Telecommunications – Receiver or analog modulated signal frequency converter – Measuring or testing of receiver
Patent
1996-06-26
1998-08-04
Eisenzopf, Reinhard J.
Telecommunications
Receiver or analog modulated signal frequency converter
Measuring or testing of receiver
455 671, 455424, H04B 1702
Patent
active
057909440
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a method for measuring gain error in a receiver of a base station of a cellular system and for improving field strength measurement, this method comprising the steps of converting the frequency of a signal generated in a transmitter unit to be adapted to a receiver unit and passing the signal to the receiver unit, and generating a control signal from the signal for indicating field strength.
The invention further relates to equipment for measuring gain error in a receiver of a base station of a cellular system and for improving field strength measurement, this equipment comprising a transmitter unit, which comprises a transmitter and a power regulator of the transmitter; a receiver, which comprises a receiver unit, a distribution amplifier and a band-pass filter; a numerical signal processing unit; and a control unit, which controls the transmitter unit and the receiver.
Gain variation refers in this context to the deviation of the actual gain of the receiver unit from the nominal value of the gain. This gain variation can be as wide as about .+-.10 dB at a base station, due to the wide frequency range, temperature variations and inaccuracies in component values. As regards the operation of a cellular system, variations this wide are nevertheless harmful because, for example, GSM requires that the base station should continuously measure the strength of received signals during normal traffic. This is done by means of so-called RSSI calculations (Received Signal Strength Indication), whereby the signal level of a received signal is calculated on the basis of a signal obtained from the output of the base-station receiver. It is apparent that the calculated RSSI value deviates significantly from the actual one if the gain variation of the receiver is as wide as .+-.10 dB, and the nominal value of the gain is used in the calculations.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a method and equipment for measuring the gain error in a base-station receiver and for making the RSSI value more accurate.
This method is characterized in that the power level of the signal obtained from the transmitter unit is determined before the receiver; that the power level of the signal is determined after the receiver; that the power levels of the signal determined before and after the receiver are compared to one another; and that the control signal value indicating field strength is corrected to correspond to the power level of the signal as determined before the receiver.
The equipment of the invention is further characterized in that the receiver comprises a detector element for detecting the power level of the signal coming from the transmitter unit; that after the receiver there is a detector element for determining the power level of the signal; that the control unit comprises a comparator element for comparing the power levels of the signal before and after the receiver; and that the control unit comprises a correction element for correcting the control signal indicating field strength so that it will correspond to the power level of the signal as determined before the receiver.
An essential idea of the invention is that the transmitter signal is applied directly to an available channel in the receiver and that the strength of the received test signal is measured after the receiver. Next, the power level of the test signal transmitted from the transmitter and the power level of the output signal of the receiver are compared to one another, this comparison yielding the gain between the input and output of the receiver, and thus it is possible to determine the gain error in the receiver from this gain. Another essential idea is to arrange an accurate threshold detector of the power level of the signal as close as possible to the input of the receiver, whereby it is possible to adjust the level of the transmitter test signal very accurately as desired by means of the level information produced by the threshold detector. Similarl
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Karki Tapani
Pulkkinen Jorma
Valitalo Eero
Eisenzopf Reinhard J.
Nguyen Lee
Nokia Telecommunications Oy
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