HK1220314B - Method and arrangement in a telecommunications system - Google Patents

Description

Method and apparatus in a telecommunications system

Technical Field

The present invention relates to the field of data communications, and in particular to scheduling of uplink data transmissions in a communication system.

Background Art

In communications systems operating according to the Long Term Evolution (LTE) standard based on Orthogonal Frequency Division Multiplexing (OFDM), data is transmitted between user equipment and a base station (referred to as an evolved Node B, e-NodeB) on multiple frequency resources that can be dynamically allocated to different communication sessions. A user equipment (UE) can request scheduling of resources for transmitting uplink (UL) data by sending a Scheduling Request (SR) to the e-NodeB to which it is currently connected. The e-NodeB will then respond to the scheduling request by sending a UL Grant message to the user equipment, which contains information about the frequency or frequencies on which the uplink data is to be transmitted (the timing of the scheduled resources for transmitting the uplink data is generally implicitly given by the timing of the receipt of the UL Grant message). The uplink data can then be sent by the user equipment on the scheduled time/frequency resources.

When a user equipment becomes active in an LTE system, it is typically allocated a dedicated physical uplink control channel (PUCCH), which is a dedicated control channel on which scheduling requests and other messages can be transmitted to the e-nodeB. According to the current LTE standard, the power at which a scheduling request is transmitted on the PUCCH is determined according to an expression provided in the standard (see 3GPP Technical Specification (TS) 36.213, Version 8.2.0, Section 5.1.2):

P _PUCCH (i)=min{P _MAX , P _{O_PUCCH} +PL+Δ _{TF_PUCCH} (TF)+g(i)}[dBm] (1)

in

_{PO_PUCCH} consists of cell-specific parameters ( _{PO_NOMINAL_PUCCH} ), which are broadcast (in System Information Block 2 (SIB2)) and UE-specific parameters ( _{PO_UE_PUCCH} ), which are sent to user equipment via dedicated signaling over the Radio Resource Control (RLC) protocol. _{PO_PUCCH} is a semi-static configuration parameter that is updated from time to time, typically on a timescale of several hours. _{PO_PUCCH} is used to compensate for interference but cannot track interference changes faster than the _{PO_PUCCH} update timescale.

• PL is the UE's estimate of its own path loss.

Δ _{TF_PUCCH} (TF) corresponds to the transport format specific factor signaled via RRC. Δ _{TF_PUCCH} (TF) takes the same value for all scheduling request transmissions in a cell, but can take different values when other types of information are transmitted via PUCCH; and

g(i) represents the absolute or cumulative transmit power control (TPC) command received by the user equipment from the e-nodeB (in dedicated control information (DCI) format 1, 2 or 3). The TPC command is used to adjust the transmit power of the user equipment to compensate for variations in the noise and interference levels in the cell.

Therefore, the transmit power with which the scheduling request will be transmitted on the PUCCH channel depends on the semi-static parameter P _{O_PUCCH} , the path loss estimate PL made by the user equipment, the transport format specific compensation Δ _{TF_PUCCH} (TF) and the TPC command received from the e-nodeB. Expression (1) has been derived to ensure that the user equipment transmits at an appropriate power in order to keep interference low while maintaining adequate quality of service.

However, there may be situations where the transmission power given by expression (1) is insufficient, so that the e-nodeB to which the user equipment is currently connected cannot hear the scheduling request transmitted on the PUCCH channel. This can be the case, for example, when the interference in the cell in which the user equipment is active varies on a time scale shorter than the time scale of the transmission of the TPC command from the e-nodeB, or when there is a lack of TPC commands on a time scale shorter than the time scale of the _{PO_PUCCH} update. TPC commands are generally transmitted to the user equipment when there is dynamically scheduled downlink data to be transmitted to the user equipment. If there is no dynamically scheduled downlink data to be transmitted to the user equipment within a certain time period, it is possible that the most recently transmitted TPC command does not provide appropriate compensation for the current interference in the cell.

If the combination of _{PO_PUCCH} and any TPC commands is not an adequate compensation for interference plus noise, the user equipment will repeatedly resend its scheduling request using the same power until the user equipment is granted. Under unsuitable circumstances, the user equipment may end up in a nearly infinite loop sending scheduling requests that the e-NodeB will never hear. A similar situation can occur if the scheduling request fails for some other reason, for example, when the user equipment fails to transmit the correct scheduling request, or transmits them on the wrong resources.

As can be seen from the above, there is a need to improve the robustness of the scheduling request procedure in a mobile radio communications system operating according to the LTE standard.

This need has been addressed in the standardization proposal R2-083436, 3GPP TSG-RAN WG2#62bis, which discloses a solution to the problem of endless scheduling request transmissions by reusing the recovery procedure originally standardized to stop endless transmission attempts on the Random Access Channel (RACH). In this solution, the Medium Access Control (MAC) protocol indicates to the RRC protocol when a problem with a scheduling request on the PUCCH has been identified, based on a timer or counter. When such a problem has been identified, RRC starts a timer called T312. If the scheduling request is successfully received by the e-NodeB before timer T312 expires, MAC notifies RRC. However, if recovery has not occurred by the time timer T312 expires, RRC will take further actions according to the specifications for radio link failures (e.g., for handling random access channel failures). This is further described in TS 36.331 v8.2.0, section 5.3.10, "Radio link failure related actions."

While the approach described in standardization proposal R2-083436 will ensure that a user equipment will never end up in a situation where it transmits an endless number of scheduling requests that are never heard, it does so at a significant cost. Performing the process of expiration standardization for T310 is time consuming and requires extensive signaling.

Summary of the Invention

It is an object of the present invention to find an efficient way to avoid that a user equipment ends up in a situation where it unsuccessfully transmits a large or endless number of scheduling requests.

This object is achieved by a method for requesting scheduling of resources to be used for uplink communication of data from a user equipment in a communication system, wherein the number of times the user equipment will repeatedly transmit a scheduling request related to data on a dedicated uplink control channel when no uplink resources are granted is limited by monitoring in the user equipment whether a threshold indicating a maximum limit has been reached. In response to the threshold being reached, a random access transmission on a random access channel is initiated.

The object is also achieved by a user equipment for communicating in a communication system. The user equipment is arranged such that the number of scheduling requests relating to the same uplink data that the user equipment will repeatedly transmit on an uplink control channel when not granted uplink resources is limited, as the user equipment is adapted to monitor whether a maximum limit has been reached. The user equipment is adapted to initiate a random access transmission on a random access channel in response to the maximum limit being reached.

The present method and apparatus significantly reduces the time and signaling required to provide scheduled uplink resources to user equipment with poor power settings on the uplink control channel, thereby improving the user experience and reducing bandwidth consumption and interference in the communication system, as well as power consumption in the user equipment. By applying embodiments of the present invention, it is not necessary to perform a radio resource control connection re-establishment procedure in the time interval after a threshold is reached and before the initiation of a random access transmission. For example, the cell to which the user equipment is connected when the maximum value is reached can be maintained as the selected cell during and after the random access procedure without performing a cell evaluation.

The time required to provide an uplink grant to a user equipment is not only reduced due to the fact that less signaling will be transmitted between the user equipment and the radio base station, but it can also be reduced by setting the maximum limit to a lower value, because the cost of determining that the request procedure on the PUCCH was unsuccessful and thus exiting the scheduling request procedure will be less than in the prior art solution. The risk of setting the limit lower is thus reduced. In addition, there will be less internal interaction between the protocol layers of the user equipment (for example, between MAC and RRC).

An embodiment of the method of the present invention may comprise the steps of: initiating a metric for limiting the number of transmitted scheduling requests; checking whether the metric has reached a threshold, and transmitting a scheduling request on an uplink control channel if uplink resources have not been granted and the metric has not reached the threshold, and repeating the steps of checking, and transmitting a random access transmission on a random access channel if uplink resources have not been granted and the metric has reached the threshold.

In one embodiment of the present invention, uplink control channel resources are retained by the user equipment even if uplink resources have not yet been granted when the threshold is reached. This further reduces the amount of signaling, as these resources do not have to be configured via reconfiguration messages transmitted from the radio base station, and the need to signal such messages is eliminated. In this embodiment, the method may further include an indication in the random access transmission that the uplink control channel has not been released. In another embodiment, the uplink control channel is released when the maximum limit is reached.

The object is also achieved by a computer program product for use in a procedure for requesting scheduling of uplink resources.The computer program product may advantageously be stored on memory means adapted to be included in a user equipment.

Furthermore, the object is achieved by a radio base station for communicating with user equipment in a communication system, the radio base station being arranged to receive a random access transmission from the user equipment, wherein the radio base station is adapted to determine whether the user equipment from which the random access transmission has been received has access rights to dedicated uplink control channel resources for transmitting scheduling requests; and wherein the radio base station is further adapted to send a power control command to the user equipment in response to determining that the user equipment has access rights to the dedicated uplink control channel resources for transmitting scheduling requests, the power control command comprising an instruction to set a power level at which the scheduling request is transmitted on the dedicated uplink control channel resources to a higher level. By means of the radio base station of the present invention, it is achieved that the power level at which the user equipment will transmit is adjusted, thereby reducing the risk of further unsuccessful scheduling request transmissions.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention and its advantages, reference is now made to the following description taken in conjunction with the accompanying drawings, in which:

FIG1 is a schematic overview of a communication system operating according to the LTE standard.

Figure 2 is a signalling diagram illustrating a scenario where the user equipment successfully signals a scheduling request to the e-nodeB on the second attempt.

Figure 3a is a signaling diagram according to an embodiment of the present invention in a scenario where the user equipment does not receive a UL-SCH grant even after repeated scheduling request transmissions on the PUCCH.

FIG. 3 b is a signaling diagram according to another embodiment of the present invention in a situation similar to that of FIG. 3 a .

FIG3 c is a signaling diagram according to an embodiment of the present invention, wherein the e-nodeB acts to improve the power setting of the PUCCH.

FIG4 a is a flow chart illustrating an embodiment of the present invention.

FIG4 b is a flow chart illustrating another embodiment of the present invention.

FIG5 is a schematic diagram illustrating an embodiment of a user equipment according to the present invention.

DETAILED DESCRIPTION

A mobile radio communication system operating according to the LTE standard is schematically illustrated in Figure 1. The communication system 100 of Figure 1 comprises a plurality of user equipment 105 and a plurality of radio base stations 110, referred to below as e-nodeBs 110. The user equipment 105 can communicate wirelessly with the e-nodeBs 110 via a radio interface 115.

According to the LTE standard, the e-nodeB 110 can allocate periodic resources on the Physical Uplink Control Channel (PUCCH) to the user equipment 105. The resources on the PUCCH channel can be used for dedicated signaling of scheduling requests from the user equipment 105 to the e-nodeB 110, for example.

A scheduling request signaling scenario according to existing standards is shown in FIG2 , where it is assumed that a PUCCH SR resource has been configured for the user equipment 105. At event 2A, the user equipment 105 detects data to be transmitted on the uplink. The user equipment 105 then transmits a scheduling request 2Bi on the PUCCH to the e-nodeB 110 to which the user equipment 105 is currently connected in order to request uplink transmission resources. The power at which the scheduling request 2Bi is transmitted is determined by expression (1). In the scenario shown in FIG2 , the e-nodeB 110 does not respond to the first scheduling request 2Bi. This may be because, for example, the power at which the scheduling request is transmitted is too low compared to the interference in the cell, so that the e-nodeB 110 cannot detect the scheduling request 2Bi. Subsequently, the user equipment 105 transmits a scheduling request 2Bii on its next available PUCCH SR resource, which is identical to the scheduling request 2Bi and is transmitted at the same power (SR resources occur periodically). In the scenario of Figure 2, the scheduling request 2Bii is successfully received by the e-nodeB, which responds by sending an uplink scheduling (UL-SCH) grant message 2D to the user equipment 105. Subsequently, in data transmission 2E, the user equipment 105 can transmit the uplink data detected at event 2A by using the transmission resources allocated in the UL-SCH grant message 2D.

As shown in FIG2 , current standards specify that if the user equipment 105 does not receive an UL grant message 2D after sending a scheduling request 2B but before its next available PUCCH SR resource occurs, then another identical scheduling request 2B will be sent by the user equipment 105 to the e-nodeB 110 at the same power level. In most cases, this process will ensure that the e-nodeB 110 receives the scheduling request 2B without significantly affecting the interference situation in and around the cell. However, as mentioned above, there may be situations where the power level given by expression (1) is too low compared to the interference and noise levels in the cell, so that the scheduling request 2B transmitted from the user equipment 105 to the e-nodeB 110 will never be detected by the e-nodeB 110, or there may be situations where the scheduling request 2B will only be detected by the e-nodeB 110 after the user equipment 105 has transmitted many scheduling requests 2B. Although such numerous or endless transmissions of scheduling requests 2B will generally be quite rare, the problems that arise when it does occur can be considerable.

As mentioned above, standardization proposal R2-083436 has proposed limiting the situation of endless scheduling request transmission by using the same procedure of setting timer T312 (which has been proposed to limit endless RACH attempts). However, while meeting the requirements for stopping endless scheduling request transmission and thus improving the performance of communication system 100, this procedure itself has the disadvantages of being slow and signaling-intensive because it was originally intended to solve a problem that is more serious than the failure to receive scheduling requests. A much more effective way to stop endless scheduling request transmission will be described below.

According to the present invention, the problem of many or even endless scheduling request transmissions from the user equipment 105 can be effectively solved by sending a random access (RA) transmission on a random access channel (RACH) from the user equipment 105 when the user equipment 105 determines that it has entered a state of repeated unsuccessful scheduling request transmissions 2B.

The RACH control channel is shared by all user equipment 105 within a cell and is used by user equipment 105 to signal the e-nodeB 110 of the cell when dedicated resources have not yet been allocated to the user equipment 105, for example, for initial access at power-up or handover of the user equipment 105 between cells, or to request transmission resources for uplink data when PUCCH SR resources have not yet been assigned to the user equipment 105. Since the RACH is a shared, contention-based channel, it is generally desirable to maintain a low signaling load on the channel in order to minimize the risk of collisions between different user equipment 105 on the channel and to maintain low interference on the channel. However, the advantage of breaking the deadlock situation of repeated unsuccessful scheduling request transmissions without having to go through a re-establishment procedure may outweigh the disadvantages of transmitting on the RACH.

By using the random access procedure as a fallback when the user equipment 105 has transmitted many unsuccessful transmission requests on the dedicated PUCCH channel, the state of repeated transmission of unsuccessful scheduled transmission requests can be effectively broken without having to use the radio link failure procedure. The power at which the first RA transmission is transmitted on the RACH is given by an expression different from (1), and if the RA transmission on the RA channel fails and the RA transmission does not reach the e-nodeB 110 for some reason, the user equipment 105 will transmit another RA transmission at a higher power. For subsequent RA transmissions, the power will be increased until the RA transmission reaches the e-nodeB 110 (or until the maximum power level has been reached, or the maximum number of RA transmissions has been transmitted, at which point the radio link failure procedure of TS 36.331 section 5.3.7 will be executed). Therefore, the probability that the e-nodeB can hear the user equipment 105 is greatly improved compared to existing standards.

Furthermore, by transmitting an RA message on the RACH rather than setting timer T312 and performing a radio link failure upon its expiration, significant improvements are achieved in terms of recovery time and reduced signaling. Entering the radio link failure procedure to break the cycle of unsuccessful scheduling request transmissions, as proposed in the standardization proposal R2-083436, involves multiple actions, which can be avoided using the method according to the present invention. The set of radio link failure actions to be performed in the procedure proposed in R2-083436, but not required when using the method according to the present invention, are collectively referred to as the RRC connection re-establishment procedure. RRC connection re-establishment includes a cell reselection procedure, a MAC reset, and the re-establishment of radio link control (RLC) for all radio bearers (see TS 36.331 v8.2.0, sections 5.3.7 and 5.7.10). These actions are not required when using the method according to the present invention to break the cycle of unsuccessful scheduling requests. The cell to which the user equipment is connected when the threshold is reached can remain the selected cell without any cell evaluation, and the MAC and RLC configurations can remain the same as before the metric reached the threshold. Therefore, the user experience of a person or machine waiting for the user equipment 105 to transmit uplink data will be greatly improved.

The present invention can be advantageously applied to any communication standard in which scheduling requests are typically transmitted via a dedicated control channel whose power does not increase between retransmission attempts, and in which a control channel whose power increases between transmission attempts exists. The dedicated control channel whose power does not increase between retransmission attempts is referred to herein as an uplink control channel, of which the LTE PUCCH is an example. The control channel whose power increases between retransmission attempts is referred to herein as a random access channel, of which the LTE RACH is an example. However, to simplify the description, the present invention will be described below in accordance with the LTE standard, and the uplink control channel will be exemplified by the LTE PUCCH, while the random access channel will be exemplified by the LTE RACH.

Fig. 3a is a flow chart illustrating an embodiment of the invention in a scenario where the e-nodeB 110 does not detect any scheduling request 2B transmitted from the user equipment 2a even after the transmission of many scheduling requests 2B.

At event 2A in FIG. 3 a , user equipment 105 detects data to be transmitted on the uplink via e-nodeB 110. Upon detecting such uplink data, a timer is started at event 3A. The counter will be used to determine if/when the user equipment 105 should consider any repeated transmissions of a scheduling request 2B to be unsuccessful. The counter can, for example, be a timer that counts the amount of time that has elapsed since the counter was started, or a counter that counts the number of scheduling requests transmitted since the counter was started. After starting the counter, user equipment 105 transmits a first scheduling request 2Bi on the PUCCH channel (alternatively, event 3A, which starts the counter, can occur immediately after, rather than before, the transmission of the first scheduling request 2Bi).

In the scenario of Figure 3a, user equipment 105 does not receive a response from e-nodeB 110 before the occurrence of its next PUCCH SR resource at event 2Ci. In practice, the transmission of scheduling request 2B occurs multiple times in the scenario of Figure 3B without user equipment 105 receiving any response from e-nodeB 110. At event 3B, after the transmission of the nth scheduling request 2Bn, the counter started at event 3A reaches a threshold representing a maximum limit, thus indicating that the attempt to transmit a scheduling request on the PUCCH channel should be considered unsuccessful. The maximum limit can be, for example, the maximum amount of time since the counter was started or the maximum number of scheduling requests that have been transmitted.

In response to the counter reaching the threshold at event 3B, an RA transmission 3C is sent on the RA channel. If this RA transmission 3C is successfully received by the e-nodeB 110, as is the case in the scenario of Figure 3a, the e-nodeB 110 will respond by sending a resource assignment message 3D indicating the resources that should be used by the mobile station 105 for further signaling. The user equipment 105 will respond by sending a message 3E in which it identifies itself to the e-nodeB 110.

When the e-nodeB 110 receives message 3E, if suitable uplink resources are available in the cell, the e-nodeB 110 will grant uplink resources to the user equipment 105 by sending a UL-SCH grant message 2D to the user equipment 105. Furthermore, upon receiving message 3E, the e-nodeB 110 will know that the RA transmission 3C was sent by the user equipment 105 to which dedicated PUCCH SR resources have been allocated, and can therefore infer that the reason the user equipment 105 sent the RA transmission 3C is that the transmission of the scheduling request 2B on the PUCCH was unsuccessful. The e-nodeB can then advantageously react to improve the power setting of the PUCCH for the user equipment 105, for example, by transmitting a suitable TPC command to the user equipment 105, or by updating the value of the UE-specific parameter _{PO_UE_PUCCH} in a message to the user equipment 105, thereby updating the parameter _{PO_PUCCH} (alternatively, the cell-specific parameter _{PO_NOMINAL_PUCCH} can be updated).

If the RA transmission 3C is not safely received by the e-nodeB 110, so that the user equipment 105 does not receive a response within a predetermined time limit, the user equipment 105 will retransmit the RA message 3C, but at a higher power level than the first RA transmission. As a result, the chance that the e-nodeB 110 will eventually hear the RA transmission on the RACH is much higher than if the e-nodeB 110 heard a repeated scheduling request transmission on the PUCCH when the PUCCH power level was insufficient. Retransmission of RA messages at increased power levels is part of the prior art and is not shown in FIG3 a.

When the counter threshold is reached at event 3B, user equipment 105 can either retain PUCCH resources and/or any assigned sounding reference symbols (SRS), or release such resources (sounding reference symbols are transmitted by user equipment 105 (if configured to do so) and used by receiving e-nodeB 110 to derive information about uplink transport channels). In the embodiment of the present invention shown in FIG3 a , PUCCH and/or SRS resources are maintained. One advantage of retaining PUCCH and/or SRS resources is that no reconfiguration message has to be transmitted from e-nodeB 110 to reassign such resources, thereby further reducing the amount of signaling. However, even if PUCCH and/or SRS resources are released and then reconfigured, the present invention offers significant advantages over the prior art.

FIG3 b shows a signaling diagram illustrating an embodiment in which user equipment 105 releases PUCCH and/or SRS resources. Prior to event 3B, in which a counter reaches a threshold, the process of FIG3 b is identical to the process of FIG3 a. In FIG3 b , any PUCCH resources and/or sounding reference symbols allocated to user equipment 105 are released at event 3F before an RA transmission is sent on the RACH when the counter has reached the threshold. Alternatively, event 3F, in which PUCCH and SRS resources for user equipment 105 are released, can occur after RA transmission 3C is sent. Subsequently, knowing that user equipment 105 has released its configured PUCCH and SRS resources, e-nodeB 110 can take appropriate action, such as assigning PUCCH and/or SRS resources to user equipment 105 in a known manner.

Furthermore, when configuring new PUCCH resources to the user equipment 105, the e-nodeB 110 can advantageously exploit the knowledge that the power of previous transmissions by the user equipment over PUCCH was too low when selecting an appropriate value for the parameter _{PO_UE_PUCCH} .

FIG3 c illustrates an exemplary scenario in accordance with an embodiment of the present invention, wherein, in response to determining that user equipment 105 transmitting on the RACH has access to PUCCH SR resources, the e-nodeB adjusts the power level used by user equipment 105 for PUCCH transmissions. This scenario can be applied to either of the embodiments illustrated in FIG3 a and FIG3 b , respectively. At event 3B in FIG3 c , the counter reaches its threshold. In response, user equipment 105 transmits an RA transmission 3C to e-nodeB 110 (while simultaneously releasing or maintaining any PUCCH and/or SRS resources). As described above in conjunction with FIG3 a , e-nodeB 110 subsequently responds by sending a resource assignment message 3D to user equipment 105, which in turn responds by transmitting message 3E, in which user equipment 105 identifies itself. In event 3G of Figure 3c, e-nodeB 110 determines that user equipment 105 has access to the PUCCH SR resources and therefore concludes that user equipment 105 has been unsuccessful in transmitting a scheduling request via PUCCH. Subsequently, e-nodeB 110 transmits a power adjustment command to user equipment 105, instructing user equipment 105 to increase the power level at which the PUCCH SR transmission was transmitted. As described above, such a power adjustment command can, for example, be a TPC command specifically applicable when PUCCH/SRS resources are maintained, or a message that causes user equipment 105 to apply a different value for the parameter _{PO_PUCCH} . Event 3G and the transmission of the power adjustment command can occur at any time after the receipt of message 3E.

According to existing standards, the e-nodeB 110 will provide the user equipment 105 with a new timing advance (TA) value when receiving an RA transmission from the user equipment 105. However, according to the present invention, in both embodiments of releasing PUCCH and/or SRS resources and retaining them, the e-nodeB 110 can be adapted to recognize that the RA transmission 3C is sent by a user equipment that is still synchronized with the e-nodeB 110 (in UL synchronization), and a new TA value will not need to be transmitted. As a result, there will be even less signaling to be transmitted over the radio interface 115.

If the communication system 100 allows a user equipment 105 to retain its PUCCH and/or SRS resources when transmitting an RA when a counter reaches its threshold, as shown in FIG3a, or to release such resources, as shown in FIG3b, it would be advantageous if the e-nodeB 110 had a way to determine whether a particular user equipment 105 that was allocated PUCCH and/or SRS resources and from which the e-nodeB 110 received an RA message 3C has retained its PUCCH and/or SRS resources, or whether the user equipment 105 has released its previously allocated PUCCH and/or SRS resources. The indication of whether the user equipment 105 has released the PUCCH and/or SRS resources can be provided, for example, by the value of the preamble transmitted in the RA message 3C. A preamble is a bit sequence that the user equipment 105 randomly selects from a set of allowed preambles and includes in the RA transmission to allow for contention resolution. A set of allowed RA preambles can be reserved for user equipment 105 that has retained its PUCCH and/or SRS resources. Alternatively, other means of indicating to the e-nodeB 110 whether the user equipment has saved or released its PUCCH and/or SRS resources can be used. In some communication systems 100, it may be predefined whether the user equipment 105 should keep or release its PUCCH and/or SRS resources when sending an RA transmission 3C when the event 3B counter reaches its threshold.

Figure 4a is a flow chart illustrating an embodiment of the method of the present invention. In step 400, data to be transmitted on the uplink is detected. In step 405, an SR restriction metric is enabled, which is used to limit the number of scheduling requests 2B to be transmitted on the PUCCH before determining that the transmission of a scheduling request on the PUCCH was unsuccessful. The SR restriction metric can generally be the number of scheduling requests transmitted on the PUCCH, in which case this number is generally set to zero in step 405, or the time elapsed since the metric was enabled or since the first scheduling request was transmitted after uplink data was detected in step 400. In step 415, a check is then made to see whether UL resources that could be used by the uplink data detected in step 400 have been scheduled. If so, the scheduling request process ends in step 420, and the uplink data is transmitted on the scheduled resources. However, if UL resources have not yet been granted, a check is made in step 430 to see whether a threshold for the SR restriction metric has been reached. When the metric is the number of scheduling requests transmitted on the PUCCH, the metric should be incremented after each scheduling request transmission on the PUCCH and before proceeding to step 430. In the flowchart of Figure 4a, the metric is incremented in step 425, which is entered after it has been determined in step 415 that uplink resources are not scheduled. However, step 425 can be incremented at any stage before the threshold check in step 420. Furthermore, as indicated by the dashed line around the box representing step 425, when the metric is the amount of time that has elapsed since the metric was initiated in step 405, there will generally be no discrete incrementing step 425; instead, the metric will continuously increase as time passes.

If it is found in step 430 that the threshold value of the SR restriction metric has not been reached, the process proceeds to step 435, in which a Scheduling Request 2B is transmitted on the PUCCH. Thereafter, the process proceeds to step 415 again. On the other hand, if it is found in step 430 that the threshold value of the metric has been reached, the process proceeds to step 440. When the metric is the number of Scheduling Requests transmitted on the PUCCH since the metric was started in step 405, the threshold value can generally be one of 4, 8, 16, or 32 Scheduling Request 2B transmissions, but other values may also be used.

In step 440, an RA transmission 3C is transmitted via the RACH. As described above, RA transmission 3C is transmitted at a different power than scheduling request transmission 2B. Furthermore, if the user equipment does not receive a response to the RA transmission from e-nodeB 110, another RA transmission 3C will be sent at a higher power. When e-nodeB 110 detects an RA transmission 3C from user equipment 105 that has been assigned dedicated PUCCH SR resources, the e-nodeB will typically choose to schedule the resources for the user equipment (see Figures 3a and 3b). Therefore, by performing the RA transmission 3C in step 440, the cycle of unsuccessful scheduling request transmissions on the PUCCH detected in step 430 is effectively broken.

FIG4 b shows a flowchart illustrating an embodiment of the present invention in which user equipment 105 releases its assigned PUCCH and/or SRS resources when an SR restriction metric reaches its threshold. Prior to step 435, the flowchart of FIG4 b is identical to the flowchart of FIG4 a. However, in the embodiment shown in FIG4 b , upon determining in step 430 that the restriction metric threshold has been reached, the PUCCH resources and/or any sounding reference symbols allocated to user equipment 105 are released in step 437. When the PUCCH and/or SRS resources have been released, the process proceeds to step 440 , in which an RA transmission 3C is sent on the RACH to e-nodeB 110. In communications systems 100 in which the release of any assigned PUCCH and/or SRS resources when the threshold has been reached is optional, the RA transmission sent in step 440 can include an indication of whether the PUCCH and/or SRS resources have been released, as described above.

4a and 4b, the user equipment 105 will typically stop the repeated transmission of the scheduling request 2B on the PUCCH. However, in the embodiment shown in FIG4a, even after the transmission of the RA transmission 3C in step 440, further scheduling request transmissions can be sent on the PUCCH.

4a and 4b can be varied in many ways. For example, the first scheduling request 2B can be transmitted before checking whether any UL resources have been scheduled in step 415; the SR limit metric activation of step 405 can be performed after the transmission of the first scheduling request, and so on.

The method shown in Figures 4a and 4b can be advantageously performed in the user equipment 105. Step 415 can be advantageously performed in each transmission time interval (TTI) after the scheduling request transmission of step 435 is performed. The check performed in step 415 can be a check as to whether uplink resources have been scheduled for the current TTI or whether uplink resources are scheduled for any current or future TTI.

The inventive method shown in Figures 3 and 4 can be implemented at any protocol layer, and can be implemented, for example, by using MAC and/or RRC.

FIG5 schematically illustrates an example of a user equipment 105 in which the present invention may be applied. User equipment 105 includes, among other things, a transceiver 500 connected to an antenna 501 for transmitting and receiving signals and user data. Transceiver 500 is also connected to, among other things, a UL resource monitoring mechanism 505, which is adapted to receive, via transceiver 500, information regarding transmission resources scheduled for user equipment 105. UL resource monitoring mechanism 505 is also connected to a UL data detection mechanism 510, which is adapted to detect any uplink data to be transmitted from user equipment 105. UL data detection mechanism 510 can, for example, be part of or connected to a user application in user equipment 105. UL data detection mechanism 510 is adapted to notify UL resource monitoring mechanism 505 of the detected uplink data via transmission of signal 515.

Upon receipt of an indication signal 515 indicating that uplink data to be transmitted has been detected, the UL resource monitoring mechanism 505 is adapted to determine whether any uplink transmission resources are available for the uplink data. If so, the data is transmitted using the transceiver 500 in a known manner. However, if uplink resources have not yet been scheduled, the UL resource monitoring mechanism of FIG. 5 is adapted to send a signal 525 to a comparator mechanism 520 to which the UL resource monitoring mechanism 505 is connected. The UL resource monitoring mechanism 505 can also advantageously be adapted to monitor when the next PUCCH SR resource occurs. If the UL resource monitoring mechanism 505 detects that uplink resources for transmitting the detected data have not yet been granted at the time of the next PUCCH SR resource occurrence, the UL resource monitoring mechanism 505 is then advantageously adapted to resend a signal 525 to the comparator mechanism 520.

5 includes a counter 525, a memory 535 adapted to store a (typically predetermined) threshold value, and a comparator 540 coupled to an output 545 of the counter 530 and an output 550 of the memory 535 and adapted to compare the two outputs. The comparator 540 is further adapted to generate an output 555 in response to a comparison of the outputs 545 and 550.

The counter 530 of the comparator mechanism 520 may, for example, be a timer adapted to count the time elapsed since the counter 530 was started, or the counter may be adapted to count the number of signals received by the comparator mechanism 520 from the UL resource mechanism 505 or the number of scheduling requests transmitted via the PUCCH since the counter 530 was started.

The comparator mechanism 520 of Figure 5 is arranged such that the comparator 540 is triggered by the receipt of a signal 525 from the UL resource monitoring mechanism. If the counter 530 is adapted to count the number of scheduling requests transmitted by the user equipment 105 or the number of signals 525 received by the comparator mechanism 520, the comparator mechanism 520 will also be adapted to increment the counter 530 upon receipt of the signal 525, either before or after the comparator 540 performs the comparison (the threshold value will be set accordingly).

The UL resource monitoring mechanism 505 of FIG. 5 can advantageously be adapted to send a signal 560 to the comparator mechanism 520 upon successful uplink scheduling (i.e., receipt of a UL-SCH grant message 2D), indicating that the value of the counter 530 should be set to zero. Alternatively, the signal 560 indicating that the counter 530 should be set to zero can be sent in conjunction with the transmission of a first signal 525 after UL data has been detected. When the counter 530 is a timer, the comparator mechanism 520 can advantageously be adapted to initiate (start) the counter 530 upon receipt of the first signal 525 received from the UL resource monitoring mechanism 505, after the counter has been set to zero. When the counter 530 is adapted to count the number of signals received from the UL resource monitoring mechanism 505 or the number of transmitted scheduling requests 2B, setting the counter 530 to zero can be considered an initiation of the counter 530, or a separate initiation can be applied. Although shown as separate signals in FIG. 5 , signals 525 and 560 can be represented by two possible values of the signal.

As described above, the comparator mechanism 520 is adapted to generate an output signal 555 indicating whether the value of the counter 530 has reached its threshold. The comparator mechanism 520 is further adapted to feed this output 555 to the SR mechanism 570, which is adapted to determine whether a scheduling request 2B should be transmitted on the PUCCH or whether an RA transmission 3C should be sent on the RACH based on the comparator output 555. The SR mechanism 570 is further adapted to direct the transceiver 500, via output 575, to send a scheduling request on the PUCCH (if the output 555 indicates that the value of the timer 530 has not reached its threshold) and to send an RA transmission 3C on the RACH (if the output 555 indicates that the value of the counter 530 has reached its threshold).

5 can be implemented in other ways, and the embodiment shown in FIG5 is given as an example only. For example, the SR mechanism 570 can be implemented as part of the comparator mechanism 520 or the transceiver 500; the UL resource monitoring mechanism 505 can be implemented as part of the comparator mechanism 520, etc.

While the present invention will function appropriately without any modification of the current e-nodeB 110, the communication system 100 can also be further improved by modifying the e-nodeB 110. As described above, the e-nodeB 110 can be arranged to infer that the RA transmission 3C was sent from the user equipment 105 that unsuccessfully attempted to send a scheduling request transmission 2B on the PUCCH by identifying that the sender of the RA transmission 3C has access to the PUCCH resources. As described above, the e-nodeB 110 can also advantageously be adapted to update any parameters of expression (1) under the control of the e-nodeB 110 in response to such inference and/or refrain from sending a new TA value to the user equipment 105. In a communication system 100 in which a user equipment 105 is capable of retaining or releasing its PUCCH and/or SRS resources when sending an RA transmission 3C, the e-nodeB 110 can advantageously be adapted to interpret information in the RA transmission 3C regarding whether the PUCCH and/or SRS resources have been retained, for example, by identifying that the preamble included in the RA transmission 3C belongs to or does not belong to a set of preambles reserved for the user equipment 105 that has released its PUCCH resources. Furthermore, the e-nodeB 110 can be adapted so that, in response to an RA transmission 3C from a user equipment 105 that has retained its PUCCH and/or SRS resources, a reconfiguration message for reconfiguring the PUCCH and/or SRS will not be transmitted. Furthermore, the e-nodeB can be arranged to identify, in response to an RA transmission 3C from a user equipment that has released its PUCCH and/or SRS resources, that the PUCCH and/or SRS resources are available for allocation to the user equipment 105 that requires such resources.

The UL data detection mechanism 510, the UL resource monitoring mechanism 505, the comparator mechanism 520 and the SR mechanism 570 as well as the mechanisms in the e-nodeB 110 suitable for concluding that the user equipment 105 has unsuccessfully transmitted on the PUCCH (see event 3G of FIG. 3c ) can advantageously be implemented as a suitable combination of hardware and software.

Those skilled in the art will appreciate that the present invention is not limited to the embodiments disclosed in the drawings and the above detailed description, which are presented for illustrative purposes only, but that the invention can be implemented in many different ways and is defined by the appended claims.

Abbreviations

DCI dedicated control information

e-nodeB Evolved Node B

OFDM Orthogonal Frequency Division Multiplexing

PUCCH Physical Uplink Control Channel

RA Random Access

RACH Random Access Channel

RAN Radio Access Network

RLC Radio Link Control

RRC Radio Resource Control

SIB System Information Block

SR Scheduling Request

SRS Sounding Reference Symbol

TPC Transmit Power Control

TS Technical Specification

TSG Technical Specification Group

TTI Transmission Time Interval

UE User Equipment

UL Uplink

WG Working Group

Claims (15)

1. A method in a communication system (100) in which a user equipment (105) can wirelessly communicate with a radio base station (110), wherein the number of data-related scheduling requests (2B) repeatedly transmitted by the user equipment on a dedicated uplink control channel before being granted uplink resources is limited by monitoring (425, 430) in the user equipment to see if a threshold representing a maximum limit has been reached, characterized by the following steps: In the user equipment (105), a random access transmission (3C) is initiated on the random access channel in response to the threshold being reached. 2. The method of claim 1, comprising the following steps: In the user equipment, initiate (405) a metric for limiting the number of scheduled requests transmitted; In the user equipment, check (430) whether the metric has reached a threshold, and if uplink resources have not been granted and the metric has not reached the threshold: The user equipment (105) then transmits a scheduling request (2B) (435) to the radio base station (110) on the uplink control channel, and repeats the checking steps. If uplink resources have not yet been granted and the metric has reached the threshold: The user equipment then transmits (440) random access transmission (3C) on the random access channel. 3. The method of claim 1 or 2, wherein when the threshold has been reached, the cell to which the user equipment is currently connected will remain as the selected cell without performing cell evaluation. 4. The method as described in any one of claims 1-2, wherein, If uplink resources have not yet been granted and the threshold has been reached, the method further includes the user equipment releasing (3F; 437) uplink control channel resources and/or any assigned probe reference symbols. 5. The method of any one of claims 1-2, wherein if uplink resources have not yet been granted and the threshold has been reached, the method further comprises: The user equipment includes an indication in the random access transmission indicating whether the uplink control channel has been released. 6. The method as described in any one of claims 1-2, comprising: The radio base station (110) determines whether the (3G) user equipment has access to the dedicated uplink control channel resources for transmitting scheduling requests, wherein the radio base station has received random access transmissions from the user equipment; and In response to determining that the user equipment has access rights to the dedicated uplink control channel resources for transmitting scheduling requests, the radio base station sends a power control command (3H) to the user equipment. 7. A communication system (100) in which a user equipment (105) can wirelessly communicate with a radio base station (110), the user equipment including a transceiver (500) and arranged such that the number of scheduling requests (2B) related to the same uplink data (2E) that the user equipment will repeatedly transmit on the uplink control channel before being granted uplink resources is limited, because the user equipment is adapted to monitor whether a maximum limit has been reached, the user equipment being characterized in that the user equipment is adapted to: In response to the stated maximum limit being reached, a random access transmission (3C) is initiated on the random access channel. 8. The communication system (100) of claim 7, wherein the user equipment operating in the communication system comprises: Component (505) for starting a counter (530) to limit the number of scheduling requests to be transmitted; Components (520, 540) for comparing the output (545) of the counter and the threshold (550) representing the maximum limit, and for generating a comparison output (555) based on the result of the comparison. The component (570) is used to determine, based on the comparison output, whether a scheduling request should be transmitted on the uplink control channel or whether a random access transmission should be performed on the random access channel, and to guide the transceiver accordingly. 9. The communication system (100) as claimed in claim 7, wherein The transceiver (500) included in the user equipment is capable of: Receive uplink scheduling information (2D); Transmit a scheduling request (2B) on the uplink control channel; and Transmitting random access transmissions (3C) over a random access channel; The user equipment also includes: An uplink resource monitoring mechanism (505) is connected to the transceiver and is able to determine whether any uplink resource is available for data transmission and generate uplink resource monitoring output (525, 560) based on the determination result. A counter (530) is capable of counting a metric used to limit the number of scheduling requests for transmission, the metric being the number of scheduling requests for transmission or the time. A memory (530) is used to store a threshold representing the maximum limit; A comparator (540) is arranged to receive the threshold and the output of the counter, the comparator being adapted to compare the output of the counter and the threshold and generate a comparison output (555); The scheduling request mechanism (570) is adapted to receive the comparison output and determine, based on the comparison output, whether the scheduling request should be transmitted on the uplink control channel or whether the random access transmission should be performed on the random access channel, and is also adapted to guide the transceiver accordingly. 10. The communication system (100) according to any one of claims 7-8, wherein The user equipment is also adapted to release any dedicated uplink control channels when the maximum value has been reached if uplink resources have not yet been granted. 11. The communication system (100) according to any one of claims 7-8, wherein The user equipment is also adapted to include information in the random access transmission indicating that the user equipment has not yet released the uplink control channel. 12. The communication system (100) as claimed in claim 8, wherein The counter included in the user equipment is arranged to increase its value when a scheduling request is transmitted on the uplink control channel. 13. The communication system (100) as claimed in claim 8, wherein The counter included in the user equipment is arranged to measure the time elapsed since the counter was started. 14. The communication system (100) according to any one of claims 7-9, wherein the radio base station (110) is arranged as follows: Determine whether a (3G) user equipment has access to a dedicated uplink control channel resource for transmitting a scheduling request, wherein the radio base station has received a random access transmission from the user equipment; and In response to determining that the user equipment has access rights to the dedicated uplink control channel resources for transmitting scheduling requests, a power control command (3H) is sent to the user equipment. 15. A computer-readable storage medium having stored computer instructions that, when executed on a processor, cause the processor to perform the method as described in any one of claims 1-6.