Telecommunications – Transmitter and receiver at separate stations – Having measuring – testing – or monitoring of system or part
Patent
1993-02-05
1996-01-23
Eisenzopf, Reinhard J.
Telecommunications
Transmitter and receiver at separate stations
Having measuring, testing, or monitoring of system or part
455 561, 375216, H04B 726
Patent
active
054871786
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a base station for a radio system, the base station comprising, for monitoring the quality of a radio link between the base station and mobile stations, generator means for generating a square wave signal having a desired monitoring signal frequency; control means for setting the frequency of the square wave signal; a filter means for generating a monitoring signal from the square wave signal; and a transmitter means for transmitting the monitoring signal to the mobile radio station.
In the Nordic Mobile Telephone (NMT) system, the quality of the radio link between a base station and a mobile telephone is monitored by means of special monitoring signals. The base station generates a monitoring signal by lowpass filtering from a clock signal having a desired monitoring signal frequency. The NMT system utilizes four monitoring signal frequencies at intervals of 30 Hz. The base station transmits a monitoring signal to a mobile telephone which returns the monitoring signal immediately to the base station, and the base station determines the quality of the used radio link, especially the signal-noise ratio, by means of the received monitoring signal. A radio system base station utilizing such a monitoring signal is disclosed in FI Patent Application 900620.
The new NMT systems include recommendations (ref. Addendum to NMT-Specification DOC 900-4 DRAFT dated 8.1. 1991) stating that a digital monitoring signal should be used in addition to an analog monitoring signal, and that the bit error ratio of the received digital monitoring signal should be used in addition to its S/N ratio as a criterion of quality. When the quality of the speech connection is above a predetermined threshold value, a digital monitoring signal is used, and when it is below the threshold value, an analog monitoring signal is used. The digital monitoring signal should be modulated so that the frequency 3,975 Hz corresponds to the digital logical state "1", and the frequency 4,025 Hz corresponds to the logical state "0". The decision to handover the call from one base station to another is also made on the basis of the monitoring signal.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a base station capable of processing both analog and digital monitoring signals.
This is achieved by means of a base station of the type described in the introductory part of this specification, which according to the invention is characterized in that the control means comprise a first and a second mode of operation, the control means controlling the generator means in the first mode of operation to transmit an analog monitoring signal by maintaining the frequency of the square wave signal generated by the generator means at a constant value throughout the duration of the monitored radio link, and the control means controlling the generator means in the second mode of operation to transmit a digital monitoring signal by varying the frequency of the square wave signal generated by the generator means during the monitored radio link in response to changes in the logical state of the monitoring signal between a first frequency corresponding to the first logical state and a second frequency corresponding to the second logical state.
In practicing the invention, the same circuitry can be used for the generation of both the analog and the digital monitoring signals. The desired monitoring signal type is obtained simply by means of software selecting the frequency control mode corresponding to the desired type. The invention enables the use of the same monitoring signal circuitry both in the new and in the old systems.
The invention enables a very simple and advantageous realization of the monitoring signal generation circuitry.
BRIEF DESCRIPTION OF THE DRAWING
The invention will now be described in more detail by means of an illustrating embodiment with reference to the attached drawing, in which:
FIG. 1 shows a block diagram of a base station section required for the generation of
REFERENCES:
patent: 4481489 (1984-11-01), Kurby
patent: 4723303 (1988-02-01), Koch
patent: 5008953 (1991-04-01), Dahlin et al.
WO, A1, 9112675 (Telenokia Oy) 22 Aug. 1991, p. 1, Line 1-Line 17.
NMT Doc 300-4, Oct. 1, 1992, Chapter 8.
NMT Doc 300-4, Oct. 1, 1992, Addenda of Feb. 7, 1991 pp. 6-8 & 26-30.
Eisenzopf Reinhard J.
Nokia Telecommunications Oy
Sobutka Philip J.
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