Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
1999-03-29
2001-11-20
Trost, William (Department: 2683)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S432300, C455S434000, C455S435100, C455S440000, C455S443000, C455S008000, C455S009000, C455S067150
Reexamination Certificate
active
06321083
ABSTRACT:
FIELD OF INVENTION
The invention relates to a method for determining traffic distribution in a mobile communication system.
BACKGROUND ART
The geographical area covered by cellular mobile communication systems is divided into smaller radio areas, i.e. radio cells to attain a better use of the frequency channel by means of the reuse of frequencies. The size of radio cells and the number of channel resources allocated to them (radio channels/traffic channels) vary depending on many factors, such as the required capacity, terrain, the used transmission powers, etc. The object is to estimate these factors as well as possible as early as the planning stage of the cellular network in such a manner that it is possible to provide a service of a sufficient quantity and quality in all parts of the radio network. As network planning is anyway based on estimates and forecasts and the need for capacity is continuously changing by areas, the distribution of loading is continuously monitored in built networks, too and possible problem areas are attempted to be discovered. General information about loading is derived from various call statistics with which even cell-specific accuracy can be attained. As a result, it possible to increase channel capacity in an overloaded cell, or to modify the network in some other way. Various call statistics do not, however, provide any information about how traffic load is distributed geographically inside an individual cell. If this information could be collected from the network, it would enable a more accurate focusing of additional capacity (additional frequencies) to the places of a cell with a great amount of traffic (so-called hot spots) or even to establish a new cell in this place.
In practice, the location of spots hot with traffic requires the location of the individual mobile stations having an ongoing call. Prior art discloses several different methods for locating mobile stations for other purposes than traffic monitoring.
WO 9507587 discloses a method where the mobile station measures the signal strengths of surrounding base stations. The rough location and distance of the mobile stations from each base station is determined on the basis of the signal strengths. A theoretical geographical distance between the transmission and reception is calculated from radio path attenuation which is determined as the difference between the transmitted and received signal strength.
In WO 9205672 the mobile station listens to the control channels of surrounding base stations and selects at least three base stations and establishes a call to them. Each base station calculates its distance to the mobile station by using a timing advance value. The location of the mobile station can be determined by means of at least three calculated distances.
EP-0320913 teaches a location method where base stations whose locations are known transmit identifier signals and an accurate time pulse in sync with one another. The times of arrival of time pulses at different base stations are proportional to the distance between the mobile station and the base station, in which case the location of the mobile station can be determined by using at least three base stations.
These known location methods of mobile stations, intended for locating individual mobile stations, are, however, too complicated and difficult to calculate or even completely unsuitable when the distribution of a great number of calls is to be surveyed by area and time inside a cell. Furthermore, most of them require additional functions from the mobile station and the base stations, cause extra radio traffic, increase signalling load, etc.
SUMMARY OF INVENTION
The object of the present invention is a method for determining the geographical distribution of traffic in a cell accurately enough but without additional functions in mobile stations and base stations and without increasing signalling load.
This is attained with a method of the invention for locating hot spots of telephone traffic in a cell in a digital cellular mobile system. The method is characterized in that it comprises the steps of
broadcasting an adjacent cell list to mobile stations in the cell,
measuring the received signal level of the adjacent cells in the mobile stations with an ongoing call,
reporting the measuring results from the mobile stations to the cellular network,
determining for each mobile station a quantity representing the distance between the mobile station and the serving base station,
determining a hot spot of telephone traffic in the cell by means of the adjacent cell measurement and said quantities.
The invention also relates to an arrangement according to claim
8
for locating hot spots of telephone traffic in a cell in a digital cellular mobile system.
The present invention employs two basic measurements used in digital radio systems, especially in time division multiple access (TDMA) radio systems: timing advance and adjacent cell measurement. In place of timing advance measurement, some other routine measurement can also be used to give as a result a quantity which directly informs the distance between the mobile station and the serving base station, or from which this distance can be deduced. This kind of other measurement may be based on signal level measurement, for example.
In timing advance measurement the serving base station measures the time offset between its own transmission and the transmission received from the mobile station and on the basis of the offset, determines a suitable timing advance for the mobile station. The timing advance is used for compensating the propagation delay caused by the distance between the base station and the mobile station. It is possible to calculate from this timing advance the distance travelled by a radio signal moving with the speed of light, from which distance the distance of the base station from the mobile station is derived by taking into consideration that the radio signal has once moved back and forth between the base station and the mobile station. In practice, depending on the resolution of timing advance, a specific distance range where the mobile station is located will be derived. Timing advance does not, however, inform the direction of location of the mobile station with respect to the base station, wherefore the location of the mobile station can be determined to be only in the area between two base-station-centric circles with different radii. This is as such too inaccurate information about the location of the mobile station.
In adjacent cell measurement the mobile station continuously measures the signals of adjacent cells closest to the serving base station for a possible crossover. In a broadcast the serving base station informs the mobile station of the adjacent base stations that it should measure. The mobile station sends regularly measurement results as a report message via the serving base station to the cellular network. It is also possible to determine on the basis of the signal strengths of these adjacent cells the location of the mobile station when there is information about the coverage area of individual adjacent cells. It is not, however, possible to determine unambiguously in this way the location of the mobile station as (because of terrain conditions) the signal level of the adjacent cell can be the same in different parts of the serving cell.
The present invention utilizes simultaneously both adjacent cell and timing advance measurement results. In this way they exclude the inaccuracies of each other and enable very accurate location determination for monitoring traffic distribution. It is possible to proceed so that by means of timing advance a set of circular, base-station-centric distance areas are determined and by means of adjacent cell measurements it is determined in which direction the mobile station is to the base station.
As both measurements already exist, they do not cause any additional demands on base stations or mobile stations. The mobile communication system should only be provided with means that collect and/or process t
Aalto Risto
Vaara Tomi
Altera Law Group LLC
Ferguson Keith
Nokia Telecommunications Oy
Trost William
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