Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
1998-11-23
2001-07-31
Woo, Stella (Department: 2643)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S446000, C455S447000, C455S449000, C455S560000, C455S561000, C455S562100
Reexamination Certificate
active
06269247
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The field of the invention is that of cellular mobile radio systems. To be more precise, the invention concerns the spatial location of a mobile station in a cell of a communication network with relatively good accuracy and in particular with sufficient accuracy for space division multiple access (SDMA) systems.
The invention applies to any cellular network, and in particular, although not exclusively, a GSM network.
To be more precise, the present invention concerns a method of spatial location of a mobile station moving in a cell of a communication network and a corresponding base station with omnidirectional antenna controlling the cell, mobile stations of the communication network and signaling.
2. Description of the Prior Art
A conventional mobile radio network comprises cells in each of which one or more mobile stations move around. Each cell is controlled by a base station. In this context the network can be any mobile radio network, in particular with regard to the shape and the number of cells.
In SDMA systems the cell is divided into a plurality of angular sectors centered on the base station. The base station must therefore be able to determine the angular sector containing a mobile station. In particular this enables the choice of a traffic channel (associated with a particular frequency) to be allocated to the mobile station.
An array of antennas is conventionally used associated with a specific algorithm, for example an ESPRIT type algorithm (Estimation of Signal Parameters via Rotational Invariance Techniques) or a MUSIC type algorithm (MUltiple Slgnal Classification).
The above prior art methods have the drawbacks of being complex, of requiring large volumes of computation and of using a plurality of antennas in each base station.
U.S. Pat. No. 5,508,707 describes a method of determining the geographical position of mobile stations sending an emergency call. The process disclosed comprises the following steps:
determining the contours (in terms of maximum and minimum error estimates) of the coverage areas of the base stations that can receive a call transmitted by a mobile unit to define a first bounding area that describes the relative position of the mobile unit;
determining which lobes (in an SDMA system) or which filters (in a non-SDMA system) of various base stations are in communication with the mobile unit to determine a second bounding area that describes the relative position of the mobile unit;
determining where the first and second bounding areas intersect so as to obtain a relatively precise description of the position of the mobile unit.
Accordingly, the above method necessitates a plurality of base stations.
What is more, the above method, like those described above, has the drawback of using an array of antennas to determine a precise location of the mobile station, which necessitates complex processing and represents a solution that is difficult to implement.
An objective of the invention is to mitigate the various drawbacks of the prior art.
To be more precise, a first objective of the invention is to provides a simple method of spatial location of a mobile station moving around in a cell and means associated with that method making it simple and easy to implement.
A complementary objective of the invention is to provide a method of the above kind that requires only one omnidirectional antenna in each base station.
Another objective of the invention is to provide a method of the above kind which optimizes the allocation of communication resources.
SUMMARY OF THE INVENTION
The above objectives, together with others that will become apparent hereinafter, are achieved in accordance with the invention by a method for spatially locating a mobile station in a cell of a mobile radio network, said cell being of the type controlled by a base station with an omnidirectional antenna wherein said cell is divided into a plurality of angular sectors centered on said base station, a separate location signal element is allocated to each angular sector, said mobile station sends a signaling packet carrying all of said location signal elements, and said base station comprises for each angular sector means for modifying the signaling packet sent by the mobile station before it is received by said omnidirectional antenna, said modification being specific to said angular sector, and means for determining, from the signaling packet received by said omnidirectional antenna, the modification made by one of said modifier means and for deducing therefrom the angular sector in which said mobile station is located.
The general principle of the invention is therefore to assign a distinct location signal element to each of said angular sectors of an SDMA cell so that the various angular sectors can be distinguished from each other.
Accordingly, the angular sector in which the mobile station is located is determined without using an array of antennas or complex calculations.
Note that the invention does not impose any restriction as to the nature of the location signal element.
Advantageously, each location signal element corresponds to a predetermined frequency range or frequency and said modifier means each perform filtering in accordance with the predetermined frequency range or frequency assigned to the angular sector for which said modifier means are operative.
In a preferred embodiment of the invention, said signaling packet transmitted by the mobile station is a reference signal the instantaneous frequency of which changes continuously over a given time period so as to take in succession all frequency values allocated to said angular sectors.
A reference signal of the above kind is generally called a “chirp” signal.
Advantageously, said reference signal is also used to synchronize said base station and said mobile station. This means that it is not necessary to add any additional hardware to the mobile station. A signal already provided by the mobile station is used for an additional function. Accordingly, implementing the present invention represents a low cost in the base station and a zero cost in the mobile stations. What is more, no additional signaling element is transmitted.
Advantageously, said location signal elements belong to the group comprising: frequencies, frequency ranges, specific combinations of at least two frequencies, and temporal sequences of specific frequencies.
Clearly the modifier means and the means for determining the modification are adapted to suit the type of locating signal element used.
Preferably, said mobile station transmits said signaling packet when setting up a call with said base station and/or periodically.
The invention also concerns a base station having an omnidirectional antenna and controlling a cell of a mobile radio network using the above method. A base station of the above kind includes, for each angular sector, means for modifying the signaling packet transmitted by said mobile station before it is received by said omnidirectional antenna, said modification being specific to said angular sector, and means for determining from the signaling packet received by said omnidirectional antenna the modification made by one of said modifier means and for deducing therefrom the angular sector in which said mobile station is located.
In other words the base station is provided, for each angular sector, with means adapted to modify the signaling packet in a fashion specific to the sector concerned. The signaling packet modified in this way is received by the omnidirectional antenna and other (determination) means determine the modifications made and therefore the angular sector in which the mobile station is located.
In a preferred embodiment, the modifier means each comprise filter means responsive to the predetermined frequency range or frequency assigned to the angular sector for which said modifier means are operative.
More generally, the modifier means can each comprise a battery of logic gates, a comparator, a filter, a level detector, combination of the above or other
Alcatel
Sughrue Mion Zinn Macpeak & Seas, PLLC
Taylor Barry W.
Woo Stella
LandOfFree
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