Errors distribution in SFH mobile radio systems with application to ARQ

The errors distribution for packet transmission over mobile radio systems employing slow frequency hopping (SFH) with non-ideal interleaving is studied. Then, a new analytical methodology is presented to evaluate automatic repeat request (ARQ) techniques, taking into account forward error correction (FEC) and non-ideally interleaved SFH over Rayleigh fading channels. The selective repeat (SR) ARQ and the type I hybrid ARQ/FEC techniques are compared when varying the number of bits per hop, so gradually passing from the non-interleaved non-SFH case to the perfect interleaved case. It is found that the use of SFH and/or interleaving deteriorates the efficiency of the transmission: in other words, when ARQ is applied to slow fading channels the best performance are obtained without SFH and interleaving. The ARQ/FEC technique analyzed gives marginal improvements with respect to pure SR only when perfect interleaving and SFH are applied