Pulse or digital communications – Spread spectrum – Frequency hopping
Reexamination Certificate
1998-07-10
2001-06-19
Vo, Don N. (Department: 2631)
Pulse or digital communications
Spread spectrum
Frequency hopping
Reexamination Certificate
active
06249540
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates in general to the field of cordless communication systems and, more particularly, to a method and system for shifting frequency subsets to avoid base station interference in a frequency hopping cordless telephone system.
BACKGROUND OF THE INVENTION
Cordless or wireless communications systems are widely used to provide users with mobile communications. In general, the term cordless can refer to any form of air wave transmission using a set of radio frequencies. Conventional implementations of cordless systems, for example, include both public cordless systems and in-building cordless systems. In public systems, there are numerous service providers that allow users to make and receive calls virtually anywhere within a service area. Such service providers offer solutions based on a number of different technologies and standards. Typically, the service providers have purchased a license from the federal government (i.e., Federal Communications Commission) to use a specific portion of the radio spectrum within specific markets.
In contrast to public systems, in-building cordless systems can avoid the costs of radio spectrum licenses by using unlicensed radio frequencies. In-building systems typically have a common configuration or topography in that there is a radio exchange that is adjunct to or integrated with a private branch exchange (PBX). Base stations (or fixed parts) are equipped with radio antennas that connect to the radio exchange. The base stations also transmit radio signals to and receive radio signals from cordless handsets (portable parts) within a limited range.
With respect to unlicensed radio frequencies, cordless systems often use the ISM (Industrial, Scientific and Medical) band. In the United States, ISM based devices are regulated by and must follow Federal Communications Commission (FCC) guidelines. In general, FCC guidelines implement restrictions on the use of frequencies within the ISM band. For example, devices are allowed to communicate at a particular frequency only with a defined bandwidth for a defined period of time and with a defined signal power level. Since the ISM band is unlicensed, it is used by many vendors for various types of cordless devices (e.g., medical monitoring devices, wireless LANs, printers, speakers, security systems and in-building cordless systems). Consequently, radio frequency (RF) interference can be a significant problem with using the ISM band.
For a cordless telephone system using the ISM band, the FCC restrictions produce a need to implement a frequency hopping scheme to ensure that the cordless system does not violate restrictions on the use of frequencies within the ISM band. Frequency hopping can achieve this by allowing base stations and handsets to move in sync from frequency to frequency in the time domain. Further, when implementing such a frequency hopping scheme, there is a need to implement a scheme for avoiding bad channels or frequencies due to RF interference and other problems.
SUMMARY OF THE INVENTION
In accordance with the present invention, a method and system for shifting frequency subsets to avoid base station interference in a frequency hopping cordless telephone system are disclosed that provide advantages over conventional cordless telephone systems.
According to one aspect of the present invention, a base station communicates with the handsets using frequencies selected from active frequency subsets. Frequency subsets are shifted to avoid interference by selecting frequencies initially from a defined number of active frequency subsets where each of the active frequency subsets is used before repeating an active frequency subset. The number of active frequency subsets is then changed for a defined period of time to change the period with which the active frequency subsets are used. After the defined period of time, the number of active frequency subsets is returned to the defined number of active frequency subsets.
A technical advantage of the present invention is the ability automatically to shift the period with which a base station uses frequencies from a particular frequency subset. This shift can be performed in response to interference identified with the frequency subset and as an integrated part of substituting a blocked frequency subset for an active frequency subset.
Other technical advantages should be apparent to one of ordinary skill in the art in view of the specification, drawings and claims.
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Dicker Olaf
Kockmann Juergen
Sastrodjojo Paulus
Sydon Uwe
Siemens Information and Communication Network, Inc.
Vo Don N.
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