Very Short Channel Codes for Burst-Type Transmissions

Modern frequency hopping transmission systems in the very high frequency (VHF) band strive for hopping intervals of about one millisecond. Combined with typical VHF baud rates the transmission bursts have a block size of several tens of bits. In this paper soft output channel codes for such short block sizes are investigated in two different continuous phase modulation (CPM) transmission schemes. An optimal and a near optimal convolutional tail-biting decoder are compared to a Polar decoder in terms of bit and word (burst) error rate and computational complexity. Theoretical performance bounds are considered as well. Furthermore it is evaluated how many iterations between the channel decoder and the CPM detector are reasonable. In both CPM schemes the Polar decoder performs better than the tail-biting decoders and additionally requires significantly less computational power than the optimal tail-biting decoder and at most is approximately equally complex as the near optimal one. More than two decoder detector iterations did not show any more performance improvement.