ARUM: Polar-Coded HARQ Scheme Based on Incremental Channel Polarization

A hybrid automatic repeat request (HARQ) scheme for polar codes, called active-bit relocation under masks (ARUM), is proposed. In each transmission, the data bits are encoded and bitwisely XOR-masked using a binary vector before being transmitted through the channel. The masking process combines multiple transmissions together and forms another step of intertransmission channel transform. The reliabilities are updated after every transmission, and the less reliable bits in earlier ones are relocated to the more reliable positions at the latest transmitted block. ARUM is a very flexible HARQ scheme that allows varying mother code length and arbitrary rate-matching scheme. Simulation shows that ARUM can obtain near-optimal coding gain after combining multiple transmission blocks.