Telecommunications – Transmitter and receiver at same station – Radiotelephone equipment detail
Patent
1997-10-28
2000-03-07
Urban, Edward F.
Telecommunications
Transmitter and receiver at same station
Radiotelephone equipment detail
455447, 455561, H04Q 720
Patent
active
060352191
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method of assigning carrier frequencies to base stations in a cellular radio telecommunications network, and to a radio telecommunications network including such frequency assignments.
In known cellular radio systems, such as for mobile telephones, a network of base stations are provided each having antennas. Mobile subscriber units have antennas which are necessarily omni-directional as subscribers often move around, both within cells and from one cell to another. In consequence, a seven-cell frequency reuse pattern is common, as described, for example, in Cellular Radio Systems, Balston D M Macario RCV Editors, Artech House Inc, 1993, page 9 to 13.
The invention is defined in the claims to which reference should now be made. Preferred features are laid out in the dependent claims.
The present invention preferably provides a cellular telecommunications network including spaced apart base stations, each base station comprising three directional antennas for transmission and reception of signals to subscriber units, eight frequency groups being assigned among the antennas such that each frequency group is reused on average at three out of every eight base stations.
The azimuthal look directions of the three antennas of a base station are preferably substantially 120.degree. from each other. The base stations are preferably spaced so as to be equidistant from its six nearest neighboring stations, and to lie in alternating parallel first and second rows such that antennas in first rows point at 0.degree., 120.degree. and 240.degree. azimuthal angles, and antennas in second rows point at 60.degree., 180.degree. and 300.degree. azimuthal angles. The azimuthal angles are preferably clockwise and with north being 0.degree..
A preferred base station has an antenna with a look direction using the same frequency group as an oppositely--directed look direction of an antenna of a neighboring base station in an adjacent row.
Frequency groups are preferably assigned according to any of the following rules: station, every sixth base along a row, every twenty-fourth base station along a column, 180.degree. azimuth angle are assigned alternating frequency groups along the row, and the antennas in the row having other look directions are assigned other frequency groups such that the frequency groups are not reused in adjacent antenna coverage areas. In particular, frequency groups f.sub.1, f.sub.3, f.sub.4 are used in base stations at column i, row n; frequency groups f.sub.2, f.sub.5, f.sub.3 are used in column i+1, row n, frequency groups f.sub.1, f.sub.4, f.sub.5 are used in column i+2, row n. column i, row n where the frequency groups are selected as row n, station at column i row n,
The antennas at base stations in the network are preferably 120.degree. beamwidth directional antennas, but might be of lower beamwidth, such as 60 to 85.degree..
The network can comprise a selection of base stations configured and having frequency groups assigned so as to avoid selected poor communication paths, specifically those having high co-channel interference. To avoid selected poor communication paths, alternate rows of base stations in the network can substantially use alternate signal polarisations. Selected base stations can have polarisations different to other members of their row so as to avoid selected poor communication paths.
The present invention is preferably for use with subscriber units having directional antennas. Preferably the direction(s) and location(s) of the or each antenna of a subscriber unit are fixed.
The present invention also relates to corresponding methods of frequency group assignment.
A frequency group can be a frequency, a range of frequencies or a selection of frequencies.
A preferred embodiment of the present invention will now be described by way of example and with reference to the drawings in which:
FIG. 1 illustrates a single base station with three antennas;
FIG. 2 illustrates the allocation of frequency bands within the base station network;
FIG. 3 illustrate
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Jan-Erik Stjernvall, Ericsson Radio Systems AB, "Calculation of Capacity and Co-Channel Interference In A Cellular System", Feb. 5-7 1985, Espoo, Finland.
Gesesse Tilahun
Ionica International Limited
Urban Edward F.
LandOfFree
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