multiplexing in this RX chip.

FPGA Implementation of Sphere Detector for Spatial Multiplexing MIMO System

Multiple Input Multiple Output (MIMO (techniquesuse multiple antennas at both transmitter and receiver forincreasing the channel reliability and enhancing the spectralefficiency of wireless communication system.MIMO Spatial Multiplexing (SM) is a technology that can increase the channelcapacity without additional spectral resources. The implementation of MIMO detection techniques become a difficult missionas the computational complexity increases with the number of transmitting antenna and constellation size. So designing detection techniques that can recover transmitted signals from SpatialMultiplexing (SM) MIMO with reduced complexity and highperformance is challenging. In this survey, the general model ofMIMO communication system is presented in addition to multipleMIMO Spatial Multiplexing (SM) detection techniques. These detection techniques are divided into different categories, such as linear detection, Non-linear detection and tree-search detection. Detailed discussions on the advantages and disadvantages of each detection algorithm are introduced. Hardware implementation of Sphere Decoder (SD) algorithm using VHDL/FPGA is also presented