GB2448367A

GB2448367A - Transmission power adjustment

Info

Publication number: GB2448367A
Application number: GB0707180A
Authority: GB
Inventors: Ajay Vachhani
Original assignee: NEC Corp
Current assignee: NEC Corp
Priority date: 2007-04-13
Filing date: 2007-04-13
Publication date: 2008-10-15
Anticipated expiration: 2027-04-13
Also published as: GB2448367B; GB0707180D0

Abstract

A method for adjusting the transmit power of an access point in a mobile communication comprises the steps of paging each piece of user equipment registered with an access point, receiving a response from each piece of user equipment, the response including measurement data relating to a signal received by the user equipment from the access point, storing the measurement data, determining whether any adjustment to the transmit power is required in dependence on the measurement data, and adjusting the transmit power in dependence on the result of the determination.

Description

Transmission Power Adjustment

Field of the Invention

This invention relates to a method and apparatus for adjusting the transmission power of a radio base station in a mobile communications system and in particular to the adjustment of transmission power for an access point for a home gateway also known as a Femto cell of the type which is used to provide access to a mobile communication system over a short range such as within a building or within a particular room in a building.

Background of the Invention

Mobile communications systems operate on a cellular basis in which transmission and receiver base stations coupled to a network provide transmission and reception to user equipment (UE) such as mobile telephones in each cell in a network. There is usually a single base station in each cell. Base stations and cells are usually referred to as macro base stations and macro cells.

Smaller cell site called Pico sites have been proposed. These cover a smaller area such as a complex of buildings. Still smaller cell sites named Femto cells are proposed. This is a term used by mobile operators to refer to cell sites of the type which attempt to solve the often expensive problem of providing complete in-building coverage. Pico cells can have problems with local multi-path distortion etc in providing coverage to a complete budding.

A Femto cell which is often referred to as an access point/home gateway is a small plug and play device which communicates with user equipment such as mobile handsets using standard 20 or 3G transmission and reception. It is connected to the network via a broadband service using either xDSL (digital subscriber loop) or Wimax technology. Optionally a Femto cell can incorporate the functionality of a broadband router so that a user has a completely integrated device, It is of course essential that it integrates seamlessly with the core network of the mobile communications systems so that it can be remotely managed and updated.

When an access point is initially installed, it will use a default transmit power in order to achieve good coverage of the area it is supposed to cover. In the case of a Femto cell it will be trying to attempt coverage of the building in which it is installed, such as a house. It is important that the access point does not use higher transmit power than required so that a low level of interference is maintained with any macro cell in which it is positioned and any neighbouring access point. Once an access point has been installed, its transmit power can be adjusted to a level at which its performance is optimum.

Summary of the Invention

We have appreciated that an access point can be configured to collate performance results measured from various pieces of liE in communication with the access point. Some of these results cover effects such as path loss, Received Signal Code Power (RSCP) Quality Ec/No (The Chip Energy compared to its noise) and use these as factors in power control, whereby transmit power can be dynamically altered. Such a method can be used to after the initial standard transmit power and also to readjust power levels dynamically where it is appropriate.

We have also appreciated, that UEs which are registered with an access point may be in idle mode for a long time and at the same time may move around the area covered by the access point. Movement to a different location can cause different performance issues and may require an adjustment to the transmit power from the access point. If the UE remains

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in idle mode then the UE cannot provide feedback information on path loss and so on to the access point.

Furthermore, there may be a number of UEs in different locations.

Collecting performance information from all of these may take a long time (if it can ever be completed). This means it is a long time before the transmit power can be adjusted at the access point.

We have appreciated that in 3G mobile communications there are messaging layers which may be utilised to monitor and transmit performance of an access point by UE and thus to provide performance data back to the access point for use in controlling the transmit power.

In accordance with one embodiment of the invention an access point repeatedly pages the user equipment which is registered with the access point by broadcasting a radio resource control connection request to each piece of user equipment registered with it. The message will be of a predetermined type or will include predetermined data to indicate that the message is being sent for the purposes of monitoring transmit power of the access point. Therefore, the UE which receives the message will send an RRC (Radio Resource Controller) connection request message in response that will include measurement results, such as path loss RSCP and/or Ec/No relating to the transmit power of the signal received at the UE. The access point may then use this information along with information received from other UE to adjust the transmit power as appropriate.

Brief Description of the Drawings

A preferred embodiment of the invention will now be described in detail by way of example with reference to the accompanying drawings in which:

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Figure 1 shows schematically a 3G access point such as a Femto cell in communication with a number of pieces of user equipment; Figure 2 shows the messaging which takes place between an access point and a piece of user equipment in an embodiment of the invention; and Figure 3 shows schematically the equipment used at that access point in the embodiment of the invention.

Detailed Description of Preferred Embodiment

Figure 1 shows an access point 2 which is coupled to a network. This comprises an antenna 4 coupled, or integrated into a controller and transmit/receive unit. In the case of a Femto cell, this will cover a relatively small area such as a house. User equipment such as a mobile phone 6 or a laptop with a data card 8 may be within the house and therefore capable of communicating with the access point 2. When UE initially comes into range of the access point 2, it will register with the access point as being a primary access point on the network for transmission and reception of data.

When an access point is initially installed, its transmit power is set to a default value. Once one or more pieces of user equipment have registered with the access point, it is capable of adjusting the transmit power in dependence on data monitored by the piece or pieces of user equipment registered with it. This is done in the following manner.

After the access point has been installed and registered with a piece of user equipment, it broadcasts system information to the user equipment.

This will comprise appropriate parameters for requesting intra and inter frequency, inter RAT [Radio Access Technology] measurements from the user equipment. These are effectively rule's for user equipment to perform

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measurements and provide to Access Point when sending RRC connection request.

Once rules have been set up with a piece of user equipment via the radio resource control layer, each piece of user equipment is then periodically paged with a paging message from the access point. In response to a paging message, the user equipment sends back a RRC connection request message. This includes with it a measurement report using data set out in the rules previously established. The access point stores the measurement report for later processing.

The access point stores a record of the user equipment to which it has sent a paging request. Therefore, when it receives a response to the paging request, it knows what prompted that paging request and therefore generates a RRC connection reject message which is transmitted to the user equipment. The parameter "wait time" in RRC connection reject message is set to zero. This prevents the user equipment from resending the RRC connection request message. This process is illustrated in Figure 2.

A block diagram of the access point in Figure 1 is shown in Figure 3. This shows the modifications required for an embodiment of the invention to operate.

The access point comprises a transmitter receiver 10 coupled to the antenna 4. This in turn is under the control of a controller 12 which is coupled to the network.

When the access point is installed, a set of default measurement rules are stored in a memory 14. These are sent by the controller 12 via the transmitter receiver 10 and the antenna 4 to user equipment within the cell when it registers with the access point. The user equipment then has details of the data required by the access point with which it is registered

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on the signal it receives from that access point. The measurement rules may be changed by the user using a local computer connection, or may be changed by the network via the controller 12.

The controller 12 causes the transmitter receiver to periodically page the user equipment registered with it. It receives back as a response to this an RRC connection request from each piece of user equipment. This request includes the measurement report as defined in the measurement rules. The measurement report is supplied to the controller 12 which stores it in a results store 16. When all pieces of user equipment registered with the access point have provided a measurement report, the results are all supplied to a results analysis unit 18. This examines data such as path-loss from the measurement reports and provides the results of the analysis to a transmitter power controller 20. This is configured to use the results analysis to provide any appropriate adjustment to the transmit power of the transmitter/receiver 10.

The power may be adjusted, for example after a predetermined period of time, when the measurement reports indicate that a change is required, or when all UE has sent a report.

It will be appreciated that using such a system enables the speed of adjustment of the transmit power of an access point to be improved, thereby improving the quality of transmissions to user equipment registered with the access point. This therefore enables the access point to transmit at the maximum power required to establish communication with user equipment, and at no higher power, thereby diminishing the interference with any macro cell and any other access points in the vicinity.

The transmit power of the access point can be dynamically adjusted.

Thus, if all the user equipment moves closer to the access point then the transmit power can be reduced. If it moves further away then the transmit power can be increased.

As well as the measurements relating to the received power of the transmissions from the access point, user equipment can be arranged to provide data relating to the quality of received data such as the number of bit errors received from the access point.

Claims

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Claims A method for adjusting the transmit power of an access point in a mobile communication system comprising the steps of paging each piece of user equipment registered with an access point, receiving a response from each piece of user equipment, the response including measurement data relating to a signal received by the user equipment from the access point, storing the measurement data, determining whether any adjustment to the transmit power is required in dependence on the measurement data, and adjusting the transmit power in dependence on the result of the determination.
2. A method for adjusting the transmit power of an access point in a mobile communication system according to claim I in which the measurement data comprises one or more of path loss measurement data, Received Signal Code Power measurement data, or Quality data.
3. A method for adjusting the transmit power of an access pointing a mobile communication system according to claim I further comprising the step of the access point storing a record identifying the user equipment to which it has sent a paging request.
4. A method for adjusting the transmit power of an access point in a mobile communication system according to any one of claims 1, 2 or 3 further comprising the step of the access point comparing an identifier of the user equipment responding to the paging signal and if it is determined that the identifier of the user equipment responding to the paging signal matches an identifier stored in the access point, recording that the access point has paged the user equipment, the access point further generating and transmitting an RRC connection reject message to the user equipment thereby preventing the user equipment from sending further RRC connection requests.

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5. A method for adjusting the transmit power of an access point in a mobile communication system according to any preceding claim in which the user equipment repeatedly responds to the paging signal transmitted by the access point.
6. A method for adjusting the transmit power of an access point in a mobile communication system according to any preceding claim in which the transmit power is adjusted after a predetermined period of time has expired.
7. A method for adjusting the transmit power of an access point in a mobile communication system according to any preceding claim in which the transmit power is adjusted after all user equipment(s) registered with the access point have transmitted a response to the paging signal to the access point.
8. A method for adjusting the transmit power of an access point in a mobile communications system according to any preceding claim in which the transmit power is continuously adjusted in time.
9. A method for adjusting the transmit power of an access point in a mobile communication system according to claim 4 in which the wait time parameter in the Radio Resource Control connection reject message is set to zero.
10. An access point for use in a mobile communications network comprising means for paging user equipment registered with the access point, means for receiving a response from the user equipment, the response including measurement data relating to the signal received by the user equipment from the access point, means for storing the measurement data received from each piece of user equipment, means for analysing the stored data, and means for adjusting the transmit power of the access point in dependence on the result of the analysis.
11. An access point for use in a mobile communications network according to claim 10 further comprising means for storing a record identifying the user equipment to which the access point has sent a paging request.
12. An access point for use in a mobile communications network according to any one of claims 10, or 11 further comprising means for comparing the identifier of the user equipment responding to the paging signal and means for determining if the identifier of the user equipment responding to the paging signal matches an identifier stored in the access point, and means for recording that the access point has paged the user equipment, and means for generating and transmitting an RRC connection reject message to the user thereby preventing the user equipment from sending further RRC connection requests if it is determined that the identifier of the user equipment responding to the paging signal matches an identifier stored in the access point.
13. An access point for use in a mobile communications network substantially as herein described with reference to the accompanying drawings.
14. A method for adjusting the transmit power of an access point in a mobile communication system substantially as herein described with reference to the accompanying drawings.