WO2011023595A2

WO2011023595A2 - A method of controlling uplink transmission power in a communications network

Info

Publication number: WO2011023595A2
Application number: PCT/EP2010/061970
Authority: WO
Inventors: Harri Jokinen; Eddie Riddington
Original assignee: Nokia Siemens Networks Oy; Nokia Corporation
Priority date: 2009-08-25
Filing date: 2010-08-17
Publication date: 2011-03-03
Also published as: CA2915213C; WO2011023595A3; CA2915213A1; CA2805514A1

Abstract

A method of controlling uplink transmission power in a communications network is provided. The network includes a network node and a mobile station. The mobile station is allowed to autonomously reduce its transmission power on a transmission channel until the network node signals a mobile station power level different from a predetermined power level to the mobile station. The network node controls the transmission power of the mobile station when said mobile station power level is signalled to the mobile station.

Description

A METHOD OF CONTROLLING UPLINK TRANSMISSION POWER IN A

COMMUNICATIONS NETWORK

FIELD OF THE INVENTION

The invention generally relates to a method of controlling uplink transmission power in a communications network.

BACKGROUND OF THE INVENTION

In the GSM standard specifying call set up procedures in GSM/EDGE communications networks, it is currently specified that a mobile station shall use maximum transmit power on the random access channel (RACH) in the uplink. By maximum power, it is meant the maximum power supported by the mobile station or the maximum allowed by system information parame- ters for a particular cell in the network, whichever is lower .

Maximum power is also normally used as the power level during the initial period of the stand alone dedicated control chan- nel (SDCCH) and traffic channel (TCH) in/-signalling only mode. This is while the network performs an averaging of uplink measurements to obtain a sufficiently reliable estimate of the condition of the channel (averaging is network controlled and normally takes a few slow associated control channel (SACCH) periods) and also while the first power command to correct the initial power level is signalled to the mobile (signalling a power command from the base station to the mobile station takes one SACCH period) . However, unnecessary use of maximum power can cause unwanted interference in the cell and may lead to blocking or desensi- tisation of the base station receiver. It can also prevent the establishment of a call when the battery of the mobile station is low (or cold) .

A method of reducing uplink transmission power has been proposed, which allows the mobile station to reduce its trans^¬ mission power on the RACH when the received level average (RLA) exceeds a pre-defined threshold set by the standard. RLA is measured by the mobile station on each carrier on the downlink and can be used to estimate path loss in the uplink (and hence the received uplink power) . It has also been proposed to extend the method of reducing uplink transmission power to the SDCCH or TCH (signalling only mode) channels by leaving out any optional uplink power commands that may be used by the network to signal the initial uplink power to use on these channels.

However, in addition to the optional uplink power commands are uplink power commands which are sent at regular intervals on the SACCH. If the mobile station ignores these uplink power commands while it is using the method of reducing up- link transmission power then the network will have completely lost control of the uplink power on these channels during this time. The mobile station may autonomously apply power reduction due to the RLA exceeding the threshold but the network may want the mobile station to increase its power due to excessively high interference, for example. SUMMARY OF THE INVENTION

Accordingly, the invention provides a method of controlling uplink transmission power in a communications network. The communications network includes a network node and a mobile station. The mobile station is allowed to autonomously reduce its transmission power on a transmission channel until the network node signals a mobile station power level differ^¬ ent from a predetermined power level to the mobile station. The network node controls the transmission power of the mobile station when the mobile station power level is signalled to the mobile station.

The mobile station is permitted to autonomously reduce its transmission power as long as the network node signals a predetermined power level to the mobile station. However, if the mobile station is using autonomous power reduction and the network node signals an allowed mobile station power level to the mobile station that is different from the prede- termined power level, the mobile station ceases to autono^¬ mously reduce its transmission power. The network node then takes over control of the transmission power of the mobile station . Since the mobile station may reduce its transmission power autonomously, minimal changes or no changes at all are required to be made to the base station subsystem (BSS) in or^¬ der to implement the method according to the invention, making it low cost and simple to implement.

Optionally, a mobile shall not be allowed to autonomously re^¬ duce its transmission power on the same transmission channel again once the network node has taken over control of the transmission power of the mobile station by signalling an al- lowed mobile station power level to the mobile station that is different from the predetermined power level. If the network node has taken over control of the transmission power level of the mobile station on a particular channel, the mo- bile station can be prevented from autonomously reducing its transmission power on the same channel again during a particular call. The mobile station can be permitted to autonomously reduce its transmission power when the network node signals the predetermined power level to the mobile station.

Preferably the network node signals to the mobile station the transmission power it should use when the network node signals the mobile station power level different to the predetermined power level.

The predetermined power level can be the initial power level that the mobile station shall use on the transmission channel. This is often the maximum power level allowed by a mobile station in a cell of the network in which the network node is located. The network node can signal to the mobile station the predetermined power level plus or minus one power level when it wants the mobile station to use the predetermined power level. In one embodiment of the invention, the network node detects the power level of the mobile station. The network node may determine when the mobile station is autonomously reducing its transmission power on the transmission channel from a reported actual mobile station power level. The network node may then modify its power control procedures so that maximum power plus or minus one power level is signalled instead of maximum power. If the network node has taken over control of the transmission power level of the mobile station on a particular channel, it will be able to signal maximum power. The transmission channel may be a stand alone dedicated channel (SDCCH) or a traffic channel (TCH) in signalling only mode. Preferably, the mobile station is allowed to autono- mously reduce its transmission power at the beginning of transmission on the stand alone dedicated channel or on the traffic channel in signalling only mode.

When the mobile station power level different from the prede- termmed power level is signalled to the mobile station, and the network node has taken control of the mobile station transmission power, the network node may keep control of the mobile station transmission power for the duration of transmission on the channel.

The network node may indicate to the mobile station that the network supports the mobile station autonomously reducing its transmission power. This can be achieved, for example, by providing an indicator bit on the broadcast channel and is advantageous in cases where autonomous reduction of the mo^¬ bile station transmission power would have an impact on legacy networks (e.g. legacy power control algorithms) .

The invention also provides a network node. The network node includes a transmitter and a controller. The transmitter is adapted to signal a mobile station transmission power level to a mobile station. The controller is adapted to control transmission power of the mobile station on a transmission channel when the mobile station transmission power level is different from a predetermined power level. If the allowed mobile station power level is different from the predeter^¬ mined power level, the network node then takes over control of the transmission power of the mobile station. Preferably, the network node has a detector for detecting the transmission power of the mobile station. For example, the detector can detect when the mobile station is using autonomous power reduction from a reported actual mobile station power level received at the network node.

The invention further provides a mobile station having a receiver and a power control unit. The power control unit is configured in operation to autonomously reduce the transmis- sion power of the mobile station on a transmission channel until a signal indicating a mobile station power level different from a predetermined power level is received by the receiver. The power control unit of the mobile station is permitted to autonomously reduce the mobile station transmis- sion power as long as the receiver of the mobile station receives a signal indicating a predetermined allowed power level. When the receiver receives a signal indicating a power level different to the predetermined power level, and if the power control unit is currently using autonomous power reduction, the power control unit stops autonomously reducing the transmission power of the mobile station.

Preferably, the power control unit is configured to adjust the transmission power based on a network power command re- ceived by the receiver when the signal indicating said mobile station power level is received by the receiver. When the receiver receives the signal indicating a power level different to the predetermined power level, the network takes over control of the mobile station transmission power so that, in- stead of autonomously reducing the transmission power, the power control unit adjusts the transmission power of the mo^¬ bile station based on a command received from the network by the receiver. The invention will now be described, by way of example only, with reference to specific embodiments, and to the accompanying drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a simplified schematic diagram of a communi- cations network for implementing the method according to an embodiment of the invention;

Figure 2 is a simplified schematic diagram of a network node of a communications network for implementing the method according to an embodiment of the invention; and

Figure 3 is a simplified schematic diagram of a mobile station of a communications network for implementing the method according to an embodiment of the invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS Figure 1 shows a radio communications network, which includes a network node, in this case a base station N, located in a cell of the network. A mobile station UE, for example a mobile telephone or PDA, can communicate via the base station N.

The base station N and the mobile station UE are shown sche^¬ matically in more detail in Figures 2 and 3, respectively. The base station N includes a transmitter T for transmitting data to the rest of the network and a controller C coupled to the transmitter T. A receiver R is provided for receiving data from the mobile station UE and other network components, such as other mobile stations, and is coupled to a detector, which detects the transmission power level being used by the mobile station UE. The mobile station UE includes a transmitter TM and a receiver RM, both coupled to a power control unit PCU. For clarity and simplicity, Figures 1-3 only show the components required for the invention.

In operation, the transmitter T in the base station N broadcasts to the mobile station UE on the BCCH channel the maxi^¬ mum transmission power level allowed in the cell of the network where it is located. Furthermore, the base station N indicates, by means of an indicator bit on the BCCH channel, that the network supports the mobile station UE autonomously reducing its transmission power level. While the receiver RM of the mobile station UE is receiving the broadcast from the base station N that the cell maximum transmission power is allowed, the power control unit PCU of the mobile station UE starts to autonomously reduce the transmission power of the mobile station UE at the beginning of transmission by the mobile station UE on a transmission channel (e.g. SDCCH or TCH in signalling only mode) being used by the transmitter TM for transmitting data from the mobile station UE. The power control unit PCU of the mobile station UE continues to autonomously reduce the transmission power of the mobile station UE while the network is broadcasting (via the base station N) the maximum allowed cell transmission power. The network will permit the UE to autonomously reduce its transmission power as long as the maximum cell transmission power is being broadcast . If, however, the allowed cell transmission power is required to change, for example due to excessive interference in the cell, the base station N broadcasts a signal containing a mobile station transmit power level that is different from the maximum allowed in the cell. This signal is received at the receiver RM of the mobile station UE, which stops the power control unit PCU of the mobile station UE from autonomously reducing the transmission power of the mobile station UE on the transmission channel being used. The controller C of the base station N then controls the base station transmitter T to transmit a power command signal, which is received at the receiver RM of the mobile station UE and controls the power control unit PCU to adjust the transmission power of the mobile station UE. Control of the transmission power of the mobile station UE on the transmission channel is then kept by the network for the rest of the duration of the transmission channel and the network prevents the mobile station UE from autonomously reducing its transmission power level on that channel again.

In an alternative embodiment, the network can modify its power control procedures so that maximum cell transmission power plus or minus one power level is signalled by the base station N instead of maximum power when autonomous power re- duction is being used by the mobile station UE. In this case, the detector D in the base station N detects the actual transmission power being used by the mobile station UE on the transmission channel so can determine if autonomous power reduction is being used by the mobile station UE. If the de- tector D detects that autonomous power reduction is being used by the mobile station UE, the controller C can then control the transmitter T of the base station N to transmit the cell maximum allowed power plus or minus one power level to the mobile station UE. If the network needs to signal the maximum transmission power allowed in a particular cell, the base station N may command the mobile station UE, by a signal on the BCCH channel to use maximum transmission power minus one power control level and subsequently increase this to a maximum, once the network assumes control of uplink power. Signalling of the power commands from the base station N to the mobile station UE may be achieved by setting an indicator bit on the BCCH channel, for example.

Alternatively, the base station N may command the mobile sta^¬ tion UE to use the maximum transmission power allowed in the cell plus one power control level. For example, if the cell maximum transmission power was set at 2W for a GSM 900 network, then at one power control level higher the mobile sta^¬ tion UE would immediately follow a transmission power of 2W. If the cell maximum power was set to be lower than this, then the network would have to revert to the actual cell maximum power after some time.

Although the invention has been described hereinabove with reference to specific embodiments, it is not limited to these embodiments and no doubt further alternatives will occur to the skilled person that lie within the scope of the invention as claimed.

For example, the control functionality of the base station may be located in a separate radio network controller (RNC) coupled to the base station.

Claims

1. A method of controlling uplink transmission power in a communications network including a network node and a mobile station, wherein the mobile station is allowed to autonomously reduce its transmission power on a transmission channel until the network node signals a mobile station power level different from a predetermined power level to the mo- bile station, and the network node controls the transmission power of the mobile station when said mobile station power level is signalled to the mobile station.

2. The method according to claim 1, wherein the network node signals to the mobile station the transmission power it should use when the network node signals said mobile station power level.

3. The method according to claim 1 or claim 2, wherein the predetermined power level is an initial power level that shall be used by the mobile station on the transmission channel .

4. The method according to claim 3, wherein the initial power level is the maximum power level that is allowed in a cell of the network in which the network node is located.

5. The method according to any of claims 1 to 4, wherein the network node signals to the mobile station the predetermined power level plus or one power level when the network node wishes the mobile station to use the predeter^¬ mined power level.

6. The method according to any of claims 1 to 5, wherein the network node detects the power level of the mobile station.

7. The method according to any of claims 1 to 6, wherein the transmission channel is a stand alone dedicated channel or a traffic channel in signalling only mode.

8. The method according to claim 7, wherein the mobile station is allowed to autonomously reduce its transmission power at the beginning of transmission on the stand alone dedicated channel or on the traffic channel in signalling only mode.

9. The method according to any of claims 1 to 8, wherein when the mobile station power level different from the predetermined power level is signalled to the mobile station, and the network node has taken control of the mobile station transmission power, the network node keeps control of the mobile station transmission power for the duration of transmission on the channel.

10. The method according to any of claims 1 to 8, wherein the network node indicates to the mobile station that the network supports the mobile station autonomously reducing its transmission power.

11. A network node comprising a transmitter and a controller, wherein the transmitter is adapted to signal a mo- bile station transmission power level to a mobile station, and the controller is adapted to control transmission power of the mobile station on a transmission channel when the mobile station transmission power level is different from a predetermined power level .

12. The network node according to claim 11, further comprising a detector for detecting the transmission power of the mobile station.

13. A mobile station comprising a receiver and a power control unit, wherein the power control unit is configured m operation to autonomously reduce the transmission power of the mobile station on a transmission channel until a signal indicating a mobile station power level different from a predetermined power level is received by the receiver.

14. The mobile station according to claim 13, wherein the power control unit is configured to adjust the transmis- sion power based on a network power command received by the receiver when the signal indicating said mobile station power level is received by the receiver.