Broadcasting of digital audio, utilizing some unoccupied analog TV bandwidth, requires the use of a guard band to avoid interference with analog TV signal from DAB signal, using OFDM. By adjusting DAB center-frequencies to those of TV signal we have observed a ratio of desired to undesired signals and a ratio of signal to noise.
This paper describes comparison of modulation methods, feasibility of 64QAM-OFDM using vacant frequency band of conventional TV channel, effect of SFN for terrestrial digital television broadcasting (DTV). Terrestrial DTV is going to put into operation in Europe and America. In Japan, discussion about DTV is actively performed to standardize the specification until 2000. OFDM, Orthogonal Frequency Division Multiplexing, is advantageous to multipath distortion and SFN (Single Frequency Network) for terrestrial DTV. Therefore, field tests using NHK's two experimental stations were conducted, and then field strength, BER of DQPSK-OFDM and 64QAM-OFDM, etc. were measured.
Digital video compression systems which should be introduced into broadcast program production have been studied from the view point of picture quality in cascaded coding. Digital video coding technologies are being implemented in program production equipment, which will be connected in tandem, resulting in cascaded video coding. Coding experiments and subjective evaluation were carried out to determine picture quality in cascaded video coding. The results provide us guidelines for introduction of video codec into a total digital broadcasting system.
In order to develop the digital broadcasting, it is necessary to check the compressed CM picture with various image sequences. We have estimated the compressed CM picture quality based on the double-stimulus continuous quality-scale (DSCQS) method described in ITU-R Rec.BT.500. As a result of this method, a relationship between bitrate and CM picture quality for digital broadcasting has been discussed through compressed pictures and subjective assessment tests.