A Simple Delay Time Estimation Method and Its Application to Adaptive OFDM Transmissions for Vehicular Wireless Networks

In this paper, we propose a simple in-service delay time estimation method and two adaptive transmission schemes, that is, adaptive GI length transmission scheme and adaptive modulation transmission scheme, based on the estimation method for broadband vehicular OFDM transmissions. The simple in-service delay time estimation method uses the characteristic that the symmetry of received signal point distribution collapses in multipath propagation environments, obtains the useful information about the delay spread and average BER from the accumulative average value of the detector outputs of sub-carriers of OFDM signals. The proposed adaptive transmission schemes utilize the measured delay time relative information to adaptively change the GI length or modulation method of OFDM signals, achieving high transmission quality and efficiency simultaneously. Assuming a two-ray Rayleigh fading multipath channel model, the effectiveness of these proposed schemes has been confirmed by computation simulations.