Improving OFDM Using Delay-Doppler Channel Estimation

In high-mobility environments, rapid channel variations and intercarrier interference (ICI) hinder the performance of orthogonal frequency division multiplexing (OFDM). Delay-Doppler-based modulation schemes such as ‘orthogonal time-frequency space’ (OTFS) and ‘orthogonal delay-Doppler division multiplexing’ (ODDM) have been proposed to enable reliable transmission in high-mobility environments. However, they come at the expense of increased latency and increased equalisation complexity. In this work, we present a collection of processes to improve the performance of OFDM systems by leveraging delay-Doppler-based processing. First, we propose a segmentation method that significantly improves the accuracy of the generated time-frequency channel response by eliminating the accumulation of phase rotation error across the frame. We then use this method to improve our previous iterative path identification method, where the influence of the identified path is estimated and accounted for. The segmentation method is improved by developing the two-tap equivalent model, improving the accuracy of the generated time-frequency response by adjusting the frequency of the generated phase rotation. Last, we provide a method for estimating the off-diagonal components of the channel so that the bit error rate (BER) remains robust as the maximum Doppler shift increases. We show that the proposed algorithm provides a 2.5 to 10 dB performance improvement over traditional interpolation-based single-tap equalisation at low and high signal-to-noise ratios (SNR)s.