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During the past decade, there has been an increasing interest in the audio-based indoor localization approach, which has benefited from the high precision, high privacy, and high security of the passive time difference of arrival (TDoA) positioning. However, the limited bandwidth, and complexity in real-time ID encoding and decoding under an actual reverberate environment make it difficult to achieve wide-area (>1500m2) localization in off-the-shelf smartphones. Plenty of previous work applied to a single region localization only with a small range. In this paper, a hybrid acoustic signal transmission architecture based on frequency division multiple access (FDMA), time division multiple access (TDMA), and space division multiple access (SDMA) is perfected to cover the acoustic signal to a wider range. With the prior information of the Bluetooth and floor-plan, smartphones estimate which cell themselves are located in accurately. We further propose the strategies of data bias integrity monitoring, dynamic variance adjustment based on the micro-electro-mechanical systems (MEMS) sensors, and the floor-plan restraint to enhance the particle filter and make the smartphones tracking smarter and more robust. The proposed prototype system can provide decimeter-level localization accuracy and stable 1Hz update rate in several typical wide indoor environments with less infrastructure.

This paper studies the cross-layer challenges and performance of Hybrid Beamforming (HBF) and Multi-User Multiple-Input Multiple-Output (MU-MIMO) in 5G millimeter wave (mmWave) cellular networks with full-stack TCP/IP traffic and MAC scheduling. While previous research on HBF and MU-MIMO has focused on link-level analysis of full-buffer transmissions, this work reveals the interplay between HBF techniques and the higher layers of the protocol stack. To this aim, prior work on full stack simulation of mmWave cellular network has been extended by including the modeling of MU-MIMO and HBF. Our results reveal novel relations between the networking layers and the HBF MU-MIMO performance in the physical layer. Particularly, throughput can be increased in 5G networks by means of Spatial Division Multiple Access (SDMA). However, in order to achieve such benefits it is necessary to take into account certain trade-offs and the implementation complexity of a full-stack HBF solution., Comment: 30 pages, 4 figures, 1 table. This is the author's pre-print version of a manuscript to be submitted

Ambient backscatter communication (BackCom) is faced with the challenge that a single BackCom device can occupy multiple orthogonal resource blocks unintentionally. As a result, in order to avoid co-channel interference, a conventional approach is to serve multiple BackCom devices in different time slots, which reduces both spectral efficiency and connectivity. This letter demonstrates that the use of non-orthogonal multiple access (NOMA) can efficiently improve the system throughput and support massive connectivity in ambient BackCom networks. In particular, two transceiver design approaches are developed in the letter to realize different tradeoffs between system performance and complexity.

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.

In this letter, an uplink space division multiple access scheme based on the Doppler effect is proposed for wireless multi-user communication systems. By rotating the receive antenna array or using a circular sampling method, different Doppler frequency shifts are introduced to the received signals from different directions, and then different user’s signal can be separated in frequency domain. To maximize the inter-user interference (IUI)-free bandwidth, a max-min criterion is proposed for antenna switching control. The main advantage of the proposed scheme over the conventional space division multiple access (SDMA) schemes is that it needs less number of analog receive chain. Then simulations are carried out to evaluate the performance of the proposed scheme in terms of channel capacity. Simulation results show that the proposed scheme achieves a significant capacity gain, and its capacity is very close to that of a single user system without IUI.

For ultralow-power Internet of Things, we consider a monostatic multiantenna backscatter communication network (MBCN) supporting massive devices through nonorthogonal multiple access (NOMA) over space division multiple access (SDMA). For the network, we optimize the transmit beamforming (BF) for signal excitation of a reader, reflection coefficients of devices for backscattering and energy harvesting, and receive BF for information decoding at the reader toward the maximum fairness in data collection. We first show that the optimization problem for the MBCN without successive interference cancellation (SIC) has a similarity with the problem considered for a wireless power communication network but the conventional algorithm is not applicable to the MBCN with SIC. Thus, we propose a new alternating optimization algorithm that is applicable to both problems with and without SIC at a lower complexity. Simulation results show that the proposed algorithm provides a remarkable gain over the conventional one for the MBCN with SIC while exhibiting a similar performance for the MBCN without SIC. In addition, NOMA/SDMA enhanced by the proposed algorithm increases the minimum system throughput as well as the total energy harvested in the network by utilizing limited resources more effectively for a larger number of devices.

Due to the increasingly complicated communication scenarios and network architectures as well as growing traffic demands for high speed connectivity, dynamic spectrum allocation in fifth generation (5G) networks becomes insufficient to guarantee the satisfaction of main network requirements in terms of spectrum efficiency (SE), scalability, delay, and energy efficiency (EE). Enormous multiple access schemes and cognitive radio (CR) network scenarios come to fulfill these requirements and enhance network functionalities. With multiple access schemes, users are able to transmit their data streams simultaneously under maximum capacity constraints. On the other hand, vacant spectrum holes are exploited in an opportunistic manner via CR and software defined radio. In order to exploit these spectrum holes as well as meeting different network requirements, several multiple access techniques have been presented that have been initiated through the adoption of orthogonal multiple access (OMA) scheme. Additionally, non-orthogonal multiple access (NOMA) and space division multiple access (SDMA) are presented to achieve a promising multiplexing gain as well as to address the inefficient spectrum utilization incurred with OMA schemes. However, such multiplexing gain is limited as it depend on the channel conditions. Accordingly, a generalized multiple access scheme has been presented recently, namely rate splitting multiple access (RSMA), to further enhance the SE. In this paper, we provide a comprehensive study regarding the key multiple access schemes presented for CRNs to further enhance the use of spectral resources, and additionally highlights the key implementation challenges and the enabling techniques addressed to overcome it. We have given a special attention to the enhances provided by RSMA as compared with OMA, SDMA, and NOMA techniques. Finally, some open issues are spotted to shed lights on the need for further studies and future research efforts.

This paper studies the maximum throughput achievable with optimal scheduling in multi-hop mmWave picocellular networks with Multi-user Multiple-Input Multiple-Output (MU-MIMO) radios. MU-MIMO enables simultaneous transmission to multiple receivers (Space Division Multiplexing) and simultaneous reception from multiple transmitters (Space Division Multiple Access). The main contribution is the extension to MU-MIMO of the Network Utility Maximization (NUM) scheduling framework for multi-hop networks. We generalize to MU-MIMO the classic proof that Maximum Back Pressure (MBP) scheduling is NUM optimal. MBP requires the solution of an optimization that becomes harder with MU-MIMO radios. In prior models with one-to-one transmission and reception, each valid schedule was a matching over a graph. However, with MU-MIMO each valid schedule is, instead, a Directed Bipartite SubGraph (DBSG). In the general case this prevents finding efficient algorithms to solve the scheduler. We make MU-MIMO MBP scheduling tractable by assuming fixed power allocation, so the optimal scheduler is the Maximum Weighted DBSG. The MWDBSG problem can be solved using standard Mixed Integer Linear Programing. We simulate multi-hop mmWave picocellular networks and show that a MU-MIMO MBP scheduler enables a 160% increase in network throughput versus the classic one-to-one MBP scheduler, while fair rate allocation mechanisms are used in both cases., Published in IEEE Transactions on Wireless Communications

Considering a two-user multi-antenna Broadcast Channel, this paper shows that linearly precoded Rate-Splitting (RS) with Successive Interference Cancellation (SIC) receivers is a flexible framework for non-orthogonal transmission that generalizes, and subsumes as special cases, four seemingly different strategies, namely Space Division Multiple Access (SDMA) based on linear precoding, Orthogonal Multiple Access (OMA), Non- Orthogonal Multiple Access (NOMA) based on linearly precoded superposition coding with SIC, and physical-layer multicasting. The paper studies the sum-rate and shows analytically how RS unifies, outperforms, and specializes to SDMA, OMA, NOMA, and multicasting as a function of the disparity of the channel strengths and the angle between the user channel directions., submitted for publication

Deploying Autonomous Underwater Vehicles (AUVs) is a necessity to enable a range of civilian/military underwater applications; yet, achieving a reliable coordination among the vehicles is a challenging issue due to the time- and space-varying characteristics of the acoustic communication channel. The design of a Medium Access Control (MAC) based on a probabilistic Space Division Multiple Access (SDMA) method for short/medium distances (less than $2\; \mathrm {km}$ 2 km ) is presented. This method considers the inherent vehicle position uncertainty due to the inaccuracies in models and the drift of the vehicles. It minimizes the acoustic interference statistically by considering the angular position of neighboring vehicles via a two-step estimation and by keeping the transmitter antenna's beamwidth of each vehicle at an optimal value. Such value is chosen considering three contrasting goals, i.e.: $(i)$ ( i ) spreading the signal beam towards the vehicle to combat position uncertainty using a coarse estimation; $(ii)$ ( i i ) focusing the beam to reduce acoustic energy dispersion through a fine estimation; and $(iii)$ ( i i i ) minimizing interference to other vehicles. Simulation results in a sparse underwater network show that this approach mitigates interference, reduces the probability of retransmission, and achieves higher data rates over conventional underwater MAC techniques.

The increased proliferation of connected devices requires a paradigm shift towards the development of innovative technologies for the next generation of wireless systems. One of the key challenges, however, is the spectrum scarcity, owing to the unprecedented broadband penetration rate in recent years. Visible light communications (VLC) has recently emerged as a possible solution to enable high-speed short-range communications. However, VLC systems suffer from several limitations, including the limited modulation bandwidth of light-emitting diodes. Consequently, several multiple access techniques (MA), e.g., space-division multiple access (SDMA) and non-orthogonal multiple access (NOMA), have been considered for VLC networks. Despite their promising multiplexing gains, their performance is somewhat limited. In this article, we first provide an overview of the key MA technologies used in VLC systems. Then, we introduce rate-splitting multiple access (RSMA), which was initially proposed for RF systems and discuss its potentials in VLC systems. Through system modeling and simulations of an RSMA-based two-use scenario, we illustrate the flexibility of RSMA in generalizing NOMA and SDMA, as well as its superiority in terms of weighted sum rate (WSR) in VLC. Finally, we discuss challenges, open issues, and research directions, which will enable the practical realization of RSMA in VLC., 19 pages, 14 figures. arXiv admin note: substantial text overlap with arXiv:2002.07583

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.

To support multiple users in an indoor multiple-input multiple-output visible light communication (MIMO-VLC) system adopting spatial multiplexing, orthogonal frequency division multiple access (OFDMA) is usually adopted, where the overall modulation bandwidth is shared by all the users. In this paper, by fully exploiting the spatial distributions of light-emitting diode (LED) transmitters in the ceiling and end users around the receiving plane, we propose a space division multiple access (SDMA) technique for indoor spatial multiplexing-based MIMO-VLC systems. When applying SDMA, users within the MIMO-VLC system are divided into different user groups (UGs) based on their spatial locations with respect to different LED transmitters. Specifically, each UG can use the overall modulation bandwidth of the system. For efficient implementation of SDMA, two distributed user grouping (DUG) approaches are proposed, including basic DUG and transmit diversity-enhanced DUG (TD-DUG), and a two-step resource allocation algorithm is further designed. The achievable rates of the MIMO-VLC system employing SDMA with both basic DUG and TD-DUG are derived accordingly. To verify the superiority of SDMA over conventional OFDMA, detailed analytical and simulation results are presented. Moreover, a proof-of-concept experiment is conducted to demonstrate the advantage of SDMA in a practical spatial multiplexing-based MIMO-VLC system.

Rate-Splitting Multiple Access (RSMA) is a flexible and robust multiple access scheme for downlink multi-antenna wireless networks. RSMA relies on Rate-Splitting (RS) at the transmitter and Successive Interference Cancellation (SIC) at the receivers. In this work, we study the performance of RSMA in the scenarios related with the important core services of New Radio (NR) and 6G, namely, enhanced Ultra-Reliable and Low-Latency (URLLC) and enhanced Mobile Broadband Communications (eMBB). We present the optimal system designs employing RSMA that target short-packet and low-latency communications as well as robust communications with high-throughput under the practical and important setup of imperfect Channel State Information at Transmitter (CSIT) originating from user mobility and latency/delay (between CSI acquisition and data transmission) in the network. We demonstrate via numerical results that RSMA achieves significantly higher performance than Space Division Multiple Access (SDMA) and Non-Orthogonal Multiple Access (NOMA), and is capable of addressing the requirements for enhanced URLLC and eMBB in 6G efficiently.

Rate-Splitting Multiple Access (RSMA) is a robust multiple access scheme for downlink multi-antenna wireless networks. In this work, we investigate a novel application of RSMA for joint communications and jamming with a Multi-Carrier (MC) waveform in Multiple Input Single Output (MISO) Broadcast Channel (BC). Our aim is to simultaneously communicate with Information Users (IU) and jam Adversarial Users (AU) to disrupt their communications in a setting where all users perform broadband communications by MC waveforms in their respective networks. We consider the practical setting of imperfect CSI at transmitter (CSIT) for the IUs and statistical CSIT for AUs. The optimal information and jamming precoders are designed to maximize the sum-rate under jamming power constraints on the pilot subcarriers of AUs, a jamming method considered to be among the most destructive methods for MC waveforms under the considered system model. We compare the sum-rate performance of RSMA and Space Division Multiple Access (SDMA) schemes by numerical results to demonstrate that RSMA achieves a significant sum-rate gain compared to SDMA.

International audience; We present a concept for networked optical wireless communications, also denoted as LiFi, to meet the requirements of industrial wireless applications. These are primarily mobility support with moderate data rates per device, reliable real-time communication, and integrated positioning. We describe a distributed multiuser multiple-input multiple-output architecture, serving mobile devices via an optical wireless infrastructure. The system consists of a central unit, being connected to a number of distributed optical frontends covering a larger area. Our main contribution is a medium access control protocol based on space division multiple access. Evaluation results demonstrate the advantages of joint transmission from adjacent optical frontends and the dynamic switching between spatial diversity and multiplexing. The relevance of spatial multiplexing becomes obvious through channel measurements in an indoor scenario. Moreover, we highlight a low-power physical layer based on on-off-keying for battery-powered mobile devices. Our architecture can easily integrate positioning by simultaneously measuring the time-of-flight between multiple optical frontends and the mobile device. We highlight the use of plastic optical fiber as an analog fronthaul technology and discuss the integration with other networks. The main functions described in this paper will be supported by the upcoming IEEE Std 802.15.13.

Merging mobile edge computing (MEC) service with the wireless local area networks (WLANs) provides enormous benefits such as intensive computation capabilities. Access to high-speed WLANs has become an urgent challenge due to the fast rate of application development and user adoption. Providing increased wireless resources is one solution, but millimeter (mmWave) multi-user massive Multiple-Input Multiple-Output (MIMO) technology has also attracted attention due to a series of features such as high throughput, strong anti-interference ability, and small fading. Hence, exploring the potential of mmWave MIMO systems for WLAN could play a significant role in improving network performance, especially throughput. In this paper, we introduce mmWave and massive MIMO into traditional WLAN with MEC, which enables a large portion of spatial resources to be allocated among users, and mitigates inter-user interference. Moreover, we propose a novel media access control (MAC) protocol, named as LSMWN-MAC, to adapt to a series of unique characteristics of mmWave and massive MIMO, which adopts space division multiple access (SDMA) as one of the resource methods, taking full advantage of spatial resources. In addition, we modify the protocol and propose the MLSMWN-MAC protocol to allocate resources dynamically, a solution that is particularly suitable for scenes with 30-50 users. Simulation results show that compared to 802.11ad, the proposed two protocols can increase the saturated throughput by 4.7Gb/s and 5.4Gb/s respectively, which are close to the throughput upper limit of the mmWave MIMO system. Meanwhile, we observe that when the number of users exceeds the threshold, the performance of the LSMWN-MAC protocol using a static allocation method is superior to the MLSMWN-MAC protocol using a dynamic method. In other cases, the dynamic protocol has better performances.

In this paper, an optical adaptive antenna array system for multi-user optical mobile communication is studied. A coherent signal source is embedded in a spherical optical phased cell array with an external spherical lens system. The system can predict the signal power of the receiving end according to the channel transfer matrix and perform power compensation when transmitting the signal. Correspondingly, a pure phase lossless desired light field recovery algorithm is proposed and used for space division multiple access and free power allocation of antenna array systems. A small-scale optical adaptive antenna array experimental system is built and tested with good performance and consistent with the expected results.

It is well known that cellular mobile phone systems have evolved from 1G and 2G that use frequency and time division multiple access (FDMA and TDMA) systems respectively, to code division multiple access (CDMA) of third generation (3G) systems (Chen et al., 2006). Furthermore, the exploitation of spatial diversity from the emergence of advance antenna technologies such as smart antenna and space time signal processing have given rise to induce another multiple access scheme called space division multiple access (SDMA) systems (Fang, 2002). Among these schemes, the system capacity and spectrum efficiency are the key factors to compare the performances of various mobile communication systems. Since radio frequency (RF) spectrum is a limited resource, these techniques have approached their fundamental limitations. Flexible utilization of such resources in space, time and code has led to great improvement in system capacity. For a given bandwidth, the system capacity for narrowband radio systems such as FDMA and TDMA is dimension or bandwidth limited. In contrast, the system capacity of CDMA and SDMA systems is interference limited. Any reduction in interference in CDMA and SDMA systems converts directly and linearly into increased capacity (Yu et al., 2004), (Chen et al., 2008). Multiple access schemes such as FDMA and TDMA increase their system capacity and spectrum efficiency by dividing the different network planning phases more clearly into individual parts to allow different frequencies to be used at different time moments (Castaeda & Lara, 2008). In CDMA systems, the same frequency is used simultaneously in adjacent cells and the interference level should be taken into account in the coverageplanning phase (Niemela & Lempiainen, 2003). Furthermore, cell splitting and sectorisation to form SDMA systems with use of directional antenna could also result in increase of system capacity and spectrum efficiency over the omnidirectional antenna system (Godara, 27

In this paper, we take a critical and fresh look at the downlink multi-antenna NOMA literature. Instead of contrasting NOMA with OMA, we contrast NOMA with two other baselines. The first is conventional Multi-User Linear Precoding (MULP). The second is Rate-Splitting Multiple Access (RSMA) based on multi-antenna Rate-Splitting (RS) and SIC. We show that there is some confusion about the benefits of NOMA, and we dispel the associated misconceptions. First, we highlight why NOMA is inefficient in multi-antenna settings based on basic multiplexing gain analysis. We stress that the issue lies in how the NOMA literature has been hastily applied to multi-antenna setups, resulting in a misuse of spatial dimensions and therefore loss in multiplexing gains and rate. Second, we show that NOMA incurs a severe multiplexing gain loss despite an increased receiver complexity due to an inefficient use of SIC receivers. Third, we emphasize that much of the merits of NOMA are due to the constant comparison to OMA instead of comparing it to MULP and RS baselines. We then expose the pivotal design constraint that multi-antenna NOMA requires one user to fully decode the messages of the other users. This design constraint is responsible for the multiplexing gain erosion, rate loss, and inefficient use of SIC receivers in multi-antenna settings. Our results confirm that NOMA should not be applied blindly to multi-antenna settings, highlight the scenarios where MULP outperforms NOMA and vice versa, and demonstrate the inefficiency, performance loss and complexity disadvantages of NOMA compared to RS. The first takeaway message is that, while NOMA is not beneficial in most multi-antenna deployments. The second takeaway message is that other non-orthogonal transmission frameworks, such as RS, exist which fully exploit the multiplexing gain and the benefits of SIC to boost the rate in multi-antenna settings., Comment: submitted for publication

In order to manage the increasing interference between radar and communication systems, joint radar and communication (RadCom) systems have attracted increased attention in recent years, with the studies so far considering the assumption of perfect Channel State Information at the Transmitter (CSIT). However, such an assumption is unrealistic and neglects the inevitable CSIT errors that need to be considered to fully exploit the multi-antenna processing and interference management capabilities of a joint RadCom system. In this work, a joint RadCom system is designed which marries the capabilities of a Multiple-Input Multiple-Output (MIMO) radar with Rate-Splitting Multiple Access (RSMA), a powerful downlink communications scheme based on linearly precoded Rate-Splitting (RS) to partially decode multi-user interference (MUI) and partially treat it as noise. In this way, the RadCom precoders are optimized in the presence of partial CSIT to simultaneously maximize the Average Weighted Sum-Rate (AWSR) under QoS rate constraints and minimize the RadCom Beampattern Squared Error (BSE) against an ideal MIMO radar beampattern. Simulation results demonstrate that RSMA provides the RadCom with more robustness, flexibility and user rate fairness compared to the baseline joint RadCom system based on Space Division Multiple Access (SDMA).

In this paper, we introduce the design of a multi-antenna Joint Radar-Communication (JRC) system with Rate Splitting Multiple Access (RSMA) and low resolution Digital-to-Analog Converter (DAC) units. Using RSMA, the communication messages are split into private and common parts, then precoded and quantized before transmission. We use a problem formulation to design the JRC system with RSMA and low resolution DACs by maximizing communication sum-rate and the proximity of the resulting JRC waveform to an optimal radar beampattern under an average transmit power constraint. We solve the joint sum-rate maximization and beampattern error minimization problem using Alternating Direction Method of Multipliers (ADMM) method. The numerical results show that RSMA achieves a significantly higher sum-rate compared to Space Division Multiple Access (SDMA) while providing the same Normalized Mean Square Error (NMSE) for the designed radar beampattern.

We investigate the throughput of a multi-user multiple-input multiple-output aviation network where multiple aircraft are connected to a High Throughput Satellite (HTS). We assume full frequency reuse in the downlink and a multibeam antenna architecture with multiple reflectors on the HTS. To maximize the system throughput, we apply zero forcing precoding along with a scheduling algorithm to group multiple aircraft that are simultaneously served with data via space division multiple access. For a more realistic scenario, the flight paths of the airplanes are based on real airline routes, and interference from terrestrial fixed service stations is considered. Our simulation results show that the proposed concept enables a massive throughput increase while the required update rate of the precoder coefficients and the user groups remain moderate.

Rate-splitting multiple access (RSMA) is a promising technique for downlink multi-antenna communications owning to its capability of enhancing the system performance in a wide range of network loads, user deployments and channel state information at the transmitter (CSIT) inaccuracies. In this paper, we investigate the achievable rate performance of RSMA in a multi-user multiple-input single-output (MU-MISO) network where only slow-varying statistical channel state information (CSI) is available at the transmitter. RSMA-based statistical beamforming and the split of the common stream is optimized with the objective of maximizing the minimum user rate subject to a sum power budget of the transmitter. Two statistical CSIT scenarios are investigated, namely the Rayleigh fading channels with only spatial correlations known at the transmitter, and the uniform linear array (ULA) deployment with only channel amplitudes and mean of phase known at the transmitter. Numerical results demonstrate the explicit max min fairness (MMF) rate gain of RSMA over space division multiple access (SDMA) in both scenarios. Moreover, we demonstrate that RSMA is more robust to the inaccuracy of statistical CSIT., conference

Visible light communication (VLC) has been emerged as a technology that can increase the channel capacity in the next generations of wireless technologies by exploiting the largely unutilized, licence-free and huge visible light portion of the electromagnetic spectrum. In order to enable high-speed short-range wireless communications, VLC utilizes the installed high-switching rate light emitting diodes (LEDs) in the ceilings of indoor environments, which are primarily used for illumination, to modulate the signals into visible light intensity. However, VLC suffers from several limitations, such as the limited modulation bandwidth and the coverage area of LEDs that degrade the overall system spectral efficiency (SE). In this respect, the present contribution proposes rate splitting multiple access (RSMA) for multi-cell indoor VLC systems as a mean to enhance the overall system SE and energy efficiency (EE) as well as to provide ubiquitous indoor coverage and to address user mobility issues. Moreover, we utilize coordinated beamforming to design the precoders of the common and the private streams in each cell aiming to enhance the performance of cell-edge users. Finally, the formulated sum of the mean squared error optimization problem is solved sub-optimally using an alternating optimization approach. Extensive computer simulations demonstrate that RSMA improves the overall system performance in terms of the SE and EE compared to the recently used multiple access techniques, such as space division multiple access with coordinated beamforming which constitutes a special case of it. acceptedVersion

A novel rate splitting space division multiple access (SDMA) scheme based on grouped code index modulation (GrCIM) is proposed for the sixth generation (6G) downlink transmission. The proposed RSMA-GrCIM scheme transmits information to multiple user equipments (UEs) through the space division multiple access (SDMA) technique, and exploits code index modulation for rate splitting. Since the CIM scheme conveys information bits via the index of the selected Walsh code and binary phase shift keying (BPSK) signal, our RSMA scheme transmits the private messages of each user through the indices, and the common messages via the BPSK signal. Moreover, the Walsh code set is grouped into several orthogonal subsets to eliminate the interference from other users. A maximum likelihood (ML) detector is used to recovery the source bits, and a mathematical analysis is provided for the upper bound bit error ratio (BER) of each user. Comparisons are also made between our proposed scheme and the traditional SDMA scheme in spectrum utilization, number of available UEs, etc. Numerical results are given to verify the effectiveness of the proposed SDMA-GrCIM scheme.

This paper investigates the uplink space division multiple access in a satellite-aerial-terrestrial network, where multiple users access to satellite with the aid of a unmanned aerial vehicle, and the two hops adopt radio frequency (RF) and free space optical (FSO), respectively. We first formulate an optimization problem to maximize the ergodic sum rate (ESR) of the considered system. Then a statistical channel state information (CSI)-based beamforming (BF) scheme is proposed to solve the non-convex ESR maximization problem. The main advantage of the proposed method is that only statistical CSI is used to obtain BF vectors so that a low implementation complexity can be achieved. Then, by assuming that the RF and FSO links undergo Nakagami-m and Gamma-Gamma fading, respectively, closed-form expression for ESR of the considered system is derived. Simulation results validate the derived expression and confirm the effectiveness of the proposed BF scheme.

Development and operation of 5G wireless radio access networks (RAN) are defined by the transition to mmWave, which enables the practical implementation of massive MIMO systems with spatial signal processing and adaptive beamforming (AB). The aim of current research is to evaluate the performance of location-aware beamforming from the space division multiple access (SDMA) point of view. We develop a simulation model for beamforming and spatial multiplexing performance evaluation depending on the array pattern, a number of array elements, and angular separation in 5G UDN. Different beamforming scenarios for UDN networks using beam-alignment are considered. Optimistic and pessimistic scenarios for a signal-of-interest (SOI) and signal-not-of-interest (SNOI) are defined for various station’s angular separation and numbers of antenna elements. The developed model contributes to spatial multiplexing performance evaluation in 5G UDN in terms of interference suppression rate (ISR) as a relation of SOI to SNOI levels for two neighboring stations with preliminary angular separation.

As we know that in today’s era of communication, a number of mobile users are growing very fast. So, an efficient use of channel is required to counter the problem of multiple access of users in the network. In literature, many multiple access schemes have been suggested to increase the throughput of the wireless communication channel. Except traditional multiple access such as frequency division multiple access (FDMA) and time division multiple access (TDMA), some advanced schemes like non-orthogonal multiple access (NOMA), space division multiple access (SDMA), and rate splitting multiple access (RSMA) have also been suggested for 5G and beyond communication networks. In this paper, the recent and advanced multiple access schemes are reviewed and studied for different parameters like network load, complexity, style of design, etc. On the basis of analysis, this is concluded that RSMA gives better results as compare to other MA schemes for 5G and beyond networks.

This paper considers a mono-static backscatter communication system with a multi-antenna reader and multiple devices for ultra-low power intemet-of-things. For the system, we present some practical issues to support multiple devices in space division multiple access via coherent detection. We design a frame structure with channel estimation and multiple access phases. The linear channel estimates of the backscatter channels with orthogonal pilots are derived and the effect of the channel estimation errors on the coherent detection are investigated through simulation. The results show that the minimum mean square error estimates improve the detection performance slightly compared to the least square estimate due to a structure of the backscatter channels.

Importance of three-dimensional beamforming in 5G wireless networks is due to increasing density of stations. Alignment of transmitter and receiver beams can lead to substantial interference suppression. Deficiency of current works in the area of multi user models with beamforming is the lack of dependency of interference suppression rate on the system level versus half-power beamwidth on the link level in an explicit form. Contribution of current research is system level simulation model, which demonstrates, that location aware beamforming with azimuth beam narrowing from 60° to 10° results in approximately 15-dB interference suppression for hexagonal layout with partial and full frequency reuse, which proves space division multiple access capabilities growth in spite of increasing density of neighboring stations.

Visible light communication (VLC) systems are typically operating at low data rates (hundreds of Mb/s up to 1 Gb/s). Operation at higher data rates can be feasible for VLC systems by implementing massive multiple-input and multiple-output (MIMO) techniques. The proposed VLC systems consists of multiple luminaires powered by light emitting diodes (LEDs) which are acting as transmitters and optical imaging receiver that includes massive number of separated multiple photodetectors. The massive MIMO-VLC system employs a space division multiple access (SDMA) to support multi-users in addition to the increase the data rate of a single user and improve the received signal to noise ratio (SNR) through use the spatial multiplying (SM), maximal ratio combining (MRC) and transmit/receive diversity (TxD, RxD) techniques, respectively. The result show that our massive MIMO-VLC systems able to work at a high data rate of 4 Gb/s for a single user scenario while considering the effect of mobility and diffuse reflections. In addition, the results show that our proposed system able to work at a high data rate of 1.5 Gb/s for multi-user scenario in presence of the multi-user interfere (MUI).

International audience; Digital beamsteering (DBS) is an appealing technique to overcome the severe millimeter-wave path loss, with less complexity and less channel feedback. In multiuser systems, DBS generates a beam toward each user. However, in congested cells, such a system suffers from high inter-user interference causing by the neighboring beams. In this paper, a new approach of space division multiple access (SDMA) with power-domain non-orthogonal multiple access (PD-NOMA) is considered for millimeter-wave channel to significantly reduce the inter-user interference and thus enhance the overall throughput. The proposed scheme is designed by selecting the users located at the same direction to share one beam, in which PD-NOMA multiplexes the users in power domain. The proposed user clustering method built upon an interference metric, and followed by a fixed power allocation method based on the received power, makes possible the design of a low-feedback NOMA-DBS scheme. Simulation results, based on the New York university mm-wave simulator, show that the multiuser MIMO system can achieve higher sum-rate with our proposed joint SDMA and PD-NOMA scheme, with respect to only SDMA (e.g., up to 20 bps/Hz rate gain for 45 users in the cell).

With the popularization of light-emitting diodes (LEDs) for indoor illumination, visible light communication (VLC) technology using LEDs as optical sources has gained an enormous amount of attention. In most indoor lighting places, lighting systems are composed of a set of LEDs rather than single LED, which is favorable for space-division multiple-access (SDMA) technology. For a SDMA VLC system, one of the major problems is high multi-user interference (MUI), especially in the case that different users have similar geometrical locations. In light of this, a reduced-complexity user-grouping algorithm with mutual spatial correlation as the user-grouping metric is developed. Within a timeslot, only the users with low correlation between each other are served simultaneously, while the users with high correlation are served in different timeslots. Further more, two kinds of optimal linear precoding designs are studied based on the results of user assignment. Groups of simulate results are taken to characterize the performance of both the user-grouping algorithm and the precoding design.

In the presented work, a comparative analysis of the bandwidth of information networks of mobile communications is carried out, with a change in the frequency resource of the network and the spatial selectivity of the antenna systems of base stations. It was shown that the use of adaptive antenna systems at the base station allows to achieve a significantly larger increase in network bandwidth compared to an increase in the frequency resource. It is also possible to implement parallel data reception with simultaneous suppression of interfering signals and to coordinate the maximum coverage area of the base station both in the downlink and in the uplink. This allowed us to propose methods to increase the bandwidth of the information network, based on spatial and random methods, in which complex signals are used to coordinate the energy budgets of the downlink and uplink.

This paper newly proposes a frequency domain backoff scheme dedicated to continuous beamforming space division multiple access (CB-SDMA) on massive antenna systems for wireless entrance (MAS-WE). The entrance base station (EBS) has individual base band signal processing units for respective relay stations (RSs) to be accommodated. EBS then continuously applies beamforming weight to transmission/reception signals. CB-SDMA yields virtual point-to-point backhaul link where radio resource control messages and complicated multiuser scheduling are not required. This simplified structure allows RSs to work in a distributed manner. However, one issue remains to be resolved; overloaded multiple access resulting in collision due to its random access nature. The frequency domain backoff mechanism is introduced instead of the time domain one. It can flexibly avoid co-channel interference caused by excessive spatial multiplexing. Computer simulation verifies its superiority in terms of system throughput and packet delay.

This paper investigates the spectral efficiency (SE) of downlink massive MIMO systems, where we consider the Ricean fading channels and utilize the zero forcing precoder at the base state. An exact expression for the SE is derived and the tight lower and upper bounds are presented by utilizing the modified Jensen’s inequality. Our results show that as the number of transmit antennas grows to infinite or in the high signal-to-noise ratios regime, the lower and upper bound coincide, which are approximately equal to the exact expression for the spectral efficiency of system. In addition, we reduce the Ricean fading channels to the Rayleigh fading case, a tractable lower bound of SE is obtained, which is shown that our results cover a series of previous works as special cases. Finally, numerical results are presented to validate the theoretical analysis.

Rate-Splitting Multiple Access (RSMA) is an emerging flexible, robust and powerful multiple access scheme for downlink multi-antenna wireless networks. RSMA relies on multi-antenna Rate-Splitting (RS) strategies at the transmitter and Successive Interference Cancellation (SIC) at the receivers, and has the unique ability to partially decode interference and partially treat interference as noise so as to softly bridge the two extremes of fully decoding interference (as in Non-Orthogonal Multiple Access, NOMA) and treating interference as noise (as in Space Division Multiple Access, SDMA or Multi-User Multiple-Input Multiple-Output, MU-MIMO). RSMA has been shown to provide significant room for spectral efficiency, energy efficiency, Quality-of-Service enhancements, robustness to Channel State Information (CSI) imperfections, as well as feedback overhead and complexity reduction, in a wide range of network loads (underloaded and overloaded regimes) and user deployments (with a diversity of channel directions, channel strengths and qualities). RSMA is also deeply rooted and motivated by recent advances in understanding the fundamental limits of multi-antenna networks with imperfect CSI at the Transmitter (CSIT). In this work, we leverage recent results on the optimization of RSMA and design for the first time its physical layer, accounting for modulation, coding (using polar codes), message split, adaptive modulation and coding, and SIC receiver. Link-level evaluations confirm the significant throughput benefits of RSMA over various baselines as SDMA and NOMA., Comment: 6 pages, 3 figures

The fifth-generation (5G) wireless networks will utilize higher frequency mmWave bands with wider bandwidth to increase system capacity in Ultra-Dense Network (UDN) scenarios. Massive multiple-input multiple-output (mMIMO) and beamforming (BF) technology have attracted much attention to compensate for path-loss at higher frequency bands. Using new protocols and procedures, e.g. spatial beam management, motivates to evaluate 3D Beamforming (3DBF) and Full-Dimensional MIMO (FD-MIMO) performance for Space Division Multiple Access (SDMA) with spatial separation of user equipment (UE) in UDN 5G wireless networks. Intelligent SDMA should take into account UE location and include preliminary positioning procedures to steer the transmitted signal of interest (SOI) toward the desired direction and simultaneously, avoiding signal of no interest (SNOI) transmission or reception from the unwanted direction. The purpose of this work is to evaluate the performance of interference suppression rate (ISR) as a relation of SOI to SNOI levels in 5G UDN using MISO (Multiple Input Single Output) when Base Station (BS) implements Adaptive Beamforming (AB) for two neighboring UE angular and distance separation scenarios. SOI to SNOI rate is evaluated for linear and planar antenna array patterns with several elements and contribute to the development of recommendations for UE separation in 5G UDN for spatial multiplexing and SDMA.

This paper studies optimal resource allocation in the wireless powered communication networks (WPCN) combined with time reversal (TR) in which one hybrid access point (H-AP) broadcasts constant wireless energy to a set of distributed users in the downlink (DL) and receives information from the users via space division multiple access (SDMA) in the uplink (UL). Inevitable interferences will occur when users transmit information in the UL simultaneously and the special space-time focusing of TR is used to suppress the interferences. An efficient protocol is proposed to support wireless energy transfer (WET) and TR in the DL and wireless information transmission in the UL for the proposed TR-WPCN. We optimize the time allocations to the H-AP for DL WET, DL TR, and UL WIT to maximize the sum throughput. Due to the nonconvexity of the studied optimization problem, we optimize variables successively, where the nonconvex optimization problem is transformed into the convex optimization problem. The approximate convex optimization problem can then be solved iteratively combined with the dichotomy method. Simulation results show that the proposed scheme can effectively suppress interferences and improve system performance.

In this study, the design of an adaptive medium access control (MAC) protocol based on the space-division–time-division multiple access (SD-TDMA) mechanism is presented to improve the utilisation and fairness of the time-slot allocation scheme in the vehicular ad hoc network. The SD-TDMA mechanism dynamically allocates time-slots owing to a dynamic topology. This protocol reduces transmission collisions through user detection procedures. Most users can thus access the service channel (SCH) without conflict and acquire time slots according to the mapping between geographic locations and time slots. Users failing to access the channel in user detection procedures can send request access packets in security channels to again participate in SCH time-slot allocation during the SCH interval. Simulations are conducted to evaluate the performance of the proposed method in urban scenarios. The SD-TDMA mechanism is compared with an SDMA-based MAC protocol, the IEEE 802.11p distributed coordination function and an MAC protocol based on transmission sequences. Owing to the decreased rate of transmission collisions and the dynamic time-slot allocation scheme, it is shown that the SD-TDMA mechanism provides a significantly higher utilisation of time slots and better fairness of data transmission than existing approaches.

We study the performance of space division multiple access (SDMA) under a non-ideal engineering situation. When the SDMA channel is of high inter-layer correlation and the condition number is large, the multiple user multiple input and multiple output user equipment (MUMIMOUE) grouping should be optimized, and in some cases further dimension-reduction should be applied. As the channel measuring is always non-ideal, we use two methods, feedback mode and non-feedback mode, in terms of performance and overhead. It is proposed that the non-feedback mode is preferable even for some non-reciprocal channels. Principle analysis and test results are given.

The data gathering technique in wireless sensor network may result in high latency, energy consumption and buffer overflow and less efficiency. In order to overcome these issues, this paper proposes a Cluster based Mobile Data Gathering technique using space division multiple access (SDMA) and particle swarm optimization (PSO) techniques. In this system, the sensor hubs are isolated into groups. Mobile data collectors (MDC) are deployed with multiple antennas which operate on SDMA technique. To schedule visiting locations of MDC, anchor points are selected using PSO algorithm. The wellness capacity of PSO is framed as far as network, hub degree, hub similarity and the separation between the sensors of two neighboring bunches. The MDC visits chose stays by arranging its timetable utilizing the minimum covering spanning tree Algorithm. When a MDC reaches the anchor point, the cluster members are scheduled to communicate with the MDG. Using the SDMA technique, two cluster members which are compatible can transmit the data simultaneously to the MDG. Simulation results prove that the vitality utilization and deferral are decreased while the packet delivery ratio is increased, if there should arise an occurrence of the proposed strategy.