Comparision of frequency and time domain differential modulation in an OFDM system for wireless ATM

Wireless ATM systems at 5.2 GHz will use OFDM as the transmission scheme to combat the frequency selective radio channel. Differential modulation, e.g. DQPSK, is proposed in combination with OFDM to provides a cost-effective solution without the need for equalization. Depending on whether the differential modulated symbols are placed on the same sub-carrier of adjacent OFDM symbols or on different sub-carriers of the same OFDM symbol time domain and frequency domain modulation can be distinguished. Based on new closed-form BER expressions for OFDM/DQPSK transmission schemes with frequency and time domain differential modulation the performance with regard to the radio channel characteristic and the protocols for wireless ATM at 5.2 GHz are investigated