Random Beamforming Research Articles

Energy‐efficient scheme using multiple antennas in secure distributed detection

Here, the authors propose an energy-efficient strategy using multiple antennas for secure distributed detection in wireless sensor networks (WSNs). In multiple access channel, it is possible to communicate between sensors and ally fusion centre with perfect secrecy by an encryption with channel state information (CSI). However, the sensors in an active group may need to constantly report in the encryption as long as the CSI remains unchanged, which deteriorates the energy efficiency in terms of the lifetime of WSN. The authors solve the problem by using random beamforming (e.g. antenna subset modulation). Furthermore, the authors investigate the impact of the number of active antennas on the network lifetime. Through the analysis and simulation, the authors demonstrate that the proposed strategy has a higher energy efficiency than the conventional strategy, while maintaining the same reliability and security.

A New Approach to User Scheduling in Massive Multi-User MIMO Broadcast Channels

In this paper, a new two-phase-feedback-based user-scheduling-and-beamforming method is proposed for multi-user multiple-input multiple-output downlink in the context of two-stage beamforming. The key ideas of the proposed method are: 1) to use a set of orthogonal reference beams and construct a cone around each reference beam to select “nearly-optimal” semi-orthogonal users based only on channel quality indicator feedback; and 2) to apply post-user-selection beam design with zero-forcing beamforming (ZFBF) based on channel state information (CSI) feedback only from the selected users. It is proven that the proposed scheduling-and-beamforming method is asymptotically optimal as the number of users increase. Furthermore, the proposed scheduling-and-beamforming method almost achieves the performance of the existing semi-orthogonal user selection with ZFBF that requires full CSI for all users, with a significantly reduced amount of required channel information which is even less than that required by random beamforming.

Optimal User Scheduling and Power Allocation for Millimeter Wave NOMA Systems

This paper investigates the application of non-orthogonal multiple access (NOMA) in millimeter wave (mm-Wave) communications by exploiting beamforming, user scheduling, and power allocation. Random beamforming is invoked for reducing the feedback overhead of the considered system. A non-convex optimization problem for maximizing the sum rate is formulated, which is proved to be NP-hard. The branch and bound approach is invoked to obtain the $\epsilon$ -optimal power allocation policy, which is proved to converge to a global optimal solution. To elaborate further, a low-complexity suboptimal approach is developed for striking a good computational complexity-optimality tradeoff, where the matching theory and successive convex approximation techniques are invoked for tackling the user scheduling and power allocation problems, respectively. Simulation results reveal that: 1) the proposed low complexity solution achieves a near-optimal performance and 2) the proposed mm-Wave NOMA system is capable of outperforming conventional mm-Wave orthogonal multiple access systems in terms of sum rate and the number of served users.

Sum Rate Analysis for Multi-Cell Random Beamforming With Heterogeneous Schedule Probabilities

In this letter, the closed form sum rate for the random beamforming is analyzed over the downlink multiple-input single-output and multiple input multiple-output interfering broadcast channel with finite users. The analysis approach is based on the limiting throughput distribution theorem, and can be applied for the multi-cell interference scenarios with heterogeneous signal to interference-plus-noise ratio (SINR) distributions and user schedule probabilities. It is proved that both the exact and the asymptotic sum rates achieved from SINR/signal-to-interference ratio analysis will converge to the Gumbel type distribution. The effectiveness of the proposed analytical framework is confirmed by simulation results.

Low-Complexity QoS-Aware Coordinated Scheduling for Heterogeneous Networks

In this paper, we consider a heterogenous network in which low-power indoor femtocells are deployed in the coverage area of the existing macrobase station (MBS). This paper proposes a novel coordinated random beamforming and user-scheduling strategy to improve the throughput of users served by the femtocell access point (FAP) while satisfying the quality-of-service (QoS) requirements of users served by both MBS and FAP. The strategy, termed as QoS-aware coordinated scheduling (QACS), requires limited coordination between the MBS and FAP, i.e., only the indexes of the qualified beams are shared. Exact statistical analysis for the ergodic achievable rate of both FAP and MBS with the proposed strategy are presented. Scheduling fairness is also addressed for the proposed QACS.

Performance analysis of random beamforming for multiuser spectrum sharing networks

This study analyses a comprehensive performance of multiuser spectrum sharing networks using random beamforming (RBF). In the considered cognitive radio (CR) system, a secondary broadcast station (SBS) coexisting with a pair of primary transceivers broadcasts the information to multiple secondary users. The authors first consider that the CR-RBF system does not undergo interference from the primary network. In doing so, an exact expression is derived for the cumulative distribution function (CDF) of signal to interference plus noise ratio (SINR). Resorting to the derived CDF, the authors obtain an exact closed-form expression of outage probability. In addition, the closed-form expressions of the moment of SINR and other performance are provided, respectively, which provide an efficient method to evaluate key parameters on the considered system. Next, the authors also consider that the CR-RBF system undergoes interference from the primary network. Numerical simulations are presented to validate the correctness of the authors' analytical results. Unlike non-CR RBF system, increasing the number of antennas improves the performance achieved by CR-RBF systems when the maximum allowable power of SBS is less than a certain value. Otherwise, increasing the number of antennas decreases the performance achieved by CR-RBF systems.

Degrees of Freedom of the MIMO $2 \times 2$ Interference Network with General Message Sets

We establish the degrees of freedom (DoF) region for the multiple-input multiple-output (MIMO) two-transmitter, and two-receiver ( $2 \times 2$ ) interference network with a general message set consisting of nine messages, one for each pair of a subset of transmitters at which that message is known and a subset of receivers where that message is desired. An outer bound on the general nine-message $2 \times 2$ interference network is obtained and it is shown to be tight, thereby establishing the DoF region for the most general antenna setting wherein the four nodes have an arbitrary number of antennas each. The DoF-optimal scheme is applicable to the MIMO $2 \times 2$ interference network with constant channel coefficients, and hence, a fortiori , to time/frequency varying channel scenarios. In particular, a linear precoding scheme is proposed that can achieve all the DoF tuples in the DoF region. In it, the precise roles played by transmit zero-forcing, interference alignment, random beamforming, symbol extensions, and asymmetric complex signaling (ACS) are delineated. For instance, we identify a class of antenna settings, in which ACS is required to achieve the fractional-valued corner points. Evidently, the DoF regions of all previously unknown cases of the $2 \times 2$ interference network with a subset of the nine-messages are newly established as special cases of the general result of this paper. For instance, the DoF region of the well-known four-message (and even three-message) MIMO $X$ channel is newly established. This problem had remained open despite previous studies, which had found inner and outer bounds that were not tight in general. Hence, the DoF regions of all special cases obtained from the general DoF region of the nine-message $2\times 2$ interference network of this paper that include at least three of the four $X$ channel messages are new, among many others. This paper sheds light on how the same physical $2 \times 2$ interference network could be used by a suitable choice of message sets to take most advantage of the channel resource in a flexible and efficient manner.

Random Beamforming in Millimeter-Wave NOMA Networks

This paper investigates the coexistence between two key enabling technologies for the fifth generation (5G) mobile networks, non-orthogonal multiple access (NOMA) and millimeter-wave (mmWave) communications. Particularly, the application of random beamforming to the addressed mmWave-NOMA scenario is considered in this paper, in order to avoid the requirement that the base station knows all the users' channel state information. Stochastic geometry is used to characterize the performance of the proposed mmWave-NOMA transmission scheme, by using the key features of mmWave systems, e.g., mmWave transmission is highly directional and potential blockages will thin the user distribution. Two random beamforming approaches which can further reduce the system overhead are also proposed to the addressed mmWave-NOMA communication scenario, where their performance is studied by developing analytical results about sum rates and outage probabilities. Simulation results are also provided to demonstrate the performance of the proposed mmWave-NOMA transmission schemes and verify the accuracy of the developed analytical results.

Combined Beamforming with Orthogonal Space Time Block Code for MIMO-OFDM with Simple Feedback

<p>In this paper, we introduce a proposed scheme to enhance the performance of orthogonal space time block code (OSTBC) with four time slots and two antennas by combing OSTBC with random beamforming to can use it in the downlink transmission for a mobile system. Multiple-input multiple-output orthogonal frequency-division multiplexing (MIMO-OFDM) system has been recognized as one of the most promising techniques to achieve a good service and increase data rate in the next generation (4&5G) broadband wireless communications. So, we apply Space time block code (STBC) for MIMO-OFDM system with linear decoding. Also, we perform STBC with beamforming for MIMO-OFDM system to improve the performance of a system. Simulation results show that the beamforming improves bit error rate (BER) performance of OSTBC and STBC-OFDM for different types of modulation and diversity.</p>

Power Beacon Assisted Wiretap Channels With Jamming

This paper proposes a novel power beacon-assisted wiretap channel, where an energy constrained source, powered by a dedicated power beacon, aims to establish secure communications with a legitimate user in the presence of an eavesdropper. The power beacon and the source are assumed to have multiple antennas, while the legitimate user and the eavesdropper are equipped with a single antenna each. Considering a time-switching protocol, the power beacon first charges the source through wireless power transfer, and then acts as a friendly jammer to assist the source for secure communication. Depending on the available channel state information (CSI) at the power beacon, we propose several different jamming schemes for secrecy performance enhancement. Closed-form expressions are derived for the achievable secrecy outage probability of the proposed schemes. In addition, simple and accurate approximations are obtained at the high signal-to-noise ratio regime. The outcomes suggest that jamming is an effective approach to improve the secrecy performance: with full CSI available at the power beacon, employing simple zero-forcing scheme attains significant secrecy diversity gain and without the CSI of the eavesdropper link, jamming provides only some array gain. Moreover, we show that the proposed limited feedback-based random beamforming is an effective approach, which may outperform the antenna selection scheme. Furthermore, numerical results reveal that there exists a unique time switching ratio that maximizes the effective secrecy throughput.

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.

Non-orthogonal multiple access in a downlink multiuser beamforming system with limited CSI feedback

Non-orthogonal multiple access (NOMA) has been recognized as a promising multiple access technology for fifth generation (5G) mobile communication system. However, the advantage of NOMA is only verified under the ideal condition that the transmitter has the perfect knowledge of channel state information (CSI). In this paper, NOMA downlink multiuser system, in which the transmitter acquires the CSI through limited feedback channel, is studied. Two traditional beamforming technologies, zero-forcing beamforming and random beamforming, are investigated in the NOMA downlink multiuser system. Making use of the imperfect CSI feedback, channel direction information (CDI), and channel quality indicator (CQI), we propose the user selection scheme to reduce the interference between the NOMA users. Furthermore, a power allocation scheme is proposed to improve the sum-rate of NOMA system. Numerical results show that NOMA system with limited feedback channel still gains larger system rate than traditional orthogonal multiple access system. It is also shown that random beamforming is more suitable for the NOMA system with limited CSI feedback.

Performance of Quantized Random Beamforming in Delay-Tolerant Machine-Type Communication

Machine-to-machine (M2M) communication represents a new paradigm for mobile cellular networks, where a massive number of low-cost devices request the transfer of small amounts of data without human intervention. One option to tackle this problem is obtained by combining random beamforming (RBF) with opportunistic scheduling. RBF can be used to induce larger channel fluctuations, and opportunistic scheduling can be used to select M2M devices when their overall channel quality is good. Traditional RBF does not fulfill M2M requirements, because overall channel quality needs to be tracked continuously. In order to tackle this limitation, a novel codebook-based RBF architecture that identifies in advance the time instants in which overall channel quality should be reported, within a coherence time window, is proposed. This opportunistic feedback mechanism reduces signaling overhead and enables energy saving at M2M devices. A simplified methodology is presented to evaluate the system mean data rate, using for this purpose closed form formulas derived from SNR distribution approximations. Results reveal that the performance loss that is experienced for introducing the proposed modifications to traditional RBF scheme is negligible. The concepts analyzed in this paper provide useful insights, and show that codebook-based RBF with simplified opportunistic scheduling algorithms is an excellent combination to provide wide-area M2M services with low-cost devices and limited signaling overhead.

Random Beamforming in Millimeter-Wave NOMA Networks

This paper investigates the coexistence between two key enabling technologies for the fifth generation (5G) mobile networks, non-orthogonal multiple access (NOMA) and millimeter-wave (mmWave) communications. Particularly, the application of random beamforming to the addressed mmWave-NOMA scenario is considered in this paper, in order to avoid the requirement that the base station knows all the users' channel state information. Stochastic geometry is used to characterize the performance of the proposed mmWave-NOMA transmission scheme, by using the key features of mmWave systems, e.g., mmWave transmission is highly directional and potential blockages will thin the user distribution. Two random beamforming approaches which can further reduce the system overhead are also proposed to the addressed mmWave-NOMA communication scenario, where their performance is studied by developing analytical results about sum rates and outage probabilities. Simulation results are also provided to demonstrate the performance of the proposed mmWave-NOMA transmission schemes and verify the accuracy of the developed analytical results.

Opportunistic vector channel estimation based on scalar feedback

AbstractMulti‐user diversity exploits channel fluctuations by favouring the user with the best channel. In slow fading environments, channel fluctuations are artificially created by the use of random beamforming at the transmitter, a technique called opportunistic beamforming. One drawback of opportunistic beamforming is that, it needs large number of users to achieve the capacity of a true beamforming system. On the other hand, if partial channel state information is available at the transmitter, this can be used to reduce the necessary number of users to reach this capacity. Opportunistic beamforming systems require scalar feedback from users in the system instead of the complete channel vector to reduce the feedback load. In conventional systems, these feedback values are used for scheduling only. In this letter, we propose three channel estimation methods that solely rely on the scalar feedback already available at the transmitter. We also propose an accompanying scheduling method where these estimates are used to form the beamforming vectors. Although we use the same information available in a conventional opportunistic beamforming system, the proposed scheduling scheme in conjunction with channel estimation is able to achieve higher throughput and also achieve better fairness which is verified by simulations. Copyright © 2016 John Wiley & Sons, Ltd.

Cooperative Secondary Beam Selection for Cognitive Multiuser MIMO Transmission With Random Beamforming

This paper studies the performance of a random beamforming-based secondary MIMO system, which coexists with a primary system with single primary transmitter (PT) and single primary receiver (PR). To ensure the performance requirement of the primary system, i.e., the received signal-to-interference-plus-noise-ratio (SINR) at PR is larger than a predefined threshold, we assume that the usability of the beam-forming vectors of the secondary MIMO system are determined with the cooperation from PR. Specifically, we propose cooperative beam selection strategies for the secondary MIMO system considering both single-user and multiuser transmission. For both cases, the PR only needs to feed back to the secondary base station (SBS) its received signal power from PT, based on which the SBS calculates the received SINR at PR corresponding to each beam, and decides those usable beams that satisfy the performance requirement of the primary system. The SBS then selects the best beam from all usable beams to serve its user. For the multiuser case, we propose and compare two cooperative beam selection strategies for the secondary MIMO system to select a maximal number of active beams for transmission, while ensuring the received SINR at PR is above the predefined SINR threshold. For both single user and multiuser case, we analyze the outage probability of the primary system and the throughput/sum-rate of the secondary system, based on which we investigate the performance tradeoff between primary and secondary systems.

On the Performance of Random Beamforming in Sparse Millimeter Wave Channels

The performance of random beamforming (RBF) with partial channel state information (CSI) feedback is investigated here for millimeter wave (mmWave) multiuser multiple-input single-output (MU-MISO) downlink systems using the uniform random multipath (UR-MP) channel model. In particular, the required number of users in the cell for RBF to yield linear sum rate scaling with respect to the number of transmit antennas is identified under the UR-MP channel model for different levels of channel sparsity. Then, the problem of user scheduling in MU-MISO downlink is considered when the number of users in the cell is not sufficiently large (sparse user regime) for the system to operate in the identified sufficient user regime. By exploiting the sparsity of mmWave radio channels, several user scheduling algorithms based on beam aggregation with reasonable amount of feedback are proposed for the sparse user regime. Our numerical results show that the proposed algorithms yield very good sum-rate performance in sparse mmWave channels.

Randomly-Directional Beamforming in Millimeter-Wave Multiuser MISO Downlink

In this paper, the performance of opportunistic random beamforming (RBF) and the multiuser (MU) gain in millimeter-wave (mm-wave) MU multiple-input single-output (MISO) downlink systems are analyzed based on the uniform random single-path (UR-SP) channel model suitable for highly directional mm-wave radio propagation channels. It is shown that under the UR-SP channel model, RBF achieves linear sum rate scaling with respect to (w.r.t.) the number of transmit antennas and, furthermore, yields optimal sum rate performance when the number of transmit antennas is large, if the number of users increases linearly w.r.t. the number of transmit antennas. Several beam training and user selection methods are investigated to yield insights into the most effective beamforming and scheduling choice for mm-wave MU-MISO in various operating conditions. Simulation results validate our analysis based on asymptotic techniques for finite cases.

Multihop Connectivity of Ad Hoc Networks With Randomly Oriented Directional Antennas

Directional antennas and beamforming can significantly improve point-to-point wireless links when perfectly aligned. In this letter we investigate the extreme opposite where antenna orientations and positions are chosen at random in the presence of Rayleigh fading. We show that while the 1-hop network connectivity is deteriorated, the multihop routes improve, especially in the dense regime. We derive closed form expressions for the expectation of the 1-hop and 2-hop degree, which are verified through computer simulations. We conclude that node density does not greatly affect the number of hops required between stations while simple random beamforming schemes do, thus returning substantial network performance benefits due to the existence of shorter multi-hop paths.

Joint Space–Frequency User Scheduling for MIMO Random Beamforming With Limited Feedback

This paper presents a joint space–frequency user scheduling approach to enhance the random beamforming (RBF) with limited feedback in multiple-input –multiple-output (MIMO) broadcast channels. Such scheme was shown to obtain the optimal scaling law of sum rate in the large number of user regime. However, for a small number of user cases, the system degrees-of-freedom cannot be well exploited, and the accuracy of predicting users' signal-to-interference-plus-noise ratios (SINRs) is also degraded. Motivated by these, two strategies are proposed to solve the problems. Specifically, the conventional spatial domain RBF is first extended to the space–frequency domain. The first strategy aims to maximize the number of active users based on users' initially predicted SINRs; the second strategy is to schedule the maximum number of users, whose preferred beams can coexist with each others, with more accurate users' SINRs prediction method. Computer simulations are carried out to examine the proposed strategies in terms of the sum rate and the number of active users. It is shown that the first strategy achieves close performance to the corresponding brute-force search with lower complexity. Moreover, the second strategy improves the performance by accurately predicting users' SINRs at the price of relatively increased complexity and feedback overhead.