Rate-splitting for polar codes on block fading channels without CSIT

This paper presents a polar code design for block fading channels when no channel state information is available at the transmitter, which involves that the frozen bits cannot be changed dynamically with the fading realizations. An outer parallel code is concatenated with an inner polarization kernel that changes the properties of the block fading channel. The rate-splitting between the parallel outer codes is optimized for minimizing the system's outage probability. We show that when polar codes are used as component outer parallel codes, the overall coding structure is a polar code whose frozen bits are designed according to the rate-splitting optimization. It is shown that this scheme achieves quasi-optimal performance at high throughput with ARQ mechanisms.