We study the tradeoffs in employing two different approaches -coding and feedback -for reliable communication over packet erasure channels. Results are shown for a scheme that combines both approaches. Inspired by this scheme, we use rate distortion results to characterize the best achievable tradeoffs for a class of joint coding-and-feedback schemes.
This paper introduces hybrid ARQ protocols for the packet erasure channel -protocols that enable tradeoffs between complexity of encoding/decoding redundant packets and the amount of feedback needed for re-transmission requests. These protocols use adaptations of Tornado codes for erasurecorrection on the forward link, and rate-distortion codes on the reverse link for feeding back the status of received packets. The resulting complexity-feedback tradeoffs are shown to be substantially better (in regimes of practical interest) than a naive protocol that simply time-shares between coding-only and feedback-only approaches.
This paper considers a simple network consisting of a source, a destination, and a relay. In this model, the sourcerelay and relay-destination links are lossless, while the sourcedestination link is subject to erasures. Four coding schemes for reliably conveying k symbols from the source to the destination are described. Three of these techniques are adapted directly from well-known point-to-point coding schemes -viz., the use of maximum-distance separable (MDS) codes and Luby Transform (LT) codes. The fourth approach is a new technique using uncoded transmission from the source in conjunction with a relay that transmits a sequence with this property: When the destination subtracts the effects of the unerased symbols from the sequence, what remains is an "LT-like" code for the erased symbols -and this property holds regardless of which symbols were erased on the source-destination link. The four approaches are compared in terms of their complexity and performance.
This paper considers two simple wireless network configurations in which the links making up the network do not interfere with one another and the assumed link loss mechanisms are erasures. The first configuration is the Msource multiple access relay channel (MARC), in which M different sources convey information to a single destination with the help of a single relay. The second configuration is the two-fold multi-relay channel (MRC), in which a pair of relays help a single source convey information to a single destination. Cut set bounds are established for these configurations, and linear programming is then employed to formulate closedform solutions for the capacity regions as a function of the link parameters; moreover, it is shown that easily-implemented capacity-approaching codes such as LDPC or Tornado codes can be used at the link level to achieve any point in the capacity region. For the erasure MARC, the results indicate that the relay should help only those sources that have a weaker direct channel to the destination than the relay itself does -regardless of the quality of the source-to-relay channels. For the erasure MRC, the solution is not as intuitive, but it displays a structure in which the relative quality of the various links determine which relays are used -and, when both are used, which relay is "primary" and which is "secondary".
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