Optimising energy efficiency of LDPC coded chase combining HARQ system

The energy efficiency of the low-density parity check (LDPC) coded chase combining hybrid automatic repeat request (HARQ) system over the additive white Gaussian noise channel is analysed. The energy efficiency can be improved by increasing the maximum transmission number (K) and reducing the transmit power. The asymptotic energy efficiency corresponding to K = ∞ equals the reciprocal of the threshold signal-to-noise ratio of the forward error correction code, which does not depend on the falling speed of the word error ratio. When the retransmission number is relatively small, optimising equal transmit power and variable transmit power can improve the energy efficiency by up to 10 and 18% respectively, compared with minimum equal power transmission.