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60
ComputeandForward TwoWay Relaying
 IET Commun
"... In this paper, a new twoway relaying scheme based on computeandforward (CMF) framework and relay selection strategies is proposed, which provides a higher throughput than the conventional twoway relaying schemes. Two cases of relays with or without feedback transmission capability are considered ..."
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In this paper, a new twoway relaying scheme based on computeandforward (CMF) framework and relay selection strategies is proposed, which provides a higher throughput than the conventional twoway relaying schemes. Two cases of relays with or without feedback transmission capability are considered. An upper bound on the computation rate of each relay is derived, and based on that, a lower bound on the outage probability of the system is presented assuming block Rayleigh fading channels. Numerical results show that while the average sum rate of the system without feedback, named as Max ComputeandForward (MCMF), reaches the derived upper bound only in low SNRs, that of the system with feedback, named as Aligned ComputeandForward (ACMF) reaches the bound in all SNRs. However, both schemes approach the derived lower bound on the outage probability in all SNRs. For the ACMF, another power assignment based on applying the constraint on the total powers of both users rather than on the power of each separately, is introduced. The result shows that the ACMF performs better under the new constraint. Moreover, the numerical results show that the outage performance, average sum rate, and symbol error rate of the proposed schemes are significantly better than those of twostep and threestep decodeandforward (DF) and amplifyandforward (AF) strategies for the examples considered. Index Terms compute and forward, max computeandforward, aligned computeandforward, feedback, twoway relaying, relay selection, outage probability, average sum rate, symbol error rate. I
On NonBinary Constellations for ChannelCoded PhysicalLayer Network Coding
"... We investigate channelcoded physicallayer network coding in a twoway relaying scenario, where the end nodes A and B choose their symbols, SA and SB, from a small nonbinary field, F, and adopt a nonbinary PSK modulation. The relay then directly decodes the networkcoded combination aSA + bSB o ..."
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We investigate channelcoded physicallayer network coding in a twoway relaying scenario, where the end nodes A and B choose their symbols, SA and SB, from a small nonbinary field, F, and adopt a nonbinary PSK modulation. The relay then directly decodes the networkcoded combination aSA + bSB over F from the noisy received superimposed channelencoded packets. The advantage of working over nonbinary fields is that it offers the opportunity to decode according to multiple decoding coefficients (a, b). As only one of the networkcoded combinations needs to be successfully decoded, a key advantage is then a reduction in error probability by attempting to decode against all choices of (a, b). In this paper, we compare different mappings between F and the PSK constellation, and prove that many have identical performance in terms of frame error rate (FER). Moreover, we derive a lower bound on the performance of decoding the networkcoded combinations. Simulation results show that if we adopt either i) concatenated ReedSolomon and convolutional coding or ii) lowdensity parity check codes, our nonbinary constellations can outperform the binary case significantly in the sense of minimizing the FER and, in particular, the ternary constellation has the best FER performance among all considered cases.
IntegerForcing Linear Receiver Design over MIMO Channels
, 2012
"... Motivated by recently presented integerforcing linear receiver architecture, we propose algorithms to design optimal integerforcing coefficient matrix such that the total achievable rate is maximized. ..."
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Motivated by recently presented integerforcing linear receiver architecture, we propose algorithms to design optimal integerforcing coefficient matrix such that the total achievable rate is maximized.
Weak secrecy in the multiway untrusted relay channel with computeandforward
 IEEE Trans. Inf. Forens. Sec
, 2015
"... We investigate the problem of secure communications in a Gaussian multiway relay channel applying the computeandforward scheme using nested lattice codes. All nodes employ halfduplex operation and can exchange confidential messages only via an untrusted relay. The relay is assumed to be honest b ..."
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We investigate the problem of secure communications in a Gaussian multiway relay channel applying the computeandforward scheme using nested lattice codes. All nodes employ halfduplex operation and can exchange confidential messages only via an untrusted relay. The relay is assumed to be honest but curious, i.e., an eavesdropper that conforms to the system rules and applies the intended relaying scheme. We start with the general case of the singleinput multipleoutput (SIMO) Luser multiway relay channel and provide an achievable secrecy rate region under a weak secrecy criterion. We show that the securely achievable sum rate is equivalent to the difference between the computation rate and the multiple access channel (MAC) capacity. Particularly, we show that all nodes must encode their messages such that the common computation rate tuple falls outside the MAC capacity region of the relay. We provide results for the singleinput singleoutput (SISO) and the multipleinput singleinput (MISO) Luser multiway relay channel as well as the twoway relay channel. We discuss these results and show the dependency between channel realization and achievable secrecy rate. We further compare our result to available results in the literature for different schemes and show that the proposed scheme operates close to the computeandforward rate without secrecy.
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.
Integer ForcingandForward Transceiver Design for MIMO MultiPair TwoWay Relaying
, 2014
"... In this paper, we propose a new transmission scheme, named as Integer ForcingandForward (IFF), for communications among multipair multipleantenna users in which each pair exchanges their messages with the help of a single multi antennas relay in the multipleaccess and broadcast phases. The prop ..."
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In this paper, we propose a new transmission scheme, named as Integer ForcingandForward (IFF), for communications among multipair multipleantenna users in which each pair exchanges their messages with the help of a single multi antennas relay in the multipleaccess and broadcast phases. The proposed scheme utilizes computeandforward (CMF) strategy and Integer Forcing Linear Receiver (IFLR) at relay, which uses equations, i.e., linear integercombinations of messages, to harness the intrapair interference. Accordingly, we propose the design of mean squared error (MSE) based transceiver, including precoder and projection matrices for the relay and users, assuming that the perfect channel state information (CSI) is available. In this regards, in the multipleaccess phase, we introduce two new MSE criteria for the related precoding and filter designs, i.e., the sum of the equations ’ MSE (SumEquation MSE) and the maximum of the equations ’ MSE (MaxEquation MSE), to exploit the equations in the relay. Moreover, in the broadcast phase, we use the two traditional MSE criteria, i.e. the sum of the users ’ mean squred errors (Sum MSE) and the maximum of the users ’ mean squared errors (Max MSE), to design the related precoding and filters for recovering relay’s equations in the users. Then, we consider a more practical scenario with imperfect CSI. For this case, IFLR receiver is modified, and another transceiver design is proposed, which take into account the effect of channels estimation error. We evaluate the performance of our proposed strategy and compare the results with the conventional amplifyandforward (AF) and decodeandforward (DF) strategies for the same scenario. The results
Networkcoded multiple access
 IEEE Transactions on Mobile Computing
, 2014
"... Abstract—This paper proposes and experimentally demonstrates a first wireless local area network (WLAN) system that jointly exploits physicallayer network coding (PNC) and multiuser decoding (MUD) to boost system throughput. We refer to this multiple access mode as NetworkCoded Multiple Access (NC ..."
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Abstract—This paper proposes and experimentally demonstrates a first wireless local area network (WLAN) system that jointly exploits physicallayer network coding (PNC) and multiuser decoding (MUD) to boost system throughput. We refer to this multiple access mode as NetworkCoded Multiple Access (NCMA). Prior studies on PNC mostly focused on relay networks. NCMA is the first realized multiple access scheme that establishes the usefulness of PNC in a nonrelay setting. NCMA allows multiple nodes to transmit simultaneously to the access point (AP) to boost throughput. In the nonrelay setting, when two nodes A and B transmit to the AP simultaneously, the AP aims to obtain both packet A and packet B rather than their networkcoded packet. An interesting question is whether network coding, specifically PNC which extracts packet A ⊕ B, can still be useful in such a setting. We provide an affirmative answer to this question with a novel twolayer decoding approach amenable to realtime implementation. Our USRP prototype indicates that NCMA can boost throughput by 100 % in the mediumhigh SNR regime (≥10dB). We believe further throughput enhancement is possible by allowing more than two users to transmit together. Index Terms—network coding, physicallayer network coding, multiuser detection, multiple access, implementation F 1
Optimized Codes for Bidirectional Relaying
"... Abstract—In this article, we study coding strategies and code optimization for bidirectional relaying using LowDensity ParityCheck codes. We attempt to achieve extreme points in the rate region using densityevolutionbased optimization and a combination of nesting and shortening of codes. The pr ..."
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Abstract—In this article, we study coding strategies and code optimization for bidirectional relaying using LowDensity ParityCheck codes. We attempt to achieve extreme points in the rate region using densityevolutionbased optimization and a combination of nesting and shortening of codes. The proposed method with specific choice of codes achieves rates close to capacity outer bounds. I.
Convolutional NetworkCoded Cooperation in MultiSource Networks with a MultiAntenna Relay
"... ar ..."
1Joint Compute and Forward for the Two Way Relay Channel with Spatially Coupled LDPC Codes
"... Abstract—We consider the design and analysis of coding schemes for the binary input two way relay channel with erasure noise. We are particularly interested in reliable physical layer network coding in which the relay performs perfect error correction prior to forwarding messages. The best known ac ..."
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Abstract—We consider the design and analysis of coding schemes for the binary input two way relay channel with erasure noise. We are particularly interested in reliable physical layer network coding in which the relay performs perfect error correction prior to forwarding messages. The best known achievable rates for this problem can be achieved through either decode and forward or compute and forward relaying. We consider a decoding paradigm called joint compute and forward which we numerically show can achieve the best of these rates with a single encoder and decoder. This is accomplished by deriving the exact performance of a message passing decoder based on joint compute and forward for spatially coupled LDPC ensembles. Index Terms—Network coding, twoway relaying, computeandforward, decodeandforward, density evolution, spatially coupled codes I.