Energy Efficient HARQ for Ultrareliability via Novel Outage Probability Bound and Geometric Programming

Hybrid automatic repeat 1 request (HARQ) is a key enabler for ultrareliable communications. This paper optimizes transmit power the initial transmission and subsequent retransmissions of HARQ with either incremental redundancy or Chase combining, aiming to minimize expected energy consumption given target outage probability latency. The main challenge due fact that complicated function variables which are nested in successive convolutions. existing works mostly use classic upper bound approximate by assuming unbounded power, then convert original problem geometric programming (GP) problem. In contrast, we propose novel much tighter taking practical limit into consideration. new resulting GP method further extended broader group channel models various fading, multiple antennas, receivers. As shown simulations, based on significantly outperforms strategies fix optimize bounding technique.