BACKGROUND AND DESCRIPTION OF RELATED ART Retransmission of data to or from a mobile station, MS, or user equipment, UE, is previously known. It is also known to use a radio link control layer of a UMTS protocol struc- ture in an acknowledged mode for dedicated channels.

In acknowledged mode, retransmissions are undertaken in case of detected transmission errors not recovered by for- ward error control. This is also called automatic repeat request, ARQ. With ARQ, retransmissions can be undertaken unless a transmitted message is (positively) acknowledged or if it is negatively acknowledged. Generally there are time limits for the respective positive and negative acknowledgements to be considered.

Within this patent application, a radio network controller, RNC, is understood as a network element including a radio resource controller. Node B is a logical node responsible for radio transmission/reception in one or more cells to/from User Equipment. A base station, BS, is a physical entity representing Node B.

Radio link control, RLC, is used within radio communica- tions systems like General Packet Radio Services, GPRS, and UMTS.

International Patent Application W00105121 describes a technique for providing a secure link in a mobile communi- cation system including mechanisms for hard handover of a link in acknowledged mode. Data is tunneled.

A channel dedicated to a specific UE is referred to as a Dedicated Channel, DCH. A channel that is not a dedicated channel is called a common or shared channel.

UK patent application GB, application no. 0027148. 6, describes channel switching between dedicated and common channels.

3rd Generation Partnership Project (3GPP): Technical Speci- fication Group Radio Access Network, Physical Layer Proce- dures, 3G TS 25.301 v3.6.0, France, September 2000, speci- fies in chapter 5 Radio Interface Protocol Architecture of a UMTS system. There are three protocol layers: - physical layer, layer 1 or L1, - 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 4 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.

Figure 1 illustrates a simplified UMTS layers 1 and 2 pro- tocol structure for the so called Uu Stratum, UuS, or Radio Stratum, between a user equipment UE and a Universal Ter- restrial Radio Access Network, UTRAN.

Radio Access Bearers, RABs, make available radio resources (and services) to user applications. For each mobile sta- tion there may be one or several RABs. Data flows (in the form of segments) from the RABs are passed to respective Radio Link Control, RLC, entities which amongst other tasks buffer the received data segments. There is one RLC entity for each RAB. In the RLC layer, RABs are mapped onto re- spective logical channels. A Medium Access Control, MAC, entity receives data transmitted in the logical channels and further maps logical channels onto a set of transport channels. One transport channel is Downlink Shared Chan- nel, DSCH.

Transport channels are finally mapped to a single physical transport channel which has a total bandwidth allocated to it by the network. In frequency division duplex mode, a physical channel is defined by code, frequency and, in the uplink, relative phase (I/Q). In time division duplex mode a physical channel is defined by code, frequency, and time- slot. The DSCH, e. g., is mapped onto one or several physi- cal channels such that a specified part of the downlink re- sources is employed.

PDCP provides mapping between Network PDUs (Protocol Data Units) of a network protocol, e. g. the Internet protocol, to an RLC entity. PDCP compresses and decompresses redun- dant Network PDU control information (header compression and decompression).

For transmissions on point-to-multipoint logical channels, BMC stores at UTRAN side Broadcast messages received from an RNC, calculates the required transmission rate and re- quests for the appropriate channel resources. It receives scheduling information from the RNC, and generates schedule messages. For transmission the messages are mapped on a

point-to-multipoint logical channel. At the UE side, BMC evaluates the schedule messages and deliver Broadcast Mes- sages to upper layer in the UE.

3G TS 25.301 also describes protocol termination, i. e. in which node of the UTRAN the radio interface protocols are terminated, or equivalently, where within UTRAN the respec- tive protocol services are accessible. Section 5.6.5 de- scribes protocol termination for DSCH. The RLC protocol for DSCH is terminated in Serving Radio Network Controller, SRNC, for both the control and user planes.

3rd Generation Partnership Project (3GPP): Technical Speci- fication Group Radio Access Network, Physical Layer Proce- dures, 3G TS 25.322 v3. 5.0, France, December 2000, speci- fies the RLC protocol. The RLC layer provides three serv- ices to the higher layers: - transparent data transfer service, - unacknowledged data transfer service, and - acknowledged data transfer Service Subsections 4.2.1.1 and 4.2.1.2 describe transparent mode entities and unacknowledged mode entities. Basically, RLC differences of the two modes reside in management of packet overhead. In transparent mode no overhead is added or re- moved by RLC. In subsection 4.2.1.3 an acknowledged mode entity, AM-entity, is described (see figure 4.4 of the 3GPP Technical Specification). In acknowledged mode automatic repeat request, ARQ, is used. The RLC sub-layer provides ARQ functionality closely coupled with the radio transmis- sion technique used. The three modes - Transparent Mode, TM, - Unacknowledged Mode, UM, and

- Acknowledged Mode, AM are hereinafter collectively referred to as RLC modes.

None of the cited documents above discloses a dynamic RLC configuration and termination point.

SUMMARY OF THE INVENTION In accordance with 3G TS 25.301, no macrodiversity is ap- plied for DSCH; i. e. a specific DSCH is transmitted in a single cell only. As described above the RLC protocol, and correspondingly the ARQ, is terminated in the SRNC. How- ever, when the DSCH is transmitted in only a single cell at a time, the retransmission delay would reduce considerably if retransmissions were terminated in the BS, as the round trip delay would be decreased.

When a UE is distant to a base station, retransmission re- quests are likely to be transmitted to one or more base stations that did not transmit data at first instance. Re- transmission will then involve transmissions between the two or more BSes and involve an RNC, nullifying the advan- tage of a termination point located in the BS, and poten- tially increasing retransmission delay.

Further, when a user equipment, like UE 1 in figure 2, is not involved in soft handover, it is advantageous in terms of time delay to have retransmissions terminated in BS 1/Node B 1, whereas when it is involved in soft handover it is advantageous to have the termination point located at an RNC.

Consequently, an object of this invention is to achieve a method and system of fast retransmissions to a UE near a BS and allowing for robust retransmissions using soft handover when necessary.

It is also an object to present an adaptive relocation of transmitting point.

These objects are met by dynamically switching between RLC configurations depending on radio conditions and UE loca- tions. The RLC configuration and the location of transmit- ting point are adapted to UE location, number of transmit- ters and PDU size. Relocation is preferably achieved by means of RLC tunneling.

Preferred embodiments of the invention, by way of examples, are described with reference to the accompanying drawings below.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 displays a layered protocol structure, according to prior art, in a radio communications system.

Figure 2 schematically illustrates a user equipment commu- nicating, according to prior art, with one or two base sta- tions.

Figure 3 shows communication with ARQ terminated in Node B, according to the invention, between a UE and a base station involved in a connection between RNC and the UE.

Figure 4 shows communication with ARQ terminated in RNC, according to the invention, between a UE and two base sta- tions involved in a connection between RNC and the UE.

Figure 5 schematically illustrates two protocol layers, according to the invention, from a multilayer protocol.

Figure 6 illustrates the principle, according to the in- vention, of RLC relocation.

DESCRIPTION OF PREFERRED EMBODIMENTS With reference to figure 3, Node B 1 and Node B 2 are logi- cal nodes responsible for radio transmission/reception in one or more cells to/from the User Equipment UE. BS 1 and BS 2 are physical entities representing Node B 1 and Node B 2 respectively. Node B 1 and Node B 2 terminate the air interface, called Uu interface within UMTS, between UE and respective Node B towards the radio network controller RNC. In UMTS the interface between a Node B and an RNC is called Iub interface.

In an exemplary situation UE communicates over a radio link associated with BS 1. Packet switched data is transmitted in protocol data units, PDUs, in both directions. If a protocol data unit PDU is received in error and the error is not recovered by forward error correction, the PDU is retransmitted.

In accordance with 3G TS 25.301, no macrodiversity is ap- plied for DSCH; i. e., a specific DSCH is transmitted in a single cell only. As described above the RLC protocol, and correspondingly the ARQ, is terminated in the RNC, accord- ing to prior art. However, when the DSCH is transmitted in only a single cell at a time, the retransmission delay is reduced considerably by terminating retransmissions in BS 1 or Node B 1 in place of RNC as the round trip delay is thereby decreased.

An ARQ-machine is a physical entity from which retransmis- sions are initiated. In figure 3 there is an ARQ-machine ARQ in each of Node B 1 and UE.

With reference to figure 2, user equipment UE 1 being close to a base station BS 1 will in general not be involved in soft handover. A user equipment more distant to BS 1, like

user equipment UE 2, is likely to communicate over radio links associated with more than one BS, BS 1 and BS 2. In this figure the BSes are indicated to operate omnidirec- tionally. However, the invention is not limited to omnidi- rectional base stations. It can readily be used irrespec- tive of whether the base stations use directional or omni- directional antenna radiation patterns.

Excessive retransmissions reduce throughput and system per- formance. Soft handover can reduce the amount of transmis- sion errors not recovered.

In figure 4, user equipment UE is involved in soft handover for at least one link direction (up or down). A macrodi- versity or soft handover combiner for the uplink direction Comb is located at the RNC, see figure 4. When soft hand- over is used also in downlink direction a corresponding combiner in user equipment UE is utilized. Depending on the outcome of the macrodiversity combining, there may be no need for retransmission. Further, when a UE is distant to a base station, retransmission requests are likely to be transmitted to one or more base stations that did not transmit data at first instance. Retransmission will then involve transmissions between two or more base sta- tions/Nodes B and involve an RNC, nullifying the advantage of a termination point located in Node B, and potentially increasing retransmission delay. In figure 4 the ARQ- machine ARQ is located in RNC and UE respectively.

Consequently, when user equipment UE is not involved in soft handover, it is advantageous in terms of time delay to have retransmissions terminated in a Node B, Node B 1, see figure 3. When it is involved in soft handover with radio links associated with two or more Nodes B, Node B 1 and

Node B 2, it is advantageous to have the termination point located at radio network controller RNC, see figure 4.

This invention meets its objectives and solves the problems described above by introducing an ARQ machine, not being fixed to one geographical location. According to the in- vention the ARQ-machine is dynamically relocated between a Node B and an RNC as need be to achieve a sufficiently small retransmission delay. Basically, four alternatives of relocation of an ARQ-machine are known: 1. Protocol State Transfer, 2. Multiple ARQ Protocols, 3. Service Data Unit Transfer, and 4. RLC Tunneling.

A network layer PDU or L3 PDU can comprise several RLC PDUs, as illustrated in figure 5. RLC PDUs are reassembled into service data units, SDU, prior to delivery to higher layer PDU. The L3 protocol can be, e. g., the Internet Pro- tocol, IP. Upon reception from L3, SDUs are segmented into RLC PDUs.

Protocol State Transfer moves/transfers the whole protocol state, including state variables and buffers to the new network node.

With Multiple ARQ Protocols, data is secured by having two or more levels of ARQ protocols. One protocol level is run between UE and Node B, another protocol level is run be- tween UE and RNC. Upon relocation, no particular measures need to be undertaken for PDUs in the old ARQ machine, as a potential loss of data is recovered by higher level ARQ protocols.

In Service Data Unit transfer, SDUs are buffered until all RLC PDUs carrying an SDU are successfully transmitted.

Upon relocation, all stored (complete) SDUs are moved from the old ARQ-machine to the new ARQ machine. The SDUs are segmented into RLC PDUs and transmitted at the new ARQ-ma- chine.

Finally, using RLC tunneling for relocation of an ARQ-ma- chine there will be two RLC protocols considered: the old/existing RLC protocol and a new RLC protocol at the new location. One or more RLC PDUs buffered but not yet suc- cessfully transmitted to the destination from the old RLC protocol are tunneled through the new RLC protocol. The old RLC protocol does not perform the ARQ function of the tunneled RLC PDUs. In reverse direction, the old RLC pro- tocol assembles old RLC PDUs provided by the new RLC proto- col until a SDU or L3 PDU, only partially completed at the time of relocation, is completed. Subsequent SDUs or L3 PDUs will be assembled at the new RLC protocol. In UMTS the ARQ protocols are RLC protocols. This invention also applies if other than the RLC protocol is used for ARQ.

RLC tunneling also enables RLC reconfiguration in the new retransmission point. This is important as performance can be improved in the new location by a change of e. g. PDU size.

In one embodiment two or more of the basic alternatives for relocation are implemented. However, only one alternative is on at a time the other alternatives being switched off.

Figure 6 illustrates how an ARQ-machine is dynamically re- located. When a UE is close to base station BS 1, the ARQ machine of the UTRAN-side is located in BS 1. As the UE approaches BS 2 a link associated with BS 2 will be estab- lished for soft handover. The UTRAN-side ARQ-machine will

then be relocated from ARQ I in Node B 1 to ARQ II in RNC.

If the UE moves further towards base station BS 2 the link associated with BS 1 will be released and the ARQ machine relocated from ARQ II in RNC to ARQ III in Node B 1. If only hard handover is used, the ARQ machine is preferably located in the base stations. Then, relocation of the ARQ- machine is from ARQ I in Node B 1 to ARQ III in Node B 2.

In figure 6 the UE-side ARQ-machine is never relocated.

However, due to reconfigurations of the ARQ-machine at UT- RAN-side, it can be reconfigured accordingly.

Figure 7 shows two base stations BS 1 and BS 2 and an RNC.

Initially only BS 1 is communicating with the user equip- ment UE. The base stations comprise means 1 for reconfig- uring a link layer protocol and means 2 for determining one or more communication parameters, such as number of active links, propagation path loss, signal to noise ratio, signal to interference ratio, propagation time. The one or more parameters are determined in relation to user equipment UE, involving means 8-10 for transmission of transmitted and received signal strength, signal timing and interference level respectively used in the process of determining the communication parameters. BS 1 and BS 2 also comprise means 3 for changing PDU size. As PDUs are communicated to and from user equipment UE it has corresponding means 11.

Means 5 and 6 of RNC correspond to means 1 and 2 of the base stations since both a base station and an RNC are le- gitimate RLC termination points. Means 4 of BS 1 and BS 2 and means 7 of RNC represent means for transferring a pro- tocol termination point by RLC tunneling, Service Data Unit Transfer, Multiple ARQ protocols or Protocol State Trans- fer.

A person skilled in the art readily understands that the receiver and transmitter properties of a BS or a UE are

general in nature. The use of concepts such as BS, UE or RNC within this patent application is not intended to limit the invention only to devices associated with these acro- nyms. It concerns all devices operating correspondingly, or being obvious to adapt thereto by a person skilled in the art, in relation to the invention. As an explicit non- exclusive example the invention relates to mobile stations without a subscriber identity module, SIM, as well as user equipment including one or more SIMs. Further, protocols and layers are referred to in close relation with UMTS ter- minology. However, this does not exclude applicability of the invention in other systems such as GPRS or with other protocols and layers of similar functionality.

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