METHOD AND APPARATUS FOR DERIVING SIGNAL STRENGTH ATTENUATION CHARACTERISTIC VALUES

1 . A method of deriving signal strength attenuation characteristic values for cells within a wireless communication network; the method comprising:

determining a set of cells for which signal strength attenuation characteristic values are to be derived; and

using a genetic algorithm to derive signal strength attenuation characteristic values for the set of cells based at least partly on signal strength information for signal strength measurements obtained by wireless communication subscriber units within the wireless communication network.

2 . The method of claim 1 , wherein the method comprises:

determining a set of cells for which signal strength attenuation characteristic values are to be derived;

generating a first generation of chromosome strings, each chromosome string comprising at least one signal strength attenuation characteristic value for each cell within the determined set of cells;

calculating a fitness score for each chromosome string within the first generation of chromosome strings based at least partly on signal strength information for signal strength measurements obtained by wireless communication subscriber units within the wireless communication network;

generating at least one further generation of chromosome strings;

calculating a fitness score for each chromosome string within the at least one further generation of chromosome strings based at least partly on signal strength information for signal strength measurements obtained by wireless communication subscriber units within the wireless communication network; and

deriving signal strength attenuation characteristic values for the set of cells based at least partly on the calculated fitness scores for the first and at least one further generation of chromosome strings.

3 . The method of claim 2 , wherein the first generation of chromosome strings comprises random signal strength attenuation characteristic values.

4 . The method of claim 2 , wherein calculating a fitness score for a chromosome string comprises:

defining a plurality of signature points, each signature point representing a geographical location;

calculating an expected signal strength measurement value for at least one cell at each signature point;

matching each of a plurality of signal strength measurement reports received from wireless communication subscriber units to one of the signature points based at least partly on the expected signal strength measurement values for the signature points;

calculating a fitness score for each signal strength measurement report based at least partly on the or each expected signal strength measurement value for the respective signature point and corresponding signal strength information from the signal strength measurement report; and

calculating the fitness score for the chromosome string based at least partly on the calculated fitness scores for the plurality of signal strength measurement reports.

5 . The method of claim 4 , wherein the method comprises calculating the fitness scores for the chromosome string by summing the fitness scores for the signal strength measurement reports.

6 . The method of claim 2 , wherein generating at least one further generation of chromosome strings comprises:

deriving parent chromosome strings to form part of the at least one further generation of chromosome strings; and

performing a crossover between parent chromosome strings to generate child chromosome strings to form part of the at least one further generation of chromosome strings.

7 . The method of claim 6 , wherein generating at least one further generation of chromosome strings further comprises performing mutation of the child chromosome strings.

8 . The method of claim 6 , wherein generating at least one further generation of chromosome strings comprises identifying at least one chromosome string from a current generation of chromosome strings comprising a highest fitness score and including the identified at least one chromosome string from the current generation of chromosome strings in the at least one further generation of chromosome strings.

9 . The method of claim 2 , wherein the method comprises generating further generations of chromosome strings until at least one chromosome string comprising a suitable solution for signal strength attenuation characteristic values for the set of cells is found.

10 . The method of claim 9 , wherein a chromosome string comprising a suitable solution for signal strength attenuation characteristic values for the set of cells is found when no chromosome string in a succeeding generation of chromosome strings comprises a higher fitness score than that chromosome string.

11 . The method of claim 1 , wherein the method comprises deriving signal strength attenuation characteristic values comprising slope and intercept values.

12 . The method of claim 1 , wherein determining the set of cells for which signal strength attenuation characteristic values are to be derived comprise:

taking an initial cell ID referenced within cell measurement reports; and

adding to the initial cell ID with further cell IDs referenced within the same measurement reports as the initial cell ID to form the set of cells for which signal strength attenuation characteristic values are to be derived.

13 . The method of claim 1 , wherein the method further comprises storing the derived signal strength attenuation characteristic values within at least one data storage device.

14 . A method of generating a signal strength contour model for at least one cell within a wireless communication network, the method comprising:

deriving at least one signal strength attenuation characteristic value for the at least one cell within the wireless communication network in accordance with the method of claim 1 ; and

generating a signal strength contour model for the at least one cell based at least partly on the at least one derived signal strength attenuation characteristic value.

15 . A method of geolocating a wireless communication subscriber unit comprising:

deriving signal strength attenuation characteristic values for cells within a wireless communication network in accordance with the method of claim 1 ;

receiving signal strength measurement information for a set of cells within the wireless communication network obtained by the wireless communication subscriber unit;

determining a distance between the wireless communication subscriber unit and an antenna for each cell within the set of cells based at least partly on:

(i) the derived signal strength attenuation characteristic values for the set of cells; and

(ii) the received signal strength measurement information for the set of cells within the wireless communication network obtained by the wireless communication subscriber unit; and

determining a geolocation of the wireless communication subscriber unit based at least partly on the determined distance between the wireless communication subscriber unit and an antenna for each cell within the set of cells.

16 . A non-transitory computer program product having executable program code stored therein for performing a method of deriving signal strength attenuation characteristic values for cells within a wireless communication network, the program code operable for:

determining a set of cells for which signal strength attenuation characteristic values are to be derived; and

using a genetic algorithm to derive signal strength attenuation characteristic values for the set of cells based at least partly on signal strength information for signal strength measurements obtained by wireless communication subscriber units within the wireless communication network.

17 . The non-transitory computer program product of claim 16 , wherein the non-transitory computer program product comprises at least one of: a hard disk, a CD-ROM, an optical storage device, a magnetic storage device, a Read Only Memory (ROM), a Programmable Read Only Memory (PROM), an Erasable Programmable Read Only Memory (EPROM), an Electrically Erasable Programmable Read Only Memory (EEPROM), and a Flash memory.

18 . A geolocation system comprising at least one signal strength attenuation characteristic value derivation component arranged to:

determine a set of cells for which signal strength attenuation characteristic values are to be derived; and

use a genetic algorithm to derive signal strength attenuation characteristic values for the set of cells based at least partly on signal strength information for signal strength measurements obtained by wireless communication subscriber units within the wireless communication network.

19 . The geolocation system of claim 18 , wherein the at least one signal strength attenuation characteristic value derivation component is arranged to:

determine a set of cells within a wireless communication network for which signal strength attenuation characteristic values are to be derived;

generate a first generation of chromosome strings, each chromosome string comprising at least one signal strength attenuation characteristic value for each cell within the determined set of cells;

calculate a fitness score for each chromosome string within the first generation of chromosome strings based at least partly on signal strength information for signal strength measurements obtained by wireless communication subscriber units within the wireless communication network;

generate at least one further generation of chromosome strings;

calculate a fitness score for each chromosome string within the at least one further generation of chromosome strings based at least partly on signal strength information for signal strength measurements obtained by wireless communication subscriber units within the wireless communication network; and

derive signal strength attenuation characteristic values for the set of cells based at least partly on the calculated fitness scores for the first and at least one further generation of chromosome strings.

20 . The geolocation system of claim 18 , wherein the at least one signal strength attenuation characteristic value derivation component is arranged to store the derived signal strength attenuation characteristic values within at least one data storage device.