Low Complexity Partial Retransmission ARQ with Hard-Decision Message-Passing Technique

Partial retransmission ARQ allows a sender to retransmit only part of a frame. This paper proposes a low complexity method using hard-Decision Message-Passing (hMP) technique to correct some errors and verify many correct symbols. A new feedback frame format is also presented. The tradeoff of the lower complexity is the unnecessary retransmission due to false unverified symbols. Results show this tradeoff as the percentage of false unverified symbols, which is from 1.95% to 10.28% for the (60,30) LDPC code with density of 10% and p
e
from 0.06 to 0.22 in a q-ary symmetric channel. This is very small and worth the reduction in complexity. With systematic codes, the percentage of unnecessary retransmission is decreased from 20.66% to 10.28% at p
e
= 0.22 for 10% density case. The code with density of 10% provides the best decoding performance and fewest unnecessary retransmissions.