Radio data system receiver

Abstract: An AF station can be reliably identified even if a poor reception condition occurs temporarily, while suppressing unnecessary searches. In searching an AF station by using a PI code and an AF code, it is judged whether an AF station has a different PI code or whether the PI code of an AF station cannot be identified in a predetermined time period. Such an AF station is preferentially searched a predetermined number of times. If the same AF station remains under one of such conditions a predetermined number of times, then searching this AF station is reserved for a predetermined time period.

Description: BACKGROUND OF THE INVENTION (Field of the Invention) The present invention relates to a radio data system (RDS) receiver capable of performing a reliable search for an alternative frequency (AF) broadcasting station. (Description of the Related Art) With a radio data system RDS, a listener can easily search a preferred radio program or a broadcasting station having a good reception condition. Receivers with various automatic functions can be designed by providing non-audible signals to VHF/FM transmitters. Such automatic functions include an automatic tuning by reading a broadcasting station name, a correct clock, a quick tuning to another channel for picking up traffics information, an automatic turn-on of a preselected program, a display of the contents of a listening program, and other functions. Signals for controlling these functions are digital codes superposed on main program radio signals. This RDS system is flexible so as to add future new functions. The details of these codes are defined by the technical specification of European Broadcasting Union EBU (EBU Document 3244). One of important issues to be solved by RDS is to solve a tuning trouble. In Europe, many programs can be received at various areas because VHF/FM broadcasting service areas are overlapped at a high density. This poses new problems of very difficult tuning, which are particularly conspicuous for car radios. The reasons for this reside in that the service area of a VHF/FM broadcasting differs greatly depending on a transmission power and geography, and that the service area is very small as compared with that of LF, MF, HF transmitters. It is therefore very difficult for a radio program listener to tune to a frequency having an optimum reception condition or to find a program at a desired time. A most significant innovation of RDS is a display of "program and broadcasting station names". This display is a text of 8 alphanumeric characters selected from a stipulated set of coded characters. This text is displayed i the manner similar to a digital frequency display widely used with current radio receivers. A listener can recognize which program is now broadcast and to which station the radio receiver is to be tuned. For example, for a first program of a national network, a text "BBC 1" is displayed. This "program and broadcasting station names" display function is supplemented with a voice synthesizing function of a car radio for a listener to select a program or broadcasting station. For example, a listener can tell a broadcasting station name to tune to it. Using only such a tuning method is not satisfactory in that a listener cannot judge whether the radio receiver is tuning to a frequency most suitable for the area at that time. To this end, two additional functions are required considering the fact that the same program is transmitted to various areas from a certain number of broadcasting stations. These two additional functions are achieved by program identification (PI) codes and alternative frequency (AF) codes. The PI code is not displayed. This code made of 16 bits identifies a country and area to which the program is broadcast, and a broadcasting station broadcasting the program. The list of codes is determined by each country without consultation with other countries. Therefore, the main part of this code is a key to discriminating between countries. The AF code is used, as an alternative of a voice input, to search an alternative frequency of the same program, to evaluate the signal intensity, and to make the radio receiver tune to another channel having the best reception condition. This alternative frequency search is automatically performed by the radio receiver itself, so that the listener is not required to do anything. For such an alternative frequency search, an alternative frequency list is stored in a memory of a radio receiver. Accordingly, it is possible to avoid an unnecessary search for a channel from which a program cannot be received, and to thereby simplify the search operation. Fig.3 is a flow chart showing the operation of an alternative frequency (AF) search by a conventional RDS receiver. For example, this conventional RDS receiver is disclosed by DE 40 39 117 A1. First, it is checked if AF search conditions have been established (step S21). The AF search conditions determine whether an AF search is to be executed or not. If the AF search conditions have been established, AF except for reserve-marked AF is searched from the Af list (step S22). It is then checked whether the electric field Vs of the searched AF is greater than a predetermined value Va (step S23). If Vs is greater than Vs, the broadcasting station code of the PI code of the searched AF is checked (step S24). The PI codes are made of four bytes, the first and second two bytes representing a "country code" and an "area code", and the last two bytes representing a "broadcasting station code" of the same network broadcasting station (i.e., a station broadcasting the same program). If the broadcasting station code is the same as that of the PI code of the AF station in the pre-search, the receiving station is tuned to the searched AF (step S25). At step S24 if the broadcasting code is different from that of the AF station in the pre-search or if the PI code cannot be identified within a predetermined time period due to poor reception conditions,a reserve-mark of five minutes is attached to AF stations of different PI codes or AF stations with unsynchronized PI codes, to thereby stop the AF search of these AF stations for five minutes (step S26) and a radio reception is made at the frequency in the pre-search (step S27). This step S27 is also executed if Vs is smaller than Va at step S23. As described above, in the AF search by a conventional RDS receiver, if it is judged once that the broadcasting code is different from that of the AF station at the pre-search or that the PI code cannot be identified because of poor reception conditions this AF station is judged as being unable to receive. Accordingly, an AF station to which otherwise the radio reception is to be switched, is judged as being unable to receive because of temporary poor reception conditions to be caused such as interference from a private station and the like. Therefore, the AF search becomes impossible thereafter for the time being. SUMMARY OF THE INVENTION It is an object of the present invention to provide an RDS receiver capable of performing a reliable search for an alternative frequency (AF) broadcasting station even if a poor reception condition occurs temporarily, while suppressing unnecessary searches. The above object is achieved by a radio-data system receiver according to present claim 1. A preferred embodiment is claimed in claim 2. Thus, the RDS receiver according to the invention searches an AF station by using a PI code and an AF code of RDS data and switches to a broadcasting station having a good reception condition. In searching an AF station by using a PI code and an AF code, it is judged whether an AF station has a different PI code or whether the PI code of an AF station cannot be identified in a predetermined time period. Such an AF station is preferentially searched a predetermined number of times. If the same Af station remains under one of such conditions a predetermined number of times, then searching this AF station is reserved for a predetermined time period. Brief Description of the Drawings Fig.1 is a flow chart showing the operation of an RDS receiver according to an embodiment of the present invention; Fig.2 is a block diagram showing the structure of the RDS receiver shown in Fig.1; and Fig.3 is a flow chart showing the operation of a conventional RDS receiver. Detailed Description of the Embodiment An embodiment of the present invention will be described with reference to the accompanying drawings. Fig.1 is a flow chart showing the operation of an RDS receiver according to an embodiment of the present invention, and Fig.2 is a block diagram showing the structure of the RDS receiver shown in Fig.1. Referring to Fig.2 showing the RDS receiver of this embodiment, a radio frequency signal received at an antenna ANT is amplified, tuned, and mixed at a front end F/E 1. An intermediate frequency (IF) output signal of the front end 1 is selected, IF-amplified, and frequency-modulation detected by a detector IF/DET 2. The intensity of the IF output signal is also detected by the detector 2. Noises on the signal outputted from the IF/DET 2 are suppressed by a noise canceler NC 3. This noise suppressed signal is stereophonically demodulated by a multiplexer MPX 4. The level of this signal is controlled by a volume controller 5. The signal then passes through a muting unit MUTE 6, is amplified by a power amplifier AMP 7, and reproduced as sounds from a loudspeaker SP. The detected signal from the detector 2 is RDS demodulated by an RDS demodulator 8, and supplied, as RDS data synchronized by a synchronizing microcomputer 9, to a system microcomputer 10. The S meter level signal from the detector 2 is also supplied to the system microcomputer 10. The system microcomputer 10 processes the RDS data, stores data, and controls the entirety of the RDS receiver. A combination of a low-pass filter LPF 11, phase-locked loop PLL 12, and a voltage controlled oscillator VCO built in the front end 1, performs a digital tuning operation. The low frequency components of a phase comparison output of PLL 12 derived by LPF 22 controls the VCO. The operation of the RDS receiver of this embodiment will be described with reference to Fig.1. It is checked whether AF search conditions have been established (step S1). This check includes checking whether the electric field of a broadcasting station has changed to a value smaller than a preset value, and checking whether a predetermined time has lapsed from the previous AF search (which is performed at a predetermined time interval). If the AF search conditions have been established, an AF is searched from an AF list stored in a RAM of the microcomputer. Each AF entry of the AF list has a count of an A counter. The initial value of the A counter is set to = 0. The count of the A counter changes depending upon the results of an AF search. At the first AF search, the A counts of all AF entries in the AF list are 0. At step S2, AF entries are sequentially searched to find an AF satisfying the condition Vs > Va at step S3. If the PI code of the AF with Vs > Va is the same than that of the pre-search frequency, the broadcasting station is switched to the searched AF station at step S5. At step S6, the A count for the searched AF is cleared and set to 0. In this case or at the first AF search, the A count is initially 0 and so the cleared count is also 0. If Vs > Va at step S3 but the PI code is not the same at step S4 because of some reason such as noises, then the A count is incremented by 1. Therefore, the A count is changed from 0 to 1. In this case, because the A count is not 2, reserving an AF search for five minutes is not executed at step S8. At step S9, the pre-search broadcasting station is received. The control then returns back to step S1. At the next AF search, there is an AF entry having the A count set to "1" at the initial AF search. Therefore, at step S2, this AF with A = 1 is first searched with priority over other AF with A = 0. If there is an AF entry having the A count set to "2" for reserving the AF search for five minutes, this broadcasting station will not be searched. The broadcasting station within A = 1 is a station which satisfied the condition Vs > Va but did not satisfy a coincidence of the PI code because of some reason, such as noises at the initial AF search. Such an AF broadcasting station is searched again with priority over other AF broadcasting stations. If the same PI code is obtained at step S4, then a radio reception is changed to this AF station at step S5. If, on the other hand, the same PI code cannot be obtained again at step S4, the A count is increased by 1 at step S7. In this case, the A count of "1" of this AF station is changed to A = 2 to reserve the AF search for five minutes. Namely, the AF station which satisfies the condition Vs > Va but does not satisfy the condition of the same PI code, is searched twice. If the same PI code is not obtained by the two AF searches, this AF station is made to reserve the AF search for five minutes. If the condition Vs > Va is not obtained at step S3, a radio reception is not changed to this AF station but it continues at the pre-search frequency broadcasting station (step S10). The A count of this AF station is cleared to 0. The AF broadcasting station to be searched at step S2 is first the stations with A = 1 and then the stations with A = 0. If the AF station satisfied the condition Vs > Va but did not satisfy the condition of the same PI code at the previous AF search, does not satisfy the condition Vs > Va at the present AF search, then the A count is set to A = 0. If the A count is not cleared to A = 0, the A count is set to A = 2 at the next AF search at step S7, and so this AF station is not searched thereafter for five minutes. In view of this, it is desirable to clear the A count of such an AF station. As described so far, according to the RDS receiver of the present invention, it is possible to reliably discriminate the AF stations to be searched from the AF stations which pose a problem when searched. Accordingly, it is possible not to search unnecessarily the AF stations which pose a problem when searched, reducing the possibility of receiving a different radio program. Furthermore, an AF station can be identified correctly, and a good radio reception condition can be obtained reliably by changing to this AF station.

Claims: Radio-data system receiver comprising a memory for storing an alternative frequency (AF) list which has preselected entries of AF, means for cyclically searching the entries in the AF list for radio reception and means in response to the searching results of AF receptions for changing the receiving frequency to the searched frequency when a reception of the searched frequency satisfies an alternative reception condition, which includes a first criterion and a second criterion, said first criterion being the field intensity of the received frequency and said second criterion being an identification of the PI code, characterized in that said changing means includes means marking the entry in the AF list when the reception of the searched frequency satisfies the first criterion, but fails to satisfy the second criterion, and said searching means searches the marked entry with priority at the next search cycle. The receiver according to claim 1, wherein said searching means repeatedly searches the marked entry by n times, where n is integer, and said marking means clears the mark on the entry when the reception of the searched frequency has not satisfied the second criterion even during n times of searching.

Inventors: TANAKA HIROSHI, TANAKA, HIROSHI
Applicants: KENWOOD CORP, KABUSHIKI KAISHA KENWOOD
Application year: 1992
Main classification: H04H1
IPC codes: H03J7, H04H1