Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
1999-03-29
2001-04-03
Urban, Edward F. (Department: 2683)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S450000, C455S449000, C370S329000
Reexamination Certificate
active
06212385
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates, in general, to a cellular communication system and is particularly, but not exclusively, applicable to a repeat (or re-use) pattern for such cellular communication system. More particularly, an aspect of the present invention may be employed in a cellular communication system having concentric cells.
SUMMARY OF THE PRIOR ART
As a consequence of the limited availability of frequency bandwidth for cellular communication systems generally, such as the pan-European Global System for Mobile (GSM) cellular communication, designers must employ frequency re-use techniques to optimise and increase cellular system capacity. More explicitly, a frequency bandwidth that is assigned to the communication system is divided into many channels that are themselves attributed to frequency groups. These frequency groups are then individually allocated to sectors that form a site (or cell), with the deployment of one set of frequency groups across many sites defining a cluster of sites within the communication system. As such, cell planning represents the distribution of frequency groups between a number of sectors in a cluster, while a repeat (or re-use) pattern for the system is indicated by the relationship between the number of sites that are covered by an integer number of sets of frequency groups. For example, a repeat pattern of two (2) would be achieved from the deployment of two complete sets of frequency groups to cover a cluster containing 4 sites (with each site typically containing either three (3) or six (6) sectors).
To date, repeat patterns offering a two-site repeat have proved difficult to implement because of co-channel interference and, in particular, considerable adjacent channel interference (or splatter) prevalent in current repeat patterns. In these respects and as will be understood, co-channel interference occurs when different sectors use the same frequency groups (with an intensity for the co-channel interference determined by the proximity and number of co-channel cells), whereas adjacent channel interference occurs as a result of the adjacent location of contiguous frequency bands (channels). Clearly, in a two-site repeat pattern, adjacent channel interference becomes an increasing problem.
At present, therefore, many systems (including GSM and Digital Communication System (DCS) 1800) utilise a single-layer four-site repeat pattern.
In an attempt to mitigate against the effects of adjacent channel interference in a two-site repeat pattern, “frequency hopping” schemes (such as envisaged in Code Division Multiple Access (CDMA)) offer a potential solution to the problem, although such schemes are relatively complex and commercially expensive (because of the necessity for sophisticated hand-over algorithms and the increased complexity of system infrastructure). As such, allocation of frequency groups to sectors may be on either a permanent or initial basis.
Furthermore, in an endeavour to optimise cellular systems still further, designers have recently begun to experiment with concentric cell arrangements in which a first set of frequencies having a first repeat pattern is over-layed by a second set of frequencies having a second repeat pattern. In this respect, systems have emerged that provide a four-site (by three-sector) repeat pattern with a one-site (by three sector) underlay/overlay, notwithstanding that the use of a one-site repeat pattern for a site having three sectors inherently produces adjacent channel interference (or splatter) in the one-site repeat pattern (that is potentially unacceptable to network operators).
SUMMARY OF THE INVENTION
According to a first aspect of the present invention there is provided a cellular communication system having a frequency bandwidth arranged into a plurality of frequency channels, the cellular communication system comprising neighbouring first and second sites each having sectors containing at least one frequency channel, wherein corresponding sectors in each of the neighbouring first and second site have consecutive frequency channels from the frequency bandwidth, thereby producing a two-site re-use pattern.
In a preferred embodiment, neighbouring sectors within both the first and second sites observe a next but one frequency channel relationship with adjacent frequency channels in at least one neighbouring sector.
Indeed, by providing clusters having corner illuminated, six-sectored sites, the preferred embodiment of the present invention provides a two-site repeat pattern that avoids adjacent channels and hence adjacent channel splatter.
In another preferred embodiment that supports an underlay/overlay cell configuration, the frequency bandwidth is arranged into a plurality of frequency channels for use in a two-site repeat pattern and a one-site repeat pattern of the cellular communication system, the cellular communication system further comprising neighbouring first and six-sectored sites in which each sector contains at least one frequency channel from the two-site repeat pattern and at least one frequency channel from the one-site repeat pattern, wherein corresponding sectors in each of the neighbouring first and second six-sectored sites have consecutive frequency channels of the two-site repeat pattern and identical frequency channels of the one-site repeat pattern.
Neighbouring sectors within both the first and second six-sectored sites observe a next but one frequency channel relationship with adjacent frequency channels in at least one neighbouring sector for the two-site repeat pattern.
Furthermore, in this overlay/underlay embodiment, it is preferable that a first half of the neighbouring sectors within both the first and second six-sectored sites observe a next but one frequency channel relationship with adjacent frequency channels in at least one neighbouring sector for the one-site repeat pattern and a second half of the neighbouring sectors within both the fist and second six-sectored sites observe a next but three frequency channel relationship with adjacent frequency channels in at least one neighbouring sector for the one-site repeat pattern.
The system of this embodiment of the present invention controls hand-over of a call from the one-site repeat pattern to the two-site repeat pattern in response to a relatively high interference level for the call on the one-site repeat pattern.
In a second aspect of the present invention there is provided a cellular communication system having a frequency bandwidth arranged into a plurality of frequency channels that are distributed on a consecutive frequency channel basis amongst a plurality of frequency groups, the cellular communication system comprising a cluster having neighbouring first and second six-sectored sites, each sector of each site containing a frequency group having at least one frequency channel and wherein: i) the first six-sectored site comprises a first frequency channel and at least five other frequency channels each having an integer multiple next but one frequency channel relationship to the first frequency channel, wherein neighbouring sectors in the first six-sectored site each contain a frequency group having respective frequency channels that observe a next but one frequency channel relationship with frequency channels in at least one neighbouring frequency group; ii) the second six-sectored site comprises a second frequency channel, consecutive in frequency to the first frequency channel, and at least five other frequency channels each having an integer multiple next but one frequency channel relationship to the second frequency channel, wherein neighbouring sectors in the second six-sectored site each contain a frequency group having respective frequency channels that observe a next but one frequency channel relationship with at least one neighbouring frequency group; and iii) consecutive frequency channels of the frequency bandwidth are assigned to corresponding sectors in each of the neighbouring first and second six-sectored sites to produce a two-site re-use pattern for the clus
Saunders Simon
Thomas Howard
Xiang Jun
Creps Heather L.
Jama Isaak R.
Motorola Inc.
Urban Edward F.
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