Adaptive modulation techniques for duplex OFDM transmission

TLDR

The study analyzes the design tradeoffs of turbo‑coded burst‑by‑burst adaptive OFDM wideband transceivers. It employs turbo coding, burst‑by‑burst adaptation, and OFDM wideband transceivers to adjust modem mode switching and spectral pre‑equalization. The results show that higher throughput requires more low‑quality subcarriers for high‑order modes, while turbo coding and modem mode switching can achieve near‑error‑free performance at reduced throughput; trellis‑based blind modem mode detection is most powerful, and spectral pre‑equalization tradeoffs confirm that AOFDM enables flexible adjustment of integrity and throughput with or without turbo coding.

Abstract

The design tradeoffs of turbo-coded burst-by-burst adaptive orthogonal frequency division multiplex (OFDM) wideband transceivers are analyzed. We demonstrate that upon aiming for a higher throughput a higher proportion of low-quality OFDM subcarriers has to be used for the transmission of inherently vulnerable high-order modem modes, transmitting several bits per subcarrier. Upon invoking turbo coding and adjusting the modem mode switching regime near-error-free performance can be achieved at the cost of a reduced throughput. Various blind modem mode detection techniques have also been investigated and the most complex channel coding trellis-based detection algorithm was found to be the most powerful. Last, the design tradeoffs of spectral pre-equalization have been explored and quantified. We concluded that AOFDM provides a convenient framework for adjusting the required target integrity and throughput both with and without turbo channel coding.