Energy-Delay Tradeoff Comparison of Transmission Schemes with Limited CSI Feedback

Due to increasing energy cost and various environmental issues, energy efficiency becomes an important issue in wireless communications where spectral efficiency has been considered as a key performance measure. If transmission schemes can be flexible to allow varying average transmission delay (or throughput), the energy-delay tradeoff (EDT) can be exploited. In general, the longer (average) transmission delay, the better energy efficiency can be achieved. In this paper, we study various transmission schemes with limited channel state information (CSI) feedback that can have flexible transmission delay in wireless communications, including hybrid automatic repeat request (HARQ) protocols, and derive EDT characteristics over fading channels. An opportunistic transmission scheme that relies on prior CSI feedback is studied for comparisons with HARQ protocols in terms of EDT. In order to improve the energy efficiency of HARQ, a modified transmission scheme that employs prior CSI feedback is proposed and analyzed to understand its EDT characteristics.