Per-prediction for PHY mode selection in OFDM communication systems

Modern wireless communication standards like HiperLAN/2 or IEEE802.11a provide a high degree of flexibility on the physical layer (PHY) allowing the data link control (DLC) layer to choose transmission parameters with respect to the currently observed link quality. This possibility of so-called link adaptation (LA) is a key element for meeting quality of service (QoS) requirements and optimizing system performance. The decisions made by the LA algorithm are typically based on a prediction of the packet error rate (PER) implied by a certain transmit parameter setting. With most existing LA schemes, this prediction is based on the observed signal-to-noise ratio (SNR) or carrier-to-interference ratio (CIR), respectively. For frequency selective channels, however, the SNR alone does not adequately describe the channel quality. It is shown in this paper that LA schemes based on an accurate description of the momentary channel status can outperform conventional schemes with respect to throughput and reliability. Based on a novel "indicator" concept, schemes for obtaining an accurate prediction of the PER by evaluation of the channel transfer function are presented and evaluated by software simulation.