Subcarrier Delay Spread Based Adaptive OFDM for Mobile Wideband Waveguide Channels

We propose the use of subcarrier delay spread based adaptive orthogonal frequency division multiplexing (OFDM) for communication through wideband waveguide channels. The technique has important communication applications when robots or vehicles are traveling inside waveguide channels such as tunnels or pipes. The delay spread in these mobile wideband waveguide channels varies significantly across subcarriers because propagation occurs in modes whose characteristics change significantly with frequency. Using knowledge of the delay spread in each subcarrier can then be used to adaptively select and avoid subcarriers with delay spread exceeding the cyclic prefix length. With this approach it is possible to create an OFDM system that is more efficient than systems satisfying the delay spread of all subcarriers. In this paper, we therefore propose subcarrier delay spread based adaptive OFDM to enhance the performance of OFDM systems operating in mobile wideband waveguide channels. To identify the delay spread of individual subcarriers we propose two methods. Using these methods, we provide simulation results to demonstrate the effectiveness of the technique. We also make use of experimental waveguide channel measurements to demonstrate the technique in realistic settings. Results show that performance can be significantly improved by using the proposed approach.