Hybrid ARQ using Modulation Switching

Multilevel modulation schemes have variations in bit-reliabilities and each has different symbol reliabilities. Choosing the modulation scheme which has the greatest symbol reliability at target SNR on retransmissions offers more chances to get higher Hybrid ARQ performance by making the sum of total bit-reliabilities greater in the entire decoding block. This paper presents a novel Hybrid ARQ scheme which is focused on reducing the number of bits whose reliabilities are low and increasing the total sum of reliabilities of transmitted bits. Proposed Hybrid ARQ scheme achieves more performance gain when in combination with modulation level switching.