Method and system for solving cellular communications frequency planning problem

• US 6,047,186 A
• Filed: 10/06/1997
• Issued: 04/04/2000
• Est. Priority Date: 10/06/1997
• Status: Expired due to Fees

• Current Assignee: Nortel Networks Limited (Nortel Networks Corporation)
• Original Assignee: Nortel Networks Corporation
• Inventors: Han, Xu, Yu, Chang, Madhavapeddy, Seshagiri Rao, Subramanian, Sairam
• Primary Examiner(s): Trost, William G.
• Assistant Examiner(s): Trinh, Sonny
• Application Number:
  US08/944,376
• Time in Patent Office: 911 Days
• Field of Search: 455/447, 455/450, 455/464, 455/505, 455/446, 455/561, 455/62, 455/452, 455/453, 455/448, 455/449, 455/63
• US Class Current: 455/446
• CPC Class Codes: H04W 16/10 Dynamic resource partitioning

Abstract

The foregoing objects are achieved as is now described. Provided are a method and system for utilization with wireless communications systems having a cellular architecture covering a geographic area. The method and system accomplish their objects via the following. The geographic area is defined. One or more pairs of the sectors within the defined geographic area wherein a weak connection zone exists are determined. The geographic area is decomposed into two or more sub-areas wherein each sub-area is isolated from other sub-areas by the determined one or more pairs of sectors having a weak connection zone. A first of the sub-areas is selected. Frequency groups are assigned to each sector within the first selected sub-area such that signal to noise ratio is optimized. Thereafter, a second of the sub-areas is selected. One or more sectors within the second selected one of the sub-areas which are linked to sectors within the first selected sub-area are selected. Frequency groups are assigned to the selected sectors within the selected second of the sub-areas such that signal to noise ratio in the selected sector within the selected second of the sub-areas is optimized. Thereafter, frequency groups are assigned to every other sector within the selected second of the sub-areas such that signal to noise ratio is optimized across the second selected sub-area and such that signal to noise ratio over the defined geographic area is optimized.

Claims

1. A method for use with wireless communications systems having a cellular architecture covering a defined geographic area, and wherein said geographic area is populated by a plurality of cells and wherein each of said plurality of cells is subdivided into sectors, and wherein said wireless communications system has a plurality of groups of channels, and wherein said method assigns specific groups of channels drawn from said plurality of groups of channels to each sector such that signal to noise ratio over said geographic area is optimized, said method comprising the steps of:

determining one or more pairs of said sectors within said defined geographic area wherein a weak connection zone exists;

in response to said determining step, decomposing said defined geographic area into two or more sub-areas composed of one or more of said sectors and wherein each sub-area is isolated from other sub-areas by said determined one or more pairs of sectors having a weak connection zone;

determining whether a first of said sub-areas is of solvable size, wherein if said first of said sub-areas is not of solvable size, defining a geographic area equal to said first of said sub-areas, and thereafter recursively engaging in said decomposing step and subsequent steps to yield a solvable sub-area;

assigning frequency groups to each sector within a selected first sub-area of said solvable sub-area such that signal to noise ratio is optimized across said selected first sub-area;

thereafter,

assigning a frequency group or groups to a selected one or more sectors within a selected second of said solvable sub-areas which are linked to one or more sectors within said selected first sub-area such that signal to noise ratios in said selected one or more sectors within said selected second of said solvable sub-areas is optimized; and

thereafter, assigning frequency groups to every other sector within said selected second of said solvable sub-areas such that signal to noise ratio is optimized across said selected second of said solvable sub-areas such that signal to noise ratio over said defined geographic area is optimized.

2. The method of claim 1, wherein said step of thereafter assigning frequency groups to every other sector within said selected second of said sub-areas further comprises the steps of:

determining whether said selected second of said sub-areas is of solvable size;

in response to a determination that said selected second of said sub-areas is not of solvable size, defining a geographic area equal to said selected second of said sub-areas; and

with said geographic area so defined, thereafter recursively engaging in said decomposing step and subsequent steps.

3. The method of claim 1, comprising the steps of:

determining a number of frequencies required by each sector;

selecting a specific frequency group;

determining which sectors have been assigned said selected specific frequency group;

creating a sub-set of said determined sectors whose said determined number of frequencies required is less than all of the available frequencies in said selected specific frequency group;

selectively removing two sectors in said created sub-set which have a maximum likelihood of interference;

assigning frequencies to said selected sectors from said selected specific frequency group such that likelihood of interference between the selected sectors is minimized; and

thereafter repeating said selectively removing two sectors and said assigning frequencies steps until said sub-set is empty or has only one remaining member.

4. The method claim 3 wherein said step of determining a number of frequencies required by each sector comprises the steps of:

obtaining network traffic information for one or more sectors; and

in response to said obtaining step, determining the number of frequencies necessary to carry expected network traffic in said one or more sectors.

5. The method of claim 1 further comprising the step of treating each individual frequency as if it were in fact a frequency group such that each individual frequency is treated and thus subsequently assigned as if it were a group.

6. A system for use with wireless communications systems having a cellular architecture covering a defined geographic area, and wherein said geographic area is populated by a plurality of cells and wherein each of said plurality of cells is subdivided into sectors, and wherein said wireless communications system has a plurality of groups of channels, and wherein said system assigns specific groups of channels drawn from said plurality of groups of channels to each sector such that signal to noise ratio over said geographic area is optimized, said system comprising the steps of:

means for determining one or more pairs of said sectors within said defined geographic area wherein a weak connection zone exists;

means responsive to said means for determining, for decomposing said defined geographic area into two or more sub-areas composed of one or more of said sectors and wherein each sub-area is isolated from other sub-areas by said determined one or more pairs of sectors having a weak connection zone;

means for determining whether a first of said sub-areas is of solvable size, wherein if said first of said sub-areas is not of solvable size, for defining a geographic area equal to said first of said sub-areas, and thereafter recursively engaging in said decomposing step and subsequent steps to yield a solvable sub-area;

means for assigning frequency groups to each sector within a selected first sub-area of said solvable sub-area such that signal to noise ratio is optimized across said selected first sub-area;

means for thereafter assigning a frequency group or groups to a selected one or more sectors within a selected second of said solvable sub-areas which are linked to one or more sectors within said selected first sub-area such that signal to noise ratios in said selected one or more sectors within said selected second of said solvable sub-areas is optimized; and

means for thereafter assigning frequency groups to every other sector within said selected second of said solvable sub-areas such that signal to noise ratio is optimized across said selected second of said solvable sub-areas such that signal to noise ratio over said defined geographic area is optimized.

7. The system of claim 6, wherein said means for thereafter assigning frequency groups to every other sector within said selected second of said sub-areas further comprises:

means for determining whether said selected second of said sub-areas is of solvable size;

means responsive to a determination that said selected second of said sub-areas is not of solvable size, for defining a geographic area equal to said selected second of said sub-areas; and

with said geographic area so defined, means for thereafter recursively engaging in said decomposing step and subsequent steps.

8. The system of claim 6, comprising:

means for determining a number of frequencies required by each sector;

means for selecting a specific frequency group;

means for determining which sectors have been assigned said selected specific frequency group;

means for creating a sub-set of said determined sectors whose said determined number of frequencies required is less than all of the available frequencies in said selected specific frequency group;

means for selectively removing two sectors in said created sub-set which have a maximum likelihood of interference;

means for assigning frequencies to said selected sectors from said selected specific frequency group such that likelihood of interference between the selected sectors is minimized; and

means for thereafter repeating said selectively removing two sectors and said assigning frequencies steps until said sub-set is empty or has only one remaining member.

9. The system of claim 8 wherein said means for determining a number of frequencies required by each sector comprises:

means for obtaining network traffic information for one or more sectors; and

means responsive to said obtaining step, for determining the number of frequencies necessary to carry expected network traffic in said one or more sectors.

10. The system of claim 6 further comprising means for treating each individual frequency as if it were in fact a frequency group such that each individual frequency is treated and thus subsequently assigned as if it were a group.

11. A method for use in a wireless communications system having a cellular architecture covering a defined geographic area, and wherein said defined geographic area is populated by a plurality of cells and wherein each of said plurality of cells is subdivided into sectors, and wherein said wireless communications system has a plurality of groups of channels, and wherein said method assigns a specific group of channels, drawn from said plurality of groups of channels, to a particular one of said sectors such that the signal to noise ratio within said particular one is optimized is optimized, said method comprising the steps of:

assigning to said particular one of said sectors a group, drawn from said plurality of groups of channels, of available channels;

determining an aggregate interference in said particular one of said sectors arising from active groups of channels other than said group assigned to said particular one of said sectors, wherein aggregate interference is determined by summing one or more received signal strengths on frequencies other than those frequencies assigned to said particular one of said sectors;

calculating a signal to noise ratio drawn upon a signal strength of said group of channels assigned to said particular one of said sectors and said determined aggregate interference;

thereafter repeating said assigning, determining, and calculating steps until all available groups of channels have been assigned to said particular one of said sectors and said determining and calculating steps have been engaged in for all said available groups; and

selecting for permanent assignment to said particular one of said sectors that group having the best calculated signal to noise ratio.

12. A system for use in a wireless communications system having a cellular architecture covering a defined geographic area, and wherein said defined geographic area is populated by a plurality of cells and wherein each of said plurality of cells is subdivided into sectors, and wherein said wireless communications system has a plurality of groups of channels, and wherein said system assigns a specific group of channels, drawn from said plurality of groups of channels, to a particular one of said sectors such that the signal to noise ratio within said particular one is optimized is optimized, said system comprising:

means for assigning to said particular one of said sectors a group, drawn from said plurality of groups of channels, of available channels;

means for determining an aggregate interference in said particular one of said sectors arising from active groups of channels other than said group assigned to said particular one of said sectors, wherein aggregate interference is calculated as a sum of one or more received signal strengths on frequencies other than those frequencies assigned to said particular one of said sectors;

means for calculating a signal to noise ratio drawn upon a signal strength of said group of channels assigned to said particular one of said sectors and said determined aggregate interference;

means for thereafter repeating said assigning, determining, and calculating steps until all available groups of channels have been assigned to said particular one of said sectors and said determining and calculating steps have been engaged in for all said available groups; and

means for selecting for permanent assignment to said particular one of said sectors that group having the best calculated signal to noise ratio.