Doppler Spread Suppression Technique for an L-Band Digital Radio Broadcast System

The orthogonal frequency division multiplex (OFDM), which is at the heart of many digital broadcasting and wireless standards, is very sensitive to Doppler spread induced by time variations of the mobile channel. This undesirable effect can be particularly detrimental to system performance when such a system is used for vehicular reception at high frequency bands since the maximum Doppler frequency f_dmax is proportional to the radio frequency of the received signal and vehicle speed. In this paper we propose to study the performance of a dual-antenna Doppler spread mitigation technique applied to a mobile digital radio broadcast system (Canadian DAB system in mode IV). This technique uses a linear antenna array, parallel to the direction of motion of the vehicle, and estimates the received signal at a virtual point by using space domain minimum mean square error (MMSE) type interpolation. Laboratory test results show that this scheme can effectively reduce bit error degradations caused by the spread of the Doppler spectrum at high vehicle speeds. Field tests have been performed and analysis of the collected data is underway to validate the proposed technique for an L-band DAB system.