Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Patent
1996-04-08
1998-12-01
Eisenzopf, Reinhard J.
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
455437, 455438, 455522, 455525, 455 671, 4552261, H04Q 722
Patent
active
058452087
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a method for estimating received power in a cellular radio system comprising in each cell at least one base station communicating with mobile stations within its coverage area, in which system mobile stations measure strength of the signal received from a base station, and report the measurement results to the respective base station equipment, and each the base station measures strength of the signals received from the respective mobile stations.
It is typical of a cellular radio environment that conditions for radio wave propagation change constantly. This is due to changes in the location of mobile stations with respect to the base station, as well as changes in the environment of mobile stations. In the connection between a mobile station and a base station, the attenuation to which radio waves are subjected on the radio path thus varies constantly. Consequently, especially the transmission power used by the mobile station must be monitored continuously, and adjusted at each moment of time. Generally, the aim is to minimize the transmission power used by the mobile station, so that both power consumption of the station and interference caused by the station to other connections will be minimal. Power adjustment is particularly critical in CDMA systems, in which the aim is that each base station receive the transmission of the mobile stations within its coverage area by using the same power level when possible.
As attenuation on the radio path between a base station and each respective mobile station varies, there must constantly be a possibility to hand over the communication to another base station as rapidly as possible, before the connection to the old base station is broken.
The speed and accuracy of both power adjustment and handover depend on the quality control of the connection between the respective mobile station and the respective base station. In practice, this has been carried out in such a way that both the respective base station and the respective mobile station measure the power level of the received signal. The mobile station reports the measurement results to the base station, which transmits power adjustment commands to the mobile station, and, as the signal weakens, makes the handover decision.
The power level of the received signal is a continuously changing variable, and instantaneous measurement results contain some inaccuracy, such as measurement noise and time-dependent error caused by the actual measurement devices. Therefore, the measurement results are not useful as such, but they must be processed in some way to minimize the effect of measurement errors.
In prior art systems, measurement results of received power are filtered, i.e. averaged, within a time window of a certain size. When this procedure is applied, the worst error peaks can be eliminated from the measurement results. The prior art method has the advantage of being simple to implement, but it has the drawback of being unadaptable to the behavior of rapidly changing data. A way to improve the prior art method is to adjust the width of the time window, but this approach is also unable to model a changing signal sufficiently well, and thus is not useful in predicting the future behavior of the signal.
SUMMARY OF THE INVENTION
It is thus an object of the present invention to utilize the measurement results better than heretofore, by using statistical methods in processing the measurement results. In particular, these methods allow considerably better prediction of the behavior of the signal power level than heretofore, thus allowing remarkably more rapid reactions to changes in the quality of the connection. Therefore, power adjustment may be carried out more accurately than heretofore, and abrupt handover situations may be responded to more rapidly. In addition to prediction, the methods enable more accurate estimates of the reliability of the measurement results, as well as estimates of possibly missing measurement values.
This is achieved with a method of
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Hottinen Ari
Jolma Petri
Karkkainen Ari
Keskitalo Ilkka
Kiema Arto
Eisenzopf Reinhard J.
Nokia Telecommunications Oy
Sobutka Philip J.
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