Full-duplex delay-and-forward relaying

Kai Cheng Hsu, Ching-Ju Lin, Hung Yu Wei

Research output: Chapter in Book/Report/Conference proceedingConference contributionpeer-review

7 Scopus citations


A full-duplex radio can transmit and receive simultaneously, and, hence, is a natural fit for realizing an in-band relay system. Most of existing full-duplex relay designs, however, simply forward an amplified version of the received signal without decoding it, and, thereby, also amplify the noise at the relay, offsetting throughput gains of full-duplex relaying. To overcome this issue, we explore an alternative: demodulate-and-forward. This paper presents the design and implementation of DelayForward (DF), a practical system that fully extracts the relay gains of full-duplex demodulate-and-forward mechanism. DF allows a relay to remove its noise from the signal it receives via demodulation and forward the clean signal to destination with a small delay. While such delay-and-forward mechanism avoids forwarding the noise at the relay, the half-duplex destination, however, now receives the combination of the direct signal from a source and the delayed signal from a relay. Unlike previous theoretical work, which mainly focuses on deriving the capacity of demodulate-and-forward relaying, we observe that such combined signals have a structure similar to the convolutional code, and, hence, propose a novel viterbi-type decoder to recover data from those combined signals in practice. Another challenge is that the performance of full-duplex relay is inherently bounded by the minimum of the relay's SNR and the destination's SNR. To break this limitation, we further develop a power allocation scheme to optimize the capacity of DF. We have built a prototype of DF using USRP software radios. Experimental results show that our power-adaptive DF delivers the throughput gain of 1.25×, on average, over the state-of-the-art full-duplex relay design. The gain is as high as 2.03× for the more challenged clients.

Original languageEnglish
Title of host publicationMobiHoc 2016 - Proceedings of the 17th ACM International Symposium on Mobile Ad Hoc Networking and Computing
PublisherAssociation for Computing Machinery
Number of pages10
ISBN (Electronic)9781450341844
StatePublished - 5 Jul 2016
Event17th ACM International Symposium on Mobile Ad Hoc Networking and Computing, MobiHoc 2016 - Paderborn, Germany
Duration: 5 Jul 20168 Jul 2016

Publication series

NameProceedings of the International Symposium on Mobile Ad Hoc Networking and Computing (MobiHoc)


Conference17th ACM International Symposium on Mobile Ad Hoc Networking and Computing, MobiHoc 2016


  • Demodulate-and-forward
  • Full-Duplex
  • Relay

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