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103
Achievable rate regions and performance comparison of half duplex bidirectional relaying protocols
 IEEE Trans. Inf. Theory
, 2011
"... Abstract—In a bidirectional relay channel, two nodes wish to exchange independent messages over a shared wireless halfduplex channel with the help of a relay. In this paper, we derive achievable rate regions for four new halfduplex protocols and compare these to four existing halfduplex protoc ..."
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Cited by 29 (2 self)
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Abstract—In a bidirectional relay channel, two nodes wish to exchange independent messages over a shared wireless halfduplex channel with the help of a relay. In this paper, we derive achievable rate regions for four new halfduplex protocols and compare these to four existing halfduplex protocols and outer bounds. In time, our protocols consist of either two or three phases. In the two phase protocols, both users simultaneously transmit during the first phase and the relay alone transmits during the second phase, while in the three phase protocol the two users sequentially transmit followed by a transmission from the relay. The relay may forward information in one of four manners; we outline existing amplify and forward (AF), decode and forward (DF), lattice based, and compress and forward (CF) relaying schemes and introduce the novel mixed forward scheme. The latter is a combination of CF in one direction and DF in the other. We derive achievable rate regions for the CF andMixed relaying schemes for the two and three phase protocols. We provide a comprehensive treatment of eight possible halfduplex bidirectional relaying protocols in Gaussian noise, obtaining their relative performance under different SNR and relay geometries. Index Terms—Achievable rate regions, bidirectional communication, compress and forward, relaying. I.
Nested lattice codes for Gaussian relay networks with interference
 IEEE Trans. Inf. Theory
, 2011
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The Gaussian interference relay channel: Improved achievable rates and sum rate upperbounds using a potent relay
 IEEE Transactions on Information Theory, Special Issue on Interference Networks
, 2011
"... Abstract—We consider the Gaussian interference channel with an intermediate relay as a main building block for cooperative interference networks. On the achievability side, we consider compressandforward based strategies. Specifically, a generalized compressandforward strategy, where the destina ..."
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Cited by 23 (5 self)
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Abstract—We consider the Gaussian interference channel with an intermediate relay as a main building block for cooperative interference networks. On the achievability side, we consider compressandforward based strategies. Specifically, a generalized compressandforward strategy, where the destinations jointly decode the compression indices and the source messages, is shown to improve upon the compressandforward strategy which sequentially decodes the compression indices and source messages, and the recently proposed generalized hashandforward strategy. We also construct a nested lattice code based computeandforward relaying scheme, which outperforms other relaying schemes when the direct link is weak. In this case, it is shown that, with a relay, the interference link can be useful for decoding the source messages. Noting the need for upperbounding the capacity for this channel, we propose a new technique with which the sum rate can be bounded. In particular, the sum capacity is upperbounded by considering the channel when the relay node has abundant power and is named potent for that reason. For the Gaussian interference relay channel with potent relay, we study the strong and the weak interference regimes and establish the sum capacity, which, in turn, serve as upperbounds for the sum capacity of the GIFRC with finite relay power. Numerical results demonstrate that upperbounds are tighter than the cutset bound, and coincide with known achievable sum rates for many scenarios of interest. Additionally, the degrees of freedom of the GIFRC are shown to be 2 when the relay has large power, achievable using compressandforward. Index Terms—Generalized compressandforward, interference relay channel, lattice codes, potent relay outerbound, sum capacity.
Successive ComputeandForward
"... Abstract—In prior work, we proposed the computeandforward framework for sending linear combinations of messages to relays. In this note, we extend the notion of successive interference cancellation to the computeandforward setting. We find that once a relay has decoded a linear combination, it ca ..."
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Cited by 18 (3 self)
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Abstract—In prior work, we proposed the computeandforward framework for sending linear combinations of messages to relays. In this note, we extend the notion of successive interference cancellation to the computeandforward setting. We find that once a relay has decoded a linear combination, it can mix it with its channel output to create a new effective channel output. The resulting effective channel can be tuned so that it is more suitable for decoding a second linear combination than the original channel. I.
Multipleinput multipleoutput twoway relaying: A spacedivision approach
 IEEE TRANS. INF. THEORY
, 2013
"... We propose a novel spacedivisionbased networkcoding scheme for multipleinput multipleoutput (MIMO) twoway relay channels (TWRCs), in which two multiantenna users exchange information via a multiantenna relay. In the proposed scheme, the overall signal space at the relay is divided into two s ..."
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Cited by 16 (11 self)
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We propose a novel spacedivisionbased networkcoding scheme for multipleinput multipleoutput (MIMO) twoway relay channels (TWRCs), in which two multiantenna users exchange information via a multiantenna relay. In the proposed scheme, the overall signal space at the relay is divided into two subspaces. In one subspace, the spatial streams of the two users have nearly orthogonal directions and are completely decoded at the relay. In the other subspace, the signal directions of the two users are nearly parallel, and linear functions of the spatial streams are computed at the relay, following the principle of physicallayer network coding. Based on the recovered messages and messagefunctions, the relay generates and forwards networkcoded messages to the two users. We show that, at high signaltonoise ratio, the proposed scheme achieves the asymptotic sumrate capacity of the MIMO TWRC within bits per userantenna, for any antenna configuration and any channel realization. We perform largesystem analysis to derive the average sumrate of the proposed scheme over Rayleighfading MIMO TWRCs. We show that the average asymptotic sumrate gap to the capacity is at most 0.053 bits per relayantenna. It is demonstrated that the proposed scheme significantly outperforms the existing schemes.
Degrees of Freedom for the MIMO MultiWay Relay Channel
"... Abstract — This paper investigates the degrees of freedom (DoF) of the Lcluster, Kuser MIMO multiway relay channel, where users in each cluster wish to exchange messages within the cluster, and they can only communicate through the relay. A novel DoF upper bound is derived by providing users with ..."
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Cited by 13 (0 self)
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Abstract — This paper investigates the degrees of freedom (DoF) of the Lcluster, Kuser MIMO multiway relay channel, where users in each cluster wish to exchange messages within the cluster, and they can only communicate through the relay. A novel DoF upper bound is derived by providing users with carefully designed genie information. Achievable DoF is identified using signal space alignment and multipleaccess transmission. For the twocluster MIMO multiway relay channel with two users in each cluster, the DoF is established for the general case when users and the relay have arbitrary number of antennas, and it is shown that the DoF upper bound can be achieved using signal space alignment or multipleaccess transmission, or a combination of both. The result is then generalized to the three user case. For the Lcluster Kuser MIMO multiway relay channel in the symmetric setting, conditions under which the DoF upper bound can be achieved are established. In addition to being shown to be tight in a variety of scenarios of interests of the multiway relay channel, the newly derived upperbound also establishes the optimality of several previously established achievable DoF results for multiuser relay channels that are special cases of the multiway relay channel. Index Terms — MIMO multiway relay channel, degrees of freedom, signal space alignment, interference alignment. I.
Lattice codes for the Gaussian relay channel: DecodeandForward and CompressandForward,” [Online]. Available: http://arxiv.org/pdf/1111.0084v1.pdf
"... Abstract—Lattice codes are known to achieve capacity in the Gaussian pointtopoint channel, achieving the same rates as i.i.d. random Gaussian codebooks. Lattice codes are also known to outperform random codes for certain channel models that are able to exploit their linearity. In this paper, we sh ..."
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Cited by 12 (3 self)
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Abstract—Lattice codes are known to achieve capacity in the Gaussian pointtopoint channel, achieving the same rates as i.i.d. random Gaussian codebooks. Lattice codes are also known to outperform random codes for certain channel models that are able to exploit their linearity. In this paper, we show that lattice codes may be used to achieve the same performance as known i.i.d. Gaussian random coding techniques for the Gaussian relay channel, and show several examples of how this may be combined with the linearity of lattices codes in multisource relay networks. In particular, we present a nested lattice list decoding technique in which lattice codes are shown to achieve the decodeandforward (DF) rate of single source, single destination Gaussian relay channels with one or more relays. We next present two examples of how this DF scheme may be combined with the linearity of lattice codes to achieve new rate regions which for some channel conditions outperform analogous known Gaussian random coding techniques in multisource relay channels. That is, we derive a new achievable rate region for the twoway relay channel with direct links and compare it to existing schemes, and derive a new achievable rate region for the multiple access relay channel. We furthermore present a lattice compressandforward (CF) scheme for the Gaussian relay channel which exploits a lattice Wyner–Ziv binning scheme and achieves the same rate as the Cover–El Gamal CF rate evaluated for Gaussian random codes. These results suggest that structured/lattice codes may be used to mimic, and sometimes outperform, random Gaussian codes in general Gaussian networks. Index Terms—Compress and forward, decode and forward, Gaussian relay channel, lattice codes, relay channel. I.
Reduceddimension cooperative precoding for MIMO twoway relay channels
 IEEE Trans. Wireless Commun
, 2012
"... Abstract—We investigate efficient communications over MIMO twoway relay channels (TWRCs) of nT < nR, where nT denotes the number of antennas at each user and nR denotes that at the relay. We propose a new reduceddimension (RD) cooperative precoding scheme. In the proposed scheme, the two users ..."
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Cited by 8 (8 self)
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Abstract—We investigate efficient communications over MIMO twoway relay channels (TWRCs) of nT < nR, where nT denotes the number of antennas at each user and nR denotes that at the relay. We propose a new reduceddimension (RD) cooperative precoding scheme. In the proposed scheme, the two users cooperatively create nT aligned eigenmodes, supporting nT streams of physicallayer network coding. We investigate the design of the RD cooperative precoder and derive an asymptotically optimal solution. We analytically show that, in the worst case, the proposed scheme is within 1 2 bit per transmit antenna of the asymptotic sumcapacity of the MIMO TWRC. For fading MIMO TWRCs with i.i.d. Gaussian coefficients, we derive a closedform expression of the average sumrate of the proposed scheme using large system analysis. Our analytical result shows that, for a large system with nT nR = 1 2, the proposed scheme is less than 0.16 bit per transmit antenna away from the capacity. Furthermore, this gap reduces as nT nR increases, and vanishes as nT nR tends to 1. It is demonstrated that the proposed scheme can significantly outperform other existing schemes in the literature. Index Terms—MIMO, twoway relay channel, physicallayer network coding, precoding, capacity. I.
MIMO multiway relaying with clustered full data exchange: Signal space alignment and degrees of freedom
 IEEE Trans. Wireless Commun
, 2014
"... Abstract—Recently, much research interest has been attracted towards the design of efficient communication mechanisms for multipleinput multipleoutput (MIMO) multiway relay channels (mRCs). In this paper, we investigate achievable degrees of freedom (DoF) of the MIMO mRC with L clusters and K user ..."
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Cited by 7 (3 self)
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Abstract—Recently, much research interest has been attracted towards the design of efficient communication mechanisms for multipleinput multipleoutput (MIMO) multiway relay channels (mRCs). In this paper, we investigate achievable degrees of freedom (DoF) of the MIMO mRC with L clusters and K users per cluster, where each user is equipped with M antennas and the relay with N antennas. Our analysis is focused on a new data exchange model, termed clustered full data exchange, i.e., each user in a cluster wants to learn the messages of all the other users in the same cluster. Novel signal alignment techniques are developed to jointly and systematically construct the beamforming matrices at the users and the relay for efficient implementation of physicallayer network coding. Based on that, we derive an achievable DoF of the MIMO mRC with an arbitrary network configuration of L and K, as well as with an arbitrary antenna configuration of M and N. We show that our proposed scheme achieves the DoF capacity when M
Physicallayer MIMO relaying
 In Proc. Int. Symp. Inform. Theory (ISIT
"... Abstract—The physicallayer network coding (PNC) approach provides improved performance in many scenarios over “traditional ” relaying techniques or network coding. This work addresses the generalization of PNC to wireless scenarios where network nodes have multiple antennas. We use a recent matri ..."
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Cited by 7 (7 self)
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Abstract—The physicallayer network coding (PNC) approach provides improved performance in many scenarios over “traditional ” relaying techniques or network coding. This work addresses the generalization of PNC to wireless scenarios where network nodes have multiple antennas. We use a recent matrix decomposition, which allows, by linear pre and postprocessing, to simultaneously transform both channel matrices to triangular forms, where the diagonal entries, corresponding to both channels, are equal. This decomposition, in conjunction with precoding, allows to convert any twoinput multipleaccess channel (MAC) into parallel MACs, over which singleantenna PNC may be used. The technique is demonstrated using the twoway relay channel with multiple antennas. For this case it is shown that, in the high signaltonoise regime, the scheme approaches the cutset bound, thus establishing the asymptotic network capacity. Index Terms—network modulation, physicallayer network coding, network capacity, multiple access channel, structured codes, nested lattices, MIMO channels, twoway relay channel I.