WO2010101508A1

WO2010101508A1 - A method of power control

Info

Publication number: WO2010101508A1
Application number: PCT/SE2010/050149
Authority: WO
Inventors: Johan Bergman; Klas Johansson; Kai-Erik Sunell
Original assignee: Telefonaktiebolaget L M Ericsson (Publ)
Priority date: 2009-03-05
Filing date: 2010-02-09
Publication date: 2010-09-10

Abstract

In a method for controlling transmit power in a user equipment knowledge of the DPCCH power level on the primary earner when initiating transmission of DPCCH on the secondary carrier is exploited. Also for UEs the power allocated to DPCCH on the secondary carrier is limited in order to not degrade coverage and control channel quality on the primary carrier.

Description

A METHOD OF POWER CONTROL

TECHNICAL FIELD

The present invention relates to a method and a device for controlling power in a user equipment for use in a cellular radio system.

BACKGROUND Dual-Carrier High-Speed Downlink Packet Access (DC-HSDPA, also known as Dual-Cell HSDPA) is specified in the 3^rd Generation Partnership Project (3GPP) Release 8 (Rel-8). DC- HSDPA enables reception of data from two cells simultaneously, transmitted on two adjacent earners in the same base station and sector, to individual terminals (or user equipment, UE).

As a next step, Dual-Carrier High-Speed Uplink Packet Access (DC-HSUPA) is specified in 3GPP Release 9 (Rel-9).

Although the additional spectrum bandwidth associated with multi-carrier operation does not increase "spectral efficiency" (maximum achievable throughput per cell per Hz [bps/cell/Hz]), the experienced user data rates are increased significantly. In particular, for bursty packet data traffic at low and moderate load, the data rate is proportional to the number of carriers exploited. Moreover, power inefficient higher order modulation schemes such as 16 Quadrature Amplitude Modulation (QAM) can be avoided (which is especially important in the up-link, UL) and the practical as well as theoretical peak data rate of the system are naturally increased.

DC-HSUPA may be specified as an aggregation of legacy (Rel-8, single-carrier) HSUPA. In the discussion herein focus is on DC-HSUPA. However, all concepts and ideas are readily extendable to Multi-Carrier-HSUPA (MC-HSUPA) operation over more than two uplink earners.

Handover and radio access bearer admission control is presumed to be conducted in the Radio Network Controller (RNC) based on measurements of path loss etc on a primary earner (alternatively referred to as an anchor carrier) of the serving HSDPA/HSUPA cell. Notice though, that in case of a distributed Radio access Network (RAN) architecture where the base station Node-B and RNC functionality as defined in 3GPP specifications are collocated in a base station, the base station would naturally handle also these functionalities. In a DC-HSUPA capable Node-B, the other carrier, which is referred to as a secondary carrier, is assumed to be configured by the RNC for a given DC-HSUPA capable UE and then scheduled and activated by Node-B whenever feasible and useful (with the standard objective function to maximize the supported traffic volumes, or aggregate system throughput, subject to fairness criteria and quality of service constraints, such as minimum bit rate or maximum latency requirements). A primary carrier, on the other hand, may not be temporarily deactivated by the Node-B: to deactivate a certain primary carrier for a connection, the connection is either released, or an inter- frequency handover is perfoπned (in which case another earner will become the primary earner).

For each user connected in DC-HSUPA mode, the serving Node-B hence controls whether or not a secondary earner is activated, and a separate grant is selected for each activated carrier.

Furthermore, if a secondary carrier is activated by Node-B, it is assumed that the Dedicated Physical Control Channel (DPCCH), which includes a sequence of pilot bits, is transmitted on that earner, and the Node-B hence tries to detect this signal.

In the legacy Wideband Code Division Multiple Access (WCDMA) systems certain power control procedures apply for the DPCCH. Even though DPCCH power control is assumed to be handled independently per carrier, a coupling between the carriers is introduced because the total transmit power in the UE is shared between all earners. Hence, if the DPCCH power is significant (compared to the maximum output power), and DPCCH is configured to be transmitted on multiple earners, the power may not be sufficient.

Moreover, in a single-carrier system, the transmitter has only rudimentary knowledge of the channel characteristics at call setup. Hence a DPCCH power ramping procedure was introduced in 3GPP specifications release 99 in order to minimize interference (which is especially important in a CDMA system to avoid near-far effects); see further 3GPP Technical Specification TS 25.214 V8.4.0. The power ramping procedure at radio link setup is however quite slow in order to minimize the risk for large overshoots causing undesired interference.

Hence, there exist a need for a method and a system that is able to improve power allocation in transmission of data.

SUMMARY

It is an object of the present invention to overcome or at least reduce some of the problems associated with existing methods for power allocation.

This object and others are obtained by the method and the device as set out in the appended claims.

According to one embodiment of the invention, knowledge of the DPCCH power level on the primary earner when initiating transmission of DPCCH on the secondary carrier is exploited.

According to another embodiment of the invention, the power allocated to DPCCH on the secondary carrier of a UE is limited in order to not degrade coverage and control channel quality on the primary carrier. This can be particularly useful for UEs that are power constrained.

According to one embodiment of the invention a method of uplink power control in a User Equipment (UE) is provided. The UE is configured for multi carrier uplink transmissions on a set of carriers comprising a primary carrier and at least one secondary carrier, wherein uplink transmissions on the primary carrier have been initiated prior to uplink transmissions on a secondary earner. The method comprising the steps of:

- determining an initial transmit power for a Dedicated Physical Control Channel on said secondary carrier, wherein said initial transmit power is a function of measured statistics for transmit power of a Dedicated Physical Control Channel on said primary carrier. Hereby knowledge of the DPCCH power level on the primary earner when initiating transmission of DPCCH on the secondary carrier can be exploited resulting in a faster and more accurate DPCCH synchronization procedure compared to a legacy power ramping procedure. In accordance with one embodiment the initial transmit power is a function of an estimate of an average transmit power of the Dedicated Physical Control Channel on the primary carrier.

In accordance with one embodiment the initial transmit power is a function of an estimate of a median transmit power of the Dedicated Physical Control Channel on the primary earner.

In accordance with one embodiment the initial transmit power is a function not only of said measured statistics for transmit power of said Dedicated Physical Control Channel on said primary earner but also of measured statistics for transmit power of Dedicated Physical Control Channel of any additional secondary carrier in said set of carriers.

In accordance with one embodiment the method further comprises controlling the transmit power of said Dedicated Physical Control Channel on said secondary carrier such that the uplink transmit power does not exceed a defined maximum allowed transmit power defined by one or more of:

- a function of an estimate of the current Dedicated Physical Control Channel transmit power on said primary earner,

- a function of available transmit power in said UE considering an estimate of the current total transmit power on said primary carrier;

- a maximum fraction of a maximum available transmit power in said UE, wherein any transmit power commands ordering an increase of said transmit power of said Dedicated Physical Control Channel on said secondary carrier to a level exceeding said defined maximum allowed transmit power are ignored.

According to one embodiment of the invention a method of uplink power control in a User Equipment (UE) is provided. The UE is configured for multi carrier uplink transmissions on a set of carriers including a primary earner and at least one secondary carrier, wherein uplink transmissions on said primary carrier have been initiated prior to uplink transmissions on said secondary earner. The method comprises the steps of: - controlling a transmit power of a Dedicated Physical Control Channel on said at least one secondary earner such that the uplink transmit power does not exceed a defined maximum allowed transmit power defined by one or more of:

- a function of available transmit power in said UE considering an estimate of the current total transmit power on said primary earner;

- a maximum fraction of a maximum available transmit power in said UE, wherein any transmit power commands ordering an increase of said transmit power of said Dedicated Physical Control Channel on said secondary carrier to a level exceeding said defined maximum allowed transmit power are ignored. Hereby the power allocated to DPCCH on the secondary earner is limited in order to not degrade coverage and control channel quality on the primary earner.

The invention also extends to a UE configured to execute the methods above.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described in more detail by way of non-limiting examples and with reference to the accompanying drawings, in which:

- Fig. 1 shows a block diagram illustrating a cellular radio network,

- Fig. 2 depicts an exemplary configuration of receivers and transmitters in a User Equipment,

- Fig. 3 depicts an exemplary configuration of receivers and transmitters in a User Equipment,

- Fig 4 is a flow chart illustrating some procedural steps performed when controlling the output power in a user equipment in accordance with one embodiment, and

- Fig. 5 is a flow chart illustrating some procedural steps performed when controlling the output power in a user equipment in accordance with another embodiment.

DETAILED DESCRIPTION The present invention will now be described in more detail by way of non-limiting examples. In Fig. 1 a general view of an exemplary cellular radio system 100 is depicted. The system can for example be a Multi carrier HSUPA system, in particular a Dual Carrier HSUPA system. The system comprises a number of radio base stations 101, here denoted NodeBs. A mobile station 103, here also denoted User Equipment UE, that is in a geographical area covered by the radio base station can connect to the radio base station over an air-interface The mobile station 103 comprises a number of transmitters and receivers 104 and further can comprise a module 107 adapted to control the UE to perfoπn functions to be performed. The module 107 can for example be implemented using a microcontroller operating on a set of computer software instructions stored on a memory in the module 107.

In accordance with one embodiment an initial transmit power for DPCCH on a secondary carrier is set to a function of estimated statistics (e.g. mean, median, and variance) of the current DPCCH transmit power on a primary carrier. In Fig. 2 an exemplary configuration of receivers and transmitters 104 in a User Equipment is depicted. In Fig. 2 two transmitter (Tx) and receiver (Rx) chains in a UE operating on different carrier frequencies (denoted 1 and 2) in a MC- HSUPA system is depicted. The initial power of the transmitter on frequency 2 is derived based on an estimate of the expected output power on frequency 1. The initial transmit power in the secondary earner can be set using different functions of estimated statistics. For example, the initial transmit power on the secondary earner can be an estimate of the average DPCCH power on the primary earner minus a pre-calculated offset in order to account for, for example, expected difference in path gain on the secondary carrier frequency compared to the primary earner frequency.

In this way, it is possible to exploit the fact that there is a high probability of strong con-elation in average path loss (and possibly also a significant correlation in fading) between the earners. Furthermore, assuming that the earners have the same timing, the synchronization in the radio base station NodeB to a secondary earner will be simplified to a large extent, since the multi- path delay estimates from the primary earner can serve as a first approximation for multi-path delays for the secondary carrier.

In this way, because the initial power level for the secondary carrier will be relatively close to the final power level and the timing for the secondary carrier is known, the ramping procedure can be significantly faster and more accurate than in the initial synchronization procedure for legacy (single-carrier) case as described in chapter 4.3 of 3GPP technical specification TS 25.214 v8.4.0).

An alternative second embodiment is to let the maximum DPCCH allowed transmit power for the secondary carrier be determined by any of the following methods:

1. a (diminishing) function of the current estimated (average or median) DPCCH power on the primary earner, 2. a (diminishing) function of the current estimated (average or median) power available considering total transmit power on the primary earner (including control plane and user plane channels),

3. a maximum fraction of the maximum transmit power available,

4. a function of the above methods 1 or 2 up to a limit, which is given by method 3.

The DPCCH power can be either the most recent value, or a filtered estimate of, for example, the average or median DPCCH power; see the example in Fig. 3. In Fig. 3 a schematic picture of two transmitter (Tx) and receiver (Rx) chains in a UE 103 operating on different carrier frequencies (denoted 1 and 2) in a MC-HSUPA system 100. The maximum power of the transmitter on frequency 2 is derived based on an estimate of the expected output power on frequency 1.If the power of DPCCH should not be increased, TPC up commands are simply neglected. The actual function and its parameters, such as back-off and ramping rate, can be hard-coded by the standard or configured e.g. through Radio Resource Control (RRC) signaling from the Radio Access Network (RAN) to the UE and corresponding Iub/Iur signaling within RAN if necessary. Note that the methods and devices are applicable for cases with more than two carriers, e.g. three earners, in which case one of the carriers can be considered as the primary carrier and the other two carriers can be considered as secondary carriers.

In another embodiment, the initial transmission power and/or the maximum transmission power for a particular secondary carrier can be set as functions not only of the statistics of the primary earner but also of the other secondary carriers. In accordance with one embodiment a method of uplink power control in a UE is provided with said UE configured for multi carrier uplink transmissions on a set of earners including a primary carrier and a secondary carrier, wherein uplink transmissions on said primary carrier have been initiated prior to uplink transmissions on said at least one secondary carrier and where the method comprises determining an initial transmit power for a Dedicated Physical Control Channel on said secondary earner, wherein said initial transmit power is a function of measured statistics for transmit power of a Dedicated Physical Control Channel on said primary carrier.

In Fig. 4 a flow chart illustrating some procedural steps performed in a UE when performing such a power control is depicted. First, in a step 401, transmission on a primary carrier is initiated and started. Next, in a step 403, transmission on a secondary carrier is initiated. The initial transmit power for a Dedicated Physical Control Channel on the secondary earner is then determined as a function of measured statistics for transmit power of a Dedicated Physical Control Channel on the primary earner in a step 405. The transmission on the secondary carrier is then started using the determined initial transmit power for the Dedicated Physical Control Channel in a step 407.

In accordance with one embodiment the initial transmit power is a function of an estimate of an average transmit power of the Dedicated Physical Control Channel.

In accordance with one embodiment the initial transmit power is a function of an estimate of a median transmit power of said Dedicated Physical Control Channel.

In accordance with one embodiment the initial transmit power is a function not only of said measured statistics for transmit power of said Dedicated Physical Control Channel on said primary carrier but also measured statistics for transmit power of Dedicated Physical Control Channel of any additional secondary carrier in said set of earners. In accordance with one embodiment the method further comprises controlling transmit power of said Dedicated Physical Control Channel on said secondary carrier such that the uplink transmit power does not exceed a defined maximum allowed transmit power defined by one or more of:

- a function of an estimate of the current Dedicated Physical Control Channel transmit power on said primary carrier,

- a maximum fraction of a maximum available transmit power in said UE, wherein any transmit power commands ordering an increase of said transmit power of said Dedicated Physical Control Channel on said secondary carrier to a level exceeding said defined maximum allowed transmit power is ignored.

In accordance with one embodiment a method of uplink power control in a UE is provided. The

UE is configured for multi carrier uplink transmissions on a set of carriers including a primary carrier and a secondary carrier, wherein uplink transmissions on said primary carrier has been initiated prior to uplink transmissions on said secondary carrier. The method comprises: controlling a transmit power of a Dedicated Physical Control Channel on said secondary earner such that the uplink transmit power does not exceed a defined maximum allowed transmit power defined by one or more of: a function of an estimate of the current Dedicated Physical Control Channel transmit power on said primary carrier, a function of available transmit power in said UE considering an estimate of the current total transmit power on said primary carrier; a maximum fraction of a maximum available transmit power in said UE, wherein any transmit power commands ordering an increase of said transmit power of said

Dedicated Physical Control Channel on said secondary carrier to a level exceeding said defined maximum allowed transmit power is ignored.

In Fig. 5 a flow chart illustrating some procedural steps performed in a UE when performing such a power control is depicted. First, in a step 501, transmission on a primary carrier is initiated and started. Next, in a step 503, transmission on a secondary earner is initiated and started using an initial transmission power. The transmit power for the Dedicated Physical Control Channel on the secondary carrier is then continuously controlled to not exceed a defined maximum allowed transmit power where the maximum allowed transmit power is set as any of the levels defined above in a step 505. Thus, the defined maximum allowed transmit power is set to one or more of: a function of an estimate of the current Dedicated Physical Control Channel transmit power on said primary carrier, a function of available transmit power in said UE considering an estimate of the current total transmit power on said primary carrier; a maximum fraction of a maximum available transmit power in said UE.

When a transmit power command ordering an increase of the transmit power of the Dedicated Physical Control Channel on the secondary earner to a level exceeding the defined maximum allowed transmit power is received the order is ignored.

Using the methods and devices as described herein will provide DPCCH synchronization procedures that are faster and more accurate compared to a legacy power ramping procedure. Moreover, even though the output power in a UE is shared between carriers, a competition of resources for DPCCH on multiple carriers will not cause a UE to lose coverage (synchronization with RAN).

Claims

1. A method of uplink power control in a User Equipment, UE, where the UE is configured for multi earner uplink transmissions on a set of carriers comprising a primary carrier and at least one secondary carrier, wherein uplink transmissions on the primary earner have been initiated (401) prior to uplink transmissions on a secondary carrier, the method comprising the steps of: - deteπnining (405) an initial transmit power for a Dedicated Physical Control Channel on said secondary carrier, wherein said initial transmit power is a function of measured statistics for transmit power of a Dedicated Physical Control Channel on said primary carrier.

2. The method according to claim 1 , wherein the initial transmit power is a function of an estimate of an average transmit power of the Dedicated Physical Control Channel on the primary carrier.

3. The method according to claim 1, wherein the initial transmit power is a function of an estimate of a median transmit power of the Dedicated Physical Control Channel on the primary carrier.

4. The method according to any one of claims 1 - 3, wherein the initial transmit power is a function not only of said measured statistics for transmit power of said Dedicated Physical

Control Channel on said primary carrier but also of measured statistics for transmit power of Dedicated Physical Control Channel of any additional secondary carrier in said set of carriers.

5. The method according to any one of claims 1 - 4, wherein the method further comprises the step of: controlling the transmit power of said Dedicated Physical Control Channel on said secondary carrier such that the uplink transmit power does not exceed a defined maximum allowed transmit power defined by one or more of:

- a function of an estimate of the current Dedicated Physical Control Channel transmit power on said primary carrier, - a function of available transmit power in said UE considering an estimate of the current total transmit power on said primary carrier;

6. A method of uplink power control in a User Equipment, UE, where the UE is configured for multi earner uplink transmissions on a set of carriers including a primary earner and at least one secondary carrier, wherein uplink transmissions on said primary earner has been initiated (501) prior to uplink transmissions on said secondary earner, the method comprising the steps of:

- controlling (505) a transmit power of a Dedicated Physical Control Channel on said at least one secondary carrier such that the uplink transmit power does not exceed a defined maximum allowed transmit power defined by one or more of: - a function of an estimate of the current Dedicated Physical Control Channel transmit power on said primary earner,

- a maximum fraction of a maximum available transmit power in said UE,

wherein any transmit power commands ordering an increase of said transmit power of said Dedicated Physical Control Channel on said secondary earner to a level exceeding said defined maximum allowed transmit power are ignored.

7. A User Equipment (103) configured for multi earner uplink transmissions on a set of carriers comprising a primary carrier and at least one secondary carrier, the User Equipment comprising:

- means (107) for determining an initial transmit power for a Dedicated Physical Control Channel on said secondary earner, wherein said initial transmit power is a function of measured statistics for transmit power of a Dedicated Physical Control Channel on said primary earner.

8. The User Equipment according to claim 7, wherein the initial transmit power is a function of an estimate of an average transmit power of the Dedicated Physical Control Channel on the primary earner.

9. The User Equipment method according to claim 7, wherein the initial transmit power is a function of an estimate of a median transmit power of the Dedicated Physical Control Channel on the primary carrier.

10. The User Equipment according to any one of claims 7 - 9, wherein the initial transmit power is a function not only of said measured statistics for transmit power of said Dedicated Physical

1 1. The User Equipment according to any one of claims 7 - 10, wherein the User Equipment further comprises :

- means (107) for controlling the transmit power of said Dedicated Physical Control Channel on said secondary earner such that the uplink transmit power does not exceed a defined maximum allowed transmit power defined by one or more of:

- a maximum fraction of a maximum available transmit power in said UE, and

- means (107) for ignoring any transmit power commands ordering an increase of said transmit power of said Dedicated Physical Control Channel on said secondary carrier to a level exceeding said defined maximum allowed transmit power.

12. A User Equipment (103) configured for multi carrier uplink transmissions on a set of earners including a primary earner and at least one secondary carrier, the User Equipment method comprising: - means (107) for controlling a transmit power of a Dedicated Physical Control Channel on said at least one secondary carrier such that the uplink transmit power does not exceed a defined maximum allowed transmit power defined by one or more of:

- a maximum fraction of a maximum available transmit power in said UE, and