Telecommunications – Receiver or analog modulated signal frequency converter – Signal selection based on frequency
Reexamination Certificate
1997-12-08
2001-02-27
Tsang, Fan (Department: 2746)
Telecommunications
Receiver or analog modulated signal frequency converter
Signal selection based on frequency
C455S158500, C455S186200, C370S486000
Reexamination Certificate
active
06195538
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
The present invention relates to a receiver for receiving text-based multiplex broadcasts.
2. Description of Related Art
For example, in Japan, FM broadcasts called “FM text-based multiplex broadcast” are realized in which character information data or the like are multiplexed and transmitted together with the original audio broadcast program.
Such FM text-based multiplex broadcast in Japan is called a DARC (Data Radio Channel) method, which was developed with NHK Broadcasting Technology Research Institute as leader. The multiplexing standard for digital data such as character information is as follows:
Subcarrier frequency: 76 kHz
Transmission rate: 16 kilobits/sec.
Modulation method: LMSK (Level Controlled Minimum Shift Keying)
Error correction method: (272, 190) product code using compacted difference set cyclic code
The LMSK signal is frequency multiplexed together with the audio signal (monaural signal or stereo composite signal) in the original audio broadcast program, and the frequency multiplex signal is transmitted.
Program services such as character information can be classified into levels
1
,
2
and
3
. In all three cases, character information or the like is displayed using a dot display. In level
1
, the information is provided as character information in a service for a FM receiver capable of displaying 15.5 characters×2.5 lines including a header.
In level
2
, the information is provided as characters and figures in a service for a FM receiver capable of displaying 15.5 characters×8.5 lines including a header. Level
3
is for traffic information services provided for FM receivers capable of displaying detailed maps using CD-ROM or the like, namely, navigation systems.
Level
1
program services can be utilized for news, weather forecasts, traffic information, entertainment, main supplementary programs and the like. In this case, the entertainment would include services providing fortune-telling, messages from listeners, quizzes, town information and the like.
The main supplementary program provides information for supplementing the original audio broadcast program such as the title of the musical composition, the performer's name, telephone and fax numbers for requests when the original audio broadcast program is, for example, a music program. In this respect, the main supplementary program will be hereinafter referred to as “program information” or “program linkage”.
In addition to the above program service, “emergency information” may also be provided as required at the time of emergencies.
Data Structure
FIG. 7A
shows the frame structure of a data signal which is multiplexed in the FM text-based multiplex broadcast of the DARC method. One frame of this data signal is composed of 272 blocks with each block comprising 288 bits.
One frame comprising 272 blocks is divided into 190 data packet blocks, and 82 vertical parity packet blocks, with the 82 vertical parity packet blocks being distributed and transmitted in the frame.
A 16-bit BIC (Block Identity Code) is added to the head of each block. Four kinds of BIC are used for distinguishing each of the parity packets, and thus the heads of the frame can be discerned.
The data packet block has a 176-bit data packet following the BIC, after which a 14-bit CRC (Cyclic Redundancy Check) code is added, followed by an 82-bit horizontal parity check code.
In this case, the CRC code is added for detecting residual errors after error correction using a product code.
The vertical parity packet block is provided to have a 272-bit vertical parity packet following the BIC.
The data packet consists of a 32-bit prefix and a 144-bit data block following it as shown in FIG.
7
B.
The prefix consists of a service identity code, a decode identity flag, an information end flag, an updating flag, a data group number, a page number, a data link code, and a data packet number as shown in FIG.
7
C.
In this case, the service identity code consists of 4 bits, and is for discerning the program contents and the like.
Regarding level
1
,
0: Undefined
1: General information for sequential reception processing
2: General information for recording and reception processing
4: Traffic information
In this case, the sequential reception processing is a mode for the FM receiver starting decoding processing for displaying on receipt of the first data packet of the program data or the page data. This sequential reception processing is carried out for a program for which it is required on the transmission side to control timing of displaying on the receiving side or for a program for which the information will not be displayed in time if the decoding processing is started after the last packet of the data group is obtained.
The recording and reception processing is a mode for not starting the decoding processing for displaying until all of the data for the program data or the page data are received and error correction is carried out using CRC code for every data group. Therefore, it is possible in the character program in the recording and reception processing to control the timing of displaying on the FM receiver side.
In the prefix, the decode identity flag is “1” when the error correction circuit for the FM receiver outputs data by decoding in the horizontal direction only, and “0” when the data are outputted after decoding in the horizontal direction and the vertical direction.
The sequential reception processing, when the decode identity flag is “0”, is defined in such a manner that decoding processing for displaying each of the data packets is carried out at the time when the FM receiver receives the BIC at the head of the 302nd packet from the reception of the BIC at the head of respective data packets.
The information end flag is “1” when transmission of a data group with a certain data group number is completed, and “0” when this is not the case. The updating flag is incremented by one every time a data group is updated.
The data group number is formed of a program number and a page number. The program number is 8 bits, and is from 0 to 255. It is assigned as follows:
0: Main menu
1 to 253: General character program (such as news and weather forecast)
254: Main supplementary program (program information or information linkage)
255: Emergency information.
Further, the page number is 6 bits and is from 1 to 62, i.e., one program can have a maximum of 62 pages. One page corresponds to one data group, with one data group comprising one or a plurality of data blocks.
Furthermore, in the prefix, when the data is so large that the number of data packets belonging to one data group exceeds the maximum value of the data packet number, the data group is divided into a maximum of 4 data groups. When the data group is then transmitted with the same data group number having different data link codes, the data link code is used for linking each of the data groups in the order of 0→1→2→3. The data packet number is allocated in sequence from “0”.
The foregoing expresses a data format using the DARC method. Since the data transfer rate and the frame size are as described above, the time required for broadcasting or transmitting data for one frame is a little less than five seconds (=288 bits×272 blocks/16 kilobits).
Example of Display of Character Program
The FM receiver corresponding to level
1
is provided with a display element DSP such as an LCD as shown in
FIG. 8
, having a display area capable of displaying 15.5 characters×2.5 lines (248 dots in width by 40 dots in length). In the display area, the 0.5 line area in the upper portion thereof is for displaying the header, and the 2 lines area in the lower portion is for displaying the text.
When the FM receiver receives the text-based multiplex broadcast, the first page of a main menu is displayed on the display element DSP as shown in FIG.
9
A. When a predetermined key operation is performed while the first page is displayed in such a way, the next page of the main menu is disp
Maioli Jay H.
Sobutka Philip J.
Sony Corporation
Tsang Fan
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