Monitoring and alarm circuitry for a base station transmitting supervising signals to one or more mobile radio stations

Claim 1

In a base station for a radio system having apparatus for monitoring radio link quality between the base station and at least one mobile radio station by transmitting a test signal from the base station to the mobile radio station, retransmitting from the mobile radio station back to the base station a response signal based on the test signal as received by the mobile radio station, and determining signal-to-noise ratio of the response signal as received by the base station, an apparatus improvement for ensuring that signal strength of the test signal remains within pre-selected limits and thereby has a given range of effect on the frequency range of said test signal and, therefore, on the signal-to-noise ratio of the response signal as received by the base station, said apparatus improvement comprising: a signal generator for generating a baseband supervising signal having a desired baseband frequency; a measuring device for monitoring signal strength of said baseband supervising signal; a frequency modulator for frequency-modulating said baseband supervising signal on a radio-frequency carrier and for transmitting a modulated test signal thereby produced, for reception by the mobile radio station; a receiver for detecting the response signal transmitted by the mobile radio station based on reception at the mobile radio station of said modulated test signal; said measuring device comprising an A/D converter effectively coupled to said signal generator for obtaining time-spaced digital samples indicative of signal strength of said baseband supervising signal; a memory device effectively coupled to said measuring device for storing at least one reference correlation between signal strength of said baseband supervising signal, and a preselected desirable frequency deviation of said modulated test signal; a signal processor effectively coupled between said A/D converter and said memory device, for comparing said digital samples with said at least one reference correlation; and an alarm device effectively included in said signal processor for providing an alarm when comparisons provided by said signal processor indicate that signal strength of said baseband supervising signal correlate to a frequency deviation of said modulated test signal which differs by a preselected excessive amount in relation to said at least one reference correlation.