Cognitive access policies under a primary ARQ process via chain decoding

Nicolò Michelusi, Petar Popovski, Michele Zorzi

Research output: Contribution to conferencePaperpeer-review

10 Scopus citations


This paper introduces a novel technique for access by a cognitive Secondary User (SU) to a spectrum with an incumbent Primary User (PU), which uses Type-I Hybrid ARQ. The technique allows the SU to perform selective retransmissions of previously corrupted SU data packets. The temporal redundancy introduced by the primary ARQ protocol and by the selective SU retransmission process can be exploited by the SU receiver to perform Interference Cancellation (IC) over the entire interference pattern, thus creating a "clean" channel for the decoding of the concurrent message. The chain decoding technique, initiated by a successful decoding operation of a SU or PU message, consists in the iterative application of IC, as previously corrupted messages become decodable. Based on this scheme, we design an optimal policy that maximizes the SU throughput under a constraint on the average long-term PU throughput degradation. We show that the optimal policy can be found by first optimizing the SU access policy using a Markov Decision Process formulation, and then applying a chain decoding protocol defined by five basic rules. Such an approach enables a compact state representation of the protocol, and its efficient numerical optimization. Finally, we show by numerical results the throughput benefit of the proposed technique.

Original languageEnglish (US)
Number of pages8
StatePublished - 2013
Externally publishedYes
Event2013 Information Theory and Applications Workshop, ITA 2013 - San Diego, CA, United States
Duration: Feb 10 2013Feb 15 2013


Other2013 Information Theory and Applications Workshop, ITA 2013
Country/TerritoryUnited States
CitySan Diego, CA

ASJC Scopus subject areas

  • Computer Science Applications
  • Information Systems


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