Digital transmission of high bit rate signals using 16DAPSK-OFDM modulation scheme

Radio transmission signals are distorted by multipath propagation and signal level fading in the channel. In the case of digital transmission systems, the distortion of signals causes a degradation of bit error performance. It is an especially severe problem with digital outside-broadcasting-link (OBL) which has to transmit, for example, digital HDTV signals at more than about 45 Mbps. The OFDM modulation scheme can mitigate the adverse effects of multipath fading. An experimental OFDM modem has been developed to enable stable transmission of digital HDTV sources in an OBL. The experimental modem distributes transmitting digital data to 688 carriers in a bandwidth of about 13.5 MHz using the 16DAPSK for each OFDM carrier. A combination of 8DPSK and 2DASK is adopted as the 16DAPSK and another combination of 8DPSK and coherent 2ASK instead of 2DASK is also considered. Indoor transmission experiments confirmed that the 16DAPSK-OFDM is feasible for transmitting high bit rate signals, even under severe propagation conditions