Abstract
In a bi-directional relay channel, two nodes wish to exchange independent messages over a shared wireless half-duplex channel with the help of a relay. In this paper, we derive achievable rate regions for four new half-duplex protocols and compare these to four existing half-duplex 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 and Mixed relaying schemes for the two and three phase protocols. We provide a comprehensive treatment of eight possible half-duplex bi-directional relaying protocols in Gaussian noise, obtaining their relative performance under different SNR and relay geometries.
Highlights
Bi-directional relay channels, or wireless channels in which two nodes1 wish to exchange independent messages with the help of a third relay node r, are both of theoretical and practical interest
A large portion of the results presented will focus on the Compress and Forward (CF)-forwarding scheme, which is seen as an alternative to Decode and Forward (DF) forwarding that is slightly less computationally expensive and may lead to increased rates due to the lack of decoding required at relay nodes
We see that in the high SNR region the sum rate of the Lattice DF Multiple Access Broadcast (MABC) protocol is very close to the outer bound; we show that this gap may be bounded by 1 bit
Summary
Bi-directional relay channels, or wireless channels in which two nodes (a and b) wish to exchange independent messages with the help of a third relay node r, are both of theoretical and practical interest. Due to the half-duplex assumption, during phase 1 both source nodes are transmitting and cannot obtain any “side information” regarding the other nodes’ transmission It may be spectrally efficient since it has less phases than the TDBC protocol and may take advantage of the multiple-access channel in phase 1. 5) Lattice Forward (for Gaussian noise channels only): for MABC protocols where a multiple access channel exists in the first phase, it may be more spectrally efficient to directly decode and forward a linear combination of the transmitted codewords. In [17], [18] lattice codes are used at the terminal nodes for the Gaussian channel in the MABC protocol, allowing the relay to decode a combination of the transmitted messages. We derive achievable regions for new CF and mixed relaying schemes in both the TDBC and MABC half-duplex protocols.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
