GB2378089A

GB2378089A - Adaptive cellular communication topology

Info

Publication number: GB2378089A
Application number: GB0118118A
Authority: GB
Inventors: Vagan Shakhgildian; Charlotte Catherine Baden
Original assignee: Motorola Inc
Current assignee: Motorola Solutions Inc
Priority date: 2001-07-24
Filing date: 2001-07-24
Publication date: 2003-01-29
Also published as: GB0118118D0

Abstract

In a first time period, eg peak hours, a network is configured with a number of microcells. During a second time interval (off-peak) one of the base stations is used to cover the whole area. The base station providing macro-cellular coverage may transmit at a higher power than during predetermined busy times. Adaptive transmissive arrays may be enabled/ disabled or available antennas allocated to a different number of cell sectors in order to vary the coverage. The macrocell base station may be above roof level, and the microcell below roof level. The set times may be adaptively determined according to traffic levels in the area. Peak hours may correspond to a larger number of users and slower speed and quiet time to a lower number of users and higher speeds. The sleeping base stations may be used to collect uplink information.

Description

ADAPTIVE CELLULAR COMMUNICATION TOPOLOGY Field of the Invention The present invention relates to cellular communication systems. The invention is applicable to, but not limited to, 2G systems, e. g. Global System for Mobile Communications (GSM) and 3G systems, e. g. Universal Mobile Telecommunication System (UMTS).

Background of the Invention In the field of this invention it is known that user traffic patterns often vary depending on the time of the day or for other time-related reasons. In particular, it is not uncommon that at certain times of the day (for example in a shopping area) the network has to cope with a very large number of slowly moving users.

To ensure that such time-related system requirements are accommodated for, the operator often covers a coverage area with contiguous micro-cells, characterised by lower power, and often sub-roof-top locations. These are optimised for maximum capacity rather than coverage and also for low mobile speeds. The latter means that the operator may, for example, equip the base stations with downlink transmit (Tx) adaptive arrays or may enable uplink synchronous mode to reduce uplink interference in

case of a code division multiple access (CDMA) based system.

At a different time of the day (for example in the evening when the shops are closed) the capacity demand is greatly reduced. However there is still a need to provide cellular coverage in the area. In addition, the majority of the users are now higher speed users, for example cellular phone users driving in their cars.

However, in these changed circumstances, the existing micro-cellular network topology may become sub-optimum.

For example, in a high-speed environment, a user will have to experience a large number of handovers. This results in an increased probability of a missed handover, for example due to the known problem of"fast rising pilotin CDMA. As a consequence, there is a danger of significant increase in system interference.

Furthermore, such a handover scenario causes a large processing load on the network. In addition, downlink transmit power, and in particular the pilot power, is wasted as the number of users in the area is much smaller than during the peak time.

Thus, there exists a need in the field of the present invention to provide a way of improving handling the differing requirements that arise at different times, such that the abovementioned disadvantages may be alleviated.

Statement of Invention In a first aspect, the present invention provides a method of operating a cellular communication system, as claimed in claim 1.

In a second aspect, the present invention provides a cellular communication base station, as claimed in claim

11.

In a third aspect, the present invention provides a cellular communication system, as claimed in claim 12.

Further aspects are as claimed in the dependent claims.

Brief Description of the Drawings Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: FIG. 1 schematically illustrates cellular communication coverage of an area during a first time period ; and FIG. 2 schematically illustrates cellular communication coverage of the area shown in FIG. 1 during a second time period.

Description of Preferred Embodiments In summary, in a first embodiment, in peak hours an area of a cellular communication system or network is configured with plural micro-cells, as shown in FIG. 1.

In contrast, in off-peak hours the same area is reconfigured with a single macro-cell, as shown in FIG. 2.

This re-configuration is achieved by one of the base transceiver stations (BTSs) or Node Bs (in a UMTS system) providing a micro-cell in the first time period being reconfigured to provide the macro-cell in the second time period. Thus an adaptive system/network topology is provided. This adaptation may be applied to plural areas of a system/network.

In this embodiment the cellular communication system is a GSM system, but it will be appreciated that the invention may also be applied to other cellular communication systems, such as UMTS systems.

FIG. 1 shows six base transceiver stations 1-6 configured to provide micro-cells 11-16 (i. e. areas of coverage) respectively. Each cell comprises three sectors, for example cell 11 comprises sectors 21-23. In this embodiment base station 1 has a total of twelve transmitting antennas, and these are configured such that four antennas transmit in each sector 21-23 in an adaptive array arrangement.

The antenna and other parts of the base station 1 are located above roof-level. Some or all of the other base stations, i. e. base stations 2-6, are located below rooflevel.

The arrangement shown in FIG. 1 is the configuration employed during a first time period. In this example, the total area covered by cells 11-16 is a shopping area, and the first time period is the shop opening hours each day.

This configuration enables large numbers of shoppers to be accommodated by the system, and also the requirement for handover between each micro-cell 11-16 is not unduly burdensome, or difficult to implement, as the majority of the users are on foot, i. e. relatively slow moving.

Then, for a second time period, in this example the time when the shops are closed, the arrangement is reconfigured and operates as shown in FIG. 2. Base transceiver station 1 is reconfigured to operate at a higher power, thus enabling the base transceiver station 1 to provide a cell 17 that covers the whole area that was earlier covered by the six cells 11-16. Additionally, the twelve antennas of base station 1 are reconfigured by disabling the adaptive array aspect and arranging them so that six groups of two antenna each provide a respective sector 31-36, as shown.

Base station 1 was designated for such role at the time of network planning and deployment and is pre-disposed to be able to operate at the higher power. Preferably the operator is expected to carry macro cellular planning

procedures as well as micro cellular. Location of base station 1 is thus chosen as a compromise between microcellular and macro-cellular requirements and as a consequence is preferably placed above the rooftop level (as in this example).

The arrangement of FIG. 2 provides a more suitable service during the second time period than the first arrangement would. The resources, including processing power, of the micro-cellular arrangement are reconfigured, for example outside shopping hours where there are fewer users, to be more efficient by operating as just one macro-cell 17.

Also, in this example vehicles are allowed in the coverage area during the second time period, but not the first time period, and users in these vehicles, thus faster moving users, are accommodated better by this single macro-cell arrangement as less handovers are required. Thus, it may be said that the network is now more optimal for coverage rather than capacity.

The other base stations, i. e. base stations 2-6 do not provide service during this second time period. They are in effect put into a"sleep mode". However, they may be operated as required to maintain operating readiness.

Optionally, they may still be used to collect uplink measurements, e. g. for position determining purposes, or

indeed any other desired uplink transmissions as required in any particular circumstances.

In the above embodiment, the cellular communication system is a GSM system. In other embodiments the system may be a UMTS system. In the case of a UMTS system, when reconfigured to the macro-cell arrangement, the power is preferably increased by the pilot power in the downlink being increased.

In the above embodiments, the first and second time periods are predetermined, i. e. in the above examples they correspond to opening and closing times of the shopping area.

Alternatively, the first and second time periods may be determined adaptively according to a cellular communication traffic condition in the area. For example, the number of users and number of handovers may be monitored while the arrangement of FIG. 1 is being used.

If the number of users drops below a given number and/or the number or rate of handovers increases above a given number, then the system is reconfigured to the arrangement shown in FIG. 2, and so on.

It will be appreciated that the above-described embodiments are merely exemplary. For example, when applied to other situations (i. e. not necessarily a shopping area), other reasons for defining the different time periods will arise. Such reasons may be based on peak hours or some other type of difference of usage with

respect to time. Also, for example, details such as the number and relative arrangement of the base stations, the number and arrangement of sectors and antennas, etc may be varied as required. Also, for example, the invention may be implemented in cellular communication systems other than GSM or UMTS.

It will be understood that the adaptive network topology described above tends to provide the following advantages, singly or in combination: (i) allows networks to be optimised for the actual traffic conditions being experienced at a particular time.

(ii) allows the number of hard handovers in the network to be managed and the resulting network load and the probability of missed handovers to be reduced.

(iii) allows the number of soft handovers required in the network to be substantially reduced when appropriate.

(iv) power efficiency can also be increased, since downlink power can be managed to match the number of users in the coverage area.

Whilst the specific, and preferred, implementations of the present invention are described above, it is clear that variations and modifications of such inventive concepts could be readily applied by one skilled in the art.

Claims

Claims 1. A method of operating a cellular communication system, comprising the steps of: providing coverage for an area during a first time period by using a plurality of base stations to each cover a respective part of the area; and providing coverage for the area during a second time period by using one of the plurality of base stations to cover the whole area.
2. The method according to claim 1, wherein during the first time period each of the plurality of base stations operates to. provide a microcell; and during the second time period the base station covering the whole area operates to provide a macrocell.
3. The method according to claim 1 or 2, wherein during the second time period the base station covering the whole area transmits with higher power than during the first time period.
4. The method according to any preceding claim, the method further comprising the steps of: disabling adaptive transmissive arrays of the base station covering the whole area during the second time period; and enabling the adaptive transmissive arrays during the first time period.

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5. The method according to any preceding claim, wherein a reconfiguration process applied to the base station to prepare the base station to cover the whole area during the second time period comprises the step of: allocating available antennas into a different number of cell sectors in the second time period compared to the first time period.
6. The method according to any preceding claim, wherein the base station covering the whole area during the second time period is located above roof-level; and one or more of the other base stations of the plurality of base stations are located below roof-level.
7. The method according to any preceding claim, wherein the first and second time periods are predetermined.
8. The method according to any of claims 1 to 6, the method further comprising the step of: adaptively determining the first and second time periods according to a cellular communication traffic condition in the area.
9. The method according to any preceding claim, wherein the first and second time periods are predetermined such that the first time period substantially corresponds to a relatively larger number of users and/or a relatively slower speed of users, and the second time period substantially corresponds to a

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relatively lower number of users and/or a relatively faster speed of users.
10. The method according to any preceding claim, wherein during the second time period, the remaining base stations of the plurality of base stations collect uplink measurements.
11. A cellular communication base station adapted to be re-configurable in operation for use in the method according to any of claims 1 to 10.
12. A cellular communication system adapted to be reconfigurable in operation for use in the method according to any of claims 1 to 10.
13. A method or communication system substantially as hereinbefore described with reference to the accompanying drawings.