Communication Schemes for Gaussian Two-way Relay Networks

Trillingsgaard, Kasper Fløe

4. term

Elektronics and IT, Master (Elite Wireless Communication)

2013

2013-06-06

71 pages

Trådløse relæer forventes at få stor indflydelse i fremtidens trådløse netværk. Denne rapport omhandler to relaterede emner: interaktiv to-vejs kommunikation via et relæ og udvidelse af strategier for netværkskodning i relæ netværk til større netværk. Første del af rapporten forsøger at øge de opnåelige transmissions rater for et tre-terminals relæ netvæk med to-vejs kommunikation ved brug af interaktive amplify-and-forward strategier. To interaktive metoder er introduceret og de opnåelige transmissions rater bliver beregnet. Ved brug af simulering vises dog at metoderne ikke opnår bedre transmissions rater end den tradionelle amplify-and-forward metode. Anden del af rapporten omhandler koordinerede relæer, som er en generalisering af det simple tre-terminals relæ netværk. Der tages udgangspunkt i to mere avancerede relæ netværk, og der designes kommunikationsstrategier, som muliggøre effektiv kommunikation ved brug af principperne alignment og zero-forcing. To grundlæggende kommunikationsstrategier, kaldet precode-and-forward og decode-and-forward, udvides til disse mere avancerede relæ netværk. Herefter beregnes de opnåelige transmissions rater og sammenlignes. Simuleringer viser at precode-and-forward giver de bedste resultater ved høj signalstøjforhold, hvorimod decode-and-forward fungerer godt ved lave signalstøjforhold. Den endelige konklusion er at principperne, alignment og zero-forcing, skalere til større netværk.

Relaying is a transmission technique that promises coverage extension and an increased spectral efficiency. The advent of two-way relaying based on network coding opened a large design space in wireless networks. Two related topics are addressed in this thesis: interactive two-way relaying and extension of the wireless network coding principle to larger networks. The first part attempts to increase the achievable rates of the amplify-and-forward scheme for the traditional two-way relay channel using interaction. Two extended amplify-and-forward schemes are put forth, and the achievable rates are computed. Simulation results, however, show that no improvements are achieved using the proposed schemes. This once more confirms why there are so few interactive communication strategies in information theory that lead to nontrivial improvements. The second part addresses coordinated relaying, which is a generalization of two-way relaying. In particular, the study focuses on the shared relay, in which two base stations wish to attain two-way communication to two terminals through one relay. The relay schemes, precode-and-forward and decode-and-forward, are extended to this relay network using the concepts of zero-forcing and alignment. The simulation results show that the decode-and-forward scheme performs well at low SNR while precode-and-forward is better at high SNR. Finally, it is illustrated how these concepts can scale to larger networks.

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