Beamforming Matrix Research Articles

A Precoding Method for Multiple Antenna System on the Riemannian Manifold

In this paper, a precoding scheme for multiple antenna systems with space-time coding over correlated Ricean channels is proposed. Based on the channel mean and receive- side spatial correlation, the proposed scheme obtains the solution of the power allocation and beamforming matrix of the precoder iteratively. Unlike most of existing precoder designs in literatures that have expensive computations and cannot guarantee the design algorithms to converge, the convergence of the proposed scheme is guaranteed. By exploiting the special structure of beamforming matrix, a steepest descent method on the Riemannian manifold is proposed for the optimization of beamforming matrix. Simulation results show that the proposed optimal scheme not only achieves superior bit error rate (BER) performance to those of the existing ones, but also provides a guaranteed-convergent solution under different channel conditions. 

DESIGN AND IMPLEMENTATION OF A COMPACT PRACTICAL PASSIVE BEAM-FORMING MATRIX FOR 3D S-BAND RADAR

In this paper a compact two-layer microstrip passive beam-forming matrix in the 2.9- 3.1 GHz frequency band is designed, fabricated, and measured. This 13 × 6 matrix is a passive circuit that can transform the 13 patterns of an antenna array into six possible beams to decrease the complexity for multiplexing/demultiplexing operation in three dimensional Radar. The 90 degrees hybrid couplers with high isolation between two signals and phase shifters between the couplers are used to provide proper signals in outputs. The matrix structure consists of metal walls around transmission lines to eliminate the surface waves. Also, a coaxial to microstrip transition is used to extract accurate measurement results. A special box is designed to cover matrix which has many design considerations such as cutoff frequency, destructive effects on couplers and other parts of matrix, and all of these effects are analyzed and considered to achieve the optimum performance in this paper. The matrix is designed on a substrate Rogers RT5880 with er =2 .2, substrate height = 0.787 mm, and loss tangent = 0.0009. Also the thickness of the copper cladding layer is 17µm. The maximum amplitude and phase errors in outputs are 0.6 dB and 7 ◦ , respectively, and VSWRs are less than 1.35 in the matrix bandwidth with at least 20 dB isolation between all ports.

Novel compact inverted U‐shaped directional coupler using parallel dual transmission lines technique

ABSTRACTA novel compact design of a 3‐dB inverted U‐shaped directional coupler using dual parallel transmission lines on double layer substrates is presented in this article. Dual parallel transmission lines technique is used as a replacement of the conventional single transmission line. Hence, a smaller size and wider bandwidth of directional coupler is successfully achieved. The proposed coupler is highly adaptable to various microwave applications for microwave circuitry such as the Butler Matrix (BM) beamforming network. The reduction in size gives better flexibility for the integrated structure of BM system. The proposed 2.45‐GHz coupler successfully obtaining size reduction up to 40% compared to the rectangular multilayer directional coupler. In addition, 25% bandwidth performance was achieved. Dimension and S‐parameter performance comparison has been made between the proposed coupler which use dual parallel transmission lines technique in multilayer structure and rectangular multilayer coupler. The measurement results are in good agreement with simulated ones in terms return loss, coupling, through and isolation. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:251–256, 2014

An Beamforming Algorithm on Limited Feedback MIMO two-Way Relay Cognitive Networks

In this paper, we study many antenna beamforming algorithm research in cognitive radio two-way relay system. In this system, two primary users exchange information by second users, and the second users to configure multiple antennas, a user through the superposition signal sends it to the primary users, therefore in this article research the key problem is how to divide the primary user information of the signal power and power of user information signal; How to design the main users of beamforming matrix; How to design the beam forming matrix of users. This paper uses the maximum system capacity optimization guidelines, even is a convex optimization problem, this paper adopts positive semidefinite optimization and second-order cone optimization, closed solution is obtained. The simulation results show that this method due to previous beam forming algorithm.

Beamspace Root-MUSIC Algorithm for Joint DOD DOA Estimation in Bistatic MIMO Radar

The computational complexity for the direction of departure (DOD) and direction of arrival (DOA) estimation in bistatic MIMO radar increases very rapidly with the number of sensors. To reduced computational complexity, a beamspace Root-MUSIC algorithm for joint DOD and DOA is proposed in this paper. Ingenuous mathematical manipulations utilizing the properties of common out-of-band nulls offered by discrete Fourier transform matrix beamformer are proposed to restore the Vandermonde structure with a reduced degree, which is lost in beamspace transformation for both the transmit array and the receive array. Then the DOD and DOA can be estimated via polynomials root finding procedure. The proposed algorithm can work in reduced dimension beamspace data and reduced degree polynomial root finding procedure in the final stage of Root-MUSIC. Moreover, automatic paring between the DODs and DOAs can be obtained. Simulation results demonstrate that the effectiveness of the proposed algorithm.

QoS Guarantees in AF Relay Networks with Multiple Source-Destination Pairs in the Presence of Imperfect CSI

A relay network approach is proposed that allows multiple source-destination pairs to communicate simultaneously. The communication is enabled by a multi-antenna amplify-and-forward relay and is implemented in two slots; in the first slot, the sources transmit, and in the second slot, the relay forwards the received signals after processing them through a Zeroforcing Beamforming (ZFBF) matrix. The relay determines the ZFBF matrix so that the transmit power is minimized while the SINR of each destination meets a predefined constraint. Initially, the design is based on perfect channel state information (CSI). Imperfect CSI results in interference at the destinations. This effect can be controlled by increasing the number of relay antennas, or by optimally selecting the antennas to be used. Antenna selection schemes are proposed, which minimize the outage probability, or the destination interference. Also, an iterative scheme is proposed, whereby the amplitudes of the beamforming weights of all source-destination pairs are iteratively increased so that the worst case SINRs meet the requirements of the destinations. It is shown that this approach, coupled with antenna selection, greatly reduces the outage probability.

Reduced Complexity Beamforming with Optimal Power Allocation in Two-Way Multi-Antenna Relay Systems

This paper introduces a new beamforming method for a two-way relay system, where two single-antenna terminals exchange messages via a multi-antenna amplify-and-forward (AF) relay operating in the half-duplex mode. The optimization problem under consideration is to design a relay beamforming matrix that maximizes the achievable weighted sum rate under the relay power constraint, given the channel state information. This problem is non-convex, and iterative optimization algorithms and suboptimal beamformers with reduced complexity have been developed in previous works. In this paper, we develop an alternative suboptimal scheme by converting the original non-convex optimization into convex optimization. This conversion is made possible through some changes of variables and an additional condition. The simulation results demonstrate that the proposed method performs almost as well as the optimal scheme and can yield larger achievable rates than conventional suboptimal beamformers.

Beamforming in Non-Regenerative MIMO Broadcast Relay Networks

This paper studies a multiple-input multiple-output (MIMO) broadcast relay channel (BRC), in which a multiple-antenna base station (BS) communicates with multiple-antenna users through an infrastructure-based multiple-antenna relay station (RS). Applying dirty paper coding (DPC) at the BS and linear processing at the RS, our aim is to find the input covariance matrices and the RS beamforming matrix that maximize the system sum-rate. To solve this non-convex problem, a more tractable dual multiple access relay channel (MARC) is investigated and an alternating-minimization algorithm is proposed. Furthermore, the mapping from the resulting covariance matrices for the MARC to the covariance matrices for the BRC is derived. Unlike other existing single-antenna-user schemes, our solution is applicable to a more general network with any number of antennas at the users. Compared with two such single-antenna-user schemes, simulations show that the proposed scheme outperforms the all-pass relay design and performs similarly to the SVD-relay design. Moreover, the proposed design performs close to the sum-rate upper bound with the performance gap decreasing with increasing number of antennas per user. It is also observed that having more antennas at the RS than at the BS is desirable for better system performance.

A 60-GHz Active Receiving Switched-Beam Antenna Array With Integrated Butler Matrix and GaAs Amplifiers

This paper presents for the first time a 60-GHz receiving switched-beam antenna on organic liquid crystal polymer (LCP) platform. A 4 × 1 quasi-Yagi array is incorporated with a 4 × 4 Butler matrix beamforming network and GaAs low-noise amplifiers on an LCP substrate. The active beam is controlled by GaAs single-pole-double-throw switches to access the four output states of the Butler matrix. The entire 4 × 1 active array is 1.4 cm × 1.75 cm and consumes 1.1 W of dc power. Successful comparisons of the measured and simulated results verify a working phased array with a return loss better than 10 dB across the frequency band of 56.7-63.7 GHz. A comparison of radiation patterns demonstrate beam steering of ±40° with a peak active gain of 27.5 dB. The combined antenna and receiver noise performance at 60 GHz exhibits an estimated merit G/T of -18.6 dB/K and noise figure of 5.4 dB.

MIMO Broadcast Channels Based on SINR Feedback using a Non-Orthogonal Beamforming Matrix

The signal to interference plus noise ratio (SINR) feedback has been utilized in random beamforming (RBF) to select users for multiple-input multiple-output (MIMO) systems where a large number of users are required to obtain a multi-user diversity gain. However, if the number of users is not large enough, it may be difficult to obtain the performance gain and be easy to have a performance degradation conversely. To resolve this problem, it is necessary to find orthogonal random beams close to the channel matrix of selected users. In this paper, we present RBF using a non-orthogonal beamforming matrix (RBF NOBM), demonstrating an efficient search of random beams correlated with the channel matrix of selected users over a small number of users. For single user RBF using NOBM (SU-RBF NOBM) with two transmit antennas, the beamforming matrix for user data service is obtained through closed form expressions, and SU-RBF NOBM is then expanded to more than two transmit antennas. We also propose user selection algorithms for SU-RBF NOBM and multi-user RBF using NOBM (MU-RBF NOBM). Via simulation results, we demonstrate that the performances of RBF NOBM represent significant improvements compared to conventional beamforming schemes.

다중 사용자 MIMO 시스템에서 최소 제곱 기법을 이용한 새로운 간섭 정렬 기법

In this paper, the scheme for designing optimal beamforming matrix for interference control is proposed. The optimal beamforming matrix is found though linear combination of interference alignment conditions and renewal of linear combination coefficient. The proposed scheme has advantages that the complexity is reduced and there is no multiplying operation in matrix calculations even if proposed scheme has the form similar to that of existing least square based scheme. The simulation results show that proposed scheme has about 4bps/Hz higher gain than existing least square scheme. Also there is no additional multiplying calculation and increase of matrix size when the number of transmit and receive antennas is increased.

Beamforming matrix quantization with variable feedback rate

We propose a new technique to quantize and feedback the parameters when a beamforming matrix is compressed with the Givens Rotation (GR). We suggest to feedback the parameters with variable feedback rate, and use efficient source coding and codebook to quantize the GR parameters. The variable feedback rate means that the number of bits used to represent the quantized beamforming matrix is based on the value of the matrix itself. And due to the non-uniform distribution of the GR parameters, source coding and code book can be designed to quantize those parameters in a more effective manner. Compared with the fixed feedback rate scheme, the proposed method delivers a better performance without incurring additional feedback bandwidth.

Cooperative Beamforming for Single-Carrier Frequency-Domain Equalization Systems with Multiple Relays

We consider cooperative beamforming (BF) for block-based single-carrier frequency-domain equalization (SC- FDE) in a wireless network consisting of one single-antenna source, one single-antenna destination, and multiple multi- antenna relays. Adopting the minimum mean squared error as optimality criterion, the optimal frequency-domain linear equalization (LE) and decision-feedback equalization (DFE) receivers are derived and corresponding objective functions for relay BF matrix optimization are specified. For a sum relay power constraint, we obtain the structure of the optimal relay BF matrices in closed form. While the structure of the optimal relay BF matrices is identical for LE and DFE as well as for an idealized matched filter receiver, the solution of the remaining power allocation problem depends on the adopted receiver. The power allocation problem is shown to be convex for all considered receivers and an efficient numerical algorithm for finding the optimal power allocation is provided. Furthermore, to reduce complexity, two suboptimal power allocation schemes assigning identical powers to all relays and/or frequencies are proposed and shown to lead to only a small loss in performance and a remarkable robustness against imperfect channel state information.

Research on Opportunistic Beamforming Technology in Sparse Network

In this work, an opportunistic beamforming method combined with OFDM technology is proposed to solve the mismatchment of channel beam-forming matrix and vector-matrix in sparse network. Firstly, introduce a two-stage framework, as scheduling and ultimately beamforming, propose beam power control techniques that do not change the direction of the second-stage beams. Then we adapt this scheme to the multi-carrier scenario, such as OFDM systems, in order to improve the whole system’s performance. Simulation results show that this two-stage OBF adjoined to beam power control techniques scheme can improve the total throughput in sparse network system.

Efficient Linear Transmission Strategy for MIMO Relaying Broadcast Channels with Direct Links

In this letter, a novel linear transmission strategy to design the linear precoding matrix (PM) at base station (BS) and the beamforming matrix (BM) at relay station (RS) for multiple-input multiple-output (MIMO) relaying broadcast channels with direct channel (DC) is proposed, in which a linear PM is designed at BS based on DC, and the RS utilizes the PM, the backward channel and the forward channel to design the linear BM. We then give a quite tight lower bound of the achievable sum-rate of the network with the proposed strategy to measure the performance. The sum-rates achieved by the proposed strategy is compared with other schemes without considering the DC in design in simulations, which shows that the proposed strategy outperforms the existing methods when RS is close to BS.

다중 안테나 빔형성 메트릭스 변환 기법 및 사용자 선택 기법

Random beamforming (RBF) uses the signal to interference plus noise ratio (SINR) feedback to select users in multiple-input multiple-output (MIMO) systems. A large number of users are required to obtain the gain of multi-user diversity for a downlink transmission. However, if the number is not large enough, it may be difficult to obtain multi-user diversity, leading to a rapid degradation in performance. To resolve this problem, we propose the beamforming matrix transformation and the user scheduling method. The beamforming matrix transformation scheme uses the SINRs of each users and have a better performance than conventional schemes over a small number of users. In addition, we propose the user scheduling scheme corresponding to the beamforming matrix transformation. In simulation results, we demonstrate that the sum-rate can be improved according to the number of users.

MSMSE-based optimal beamforming design and simplification on AF MIMO two-way relay channels

An optimal cooperative beamforming for the amplify-and-forward (AF) MIMO two-way relay channels was designed. Supposing the channel state information (CSI) was perfectly known by the receiver and transmitter as well as the relay, optimal beamforming vectors (matrices) of all nodes were jointly designed based on the criterion of minimizing the sum mean square errors (MSMSE). The analysis result shows that the performance effect of transmitting and receiving beamforming pairs is to maximize the receive signal-to-noise ratio (SNR) at two communication nodes, and the rank of the optimal relay beamforming matrix is no larger than two when there is only one data stream at each source node. A simplified algorithm was put forward to accomplish the design based on the analysis conclusions. Simulation results provide that the system performance, which is characterized in terms of bit error rates (BER), is significantly improved by cooperative beamforming, and the performance of the simplified method is not only very close to the optimal one but also with faster iteration speed and much lower computational complexity.

On the Sumrate of Amplify-and-Forward Relay Networks with Multiple Source-Destination Pairs

The paper considers a network scenario in which multiple source-destination node pairs need to communicate simultaneously. Each source and destination is equipped with one antenna and the communication is assisted by a multi-antenna relay operating in Amplify-and-Forward fashion. The communication occurs in two slots; in the first slot, the sources transmit simultaneously, and in the second slot, the relay retransmits the signals which were received by its antennas during the first slot, after linearly processing them via a Zeroforcing Beamforming (ZFBF) matrix. Two different designs for the ZFBF matrix are proposed. The first design allocates the relay power so that all data streams have the same useful power. The second design adjusts the relay weights for all S-D pairs in a way that maximizes the sumrate. It is shown analytically that, when the source or relay power is high, the proposed sumrate maximization method has the same ergodic sumrate as the cut-set bound with two identical slots and a ZF precoder in the broadcast hop or a ZF equalizer in the multiple access hop, or maintains a constant gap from the cut-set bound with a ZF precoder in the broadcast hop. Although initially perfect channel state information (CSI) is assumed available at the relay, an upper bound of the ergodic sumrate loss caused by relay CSI errors is also derived.

Optimal Linear MMSE Beamforming for Two Way Multi-Antenna Relay Systems

This letter addresses the beamforming issues for two way relay systems assuming that two source nodes S1 and S2 are equipped with single antenna each and relay node R with multiple antennas. We derive the optimal linear beamforming matrix at R in closed form based on convex optimization techniques, aiming to minimize the weighted mean squared error (MSE). To reduce complexity for implementation, two alternative relay schemes are also presented. In addition, all the proposed schemes' performance are analyzed and compared in terms of mean squared error (MSE) and computation complexity.

Opportunistic Beamforming With Single Beamforming Matrix for Virtual Antenna Arrays

Opportunistic beamforming is a promising technique for downlink channels in cellular systems. When opportunistic beamforming is to support multiple users at a time, it is important to form multiple beams with as little interference as possible. In the conventional approach with limited feedback of channel state information from users, the best beamforming matrix can be selected from a set of multiple beamforming matrices. Thus, at each time when a different set of users are selected by a scheduler, a new beamforming matrix has to be found, which may require excessive complexity. To avoid this problem, in this paper, we propose an opportunistic beamforming approach with a single fixed beamforming matrix for stationary users. Since the beams are fixed, we only need to perform user selection (and power allocation if necessary). It is also shown that the proposed approach is suited for a distributed virtual antenna array built by multiple base station or access point units, since the intercorrelation between the users' channel vectors in this case allows effective opportunistic beamforming based on user classification in conjunction with a single beamforming matrix.