RDS signal detection device

Details RDS signal detection device RDS signal detection device

1997-04-21

2001-07-03

Tse, Young T. (Department: 2634)

Pulse or digital communications

Receivers

Angle modulation

C375S324000, C375S361000, C375S340000, C329S304000, C329S345000

Reexamination Certificate

active

06256359

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a Radio Data System (RDS) signal detection device incorporated in a device to receive and demodulate RDS broadcasting signals, which judges whether signals received are RDS signals or not.
2. Description of the Prior Art
In an RDS broadcast mainly broadcast in Europe, automatic reception control of broadcasting stations which broadcast the same programs is performed using Alternative Frequency (AF) codes contained in data transmitted. In this case, it is necessary to search for a station having the best reception among stations listed in an AF code list and broadcasting the same program. It is also necessary to switch to the selected station as soon as possible. Therefore, selection of the best reception station has been conventionally performed by detecting the strength of reception electric field at each station while output sounds are muted for a very brief duration that is not uncomfortable for listeners so that a reception station is switched to an AF station.
In reception control as described above, the reception station selected according to the AF code can be a non-RDS station, or reception sensitivity of the station is sometimes not good enough to receive RDS data. In cases like these, a Program Identification code (PI code) for judging whether the station selected is a station to broadcast the same program is not detected, and as a consequence selection of a proper station is not performed. Therefore, re-selection of a station on the AF list having a second best strength of reception electric field is performed. For a quicker, more accurate selection, it is necessary to judge, as soon as possible, whether a station switched to is an RDS station or not. Likewise, if only RDS stations are sought and selected or memorized, it is necessary to judge, as soon as possible, whether the station selected is an RDS station or not.
A judging action of an RDS station such as that described above has conventionally been performed by detecting block synchronization or group synchronization of RDS data after broadcasting signal reception has been started by the selected station which was assumed to be an AF station.
The RDS data is configured in blocks of 26 bits. A certain synchronization pattern (offset words) is added to each block. Block synchronization is established by detecting the periodicity of the patterns. One group is configured in four blocks, and group synchronization is established by judging an order of offset words. Conventionally, at least 44 msec, which is equivalent to the length of two blocks, was necessary, since synchronization establishment of RDS data was used to judge an RDS station. Depending on reception conditions, about 200 msec is necessary for judgment because more than 100 msec is necessary for synchronization establishment. Therefore, switching of reception stations may be delayed, or listeners may feel uncomfortable due to a long muting period.
SUMMARY OF THE INVENTION
RDS signals are differentially coded and then biphase coded to suppress power of signals with closer carrier frequencies. In biphase coding, for example, a signal of data 1 is expressed by (1,0), and (0,1) is for a signal of 0. Therefore, one symbol is converted and coded into two symbols. The amplitudes of the carrier frequency signals are modulated by the biphase coding signals. They are then multiplexed into FM base band signals and become actual broadcasting waves.
The present invention takes advantage of the RDS signals which are biphased, and judges whether received signals are RDS signals or not by detecting the existence of pairs of coded symbols within the received signals.
In other words, the present invention distinguishes RDS signals by first detecting inversion of signals within a biphase symbol pair and then by detecting continuity or a ratio of inversion for a certain duration. Another method of RDS signal judgment is to detect, using the same method as described above, stability of output from a pair judgment circuit which detects a combination of biphase symbols.
As described above, it is possible to distinguish an RDS station, before synchronization detection of RDS data, for a much shorter time (e.g., 20 msec) by detecting RDS signals using a demodulator using a characteristic of biphase signals.


REFERENCES:
patent: 4361895 (1982-11-01), Khoudari
patent: 4862513 (1989-08-01), Bragas
patent: 5001728 (1991-03-01), Fuldner
patent: 5175507 (1992-12-01), Roither
patent: 5200980 (1993-04-01), Briddell
patent: 5399987 (1995-03-01), Yamamoto et al.
patent: 5414384 (1995-05-01), Hegeler
patent: 5661761 (1997-08-01), Iwamatsu
patent: 5745845 (1998-04-01), Suenaga et al.
patent: 5777511 (1998-07-01), Masumoto et al.
patent: 5778031 (1998-07-01), Hiramatsu
patent: 5867533 (1999-02-01), Fleek et al.
patent: 6038434 (2000-03-01), Miyake
patent: 6118831 (2000-09-01), Masumoto et al.
patent: 0717517 (1996-06-01), None
patent: 8037543 (1996-02-01), None
patent: 08084161 (1996-03-01), None

Affiliated with

Also associated with

Rating

RDS signal detection device does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with RDS signal detection device, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and RDS signal detection device will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2498036