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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
ComputeandForward: Finding the Best Equation
"... Abstract — ComputeandForward is an emerging technique to deal with interference. It allows the receiver to decode a suitably chosen integer linear combination of the transmitted messages. The integer coefficients should be adapted to the channel fading state. Optimizing these coefficients is a Sho ..."
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Abstract — ComputeandForward is an emerging technique to deal with interference. It allows the receiver to decode a suitably chosen integer linear combination of the transmitted messages. The integer coefficients should be adapted to the channel fading state. Optimizing these coefficients is a Shortest Lattice Vector (SLV) problem. In general, the SLV problem is known to be prohibitively complex. In this paper, we show that the particular SLV instance resulting from the ComputeandForward problem can be solved in low polynomial complexity and give an explicit deterministic algorithm that is guaranteed to find the optimal solution. I.
1Distributed ComputeandForward Based Relaying Strategies in MultiUser MultiRelay Networks
"... The computeandforward (CMF) relaying technique, proposed by Nazer et al., provides a substantially higher network coding throughput in multiuser cooperative networks, compared to the other conventional relaying techniques. The improvement is due to exploiting the multiuser interference rather tha ..."
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The computeandforward (CMF) relaying technique, proposed by Nazer et al., provides a substantially higher network coding throughput in multiuser cooperative networks, compared to the other conventional relaying techniques. The improvement is due to exploiting the multiuser interference rather than avoiding it. However, a major drawback of this strategy is that the equations decoded by different relays are not necessarily linearly independent, and hence a rank failure may occur at the destination; which results in a substantial reduction of the system rate as well as the diversity order. In this paper, we propose three practical distributed schemes to deal with the problem in a multiuser multirelay network without central coordinator, in which the relays have not any prior information about each other. In first scheme, a new relaying strategy based on CMF, named incremental computeandforward (ICMF), is proposed that requires cooperation among relays. Second, a novel simple strategy, called amplifyforward and compute (AFC), is introduced in which the equations are recovered in the destination rather than in the relays. Finally, the two schemes ICMF and AFC strategies are combined to present hybrid computeamplify and forward (HCAF) relaying scheme, which improves the performance of the ICMF considerably. We evaluate the performance of our proposed strategies and compare the results with those of the conventional CMF strategy and also the well known Decode and Forward (DF) strategy. The results indicate the substantial superiority of the proposed schemes, specially at the higher number of users and also relays.