Doppler Spread Estimation and Channel Update Period Tuning in OFDM-Based Vehicular Communication Systems

Decision directed channel estimation (DD-CE) techniques turn useful for transmissions in time-varying wireless vehicular channels. CE has to be updated several times during the transmission of long data frames. Related works assume that, for IEEE802.11p-compliant physical layer systems, DDCE is performed for every input OFDM symbol, hence independently of the experienced Doppler effect. The purpose of this paper is twofold. First, it is shown how the estimation of the Doppler spread can be reliably performed in vehicular scenarios, and, moreover, an improved yet simplified version of the hybrid autocorrelation-based estimator is proposed. Second, it is discussed how the resulting vehicle relative speed estimate can be used to tune the CE update refresh period accordingly (and thus reduce the power consumption and processing time at the receiver for low to medium speed ranges). In order to reach this goal, it is introduced a novel method that relates the CE update rate to a maximum pre-established threshold value of the signal-to-noise ratio degradation due to CE update delay.