Telecommunications – Carrier wave repeater or relay system – With delay or recording
Reexamination Certificate
1999-08-31
2003-03-18
Legree, Tracy (Department: 2681)
Telecommunications
Carrier wave repeater or relay system
With delay or recording
C455S015000, C455S012100, C455S010000, C370S343000, C370S316000
Reexamination Certificate
active
06535717
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to a method and system for transmitting a signal and receiving and reproducing the signal in a digital broadcasting situation, and a transmitting apparatus and a receiving and reproducing apparatus used in a digital broadcasting situation, suitable for a system for receiving digital satellite broadcasting by a receiver carried in a mobile unit.
(2) Description of Related Art
Recently, in parallel with putting digital satellite broadcasting into practice, there have been developed and proposed various image data compression system, audio data compression system and the like. Also, there are discussed systems of various manner for receiving digital satellite broadcasting by a receiver carried in a mobile unit.
When a satellite broadcasting is to be received, in general, it is necessary to prepare a parabolic antenna for receiving the radio wave of which frequency is allocated by the authority. Therefore, it was unrealistic for a user of the mobile unit to prepare such. an antenna to receive the satellite broadcasting. However, since an S-band (2.6 GHz band) frequency band, which is particularly unsusceptible against rain, is allocated for mobile units to receive the satellite broadcasting, it becomes realistic, for the mobile user for whom proper receiving means was not available, to receive the satellite broadcasting.
When broadcasting is provided for mobile users, a broadcasting receiver receives and reproduces the broadcast digital signal while it is carried in or with moving bodies such as a vehicle, a person, a ship or the like. Therefore, if these moving bodies pass an area near a building, a tree, a bridge, a tunnel or the like, the radio wave transmission path tends to suffer from radio wave cut due to an obstacle. Further, if the receiver is utilized in a stationary fashion, the radio wave transmitted from the broadcasting station also will suffer from radio wave cut due to a moving obstacle, with the result that the broadcast program will suffer from reproduction interruption. Therefore, the receiving side of the broadcast system cannot be provided with a satisfactory broadcasting service due to the disturbance in picture reproduction or audio reproduction. With regard to the disturbance in picture reproduction, if a compensation technology such as a still image retention or the like is effected in the receiving apparatus, uncomfortable feeling of a viewer can be relieved effectively with a relatively easy effort, and it is possible to reproduce images at an acceptable level in visual sensation standpoint. Conversely, if sound reproduction is interrupted on the receiving apparatus, uncomfortable feeling of a listener cannot be relieved effectively with a relatively easy effort even if a countermeasure such as muting or the like is taken. Particularly when an audio broadcasting is provided for mobile users and a driver of a vehicle is paying his/her attention to the reproduced sound intensively, the uncomfortable feeling due to the sound break will affect more badly. Thus, there is a great need in improving the audibility under such situation. Further, under broadcasting situation in which point-to-multipoint communication is carried out, it is substantially impossible to provide a retransmission service for each of the viewers or listeners upon request from receivers of these viewers or listeners. Therefore, it is a responsibility for the communication system to continue the reproduction of the broadcast program without issuing or responding to the retransmission request even if the radio wave cut is brought about.
In order to avoid the above problems, the following countermeasures have been taken.
{circle around (1)} A gap filler (radio wave relaying station or retransmission equipment) or the like is installed at a shadow area of a building, a tree, a bridge or the like to which radio wave is not satisfactorily supplied. Alternatively, a plural number of broadcasting satellites remote from one another are utilized for transmitting radio waves.
{circle around (2)} Under estimation of time duration of radio wave cut expected when broadcasting is interrupted due to an obstacle in the radio wave path, degree of interleave is decided so that the estimated time duration of radio wave cut can be sufficiently recovered. Thereafter, receiving error in a burst fashion is spread so that error is distributed in a random fashion and then the random error is corrected by using an error correction scheme such as Viterbi coding or Reed-Solomon coding.
{circle around (3)} A plurality of channels are prepared for broadcasting a program at the same quality, and each of the signals of the respective channels are transmitted so as to have a time lag larger than the expected radio wave cut time relative to another, whereby any of the transmitted signals with the time lag among them can be successfully received on the receiving side with the result that the broadcast program can be continuously reproduced.
However, according to the countermeasure numbered one, in order to eliminate all areas in which radio wave is not satisfactorily supplied, great number of gap fillers are necessary, which fact necessitates large amount of investment for supplying and installing the equipment. Further, it is difficult to utilize a plural number of satellites from a practical viewpoint. According to the countermeasure numbered two, it is difficult to correct completely error caused from the radio wave obstacles by the scheme composed of interleave and error correction code. When a program is broadcast in a digital manner, the broadcast program is encoded and compressed in every frame. Therefore, even if a frame contains only one bit error, the frame will not be decoded. Furthermore, according to the countermeasure numbered three, if a broadcasting program of the same quality is broadcast by using a plural number of channels, although it offers a satisfactory solution against the radio wave transmission problem, frequency bands cannot be effectively utilized in spite of the fact that the frequency band is a limited resource.
SUMMARY OF THE INVENTION
The present invention is made in view of the above aspect. According to the present invention for a system in which digital satellite broadcasting using S-band for example is received by a receiver carried in a mobile unit, when a time diversity system in which identical data are transmitted a plural number of times, the invention is employed in a mobile satellite broadcasting system to cope with an obstacle in the broadcast radio wave transmission, a plural number of high quality signals, which require the same bandwidth, are not prepared for transmission from the transmitting side, but a low quality signal data, which requires relatively small bandwidth, is transmitted before the high quality signal data is transmitted. When a receiving side receives the broadcasting program, the receiving side selectively reproduces the low quality signal data having the small transmission bandwidth to recover the reproduction of the broadcasting program with the high quality signal. According to the method of transmitting a signal and receiving and reproducing the signal in a digital broadcasting situation, the system for transmitting a signal and receiving and reproducing the signal in a digital broadcasting situation, and the transmitting apparatus and the receiving apparatus used in a digital broadcasting situation of the present invention, since the low quality signal having a relatively small bandwidth is selectively utilized for recovering the program data transmission with the high quality signal, the frequency band for broadcasting can be effectively utilized, and a number of broadcasting programs can be transmitted within a limited width of frequency band. Furthermore, investment on the broadcasting equipment such as a gap filler or the like can be minimized.
According to the proposed method of the present invention in which a signal is transmitted from a transmitting side and the
Katoh Tadayoshi
Matsushima Kazuhisa
Okubo Hiroshi
Saito Takashi
Yokoyama Hideaki
Katten Muchin Zavis & Rosenman
Legree Tracy
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