The power cost of over-designing codes

In “modern” coding theory, the goal of code-design often boils down to maximizing the code girth because from a traditional transmit-power perspective, larger girths ensure better performance. In this paper, we provide an experimental example showing that maximizing code girth can hurt: codes with larger girth can consume significantly larger decoding power. This is because larger girths require increased length of decoder interconnects. Concretely, we show that for (3,4)-regular LDPC codes of girth 6 and 8 decoded using Gallager-A decoding algorithm, the decoders for girth 8 codes can consume up to 36% more power than those for girth 6 codes at high decoding throughputs. Existing results in theoretical literature suggest that this effect will be greatly exaggerated at larger girths and degrees.