High capacity cell planning based on fractional frequency reuse

• US 6,128,497 A
• Filed: 03/10/1998
• Issued: 10/03/2000
• Est. Priority Date: 12/03/1997
• Status: Expired due to Term

• Current Assignee: RPX Clearinghouse LLC (RPX Corporation)
• Original Assignee: Nortel Networks Limited (Nortel Networks Corporation)
• Inventors: Faruque, Saleh
• Primary Examiner(s): Maung, Nay
• Assistant Examiner(s): Vuong, Quochien B.
• Application Number:
  US09/038,372
• Time in Patent Office: 938 Days
• Field of Search: 455/446, 455/447, 455/448, 455/449
• US Class Current: 455/447
• CPC Class Codes: H04W 16/02 Resource partitioning among network components, e.g. reuse partitioning
• CPC Class Codes: H04W 16/12 Fixed resource partitioning
• CPC Class Codes: H04W 16/24 Cell structures

Abstract

The fractional frequency reuse plan groups available frequencies into 16 frequency groups. These frequency groups are then allocated to a group of sectors such that a four by four matrix results. The top two rows of the matrix are alternating odd numbered frequency groups while the bottom two rows of the matrix are alternating even numbered frequency groups. This group of frequencies is then reused in such a way that three adjacent reuses of a frequency group forms an apex of a triangle. Each reuse on the triangle appears as back-to-back, radiating in different direction, 120° apart. This frequency reuse plan generates an N=5.333 system.

Claims

1. A method for fractional frequency allocation in a cellular radiotelephone system, the cellular radiatelephone system having a plurality of available frequencies and comprising a plurality of cells, the method comprising the steps of:

forming a group of cells comprising a subset of the plurality of cells;

grouping the plurality of available frequencies into a plurality of frequency groups;

assigning a different frequency group, of the plurality of frequency groups, to each cell of the group of cells; and

reusing the frequency groups within the group of cells such that a first use of a first frequency group and a first and second reuse of the first frequency group are each located at a respective apex of a first triangle, each first frequency group use radiating 120°

from the other use, there being no other triangles having apexes coincident with use of the first frequency group, which other triangles are congruent with or similar to the first triangle and which abut, are adjacent to, or are proximate to the first triangle.

2. The method of claim 1 wherein the group of cells is comprised of a plurality of tri-cell clusters, each cell of the tri-cell cluster being radiated by a directional antenna in the center of the tri-cell cluster.

3. A method for fractional frequency reuse in a cellular radiotelephone system, the cellular radiotelephone system having a plurality of available frequencies and comprising a plurality of cells, the method comprising the steps of:

forming a tri-cell cluster comprising a subset of the plurality of cells;

forming a group of cells comprising a plurality of tri-cell clusters;

grouping the plurality of available frequencies into a plurality of frequency groups;

assigning a different frequency group of the plurality of frequency groups to each cell of the group of cells in a manner such that odd numbered frequency groups comprise a first and second row of cells and even numbered frequency groups comprise a third and fourth row of cells; and

reusing the frequency groups such that three adjacent reuses of a first frequency group form a triangle, each reuse radiating in a direction that is 120°

from the other two uses.

4. The method of claim 3 wherein the step of reusing includes reusing each adjacent frequency group reuse in a different direction than the other two frequency group reuses.

5. The method of claim 3 wherein the step of reusing includes reusing the groups cells such that an N=5.333 cellular radiotelephone system results.

6. A method of allocating fractional frequencies in a cellular radiotelephone system, the system having a plurality of available frequencies and a plurality of cells, the method comprising:

ordering the plurality of cells as rows of abutting cells and columns of abutting cells, the centers of the cells in a row being offset from the centers of the immediately adjacent cells in the rows on either side thereof, the offset being in the direction in which the rows extend, the columns extending in a direction which is oblique to the rows, and the centers of the cells in a column being offset in a direction parallel to the columns from the centers of the immediately adjacent cells in the columns on either side thereof;

forming similar cell clusters of three cells each, two of the cells in each cluster being from one row and one cell being from an adjacent row, each cell in a cluster abutting the other two cells of the cluster so that there is defined a cluster center which is a point common to all three cells in a cluster;

locating three directional antennae at the center of each cluster, each antenna of each cluster being capable of radiating energy over a respective one of the cells in the cluster; and

assigning odd frequency groups to first and second rows of cells and even frequency groups to third and fourth rows of cells, and then extending frequency assignment along each row and column and above and below the rows and columns, the odd frequencies repeating in the first and second rows and the even frequencies repeating in the third and fourth rows, there being below the fourth row additional first, second, third and fourth rows, and above the first row other fourth, third, second and first rows, so that each antenna at the center of each cluster of cells radiates a frequency group that is different from the frequency group radiated by the other two antennae of the cluster and the three frequency groups of any cluster are not radiated from another cluster in the vicinity, and so that reuses of any frequency group occur as three adjacent uses thereof which define the apices of a triangle and the direction of radiation of the frequency groups at the apices are 120°

apart.

7. A method as in claim 6, wherein:

the frequency group assigning step is achieved by

creating a matrix of numbers the first two rows of which comprise serial odd numbers and the third and fourth rows of which comprise serial even numbers, the matrix also having number-containing columns, each number identifying one of the frequency groups; and

mapping the numbers of the matrix directly onto respective individual cells of the plurality of cells by assigning the numbers in each matrix row to a corresponding cell row and, as a result, assigning the numbers in each matrix column to a corresponding cell column.

8. A method as in claim 7, wherein:

the number of frequency groups is sixteen, and the matrix comprises four rows and four columns.

9. A method as in claim 6 wherein N=5.33.

10. A method of allocating fractional frequencies in a cellular radiotelephone system, the system having a plurality of available frequencies and a plurality of nominally hexagonally configured cells, the method comprising:

ordering the cells as rows of abutting cells and columns of abutting cells, the centers of the cells in a row being offset from the centers of the immediately adjacent cells in the rows on either side thereof, the offset being in the direction in which the rows extend, the columns extending in a direction which is oblique to the rows, and the centers of the cells in a column being offset in a direction parallel to the columns from the centers of the immediately adjacent cells in the columns on either side thereof;

forming cell clusters of three cells each, two of the cells in each cluster being from one row and one cell being from an adjacent row, each cell in a cluster abutting the other two cells of the cluster so that there is defined a cluster center which is a point common to all three cells in a cluster, the centers of the cells in each cluster defining a first triangle having a base parallel to the rows and a vertex separated from the base in a direction normal to the base and the rows;

locating three directional antennae at the center of each cluster, each antenna of each cluster being capable of radiating energy over a respective one of the cells in the cluster;

assigning alternate odd frequency groups to first and second rows of cells and alternate even frequency groups to third and fourth rows of cells, and then extending frequency assignment along each row and column and above and below the rows and columns, the odd frequencies repeating in the first and second rows and the even frequencies repeating in the third and fourth rows, there being below the fourth row additional first, second, third and fourth rows, and above the first row other fourth, third, second and first rows, so that each antenna at the center of each cluster of cells radiates a frequency group that is different from the frequency group radiated by the other two antennae of the cluster and the three frequency groups of any cluster are not radiated from another cluster in the vicinity, and so that reuse of any frequency group occurs as three adjacent uses thereof which define the apices of a second triangle and the direction of radiation of the frequency groups at the apices are 120°

apart, the first and second triangles being similar with their three pairs of sides being generally parallel.

11. A method as in claim 10, wherein reuse results in N=5.33.