Terrestrial digital broadcast in Japan is designed so as to permit various broadcast services by dividing a band into 13 segments. For example, in some regions in the country, 12 segments of the divided 13 segments are used for broadcast for fixed receivers and remaining one segment is used for one-segment broadcast for portable terminals and mobile units. These two broadcast methods are sent in different modulation methods. For example, 12-segment broadcast uses 64 QAM having a high transmission efficiency and carries out high-definition broadcast, multi-channel transmission, and the like. On the other hand, one-segment broadcast uses QPSK having a low transmission efficiency but an excellent error resistance property. Currently, the 12-segment broadcast and the one-segment broadcast send the same contents. Then, equipment such as a vehicle-installed television capable of receiving both broadcasting methods receives broadcast by automatically switching between the 12-segment broadcast and the one-segment broadcast depending upon the receiving state.
However, even when these two broadcast methods send the same contents, time required for encoding processing and time required for decoding processing are different. Therefore, seamless switching cannot be realized only by simply switching the decoded outputs of the two broadcast methods. Then, senders and receivers have been proposed in which output timing of the two broadcast methods are made to be the same with the encoding and decoding times taken into consideration.
FIG. 20 is a block diagram showing a configuration of the above-mentioned conventional receiver (see, for example, patent document 1). A receiver shown in FIG. 20 includes demodulator 1901, first decoder 1902a, second decoder 1902b, delay unit 1903, synthesizer 1904, and display device 1905. A signal demodulated and error-corrected by demodulator 1901 is output to decoder 1902a and delay unit 1903. A signal delayed by delay unit 1903 is output to decoder 1902b. Video signals output from decoder 1902a and decoder 1902b are input into synthesizer 1904. Then, synthesizer 1904 evaluates the image qualities of the input video signals and determines which video signal of decoder 1902a or decoder 1902b is to be output to display device 1905 and carries out switching. Thus, it has been proposed that a signal is delayed for a certain time by using a delay unit, so that the delay amounts of the two broadcast methods are matched to each other.
Thus, in a conventional receiver, a video image having a smaller delay in the two broadcast methods is delayed so as to match a video signal and an audio signal to a video image having a larger delay. Therefore, even when the channel having a smaller delay is changed, an additional time is required until a video signal and an audio signal are output because of delay. Therefore, for example, at the time of searching for a desired program by sequentially changing channels, additional delay occurs every time the channel is changed. A user has to wait for the output of a video signal and an audio signal in order to confirm the contents of program every time the user changes a channel. Therefore, there has been a problem that it takes a long time to search for a desired program.    [Patent document 1] Japanese Patent Unexamined Publication No. 2002-232792.
USPTO Backgrounds
USPTO Backgrounds