TECHNICAL FIELD OF THE INVENTION

The present invention relates to wireless communications. More especially it relates to wireless high speed packet data communications. Particularly it relates to transmission power control of high-speed packet data communications.

BACKGROUND AND DESCRIPTION OF RELATED ART

Transmission power control of dedicated and shared chan- nels, such as DPDCH (Dedicated Physical Data Channel) and DPCCH (Dedicated Physical Control Channel) in UMTS (Universal Mobile Telecommunications System) , is previously known.

Figure 1 shows schematically selected elements of a UMTS communications system according to prior art. Protocol Data Units, PDUs, are communicated downlink, DL, to user equipment «UE» and uplink from the user equipment «UE». Information disassembled/reassembled into appropriately sized protocol data units «PDU» are transferred to a presumed receiver. The communications path involves a radio base station, RBS, «BS1/Node B 1» and a radio network controller «RNC», the radio base station «BS1/Node B 1» is connected to the RNC over an Iub interface and to the UE over a radio interface. Also depicted is a second radio base station «BS2/Node B 2» not participating in the par- ticular information transfer at the time instant depicted in the figure. Node B is a logical node responsible for radio transmission/reception in one or more cells to/from a User Equipment. A base station, BS, or radio base station is a physical entity representing Node B.

Figure 2 displays schematically selected elements involved in soft handover diversity in a UMTS communications system according to prior art. In uplink direction, PDUs, transmitted from UE are received over different radio links, il- lustrated by two radio base stations «BS I/Node B 1» «BS 2/Node B 2» receiving transmitted protocol data units «PDU» over the radio interface. The protocol data units are forwarded to radio network controller «RNC». RNC combines received PDUs according to selection diversity com- bining. In downlink direction protocol data units are transferred to UE over the radio network controller «RNC» and the two radio base stations «BS I/Node B 1» «BS 2/Node B 2». Identical PDUs transmitted over the radio interface from the radio base stations «BS I/Node B 1» «BS 2/Node B 2» are combined in the receiver of UE.

Figure 3 shows a layered protocol structure, a protocol stack for HS-DSCH. The L2 MAC layer is divided into two sub-layers, an L2 MAC sub-layer and a MAC-hs sub-layer. The MAC-hs plus the MAC layer could be regarded as one sin- gle MAC layer extended to also include hybrid ARQ (Automatic Repeat Request) , HARQ, functionality, allowing combining of successively received (re-) transmissions. However, for reasons of explanation they are preferably regarded as separate sub-layers. Further, on the network side, considering them as separate protocol sub-layers physically better corresponds to the physical entities where they reside. As illustrated in figure 3 on the UTRAN-side (or network side) L2 MAC sub-layer is preferably located in RNC, whereas L2 MAC-hs sub-layer is located in Node B. As the hybrid ARQ protocol combines successively received retransmissions it is a great advantage to have this protocol close to the physical layer and, particularly, in Node B. RLC/MAC control blocks are used to transport RLC/MAC control messages. In an RLC/MAC control

block, all transported segments are of the same RLC/MAC control message. RLC/MAC control blocks are sent at a higher priority than RLC data blocks. RLC/MAC control blocks are sent on ADCH (Associated Dedicated Channel) .

3 ^rd Generation Partnership Project (3GPP) : Technical Specification Group Radio Access Network, Physical Layer Procedures, 3G TS 25.301 v3.6.0, France, September 2000, specifies in chapter 5 Radio Interface Protocol Architecture of a UMTS system. There are three protocol layers: - physical layer, layer 1 or Ll,

- data link layer, layer 2 or L2, and

- network layer, layer 3 or L3.

Layer 2, L2, and layer 3, L3 are divided into Control and User Planes. Layer 2 consists of two sub-layers, RLC and MAC, for the Control Plane and four sub-layers, BMC, PDCP, RLC and MAC, for the User Plane. The acronyms BMC, PDCP, RLC and MAC denote Broadcast/Multicast Control, Packet Data Convergence Protocol, Radio Link Control and Medium Access Control respectively.

3 ^rd Generation Partnership Project (3GPP) : Technical Specification Group Radio Access Network, Spreading and modulation (FDD) (Release 6), 3GPP TS 25.213 vβ.0.0, France, December 2003, describes spreading and modulation for UTRA (Universal Terrestrial Radio Access) Physical Layer FDD (Frequency Division Duplex) mode. Section 4.2 of the Technical Specification describes uplink spreading of, e.g., DPCCH, DPDCHs and HS-DPCCH (High Speed Dedicated Physical Control Channel) . HS-DPCCH is a control channel (in uplink direction) for HSDPA (High Speed Downlink Packet Access) carrying feedback information. After channelization, the real-valued spread signals are weighted by gain factors, β _c for DPCCH, β _ά for all DPDCHs and /JL for HS-DPCCH (if one is

active) . The β _c and β& values are signaled by higher layers or calculated. At every instant in time, at least one of the values β _c and β _d has the amplitude 1.0. The β _c and β _& values are quantized into 4-bit words corresponding to the nominator of a rational number with 15 in the denominator.

3 ^rd Generation Partnership Project (3GPP) : Technical Specification Group Radio Access Network, Physical layer procedures (FDD), (Release 6), 3GPP TS 25.214 v6.3.0, France, September 2004, specifies and establishes the characteris- tics of the physicals layer procedures in the FDD mode of UTRA. Paragraph 5.1.2.5A defines setting of uplink DPCCH/HS-DPCCH power difference. When an HS-DPCCH is active, the power offset Δ _H S-DPCCH for each HS-DPCCH slot shall be set as follows. For HS-DPCCH slots carrying HARQ Ac- knowledgement:

- ΔHS-DPCCH = ΔACK if the corresponding HARQ Acknowledgement is equal to 1.

- ΔHS-DPCCH = Δ _NAC κ if the corresponding HARQ Acknowledgement is equal to 0.

For HS-DPCCH slots carrying CQI:

-" ΔHS-DPCCH ⁼ ΔQQI

The values for Δ _A cκ/ Δ _NA cκ and Δ _C QI are set by higher layers. Then, in non-compressed frames, the gain factor βh _S is calculated according to

_y 6i _la = _y g' _c .10 ^Δ Hs-DK:cH ^/20 ,

where β _c value is signaled by higher-layer or calculated as described in the technical specification. During the pe-

riod between the start and end of a compressed DPCCH frame, when HS-DPCCH is transmitted, /L is calculated according to

ilot . c βh _S = A, _C ,j-10 ^A HS-DPCCH /20 Λf ■Np ■Npilot . N

where /3 _c ,c,j is calculated as described in the technical specification, -V _p ii _o t,c is the number of pilot bits per slot on the DPCCH in compressed frames, and -V _P ii _ot ,N is the number of pilot bits per slot in non-compressed frames.

Thus the gain factor /L ₃ varies depending on the current power offset Δ _HS - _D PCC _H and on whether the uplink DPCCH is cur- rently in a compressed frame.

3 ^rd Generation Partnership Project (3GPP) : Technical Specification Group Radio Access Network, UTRAN Iub interface NBAP signalling (Release 6), 3GPP TS 25.433 v6.3.0, France, September 2004, specifies the radio network layer signaling protocol called Node B Application Part, NBAP, specification to be used for Control Plane over Iub Interface. A number of information elements, IEs, are explained:

- The CQI Power Offset, Δ _CQI , IE indicates Power offset used in the UL between the HS-DPCCH slots carrying CQI (Channel Quality Indication) information and the associated DPCCH.

- The NACK Power Offset, \ _ΆCK , IE indicates Power offset used in the UL between the HS-DPCCH slot carrying HARQ NACK information and the associ- ated DPCCH.

The ACK Power Offset, Δ _ACK , IE indicates Power offset used in the UL between the HS-DPCCH slot carrying HARQ ACK information and the associated DPCCH.

- The CQI Repetition Factor IE indicates the number of consecutive repetitions of the CQI.

- The CQI Feedback Cycle k IE provides the duration of the CQI feedback cycle.

- The ACK-NACK Repetition Factor IE indicates the number of consecutive repetitions of the ACK and NACK.

According to 3GPP TS 25.433 it shall be possible to initiate changes to CQI repetition factor and feedback cycle, as well as ACK-NACK repetition factors from Radio Link Parameter update. The Radio Link Parameter Update procedure is executed by the Node B when the update of HS-DSCH related radio link parameter values are needed on the Node B side. With this procedure. Node B can suggest some HS-DSCH re- lated Radio Link Parameter values to RNC. In FDD (Frequency Division Duplex) mode, if Node B needs to update the CQI Feedback Cycle k, CQI Repetition Factor, ACK-NACK Repetition Factor, CQI Power Offset, ACK Power Offset and/or NACK Power Offset, the Node B shall initiate RADIO LINK PA- RAMETER UPDATE INDICATION message including CQI Feedback Cycle k IE, CQI Repetition Factor IE, ACK-NACK Repetition Factor IE, CQI Power Offset IE, ACiT Power Offset IE and/or NACK Power Offset IE.

European Telecommunications Standards Institute 2004: ETSI TS 125 401 V5.9.0, Universal Mobile Telecommunications System (UMTS); UTRAN overall description (3GPP TS 25.401 version 5.9.0 Release 5), France, September 2004, lists in section 3 a number of definitions and abbreviations, and defines a radio link as a logical association between a single User Equipment and a single UTRAN access point. Its physical realization comprises one or more radio bearer transmissions. A Radio Link Set, RLS, is a set of one or

more Radio Links that has a common generation of Transmit Power Control, TPC, commands in the DL. A UTRAN Access Point is a conceptual point within the UTRAN performing radio transmission and reception. A UTRAN access point is associated with one specific cell, i.e. there exists one UTRAN access point for each cell. It is the UTRAN-side end point of a radio link.

None of the cited documents above discloses a method and system of adjusting transmission power control parameters of one or more wireless links not involved in soft handover in relation to wireless one or more links involved in soft handover or coordination of such parameters.

SUMMARY OF THE INVENTION

Setting of transmission power control offsets for HS-DPCCH as an example from the UMTS specification, when the number of links involved for HS-DPCCH coincides with the number of links for the channel, typically DPCCH, or channels, such as DPCCH and DPDCH, to which the power offset relates is straight forward, at least as long as the links are served by the same base station. However, in soft handover situations or in situations where the links are served by different base station, prior art solution imposes problems.

The ADCH can be in soft handover, like any other ordinary DCH. HSDPA and HS-DSCH cannot. When the ADCH is communi- eating with more than one cell in a soft handover situation it is power controlled by outer loop and inner loop power control. The reference for /L ₃ is either DPDCH or DPCCH, or both. In the uplink DPDCH and DPCCH are power controlled by the outer and inner loop. During soft handover, the fact that DPDCH and DPCCH perceive a diversity effect is considered in the inner and outer loop power control. The information on DPDCH concerning outer loop power control is

terminated in RNC. HS-DPCCH is terminated in Node B serving a present user equipment entity. Consequently, according to prior art it is power controlled as if it would enjoy a diversity effect corresponding to DPCCH or DPDCH when in soft handover, when it actually perceives no diversity gain, since it communicates over a single diversity branch. During soft handover there is consequently a great risk that channel quality of HS-DPCCH can seriously degrade, which jeopardizes both ARQ feedback and CQI information to the HS scheduling entity.

Consequently, there is a need of providing uplink transmission power control compensating for diversity mismatch between various links, sharing control parameters.

An object of the invention is to compensate transmission power control of uplink physical channels sharing one or more power control parameters, in relation to the number of radio links involved in a connection.

Another object is to provide transmission power control by means of a limited number of transmission power control pa- rameters, for uplink physical channels of different diversity order.

It is also an object of the invention to provide a method and system for efficient, signaling of transmission power control.

Finally, it is an object to provide a method and system for signaling of transmission power control optimized for parameter matching.

These objects are met by a method and system of updating uplink power offset parameters, determining a transmission power offset of different uplink physical channels depend-

ing on the cardinality of Radio Link Set or number of radio base stations, RBSes, in an active set.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows schematically selected elements of a UMTS communications system according to prior art.

Figure 2 displays schematically selected elements involved in soft handover diversity in a UMTS communications system according to prior art.

Figure 3 shows a layered protocol structure, a protocol stack for HS-DSCH according to prior art.

Figure 4 illustrates an active set comprising three radio links involving user equipment «UE» and three radio base stations «BS 2», «BS 3», «BS 4» during a soft handover.

Figure 5 shows uplink channel structure of ADCH. For high-speed communications an HS-DPCCH is included.

Figure 6 depicts signaling triggered by RBS according to a first mode of the invention.

Figure 7 monitors signaling triggered by RNC according to a second mode of the invention.

Figure 8 illustrates schematically in a flow chart parameter updating according to the first mode of the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

Setting of transmission power control offsets for HS-DPCCH as an example from the UMTS specification, when the number of links involved for HS-DPCCH coincides with the number of links for the channel, typically DPCCH, or channels, such as DPCCH and DPDCH, to which the power offset relates is straight forward, at least as long as the links are served

by the same base station. However, in soft handover situations or in situations where the links are served by different base station, prior art solution imposes problems.

Figure 5 shows uplink channel structure of ADCH (Associated Downlink Control Channel) . For high-speed communications an HS-DPCCH (High-Speed Dedicated Physical Control Channel) is included. HS-DPCCH carries, e.g., feedback information requesting retransmission or (positively) acknowledging successfully received transmissions «HARQ-ACK» and channel quality information «CQI» destined for MAC-hs protocol layer. In UMTS the HARQ-ACK field of an HS-DSCH sub-frame comprises 10 bits, and the CQI field 20 bits, the sub-frame being transmitted over three time slots. The HS-DPCCH is multiplexed with other channels on ADCH. DPCCH and DPDCH are examples of ordinary channels multiplexed on ADCH, together with HS-DPCCH. The ADCH can be in soft handover, like any ordinary DCH.

Since downlink scheduling of HS-DSCH relies on CQI feedback information, transmitted on HS-DPCCH, downlink transmis- sions could be substantially deteriorated if transmission power of HS-DPCCH is not appropriately adjusted in relation to other physical channels, such as DPDCH and DPCCH, multiplexed on ADCH.

When the ADCH is communicating with more than one cell in a soft handover situation it is power controlled by outer loop and inner loop power control. The reference for β^ _s is either DPDCH or DPCCH, or both. In the uplink DPDCH and DPCCH are power controlled by the outer and inner loop. During soft handover, the fact that DPDCH and DPCCH per- ceive a diversity effect is considered in the inner and outer loop power control- The information on DPDCH concerning outer loop power control is terminated in RNC. HS-

DPCCH is terminated in Node B serving an entity of user equipment for consideration. Consequently, according to prior art it is power controlled as if it would enjoy a diversity effect of multiple communications links correspond- ing to DPCCH or DPDCH when in soft handover, when it actually perceives no diversity gain, since it communicates over a single communications link. During soft handover there is consequently a great risk that channel quality of HS-DPCCH seriously degrade, which jeopardizes both ARQ feedback and CQI information to the HS (high speed) scheduling entity and there is a great risk that no feedback information reaches Node B for downlink scheduling and ARQ acknowledgments, which risks to deteriorate downlink performance substantially.

An active set of a connection including an entity of user equipment comprises all radio base stations, RBSes, involved in the connection, whereas a radio link set is a set of one or more Radio Links that has a common generation of TPC commands in the DL. Often the Active Set and the Radio Link Set are identical. In softer handover they are not.

In softer handover there are a plurality of radio links of one single radio base station.

Figure 4 illustrates an active set comprising three radio links involving user equipment «UE» and three radio base stations «BS 2», «BS 3», «BS 4» during a soft handover. The radio base stations are controlled by different radio network controllers «SRNC» «DRNC» over Iub interfaces. The serving RNC «SRNC» is the RNC responsible for interconnecting to a core network over an Iu interface. The drift RNC «DRNC» assists the SRNC during the soft handover as it controls two of the base stations «BS 3», «BS 4» involved. The RNCs «SRNC», «DRNC» are interconnected over an Iur interface.

According to a first embodiment of the invention, for a connection the discriminating number of diversity branches for ADCH/DPCCH/DPDCH and HS-DPCCH is considered when determining gain factor /5L, and /L ₃ is updated whenever there is an increase in number of links in the active set or radio link set of the connection. When updating /^ ₃ , this is preferably made by increasing the constant power offset for the HS-DPCCH during the time at which the DPDCH relies on gains from macro-diversity.

According to a second embodiment of the invention, repetition factors for HS-DPCCH transmissions (CQI and ACK-NACK repetition factors) are updated. Of course, increased repetition factors implies increased load of control signaling. Preferably the repetition factors are not updated until uplink performance has deteriorated below a threshold. The uplink performance degradation is preferably detected from number of repeated transmission failures and retransmissions in the base station/Node B. Either common or disjoint one or more triggers are used for updating of different repetition factors.

The repetition factors may interfere with CQI feedback cycle (the frequency with which a UE reports CQI) . Therefore the repetition factor updating is preferably coordinated with the CQI feedback cycle according to the invention.

According to the first embodiment of the invention, parameters for ADCH are signaled to RBS in Radio Link Reconfiguration and Radio Bearer Setup messages in the radio bearer setup procedure. Parameters related to CQI, such as Δ _CQI , CQI repetition factor and CQI feedback cycle, are signaled to UE in downlink HS-PDSCH information message as Measurement Feedback info. Parameters related to ACK/NACK, such

as Δ _A cκ _/ Δ _NACK and ACK-NACK repetition factor, are included as Uplink DPCH power control info fields.

There are two modes of signaling according to the invention. The first mode adopts a synchronized procedure for parameter updating, and the second an unsynchronized procedure. According to the invention, a particular mode is preferably selected conditionally depending on the particular parameters.

The first mode is required when CQI repetition factor, CQI feedback cycle or ACK-NACK repetition factors are to be changed, whereas both modes are applicable for changing of power offsets. Preferably, parameter updating according to the second embodiment triggered from RBS will be signaled according to the first mode of signaling and parameter up- dating according to the first embodiment related to radio link set size updates will be signaled according to the second mode of signaling.

Figure 6 depicts signaling triggered by RBS according to the first mode. Parameter update, e.g. of CQI repetition factor, CQI feedback cycle and ACK-NACK repetition factor are triggered by radio base station «RBS» by sending of an RL Parameter Update Indication «R1» to the controlling RNC. At RL Reconfiguration Prepare «R2» new values of repetition factors are sent to the RBS with the serving HS-DSCH con- nection. With RL Reconfiguration Ready signal «R3», new values are stored in RBS. Activation time, in terms of CFN

(Connection Frame Number) , is then calculated in RNC and sent to RBS «R4» in an RL Reconfiguration Commit signal.

(Node B, RNC and UE uses CFN for DCH and Common Transport Channels frame transport references.) RNC sends «R5» the new one or more parameters, including activation time, in terms of CFN, to UE over RBS. At activation time «R6» the

new parameters are in effect. A Physical Channel Reconfiguration Complete signal confirms/completes the physical channel reconfiguration.

Figure 7 monitors signaling triggered by RNC according to the second mode. Subsequent to triggering «C1» of updating of one or more transmission power control related parameters Δ _A cκ, Δ _NA C _K and Δ _CQ i, new parameters are sent to UE over RBS in Physical Channel Reconfiguration signaling «C2». UE confirms reception and parameter updating in Physical Chan- nel Reconfiguration complete signaling.

According to the first mode, Node B initiates parameter update preferably when detecting particular CQI error patterns of received CQI, each non-reliable CQI being logged as a CQI error event, if at least one updated parameter (CQI repetition factor or ACK-NACK repetition factor) differs from the existing parameters. During soft handover or diversity combining, if CQI repetition factor is greater than 1 errors in CQI after combining of diversity branches is considered for logging, not errors in individual CQIs of the various diversity branches or repetitions of particular one or more CQIs. Preferred error patterns for triggering of HS-DPCCH parameter change are listed in table 1 together with preferred parameter settings. In the table cqiErrors refers to a predefined number of consecutive CQI error events, and cqiErrorsAbsent a predefined number of received consecutive one or more CQIs in absence of CQI error event.

Table 1

* repetition factor - feedback cycle consistency check

n _c _p _rev and n _a _prev in table 1 refer to the (existing) CQI repetition factor the (existing) ACK-NACK repetition factor, respectively, applied when the parameter update was triggered by a detected error pattern in the first column of table 1. If there are more than cqiErrors consecutive CQI error events and if n _c , the updated CQI repetition fac- tor, differs from n _c _p _r ev/ the CQI feedback cycle is updated if a repetition factor - feedback cycle consistency check indicates a conflict of the updated CQI repetition factor and existing CQI feedback cycle. In case the consistency check indicates a conflict, CQI feedback cycle is in- creased. Preferably the updated CQI feedback cycle, measured in milliseconds, is set to 2 times the CQI repetition factor. Preferably there is no corresponding decrease of CQI feedback cycle when CQI repetition factor is decreased as a CQI repetition factor decrease will generally not cause any CQI feedback cycle consistency problem. The invention, however, does not exclude a corresponding decrease of CQI feedback cycle. The procedure is illustrated schematically in a flow chart in figure 8.

When the signaling message Radio Link Parameter Update Indication has been sent to the RNC, counters of number of continuous CQI error events and number of continuous error free CQI arrivals are reset. Subsequent to the reset of the counters, there is preferably an interrupt time duration during which the counters are not updated in order to provide some time for RNC to issue updates, without having to transmit several triggers. The interrupt time duration is controlled by a timer. Updating of the counters is preferably continued at expiry of the interrupt time duration or at a CFN specified for the update. The counters are preferably reset at HS-DSCH cell change, when the serving HS-DSCH cell is changed. Potential changes of ACK-NACK repetition factor is communicated with the entity schedul- ing the repetitions, facilitating future scheduling, as an increase of ACK-NACK repetition factor limits scheduling opportunities.

According to the second mode, new power-offset factors are applied if the number of radio link sets is changed. Pref- erably there are two different sets of power control related parameters (Δ _AC κ/ Δ _NA cκ and ΔCQI, ) applied depending on the number of radio link sets. During softer handover of HS-DPCCH involving only one RBS, there is no need to trigger power offset factor update, since HS-DPCCH of different radio links are combined according to Maximum Ratio Combining.

In summary, the second mode of the invention does not require coordination between UE and Node B, but UE is updated and Node B can then be informed thereof unsynchro- nized, whereas the first mode of the invention requires coordination/synchronization of UE and Node B updates.

In this patent application acronyms such as UE, RBS, RNC, HSDPA, HS-DPCCH ₇ HS-DPDCH, HS-DSCH, ADCH, are applied. However, the invention is not limited to systems with entities with these acronyms, but holds for all communications systems operating analogously.

The invention is not intended to be limited only to the embodiments described in detail above. Changes and modifications may be made without departing from the invention. It covers all modifications within the scope of the following claims.