Telecommunications – Transmitter and receiver at separate stations – Having measuring – testing – or monitoring of system or part
Patent
1992-07-01
1995-06-06
Eisenzopf, Reinhard J.
Telecommunications
Transmitter and receiver at separate stations
Having measuring, testing, or monitoring of system or part
455 44, 455115, H04B 1700
Patent
active
054230713
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a base station for a radio system, the base station supervising the quality of a radio link between the base station and mobile stations, and includes a generator circuit for generating a supervising signal having a desired baseband frequency; a measuring circuit for monitoring the level of the baseband supervising signal; a transmitting circuit for frequency-modulating a transmitting-frequency carrier of the baseband supervising signal and transmitting it to the mobile radio station, a receiving circuit for detecting the supervising signal transmitted back from the mobile radio station and modulating it to a receiving frequency; and a signal processing circuit for determining the quality of the used radio link.
2. Description of the Related Art
In the NMT (Nordic Mobile Telephone) mobile telephone system, the quality of the radio link between a base station and a mobile telephone is supervised by special supervising signals. The base station generates a supervising signal, e.g. by lowpass-filtering from a clock signal having a desired supervising signal frequency. The NMT system utilizes four supervising signal frequencies with spacings of 30 Hz. The base station transmits a supervising signal to the mobile telephone, which returns the supervising signal immediately to the base station, and the base station determines the quality of the used radio link, especially the signal-to-noise (S/N) ratio, by way of the received supervising signal.
When the level of the baseband supervising signal generated at the base station changes for some reason before transmission, this change in level appears as a number of deviation variations in the radio-frequency signal transmitted from the base station to the mobile telephone and frequency-modulated by the supervising signal and also affects the measuring accuracy of the S/N ratio of the radio link. In order to ensure that the measured S/N ratio describes the quality of the radio link sufficiently accurately, the NMT specifications define that the deviation caused by the supervising signal must not deviate from a set value by more than 10%. Today the level of the supervising signal is monitored by a measuring circuit comprising a rectifier and comparators, for which appropriate threshold voltages corresponding to the lowest and the highest allowable level of the supervising signal are set by a calibration circuit including adjustable resistors. Such a measuring circuit is, however, slow and difficult to calibrate, as it requires at least two adjusters and four adjusting procedures.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a base station having a more accurate, more reliable, and more easily calibrateable control of the supervising signal level.
In the first embodiment of the invention, this is achieved by a base station provided with a measuring circuit comprising an A/D converter for deriving digital sample values from the baseband supervising signal. A control circuit is also provided which controls, on the basis of at least one reference value stored in a memory in connection with the calibration, a difference between the sample values and a digital sample value, corresponding to a supervising signal level causing a desired deviation in a output signal of the transmitting circuit, is no more than a predetermined difference value.
In the preferred embodiment of the invention, a microprocessor used as the control circuit calculates alarm limit values from a reference value stored in the memory in the calibration of the supervising signal, the reference value being a digital sample value provided by the A/D converter from a supervising signal level causing a desired deviation. During the calibration of the level of the supervising signal, the microprocessor is merely indicated when the measured deviation caused by the supervising signal is such as desired, whereby the microprocessor stores the sample value obtained by the A/D converter in its memo
REFERENCES:
patent: 4870699 (1989-09-01), Garner et al.
patent: 4910791 (1990-03-01), Dickinson et al.
Patent Abstracts of Japan, vol. 11, No. 314, E549, Abstract of JP 62-108624, publ 1987.
Derwent's abstract No. G90 38 D/30, SU 767 980, publ week 8130.
Patent Abstracts of Japa, vol. 9, No. 3212, E367, abstracts of JP 60-153232, publ 1985.
Eisenzopf Reinhard J.
Telenokia OY
Vo Nguyen
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