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23
Linear precoding designs for amplifyandforward multiuser twoway relay systems
 in Proc. IEEE GLOBECOM
, 2011
"... AbstractWe investigate the linear precoding designs for multiuser twoway relay system (MUTWRS) where a multiantenna basestation (BS) communicates with multiple singleantenna mobile stations (MSs) via a multiantenna relay station (RS). The amplifyandforward (AF) relay protocol is employed. Th ..."
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AbstractWe investigate the linear precoding designs for multiuser twoway relay system (MUTWRS) where a multiantenna basestation (BS) communicates with multiple singleantenna mobile stations (MSs) via a multiantenna relay station (RS). The amplifyandforward (AF) relay protocol is employed. The design goal is to optimize the precodings at BS, RS or both so as to minimize the total meansquare error (MSE) of the uplink messages while maintaining the individual signaltointerferenceplusnoise ratio (SINR) requirement for each downlink signal. We show that the BS precoding design problem can be converted to a standard second order cone programming (SOCP), while the RS precoding is nonconvex for which a local optimal solution is obtained using an iterative algorithm. A joint BSRS precoding is also obtained by alternating optimization of BS precoding and RS precoding with guaranteed convergence. Numerical results show that RSprecoding is superior to BSprecoding. Furthermore, the joint BSRS precoding can significantly outperform the two individual precoding schemes. The implementation issues including complexity and feedback overhead are also discussed.
Linear precoding for multipair twoway MIMO relay systems with maxmin fairness
 IEEE Trans. Signal Process
, 2012
"... Abstract—Twoway relaying has demonstrated significant gain in spectral efficiency by applying network coding when a pair of source nodes exchange information via a relay node. This paper is concerned with the scenario where multiple pairs of users exchange information through a common relay node e ..."
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Cited by 16 (5 self)
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Abstract—Twoway relaying has demonstrated significant gain in spectral efficiency by applying network coding when a pair of source nodes exchange information via a relay node. This paper is concerned with the scenario where multiple pairs of users exchange information through a common relay node equipped with multiple antennas. We aim to design linear precoding at the relay based on amplifyandforward strategy. The goal is to maximize the minimum achievable rate among all the users subject to a peak relay power constraint so as to achieve the maxmin fairness. We first convert this nonconvex problem into a series of semidefinite programming problems using bisection search and certain transformation techniques. A quasioptimal solution is then obtained by using semidefinite relaxation (SDR). To reduce the design complexity, we further introduce a pairwise zeroforcing (ZF) structure that eliminates the interference among different user pairs. By applying this structure, the precoding design problem is simplified to a power allocation problem which can be optimally solved. A simplified power allocation algorithm is also proposed. Simulation results show that the proposed SDRbased precoding not only achieves high minimum user rate but also maintains good sumrate performance when compared with existing schemes. It is also shown that the proposed pairwise ZF precoding with simplified power allocation strikes a good balance between performance and complexity. Index Terms—Multipleinput multipleoutput (MIMO), multiuser, nonregenerative relay, precoding, twoway relaying. I.
Wireless MIMO switching: Weighted sum mean square error and sum rate optimization
 IEEE TRANS. INF. THEORY
, 2013
"... This paper addresses joint transceiver and relay design for a wireless multipleinput multipleoutput (MIMO) switching scheme that enables data exchange amongmultiple users. Here, a multiantenna relay linearly precodes the received (uplink) signals frommultiple users and forwards the signal in the ..."
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Cited by 9 (4 self)
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This paper addresses joint transceiver and relay design for a wireless multipleinput multipleoutput (MIMO) switching scheme that enables data exchange amongmultiple users. Here, a multiantenna relay linearly precodes the received (uplink) signals frommultiple users and forwards the signal in the downlink, where the purpose of precoding is to let each user receive its desired signal with interference from other users suppressed. The problem of optimizing the precoder based on various design criteria is typically nonconvex and difficult to solve. Themain contribution of this paper is a unified approach to solve the weighted summean square error (MSE) minimization and weighted sum rate maximization problems inMIMOswitching. Specifically, an iterative algorithm is proposed for jointly optimizing the relay’s precoder and the users’ receive filters to minimize the weighted sum MSE. It is also shown that the weighted sum rate maximization problem can be reformulated as an iterated weighted sumMSEminimization problem and can, therefore, be solved similarly to the case of weighted sumMSE minimization. With properly chosen initial values, the proposed iterative algorithms are asymptotically optimal in both high and lowsignaltonoiseratio regimes for MIMO switching, either with or without selfinterference cancellation (a.k.a., physicallayer network coding). Numerical results show that the optimized MIMO switching scheme based on the proposed algorithms significantly outperforms existing approaches in the literature.
1 Coordinated Direct and Relay Transmission with Linear NonRegenerative Relay Beamforming
"... Abstract—Joint processing of multiple communication flows in wireless systems has given rise to a number of novel transmission techniques, notably the twoway relaying, but also more general traffic scenarios, such as coordinated direct and relay (CDR) transmissions. In a CDR scheme the relay has a ..."
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Cited by 9 (5 self)
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Abstract—Joint processing of multiple communication flows in wireless systems has given rise to a number of novel transmission techniques, notably the twoway relaying, but also more general traffic scenarios, such as coordinated direct and relay (CDR) transmissions. In a CDR scheme the relay has a central role in managing the interference and boosting the overall system performance. In this letter we consider the case in which an amplifyandforward relay has multiple antennas and can use beamforming to support the coordinated transmissions. We focus on one representative traffic type with one uplink user and one downlink user. Two different criteria for relay beamforming are analyzed: maximal weighted sumrate and maximization of the worstcase weighted SNR. We propose iterative optimal solutions, as well as lowcomplexity nearoptimal solutions. Index Terms—Analog network coding, relay beamforming. I.
Cellular multiuser twoway MIMO AF relaying via signal space alignment: Minimum weighted SINR maximization
 IEEE Trans. Signal Process
, 2012
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Towards the asymptotic sum capacity of the MIMO cellular twoway relay channel
 IEEE Trans. Signal Process
, 2014
"... Abstract—In this paper, we consider the transceiver and relay design for the multipleinput multipleoutput (MIMO) cellular twoway relay channel (cTWRC), where a multiantenna base station (BS) exchanges information with multiple multiantenna mobile stations via a multiantenna relay station (RS). ..."
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Cited by 5 (4 self)
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Abstract—In this paper, we consider the transceiver and relay design for the multipleinput multipleoutput (MIMO) cellular twoway relay channel (cTWRC), where a multiantenna base station (BS) exchanges information with multiple multiantenna mobile stations via a multiantenna relay station (RS). We propose a novel twoway relaying scheme to approach the sum capacity of the MIMO cTWRC. A key contribution of this work is a new nonlinear latticebased precoding technique to precompensate the interstream interference, so as to achieve efficient interferencefree lattice decoding at the relay. We derive sufficient conditions for the proposed scheme to asymptotically achieve the sum capacity of the MIMO cTWRC in the high signaltonoise ratio (SNR) regime. To fully exploit the potential of the proposed scheme, we also investigate the optimal power allocation at the BS and the RS to maximize the weighted sumrate of the MIMO cTWRC in the general SNR regime. It is shown that the problem can be formulated as a monotonic program, and a polyblock outer approximation algorithm is developed to find the globally optimal solution with guaranteed convergence. We demonstrate by numerical results that the proposed scheme significantly outperforms the existing schemes and closely approaches the sum capacity of the MIMO cTWRC in the high SNR regime. Index Terms—Cellular twoway relay channel, nested lattice coding, lattice precoding, monotonic optimization. I.
On the Maximum Achievable SumRate of Interfering TwoWay Relay Channels
"... Abstract—Hierarchical networks can provide very high data rates to multiple mobile stations (MSs) through a dense network of fixed relay nodes (RNs) fed by few hub base stations (HBSs). In order to achieve high spectral efficiencies RNs can act as twoway RNs. However the dense RN deployment gives r ..."
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Cited by 5 (1 self)
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Abstract—Hierarchical networks can provide very high data rates to multiple mobile stations (MSs) through a dense network of fixed relay nodes (RNs) fed by few hub base stations (HBSs). In order to achieve high spectral efficiencies RNs can act as twoway RNs. However the dense RN deployment gives rise to high cochannel interference (CCI) that limits sumrate performance. In this letter we consider a simple hierarchical network consisting of an HBS with two highly directional antennas communicating with two MSs via two interfering twoway RNs. To mitigate CCI and boost sumrates we propose a twoway relaying strategy based on AF combined with Network MIMO processing which is applied over the concatenation of the backhaul and access network channels. We compare our proposed strategy with a baseline DF approach and we show that it performs significantly better when CCI is dominant. Index Terms—Twoway relay channels (2WRCs), amplifyand
Bidirectional cellular relay network with distributed relaying
 IEEE J. SEL. AREAS COMMUN
, 2013
"... In this paper, we consider a bidirectional cellular relay network with distributed relays where a single base station exchanges information with multiple independent users through multiple singleantenna relays. We design the transceivers at the base station, the relays, and the users. The related o ..."
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Cited by 3 (3 self)
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In this paper, we consider a bidirectional cellular relay network with distributed relays where a single base station exchanges information with multiple independent users through multiple singleantenna relays. We design the transceivers at the base station, the relays, and the users. The related optimization problems are generally nonconvex and difficult to solve. In this paper, we propose a unified framework to design the transceiver algorithms based on two criteria, i.e. weighted sum MSE minimization and sum rate maximization. Specifically, we show that the sum rate maximization problem can be converted into an iterative weighted sum MSE minimization problem. Lowcomplexity iterative algorithms are developed for both weighted sum MSE minimization and sum rate maximization optimization problems. However, the convergence points of the proposed iterative algorithms are sensitive to the initial conditions, especially in the high signaltonoise ratio (SNR) regime. For this reason, we further derive the highSNR asymptotically optimal solutions and use them as the initials for the proposed iterative algorithms. Simulation results show that the proposed scheme can approximately double the system throughput, compared to the conventional fourstage transmission schemes.
Nonlinear Precoding Design for MIMO AmplifyandForward TwoWay Relay Systems
"... Abstract—In traditional multipleinput–multipleoutput (MIMO) channel and MIMO oneway relay system, nonlinear precoding design has shown significant performance gain over linear design. In this paper, we aim to study nonlinear precoding design for MIMO amplifyandforward (AF) twoway relay systems ..."
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Cited by 2 (1 self)
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Abstract—In traditional multipleinput–multipleoutput (MIMO) channel and MIMO oneway relay system, nonlinear precoding design has shown significant performance gain over linear design. In this paper, we aim to study nonlinear precoding design for MIMO amplifyandforward (AF) twoway relay systems, where nonlinear minimal mean square error (MMSE) decision feedback equalizers (DFEs) are used in two destinations, and linear transmit precoding is applied at the source and relay nodes. We first investigate nonlinear precoding design, where the precoding is only conducted at two sources for a fixedrelay precoder. After some transformations, we prove that this design problem is convex, and an efficient algorithm is provided to find the optimal solution. Then, we consider the nonlinear joint precoding design to further incorporate relay precoding. Due to the nonconvexity of this problem, we first propose an iterative algorithm (Algorithm I) to approach the optimal solution. It is proven that Algorithm I is convergent and can converge to a stationary point of the joint design problem. Moreover, we present a simplified iterative algorithm (Algorithm II) for joint precoding design to reduce the design complexity. It is found that Algorithm II almost achieves the same performance as Algorithm I in most cases. Our simulation results show that the proposed nonlinear joint precoding design significantly outperforms the linear joint precoding design. It is also shown that the choice between the proposed nonlinear source precoding design and the linear relay precoding design is dependent on specific conditions. Index Terms—Minimum mean square error (MMSE), multipleinput–multipleoutput (MIMO), nonlinear precoding, nonregenerative relay, twoway relaying. I.
Symbol and Bit Mapping Optimization for PhysicalLayer Network Coding with Pulse Amplitude Modulation
 IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS, ACCEPTED FOR PUBLICATION
, 2013
"... In this paper, we consider a twoway relay network in which two users exchange messages through a single relay using a physicallayer network coding (PNC) based protocol. The protocol comprises two phases of communication. In the multiple access (MA) phase, two users transmit their modulated signal ..."
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In this paper, we consider a twoway relay network in which two users exchange messages through a single relay using a physicallayer network coding (PNC) based protocol. The protocol comprises two phases of communication. In the multiple access (MA) phase, two users transmit their modulated signals concurrently to the relay, and in the broadcast (BC) phase, the relay broadcasts a networkcoded (denoised) signal to both users. Nonbinary and binary network codes are considered for uniform and nonuniform pulse amplitude modulation (PAM) adopted in the MA phase, respectively. We examine the effect of different choices of symbol mapping (i.e., mapping from the denoised signal to the modulation symbols at the relay) and bit mapping (i.e., mapping from the modulation symbols to the source bits at the user) on the system errorrate performance. A general optimization framework is proposed to determine the optimal symbol/bit mappings with joint consideration of noisy transmissions in both communication phases. Complexityreduction techniques are developed for solving the optimization problems. It is shown that the optimal symbol/bit mappings depend on the signaltonoise ratio (SNR) of the channel and the modulation scheme. A general strategy for choosing good symbol/bit mappings is also presented based on a highSNR analysis, which suggests using a symbol mapping that aligns the error patterns in both communication phases and Gray and binary bit mappings for uniform and nonuniform PAM, respectively.