1. Field of the Invention
The present invention relates to a television receiving method and a television receiver.
2. Description of the Prior Art
Today, the trend of television broadcasting has been toward digitization. In Europe and the United States, digital television broadcasting has been put to practical use. In the digital television broadcasting, voices (audios) and images (videos) are digitally coded by an MPEG (Motion Picture Expert Group)-2 system, are modulated by a digital modulation system employed in each of areas, and are transmitted. As the modulation system, an OFDM (Orthogonal Frequency Division Multiplexing) system and an 8-VSB (Vestigial Sideband) system are respectively employed in Europe and the United States. Also in Japan, experiments in a system based on the OFDM system have been conducted.
The digital broadcasting is characterized in that broadcasting of higher video quality and higher audio quality can be done in the same frequency band, as compared with conventional analog broadcasting, and approximately three programs can be simultaneously broadcast if the video quality and the audio quality in the broadcasting are approximately the same as those in the conventional analog broadcasting.
A time period during which ground wave digital broadcasting is introduced differs depending on the areas by the circumstances of the construction of broadcasting facilities. In order not to affect viewers of the conventional analog broadcasting, the analog broadcasting is continued until it is shifted to the digital broadcasting. Further, in order to promote the shift of the viewers to the digital broadcasting, there are many cases in which a program having the same contents as those of a program broadcast in the analog broadcasting is also broadcast in the digital broadcasting, and the analog broadcasting program which is being simultaneously broadcast can be also viewed in a digital broadcasting receiver.
FIG. 4 illustrates the configuration of a television receiver which is expected to be used in a time period during which digital ground wave broadcasting is introduced.
Reference numeral 100a denotes an antenna for analog television broadcasting, reference numeral 101 denotes an analog broadcasting tuner for selecting a desired channel frequency in analog broadcasting, reference numeral 102 denotes an analog broadcasting demodulator for detecting and demodulating analog broadcasting waves and converting the analog broadcasting waves into an audio/video signal, and reference numeral 103 denotes an audio/video processor for converting the audio/video signal into a signal in such a form that it can be outputted to an audio/video output device 111.
Reference numeral 100b denotes an antenna for digital television broadcasting, reference numeral 105 denotes a digital broadcasting tuner for selecting a desired frequency channel in digital broadcasting, reference numeral 106 denotes a digital broadcasting demodulator for converting received broadcasting waves into digital data, reference numeral 107 denotes an error correcting device for detecting and correcting errors by an error correcting function to which the digital data has been previously subjected, reference numeral 109 denotes an audio/video decoder for converting digital audio/video data into data in such a form that it can be outputted to the audio/video output device 111, reference numeral 110 denotes a switching device for selectively outputting received audios and videos in analog broadcasting and digital broadcasting, reference numeral 111 denotes an audio/video output device comprising a cathode ray tube, a speaker, and their peripheral circuits for outputting the received audios and videos, and reference numeral 112 denotes a control microcomputer for carrying out control of a system, for example, control of channel selection.
In a time period during which ground wave digital broadcasting is introduced, it is generally considered that digital and analog receiving systems are thus provided in a television receiver, to make both digital and analog broadcasting waves receivable. The analog broadcasting waves are inputted to one of input terminals of the switching device 110 through the antenna 100a, the analog broadcasting tuner 101, the analog broadcasting demodulator 102, and the audio/video processor 103. The digital broadcasting waves are inputted to the other input terminal of the switching device 110 through the antenna 10b, the digital broadcasting tuner 105, the digital broad casting demodulator 106, the error correcting device 107, and the audio/video decoder 109.
The control microcomputer 112 switches the switching device 110 to the analog side or the digital side upon receipt of an instruction to perform channel selection from a user, and issues an instruction to select a frequency to the analog broadcasting tuner 101 or the digital broadcasting tuner 105. Consequently, audios and videos on a channel desired by the user are outputted to the audio/video output device 111.
Even if the ground wave digital broadcasting is introduced, all areas are not covered at one time by digital broadcasting, and a time period during which the ground wave digital broadcasting is introduced differs depending on the areas. When the television receiver is moved to the outside of a service area where the ground wave digital broadcasting has not been introduced from the area where the ground wave digital broadcasting has been introduced, therefore, a program which is being viewed may, in some cases, be unreceivable. Even in the area where the ground wave digital broadcasting is introduced, it is considered that there is a place where the digital broadcasting is unreceivable, for example, a place concealed behind an office building particularly at the time of mobile receiving.
Even in the area where the ground wave digital broadcasting has been introduced, the analog broadcasting is continued for the time being in order to protect viewers. In the area where both the digital broadcasting and the analog broadcasting are done, it is considered that the receiving conditions of the analog broadcasting and the digital broadcasting differ particularly at the time of mobile receiving depending on conditions such as the difference between the propagation characteristics of analog and digital broadcasting waves and the difference in the position of a transmitting antenna. That is, even when the user enters the place concealed behind the office building where the digital broadcasting cannot be received during mobile receiving, the analog broadcasting of a certain degree of quality may be receivable. An operation for selecting a program every time the digital broadcasting cannot be received by the user is troublesome.