Collaborative Beamforming Research Articles

Distributed Collaborative Beamforming in the Presence of Angular Scattering

In this paper, a collaborative beamformer (CB) is considered to achieve a dual-hop communication from a source to a receiver, through a wireless network comprised of K independent terminals. Whereas previous works neglect the scattering effect to assume a plane-wave single-ray propagation channel termed here as monochromatic (with reference to its angular distribution), a multi-ray channel termed as polychromatic due to the presence of scattering is considered, thereby broadening the range of applications in real-world environments. Taking into account the scattering effects, the weights of the so-called polychromatic CB (P-CB) are designed so as to minimize the received noise power while maintaining the desired power equal to unity. Unfortunately, their derivation in closed-form is analytically intractable due to the complex nature of polychromatic channels. However, when the angular spread (AS) is relatively small to moderate, it is proven that a polychromatic channel may be properly approximated by two rays and hence considered as bichromatic. Exploiting this fact, we introduce a new bichromatic CB (B-CB) whose weights can be derived in closed-form and, further, accurately approximate the P-CB's weights. Yet these weights, which turn out to be locally uncomputable at every terminal, are unsuitable for a distributed implementation. In order to circumvent this shortcoming, we exploit the asymptotic expression at large K of the B-CB whose weights could be locally computed at every terminal and, further, well-approximate their original counterparts. The performances of the so-obtained bichromatic distributed CB (B-DCB) and its advantages against the monochromatic DCB (M-DCB), which is designed without accounting for scattering, are analytically proved and further verified by simulations at practical values of K.

A Special Class of Fractional QCQP and Its Applications on Cognitive Collaborative Beamforming

In this paper, we investigate a special class of the fractional quadratically constrained quadratic problem (QCQP) with more than two quadratic constraints. We propose to effectively solve this special fractional QCQP by one or two convex semidefinite programmings (SDPs). For the two SDPs, one is equivalent to the original fractional QCQP with rank-one relaxation from the Charnes-Cooper transformation and the other, exploiting the optimal value of the former SDP, always has rank-one solution, which is optimal to the former SDP. Theoretical analysis shows that our proposed non-iterative SDP-based algorithm achieves the global optimal solution to the special fractional QCQP. In specific scenarios, our proposed non-iterative SDP-based algorithm has lower computational complexity compared to the second-order cone programming (SOCP)-based and constrained concave convex procedure (CCCP)-based iterative algorithms. We apply the proposed non-iterative SDP-based algorithm on two collaborative beamforming problems in cognitive relay networks, specifically, one is the achievable rate region for two-way non-regenerative cognitive relay networks and the other is the achievable secrecy rate for one-way regenerative cognitive relay networks. Simulation results have shown that our proposed non-iterative SDP-based algorithm achieves the same performance as the SOCP-based iterative algorithm. Our proposed algorithm achieves the better performance than the CCCP-based iterative algorithm.

Energy Efficient Collaborative Beamforming in Wireless Sensor Networks

Energy efficiency is a major design issue in the context of Wireless Sensor Networks (WSN). If the acquired data is to be sent to a far-away base station, collaborative beamforming performed by the sensors may help to distribute the communication load among the nodes and to reduce fast battery depletion. However, collaborative beamforming techniques are far from optimality and in many cases we might be wasting more power than required. We consider the issue of energy efficiency in beamforming applications. Using a convex optimization framework, we propose the design of a virtual beamformer that maximizes the network lifetime while satisfying a pre-specified Quality of Service (QoS) requirement. We derive both centralized and distributed algorithms for the solution of the problem using convex optimization and consensus algorithms. In order to account for other sources of battery depletion different from that of communications beamforming, we consider an additional random energy term in the consumption model. The formulation then switches to a probabilistic design that generalizes the deterministic case. Conditions under which the general problem is convex are also provided.

干扰温度约束下的一种新的中继选择策略

协作通信中的一个关键问题是如何分配和管理中继节点，尤其在次用户系统受到干扰温度约束条件下，协作方案的设计不仅要最大限度的提高系统性能，而且需要控制次用户系统对主用户系统的干扰。针对这种情况在次用户系统中提出一种基于协作波束形成中继选择策略，该方法以最小化次用户系统中断概率为目标，推导出一个中继选择门限，保证了有限的传输功率只分配给高效的中继链路，从而提高系统传输性能。仿真结果显示，该建议方法优于单中继转发方案和全中继转发方案，能有效降低次用户系统中断概率。One of the key problems in cooperative communication is how to allocate and manage the relay nodes, especially in the secondary user system under the interference temperature constraint. The design of the collaborative scheme should not only maximize the performance of the system, but also need to control the secondary user system’s interference in the primary user system. For this situation, a relay selection strategy is proposed based on the collaborative beamforming in the secondary user system. To minimize the outage probability of the secondary user system, a threshold is determined which only allocates the transmission power to the efficient relay links to improve the transfer performance of the system. The simulation results demonstrate that the proposed strategy can effectively reduce the outage probability of the secondary user system, and more over, it is better than the Single Relay Amplify-and-Forward (SAF) scheme and the All Relays Amplify-and-Forward (AAF) scheme.

Cooperative Spectrum Access Towards Secure Information Transfer for CRNs

In cognitive radio networks (CRNs), secure information transfer is of paramount importance for primary users (PUs), while secondary users (SUs) mainly desire to ease the starvation for transmission opportunities. To meet such different requirements, cooperation between PUs and SUs can be leveraged and therefore create a win-win situation. In this paper, we investigate cooperative spectrum access for CRNs, which targets to improve the secure transmission of PUs via cooperating SUs that would be incented by certain transmission opportunities. Two types of cooperation schemes are proposed, whereby the PU either cooperates with two individual SUs or a cluster of SUs, which are referred to as relay-jammer (R-J) scheme and cluster-beamforming (C-B) scheme, respectively. In R-J scheme, two individual SUs act as a relay and a friendly jammer to improve the PU's secrecy; In return, the PU allocates a fraction of access time for the SUs' transmission. To achieve the maximum secrecy rate, joint time and power allocation is considered. Particularly, the cooperating relay and jammer determine the optimal transmission power, while the PU decides the optimal time allocation strategy. In C-B scheme, the PU cooperates with a cluster of SUs to enhance the secrecy of the primary link via collaborative beamforming, where three different approaches are proposed for the scenarios with one eavesdropper, with multiple eavesdroppers, and without eavesdroppers' information, respectively. To maximize the secrecy rate, the weight selection and time allocation are also studied. Simulation results are given to validate the proposed schemes and demonstrate that the PU can significantly enhance the secrecy through cooperation.

Circular Collaborative Beamforming for Improved Radiation Beampattern in WSN

This paper presents a novel collaborative beamforming (CB) method of wireless sensor network (WSN) by organizing sensor node location in a circular arrangement. Appropriate selection of active CB nodes and cluster is needed each time to perform CB. The nodes are modeled in circular array location in order to consider it as a circular antenna array (CAA). This newly proposed circular collaborative beamforming (CCB) is further presented to solve two different objectives, that is, sidelobe level (SLL) suppression and first null beamwidth (FNBW). Analyses obtained are compared to those from previous work. The findings demonstrate a better CB performance of intelligent capability, and the difference is shown in normalized power characteristic.

Energy-efficient data dissemination using beamforming in wireless sensor networks

Energy conservation is essential in Wireless Sensor Networks (WSNs) because of limited energy in nodes' batteries. Collaborative beamforming uses multiple transmitters to form antenna arrays; the electromagnetic waves from these antenna arrays can create constructive interferences at the receiver and increase the transmission distance. Each transmitter can use lower power and save energy, since the energy consumption is spread over multiple transmitters. Each beamforming transmission requires multiple collaborative transmitters. Repetitively using the same transmitters will deplete their energy and create coverage holes in the sensing area. To prevent holes, energy should be balanced by using different transmitters. This article investigates the factors that can affect the energy consumption and network lifetime when using beamforming. We present an algorithm for selecting the transmitters in order to prolong the network lifetime. Compared with an existing beamforming transmitters scheduling algorithm, our algorithm doubles the network lifetime. When compared with direct transmission or multihop transmissions towards a receiver far away from the sensing area, our approach can increase the network's lifetime substantially.

SNR and throughput analysis of distributed collaborative beamforming in locally‐scattered environments

ABSTRACTThree main collaborative beamforming (CB) solutions based on different channel models exist: the optimal CSI‐based CB (OCB), the conventional or monochromatic (i.e., single‐ray) distributed CB (M‐DCB), and the recently developed bichromatic (i.e., two‐ray) distributed CB (B‐DCB). In this paper, we perform an analytical comparison, under practical constraints, between these CB solutions in terms of achieved signal‐to‐noise ratio (SNR) as well as achieved throughput. Assuming the presence of local scattering in the source vicinity and accounting for implementation errors incurred by each CB solution, we derive for the first time closed‐form expressions of their true achieved SNRs. For low angular spread (AS), where both solutions nominally achieve the same SNR in ideal conditions, we show that the B‐DCB always outperforms OCB, more so and at larger regions of AS values when errors increase. Excluding exceptional circumstances of unrealistic low quantization levels (i.e., very large quantization errors) that are hard to justify in practice, we also show that the new B‐DCB always outperforms the M‐DCB as recently found nominally in ideal conditions. This work is also the first to push the performance analysis of CB to the throughput level by taking into account the feedback overhead cost incurred by each solution. We prove both by concordant analysis and simulations that the B‐DCB is able to outperform, even for high AS values, the OCB which is penalized by its prohibitive implementation overhead, especially for a large number of collaborating terminals and/or high Doppler frequencies. Indeed, it is shown that the operational regions in terms of AS values over which the new B‐DCB is favored against OCB in terms of achieved throughput can reach up to 40°. Copyright © 2012 John Wiley & Sons, Ltd.

Relaying technologies for smart grid communications

Wireless technologies can support a broad range of smart grid applications including advanced metering infrastructure and demand response. However, there are many formidable challenges when wireless technologies are applied to the smart gird, such as the trade-offs between wireless coverage and capacity, the high reliability requirement for communication, and limited spectral resources. Relaying has emerged as one of the most promising candidate solutions for addressing these issues. In this article, an introduction to various relaying strategies is presented, together with a discussion of how to improve spectral efficiency and coverage in relay-based information and communications technology infrastructure for smart grid applications. Special attention is paid to the use of unidirectional relaying, collaborative beamforming, and bidirectional relaying strategies.

Optimal designs of collaborative relay-assisted multiuser beamforming for cellular systems

With careful calculation of signal forwarding weights, relay nodes can be used to work collaboratively to enhance downlink transmission performance by forming a virtual multiple-input multiple-output beamforming system. Although collaborative relay beamforming schemes for single user have been widely investigated for cellular systems in previous literatures, there are few studies on the relay beamforming for multiusers. In this paper, we study the collaborative downlink signal transmission with multiple amplify-and-forward relay nodes for multiusers in cellular systems. We propose two new algorithms to determine the beamforming weights with the same objective of minimizing power consumption of the relay nodes. In the first algorithm, we aim to guarantee the received signal-to-noise ratio at multiusers for the relay beamforming with orthogonal channels. We prove that the solution obtained by a semidefinite relaxation technology is optimal. In the second algorithm, we propose an iterative algorithm that jointly selects the base station antennas and optimizes the relay beamforming weights to reach the target signal-to-interference-and-noise ratio at multiusers with nonorthogonal channels. Numerical results validate our theoretical analysis and demonstrate that the proposed optimal schemes can effectively reduce the relay power consumption compared with several other beamforming approaches. Copyright © 2012 John Wiley & Sons, Ltd.

Collaborative Relay Beamforming Strategies for Multiple Destinations with Guaranteed QoS in Wireless Machine-to-Machine Networks

The Machine-to-Machine (M2M) communications allow information exchange between machine devices, which can be carried out without any human interaction. However, there are a large number of small and low-power machine devices in the wireless M2M networks. To guarantee the quality of service (QoS) requirements of the destination devices, we study the amplify-and-forward (AF) relay beamforming, where multiple relay M2M devices can transmit signals from the source M2M device to multiple destination M2M devices. In this paper, we propose two iterative strategies to jointly optimize the source antenna selection and the collaborative relay beamforming weights with the aid of perfect channel state information (CSI). The aim of the proposed strategies is to maximize the worst-case received signal-to-interference-and-noise ratio (SINR) under two different types of relay power constraints, which are the total relay power constraint and individual relay power constraints, respectively. Using the semidefinite relaxation (SDR) technique, the optimization problem of collaborative relay beamforming can be formulated as a semidefinite programming (SDP) problem, which can be optimally solved. Simulation results validate our theoretical analysis and demonstrate that after several iterations, the performance of the proposed iterative strategies can obtain near-optimal performance.

Collaborative Beamforming for Wireless Sensor Networks with Arbitrary Distributed Sensors

Collaborative beamforming (CB) has been widely used in a wireless sensor network (WSN) to improve the directivity of signals in long-distance transmission. CB performance has been analyzed for some specific node distributions such as Uniform and Gaussian distributions. However, the results obtained based on a particular distribution for a WSN under a specific condition may not be true for other WSNs under different conditions. This letter proposes a novel unified method to evaluate CB performance for various node distributions. The simulation results verify the proposed method.

Optimization of Collaborative Beamforming in Wireless Sensor Networks using Genetic Algorithm

Optimization of Collaborative Beamforming in Wireless Sensor Networks using Genetic Algorithm

Robust Peer-to-Peer Collaborative-Relay Beamforming with Ellipsoidal CSI Uncertainties

This letter considers a multiuser peer-to-peer communication network using a number of shared relays for collaborative beamforming and aims to minimize the total transmitted power of the relays whilst satisfying the targets of the signal-to-interference and noise ratios (SINRs) at the destination nodes by optimizing the relaying coefficients with imperfect channel state information (CSI). By deriving an equivalent form for the SINR constraints and an upper bound for the relay power, the problem can be tackled by solving a semi-definite program (SDP). Results reveal that the proposed technique outperforms significantly a conventional robust approach in terms of the transmitted power, and has only a mild increase in power if compared to the non-robust optimum which fails to meet the SINR targets.

A Distributed and Collaborative Beamforming algorithm for a self-organizing Wireless Sensor Network

In this paper the scenario where sensors of a Wireless Sensor Network (WSN) are able to process and transmit monitored data to a far collector is considered. The far collector may be a Base Station (BS) that gathers data from a certain number of deployed WSNs, in applications such as earthquake, tsunami, or pollution monitoring. In this paper, the possible use of Distributed and Collaborative BeaMForming (DC-BMF) technique is analyzed, with the goal of enhancing the capability of a single sensor to communicate its data to the far collector. This technique considers nodes as elements of a phased array, where the phases of the signals at each antenna node are linearly combined in order to adjust the directional gain of the whole array. In particular, a novel self-localization technique for WSNs performing DC-BMF is studied, a closed form solution for beamforming gain degradation is derived and the evaluation of the power consumption of the proposed DC-BMF algorithm is provided.

On Design of Collaborative Beamforming for Two-Way Relay Networks

We consider a two-way relay network, where two source nodes, S1 and S2, exchange information through a cluster of relay nodes. The relay nodes receive the sum signal from S1 and S2 in the first time slot. In the second time slot, each relay node multiplies its received signal by a complex coefficient and retransmits the signal to the two source nodes, which leads to a collaborative two-way beamforming system. By applying the principle of analog network coding, each receiver at S1 and S2 cancels the "self-interference" in the received signal from the relay cluster and decodes the message. This paper studies the 2-dimensional achievable rate region for such a two-way relay network with collaborative beamforming. With different assumptions of channel reciprocity between the source-relay and relay-source channels, the achievable rate region is characterized under two setups. First, with reciprocal channels, we investigate the achievable rate regions when the relay cluster is subject to a sum-power constraint or individual-power constraints. We show that the optimal beamforming vectors obtained from solving the weighted sum inverse-SNR minimization (WSISMin) problems are sufficient to characterize the corresponding achievable rate region. Furthermore, we derive the closed form solutions for those optimal beamforming vectors and consequently propose the partially distributed algorithms to implement the optimal beamforming, where each relay node only needs the local channel information and one global parameter. Second, with the non-reciprocal channels, the achievable rate regions are also characterized for both the sum-power constraint case and the individual-power constraint case. Although no closed-form solutions are available under this setup, we present efficient numerical algorithms.

Zero-Feedback, Collaborative Beamforming for Emergency Radio: Asymptotic Analysis

Collaborative beamforming among a set of distributed terminals is studied, assuming a) no specialized RF hardware for carrier frequency synchronization, and b) zero feedback from destination (either in the form of pilot signals or explicit messages). Our goal is to provide a solution for conventional radios (not necessarily wideband), when the link between a single source transmitter and destination is too weak, so that no signal can be reliably received at the destination. In such critical case, zero feedback messages from destination to the multiple transmitters cannot be assumed, even when the destination is equipped with powerful hardware. A solution is provided for conventional radios in relevant critical applications, such as in emergency radio. The proposed scheme simply exploits lack of synchronization among distributed carriers, operating at the same nominal carrier frequency. It is shown that such beamforming is possible and its performance is analytically quantified. Results include asymptotic analysis for the case of large number of transmitters.

The Effect of Local Scattering on the Gain and Beamwidth of a Collaborative Beampattern for Wireless Sensor Networks

Collaborative beamforming is an approach where sensor nodes in a wireless sensor network, deployed randomly in an area of interest, transmit a common message by forming a beampattern towards a destination. Previous statistical analysis of the averaged power beampattern considered multipath-free conditions. Herein, we express the averaged power beampattern when the signal is observed at the destination in the presence of local scattering. Assuming the spreading angles are uniformly distributed around the destination direction, we derive closed-form expressions for the maximum gain and numerically examine the beamwidth as a function of the number of nodes, the cluster size, and the scattering parameters, for node positions with a uniform distribution or a Gaussian distribution.

Sidelobe Control in Collaborative Beamforming via Node Selection

Collaborative beamforming (CB) is a power efficient method for data communications in wireless sensor networks (WSNs) which aims at increasing the transmission range in the network by radiating the power from a cluster of sensor nodes in the directions of the intended base station(s) or access point(s) (BSs/APs). The CB average beampattern expresses a deterministic behavior and can be used for characterizing/controling the transmission at intended direction(s), since the mainlobe of the CB beampattern is independent on the particular random node locations. However, the CB for a cluster formed by a limited number of collaborative nodes results in a sample beampattern with sidelobes that severely depend on the particular node locations. High level sidelobes can cause unacceptable interference when they occur at directions of unintended BSs/APs. Therefore, sidelobe control in CB has a potential to increase the network capacity and wireless channel availability by decreasing the interference. Traditional sidelobe control techniques are proposed for centralized antenna arrays and, therefore, are not suitable for WSNs. In this paper, we show that distributed, scalable, and low-complexity sidelobe control techniques suitable for CB in WSNs can be developed based on node selection technique which make use of the randomness of the node locations. A node selection algorithm with low-rate feedback is developed to search over different node combinations. The performance of the proposed algorithm is analyzed in terms of the average number of trials required to select the collaborative nodes and the resulting interference. Our simulation results approve the theoretical analysis and show that the interference is significantly reduced when node selection is used with CB.

Opportunistic collaborative beamforming with one-bit feedback

An energy-efficient opportunistic collaborative beamformer with one-bit feedback is proposed for ad hoc sensor networks transmitting a common message over independent Rayleigh fading channels to a relatively distant destination node. In contrast to conventional collaborative beamforming schemes in which each relay node uses channel state information (CSI) to pre-compensate for its channel phase and local carrier offset, the relay nodes in the proposed beamforming scheme do not perform any phase precompensation. Instead, the destination node broadcasts a relay node selection vector to the pool of available relay nodes to opportunistically select a subset of relay nodes whose transmitted signals combine in a quasicoherent manner at the destination. Since the selection vector only indicates which relay nodes are to participate in the collaborative beamformer and does not convey any CSI, only one bit of feedback is required per relay node. Theoretical analysis shows that the received signal power obtained with the proposed opportunistic collaborative beamforming scheme scales linearly with the number of available relay nodes under a fixed total power constraint. Since computation of the optimal selection vector is exponentially complex in the number of available relays, three low-complexity sub-optimal relay node selection rules are also proposed. Simulation results confirm the effectiveness of opportunistic collaborative beamforming with the low-complexity relay node selection rules.