WO2009025609A1

WO2009025609A1 - Method and arrangement in a communication network system

Info

Publication number: WO2009025609A1
Application number: PCT/SE2008/050601
Authority: WO
Inventors: Stefan Wager; Stefan Parkvall; Dirk Gerstenberger; Johan Bergman; Fredrik Gunnarsson; Bo Hagerman; Claes Tidestav; Mats SÅGFORS
Original assignee: Telefonaktiebolaget L M Ericsson (Publ)
Priority date: 2007-08-20
Filing date: 2008-05-22
Publication date: 2009-02-26
Also published as: WO2009025609A9

Abstract

The object of the present invention is to provide a mechanism for improving RACH performance. The object is achieved by a method in a user equipment (140) for random accessing the user equipment (140) to a base station (120). The user equipment (140) and the base station (120) are comprised in a communication network system (110). An acknowledgement to send a message to the network node (110,120) is received (203,301) from a network node (110,120) comprised in the communication network system (100). The user equipment then sends (204,302) the message to the network node (110,120) using Hybrid Automatic Retransmission reQuest HARQ being in a CELL_FACH state.

Description

METHOD AND ARRANGEMENT IN A COMMUNICATION NETWORK SYSTEM

TECHNICAL FIELD

The present invention relates to a method and an arrangement in a user equipment and a method and an arrangement in a network node. In particular, it relates to random accessing a user equipment to a base station.

BACKGROUND

In a common radio network architecture a user equipment may be a mobile terminal by which a subscriber can access services offered by an operator's core network. A radio access network is the part of the network that is responsible for the radio transmission and control of the radio connection. A radio network subsystem controls a number of base stations in the radio access network. A radio network controller controls radio resources and radio connectivity within a set of cells. The base station handles the radio transmission and reception within one or more cells. A cell covers a geographical area. The radio coverage in a cell is provided by radio base station equipment at the base station site. Each cell is identified by a unique identity, which is broadcast in the cell. There may be more than one cell covering the same geographical area. A radio link is a representation of the communication between a user equipment and one cell in the radio access network, lub/lur interfaces are interfaces connecting the different nodes in the radio access network. The lub interface interconnects the radio network controller to the base station. The lur interface provides interconnection between one radio network controller and another. User data is transported on so-called transport bearers on these interfaces. Dependant on the transport network used, these transport bearers may e.g. be mapped to ATM Adaptation Layer type 2 (AAL2) connections in case of an Asynchronous Transfer Mode (ATM) based transport network or User Datagram Protocol (UDP) connections in case of an Internet Protocol (IP) based transport network.

A user equipment in an idle state monitors system information of base stations within range, to inform itself about candidate base stations in the service area etc. When a user equipment needs access to services, it sends a request over the Random Access CHannels (RACH) to a radio network controller via the most suitable base station, typically the one with the most favourable radio conditions. This is performed in two steps, first a preamble of the request is sent and when acknowledged by the base station, the request message is sent. Since the uplink propagation of the RACH is only approximately known, the user equipment gradually increases the transmission power of a preamble until either it has been acknowledged via the Acquisition Channel AICH, or the maximum number of attempts has been reached. The preamble and the request message are sent via the base station to the radio network controller. Upon acknowledgement, the RACH request message is sent. After admission control, the radio network controller initiates the connection via the most suitable base station if there are available resources. Uplink coverage is thus a necessity in order to successfully complete random access.

Currently, High Speed Downlink Shared Channel (HS-DSCH) is introduced in the CELL_FACH state.

CELL_FACH state is characterised by: -The user equipment is assigned a default common or shared transport channel in the uplink (e.g. Random Access Channel (RACH)) that it can use anytime according to the access procedure for that transport channel.

-The position of the user equipment is known by UTRAN on cell level according to the cell where the user equipment last made a cell update. The HS-DSCH introduction in the CELL_FACH state may result in an imbalance in the uplink/downlink performance in this state, which in turn implies low bit rate and repetitive ramping.

SUMMARY

The object of the present invention is to provide a mechanism for improving RACH performance.

According to a first aspect of the present invention, the object is achieved by a method in a user equipment for random accessing the user equipment to a base station. The user equipment and the base station are comprised in a communication network system. The user equipment is in a CELL_FACH state. An acknowledgement to send a message to the network node is received from a network node comprised in the communication network system. The user equipment then sends the message to the network node using Hybrid Automatic Retransmission reQuest "HARQ". According to a second aspect of the present invention, the object is achieved by a method in a network node, for random accessing a user equipment to a base station. The network node, the user equipment and the base station are comprised in a communication network system. The user equipment is in a CELL_FACH state. The network node sends power control feedback to the user equipment. The network node then receives a message from the user equipment. The user equipment used Hybrid Automatic Retransmission request (HARQ) for the transmission of the message and the user equipment used the sent power control feed back for sending the message. The message is sent for the first time, or the message is resent since the user equipment did not receive any acknowledgement for a previous attempt to send the message.

According to a third aspect of the present invention, the object is achieved by an arrangement in a user equipment for random accessing the user equipment to a base station. The user equipment and the base station are comprised in a communication network system. The user equipment is arranged to be in a CELL_FACH state. The user equipment arrangement comprises a receiving unit configured to receive from a network node comprised in the communication network system, an acknowledgement to send a message to the network node. The user equipment arrangement further comprises a sending unit configured to send the message to the network node using Hybrid Automatic Retransmission reQuest "HARQ.

According to a fourth aspect of the present invention, the object is achieved by an arrangement in a network node for random accessing a user equipment to a base station. The network node, the user equipment and the base station are comprised in a communication network system. The user equipment is arranged to be in a CELL_FACH state. The network node arrangement comprises a sending unit further being configured to send power control feedback to the user equipment. The network node arrangement further comprises a receiving unit configured to receive the message from the user equipment according to the sent acknowledgement. The user equipment used Hybrid Automatic Retransmission request (HARQ) for the transmission of the message, and the user equipment used the sent power control feed back for sending the message. The message being sent for the first time, or the message is resent since the user equipment did not receive any acknowledgement for a previous attempt to send the message. Since the HARQ is introduced in the CELL_FACH state, it is possible for the user equipment to send a message to the network node, when the user equipment 140 is in CELL_FACH state, which improves RACH performance. This which otherwise was only possible when the user equipment was dedicated a physical channel, i.e. leave the CELL_FACH state and be transferred in to CELL_DCH state.

Advantages of the present invention comprise higher bit rates for uplink transmission in CELL_FACH state, lower delay and improved state transition to CELL DCH.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described in more detail with reference to attached drawings illustrating exemplary embodiments of the invention and in which:

Figure 1 is a schematic block diagram illustrating embodiments of a communication network system.

Figure 2 is a signalling scheme illustrating embodiments of a method in a communication network system.

Figure 3 is a flow chart illustrating embodiments of a method in a user equipment.

Figure 4 is a schematic block diagram illustrating embodiments of a user equipment arrangement.

Figure 5 is a flow chart illustrating embodiments of a method in a network node.

Figure 6 is a schematic block diagram illustrating embodiments of a network node arrangement.

DETAILED DESCRIPTION The invention is defined as a method and an arrangement which may be put into practice in the embodiments described below.

Figure 1 depicts a communication network system 100, such as a 3rd Generation Partnership Project (3GPP) WCDMA system, comprising a radio access network, such as e.g. the UMTS Terrestrial Radio Access Network (UTRAN) architecture. The radio access network comprises a network node such as e.g. a radio network controller 110, connected to at least one network node such as a radio base station 120. The base station 120 may be any type of base station such as e.g. a NodeB. The radio access network is connected over an interface such as e.g. a UMTS lu-interface to a core network 130. The core network 130 may be a connection-oriented external core network such as e.g. the Public Switched Telephone Network (PSTN) or the Integrated Services Digital Network (ISDN), and/or a connectionless external core network as the Internet. The UMTS lu-interface enables interconnection of Radio Network Controllers with Core Network nodes. The radio access network and the core network 130 provide communication and control for at least one user equipment 140, 141 , 142, 143. The user equipment 140 uses channels 150 such as downlink channels (i.e. base-to-user or forward) and uplink channels (i.e. user-to-base or reverse) to communicate with at least one base station 120 over a radio or air interface. In figure 1 , four user equipments 140, 141 , 142, 143 are depicted. For the simplicity, in the following description only one user equipment 140 is used in the examples, but it may be any of the user equipments 140, 141 , 142, 143.

According to some embodiments of the present solution, the communication system is herein described as a WCDMA communication system. The skilled person, however, realizes that the inventive method and arrangement works very well on all communications systems. The user equipment 140 may be a mobile station such as a mobile telephone (a "cellular" telephone) and a laptop with mobile termination and thus can be, for example, a portable, pocket, hand-held, computer-included or car-mounted mobile device which communicate voice and/or data with the radio access network.

When the user equipment 140 wishes to access a service in the radio access network, it starts the transmission procedure. In this process the user equipment 140 is in a CELL_ Forward Access Channel (FACH) state, a so-called CELL_FACH state.

In the present solution, the CELL_FACH state implies that: -A dedicated physical channel such as e.g. Enhanced Dedicated Channel (E-DCH), is assigned only temporarily to the user equipment 140 after preamble ramping.

-The user equipment 140, when High Speed (HS) capable operated, may continuously monitor HS-SCCH in the downlink.

5 -The user equipment is assigned a default common or shared transport channel in the uplink (e.g. Random Access Channel) that it can use anytime according to the access procedure for that transport channel.

-The position of the user equipment is known by UTRAN on cell level according to the cell where the user equipment last made a cell update. 10

To improve the link adaptation for the random access channel by increasing the transmitted bit rate and achieve shorter Internet Protocol (IP) packet transmission times, HARQ and network feedback is introduced in the random access procedure. The feedback may be transmitted on e.g. HS-SCCH or E-AGCH. "This may be achieved by 15 activating E-DCH for users in CELL_FACH.

The transmission procedure will be described with reference to a signalling scheme depicted in Figure 2. The scheme depicts signalling between the user equipment and a network node. The network node may be a base station or another network node such a radio control node. For the simplicity, network node in Figure 2 is denoted base station 20 120.

201. The transmission procedure in 3GPP starts with a Physical Random Access CHannel (PRACH) preamble power ramping. This means that the user equipment 140 first sends a preamble of a message such as e.g. a higher layer message to

25 request access such as a Random Access CHannel (RACH) preamble, to the base station 120. Since the uplink propagation of the random access channel is only approximately known, the user equipment 140 attempts sending the preamble and gradually increases the transmit power of the preamble for each attempt until either it has been acknowledged via an acquisition channel such as e.g. Acquisition

30 Indicator Channel (AICH), or a predetermined maximum number of attempts have been reached. This may be performed by the user equipment 140 randomly selecting one out of 16 available preamble signatures. This signature may be transmitted in one of the 15 access slots. In 3GPP, the random-access transmission may be based on a slotted ALOHA approach with fast acquisition indication. A user

35 equipment may start the random-access transmission at the beginning of a number of well-defined time intervals, denoted access slots. There are 15 access slots per two frames. If the user equipment does not detect Acquisition Indicator Channel transmission, it selects a new preamble signature, increases the transmit power by a pre-configured delta, and transmits it 3 or 4 access slots later. Once the user 5 equipment 140 has received from the base station 120 an acknowledgement that the preamble is detected, it stops the attempts of sending the preamble, i.e. the power ramping is stopped. In some embodiments the user equipment 140 sends the message without sending a preamble first.

10 202. When the base station 120 detects the preamble, it sends an acknowledgement e.g. on the acquisition channel to the user equipment 140. Up to this step, the random access procedure is part of prior art. From next step 203, and onwards the procedures differs from prior art.

15 203. When the user equipment 140 has received the acknowledgement, it transmits the message using Hybrid Automatic Retransmission request (HARQ) on a physical channel such as e.g. on Physical Random Access Channel (PRACH) or on Enhanced Dedicated Physical Data CHannel (E-DPDCH), HARQ may be a part of E-DPDCH and may be a part of PRACH. In some embodiments the preamble may

20 be used to indicate whether PRACH or E-DCH is accessed.

Transmit power

For the transmission, the user equipment 140 uses transmit power relative to the last preamble sent before being acknowledged, plus an offset depending on the chosen transport format. A transport format may in 3GPP be defined as a format

25 offered by Layer 1 to Medium Access Control (MAC) (and vice versa) for the delivery of a transport block during a Transmission Time Interval on a Transport Channel. The offset, and indirectly the max transport format may be broadcasted from the base station 120, or it may be calculated from the Uplink Interference, which is already broadcasted by the base station 120 on Broadcast Control Channel

30 (BCCH).

Transport format

The Transport Format Combination Indicator (TFCI) in the control part of the Physical Random Access Channel may be used to indicate whether legacy Random Access Channel or Enhanced Random Access Channel is used. The Transport

35 Format Combination Indicator may span 30 uncoded bits, which after (32,10) Reed Solomon (RS) coding carries 10 Transport Format Combination Indicator bits. This should be sufficient to point out both legacy formats and new Enhanced Random Access Channel formats. Some Transport Format Combination Indicator values could be reserved to indicate the usage of the new Random Access Channel. Alternatively, the indication of the new Random Access Channel may be done e.g. using an offset in the uncoded Transport Format Combination Indicator code word or inverting the Transport Format Combination Indicator bits prior to coding or in other ways.

Spreading and modulation may be the same as for Random Access Channel, except that the channelization code for Random Access Channel may also support smaller spreading factor to increase the bit rate. Current minimum is spreading Factor equal to 32, which may be reduced to 16 or 8 to support larger transport formats.

In some embodiments the E-DPDCH may be used to transmit the uplink data in the CELL_FACH state to facilitate HARQ. In this case, the same transport formats as in CELL_DCH can be supported, with a possible maximum to limit interference.

Another possibility to increase the transport format is to increase the Transmission Timing Interval and, in addition to 10 and 20 ms, also support e.g. 40 ms. This is useful to allow for reasonably large payloads without causing large interference peaks that may result from very high instantaneous data rates in a short time period. The Transmission Timing Interval of the Enhanced Random Access Channel may be indicated as part of the broadcasted system information. One drawback of a longer Transmission Timing Interval, however, is the increased risk of an outdated power ramping level. Larger transport formats open up for the use of turbo coding. Turbo codes may be defined as a class of high-performance error correction codes which are finding use in deep space satellite communications and other applications where designers seek to achieve maximal information transfer over a limited-bandwidth communication link in the presence of data-corrupting noise. In some embodiments channel coding may be similar to Enhanced Dedicated Channel (E-DCH), i.e. 1/3 rate turbo coding, puncturing and soft combining through HARQ.

204. Feedback is sent from the base station 120 to the user equipment 140. The user equipment 140 listens for feedback. In some embodiments, the feedback may be sent also during the transmission of the message in step 203 if the message is long and segmented into several packets. In some embodiments, user equipment specific feedback such as e.g. HARQ feedback, and/or power or rate control, is transmitted from the base station 120 to the user equipment 140 on a modified E- DCH Absolute Grant Channel, by using stored E-DCH Radio Network Temporary Identifier (E-RNTI). The feedback may be an instruction to the user equipment 140 to reduce the transmit power by a fixed step, e.g. 1-2dB. These embodiments are however slower compared to the embodiments using Acquisition Indicator Channel, depending on the Transmission Time Interval (TTI).

In some embodiments the modified E-DCH Absolute Grant Channel may used to control the user equipment transport format selection like in normal E-DCH operation. In some embodiments using E-DCH, the feedback is sent from base station 120.

205. This is an optional step of power ramping procedure. Since the user equipment 140 uses HARQ, it will retransmit the message offset to the first transmission, if the user equipment 140 does not receive an acknowledgement. In some embodiments, the power ramping procedure is repeated in this step, to get an updated transmit power level. This may be performed in the same way as in step 201. The preamble signature for the retransmission of the message may be the same as used for the preamble transmission as this is used by the base station 120 to correctly soft combine the transmissions. Soft combining generally means that the information obtained with each decoding attempt is preserved and incorporated with the retransmitted copies of the codeword. As the message will be soft combined with the first transmission attempt of the message sent in step 203, the transport format may not be changed. E.g. in embodiments where E-DCH is used, this second power ramping is not used.

206. This is an optional step if the power ramping procedure is used here. Further, when the base station 120 detects the preamble in 205, it sends an acknowledgement e.g. on the acquisition channel to the user equipment 140.

207. Since the user equipment 140 uses HARQ, the message is retransmitted offset to the first transmission in this step, if the user equipment 140 does not receive an acknowledgement within a predefined time e.g. on High Speed Synchronisation Control Channel (HS-SCCH) or E-DCH Absolute Grant Channel (E-AGCH) from the network node 1 10, or E-DCH HARQ Acknowledgement Indicator CHannel (E-HICH) in case of E-DCH. The E-DCH HARQ Acknowledgement Indicator Channel is a fixed rate (Spreading Factor = 128) dedicated downlink physical channel carrying the uplink E-DCH hybrid ARQ acknowledgement indicator. As a method to limit the uplink interference, the base station 120 may send on e.g. E-DCH, E-DCH Absolute

Grant Channel or High Speed Synchronisation Control Channel a command to the user equipment 140 to reduce transmit power.

208. When the base station 120 has successfully decoded the message, it transmits an Acknowledgement to the user equipment 140 e.g. on High Speed Synchronisation

Control Channel (HS-SCCH) or E-DCH Absolute Grant Channel (E-AGCH) from the network node 1 10, or E-DCH HARQ Acknowledgement Indicator CHannel (E-HICH) in case of E-DCH.

If, after a predefined number of retransmission attempts, the user equipment 140 does not receive any Acknowledgement e.g. on High Speed Synchronisation Control Channel, it may clear the HARQ buffer, i.e. the user equipment 140 stops retransmitting the packet and deletes it, and rely on higher layers for a retransmission.

The method makes it possible for the user equipment 140 to send a message to the network node 1 10, when the user equipment 140 is in CELL_FACH state which otherwise was only possible when the user equipment was dedicated a physical channel, i.e. leave the CELL_FACH state and be transferred in to CELL_DCH state.

Power control

As mentioned above the transmit power for sending and/or resending the message may be calculated using an offset to the power level of the last transmitted preamble, which the base station 120 detected. This is performed both for sending and resending the message when using PRACH, but when using E-DCH only for sending but not for resending the message, since ramping is not used for HARQ retransmissions. There may be different offsets for the physical control and data channels, as for Dedicated CHannel (DCH) For each physical channel, there is a control part carrying physical layer control information and a data part sending the higher layer information. Enhanced Data CHannel (E-DCH) like Beta values may be used to calculate the appropriate transmit power for each transport format. Beta is an energy/power ratio pre-set/given or calculated between control and data transmissions.

As a safeguard against user equipments retransmitting and/or transmitting with too high power and causing intra cell interference, the possibility for the base station 120 to send feedback to the user equipments 140 using the enhanced Random Access channels, to reduce their transmit power may be required. The feedback may be user equipment specific or sent to all user equipments 140 using the Enhanced Random Access channels. In some embodiments, common power control commands are transmitted to all user equipments 140 using the enhanced Random Access channels using the spare bits of the Acquisition Indicator Channel. The spare bits may be used to carry simple up or down commands to the user equipments 140. All user equipments 140 with active Enhanced Random Access channel transmission may require monitoring these bits.

Transport format In some embodiments the initially selected transport format for sending the message in step 203, is maintained regardless of the power control commands. Instead, more HARQ retransmissions are used to get the message from the user equipment 140 to the network node 1 10 through. Possibly the max nr of HARQ retransmissions may be for example 10 which is higher than for current E-DCH. In some embodiments, the detection of a power down command may increase the configured number of maximum transmission attempts by one.

Collision avoidance

There may be a risk that the base station 120 will try to soft combine a retransmission from the user equipment 140 with new message transmissions from a second user equipment, e.g. the user equipment 141 , who happened to select the same preamble signature as the retransmission. Below some methods to avoid this are described.

In some embodiments, this risk is reduced by letting the base station 120 only combine transmissions that are transmitted with the correct time offset to the first transmission of the message in step 203.

This risk may also be reduced in some embodiments, if the user equipment 140 is supposed to send a retransmission of the message according to step 207, in a certain access slot, the base station 120 may require making sure that no other user equipment tries to send its first transmission of its message in the same access slot with the same channelization code, i.e. with the same preamble signature. This may be performed by the base station 120 sending a Negative Acknowledgement (NACK) to the other user equipment, e.g. the second user equipment 141 on e.g. the Acquisition channel for this particular signature if it is the same as the user equipment 140 uses. For example:

In some embodiments wherein retransmissions are not preceded by preamble(s) this may be performed by: In order to avoid a collision between a retransmission from the user equipment 140 and a first transmission from the second user equipment 141 with the same preamble signature, the base station 120 sends a negative acknowledgement. Note that the base station 120 knows when the retransmission is supposed to take place. The user equipment 140 that is supposed to do the retransmission ignores the negative acknowledgement, but the second user equipment 141 aborts its transmission upon receiving the negative acknowledgement.

In some other embodiments wherein retransmissions are preceded by preambles as described in step 205 this may be performed by: When the base station 120 expects a retransmission on a certain preamble signature, the base station 120 may send a negative acknowledgement as a response to this preamble signature. The user equipment 140 that is supposed to do the retransmission interprets this negative acknowledgement as a positive acknowledgement. Any other user equipment as e.g. the second user equipment 141 will abort its transmission. A minor drawback with this scheme is that base station 120 has no way to abort a retransmission by sending a negative acknowledgement.

In some embodiments this risk is reduced by using the Transport Format Combination Indicator bits in a radio frame following a first radio frame, to indicate a user equipment identity. (The Transport Format Combination Indicator would be the same in all radio frames, so decoding it once is enough).

In some other embodiments this risk is reduced by the base station 120 combining only transmissions with the same transport format.

In yet some other embodiments this risk is reduced by reserving some scrambling sequences/preamble sequences for retransmission only.

Transport format limitation In addition to the power control described above, there may also be required to limit the transport format selection function in the user equipment 140 to avoid exceeded uplink interference. Like for the power control command, this can be done either per user equipment 140 or commonly for all user equipments 140, 141 , 142, 143, using Enhances 5 Random Access Channel.

In some embodiments common control could be realised to send a common signal from the base station 120 to all user equipments 140, 141 , 142, 143 using Enhances Random Access Channel to limit the Transport Format Combination (TFC). One alternative is again to use the spare bits of the Acquisition Channel to transmit up/down

10 commands to the user equipments 140, 141 , 142, 143. One problem with this approach is that due to missed up/down commands, the user equipments 140, 141 , 142, and 143 will have different understanding of what is the max Transport Format Combination that is allowed. A better solution may be to instead signal the max allowed Transport Format Combination using an index, which may be sent in an Acquisition Channel spare bits.

15 Another option is to send user equipment specific controls to the user equipment

140 using the E-DCH Absolute Grant Channel, like the ones used to command to reduce the transmit power in step 204. This may be combined with the power down command, so that the user equipment 140 in consecutive accesses uses a smaller Transport Format Combination.

20

The method steps in the user equipment 140 for random accessing the user equipment 140 to a base station 120 according to some embodiments will now be described with reference to a flowchart depicted in Figure 3. As mentioned above, the 25 user equipment 140 and the base station 120 are comprised in the communication network system 1 10. The network node may e.g. be a base station 120 or a radio network controller 110 and is therefore denoted network node 1 10, 120 from now on. The user equipment 140 is in a CELL_FACH state. The method comprising the steps of:

30 301. The user equipment 140 receives, from the network node 1 10, 120 comprised in the communication network system 100, an acknowledgement to send a message to the network node 110.

302. The message is sent to the network node 1 10, 120 using Hybrid Automatic 35 Retransmission reQuest "HARQ. In some embodiments, using transmit power relative to a last preamble sent before the step of receiving 203, 301 the acknowledgement, plus an offset depending on a chosen transport format.

In some embodiments the transport format used is indicated.

A TFCI value may be reserved to indicate the type of usage of the RACH. 5 The used RACH may be indicated using an offset in an uncoded TFCI code word or inverting the TFCI bits prior to coding of the TFCI code word.

Channel coding may be performed using 1/3 rate turbo coding, puncturing and soft combining through HARQ in this step of sending the message.

10 303. In this step power control feedback is obtained from the network node 110, 120. In some embodiments, the power control feedback is used in the step of sending 302 the message to the network node 1 10, 120. In that case the feedback is obtained before step 302 of sending the message.

The obtained 205 power control feedback may be transmitted from the network 15 node 110, 120 on a modified and/or non-modified E-DCH Absolute Grant Channel.

Also HARQ feedback and/or rate control may be obtained in this step. Modified and/or non-modified E-DCH Absolute Grant Channel may used to control the user equipment 140 transport format selection in this step of obtaining power control feedback. 20

304. If no acknowledgement that the message is received by the network node 110, 120 the user equipment 140 will use the HARQ for resending said message to the network node 1 10, 120. The user equipment uses the obtained power control feedback for the resending.

25 In some embodiments, the user equipment 140 receives from the base station

120, a power control command, on e.g. E-DCH, E-DCH Absolute Grant Channel or High Speed Synchronisation Control Channel, in this step of resending said message to the network node 1 10, 120. This power control command may be received on an enhanced random access channel using spare bits of the acquisition 30 indicator channel.

In some embodiments, this power control command is a power down command. In this case, a detected power down command in the power control command may trigger an increase of a configured number of maximum transmission attempts by one. 35 305. In some embodiments, the user equipment 240 receives from the base station 120, a negative acknowledgement for a particular signature if it is the user equipment 140 uses the same signature as a second user equipment 141 uses in the step of resending 304 said message to the network node 110, 120. This negative acknowledgement is ignored, since the message is to be resent.

To perform the method steps above to random accessing the user equipment 140 to the base station 120, the user equipment 140 comprises an arrangement 400 depicted in Figure 4. As mentioned above the user equipment 140 and the base station 120 are comprised in a communication network system 1 10. The user equipment 140 is arranged to be in a CELL_FACH state.

The user equipment arrangement 400 comprises a receiving unit 410 configured to receive, from the network node 1 10, 120 comprised in the communication network system 100, an acknowledgement to send a message to the network node 1 10, 120.

The user equipment arrangement 400 further comprises a sending unit 420 configured to send the message to the network node 110, 120 using Hybrid Automatic Retransmission reQuest "HARQ.

In some embodiments, the sending unit 420 further is configured to use transmit power relative to a last preamble sent before the step of receiving 203, 301 the acknowledgement, plus an offset depending on a chosen transport format.

In some embodiments the sending unit 420 further is configured to indicate the transport format used.

The sending unit 420 may further be configured to reserve a TFCI value to indicate the type of usage of the RACH.

In some embodiments, the sending unit 420 further is configured to indicate the used RACH, using an offset in an uncoded TFCI code word or inverting the TFCI bits prior to coding of the TFCI code word.

The sending unit 420 may further be configured to perform channel coding, using 1/3 rate turbo coding, puncturing and soft combining through HARQ in this step of sending the message. The user equipment arrangement 400 further comprises a feedback obtaining unit 430 configured to obtain power control feedback from the network node 110, 120.

In some embodiments, the sending unit 420 may further be configured to use the obtained power control feedback for sending the message to the network node 1 10, 120. The feedback obtaining unit 430 may further be configured to obtain the power control feedback transmitted from the network node 1 10, 120 on a modified and/or non- modified E-DCH Absolute Grant Channel.

The feedback obtaining unit 430 may further be configured to obtained also HARQ feedback and/or rate control from the network node 1 10, 120. Modified and/or non-modified E-DCH Absolute Grant Channel may be used to control the user equipment 140 transport format selection when power control feedback is obtained.

The sending unit 420 is further configured to for resending said message to the network node 110, 120, if no acknowledgement that the message is received by the network node 1 10, 120 is obtained. The sending unit 420 is further configured to use the HARQ and to use the obtained power control feedback for the resending.

In some embodiments, the receiving unit 410 is further configured to receive from the base station 120, a power control command, on e.g. E-DCH, E-DCH Absolute Grant Channel or High Speed Synchronisation Control Channel when resending the message to the network node 1 10, 120. This power control command may be received on an enhanced random access channel using spare bits of the acquisition indicator channel.

In some embodiments the user equipment arrangement 400 comprises a control unit 440 configured to trigger an increase of a configured number of maximum transmission attempts by one, if a power control command is detected as a power down command.

In some embodiments, the receiving unit 410 is further configured to receive from the base station 120, a negative acknowledgement for a particular signature if the user equipment 140 uses the same signature as a second user equipment 141 uses in the step of resending 304 said message to the network node 1 10, 120. This negative acknowledgement is ignored, since the message is to be resent. The method steps in the network node 1 10, 120, for random accessing the user equipment 140 to the base station 120, according to some embodiments will now be described with reference to a flowchart depicted in Figure 5. As mentioned above, the user equipment 140 and the base station 120 are comprised in a communication network system 1 10, the user equipment 140 being in a CELL_FACH state. The method comprises the steps of:

501. An acknowledgement to send a message from the user equipment 140 to the network node 110, 120, is sent to the user equipment 140.

502. In this step power control feedback is sent to the user equipment 140.

In some embodiments, the power control feedback is transmitted to the user equipment 140 on a modified E-DCH Absolute Grant Channel.

In some embodiments, HARQ feedback and/or rate control is further attached in this step of sending 205 power control feedback.

503. The message is received from the user equipment 140 according to the sent acknowledgement. The user equipment 140 using Hybrid Automatic Retransmission request HARQ for the transmission of the message the user equipment 140 using the sent power control feed back for sending the message.

The message being sent for the first time, or the message being resent due to the user equipment 140 not receiving any acknowledgement for a previous attempt to send the message.

In some embodiments channel coding is performed using 1/3 rate turbo coding, puncturing and soft combining through HARQ in this step of receiving the message.

To perform the method steps above for random accessing a user equipment 140) to a base station 120, the network node 1 10, 120 comprises an arrangement 600 depicted in Figure 6. As mentioned above, the network node 1 10, 120, the user equipment 140 and the base station 120 are comprised in a communication network system 1 10. The user equipment 140 is arranged to be in a CELL_FACH state. The network node arrangement 600 comprises a sending unit 610 configured to send to the user equipment 140, an acknowledgement to send a message from the user equipment 140 to the network node 110, 120.

The sending unit 610 is further configured to send power control feedback to the user equipment 140.

HARQ feedback and/or rate control may further be attached to the power control feedback sending.

The network node arrangement 600 further comprises a receiving unit 620 configured to receive the message from the user equipment 140 according to the sent acknowledgement, wherein the user equipment 140 used Hybrid Automatic Retransmission request HARQ for the transmission of the message, and wherein the user equipment 140 used the sent power control feed back for sending the message. The message being sent for the first time, or the message being resent since the user equipment 140 did not receive any acknowledgement for a previous attempt to send the message.

In some embodiments, the receiving unit 620 further is adapted to perform channel coding, using 1/3 rate turbo coding, puncturing and soft combining through HARQ when receiving the message.

Some embodiments of the present method may be described as a method of improving link adaptation for an access channel used in a random access procedure in the communication network system wherein the method comprises the step of introducing HARQ into said procedure.

Some embodiments of the present method may be described as an arrangement of improving link adaptation for an access channel used in a random access procedure in the communication network system, wherein the arrangement comprises means for introducing HARQ into said procedure.

Some embodiments of the present method may be described as a method of improving link adaptation for an access channel used in a random access procedure in the communication network system, wherein in the method comprises the steps of: Receiving power control feedback from the network system, and Using said feedback in said procedure.

According to some embodiments said feedback is user equipment specific.

According to some embodiments said feedback may be transmitted to all user equipments using said access channel.

Some embodiments of the present method may be described as an arrangement of improving link adaptation for an access channel used in a random access procedure in a communication network system, wherein the arrangement comprises: Means for receiving power control feedback from the network system and means for using said feedback in said procedure.

The present mechanism for random accessing the user equipment 140 to the base station 120, may be implemented through one or more processors, such as a processor 450 in the user equipment arrangement 400 depicted in Figure 4 or the processor 630 in the network node arrangement 600 depicted in Figure 6, together with computer program code for performing the functions of the present solution. The program code mentioned above may also be provided as a computer program product, for instance in the form of a data carrier carrying computer program code for performing the present solution when being loaded into the user equipment 140 or the network node 1 10, 120. One such carrier may be in the form of a CD ROM disc. It is however feasible with other data carriers such as a memory stick. The computer program code can furthermore be provided as pure program code on a server and downloaded to the user equipment 140 or the network node 1 10, 120 remotely.

When using the word "comprise" or "comprising" it shall be interpreted as non- limiting, i.e. meaning "consist at least of".

The present invention is not limited to the above described preferred embodiments. Various alternatives, modifications and equivalents may be used. Therefore, the above embodiments should not be taken as limiting the scope of the invention, which is defined by the appending claims.

Claims

1. A method in a user equipment (140) for random accessing the user equipment (140) to a base station (120), the user equipment (140) and the base station (120) being comprised in a communication network system (110), the user equipment (140) being in a CELL_FACH state, the method comprising the steps of: receiving (202,301 ) from a network node (1 10,120) comprised in the communication network system (100), an acknowledgement to send a message to the network node (1 10,120), sending (203,302) the message to the network node (110,120) using Hybrid

Automatic Retransmission reQuest "HARQ".

2. Method according to claim 1 , comprising the further step of obtaining (204,303) power control feedback from the network node (1 10,120), if no acknowledgement that the message is received by the network node

(1 10,120) is obtained, using the HARQ for resending (207,304) said message to the network node (1 10,120) and using the obtained power control feedback.

3. Method according to claim 2, wherein said power control feedback further is used for the step of sending (204,302) the message to the network node (1 10,120).

4. The method according to any of the claims 1-3, wherein the step of sending (204) the message is performed by using transmit power relative to a last preamble sent before the step of receiving (202,301 ) the acknowledgement, plus an offset depending on a chosen transport format.

5. The method according to any of the claims 1-4, wherein transport format used is indicated in the step of sending (203,302) the message.

6. The method according to claim 5, wherein a TFCI value is reserved to indicate the type of usage of the RACH.

7. The method according to any of the claims 1-6, wherein the step of sending (204,302) the message is performed by indicating the used RACH using an offset in an uncoded TFCI code word or inverting the TFCI bits prior to coding of the TFCI code word.

8. The method according to any of the claims 1-7, wherein channel coding is performed using 1/3 rate turbo coding, puncturing and soft combining through HARQ in the step of sending (203,302) the message.

5

9. The method according to any of the claims 1 -8, wherein the step of obtaining (204,303) power control feedback is transmitted from the network node (1 10,120) on a modified and/or non-modified E-DCH Absolute Grant Channel.

10 10. The method according to any of the claims 1 -9, wherein further HARQ feedback and/or power or rate control is obtained in the step of obtaining (204,303) power control feedback.

1 1. The method according to any of the claims 1-10, wherein modified and/or non- 15 modified E-DCH Absolute Grant Channel is used to control the user equipment (140) transport format selection in the step of obtaining (204,303) power control feedback.

12. The method according to any of the claims 2-1 1 , wherein the user equipment (140) receives from the base station (120) a power control command, on e.g. E-DCH, E-

20 DCH Absolute Grant Channel or High Speed Synchronisation Control Channel, in the step of resending (207) said message to the network node (1 10,120).

13. The method according to claim 12, wherein the power control command is received on an enhanced random access channel using spare bits of the acquisition indicator

25 channel.

14. The method according to any of the claims 12-13, wherein the power control command is a power down command, and wherein a detected power down command in the power control command triggers an increase of a configured number of

30 maximum transmission attempts by one.

15. The method according to any of the claims 2-14, comprising the further step of receiving (305) from the base station (120), a negative acknowledgement for a particular signature if it is the user equipment (140) uses the same signature as a 35 second user equipment (141 ) uses in the step of resending (207, 304) said message to the network node (110,120), and ignoring said negative acknowledgement, since the message is to be resent.

16. A method in a network node (1 10,120), for random accessing a user equipment (140) 5 to a base station (120), the network node (1 10,120), the user equipment (140) and the base station (120) being comprised in a communication network system (1 10), the user equipment (140) being in a CELL_FACH state, the method comprising the steps: sending (204,502) power control feedback to the user equipment (140); receiving (203,207,503) a message from the user equipment (140), the user 10 equipment (140) using Hybrid Automatic Retransmission request (HARQ) for the transmission of the message, wherein the user equipment (140) used the sent power control feed back for sending the message, said message being sent for the first time, or said message being resent since the user equipment (140) did not receive any 15 acknowledgement for a previous attempt to send the message.

17. The method according to claim 16, wherein channel coding is performed using 1/3 rate turbo coding, puncturing and soft combining through HARQ in the step of receiving (203,207,503) the message.

20

18. The method according to any of the claims 16-17, wherein the step of sending (204,502) power control feedback is transmitted to the user equipment (140) on a modified E-DCH Absolute Grant Channel.

25 19. The method according to any of the claims 16-18, wherein further HARQ feedback and/or power or rate control is attached in the step of sending (204,502) power control feedback.

20. An arrangement (400) in a user equipment (140) for random accessing the user 30 equipment (140) to a base station (120), the user equipment (140) and the base station (120) being comprised in a communication network system (110), the user equipment (140) is arranged to be in a CELL_FACH state, the user equipment arrangement (400) comprising: a receiving unit (410) configured to receive from a network node (1 10,120) comprised in the a communication network system (100), an acknowledgement to send a message to the network node (1 10,120), a sending unit (420) configured to send the message to the network node 5 (1 10,120) using Hybrid Automatic Retransmission reQuest "HARQ.

21. The first node arrangement (400) according to claim 20, further comprising: a feedback obtaining unit (430) configured to obtain power control feedback from the network node (1 10,120),

10 and wherein the sending unit (420) further is configured to resend said message to the network node (1 10,120) if no acknowledgement that the message is received by the network node (1 10,120), using the HARQ and using the obtained power control feedback.

15 22. An arrangement (600) in a network node (1 10,120) for random accessing a user equipment (140) to a base station (120), the network node (1 10,120), the user equipment (140) and the base station (120) being comprised in a communication network system (1 10), the user equipment (140) is arranged to be in a CELL_FACH state, the network node arrangement (600) comprising:

20 a sending unit (610) configured to send to the user equipment (140), an acknowledgement to send a message from the user equipment (140) to the network node (110,120); the sending unit (610) further being configured to send power control feedback to the user equipment (140);

25 the network node arrangement (600) comprising a receiving unit (620) configured to receive the message from the user equipment (140) according to the sent acknowledgement, wherein the user equipment (140) used Hybrid Automatic Retransmission request (HARQ) for the transmission of the message, and wherein the user equipment (140) used the sent power control feed back for sending the message,

30 said message being sent for the first time, or said message being resent since the user equipment (140) did not receive any acknowledgement for a previous attempt to send the message.