Diierential Modulation with 32-dapsk on Timevariant Mobile Channel for Hierarchical Transmission of Digital Video

| For the hierarchical transmission of digital video employing an OFDM scheme diierential and coherent modulation are compared. Special emphasis is given to limitations due to implementation aspects. We investigated a scheme adopted to a data rate ratio of 1:1 between high priority and low priority video data. For a non{moving receiver and diierential reception we obtained a loss of 2.5 dB (in signal{to{noise ratio) for the high priority and 1.5 dB for the low priority data compared to coherent reception. As the velocity of the receiver increases an additional loss of 1 dB for differential reception is observed at 50 km/h for the low priority data and at 114 km/h for high priority data at a carrier frequency of 474 MHz.