Communication Schemes for Gaussian Two-way Relay Networks
Translated title
Kommunikationsstrategierfor Gaussisk To-vejs Relæ Netværk
Author
Trillingsgaard, Kasper Fløe
Term
4. term
Publication year
2013
Submitted on
2013-06-06
Pages
71
Abstract
Relaying er en trådløs teknik, hvor et mellemled (et relæ) hjælper med at videresende signaler. Det kan både udvide dækningen og udnytte radiospektrum bedre. To-vejs relaying baseret på netværkskodning giver to ender mulighed for at udveksle data via et relæ mere effektivt. Specialet undersøger to beslægtede emner: 1) interaktiv to-vejs relaying og 2) hvordan principperne fra trådløs netværkskodning kan udvides til større, koordinerede relænetværk. I første del ser vi på den klassiske to-vejs relækanal med amplify-and-forward (forstærk-og-videresend), hvor relæet blot forstærker og udsender det, det modtager. Idéen er at bruge interaktion, så noderne kan tilpasse senere sendinger på baggrund af, hvad de tidligere har hørt. To udvidede amplify-and-forward-skemata foreslås, og de opnåelige datahastigheder beregnes. Simulationer viser dog, at de foreslåede skemata ikke giver forbedringer i forhold til kendte metoder. Dette understreger, hvorfor interaktive strategier i informationsteori sjældent giver væsentlige gevinster. Anden del omhandler koordineret relaying, en generalisering af to-vejs relaying. Her fokuseres på et delt relæ, hvor to basisstationer ønsker tovejs kommunikation med to terminaler gennem ét relæ. To relæstrategier udvides til dette net: decode-and-forward (afkod-og-videresend), hvor relæet afkoder før videresendelse, og precode-and-forward (forkod-og-videresend), hvor relæet lineært for-koder og sender uden at afkode. Designet bruger zero-forcing og alignment til at håndtere interferens. Simulationer viser, at decode-and-forward klarer sig bedst ved lavt signal-støj-forhold (SNR), mens precode-and-forward er bedre ved højt SNR. Afslutningsvis vises, hvordan disse idéer kan skaleres til større netværk.
Relaying is a wireless technique where an intermediate node (a relay) helps forward signals, extending coverage and making better use of radio spectrum. Two-way relaying based on network coding lets two endpoints exchange data via a relay more efficiently. This thesis examines two related topics: (1) interactive two-way relaying and (2) how wireless network coding ideas extend to larger, coordinated relay networks. In the first part, we study the classic two-way relay channel with amplify-and-forward, where the relay simply amplifies and rebroadcasts what it hears. The goal is to use interaction so nodes can adjust later transmissions based on earlier receptions. Two extended amplify-and-forward schemes are proposed, and their achievable information rates are computed. Simulations, however, show no improvement over standard methods. This helps explain why interactive strategies in information-theoretic models rarely yield nontrivial gains. The second part addresses coordinated relaying, a generalization of two-way relaying. We focus on a shared relay setting, where two base stations seek bidirectional communication with two terminals through a single relay. Two relay strategies are extended to this network: decode-and-forward, where the relay decodes before forwarding, and precode-and-forward, where the relay applies linear precoding and forwards without decoding. The designs use zero-forcing and alignment to manage interference. Simulations show a regime split: decode-and-forward performs best at low signal-to-noise ratio (SNR), while precode-and-forward is superior at high SNR. Finally, the thesis illustrates how these concepts can scale to larger networks.
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