WO2010093302A1

WO2010093302A1 - Handling of scheduling information transmissions

Info

Publication number: WO2010093302A1
Application number: PCT/SE2009/051502
Authority: WO
Inventors: Jose Luis Pradas; Stefan Wager
Original assignee: Telefonaktiebolaget L M Ericsson (Publ)
Priority date: 2009-02-12
Filing date: 2009-12-24
Publication date: 2010-08-19

Abstract

User Equipment operating in Enhanced CELL_FACH transmits a MAC-i PDU including Scheduling Information with TEBS= 0 using HARQ. If all HARQ retransmissions of the MAC-iPDU including Scheduling Information fail, the UE triggers transmission of new Scheduling Information if implicit release of common E-DCH resources is not activated, and the UE refrains from triggering transmission of new Scheduling Information if implicit release of common E-DCH resources is activated.

Description

HANDLING OF SCHEDULING INFORMATION TRANSMISSIONS

TECHNICAL FIELD

The present invention relates generally to wireless configuration, and in particular to the communication of Scheduling Information by a UE following failed HARQ retransmissions.

BACKGROUND

One aspect of the High Speed Packet Access (HSPA) of UMTS is Enhanced Uplink, also known as High Speed Uplink Packet Access (HSUPA). Enhanced Uplink improves performance of uplink communications - those from User Equipment (UE) to a cell base station, or Node B - using higher data rates, reduced latency, and improved system capacity. Enhanced Uplink improves performance primarily via fast scheduling and fast hybrid ARQ with soft combining. These enhancements are implemented through the Enhanced Dedicated Channel (E-DCH). Some E-DCH resource may be common. Common E-DCH resources are under direct control of a Node B and are shared by UEs in that cell in CELL_FACH and IDLE mode. A Radio Network Controller (RNC) is not involved in the assignment of these resources to UEs. Since only one cell is involved in the resource allocation, soft handover of communications on these resources is not possible.

The fundamental shared resource in Enhanced Uplink is the tolerable uplink interference. The interference depends on the transmission power of multiple UEs throughout a cell. Because uplink transmissions are non-orthogonal, fast closed-loop power control is necessary to address the near-far problem (that uplink transmissions from a UE near the Node B may swamp uplink transmissions from one far away, even if the far UE transmits at maximum power). One method of UE power control is via fast scheduling. To implement the fast scheduling, a short TTI (e.g., 2 msec) is provided, and the scheduler is located in the Node B. The scheduler, via scheduling grants (either absolute or relative), tells each UE in a cell when it can transmit uplink data, and its maximum allowed E- DCH-to-pilot power ratio (specifically, the maximum E-DPDCH-to-DPCCH power ratio). Since a higher UE uplink data rate requires a higher received power at the Node B to maintain the E_b/N₀ required for successful demodulation, controlling the UE transmission power effectively controls its maximum allowed data rate. Furthermore, controlling the UE maximum allowed transmission power ratio, rather than directly assigning the UE a data rate, allows the UE some flexibility in setting its data rate, to account for rapid changes in channel conditions, changes in the priority or quantity of information to be transmitted, and the like. While the scheduler is located in the Node B, the transmission buffers are distributed among the UEs in the cell. The UEs send scheduling requests to the Node B to indicate both a need for uplink transmission scheduling and to transmit information about buffer status and available transmit power. This information is known more generally as Scheduling Information (Sl). SI may be transmitted to the Node B alone, or as part of a user data transmission. Since SI is the only mechanism for an unscheduled UE to request resources, the SI can be sent non- scheduled (i.e., without regard to a serving grant).

Enhanced Uplink implements fast hybrid ARQ (HARQ) with soft combining to provide robustness against transmission errors. For each transport block received in the uplink, the Node B transmits a single bit to the UE to indicate successful decoding (ACK) or to request retransmission (NAK). Soft combining allows any Node B in soft handoff that received a good transmission to ACK the UE, even if the serving Node B was unable to decode a block. A UE can use different Medium Access Control (MAC) entities to support E-DCH transmissions and reception. Upper protocol layers in the UE configure which MAC entity is responsible for handling data on the E-DCH. One of the MAC entities is MAC-e. A MAC-e in the Node B is responsible for support of fast hybrid ARQ retransmission and scheduling. A MAC-e in the UE is responsible for selecting the uplink data rate within the limits set by the scheduler in the Node B MAC-e, via selecting the E-DCH Transport Format Combination (E-TFC). MAC-i is another MAC entity which can be use to support E-DCH transmissions and reception. At the Node-B, the MAC-i is a MAC entity responsible for support of fast hybrid ARQ retransmission and scheduling. At the UE, the MAC-i together with MAC-is is responsible for support for selecting the uplink data rate within the limits set by the scheduler in the Node B, and for support of fast hybrid ARQ transmission. Release 8 of the Third Generation Partnership Program (3GPP) Technical Specification

25.321 , "Medium Access Control Protocol (MAC) Specification," incorporated herein by reference in its entirety, specifies protocols regarding the transmission of Scheduling Information (Sl). In particular, according to chapters 1 1.8.1.1.2 and 11.8.1.6.3, if SI is transmitted in a MAC-i Protocol Data Unit (PDU), all HARQ retransmissions of the MAC-i PDU fail, and the SI was transmitted together with higher layer data multiplexed in the same MAC-e or MAC-i PDU, then the transmission of a new SI should be triggered.

In enhanced CELL_FACH, if implicit release of common E-DCH resources is activated, the UE will release the common E-DCH resources when the Scheduling Information has been sent and all HARQ processes have finished and the HARQ buffers are empty. A User Equipment (UE) experiencing the situation above, will try to access the network (NW) to get a new common E-DCH resource to send the SI if the UE had released the resources.

The present inventors have identified an issue not recognized in the prior art, when E_DCH is utilized in enhanced CELL_FACH state. In this condition, the UE indicates a release of common E_DCH resources by sending an SI in which the field TEBS is equal to 0. The resources are released when the HARQ processes have completed - that is, either all processes have been ACKed, or the maximum number of retransmissions has been reached. In either case, the UE will release the common E_DCH resources and stop transmissions. The network is aware that there are no more control channels, and will also know that the UE has reached the maximum number of HARQ retransmissions. Accordingly, the Node-B is aware that the UE has released the common E_DCH resources. According to the above-cited 3GPP TS 25.321 , a UE in this situation should attempt to access the network to get a new common E- DCH resource to send the Sl. However, since the purpose of the SI is to signal release of common E-DCH resources, which have already been released, and further since the Node-B is aware of such release, a new network access and SI transmission is not necessary, adds signaling overhead, and contributes to interference in the air interface.

SUMMARY

According to embodiments of the present invention disclosed and claimed herein, a UE refrains from transmitting Scheduling Information to a Node B under certain circumstances, to reduce overhead and avoid excessive interference.

One embodiment relates to a method in a User Equipment, for handling transmission of scheduling information while operating in Enhanced CELL_FACH. A MAC-i PDU including

Scheduling Information with TEBS = 0 is transmitted using HARQ. If all HARQ retransmissions of the MAC-i PDU including Scheduling Information fail, the UE triggers transmission of new Scheduling Information if implicit release of common E-DCH resources is not activated, and the UE refrains from triggering transmission of new Scheduling Information if implicit release of common E-DCH resources is activated.

Another embodiment relates to a method of transmitting data from a User Equipment in a wireless communication network in Enhanced CELL_FACH state. Data and Scheduling Information are transmitted to the network. If the maximum allowable number of HARQ retransmissions of the Scheduling Information fails, the UE refrains from triggering transmission of the Scheduling Information if implicit release of common E-DCH resources is activated.

Yet another embodiment relates to a User Equipment (UE) having one or more antennas, a transceiver communicatively coupled to the antenna, and a controller operatively coupled to the transceiver and operative to control the transceiver and the overall operation of the UE in CELL_FACH mode. The controller does not initiate a new transmission to the network through the transceiver to transmit Scheduling Information following the maximum allowable number of failed HARQ retransmissions of the Scheduling Information if the UE is in intrinsic E- DCH resource release mode.

Still another embodiment relates to a User Equipment (UE) including transmission means for transmitting a MAC-i PDU including Scheduling Information with TEBS = 0 using HARQ while the UE is operating in Enhanced CELL_FACH. The UE also includes trigger means operatively coupled to the transmission means for, if all HARQ retransmissions of said MAC-i PDU including Scheduling Information fail, triggering transmission of new Scheduling Information if implicit release of common E-DCH resources is not activated, and refraining from triggering transmission of new Scheduling Information if implicit release of common E-DCH resources is activated.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a functional block diagram of a wireless communication network.

Figure 2 is a functional block diagram of a User Equipment operative in the network of Figure 1.

Figure 3 is a flow diagram of a portion of a method of transmitting data by the UE of Figure 2.

DETAILED DESCRIPTION

For Enhanced CELL_FACH (E-DCH in CELL_FACH state and Idle mode), if all HARQ retransmissions fail for a MAC-i PDU containing Scheduling Information and Scheduling Information was transmitted together with higher layer data multiplexed in the same MAC-e or MAC-i PDU and implicit release of common E-DCH resources is activated, the UE shall not trigger transmission of new Scheduling Information. On the other hand, if the implicit release of common E-DCH resources is disabled regardless whether Scheduling Information was transmitted together with higher layer data multiplexed in the same MAC-e or MAC-i PDU or not, the UE shall trigger the transmission of new Scheduling Information. Figure 1 depicts a representative wireless communication network 10. The network 10 includes a core network 12 connecting a plurality of Radio Network Controllers (RNC) 14, 16, 18, 20. The RNC 14 controls a Node B 22, which provides radio resources for wireless communication with User Equipment (UE) 30 in its geographic area or cell 24. The RNC 14 may additionally control other Node B's 26, 28, each providing service in their respective cells. In one embodiment, the Node B 22 transmits to UEs 30 in its cell on shared channels. In particular, the Node B 22 communicates on the downlink on the High Speed Downlink Shared Channel (HS- DSCH), and the UE 30 communicates on the uplink on the Enhanced Dedicated Channel (E- DCH).

Figure 2 depicts a representative UE 30. The UE 30 send and receives wireless communication signals at one or more antenna 32, which are generated and received, respectively, by a radio frequency transceiver 34. The transceiver 34 receives data, such as speech, from and sends information, such as audio, to a user interface 36. The user interface 36 may include a microphone, speaker, text and/or graphic display, keypad, keyboard, camera, and the like, as known in the art. The transceiver 34 and user interface 36, as well as the overall operation of the UE 30, are controlled by a controller 38, such as a microprocessor or digital signal processer, executing software programs stored in memory 40.

A MAC PDU encode/decode unit 35 performs encoding and decoding of MAC layer Physical Data Units (PDU), such as MAC-e and MAC-i PDUs, under the control of the controller 38. In particular, the controller 38 may direct the MAC PDU encode/decode unit 35 to include Scheduling Information (Sl) in a MAC-i PDU for transmission to the network by the transceiver 34. Although depicted as a separate functional block, the MAC PDU encode/decode unit 35 may comprise one or more software modules executed by the controller 38. The UE 30 may be a portable device, with all components powered by a battery 42.

Additional circuits and/or functional units within the UE 30, not relevant herein, are omitted for clarity. Those of skill in the art will recognize that the transceiver 34, the MAC PDU encode/decode unit 35, and user interface 36 may be implemented with dedicated hardware, in programmable logic with appropriate firmware, as functional software modules executed on the controller 38, or any combination of these.

A UE 30 that is E-DCH in CELL_FACH enabled may send its data on a common E-DCH resource after the UE has completed a random access procedure requesting a common E-DCH resource, and the Node B 22 has assigned a common E-DCH resource to the UE 30.

Upon completing its transmission, the UE 30 indicates that its buffer is empty by sending the Scheduling Information (Sl) indicating TEBS = 0. This SI should be transmitted with the MAC-i PDU carrying the last CCCH/DCCH/DTCH data, if the UE's serving grant is sufficient to carry the SI in the same MAC-i PDU together with the remaining CCCH/DCCH/DTCH data. Otherwise, the empty buffer status report is transmitted separately with the next MAC-i PDU. There are two methods for releasing common E-DCH resources, referred to as explicit and implicit release.

With explicit release, the Node B 22 releases the common E-DCH resource by sending a grant INACTIVE on all HARQ processes on the absolute grant channel E-AGCH. Explicit release is used if the Information Element (IE) "E-DCH continuation transmission back off" is set to "infinity." With implicit release, the UE 30 releases its resources after it has transmitted the SI indicating TEBS = 0. Implicit release is used if the IE "E-DCH continuation transmission back off" is not set to "infinity."

In implicit release mode, the UE 30 will release the common E-DCH resources for CCCH transmissions when there are no MAC-i PDUs pending for transmission and it has transmitted the SI indicating TEBS = 0. Explicit release mode is not available for CCCH transmission. For DTCH/DCCH transmissions, the UE 30 will release the common E-DCH resources, if implicit release mode is configured, when there is no MAC-i PDU pending for transmission.

In a straightforward implementation of 3GPP TS 25.321 , if an SI was transmitted in a MAC-i PDU that failed, and all allowed HARQ retransmissions failed, the UE 30 would initiate a new transmission to transmit the Sl, the purpose of the SI is to communicate to the Node-B 22 that the common E-DCH resources should be released. If implicit release is configured, however, the UE 30 would have already released the E-DCH common resources, and the Node-B 22 would be aware of this. Thus, the transmission of the SI would entail a re-allocation of common E-DCH to the UE 30, and the system overhead necessary to accomplish this, to transmit information of which the Node-B 22 is already aware.

According to embodiments of the present invention, if an SI was transmitted in a MAC-i PDU, and the maximum number of HARQ retransmissions is reached, and all HARQ retransmissions fail, the UE 30 shall only trigger a new SI if DCCH/DTCH transmission and explicit release is configured, i.e. implicit release is not configured. Otherwise, the UE 30 shall not trigger a new Sl. This avoids the system overhead of the UE 30 requesting a common E- DCH resource and likely reduces interference as well. If all HARQ attempts have failed, the UE is probably experiencing poor radio conditions. Allowing the UE to trigger a new SI transmission would likely only add interference to the system. Under these conditions, the UE shall not trigger a new SI transmission, and higher protocol layers (e.g., the Radio Link Control, or RLC) will recover. On the other hand, the UE 30 does inform the Node B 22 of the buffer status TEBS = 0 when implicit release is disabled, and the Node B 22 has already assigned a common E-DCH to the UE 30. Figure 3 depicts a portion of a method 100 of transmitting data by the UE 30 according to embodiments of the present invention. The UE 30 enters CELL_FACH state (block 102), and transmits data (block 104). Upon transmitting all available data, the buffer is empty and TEBS = 0. The UE 30 transmits the TEBS in a SI within a MAC-i PDU transmission (block 106). If the transmission is successful (block 108), the UE 30 continues normal operation (block 110). If the MAC-i PDU transmission fails (block 108) and the maximum number of allowed HARQ retransmission has not been reached (block 112), the MAC-i PDU carrying the SI is retransmitted (block 106). Once the maximum number of allowed HARQ retransmissions is reached (block 1 12), the UE 30 will trigger a new transmission for the SI or not, depending on the common E-DCH resources release mode (block 114). In explicit release, the UE 30 will trigger a new transmission (block 1 16). In implicit release, the UE 30 will have released the common E-DCH resources assigned to it, and according to embodiments of the present invention, will not trigger a new transmission for the SI (block 1 18). In either case, the UE 30 then proceed with normal operation (block 1 10).

The present invention may, of course, be carried out in other ways than those specifically set forth herein without departing from essential characteristics of the invention. The present embodiments are to be considered in all respects as illustrative and not restrictive, and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.

The following acronyms, as used herein, have the following meanings: ARQ Automatic Repeat Request

HARQ Hybrid Automatic Repeat Request

E-DPDCH E-DCH Dedicated Physical Data Channel DPCCH Dedicated Physical Control Channel TTI Transmission Time Interval

E-TFC E-DCH Transport Format Combination

CCCH Common Control Channel

DCCH Dedicated Control Channel

DTCH Dedicated Traffic Channel

RACH Random Access Channel

E-AGCH E-DCH Absolute Grant Channel

TEBS Total E-DCH Buffer Status

UMTS Universal Mobile Telecommunications System

Claims

CLAIMSWhat is claimed is:

1. A method in a User Equipment (30), for handling transmission of scheduling information while operating in Enhanced CELL_FACH, the method comprising: transmitting a MAC-i PDU including Scheduling Information with TEBS = 0 using HARQ; and characterized by if all HARQ retransmissions of said MAC-i PDU including Scheduling Information fail, triggering transmission of new Scheduling Information if implicit release of common E-DCH resources is not activated, and refraining from triggering transmission of new Scheduling Information if implicit release of common E-DCH resources is activated.

2. A method of transmitting data from a User Equipment (30) in a wireless communication network in Enhanced CELL_FACH state, comprising: transmitting data to the network; transmitting Scheduling Information (Sl) to the network; and characterized by if the maximum allowable number of HARQ retransmissions of the SI fail, refraining from triggering transmission of the SI if implicit release of common E-DCH resources is activated.

3. The method of claim 2 wherein if the maximum allowable number of HARQ retransmissions of the SI fail, triggering a new transmission for the SI if implicit release of common E-DCH resources is not activated.

4. The method of claim 2 wherein the SI includes TEBS = 0.

5. A User Equipment (UE) (30) comprising: one or more antennas (32); a transceiver (34) communicatively coupled to the antenna (32); and a controller (38) operatively coupled to the transceiver (34) and operative to control the transceiver (34) and the overall operation of the UE (30) in CELL_FACH state; characterized in that the controller (38) does not initiate a new transmission to the network through the transceiver (34) to transmit Scheduling Information (Sl) following the maximum allowable number of failed HARQ retransmissions of the SI if the UE (30) is in intrinsic E-DCH resource release mode.

6. The UE (30) of claim 5 wherein the controller (38) is operative to initiate a new transmission to the network through the transceiver (34) to transmit Scheduling Information (Sl) following the maximum allowable number of failed HARQ retransmissions of the SI if the UE (30) is in extrinsic E-DCH resource release mode.

7. The UE (30) of claim 5 wherein the SI includes TEBS = 0.

8. The UE (30) of claim 5 further comprising a MAC PDU encoder/decoder (35) operative to encode a MAC-i PDU including the Sl.

9. A User Equipment (UE) (30) comprising: transmission means (35) for transmitting a MAC-i PDU including Scheduling Information with TEBS = 0 using HARQ while the UE is operating in Enhanced CELL_FACH; characterized by trigger means (38) operatively coupled to the transmission means (35) for, if all HARQ retransmissions of said MAC-i PDU including Scheduling Information fail, triggering transmission of new Scheduling Information if implicit release of common E-DCH resources is not activated, and refraining from triggering transmission of new Scheduling Information if implicit release of common E-DCH resources is activated.