GB2383232A

GB2383232A - Controlling transmission power at a base station in accordance with spare capacity in the system

Info

Publication number: GB2383232A
Application number: GB0129996A
Authority: GB
Inventors: Jeffery Torrance
Original assignee: Ubinetics Ltd
Current assignee: Aeroflex Cambridge Ltd
Priority date: 2001-12-14
Filing date: 2001-12-14
Publication date: 2003-06-18
Anticipated expiration: 2021-12-14
Also published as: WO2003052965A1; AU2002350907A1; GB0129996D0; GB2383232B

Abstract

A radio telephone system includes means (11) for determining spare capacity of the system or a part of the system. The system also includes means (11) responsive to a determination of the spare capacity exceeding a threshold for controlling a base station (15 to 21) of the system to increase the transmission power of at least one data channel of the base station. The system further includes means (11) for sending a signal to at least one mobile station (22, 23) of the system the increase in transmission power. The or each mobile station (22, 23) is responsive to said signal to control an iterative decoder (35) forming part of that mobile station to operate with a reduced number of iterations.

Description

A Radio Telephone System and a Method of Operating Same This invention relates to a radio telephone system and to a method of operating a radio telephone system.

Demand for the use of cellular telephone networks often exceeds the capacity of the networks. At other times, the demand falls far short of the capacity. Cellular telephone system operators can sometimes lose out on potential revenue when the battery of a cellular telephone becomes flat, preventing calls being made to or from that telephone.

The same applies to other types of mobile station, such as personal digital assistants (PDAs), cellular enabled laptop computers and the like.

According to a first aspect of the invention, there is provided a radio telephone system as claimed in claim 1.

According to a second aspect of the invention, there is provided a method of operating a radio telephone system as claimed in claim 7.

The radio telephone system may be a cellular telephone system, or any other kind, such as a multi-user cordless telephone system.

Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings of which: Figure 1 is a schematic drawing of a cellular telephone system embodying the invention; and Figure 2 is a schematic diagram of part of a user equipment forming part of the system of Figure 1.

Referring to Figure 1, the cellular telephone system 10 comprises generally a central control and communications system 11, first to third base station controllers 12 to 14, first to seventh base stations 15 to 21, and first and second cellular telephones 22 and

23. Each of the base stations 15 to 21 is connected to the first base station controller

12. The cellular telephone system 10 is hereafter referred to as a system conforming to knA the proposed universal mobile telephone system (UMTS) standard. Accordingly, each /I.

of the base stations 15 to 21 is hereafter termed a node B, the base station controllers 12 to 14 are termed node B controllers, and the cellular telephones 22 and 23 are each termed user equipment (UE).

Each node B 15 to 21 is able to communicate with a specific one of the UEs 22 and 23 using voice data channels having a bit rate ranging from a few bits/sec to Mbps. Each node B 15 to 21 may also communicate with the UEs 22 and 23 using data channels having data rates different to the data rate of voice data channels. Such non-voice data channels are used for wireless application protocol (WAP) services, non-WAP internet connections and video communications, for example. Each node B 15 to 21 also broadcasts to all UEs in range a control channel (CPICH), a broadcast channel (BCH) and various other channels, as is known.

The central control and communications system 11 periodically determines the usage of each of the nodes B 15 to 21, as well as the usage of nodes B (not shown) connected to the other node B controllers 13 and 14. The usage of each node B is determined having regard to the data rate of the channels that are open, as well as the number of channels.

For each node B, a threshold is determined, this threshold being a percentage of the capacity of that node B. Typically, the threshold may be between 60 and 80% of the total capacity. The determined usage for each node B 15 to 21 is then compared to the threshold for that node B, and a list of nodes B for which the threshold is not exceeded is compiled. These nodes B are hereafter referred to as low-usage nodes B. The status of each low-usage node B may change when the next periodic measurement of usage is made, and the same applies to non low-usage nodes B.

When a node B 15 to 21 is determined as being a low-usage node B, the transmission power of all voice and non-voice data channels transmitted from that node B is increased by a predetermined amount, typically in the range 10 to 40%. Preferably, the transmission power of the control and broadcast channels is also increased by the same amount, although this is not necessary. UEs in the range of these nodes B then experience an increase in the signal-to-noise ratio (SNR) or signal-to-interference ratio (SIR) of signals received from that node B, as well as an increase in received signal strength. Preferably, although not essentially, each of these nodes B signals to UEs in communication with it that the transmission power has been increased. This signalling may take the form of a periodic transmission on a broadcast channel, for example, of an indication of the transmitted power relative to the transmitted power of non low-usage nodes B.

Instead of treating the nodes B individually, nodes B may be grouped together, and the usage status of members of a group determined with reference to the usage of the group as a whole compared to the capacity of that group. Such an arrangement is used to particular advantage in microcellular environments, where the handover of UEs between nodes B can occur relatively frequently and quickly.

Referring now to Figure 2, part of the UE 22 is shown schematically. The UE 22 comprises an antenna 30, for receiving signals from nodes B, a first RF amplifier 31, a controllable gain. IF amplifier 32, an analogue-to-digital converter (ADC) 33, a Rake receiver 34, and a turbo or iterative decoder 35 connected in series. A controller 36 is connected to each component of the UE 22 (except the antenna 30), to allow control thereof. A downconverter (not shown) is connected between the amplifiers 31 and 32, as is conventional.

When a node B 15 to 21 with which the UE 22 is communicating is not a low-usage node B, operation of the UE is conventional. When signals are received from a node B transmitting at higher power, the gain of the amplifier 32 may be reduced, resulting in a reduced power consumption, without any loss of performance. This power saving results from the increased strength of the received signals. This may be achieved by a

conventional UE 22, that is a UE not specially adapted for use with this invention. Also, this does not require the UE 22 to detect any signal transmitted by a node B or any other part of the system 10 indicating that the node B which is communicating with the UE is a low-usage node B.

The increased SNR resulting from the higher transmission power of a low-usage node B is used by the UE 22 in a power saving mode as follows. The power saving mode is initiated when the UE 22 detects a signal from the system 10 indicating that the node B it is communicating with is a low-usage node B.

Firstly, the controller 36 causes the number of iterations of the turbo decoder 35 to be reduced, for example, from eight to two. Given a sufficient increase in SNR, the bit error rate (BER) of data provided by the turbo decoder 35 in the power saving mode is comparable to that obtained when not in the power saving mode with a received signal having a lower SNR. This results in the usage, and hence power consumption, of the turbo decoder 35 being reduced by a factor of four. This is of particular advantage when demodulating signals from high data rate channels, such as video data channels.

Alternatively, the Rake receiver 34 is controlled by the controller 36 such that one or more of its fingers are disabled, causing the disabled fingers to cease drawing power from the power supply (not shown) of the UE 22. Although shown schematically in Figure 2 as being achieved through the use of switches 37 to 40 in the fingers, this may alternatively be achieved at a higher level in hardware or in software.

As a further alternative, the ADC 33 is controlled by the controller 36 to sample the signal provided by the amplifier 32 at a reduced sampling rate. The sampling rate may be halved, or divided by any other multiple. This results in a reduced power consumption not only because the power consumption of the ADC 33 itself is reduced, but also because it provides fewer samples which therefore require less power consumption by a demodulator (not shown). A reduced sampling rate can be accommodated without a significant reduction in BER by virtue of the increased SIR present with signals transmitted by low-usage nodes B. The amount by which the

sampling rate can be reduced, whilst still providing an acceptable BER, depends on the increase in SNR that is obtainable from low usage nodes B.

In a preferred embodiment, the controller 36 is arranged to control the ADC 33, the Rake receiver 34 and the turbo decoder 35, or any two thereof, in a suitable manner such that maximum power saving is achieved whilst providing a sufficiently high BER or packet error rate (PER). For example, the optimum configuration may be one where the sampling rate of the ADC 33 is reduced by a factor of two, three fingers of the Rake receiver 34 are disabled, and the turbo decoder 35 is controlled to run four iterations. It will be appreciated by the skilled person how the best results can be achieved for a given situation.

Preferably, the UE 22 includes means (not shown) to measure or infer the SNR or SIR of received signals, and to control the turbo decoder 35, the ADC 33 and/or the Rake receiver 34 to operate in a manner which allows the maximum saving in power consumption whilst offering an acceptable BER or PER.

Claims

1. A radio telephone system, comprising: means for determining spare capacity of the system or a part of the system; and means responsive to a determination of the spare capacity exceeding a threshold for controlling a base station of the system to increase the transmission power of at least one data channel of the base station.

2. A system as claimed in claim 1, further comprising means to signal to at least one mobile station of the system the increase in transmission power.

3. A system as claimed in claim 2, in which the at least one mobile station is responsive to the signal to control an iterative decoder forming part of the at least one mobile station to operate with a reduced number of iterations.

4. A system as claimed in claim 2 or claim 3, in which the at least one mobile station is responsive to the signal to disable one or more fingers of a Rake receiver forming part of the at least one mobile station.

5. A system as claimed in any one of claims 2 to 4, in which the at least one mobile station is responsive to the signal to reduce the sampling rate of an analogue-to-digital converter forming part of the at least one mobile station.

6. A radio telephone system substantially as hereinbefore described with reference to and/or as shown in Figure 1 or Figure 1 and Figure 2 of the accompanying drawings.

7. A method of operating a radio telephone system, the method comprising: determining the spare capacity of the system or a part of the system; and

controlling a base station, in response to a determination of the spare capacity IZ > exceeding a threshold, to increase the transmission power of at least one data channel.

8. A method as claimed in claim 7, wherein the or each mobile station includes an analogue-to-digital converter in its signal processing data path, and the method further comprising reducing the sampling rate of the analogue-to-digital converter of the or each mobile station in response to said signal.

8. A method as claimed in claim 7, further comprising signalling to at least one mobile station the increase in transmission power.

9. A method as claimed in claim 8, further comprising disabling one or more fingers of a Rake receiver of at least one mobile station in response to the signal.

10. A method as claimed in claim 8 or claim 9, further comprising reducing the sampling rate of an analogue-to-digital converter of the at least one mobile station in response to the signal.

11. A method as claimed in any of claims 8 to 10, further comprising controlling an iterative decoder of the at least one mobile station to operate with a reduced number of iterations in response to the signal.

12. A method of operating a radio telephone system substantially as herein before described with reference to Figure 1 or Figure 1 and Figure 2 of the accompanying drawings.

Amendment to the claims have been filed as follows Claims

1. A radio telephone system comprising: means for determining spare capacity of the system or a part of the system; means responsive to a determination of the spare capacity exceeding a threshold for controlling a base station of the system to increase the transmission power of at least one data channel of the base station; and means for sending a signal to indicate the increase in transmission power to at least one mobile station of the system; wherein the or each mobile station is responsive to said signal to control an iterative decoder forming part of that mobile station to operate with a reduced number of iterations.

2. A system as claimed in claim 1, wherein the or each mobile station is responsive to said signal to disable one or more fingers of a Rake receiver forming part of that mobile station.

3. A system as claimed in claim 1 or claim 2, wherein the or each mobile station is responsive to said signal to reduce the number of bits in the signal processing data path of that mobile station.

4. A system as claimed in claim 3, wherein the or each mobile station includes an analogue-to-digital converter in its signal processing data path, and that mobile station is responsive to said signal to reduce the sampling rate of the analogue-to-digital converter.

5. A method of operating a radio telephone system comprising a base station and at least one mobile station, the method comprising: determining the spare capacity of the system or a part of the system; controlling a base station, in response to a determination of the spare capacity exceeding a threshold, to increase the transmission power of at least one data channel; and

sending a signal to indicate the increase in transmission power to the or each mobile station; wherein the method further comprises controlling an iterative decoder of the or each mobile station to operate with a reduced number of iterations in response to said signal.

6. A method as claimed in claim 5, further comprising disabling one or more fingers of a Rake receiver of the or each mobile station in response to said signal.

7. A method as claimed in claim 5 or claim 6, further comprising reducing the number of bits in the signal processing data path of the or each mobile station in response to said signal.