Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
1998-07-21
2001-06-19
Hunter, Daniel (Department: 2684)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S422100, C455S440000
Reexamination Certificate
active
06249679
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a radio transmission system having a radio coverage area in which area the transmission system is suitable for exchanging radio signals with at least one mobile station, comprising:
location means including a first control for carrying out a current location of the mobile station in the radio coverage area at given instants,
measuring means for measuring at least one receiving quality parameter of the radio signals for producing a quality level linked with this parameter.
The invention also relates to a location method of locating a mobile station in a coverage area of a radio transmission system, the method comprising location steps initiated by the mobile station to indicate to the system its position in the coverage area at given instants.
The invention finally relates to a mobile station of a radio transmission system having a coverage area in which said station and the system can exchange radio signals which have a measurable receiving quality, said station comprising location means for indicating to the system its position in the coverage area, and measuring means for measuring said receiving quality.
The invention applies to all radio telecommunications systems and, more particularly, to cellular telephony systems operating according to the GSM standard (Global System for Mobile communications), NMT standard (Nordic Mobile Telephone), DCS1800 standard (Digital Communication System operating at 1800 MHz), PCS1900 standard (Personal Communication System operating at 1900 MHz) etc.
BACKGROUND OF THE INVENTION
The cellular architecture of these systems implies location procedures for applying data about the current position of the mobile stations which are connected to the system to a central element so that this system can efficiently lead the communications to the destination stations. For this purpose, the central element manages a list of mobile stations called “system-connectable” so as to identify the stations capable of receiving communications.
As these location procedures generate a considerable amount of traffic on the radio channels, it is necessary to initiate them the least possible so as not to saturate the system.
Recommendation ETS 300 557 of ETSI (European Telecommunications Standards Institute) for the GSM standard states criterions for optimizing the management of these location procedures.
According to this Recommendation, when a location attempt fails due to the fact that the radio coverage is too weak to establish a connection (a case of RANDOM_ACCESS_FAILED), the mobile station is placed in a state called IDLE_NOT_UPDATED in which it is considered unconnectable by the system. Indeed, at the instant at which the location attempt has failed, the mobile station was in an area where the radio coverage was insufficient for the mobile station to establish a radio connection of good quality for receiving communications. The IDLE_NOT_UPDATED state is then assigned thereto to avoid a saturation of the system by the transmission of communications which have a very slim chance of reaching the destination.
The mobile station thus remains in the IDLE_NOT_UPDATED state until one of the following three events happens:
the mobile station changes cell,
a periodic location timer expires (this is the T3212 defined in the cited Recommendation),
the mobile station twice tries to establish a communication.
The role of the periodic timer is to confirm to the system every T3212×6 minutes via a periodic location the presence of the mobile station in the same geographical area. If the station changes its geographical area, a normal type of location is initiated. In case of a failure of a periodic location, the system considers the mobile turned off or unconnectable and removes the station from the list of connectable stations until a location is carried out successfully.
Thus, according to said Recommendation the periodic timer may expire between 6 minutes and 24 hours after being switched on depending on the coverage area. This implies that in highly unfavorable cases the base station is located in an area of poor coverage with shadowy areas and that neither of the other two events occurs before the periodic timer expires, the mobile station may continue to be unconnectable for several hours, which may be highly detrimental.
However, during this period of time, the mobile station may have been in a position to move without changing cell so as to benefit from a sufficient coverage for the transmission of a communication. But, since no location procedure has been initiated, according to the cited Recommendation the mobile station is still in the IDLE_NOT_UPDATED state, the system does not know the current position of the mobile station and is thus incapable of transmitting a communication to the mobile station.
SUMMARY OF THE INVENTION
It is an object of the invention to provide means for largely remedying the drawbacks left by Recommendation ETS 300 557 while defining a new condition for initiating a location procedure in the system.
Therefore, a radio transmission system as mentioned in the opening paragraph is characterized in that the location means comprise a second control activated by a decision element which co-operates with said measuring means for initiating a location called special location as a function of measured quality levels.
The new condition which is suitable for generating a location procedure thus depends on the receiving quality of the radio signals transmitted to the mobile station via the system. The decision element thus permits of initiating a special location as a function of the measured quality (special location because this is not foreseen by the standard) which location will very likely succeed.
Compared with the cited Recommendation, the invention provides the great advantage of permitting a mobile station which is reputedly unconnectable by the system to become connectable the moment it receives sufficient radio coverage that is sufficient for the mobile station to be located. Therefore, a system of the type mentioned above is provided in which the decision element comprises detection means for detecting a failure of a current location, characterized in that the triggering of the second control is determined by the detection of a failure of a current location (RANDOM_ACCESS_FAILED according to the cited standard, this failure putting the mobile station in the IDLE_NOT_UPDATED state).
With regard to a location method of the type defined in the opening paragraph, the invention provides that if a location step fails at a given instant, the mobile station having at that instant a radio coverage that does not satisfy a predefined condition called radio quality condition (that is to say, that the coverage seen from the mobile station is insufficient for establishing a connection), a new location step is automatically triggered when a coverage signal is detected indicating to the mobile station that said condition is satisfied.
Indeed, the radio coverage seen by the mobile station at a given instant may be insufficient for establishing a connection despite the fact that a quality criterion as defined in the standard used may be satisfactory. For remedying this drawback, the method provides to define a new quality condition which is compatible with the quality criterion defined in the standard for starting a location.
The invention also relates to a mobile station capable of implementing such a method. Therefore, a mobile station as defined in the opening paragraph is characterized in that it additionally comprises a control element for starting a location as a function of the results of said measurements.
The invention is highly advantageous, notably in mountainous regions and in the open field where the coverage area has shadowy areas, that is to say, areas outside the coverage of the radio system in which areas a location is impossible. Indeed, the investment in infrastructures necessary for correctly covering these areas is too high compared with the expected profitability, given the difficulti
Guilbaud Yvan
Legoupil Franck
Halajian Dicran
Hunter Daniel
Tran Pablo
U.S. Philips Corporation
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