Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
1998-11-04
2001-01-09
Eisenzopf, Reinhard J. (Department: 2745)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S067700
Reexamination Certificate
active
06173186
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the estimation of coverage area or cell radius for actual and proposed telecommunications base stations.
PRIOR ART
The estimation of the coverage area (of a predetermined minimum signal level) or cell radius of a telecommunications base station is typically made using road driven test data and either a published or derived model. Path loss and base station antenna distance data are gathered from various road locations and correlated to produce a least squares line fit with corrections for cell topology and building clutter factors. This line fit can then be used to determine a cell radius (for example the 50% reliability edge), corresponding to a predetermined (for example −90 dBm) signal level. This method is of limited value however where road tests provide data which is biased by conditions peculiar to the regions covered by road within the cell—for example increased building clutter and flatter topology than the rest of the cell. This can lead to wide variations in cell radius estimation for cells of the same geomorphology—natural topology and vegetation type as well as the level of man-made object distribution or building clutter.
Such fast and inexpensive cell radius estimation methods are typically employed in the planning and bidding stage of a network installation project. The methods rely on actual signal path loss test data obtained from cells with test base stations temporarily installed, that data being used to estimate the cell radius when an actual base station is installed. This in turn enables the network coverage area to be tested using different base station combinations. Signal strength and location readings are taken and converted to path loss and base station distance. The data is then correlated and extrapolated to estimate the cell radius as described above. The data collected on such tests is often restricted to a small part of the cell due to limited road access or limited resources for example. This small sample can often bias the overall cell radius estimation, for example due to a particularly dominant feature such as a large building or hill around the test data collection site which is not present in the rest of the cell.
The use of such cell radius estimation methods often results in inaccurate estimates which can result in significant commercial losses when the network is installed. If the cell radius has been overestimated, an additional base station may be required to boost signal levels. If the cell radii have been underestimated, additional base stations will have been installed which were not actually required. Excess concentration of base stations also causes interference problems. As the cost of base station installation is very high, it is extremely commercially advantageous to obtain accurate estimates of the number of base stations required at the planning and bidding stage prior to installation of the network.
OBJECT OF THE INVENTION
It is an object of the present invention to provide an improved telecommunications cell radius estimation method.
SUMMARY OF THE INVENTION
In a first aspect the present invention provides a method for estimating the radius of a radio telecommunications cell comprising the steps of:
determine path loss and range data from a plurality of predetermined locations within said cell;
apply a fixed gradient line fit to said data; obtain from said line fit a radius estimate for said cell corresponding to a predetermined signal level.
For the purposes of this specification, the term path loss means transmitter power (for example base station EIRP) less a measured signal level. The path loss may be determined either between a base station antenna and a mobile antenna or a mobile antenna and a base station antenna. The term range means the distance between the base station antenna and a mobile antenna.
The term fixed gradient may include a line fit comprising two or more sections, each of a different fixed gradient.
Preferably the method further comprises the additional step of: removing determined data less thana predetermined range.
Preferably the method further comprises the additional step of: removing determined data having a signal level below a predetermined signal floor level.
Preferably the method further comprises the additional step of: removing determined data with a range over which the average signal level is within a predetermined signal difference level of a predetermined signal floor level. Preferably the predetermined signal difference level corresponds to two standard deviations.
Preferably the method further comprises the additional step of: removing determined data having a path loss less than a theoretical minimum path loss.
Preferably the method further comprises the additional step of: removing determined data having a signal level above a predetermined maximum signal level. Preferably said predetermined maximum signal level is determined by the receiving device determining said data.
Preferably the method further comprises the additional step of: removing determined data having a path loss differing from the average path loss of other determined data at substantially the same range by an amount greater than a predetermined path loss difference.
Preferably the fixed gradient line fit is determined according to the equation:
A
=(&Sgr;
P.L.i−B&Sgr;Ri
)/
n
where:
A=path loss intercepts value
P.L.=path loss data
R=range data
n=number of data
B=fixed gradient
Preferably the fixed gradient is dependent on the height of the base station antenna. Preferably the fixed gradient is determined from a HATA path loss model.
In a second aspect the present invention provides a method for producing a model for use in radio telecommunications cell radius estimation comprising the steps of:
determine path loss and range data from a plurality of predetermined locations within each of a plurality of cells;
classify each cell according to geomorphology;
for each cell apply a fixed gradient line fit to said data and determine a path loss intercept at a predetermined range;
for each classification add said intercept values for each cell together with a corresponding base station height (above terrain or relative to impending clutter) to a database, apply a line fit to said database data to obtain a model of path loss intercept values versus base station antenna height for use in the estimation of cell radii for cells of a selected base station antenna height and geomorphology classification.
In a third aspect the present invention provides a method for estimating the radius of a radio communications cell comprising the steps of: determine the path loss intercept value from a model for a selected base station antenna height and geomorphology; apply a fixed gradient line to the intercept; and obtain from said line fit a radius estimate for said cell corresponding to a predetermined signal level.
In a fourth aspect the present invention provides a method of determining radio telecommunications cell radius estimates for planning a cellular network coverage area comprising the steps of: divide the network coverage area into a plurality of cells; for a predetermined percentage of said cells determine cell radius estimates according to the method of the first aspect of the invention; and for the remaining percentage of cells determine cell radius estimates according to the method of the third aspect of the invention.
REFERENCES:
patent: 5883889 (1999-03-01), Faruque
patent: 5966661 (1999-10-01), Bernardin et al.
patent: 5983106 (1999-11-01), Bernardin et al.
patent: 6006095 (1999-12-01), Bernardin et al.
patent: 6041236 (2000-03-01), Bernardin et al.
patent: 6052583 (2000-04-01), Bernardin
Hata, Empirical Formula for Propagation Loss in Land Mobile Radio Services, IEEE Transactions on Vehicular Technology, vol. VT-29, No. 3, Aug., 1980, pp. 317-325.*
Appiah Charles N.
Eisenzopf Reinhard J.
Lee Mann Smith McWilliams Sweeney & Ohlson
Nortel Networks Limited
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