Space Division Multiple Access Systems Research Articles

Joint optimal beam forming and resource allocation in intelligent reflecting surface aided wireless power transfer rate splitting multiple access system

SummaryThe intelligent reflecting surface (IRS) has recently become the most promising technology to achieve maximum beam‐forming gain with a simultaneous wireless information and power transfer (SWIPT) system. Many existing studies perform a single IRS deployment or utilize space division multiple access (SDMA) and non‐orthogonal multiple access (NOMA) schemes. However, the existing schemes face high time complexity and block signal transmission for larger indoor communications. Hence, this article introduces a dual IRS‐aided multiuser SWIPT system by implementing rate‐splitting multiple access (RSMA) systems. To enhance the minimum achievable rate and ensure the minimum harvesting energy (HE), this study proposes a joint successive convex approximation with an integrated optimization algorithm (SCA‐IOA). The proposed algorithm jointly optimizes the reflecting beam forming and power splitting (PS) coefficient of all the users effectively. The simulation results demonstrate the effectiveness of the proposed techniques and produce an outstanding performance for deploying dual IRS and implementing RSMA compared to traditional SDMA and NOMA systems.

Space Division Multiple Access Based on OIRS in Multi-User FSO System

Optical intelligent reflecting surface (OIRS) is a new type of passive programmable optical devices, and has the potential to expand the application scenarios of traditional optical wireless commnucation. In this paper, an OIRS-based space division multiple access (SDMA) technology is proposed, which realizes accurate SDMA by partitioning the signal input and control of the OIRS, so that a single OIRS can output multiple adjustable optical beams containing different information. By jointly considering the multi-path interference among OIRS regions, OIRS physical model, pointing error, and atmospheric attenuation, we build a mathematical model of the OIRS-based SDMA system. Based on the model, the closed-form expressions for the system BER and outage probability has been derived. It is shown through numerical results that the derivation results are accurate and there is an error floor cased by multi-path interference among OIRS regions. Based on theoretical analysis and simulation results, the effect of each parameter and system design have been discussed.

On the Harmonic Selection and Performance Verification in Time-Modulated Array-Based Space Division Multiple Access

The time-modulated array (TMA)-based space-division multiple access (SDMA) approach is studied and verified, including the performance analysis and experimental verification. It utilizes the multibeam characteristic of TMA to implement the SDMA. For the uplink, the main power of signals with different incident angles would be redistributed to different harmonic components after time modulation. In this case, it plays a key role in this system to determine the harmonic order, which is selected to detect the received signal. A novel harmonic selection method for the uplink TMA-based SDMA systems is proposed by maximizing the received signal power. Furthermore, a closed-form expression of the spectral efficiency is deduced to verify the advantage of the simple harmonic selection scheme. Numerical results show that the TMA-based SDMA system can significantly improve the spectral efficiency compared with traditional single radio frequency (RF) chain systems. Meanwhile, it does not increase the number of RF chains. An L-band eight-element TMA is fabricated and tested to validate the feasibility of the TMA-based SDMA method.

Trade‐offs between the quality of service, computational cost and cooling complexity in interference‐dominated multi‐user SDMA systems

The future fifth generation (5G) systems will aim to design low-cost phased array base station antenna systems at mm-waves for simultaneous multiple beamforming with enhanced spatial multiplexing, limited interference, acceptable power consumption, suitable processing complexity, and passive cooling. In this study, a multi-user space division multiple access (SDMA) model is developed to investigate the trade-off between the quality of service (QoS), computational complexity in beamforming and cooling requirements for various use cases, and a number of users. The QoS at the user ends is rated by assessing the statistical signal-to-interference-plus-noise ratios (SINRs). Two beamforming algorithms, namely conjugate beamforming (CB) and zero-forcing (ZF), are considered and compared. Depending on the deployment scenario, rotated and optimised array layouts are proposed to be used in CB with the least computational complexity while providing relatively good QoS. Different reduced-complexity ZF algorithms are introduced as a compromise between the SINR performance and computational burden. The impact of the number of simultaneously served users on the thermal management in active integrated 5G base station antenna arrays is investigated as well.

Space Division Multiple Access for Optical Attocell Network Using Angle Diversity Transmitters

In this paper, an optical space division multiple access (SDMA) scheme is proposed for optical attocell networks. In the system, the conventional single-element transmitter in each optical cell is substituted by an angle diversity transmitter which can simultaneously serve multiple active users at different positions. The type of configuration can increase the available bandwidth resource and also mitigate intercell interference in optical attocell networks. The results show that an optical SDMA scheme significantly outperforms the conventional optical time division multiple access scheme. The SDMA scheme improves the average spectral efficiency of the system by a factor of 26 for a 37-element light emitting diode angle diversity transmitter. In addition, the upper and lower bound of the optical SDMA performance are derived analytically. These bounds can precisely estimate the performance of SDMA systems. Also, the study is extended to take account of user position errors, and Monte-Carlo simulations show that the system is very robust to user position errors.

Performance Analysis for SDMA mmWave Systems: Using an Approximate Closed-Form Solution of Downlink Sum-Rate

In this paper, we analyze the performance of downlink transmission in a space division multiple access (SDMA) millimeter-wave (mmWave) system with beam selection, where antenna arrays are considered at a base station (BS) and users. Under the assumption of limited scattering environment, we propose a simplified approach to analyze the downlink performance of the SDMA system. In this scheme, the throughput for each BS beam is approximated by a binary random variable for tractable analysis and an approximate closed-form solution for the downlink sum rate is derived. It is shown that the predicted throughputs by the proposed method reasonably agree with simulation results.

Partly random multiple weighting matrices selection for orthogonal random beamforming

In the multi-user multiple-input multiple-output (MIMO) system, orthogonal random beamforming (ORBF) scheme is proposed to serve multiple users simultaneously in order to achieve the multi-user diversity gain. The opportunistic space-division multiple access system (OSDMA-S) scheme performs multiple weighting matrices during the training phase and chooses the best weighting matrix to be used to broadcast data during the transmitting phase. The OSDMA-S scheme works better than the original ORBF by decreasing the inter-user interference during the transmitting phase. To save more time in the training phase, a partly random multiple weighting matrices selection scheme is proposed in this paper. In our proposed scheme, the Base Station does not need to use several unitary matrices to broadcast pilot symbol. Actually, only one broadcasting operation is needed. Each subscriber generates several virtual equivalent channels with a set of pre-saved unitary matrices and the channel status information gained from the broadcasting operation. The signal-to-interference and noise ratio (SINR) of each beam in each virtual equivalent channel is calculated and fed back to the base station for the weighting matrix selection and multi-user scheduling. According to the theoretical analysis, the proposed scheme relatively expands the transmitting phase and reduces the interactive complexity between the Base Station and subscribers. The asymptotic analysis and the simulation results show that the proposed scheme improves the throughput performance of the multi-user MIMO system.

A Multi-Antenna Based Spectrum Sharing for IMT-Advanced SDMA Systems

We propose a simple multi-user beamforming to assist space-division multiple access (SDMA) as well as to mitigate interference from IMT-Advanced base station (BS) to fixedsatellite service (FSS) earth stations (ESs). The BS with multiple antennas forms multiple beams that steer nulls, i.e., emit quite low power (interference) to the directions of the ESs. The beamforming vectors are designed by inverting the array steering vectors corresponding to the direction angles of the ESs as well as random direction angles of the main beam lobes. In order to show the merits of the proposed method, we model interference power at the ES and compute the minimum separation distances between the BS and the ESs required for their coexistence. Even for the case of the multiple ESs, the proposed method can reduce the minimum separation distance by up to 92 percent without any expense of additional radio spectrum resources.

Space-Division Multiple Access Based on Time-Modulated Array

A novel space-division multiple-access (SDMA) method is proposed by the multibeam characteristic of the time-modulated array (TMA). The TMA generates the fundamental and harmonic components pointing to different directions. For the uplink, the users in different directions transmit the signals with the same carrier frequency to the base station with the TMA. Then, the base station distinguishes the users by the generated harmonic components. For the downlink, signals of different users are modulated to different carrier frequencies beforehand. Because of the modulation of the TMA, the downlink signals are transmitted to different directions with the same carrier frequency. Compared to the traditional SDMA systems implemented by the Butler matrix beamforming or the digital beamforming, the proposed method implements the SDMA with a single RF channel, which has advantage in the hardware complexity and cost. The uplink and downlink schemes are analyzed, and their drawbacks are discussed. A simple TMA is constructed to verify its effectiveness.

Resource allocation for multiple input multiple output‐orthogonal frequency division multiplexing ‐based space division multiple access systems

The problem of the system throughput maximisation and the fairness issue among users is considered for the downlink multiuser multiple input multiple output-orthogonal frequency division multiplexing system with MMSE precoding. Since finding the optimal solution by using the exhaustive search has very high computational burden, the authors propose a low-complexity user selection strategy plus the optimal power allocation in this study. With resorting to the mathematical simplification process, the proposed user selection scheme is designed to compare the related value of SINR. The power allocation is performed after the user selection. However, the power allocation is not in interference-free environment but in the presence of crosstalk, which is a nonlinear non-convex optimisation problem. In this study, the authors use an optimisation technique to obtain the optimal solution of the constrained non-convex nonlinear problem by replacing the objective function with a difference of two convex functions. A bisection-based strategy to solve this problem with interference-awareness to find local optimal solutions is presented in this study. Simulation results show that the performance of the proposed algorithm is close to that of the optimal solution. The trade-off between the system throughput and the fairness among users is also considered.

An SDMA-based MAC protocol for wireless ad hoc networks with smart antennas

A wireless ad hoc network consists of a set of wireless devices. The wireless devices are capable of communicating with each other without the assistance of base stations. Space Division Multiple Access (SDMA) is a new technology designed to optimize the performance of current and future mobile communication systems. In this paper, an SDMA-based MAC protocol (S-MAC) for wireless ad hoc networks with smart antennas is proposed. The proposed protocol exploits the SDMA system to allow reception of more than one packet from spatially separated transmitters. Using SDMA technology provides collision-free access to the communication medium based on the location of a node. The proposed protocol solves the hidden terminal problem, the exposed terminal problem, and the deafness problem. Simulation results demonstrate the effectiveness of the proposed S-MAC in improving throughput and increasing spatial channel reuse.

Performance of space-division multiple-access system using preprocessing based on feedback of vector-quantized channel spatial information

In this paper, we report the performance of multi-user transmitter preprocessing assisted multiple-input multiple-output downlink (DL) communication, when the channel impulse responses (CIRs) required to formulate the preprocessing matrix are fed back to the base station (BS) via feedback channels that endure noise and fading. Specifically, in our work the CIRs are estimated at the mobile stations (MSs) and are then decomposed by singular value decomposition. The magnitudes and phases associated with the right-hand side unitary matrix of each of the MSs are then vector-quantized (VQ) and conveyed to the BS as channel spatial information. This spatial information is then used to conceive the preprocessing matrix. Our study shows that the symbol-error-rate and capacity achieved with the ideal feedback scenario is close to that attained with perfect spatial information assumption. Hence, we advocate that VQ-spatial information based preprocessing comprises an efficient technique to deal with the DL multi-user interference.

Comparison of DoA Estimation Algorithms in SDMA System

With Space Division Multiple Access (SDMA) schemes employing digital signal processing algorithms in its smart antenna systems, it is possible to improve the system capacity of modern wireless communication systems by enabling user's angular separation. Angular separation ability enhances reception in Signal-of-Interest direction and minimizes interference in Signal-of-Not-Interest direction. Direction of Arrival (DoA) algorithms are used for estimation of a number of incident plane waves on the antenna array and their incidence angles. This paper compares performance of three DoA algorithms: MUSIC, root-MUSIC and Capon applied on the uniform linear array in the presence of uncorrelated white noise. The simulation results show that MUSIC outperformed root-MUSIC and Capon in both required number of snapshots and number of array elements as well as in signal-to-noise ratio requirements.

MBER Space Time Equalization assisted Multiuser Detection

A novel minimum bit-error rate (MBER) space–time-equalization (STE)-based multiuser detector (MUD) is proposed for multiple-receive-antenna-assisted space-division multiple-access systems. It is shown that the MBER-STE-aided MUD significantly outperforms the standard minimum mean-square error design in terms of the achievable bit-error rate (BER). Adaptive implementations of the MBER STE are considered, and both the block-databased and sample-by-sample adaptive MBER algorithms are proposed. The latter, referred to as the least BER (LBER) algorithm, is compared with the most popular adaptive algorithm, known as the least mean square (LMS) algorithm. It is shown that in case of binary phase-shift keying, the computational complexity of the LBER-STE is about half of that required by the classic LMS-STE. Our simulation results demonstrate that the MBER ST-DFE assisted MUD is more robust to channel estimation errors as well as to potential error propagation imposed by decision feedback errors, compared to the MMSE ST-DFE assisted MUD.

Performance of multi-user transmitter preprocessing assisted MIMO system over correlated frequency-selective channels

In this contribution we present the performance of a multi-user transmitter preprocessing (MUTP) assisted multiple-input multiple-output (MIMO) space division multiple access (SDMA) system, aided by double space time transmit diversity (DSTTD) and space time block code (STBC) processing for downlink (DL) and uplink (UL) transmissions respectively. The MUTP is invoked by singular value decomposition (SVD) which exploits the channel state information (CSI) of all the users at the base station (BS) and only an individual user’s CSI at the mobile station (MS). Specifically, in this contribution, we investigate the performance of multi-user MIMO cellular systems in frequency-selective channels from a transmitter signal processing perspective, where multiple access interference (MAI) is the dominant channel impairment. In particular, the effects of three types of delay spread distributions on MUTP assisted MIMO SDMA systems pertaining to the Long Term Evolution (LTE) channel model are analyzed. The simulation results demonstrate that MUTP can perfectly eliminate MAI in addition to obviating the need for complex multi-user detectors (MUDs) both at the BS and MS. Further, SVD-based MUTP results in better achievable symbol error rate (SER) compared to popularly known precoding schemes such as block diagonalization (BD), dirty paper coding (DPC), Tomlinson–Harashima precoding (THP) and geometric mean decomposition (GMD). Furthermore, when turbo coding is invoked, coded SVD aided MUTP results in better achievable SER than an uncoded system.

다중 사용자 다이버시티가 있는 선형 수신기 기반의 공간 분할 다중접속 시스템의 최대 전송률 분석

This paper basically considers a space-division multiple-access (SDMA) systems where all nodes including the base station and mobile stations are equipped with equal number of antennas. In the SDMA system, for each transmit antenna, the user corresponding to the largest signal-to-interference-plus-noise (SINR) is selected to be supported. In this environment with the minimum mean squared error receivers, we analyze the average throughput using the previous works.

Application of DOA Estimation Algorithms in Smart Antennas Systems

Concept of wireless communication systems which use smart antennas is based on digital signal processing algorithms. Thus, the smart antennas systems become capable to locate and track signals by the both: users and interferers and dynamically adapts the antenna pattern to enhance the reception in Signal-Of-Interest direction and minimizing interference in Signal-Of-Not-Interest direction. Hence, Space Division Multiple Access system, which uses smart antennas, is being used more often in wireless communications, because it shows improvement in channel capacity and co-channel interference. However, performance of smart antenna system greatly depends on efficiency of digital signal processing algorithms. The algorithm uses the Direction of Arrival (DOA) algorithms to estimate the number of incidents plane waves on the antenna array and their angle of incidence. This paper investigates performance of the DOA algorithms like MUSIC, ESPRIT and ROOT MUSIC on the uniform linear array in the presence of white noise. The simulation results show that MUSIC algorithm is the best. The resolution of the DOA techniques improves as number of snapshots, number of array elements and signal-to-noise ratio increases.

Receiver Multiuser Diversity Aided Multi-Stage Minimum Mean-Square Error Detection for Heavily Loaded DS-CDMA and SDMA Systems

By investigating the conditions required for successive interference cancellation multiuser detectors (SIC-MUD) to achieve near-optimum BER performance, we propose and investigate a so-called receiver multiuser diversity aided multi-stage minimum mean-square error MUD (RMD/MS-MMSE MUD), which is operated in the SIC principles. The BER performance of the RMD/MS-MMSE MUD is investigated in association with both the direct-sequence code-division multiple-access (DS-CDMA) over either Gaussian or Rayleigh fading channels, and the space-division multiple-access (SDMA) over Rayleigh fading channels. Furthermore, we consider both full-load and overload scenarios in comparison with the spreading factor N of DS-CDMA and the number of receive antennas N in SDMA. Our studies show that the RMD/MS-MMSE MUD is highly efficient for both full-load and overload systems. Specifically, the RMD/MS-MMSE MUD for the full-load systems of moderate size is capable of attaining the BER performance similar to that of the optimum maximum likelihood MUD (ML-MUD). For the overload systems, it can allow a DS-CDMA or SDMA system to support K=2N users and still achieve much better BER performance than a corresponding DS-CDMA or SDMA system using conventional MMSE-MUD to support K=N users.

셀 간 협동 CSM에서 상향 링크 용량 개선을 위한 자원 할당 알고리즘

In this paper, for a uplink space division multiple access system named cooperative spatial multiplexing(CSM), radio resource management(RRM) algorithms are proposed based on sharing uplink channel information among a serving base station(BS) and interfering BSs in a uplink coordinated wireless communication system. A constrained maximum transmit power algorithm is proposed for mobile station(MS) to limit uplink inter-cell interference(ICI). And joint scheduling algorithm among coordinated BSs is proposed to enhance uplink capacity through ICI mitigation by using channel information from interfering BSs. It is shown that the proposed RRM algorithm provides a considerable uplink capacity enhancement by effective ICI mitigation only with moderate complexity.

Codebook Based Space Division Multiple Access with Partial Side Information

In this letter, a codebook based multiuser MIMO precoding scheme is proposed for a space-division multiple access (SDMA) system with limited feedback. Focusing on the case of SDMA systems with two transmit antennas, a precoder codebook design is proposed based on the idea that a precoder inducing larger fluctuations in the signal to interference and noise ratio (SINK) at each link can lead to a larger gain in terms of multiuser diversity. It is shown that the proposed multiuser MIMO precoding outperforms existing multiuser MIMO techniques in terms of the average system throughput.