Channel estimation, overhead, and outage for PSAM-OFDM

Ever growing demand for wireless services and a dearth of quality spectrum requires more efficient use of available bandwidth. Cross-layer design has the potential for more efficient system design than is possible considering each layer in isolation. In this article, we consider goodput optimization of pilot-symbol assisted modulation with orthogonal frequency division multiplexing (PSAM-OFDM). Here goodput accounts for both the training overhead at the physical layer (PHY) and re-transmission of lost blocks at the medium access control (MAC) layer. We present a novel formulation of the cross-layer goodput metric using natural extensions of the mean and variance of the mutual information of PSAM-OFDM found in the literature. From this formulation we identify a practical tradeoff between the frequency-diversity offered by a channel and the signal overhead necessary to exploit that diversity. This has direct implications for the optimization of time-scaled OFDM signals (e.g. channelized OFDM). We show that our optimization of channel bandwidth results in higher aggregate goodput than alternatives proposed in the literature. Finally, we show that the conventional optimization of pilot power allocation to maximize physical layer throughput (considering only physical layer overhead) also maximizes the cross-layer goodput.