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T N Davidson - One of the best experts on this subject based on the ideXlab platform.
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low complexity robust miso downlink Precoder Design with per antenna power constraints
IEEE Transactions on Signal Processing, 2018Co-Authors: Mostafa Medra, T N DavidsonAbstract:This paper considers the Design of beamformers for a multiple-input single-output downlink system with per-antenna power constraints (PAPCs) that seek to mitigate the impact of the imperfections in the channel state information that is available at the base station. The goal of the Design is to minimize the outage probability of specified signal-to-interference-and-noise ratio targets, and to do so at a low computational cost. The proposed Design strategy provides an efficient way to handle PAPCs, in addition to a total power constraint, for a variety of precoding techniques, including the offset maximization approach to robust beamforming, and the nominal zero-forcing and maximum ratio transmission approaches. Through observations regarding the structure of the optimality conditions for each of the Design formulations, low-complexity iterative algorithms that involve the evaluation of closed-form expressions are developed. In systems with a large number of antennas, the computational cost of some of these algorithms can be reduced to being linear in the number of antennas, without a significant degradation in performance. Simulation results show that the proposed robust Designs can provide substantial reductions in the outage probability while satisfying the PAPCs.
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low complexity robust miso downlink Precoder Design under imperfect csi
IEEE Transactions on Signal Processing, 2016Co-Authors: Mostafa Medra, Yongwei Huang, T N DavidsonAbstract:We consider the Design of the linear Precoder for a multiple-input single-output (MISO) downlink system with quality-of-service (QoS) constraints. The broad goal is to develop low-complexity techniques that mitigate the impact of the uncertainty in the transmitter’s channel state information (CSI) by incorporating probabilistic models for the uncertainty into the Design. The proposed techniques are developed for systems based on limited feedback, and they can be easily adapted to systems that acquire CSI using estimation on the uplink and channel reciprocity. We consider the conventional problem of minimizing the transmitted power under probability of outage constraints for a target signal-to-interference-and-noise ratio (SINR), and the related problem of minimizing the outage probability under a transmitted power constraint. By approximating the outage constraint by a zero-outage region, employing a semidefinite relaxation, and applying an extension of the S-Lemma that is derived herein, these problems are converted into convex and quasi-convex problems, respectively. Insights into the structure of the solution of those problems are then used to generate an alternate Design formulation that provides greater robustness in the presence of significant uncertainties and has a quasi-closed-form solution. As illustrated by simulations, the proposed alternate Design provides significantly better performance than the conventional Designs that do not incorporate uncertainty models, and better performance than existing robust Designs in the presence of large uncertainties, and does so at a computational cost that is close to that of the conventional Designs.
Robert Schober - One of the best experts on this subject based on the ideXlab platform.
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Precoder Design and power allocation for downlink mimo noma via simultaneous triangularization
Wireless Communications and Networking Conference, 2021Co-Authors: Aravindh Krishnamoorthy, Meng Huang, Robert SchoberAbstract:In this paper, we consider the downlink Precoder Design for two-user power-domain multiple-input multiple-output (MIMO) non-orthogonal multiple access (NOMA) systems. The proposed precoding scheme is based on simultaneous triangularization and decomposes the MIMO-NOMA channels of the two users into multiple single-input single-output NOMA channels, assuming low-complexity self-interference cancellation at the users. In contrast to the precoding schemes based on simultaneous diagonalization (SD), the proposed scheme avoids inverting the MIMO channels of the users, thereby enhancing the ergodic rate performance. Furthermore, we develop a power allocation algorithm based on the convex-concave procedure, and exploit it to obtain the ergodic achievable rate region of the proposed MIMO-NOMA scheme. Our results illustrate that the proposed scheme outperforms baseline precoding schemes based on SD and orthogonal multiple access for a wide range of user rates and performs close to the dirty paper coding upper bound. The ergodic rate region can further be improved by utilizing a hybrid scheme based on time sharing between the proposed MIMO-NOMA scheme and point-to-point MIMO.
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Precoder Design and statistical power allocation for mimo noma via user assisted simultaneous diagonalization
IEEE Transactions on Communications, 2021Co-Authors: Aravindh Krishnamoorthy, Zhiguo Ding, Robert SchoberAbstract:In this paper, we investigate the downlink Precoder Design for two-user power-domain multiple-input multiple-output (MIMO) non-orthogonal multiple access (NOMA). We propose a novel user-assisted (UA) simultaneous diagonalization (SD) based MIMO-NOMA scheme that achieves SD of the MIMO channels of both users through a combination of Precoder Design and low-complexity self-interference cancellation at the users, thereby considerably lowering the overall decoding complexity compared to joint decoding. The achievable ergodic user rates of the proposed scheme are analyzed for Rayleigh fading channels based on a finite-size random matrix theory framework, which is further exploited to develop a statistical power allocation algorithm. Simulation and numerical results show that the proposed UA-SD MIMO-NOMA scheme significantly outperforms orthogonal multiple access and a benchmark Precoder Design performing SD via generalized singular value decomposition in terms of the achievable ergodic rate region for most user rates. The ergodic rate region is further enhanced by a hybrid scheme which performs time sharing between the proposed UA-SD MIMO-NOMA scheme and single-user MIMO.
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successive null space Precoder Design for downlink mu mimo with rate splitting and single stage sic
arXiv: Information Theory, 2021Co-Authors: Aravindh Krishnamoorthy, Robert SchoberAbstract:In this paper, we consider the Precoder Design for an under-loaded or critically loaded downlink multi-user multiple-input multiple-output (MU-MIMO) communication system. We propose novel precoding and decoding schemes which enhance system performance based on rate splitting at the transmitter and single-stage successive interference cancellation at the receivers. The proposed successive null-space (SNS) precoding scheme utilizes linear combinations of the null-space basis vectors of the successively augmented MIMO channel matrices of the users as precoding vectors to adjust the inter-user-interference experienced by the receivers. We formulate a non-convex weighted sum rate (WSR) optimization problem, and solve it via successive convex approximation to obtain a suboptimal solution for the precoding vectors and the associated power allocation. Our simulation results reveal that the proposed SNS Precoders outperform block diagonalization based linear and rate splitting Designs, and in many cases, have a relatively small gap to the maximum sum rate achieved by dirty paper coding.
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Precoder Design for two user uplink mimo noma with simultaneous triangularization
Global Communications Conference, 2019Co-Authors: Aravindh Krishnamoorthy, Robert SchoberAbstract:In this paper, we consider the uplink Precoder Design for two-user power-domain multiple-input multiple-output (MIMO) non-orthogonal multiple access (NOMA) systems. We propose a novel precoding scheme which utilizes simultaneous triangularization to decompose the MIMO-NOMA channels of the two users into multiple single-input single-output (SISO)-NOMA channels assuming low-complexity self-interference cancellation at the base station, thereby reducing the decoding complexity. The proposed scheme takes advantage of the available excess degrees of freedom at the base station to enhance the ergodic achievable rate. The ergodic achievable rate region of the proposed scheme is characterized using finite-size random matrix theory (RMT). Our results illustrate that the proposed scheme significantly outperforms traditional MIMO-OMA and zero forcing based MIMO-NOMA schemes, and has a small performance gap to the achievable rate region of MIMO-NOMA.
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hybrid Precoder Design for cache enabled millimeter wave radio access networks
IEEE Transactions on Wireless Communications, 2019Co-Authors: Ju Ren, Robert Schober, Yongming Huang, Yaoxue ZhangAbstract:In this paper, we study the Design of a hybrid Precoder, consisting of an analog and a digital Precoder, for the delivery phase of downlink cache-enabled millimeter-wave (mm-wave) radio access networks (CeMm-RANs). In CeMm-RANs, enhanced remote radio heads (eRRHs), which are equipped with local cache and baseband signal processing capabilities in addition to the basic functionalities of conventional RRHs, are connected to the baseband processing unit via fronthaul links. Two different fronthaul information transfer strategies are considered, namely, hard fronthaul information transfer, where hard information of uncached requested files is transmitted via the fronthaul links to a subset of eRRHs, and soft fronthaul information transfer, where the fronthaul links are used to transmit quantized baseband signals of uncached requested files. The hybrid Precoder is optimized for maximization of the minimum user rate under a fronthaul capacity constraint, an eRRH transmit power constraint, and a constant-modulus constraint on the analog Precoder. The resulting optimization problem is non-convex, and hence, the global optimal solution is difficult to obtain. Therefore, convex approximation methods are employed to tackle the non-convexity of the achievable user rate, the fronthaul capacity constraint, and the constant modulus constraint on the analog Precoder. Then, an effective algorithm with provable convergence is developed to solve the approximated optimization problem. The simulation results are provided to evaluate the performance of the proposed algorithms, where fully digital precoding is used as the benchmark. The results reveal that except for the case of a large fronthaul link capacity, soft fronthaul information transfer is preferable for CeMm-RANs. Furthermore, surprisingly, hybrid precoding outperforms fully digital precoding with soft fronthaul information transfer for medium-to-large file sizes and fronthaul capacity limited mm-wave cloud RANs.
Tho Lengoc - One of the best experts on this subject based on the ideXlab platform.
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mmse hybrid Precoder Design for millimeter wave massive mimo systems
Wireless Communications and Networking Conference, 2016Co-Authors: Ruikai Mai, Duy H N Nguyen, Tho LengocAbstract:This paper studies hybrid RF/baseband linear pre-coding Design to minimize the mean square error (MSE) for millimeter-wave massive multiple-input multiple-output (MIMO) systems using optimal linear equalizer. Instead of dealing with the objective function of sum MSE, which involves matrix inverses, we approach this problem by minimizing the Euclidean distance between the hybrid Precoder and the optimal minimum MSE Precoder. In an effort to impose the optimal structure of channel diagonalization, we separate the Design of modulus-constrained RF Precoder from the Design of unconstrained baseband pre-coder. Magnitude-least-squares approximation is introduced to formulate the RF Precoder Design problem, and is subsequently transformed into a simultaneous matrix diagonalization problem. Such transformation enables application of a simple and numerically stable Jacobi-like algorithm. The effective channel representing a cascade of the derived RF Precoder and the MIMO channel, is diagonalized by the baseband Precoder. The error performance of the proposed solution is examined by numerical results where the effectiveness is verified by its closeness to the optimal Design and its noticeable gain over sparse approximation based schemes.
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bandwidth efficient bit interleaved coded modulation over naf relay channels error performance and Precoder Design
IEEE Transactions on Vehicular Technology, 2011Co-Authors: Leonardo Jimenez Rodriguez, Nghi H Tran, Tho LengocAbstract:This paper investigates the error performance and Precoder Design for a bandwidth-efficient bit-interleaved coded modulation (BICM) system over a nonorthogonal amplify-and-forward (NAF) half-duplex single-relay channel. A tight union bound on the asymptotic bit error probability (BEP) is first derived for an arbitrary block length of 2N, which corresponds to the case of using a 2N × 2N Precoder. This bound provides a useful tool for predicting the error performance. Attention is then paid to the coded NAF system that uses a 2 × 2 Precoder, where a closed-form expression of the bound is obtained. Based on this expression, an optimal class of 2 × 2 Precoders with respect to the asymptotic performance is then developed. Unlike the optimal Precoders that are Designed for uncoded systems, the derived Precoder indicates that the source only needs to send the superposition of the first symbol and the rotated version of the second symbol in the first time slot while being silent in the remaining slot to achieve the best asymptotic performance. For good convergence property, it is further shown that a rotation angle that maximizes the minimum Euclidean distance of the superposition constellation should be used. An optimal rotation angle is then analytically determined for various modulation schemes. Both analytical and simulation results show that the proposed Precoders not only exploit full cooperative diversity but offer a significant coding gain over the optimal Precoders for uncoded NAF systems as well.
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bandwidth efficient bit interleaved coded modulation over naf relay channels error performance and Precoder Design
International Conference on Communications, 2010Co-Authors: Leonardo Jimenez Rodriguez, Nghi H Tran, Tho LengocAbstract:This paper investigates the error performance and Precoder Design for a bandwidth-efficient bit-interleaved coded modulation (BICM) system over a non-orthogonal amplify-and-forward (NAF)half-duplex single-relay channel. A tight union bound on the bit error probability (BEP) is first derived for an arbitrary block length of $2N$ using a $2N\times 2N$ Precoder. This bound provides an useful tool to predict the error performance. Attention is then devoted to the system using $2\times 2$ Precoder, where a closed-form expression of the bound is obtained. Based on this expression, an optimal $2\times 2$ Precoder applicable to any modulation scheme is developed. Different from the optimal Precoders Designed for uncoded NAF systems, the derived Precoder indicates that the source only needs to send the superposition of signals in the first time slot and being silent in the second time slot in order to achieve the best asymptotic performance. Analytical and simulation results show that the proposed Precoder not only exploits full cooperative diversity but also offers a significant coding gain over optimal Precoders for uncoded NAF systems.
Markku Juntti - One of the best experts on this subject based on the ideXlab platform.
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decentralized sum rate maximization with qos constraints for interfering broadcast channel via successive convex approximation
IEEE Transactions on Signal Processing, 2016Co-Authors: Jarkko Kaleva, Antti Tolli, Markku JunttiAbstract:Weighted sum rate maximization (WSRMax) with user specific quality-of-service (QoS) constraints and general convex transmit power constraints is considered in multi-cell multi-user multiple-input multiple-output system. The particular focus in the proposed joint transmitter-receiver Design is on tractability in terms of implementation and moderately fast changing/time correlated channel conditions. The non-convex transmit Precoder Design problem is formulated as a difference of convex functions program, for which a locally optimal solution is achieved by successive convex approximation (SCA). To achieve practically realizable Designs, two decentralized approaches with low signaling overhead are proposed. Primal decomposition based solution provides better compliance of the provided QoS constraints in slowly fading channel conditions. On the other hand, solution based on Lagrangian relaxation of the coupling rate constraints is proposed for relaxed feasibility conditions and improved convergence properties. As a special case, an iterative solution via the Karush–Kuhn–Tucker conditions of the Precoder Design problem with per base station transmit power constraints is also proposed. Finally, we propose a heuristic extension of the SCA method, which is shown to significantly improve the rate of convergence while achieving comparable sum rate with recently published methods.
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weighted sum rate maximization for mimo broadcast channels using dirty paper coding and zero forcing methods
IEEE Transactions on Communications, 2013Co-Authors: Lenam Tran, Markku Juntti, Mats Bengtsson, Bjorn OtterstenAbstract:We consider Precoder Design for maximizing the weighted sum rate (WSR) of successive zero-forcing dirty paper coding (SZF-DPC). For this problem, the existing Precoder Designs often assume a sum power constraint (SPC) and rely on the singular value decomposition (SVD). The SVD-based Designs are known to be optimal but require high complexity. We first propose a low-complexity optimal Precoder Design for SZF-DPC under SPC, using the QR decomposition. Then, we propose an efficient numerical algorithm to find the optimal Precoders subject to per-antenna power constraints (PAPCs). To this end, the Precoder Design for PAPCs is formulated as an optimization problem with a rank constraint on the covariance matrices. A well-known approach to solve this problem is to relax the rank constraints and solve the relaxed problem. Interestingly, for SZF-DPC, we are able to prove that the rank relaxation is tight. Consequently, the optimal Precoder Design for PAPCs is computed by solving the relaxed problem, for which we propose a customized interior-point method that exhibits a superlinear convergence rate. Two suboptimal Precoder Designs are also presented and compared to the optimal ones. We also show that the proposed numerical method is applicable for finding the optimal Precoders for block diagonalization scheme.
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downlink Precoder Design for coordinated regenerative multi user relaying
IEEE Transactions on Signal Processing, 2013Co-Authors: Jarkko Kaleva, Antti Tolli, Ganesh Venkatraman, Markku JunttiAbstract:Relays are used in the current wireless standards to enhance the cell throughput and coverage. In this paper, we evaluate the system performance by considering the duplexing loss with over-the-air transmission for relay with decode-and-forward as the relaying protocol. The overhead involved in providing the relay with the data prior to the transmission is often neglected. We demonstrate that the impact of relays can be even detrimental if the in-band signaling needs are not properly accounted for. Both Precoder Design and user allocation between the base station and the relay are considered. The Precoder Design objectives are transmit power minimization and throughput maximization each of which two different precoding approaches are considered. Zero-forcing Precoder Design is proposed to achieve reduced computation complexity and low signaling overhead. For higher efficiency and performance, we provide coordinated solutions, which allow more flexible interference control. We also consider user allocation by providing heuristic allocation methods.
Rui Zhang - One of the best experts on this subject based on the ideXlab platform.
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cooperative multi cell block diagonalization with per base station power constraints
Wireless Communications and Networking Conference, 2010Co-Authors: Rui ZhangAbstract:Block diagonalization (BD) is a practically favorable precoding technique that eliminates the interuser interference in downlink multiuser multiple-input multiple-output (MIMO) systems. In this paper, we apply BD to the downlink transmission in a cooperative multi-cell system, where the signals from different base stations (BSs) to all the mobile stations (MSs) are jointly Designed with the perfect knowledge of the downlink channels and transmit messages. Specifically, this paper studies the BD Precoder Design to maximize the weighted sum-rate achievable for all the MSs. The associated optimization problem can be formulated in an auxiliary MIMO broadcast channel (BC) with a set of transmit power constraints equivalent to those for different BSs in the multi-cell system. Based on convex optimization techniques, this paper Designs an efficient algorithm to solve this problem, and derives the structure of the corresponding optimal BD precoding matrix. Moreover, for the special case of single-antenna BSs and MSs, it is shown that the proposed solution leads to the optimal zero-forcing beamforming (ZF-BF) Precoder Design for the multiple-input single-output (MISO) BC with the per-antenna power constraints.
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Cooperative multi-cell block diagonalization with per-base-station power constraints
IEEE Journal on Selected Areas in Communications, 2010Co-Authors: Rui ZhangAbstract:Block diagonalization (BD) is a practical linear precoding technique that eliminates the inter-user interference in downlink multiuser multiple-input multiple-output (MIMO) systems. In this paper, we apply BD to the downlink transmission in a cooperative multi-cell MIMO system, where the signals from different base stations (BSs) to all the mobile stations (MSs) are jointly Designed with the perfect knowledge of the downlink channels and transmit messages. Specifically, we study the optimal BD Precoder Design to maximize the weighted sum-rate of all the MSs subject to a set of per-BS power constraints. This Design problem is formulated in an auxiliary MIMO broadcast channel (BC) with a set of transmit power constraints corresponding to those for individual BSs in the multi-cell system. By applying convex optimization techniques, this paper develops an efficient algorithm to solve this problem, and derives the closed-form expression for the optimal BD precoding matrix. It is revealed that the optimal BD precoding vectors for each MS in the per-BS power constraint case are in general non-orthogonal, which differs from the conventional orthogonal BD Precoder Design for the MIMO-BC under one single sum-power constraint. Moreover, for the special case of single-antenna BSs and MSs, the proposed solution reduces to the optimal zero-forcing beamforming (ZF-BF) Precoder Design for the weighted sum-rate maximization in the multiple-input single-output (MISO) BC with per-antenna power constraints. Suboptimal and low-complexity BD/ZF-BF precoding schemes are also presented, and their achievable rates are compared against those with the optimal schemes.