Multiplex communications – Communication over free space – Having a plurality of contiguous regions served by...
Reexamination Certificate
1998-11-19
2002-10-01
Chen, Wellington (Department: 2664)
Multiplex communications
Communication over free space
Having a plurality of contiguous regions served by...
C375S132000, C455S426100, C455S462000, C455S552100
Reexamination Certificate
active
06459688
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention falls within the field of radio systems.
More precisely, the invention relates to a registration method used for registering at least one dual mode mobile station (i.e. having two operating modes: “cordless” and “cellular”) with an associated private base station, the base station together with the dual mode mobile station making up a cordless radio system.
First of all, it should be pointed out that there are two main families of radio system: cordless systems and cellular systems.
Conventionally, a cordless system (of the CT2 or DECT type for instance) comprises a private base station with which there are associated one or more mobile stations. There are many known applications of such a cordless system.
Thus, in a first application, the private base station is located in a dwelling, and the user and family have one or more mobile stations operating with the private base station. In this case, the private base station is also called a home or personal base station, and the mobile stations are also called portable handsets or terminals.
In a second application, the private base station is located within the premises of a company with a plurality of employees, each of them having a mobile station operating with the private base station. In this case, the private base station is also called a company or office base station.
The private base station is connected to the public telephone network. Thus, each mobile station communicates with the public network via the private base station with which it is associated. The private base station provides for local coverage only, roughly corresponding to an area the size of an apartment, a house and garden, or business premises.
Conversely, cellular systems (of the GSM 900 or DCS 1800 types for instance) are designed to provide much wider coverage, for instance the size of a country or even of a continent. Generally speaking, a cellular radio system is implemented within a geographical network of cells. A base station (hereinafter sometimes called a cellular base station) is associated with each cell. Each user has a mobile station (also called a portable terminal) capable of communicating via the base station associated with the cell within which the user is located.
Cordless and cellular systems have been developed in parallel for some considerable length of time, hence the existence of two base station designs, i.e. those usable only in a cellular system and those usable only in a cordless system.
Recently, attempts have been made to integrate both “cordless” and “cellular” types of operation in the same mobile station—called a dual mode mobile station. Indeed, because of the complexity of the cellular system, its use costs more to the user than the use of a cordless system. In other words, subscriptions and communications are charged at a higher rate in a cellular system than in a cordless system (the rates applied in the case of a cordless system being those of the public network to which the private base station is connected). Therefore, attempts are being made to make it possible for the user to use a mobile station in “cordless” mode as often as possible (i.e. as soon as the user is within local coverage of the private base station), with “cellular” mode being used only when operation in “cordless” mode is not possible.
The first known solution, which is the easiest to implement, consists in juxtaposing in the same casing the components of both a “cordless” mobile station and those of a “cellular” mobile station.
As can be easily understood, that first solution is very expensive since the price of a dual mode mobile station implemented in that way corresponds roughly to the sum of the prices of a “cordless” mobile station plus a “cellular” mobile station.
A second known solution, which is more advantageous, has recently been proposed. It consists in designing a private base station compatible, in terms of frequency band, with the cellular system used in “cellular” mode. In other words, the private base station transmits and receives over frequencies contained within the same band as the frequencies transmitted and received by base stations of the cellular system. The operation of the private base station and of the dual mode mobile station in this case is as briefly described below.
In standby mode (i.e. so long as the dual mode mobile station has not registered or after the dual mode mobile station has registered), the private base station transmits over a beacon channel to reveal its presence to the dual mode mobile station.
As for the dual mode mobile station, when in standby in “cellular” mode, it periodically listens to the beacon channel of its associated private base station. When the dual mode mobile station enters the local coverage of its private base station, it recognizes the beacon channel and then registers with the private base station. Following this registration, the dual mode mobile station operates in “cordless” mode and can be used to directly send calls to (or receive calls from) the public network, independently of the cellular network.
It is important to note that the registration of the dual mode mobile station with the private base station constitutes a stage, executed once and for all, prior to operating in “cordless” mode. In contrast, actual “cordless” mode operation consists of carrying out successively, a plurality of call set up stages (incoming or outgoing), each set up stage being followed (except in case of problems) by a conversation stage. In other words, from the moment the dual mode mobile station is registered, a plurality of successive calls can be set up and a plurality of conversations can be processed, without requiring a new registration each time.
In active mode, after the dual mode mobile station has registered with the private base station, the private base station continues to transmit over the beacon channel, in order to warn the dual mode mobile station that a call is intended for it (incoming call) or that an access request previously sent by the dual mode mobile station (outgoing call) has been accepted.
It is obvious that with that known solution, the cost of the dual mode mobile station is much less than that of the first solution, since the same hardware is used in both “cordless” and “cellular” modes.
In counterpart, with that second known solution, because of the simultaneous use of the same frequency band, there exists a risk of interference, both between various private base stations, and between private base stations and cellular base stations.
In order to minimize this risk, it has been proposed that the beacon channel be reduced to an intermittently transmitted signal, with a low operating cycle (i.e. with time slots that are relatively far apart).
Unfortunately, this proposition is not good in terms of interference. Indeed, even though the beacon channel is transmitted with a low operating cycle, it nevertheless constitutes a source of interference with all other base stations (home or cellular) using the same beacon channel. It is therefore necessary to ensure coordination in terms of frequencies and geographical coverage, but this entails very complex purchasing and installation procedures.
SUMMARY OF THE INVENTION
A particular object of the invention is to mitigate the various drawbacks of this state of the art.
More precisely, one of the objects of the present invention is to provide a registration method used for registering a dual mode mobile station with a private base station, which would enable the risks of interference to be minimized both between various private base stations and also between private base stations and cellular base stations.
The invention also aims at providing such a method, the implementation of which requires few modifications to a dual mode mobile station compared with corresponding cellular stations already in existence.
These various objects, as well as others which appear below, are achieved according to the invention by a registration method used for registering at least one dual mode mobil
Bursztejn Jacques
Havet Maure
Kumar Vinod
Alcatel
Chen Wellington
Duong Frank
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