Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
1999-01-25
2001-12-11
Trost, William (Department: 2683)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S115200, C455S405000, C455S063300, C455S423000
Reexamination Certificate
active
06330450
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the field of wireless communications, and, more specifically, to a wireless communication system that bases control decisions on signal strength measurements.
BACKGROUND OF THE INVENTION
Some wireless communication systems base control decisions (such as handoff decisions, allocation of channels, allocation of frequencies and management of other resources) on signal strength measurements. In mobile assisted handoff, for example, each mobile station periodically measures the strengths of signals from its serving base station and from surrounding base stations. The mobile station reports these measurements to the wireless communication system. The wireless communication system determines from these signal strength measurements whether a handoff to another base station is necessary and which base station should the mobile be handed off to. Such signal strength based control decisions may be incorrect because of interference, such as noise, from sources internal and external to the wireless system.
All transmitters generate noise; that is, energy at frequencies other than the assigned operating frequency. A transmitter's noise can cause an erroneous signal strength measurement when the transmitter's noise at a particular frequency is greater than the signal strength of another transmitter assigned to that frequency. Erroneous measurements may result in incorrect control decisions, such as an unnecessary mobile station handoff or the allocation of a channel that cannot sustain a call.
SUMMARY OF THE INVENTION
The present invention provides a system and method for minimizing interference of internal and external transmitter noise to improve control decisions that are based on signal strength measurements. This invention operates in a wireless communications system that uses a plurality of frequencies for communication and that bases control decisions on signal strength measurements. In this wireless communication system, a transmitter internal to the system is transmitting a first signal at a first frequency and noise at other frequencies in a known pattern. The signal strength of the first signal at the first frequency is measured by a receiver. The noise of the transmitter of the first signal is calculated on other frequencies, using the transmitter's known noise pattern. A determination is then made whether the noise of the first signal is above a threshold on one or more of the other frequencies used by the wireless communication system. If the noise is above the threshold, corrective action is taken. Such corrective action includes disregarding the signal strength measurement on the affected frequencies and shutting off the first transmitter.
According to another aspect of this invention, noise from transmitters external to the wireless communication system may be detected by measuring signal strengths at one or more receivers across a range of frequencies and correlating the signal strength measurement to known spectral patterns of transmitters from other systems. If a correlation is above a threshold, then corrective action is taken. Such corrective action includes suspending signal strength measurements at affected frequencies and rebuilding a list of allocable frequencies.
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Wallstedt Kenneth
Ward Torbjorn
Ericsson Inc.
Tran Congvan
Trost William
Wood Phillips VanSanten Clark & Mortimer
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