Dynamic Selection of Error-Correcting Codes in Hybrid ARQ Protocols
SRI INTERNATIONAL MENLO PARK CA
Pagination or Media Count:
Packet transmission via automatic repeat request protocol over a channel with unknown, time-varying characteristics is considered. The transmitter, with two error-correcting codes at its disposal, has to decide which to use at any given time. Two algorithms for adapting the error-correcting code to the channel conditions are presented one of them assumes some knowledge of the distribution of errors in a packet, while the other makes no such assumption. Both algorithms are based on the observation that, when a packets decoding is successful, the receiver knows the number of errors in that packet. Both algorithms build a measure for link quality and update it according to the decoding results. The first algorithm makes use of the number of errors in the packet to evaluate the probability that the channel is in a given state. The second algorithm updates its measure according to the highest-rate code that could have possibly corrected that packet. When this measure is above some predefined threshold, the first code is used otherwise the second is employed. The throughput of both algorithms is ascertained and they are found to have excellent adaptivity, approaching that of a transmitter with perfect knowledge of channel conditions. Extensions to more than two codes are discussed.
- Computer Programming and Software
- Computer Systems