WO2010075872A1

WO2010075872A1 - Enhanced uplink user entity rate limitation signalling

Info

Publication number: WO2010075872A1
Application number: PCT/EP2008/068310
Authority: WO
Inventors: Pär ANKEL; Andreas Andersson
Original assignee: Telefonaktiebolaget L M Ericsson (Publ)
Priority date: 2008-12-29
Filing date: 2008-12-29
Publication date: 2010-07-08

Abstract

A Base station adapted to transmit a power grant signal (ABS GRNT E-AGCH) to an individual user entity, granting (11) the individual user entity a power threshold of a given rank (SG) The transmission from user entities to the base station being performed by means of a retransmission scheme comprising at least acknowledge (ACK) and not acknowledge (NACK) signalling from the base station, wherein the base station being adapted to carry out the following steps of, evaluating (7, 7i) ) for a given period (5, 5ii) a current parameter ((E-DCH(SG),- S-NACK(SG)) indicative of the effective bit rate (7, 7i), by comparing the current parameter with a reference value (E_DSCH (SG-I), S_NACK_MAX), depending on the evaluation, the base station, decrementing (8) the rank (SG) of the power threshold, or allowing the rank (SG) of the power threshold to be incremented (10), the base station being adapted to limiting serving grants.

Description

Enhanced uplink user entity rate limitation signalling

Field of the invention

This invention is directed to uplink resource allocation for base stations and networks. More particularly, the invention relates to the relative and / or absolute grant signalling in Enhanced Uplink (HSUPA) and corresponding effects on user entity transmit capabilities.

Background

in release 6 of the WCDMA (Wideband Code Division Multiple Access) specification, a High Speed Uplink Packet Access (HSUPA) (also called Enhanced Uplink) communication scheme is defined in addition to the downlink High Speed Data Packet Access (HSDPA) scheme in order to match the bit rates provided by the latter, so as to cater for improved interactive, background and streaming services. In prior art document 3GPP TS 25.309, "FDD Enhanced Uplink; Overall Description; Stage 2", Version V6.6.0 of 2006-04-06 the Enhanced UL (Uplink) is described.

Relevant sections can moreover be found in 3GPP References TS25.211 and TS25.321 - MAC protocol specification. 25.214 Physical Layer Procedures (FDD). 25.321 MAC protocol specification.

In fig. 1 , a HSUPA network overview (HSDPA related channels are not included in the figure) is indicated. The network comprises a Core Network communicating with a Radio Network Controller (RNC, S-RNC, D-RNC (Drifting-RNC)) over the Iu interface, or lur interface; a first base station, Node B, B1 , a second base station, Node B, B2, both base stations comprising a EUL scheduler unit. The EUL Scheduler (EUL_SCH) is also denoted the MAC-e Scheduler, and communicating with the RNC over respective lub inter- faces.

The following HSUPA channels are transmitted over the air interface; the E-AGCH to convey absolute grant signalling from the MAC-e scheduler towards the UEs, the E- RGCH for relative grant signalling, E-HICH to convey acknowledgement feedback from Node-B decoding of UE transmitted data, Dedicated Physical Channel (DPCH) or Fractional DPCH to convey Transmit Power Control (TPC) commands, Enhanced DPDCH (E-DPDCH) to convey the MAC-e payload and Enhanced DPCCH (E-DPCCH) to convey the control signalling of the MAC-e

Node B1 corresponds to the serving cell in this example (E-AGCH is only transmitted from the serving cell) and node B2 corresponds to a non-serving cell

Document 3GPP TS 25 309 FDD, Enhanced Uplink Overall description, mentioned above gives an overview of the Enhanced Uplink functionality

An overview of the HSUPA can also be found in prior art document "High Speed Uplink Packet Access (HSUPA), White Paper, application note 1 MA94", Rohde Schwarz, 01 2006 Retrieved on the internet on 20081223

According to the HSUPA specification, the Enhanced Dedicated Channel (E-DCH) high speed uplink transport channel offers a number of new features such as short Transmission Time Interval (TTI), Fast Hybrid Automatic Repeat Request (ARQ) with soft re- combining, fast scheduling for reduced delays, increased data rates and increased capacity

When a UE is setting up communication with a Node B, the setup procedure may be followed by a HSDPA session, for e g downloading / surfing an internet page using TCP Depending on the capabilities of the user entity, this may moreover involve HSUPA transmissions whereby Node B that transmits TCP messages on the HSDPA downlink channel will receive TCP acknowledgements on the E-DCH uplink to Node B Since Node-B determines, or schedules, at which pace a UE shall transmit on E-DCH, Node-B utilises the E-AGCH to convey its scheduling decisions A shorter delay, measured from the time until a TCP data segment is sent downlink until a TCP acknowledgement as a response is sent uplink, leads to a decreased downloading time of file transfers etc, due to the shorter round trip time estimate of the TCP layer

During the procedure upon which the user entity becomes ready to use a HSUPA service with Node B, the user entity is informed about which E-AGCH code it is supposed to receive downlink traffic on For this purpose, the E-AGCH, which is a shared channel within the cell, is used

E-AGCH channels are configured to a Node B in a configuration or re-configuration procedure with the RNC via the NBAP (Node B Application Part) signalling protocol Although HSUPA is similar in many respects to HSDPA, HSUPA has one very significant difference which the name of the new transport channel, Enhanced Dedicated Channel, hints at Unlike HSDPA, HSUPA does not utilize a shared channel for data transfer in the uplink In W-CDMA each UE already uses a unique scrambling code in the uplink so each UE already has a dedicated uplink connection to the network with more than ample code channel space in that connection This is in contrast to the downlink where the Node B uses a single scrambling code and then assigns different OVSF channelization codes to different UE's The shared resource in the uplink is actually the interference level at the Node B, which the network manages through the fast closed loop power control algorithm The fact that the UE has a dedicated connection to the network in the uplink influences the design of HSUPA quite considerably The goals of HSUPA were to support fast scheduling (which allows the network to rapidly change which UE's are transmitting and at what rate) and to reduce the overall transmission delay Transmis- sion delay reduction is achieved through fast hybrid ARQ retransmissions, in a manner very similar to HSDPA, and an optional shorter 2 ms TTi As the primary shared resource on the uplink is the total power arriving at the base station, HSUPA scheduling is performed by directly controlling the maximum amount of power that a UE can use to transmit at any given point in time The network has two methods for controlling the UE's transmit power on the E-DPDCH, it can either use a non-scheduled grant or a scheduled grant In the non-scheduled grant the network simply tells the UE the maximum block size that it can transmit on the E- DCH during a TTI This block size is signaled at call setup and the UE can then transmit a block of that size or less in each TTI until the call ends or the network modifies the non-scheduled grant via an RRC reconfiguration procedure The block size deterministi- cally maps to a power level, which is also configured by the network during call setup The non-scheduling grant is most suited for constant-rate delay-sensitive application such as voice-over-IP

Regarding the scheduled grant, the UE maintains a Serving Grant that it updates based on information received from the network The Serving Grant directly specifies the maximum power the UE can use on the E-DPDCH in the current TTI As E-DCH block sizes map deterministically to power levels, the UE can translate its Serving Grant to the maximum E-DCH block size it can use in a TTI (the mapping of power levels is determined by the E-TFCI Reference Power Offsets that are signaled at call setup) There are two ways the network can control the UE's Serving Grant The first is through an absolute grant, transmitted on the shared E-AGCH downlink channel, which signals a specific, absolute number for the Serving Grant The other way is through relative grants, transmitted using the downlink E-RGCH channels, that incrementally adjust a UE's Serving Grant up or down from its current value At any given point in time the UE will be listening to a single E-AGCH from its serving cell and to one or more E-RGCH's The E-AGCH is a shared channel so the UE will only update its Serving Grant if it receives a block on the E-AGCH that is destined for it (the E-RNTI identity signaled at call setup is used on the E-AGCH to direct transmissions to particular UE's) The E-RGCH is also shared by multiple UEs but on this channel the UE is listening for a particular orthogonal signature rather than a higher layer identity If it does not detect its signature in a given TTI it interprets this as a "Hold" command, and thus makes no change to its Serving Grant The above section is found from web material from Agilent Technologies, November 2008 (hjlpj/wjrelejs^

BJhβ) Retrieved on the internet on 20081223

In fig 2, a signaling scenario of a serving node B, with which the user entity may be currently attached and a neighboring non-serving node, which may experience interference from the user entity in question, is shown

The Node B MAC-e Scheduler issues "absolute grants" on the downlink E-AGCH channel, that is, messages which grant the user entity the right to transmit at given bit rates on the uplink Since bandwidth needs vary dynamically over time, it is beneficial that the power emissions by user entities are regulated speedily so that bandwidth is not unnecessarily wasted User entities transmit requests as Happy / Not Happy concerning their need for higher speeds

The E-AGCH can be defined to have a number of one to several channelization codes

The DPCCH SIR level is controlled by the outer loop (SIR target setting from RNC) and the inner loop power control (TPC) The E-DPDCH(s) has an offset relative the DPCCH, which is called E-DPDCH power offset In Figure 3 the E-DPDCH power offset relative DPCCH (linear increase with bit rate), defined in 3GPP, 25 214 and the corresponding appendix, if only one gain factor reference point is used Summary of the invention

It is a first object of the invention to improve the uplink resource allocation for user entities and base stations, wherein the base station is adapted to receive communication from a user entity on at least a channel which is subject to interference from other user entities, the base station being adapted to transmit a power grant signal (ABS GRNT E- AGCH) to an individual user entity, granting (11) the individual user entity a power threshold of a given rank (SG) within which the user entity is permitted to transmit communication signals to the base station

The invention is directed to systems the signal to noise ratio of the signal from a user entity as received by the base station being associated with a given throughput, and to systems in which the transmission from user entities to the base station is being performed by means of a retransmission scheme comprising at least acknowledge (ACK) and not acknowledge (NACK) signalling from the base station

This object has been achieved by the following subject matter

Method for a base station wherein

- the method comprises the steps of, for each individual user entity,

- evaluating (7, 7ι)) for a given period (5 5ιι) a current parameter ((E-DCH(SG), SJMACK(SG)) indicative of the effective bit rate (7, 7ι), by comparing the current pa- rameter with a reference value (E_DSCH(SG-1), S_N ACKJVIAX),

- depending on the evaluation the base station,

- - decrementing (8) the rank (SG) of the power threshold, or

- - allowing the rank (SG) of the power threshold to be incremented (10),

- the base station limiting serving grants to the incremented or decremented rank (11) The above object has also been achieved by a base station in which the above method is implemented

Base station adapted to receive communication from a user entity on at least a channel which is subject to interference from other user entities, the base station being adapted to transmit a power grant signal (ABS GRNT E-AGCH) to an individual user entity, granting (1 1) the individual user entity a power threshold of a given rank (SG) within which the user entity is permitted to transmit communication signals to the base station

The signal to noise ratio of the signal from a user entity as received by the base station being associated with a given throughput

The transmission from user entities to the base station being performed by means of a retransmission scheme comprising at least acknowledge (ACK) and not acknowledge (NACK) signalling from the base station, wherein

The base station being adapted to carry out the following steps of, for each individual user entity,

- evaluating (7, 7ι)) for a given period (5, 5ιι) a current parameter ((E-DCH(SG), S_NACK(SG)) indicative of the effective bit rate (7, 7ι), by comparing the current parameter with a reference value (E_DSCH(SG-1), S_N AC KJvIAX),

- depending on the evaluation, the base station

- - decrementing (8) the rank (SG) of the power threshold, or

- - allowing the rank (SG) of the power threshold to be incremented (10), - the base station being adapted to limiting serving grants to the incremented or decremented rank (11)

According to various aspects of the invention, an adaptive maximum granted bit rate can be applied, instead of a fixed maximum A fixed maximum needs margins, which the adaptive approach doesn't, which means higher peak rates can be achieved

Besides higher peak rate, the DPCCH SIR levels for a UE will be lower, which implies less interference in the cell The decrease in interference can be used to increase the rate for other UEs in the cell

Another benefit is that advanced power control routines, which unfortunately may show to be instable, can be avoided Further advantages of the invention will appear from the following detailed description of the invention

Brief description of the drawings

Fig 1 shows basic elements of a prior art HSUPA network and signalling,

fig 2 shows basic HSUPA network elements and exemplary power threshold sig- nailing,

fig 3 shows the bit rate as a function of E-DPCH power offset,

fig 4 shows exemplary effective bit rate results according to investigations made in association with the invention,

fig 5 shows further measurements according to the invention of the effective bit rate,

fig 6 shows an exemplary node B according to the invention,

fig 7 shows a first embodiment of a method for a base station according to the invention,

fig 8 shows a further embodiment of the invention, and

fig 9 shows a still further embodiment of the invention

Detailed description of preferred embodiments of the Invention

It has been found, that for a given first low operating power range, the E-DPDCH power offset increases - substantially linearly - with the bit rate However, the SIR level on DPCCH will also have a rather linear increase at lower rates, since the self interference from the E-DPDCH is increasing At a second high operating power range, the SIR level suddenly increases This effect has been demonstrated in fig 4 The sudden increase in SIR appears to be dependant on the self-interference between E-DPDCH₁ DPCCH, E-DPCCH, HS-DPCCH (and DPDCH, if any), - the number of channelization codes have increased (higher PAPR), less repeated bits in the channel coding, radio impairments, the type of radio channels (environment urban or non-urban), and the receiver type, e g different behaviour for RAKE, GRAKE or Interference can- cellation receivers

In fig 5, the effective bit rate of the exemplary scenario given in fig 4 - resulting after retransmissions - has been shown

It is seen that the effective bit rates increases with the power level (expressed by the service grant power level) up to a given point in fig 5, at around SG21 and SG 22 Above this point the throughput diminishes Consequently, it would be adverse to grant a UE rates that require very high SIR as the operation becomes instable and the throughput can go down for increasing power

On the other hand, it is found that the point of saturation in fig 5, at around SG21 and SG 22, is hard to predict since it is dependent on for example the radio channel

DPCCH power is increased when the number of re-transmissions increases on the E- DPDCH (via outer loop power control) The rush indicates that the increased DPCCH power doesn't help since the number of re-transmissions is still high on E-DPDCH (since the DPCCH is still increased) A high amount of re-transmissions means a high NACK rate Fig 4 shows how the NACK percentage can increase with the bit rate Fig 4 also shows specific SG Indexes corresponding to a certain bit rate

For instance, SG=22 means that a UE is allowed to transmit maximum 2 Mbps and SG=21 implies a maximum 1 7 Mbps The actual throughput for SG=22 may for example be found to be (1-0 55)*2 Mbps = 0 9 Mbps and for SG=21 it is (1-0 2)*1 7 Mbps =1 36 Mbps So in this case, it is much better to use SG=21 which provides better throughput and also lower SIR and therefore less interference in the cell

The table below indicates exemplary values

Apparently, one could interpret the results such that a fixed maximum limit, at around SG20 could be used, since performance decreases at higher SG indexes In fig 5 an exemplary relationship between the effective bit rate and the SG index has been shown But the curve depends on a number of factors, as mentioned above

According to one aspect of the invention, a temporary SG index, or rank, is found for a given user entity as the point where an increased grant no longer gives a higher throughput Subsequently, the method according to the invention is backing off from this point

According to a further aspect of the invention, the throughput on the new grant is compared with the granted rate on the next lower grant and the method according to the invention effectuates a "back off", if the next lower grant gives a higher throughput

A check of the NACK rate on the E-DPDCH is compared with a threshold as a decision to take down the grant Note that the invention is applicable and effective even for a modest DPCCH SIR increase vs bit rate

First embodiment of the invention

A first embodiment of a method according to the invention being implemented in a node B is shown in fig 6 A method for implementing the first embodiment of the invention is shown in fig 7

In step 1 , the rank of the power threshold within which the user entity is allowed to transmit is initially set to a maximum value

In step 2, a parameter related to the throughput, also denoted the effective bit rate is estimated for all ranks This is an initial step which allows step 7, to be described below, to be carried out

In step 3, the reception of packets on the E_DCH channel is awaited in the transmit time interval, TTI

In step 4ι, - when such packets is / are received - the amount of non acknowledge signals (NACK) issued by the radio base station in relation to the amount of least acknowledge signals (ACK) within a given period, is calculated In this calculation DTX, lacking packets, can be included in the calculation

In step 5, the rank of the power threshold is evaluated on a predetermined time basis, T1 , such that the power threshold can be regulated on a temporary basis It the time basis has not been met, no, the process moves on to step 9 below

In step 6, the current throughput is saved for the current rank

In step 7, - the effective bit rate is evaluated, by comparing the current parameter for the effective bit rate with a reference value (EJDSCH(SG-I), SJMACKJV1AX) The evaluation (7) involves comparing the estimated effective bit rate associated with a power threshold (E__DSCH(SG)) of a current permitted rank (SG) with an estimated effective bit rate associated with a power threshold of a lower rank (E_DSCH(SG-1)

If this is the case, proceed to step 8, if not proceed to step 9 In step 9, it is determined if the rank has been valid for longer than a predetermined time, T2 If no proceed to step 3, if yes proceed to step, in which the rank is incremented

If the criterion in step 7 is fulfilled the rank is decremented, step 8

Parallel with the above mentioned routine, the base station limiting serving grants to the incremented or decremented rank as illustrated by step 11

Hence, whenever an absolute grant, AG, or a service grant, SG, is given to a UE, the E- DCH throughput is measured during a pre-defined evaluation period The E-DCH throughput on this SG Index is considered and compared against previous results on the next lower SG index If there are no previous results on the next lower SG index (none at all or no valid once) then use the maximum transmission rate derived from the SG Index If the bit rate of the lower index + a percentage of this rate, called K, gives a higher bit rate, then reduce the SG Tag the new SG Index with "Temporary Max Rate" K is the minimum bit rate increase needed to allow the UE to use the next higher SG index The "Temporary Max Rate" is valid for a predefined period of time, before a new try at higher SG indexes is allowed

Second embodiment

A second embodiment of the invention is shown in fig 8

In relation to the first embodiment of the invention, steps 1 , 3, 5, 8, 9, 10 and 11 are the same as described under the first embodiment Step 2 and 6 of fig 7 are not performed in the second embodiment

However, according to step 4ιι instead of estimating the E-DCH throughput, a parameter, a NACK rate, relating to the percentage or NACK's detected in the Node B receiver, more specifically denoted S-NACK(SG), is based on an amount of non acknowledge signals (NACK) issued by the radio base station in relation to at an amount of least ac- knowledge signals (ACK) within a given period, T1 For instance, S__NACK(SG) can be calculated as "Number of NACK's" / ("Number of NACKs" + "Number of ACKs" + "Num- ber of DTXs") or NACKs" / ("Number of NACKs" + "Number of ACKs"), ignoring the case when nothing is sent from the UE (called DTX)

Subsequently, in step 7ι, the current parameter S_NACK(SG) is compared with a predetermined maximum rate for the amount of non acknowledge signals (NACK) issued by the radio base station in relation to at least acknowledge signals (ACK)

Third embodiment

A third embodiment of the invention is shown in fig 9

In relation to the second embodiment of the invention, step 4ιιι replaces step 4ιι and step 5ιι replaces step 5

A user entity may transmit using a given maximum transport block size (MAX_TB_SIZE(SG)) The maximum transport block size is dependent on the serving grant A user entity may however use a smaller transport block size (TB_SIZE), e g in case there is not enough data in the buffer to fill up the grant or in situations where the e g battery power of the user entity is limited

For a specific Serving Grant (SG) together with certain L3 parameters configured over NBAP, known to the person skilled in the art, the maximum transport block size (MAX_TB_SlZE(SG)) the user entity is allowed to use can be calculated

For taking these circumstances into account, according to third embodiment of the invention, the NACK rate for a given service grant, SG, is excluded form being calculated or updated, since a user entity utilizing a smaller TB Size than allowed is an indication of the user entity is not being restricted from utilizing the given serving grant for reasons given by the network interference situation, but for reasons associated with the user entity itself Hence, small transport block sizes, if not compensated for, will tend to give a misleading NACK rates

Therefore, according to step 4ιιι, an update of the probability of S_NACK(SG) for the cur- rent rank of the power threshold is only done if the detected transport block size

(TB_SIZE) for the given TTI exceeds the MAX_TB_SIZE calculated from the next lower rank, SG-1 In order to allow the comparison in step 4ιιι, a calculation of the MAX__TB_SIZE(SG-1 ) is performed

Moreover, in step 5ιι, the following is examined Has at least a given number, TBJJMIT, of transport blocks been received, which transport blocks exceeds the maximum allowed transport block size for the previous rank of the serving grant, MAX__TB_SIXE(SG-1)

If this is the case, proceed to step 7ι, if no, proceed to step 9

In 5ιι it is checked if there is more than "TB Limit" updates of the S__NACK(SG) for this specific SG

If this is the case, proceed to step 8, decrementing the serving grant, or if no, proceed to step 9, explained above

Base station according to the invention

In fig 6, an exemplary base station according to the invention is shown, also denoted Node B, being capable of operating both as a serving base station and as a non-serving base station

The base station comprises RGCH/HICH processing stages 1 - n, layer 1 processing, AGCH processing, a scheduler, respective HARQ entities for user entities 1 - n, each HARQ entity comprising plurality of HARQ receivers for receiving packets 1 - m accord- ing to the HARQ process for each user entity Node B moreover comprises Layer 1 processing means for communicating over E-AGCH and E-RGCH channels over the air interface, L1 processing means for communicating over DPCCH, E-DPCCH and E- DPDCCH channels Moreover, the base station comprises E-DPCH FP means for communicating over the iub interface MAC-e EDPCCH decoding means 1 - n is provided for HARQ entities for UE 1 - n According to the invention, the method steps concerning Node B according to the invention may be implemented as a programme in the scheduler

Claims

1 Method for a base station adapted to receive communication from a user entity on at least a channel which is subject to interference from other user entities, the base station being adapted to transmit a power grant signal (ABS GRNT E-AGCH) to an individual user entity, granting (11) the individual user entity a power threshold of a given rank (SG) within which the user entity is permitted to transmit communication signals to the base station,

the signal to noise ratio of the signal from a user entity as received by the base station being associated with a given throughput,

the transmission from user entities to the base station being performed by means of a retransmission scheme comprising at least acknowledge (ACK) and not ac- knowledge (NACK) signalling from the base station, wherein

the method comprises the steps of, for each individual user entity,

- evaluating (7, 7ι)) for a given period (5, 5ιι) a current parameter ((EJDCH(SG), S_NACK(SG)) indicative of the effective bit rate (7, 7ι), by comparing the current parameter with a reference value (EJDSCH(SG-I), S_N ACKJVl AX),

- depending on the evaluation, the base station,

- - decrementing (8) the rank (SG) of the power threshold, or

- - allowing the rank (SG) of the power threshold to be incremented (10),

- the base station limiting serving grants to the incremented or decremented rank (11)

Method according to claim 1 , wherein the current parameter (S_NACK(SG), 4ιι) is based on an amount of non acknowledge signals (NACK) issued by the radio base station in relation to an amount of least acknowledge signals (ACK) within a given period

Method according to claim 1 , wherein the current parameter (EJDCH(SG), 4ι) is based on a calculation of the effective bit rate as estimated (4ι) from the amount of non-acknowledge signals (NACK) in relation to at least acknowledge signals (ACK)

Method according to claim 3, wherein the evaluation (7) involves comparing the estimated effective bit rate associated with a power threshold (E-DSCH(SG)) of a current permitted rank (SG) with an estimated effective bit rate associated with a power threshold of a lower rank (E_DSCH(SG-1)

Method according to claim 4, wherein if the lower rank (E__DSCH(SG-1))) effective bit rate is substantially higher (7, K) than the current power threshold rank effective bit rate (E_DSCH(SG))), decreasing (8) the power threshold rank

Method according to claim 2, wherein the reference value (SJSlACK(SG)) is a pre- determined maximum rate for the amount of non acknowledge signals (NACK) issued by the radio base station in relation to at least acknowledge signals (ACK)

Method according to a previous claim, wherein if the current power threshold rank (SG) has been valid longer than for a predetermined time (9) incrementing (10) the power threshold rank (SG)

8. Method according to any of claims 2 or 6, wherein an updating (4iii) of the calculation of the current parameter only is performed if

a detected transport block size (TB__SIZE) exceeds a maximum transport block size (MAX_TB__SIZE) calculated from the next lower rank (SG-1).

9. Method according to claim 8, wherein if (5ii)

at least a given number (TBJJMIT) of transport blocks have been received, which transport blocks exceeds the maximum allowed transport block size for the previous rank of the serving grant, MAX__TB_SIXE(SG-1 ) omitting a comparison of the current parameter (7i).

Base station adapted to receive communication from a user entity on at least a channel which is subject to interference from other user entities, the base station being adapted to transmit a power grant signal (ABS GRNT E-AGCH) to an individual user entity, granting (1 1) the individual user entity a power threshold of a given rank (SG) within which the user entity is permitted to transmit communication signals to the base station,

- evaluating (7, 7ι)) for a given period (5, 5ιι) a current parameter ((E-DCH(SG), S-NACK(SG)) indicative of the effective bit rate (7, 7ι), by comparing the current parameter with a reference value (EJDSCH(SG-I ), S_N ACKJvIAX),

- depending on the evaluation, the base station,

- - decrementing (8) the rank (SG) of the power threshold, or

- - allowing the rank (SG) of the power threshold to be incremented (10),

- the base station being adapted to limiting serving grants to the incremented or decremented rank (11)

Base station according to claim 10, wherein the current parameter (S_NACK(SG), 4ιι) is based on an amount of non acknowledge signals (NACK) issued by the radio base station in relation to an amount of least acknowledge signals (ACK) within a given period Base station according to claim 10, wherein the current parameter (E-DCH(SG), 4ι) is based on a calculation of the effective bit rate as estimated (4ι) from the amount of non-acknowledge signals (NACK) in relation to at least acknowledge signals (ACK)

Base station according to claim 12, wherein the evaluation (7) involves comparing the estimated effective bit rate associated with a power threshold (E_DSCH(SG)) of a current permitted rank (SG) with an estimated effective bit rate associated with a power threshold of a lower rank (EJDSCH(SG-I )

Base station according to claim 13, wherein if the lower rank (E_DSCH(SG-1))) effective bit rate is substantially higher (7, K) than the current power threshold rank effective bit rate (E__DSCH(SG))), decreasing (8) the power threshold rank

Base station according to claim 11 , wherein the reference value is a predetermined maximum rate for the amount of non acknowledge signals (NACK) issued by the radio base station in relation to at least acknowledge signals (ACK)

Base station according to any of previous claims 10, wherein if the current power threshold rank (SG) has been valid longer than for a predetermined time incre- menting the power threshold rank (SG)

Method according to any of claims 12 or 16, wherein an updating (4ιιι) of the calculation of the current parameter only is performed if

a detected transport block size (TB-SIZE) exceeds a maximum transport block size (MAX_TB_SIZE) calculated from the next lower rank (SG-1)

9. Method according to claim 17, wherein if (5ii)

at least a given number (TEMJMIT) of transport blocks have been received, which transport blocks exceeds the maximum allowed transport block size for the previous rank of the serving grant, MAX_TB_SIXE(SG-1) omitting a comparison of the current parameter (7i).