When Are Dynamic Relaying Strategies Necessary in Half-Duplex Wireless Networks?

Abstract

Abstract-In this paper we study a simple question: when are dynamic relaying strategies essential in optimizing the diversitymultiplexing tradeoff (DMT) in half-duplex wireless relay networks? This is motivated by apparently two contrasting results even for a simple 3 node network, with a single half-duplex relay. When all channels in the system are assumed to be independent and identically fading, a static schedule where the relay listens half the time and transmits half the time combined with quantizemap-and-forward (QMF) relaying is known to achieve the fullduplex performance. However, when there is no direct link between the source and the destination, a dynamic decodeand-forward (DDF) strategy is needed to achieve the optimal tradeoff. In this case, a static schedule is strictly suboptimal and the optimal tradeoff is significantly worse than the fullduplex performance. In this paper we study the general case when the direct link is neither as strong as the other links nor fully non-existent, and identify regimes where dynamic schedules are necessary and those where static schedules are enough. We identify four qualitatively different regimes for the single relay channel where the tradeoff between diversity and multiplexing is significantly different. We show that in all these regimes one of the above two strategies is sufficient to achieve the optimal tradeoff by developing a new upper bound on the best achievable tradeoff under channel state information available only at the receivers. A natural next question is whether these two strategies are sufficient to achieve the DMT of more general half-duplex wireless networks with a larger number of relays. We propose a generalization of the two existing schemes through a dynamic QMF strategy, where the relay listens for a fraction of time depending on received CSI but not long enough to be able to decode. We show that such a dynamic QMF (DQMF) strategy is needed to achieve the optimal DMT in a parallel channel with two relays, outperforming both DDF and static QMF strategies.

Non-orthogonal compute-and-forward with joint lattice decoding for the multiple-access relay channel

“…Also on the contrary to previous works using orthogonal protocol, our protocol is non-orthogonal where the users and the relay can transmit simultaneously. We have designed a low complexity coset decoder for the destination which jointly decodes multiple users' messages from the users' † The proposed scheme may be further improved by optimally scheduling the relay's listening time (Phase 1) and transmit time (Phase 2) as [17]. However, this dynamic scheduling requires highly precise synchronization between nodes and this direction is beyond the scope of our paper.…”

On the Diversity-Multiplexing Trade-off of Hybrid Diamond Relay Channels

“…For example, we often expect to see an increase in the capacity of the network when the half-duplex relays are replaced with full-duplex ones. Regardless of this fact, for certain multiplexing gains and average SNR exponents of different links, the two networks perform the same in terms of DMT [6], [7], [25].…”

Limited Feedback Assisted Dynamic Decode-and-Forward Relaying for Multiple Access Relay Channel

“…The authors in [1] studied an opportunistic DDF for MARC where the relay selection is based on source-to-destination channel gain and have proved that the scheme achieves optimal DMT only at lower multiplexing gains. In [5], DMT of DDF protocol for generalized channels has been derived. It is shown that DDF fails to achieve optimal performance in higher multiplexing gain regime.…”