GB2313742A

GB2313742A - Channel allocation in a cellular communication system

Info

Publication number: GB2313742A
Application number: GB9708328A
Authority: GB
Inventors: Keith Andrew Olds; John Wesley Locke; Kenneth Maynard Peterson; Brian Daniel
Original assignee: Motorola Inc
Current assignee: Motorola Solutions Inc
Priority date: 1996-05-28
Filing date: 1997-04-25
Publication date: 1997-12-03
Also published as: DE19720199A1; ITRM970255A0; FR2749472A1; ITRM970255A1; JPH1056671A; GB9708328D0; IT1290601B1

Description

2313742 METHOD AND APPARATUS FOR CHANNEL ASSIGNMENT AND SELECTION IN A

CELLULAR COMMUNICATION SYSTEM

Field of the Invention

This invention relates generally to the field of wireless communication systems and methods having limited communication channels and, more specifically, to cellular communication systems employing spectrum re-use.

Background of the Invention

Wireless communication systems that rely on forming multiple beams or cells in a local geographical region suffer from co- channel interference, reduced system capacity and beam to beam or cell to cell interference. Co-channel interference and cell to cell interference are avoided by using different channel sets (frequencies) in adjacent cells. The techniques used to avoid co-channel interference and cell to cell interference reduce system capacity.

Frequency or channel re-use recovers system capacity by partitioning service areas into multiple cells and then re-using channels throughout these cells. Frequency or channel re-use is the use of radio channels on the same carrier frequency for the coverage of geographically different areas and is necessary in order to construct practical, high-capacity cellular systems in traffic-dense areas. Needless to say these radio carrier frequencies must be far enough apart to ensure that co-channel interference either does not arise or does not arise to an objectional level.

The co-channel interference and cell to cell interference are most pronounced at the overlapping beam boundaries. Subscribers in the beam boundary regions will experience interference and limited service. Multiple access techniques such as code division multiple access (CDMA) provide the ability to re- use frequencies in adjacent cells. However, at the cell boundaries, where there is some overlap of adjacent cells, the cell to cell interference and co-channel interference significantly reduces the capacity in the overlap regions.

Other re-use techniques have partitioned channels into roughly equivalent sets and distributed them across a set cellular re-use pattern such as a 7 cell or a 19 cell re-use pattern. Such systems must partition the total available channels between these numbers of sets. Such a reduction in the available channels in a cell dramatically reduces the available bandwidth. 15 Thus, what is needed is a system and method for selecting communication channels between adjacent cells that re-use channels in adjacent cells and thereby increases user capacity by providing a greater number of available channels in each cell. 20 What is also needed is a method of allocating communication channels between a first and second adjacent cells with an overlapping area wherein a subscriber unit receives interfering signals. What is also needed is a method and system for selecting a communication channel in non-overlapping regions and overlapping regions.

What is yet needed is a method for varying the re-use of communication channels according to desired interference tolerances of the system.

Brief Description of the Drawings

The invention is pointed out with particularity in the appended claims. However, a more complete understanding of the present invention may be derived by referring to the detailed description and claims when considered in connection with the figures:

FIG. 1 is a diagram showing a projection of adjacent cells in a cellular communication system, in accordance with an embodiment of the present invention; FIG. 2 is a diagram showing a plot of power levels from adjacent cells in a cellular communication system, in accordance with an embodiment of the present invention; FIG 3 is a flowchart of a method for allocating a plurality of communication channels in a communication system having first and second adjacent cells, in accordance with a preferred embodiment of the present invention; FIG. 4 is a flowchart of a method for a subscriber unit to select a communication channel in a communication system having first and second adjacent cells employing interfering communication channels, in accordance with a preferred embodiment of the present invention; and FIG. 5 illustrates a simplified block diagram of a subscriber unit for communicating in a communication system having first and second adjacent cells employing interfering communication channels, in a accordance with a preferred embodiment of the present invention.

The exemplification set out herein illustrates a preferred embodiment of the invention in one form thereof, and such exemplification is not intended to be construed as limiting in any manner.

Detailed Description of the Draw'

The present invention provides, among other things, a method of allocating communication channels in a communication system utilizing relatively stationary cells and wherein adjacent cells employ interfering communication channels to non-overlapping regions of adjacent cells and assigning non-interfering communication channels to overlapping regions of the adjacent cells.

The present invention further provides a subscriber unit and a method to select a communication channel in a communication system having adjacent cells wherein interfering communication channels are assigned to nonoverlapping regions of the adjacent cells and noninterfering communication channels are assigned to overlapping regions of the adjacent cells.

FIG. 1 is a diagram showing a projection of adjacent cells in a cellular communication system 100, in accordance with an embodiment of the present invention. In cellular communication systems, cells are placed adjacent to enable reuse of frequency spectrum.

A first adjacent cell 110 provides communication channels to users located therein. Users may relocate or other user may be present in a second adjacent cell 120 or a third adjacent cell 130. Users located within boundaries serviced by a particular cell employ channels assigned to that specific cell. Cellular boundaries typically are a function of propagation characteristics associated with a particular cell. Boundaries generally are representative of a particular signal strength of level at a distance from a transmitting source. Transmitting sources may be terrestrial base stations or in satellite cellular applications may be cells projected from space upon the Earth. Cellular boundaries may also be represented by maps or geographic plots generally associated with signal strengths as a function of distance from a transmitting source. however, maps or plots may also incorporate compensation data associated with interfering structures or terrain.

Adjacent cells 110 and 120 must provide sufficient signal strength at their boundaries to prevent the formation of Mead zones" or areas where communication services are not available. As a result, competing signal strengths at boundary areas protrude into boundary areas of other cells and create interfering signals if competing channels are not orthogonal or non-interfering. Prior art systems have employed entire orthogonal communication channel sets in adjacent cells to overcome this problem.

Such exclusive dedication of relatively evenly partitioned communication channels greatly reduces the allowable allocation of channels to any one cell and thereby restricts the number of users in any one cell.

As figuratively shown in FIG. 1, an overlapping region created by first and second overlapping regions 112 and 122 form a small portion of the total area of either of adjacent cells 110 or 120. In a typical cellular communication system having a central cell with six other adjacent cells dispersed around the central cell and employing a 5 dB separation between interfering communication channels, non-overlapping regions 111, 121, and 131 of adjacent cells 110, 120, and 130, respectively, represent about 82.6 % of the total area of adjacent cells 110, 120, or 130. Overlapping regions 112 and 122 are proportionally small to non-overlapping region 111, hence, a proportional number of non-interfering communication channels suffice to perform non-interfering communication in these regions.

In a preferred embodiment, a base station or transceiver servicing first adjacent cell 110 partitions communication channels into a larger non-overlapping set for use in non-overlapping region 111 and a smaller first overlapping set for use in first overlapping region 112.

Likewise, the base station or transceiver servicing second adjacent cell 120 partitions communication channels into a larger non-overlapping set for use in non-overlapping region 121 and a smaller second overlapping set for use in second overlapping region 122. The non-overlapping sets for non-overlapping regions 111 and 121 are equivalent as users in these areas have sufficient signal-to-noise or rather signal-to-signal margins to enable separation and non-interference of adjacent signals. However, first and second overlapping sets of communication channels for use in first and second overlapping regions 112 and 122 may not be interfering, that is to say first and second overlapping sets of communication channels must be orthogonal to each other thus preventing interference with each other in the overlapping regions. Additionally, in a standard cellular configuration with a central cell and six adjacent cells, third overlapping region 132 employs a third overlapping set orthogonal to both first and second overlapping sets. Although three orthogonal overlapping sets are generally employed for typical cellular systems, these orthogonal overlapping sets of communication channels are relatively small in number when contrasted with the reuse factor of the non-overlapping set of communication channels that are reusable in each adjacent cell in non-overlapping regions.

FIG. 2 is a diagram showing a plot of power levels from adjacent cells in a cellular communication system, in accordance with an embodiment of the present invention. A typical power plot illustrates how power or signal level of a communication channel is distributed across a cell 30 and beyond. First and second adjacent cells 110 and 120 exhibit first and second adjacent cell signal levels 210 and 220, respectively. Prior to either adjacent signal levels decaying significantly, an interfering signal region 207 occurs and defines overlapping region 208 shown 35 as a composite of first and second overlapping regions 112 and 122 from FIG. 1. -6- Depending on system parameters, such as receiver selectivity in subscriber units operating in an interfering signal region, the size of dimension of overlapping region 208 may be varied to reduce or increase the partitioning of the number of channels dedicated to first and second overlapping sets of communication channels. For subscriber units having very selective transceivers capable of retrieving a signal in the presence of nearly equal interfering signal, overlapping region 208 may be significantly reduced thus accommodating more reusable channels in the non-overlapping set.

FIG. 3 is a flowchart of a method for allocating a plurality of communication channels in a communication system having first and second adjacent cells, in accordance with a preferred embodiment of the present invention. A procedure 300 establishes the partitioning and allocation of available spectrum or channels between non-overlapping set, and overlapping sets of communication channels.

A query task 305 determines if varying or altering of overlapping region 208 (FIG. 2) is to be performed. The sizing of overlapping region 208 may be performed only once prior to defining a communication system or overlapping region 208 may dynamically altered such as with technology advances as subscriber units become increasingly more selective in tolerating competing signals, or when overlapping regions occur in less or uninhabited regions where an increase in the number of communication channels in the non-overlapping set are requested.

When varying of overlapping region is selected, a task 310 alters overlapping region 208 according to the desired interference tolerances within overlapping region 208 (FIG. 2). When altering of overlapping region 208 is complete or when varying is not selected, a task 315 partitions a plurality of communication channels into a non-overlapping set and an overlapping set. A task 320 assigns communication channels in the interfering set to non-overlapping regions 111, 121, and 131 (FIG. 1).

A task 325 partitions overlapping region 208 (FIG. 2) into first overlapping region 112 (FIG. 1) adjoining first adjacent cell 110 (FIG. 1) and second overlapping region 122 (FIG. 1) adjoining second adjacent cell 120 (FIG. 1).

A task 330 partitions the non-interfering communication channels into a first overlapping set and a second overlapping set wherein the first and second overlapping sets are non-interfering or orthogonal.

A task 335 assigns the first overlapping set to first adjacent cell 110 (FIG. 1) for use in the first overlapping region 112 (FIG. 1) and the second overlapping set to second adjacent cell 120 (FIG. 1) for use in second overlapping region 122 (FIG. 1). Services for first and second overlapping regions 112 and 122 are provided through the same base stations of transceivers providing communication for non-overlapping regions 111 and 121, respectively.

FIG. 4 is a flowchart of a method for a subscriber unit to select a communication channel in a communication system having first and second adjacent cells employing interfering communication channels, in accordance with a preferred embodiment of the present invention.

A procedure 400 is employed by a subscriber unit for determining which communication channels to employ depending on a location or perceived location within communication system 100 (FIG. 1). In one preferred embodiment, query task 405 determines if default overlapping region 208 (FIG. 2) is to be varied.

Variations may be programmed into a subscriber unit or broadcast or otherwise downloaded or communicated to a subscriber unit or a subscriber unit may dynamically alter its perception of overlapping region 208 based upon perceived or interference measurements. If signals from an adjacent cell are not interfering with a subscriber unit's communication on a non-overlapping channel, a -B- subscriber unit may elect to temporarily vary its perception of overlapping region 208 (FIG. 2) in favor or performing a handoff or selection of a communication channel from a smaller set such as an overlapping set.

When varying of overlapping region is selected, a task 410 alters overlapping region 208 (FIG. 2) according to the desired interference tolerances within overlapping region 208 (FIG. 2). When altering of overlapping region 208 is complete or when varying is not selected, a task 415, in a preferred embodiment, a subscriber unit while in first adjacent cell 110 (FIG. 1), monitors for interference of interfering communication channels from second adjacent cell 120 (FIG. 1). By monitoring or measuring interference from adjacent cells, a subscriber unit may determine if it lies within a non-overlapping area or an overlapping area.

In another preferred embodiment, a task 415' is performed to determine a location of a subscriber unit.

Determination of a location may be performed using location determining techniques such as those provided by global positioning systems (GPS) or other positioning techniques know by those of skill in the art, including programming a fixed location into a fixed subscriber unit.

A task 416 compares the location of a subscriber unit with a map of first and second adjacent cells 110 and 120 (FIG.

1). The map defines non-overlapping regions 111 and 121 and overlapping regions 112 and 122 of first and second adjacent cells 110 and 120 (all FIG. 1), respectively. A map need not be physically loaded into a subscriber unit and may even be broadcast by adjacent cells 110 and 120 on a communication or an independent broadcast channel and may be as elementary as an origin and a radius.

A query task 420 determines if interference is present either from monitoring and measuring in one preferred embodiment or from location determination from positioning data in relationship to a map or other indicia in yet another preferred embodiment.

When query task 420 determines that a subscriber unit is located within non-overlapping region 111 (FIG. 1), that is to say interfering communication channels from adjacent cell 120 (FIG. 1) do not interfere with said interfering communication channels of first adjacent cell 110, a subscriber unit communicates on interfering communication channels of the non-overlapping set.

When query task 420 determines sufficient interference exists or the subscriber unit is located in overlapping region 208 (FIG. 2), then a query task 430 determines if the subscriber unit is in first overlapping region 112 or second overlapping region 122. When the subscriber unit is located in first overlapping region 112 then a task 435 communicates on first overlapping set of non-interfering communication channels and when the subscriber unit is located in second overlapping region 122 then a task 440 communicates on second overlapping set of non-interfering communication channels.

In yet another preferred embodiment, a subscriber unit may deduce the partitioning of communication channels using an indicia either programmed into the subscriber unit or transmitted to the subscriber unit. In such an embodiment, a subscriber unit partitions overlapping region 208 (FIG. 2) into a first overlapping region 121 (FIG. 1) adjoining first adjacent cell 110 (FIG- 1) and second overlapping region 122 (FIG. 1) adjoining second adjacent cell 120 (FIG. 1). From bulk communication channels, the subscriber unit may partition non interfering communication channels into a first overlapping set and a second overlapping set with first and second overlapping sets being non-interfering, and then assign first overlapping set to first adjacent cell (FIG. 1) for use in first overlapping region 112 (FIG 1) and second overlapping set to second adjacent cell 120 (FIG. 1) for use in second overlapping region 122 (FIG.

1).

FIG. 5 illustrates a simplified block diagram of a subscriber unit for communicating in a communication system having first and second adjacent cells employing interfering communication channels, in a accordance with a 5 preferred embodiment of the present invention.

A subscriber unit 500 communicates in communication system 100 (FIG. 1) having first and second adjacent cells 110 and 120 (FIG. 1) wherein interfering communication channels are assigned to non-overlapping regions of first and second adjacent cells 110 and 120 (FIG. 1) and non interfering communication channels are assigned to overlapping region 208 (FIG. 2) of first and second adjacent cells 110 and 120 (FIG. 1). Subscriber unit 500 executes the methods and processes described above and in their various embodiments as well as operating in the environment described above and various embodiment thereof.

Subscriber unit 500 includes a transceiver 505 with antenna 510 monitors interference of interfering communication channels from adjacent cells. Transceiver 505 communicates on interfering communication channels when interfering communication channels from adjacent cells do not interfere with interfering communication channels of first adjacent cell 110 (FIG. 1) and transceiver 505 when interfering communications channels from adjacent cells interfere with interfering communication channels, communicate on first overlapping set of non-interfering communication channels when subscriber unit 500 is located in first overlapping region 112 (FIG. 1) and when subscriber unit 500 is located in second overlapping region 122, communicates on second overlapping set of non-interfering communication channels.

Subscriber unit 500 also includes a controller 515, operably coupled to transceiver 505, evaluates interfering communication channels and selects a communication channel and executes the methods described herein.

In a preferred embodiment, subscriber unit 500 includes a locator 525 for determining a location of subscriber unit 500. Locator 525 may determine a location using techniques such as those provided by global positioning systems (GPS) or other positioning techniques know by those of skill in the art, including programming a fixed location into a fixed subscriber unit 500. In this embodiment, controller 515 also compares the location of a subscriber unit with a map of first and second adjacent cells 110 and 120 (FIG. 1) stored in a map storage 520.

The map defines non-overlapping regions 111 and 121 and overlapping regions 112 and 122 of first and second adjacent cells 110 and 120 (all FIG. 1), respectively. A map need not be physically loaded into a subscriber unit and may even be broadcast by adjacent cells 110 and 120 on a communication or an independent broadcast channel and may be as elementary as an origin and a radius. Further more in yet another embodiment, a map may be varied according to desired interference tolerances within overlapping region 208 (FIG. 2).

Thus, a method of allocating a plurality of communication channels in a communication system that employs channel reuse between adjacent cells by assigning a non-overlapping set of communication channels to users located in the non-overlapping areas, and assigning overlapping sets to users located in overlapping areas has been disclosed.

Also, a method and subscriber unit for selecting a communication channel in a communication system having adjacent cells wherein interfering communication channels are assigned to non-overlapping regions of adjacent cells and non-interfering communication channels are assigned to overlapping regions of adjacent cells by monitoring interfering communication channels and communicating on interfering communication channels when such channels are not interfered with by channels from adjacent cells and when interfering communication channels from adjacent cells interfere with interfering communication channels, communicating on non-interfering communication channels has been disclosed.

It will be apparent to those skilled in the art that the disclosed invention may be modified in numerous ways and may assume many embodiments other than the preferred form specifically set out and described above.

Accordingly, it is intended by the appended claims to cover all modifications of the invention which fall within 10 the true spirit and scope of the invention.

Claims

What is claimed is:

CLAIMS 1. A method of allocating a plurality of communication channels in a communication system having first and second adjacent cells, comprising the steps of:

assigning interfering communication channels to non- overlapping regions of said first and second adjacent cells; and assigning non-interfering communication channels to an overlapping region of said first and second adjacent cells.

is
2. A method as recited in claim 1, further comprising the step of:

partitioning said overlapping region into a first overlapping region adjoining said first adjacent cell and a second overlapping region adjoining said second adjacent cell.
3. A method as recited in claim 2, wherein said assigning step comprises the steps of: 25 partitioning said non-interfering communication channels into a first overlapping set and a second overlapping set, said first and second overlapping sets being noninterfering; and assigning said first overlapping set to said first adjacent cell for use in said first overlapping region and said second overlapping set to said second adjacent cell for use in said second overlapping region.
4. A method as recited in claim 1, further comprising the step of:

varying said overlapping region according desired interference tolerances within said overlapping region.
5. A method of allocating a plurality of communication channels in a communication system employing channel reuse between first and second adjacent cells having a common overlapping area and first and second nonoverlapping areas, said common overlapping area having a first overlapping area adjoining said first nonoverlapping area and a second overlapping area adjoining said second non-overlapping area, said method comprising the steps of: partitioning said plurality of communication channels into a non-overlapping set, a first overlapping set, and a second overlapping set; assigning said non-overlapping set of said plurality of communication channels to users located in said first and said second non-overlapping areas; assigning said first overlapping set of said plurality of communication channels to users located in said first overlapping area; and 20 assigning said second overlapping set of said plurality of communication channels to users located in said second overlapping area.
6. A method for a subscriber unit to select a communication channel in a communication system having first and second adjacent cells wherein interfering communication channels are assigned to non-overlapping regions of said first and second adjacent cells and noninterfering communication channels are assigned to an overlapping region of said first and second adjacent cell, said method comprising the steps of:

while in said first adjacent cell, monitoring interference of said interfering communication channels from said second adjacent cell; when said interfering communication channels from said second adjacent cell do not interfere with said interfering communication channels of said first adjacent cell, communicating on said interfering communication channels; and when said interfering communication channels from said second adjacent cell interfere with said interfering communication channels of said first adjacent cell, communicating on said non-interfering communication channels.
7. A method as recited in claim 6, further comprising the step of:

partitioning said overlapping region into a first overlapping region adjoining said first adjacent cell and a second overlapping region adjoining said second adjacent cell.
8. A method as recited in claim 7, wherein said partitioning step further comprises the steps of: partitioning said non-interfering communication channels into a first overlapping set and a second overlapping set, said first and second overlapping sets being non-interfering; and assigning said first overlapping set to said first adjacent cell for use in said first overlapping region and said second overlapping set to said second adjacent cell for use in said second overlapping region.
9. A method as recited in claim 8, wherein said communicating on said noninterfering communication channels step comprises the steps of:

when said interfering communication channels from said second adjacent cell interfere with said interfering communication channels of said first adjacent cell, communicating on said first overlapping set of said noninterfering communication channels.
10. A method as recited in claim 6, wherein said monitoring step comprises the steps of:

determining a location of said subscriber unit; and comparing said location of said subscriber unit with a map of said first and second adjacent cells, said map defining said non-overlapping regions and said overlapping region of said first and second adjacent cells.
11. A method as recited in claim 6, further comprising the step of:

varying said overlapping region according to desired interference tolerances within said overlapping region.
12. A subscriber unit for communicating in a communication system having a first and second adjacent cells wherein interfering communication channels are assigned to non-overlapping regions of said f irst and second adjacent cells and non-interfering communication channels are assigned to an overlapping region of said first and second adjacent cells, said subscriber unit comprising:

a transceiver for monitoring interference of said interfering communication channels from said second adjacent cell while in said first adjacent cell and for communicating on said interfering communication channels when said interfering communication channels from said second adjacent cell do not interfere with said interfering communication channels of said first adjacent cell; and a controller for evaluating said interfering communication channels and selecting a communication channel.
13. A subscriber unit as recited in claim 12 wherein said overlapping region is partitioned into a first overlapping region adjoining said first adjacent cell and a second overlapping region adjoining said second adjacent cell.
14. A subscriber unit as recited in claim 13 wherein said non-interfering communication channels are partitioned into a first overlapping set and a second overlapping set, said first and second overlapping sets being non-interfering, and said first overlapping set being assigned to said first adjacent cell for use in said first overlapping region and said second overlapping set being assigned to said second adjacent cell for use in said second overlapping region.
15. A subscriber unit as recited in claim 14 wherein said transceiver, when said interfering communication channels from said second adjacent cell interfere with said interfering communication channels of said first adjacent cell, communicates on said first overlapping set of said non-interfering communication channels.
16. A subscriber unit as recited in claim 15 further comprising: a locator for determining a location of said subscriber unit; map storage having a map defining said nonoverlapping regions and said overlapping region of said first and second adjacent cells; and said controller further comparing said location of said subscriber unit in relation to said map of said first and second adjacent cells.
17. A subscriber unit as recited in claim 16 wherein said map may be varied according to desired interference tolerances within said overlapping region.
18. A subscriber unit as recited in claim 12 wherein said overlapping region may be varied according to desired interference tolerances within said overlapping region.

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