HK1133355B - Providing feedback information to target node b during a serving cell change - Google Patents

Description

Providing feedback information to a target node B during a serving cell change

Technical Field

The present invention relates to wireless communications.

Background

The third generation partnership project (3GPP) is a partnership project established in month 12 of 1998. A collaboration agreement organizes multiple communication standards bodies together to produce global specifications and technical reports for 3 rd generation mobile communication systems. High Speed Downlink Packet Access (HSDPA) is a feature introduced in release 5 of the 3GPP specifications. HSPDA uses three concepts to achieve maximum spectral efficiency, including Adaptive Modulation and Coding (AMC), fast physical layer retransmission (hybrid ARQ), and fast node B scheduling.

Fig. 1 is a block diagram of a system 100 configured to utilize HSPDA. The system 100 includes a core network 102 and a Radio Network Controller (RNC)104 in communication with the core network 102. Multiple node bs 106 communicate with the RNC (only two node bs are shown in fig. 1 for clarity, it being understood that more node bs can communicate with a single RNC). Each node B106 controls a plurality of cells 108 (again, the number of cells 108 shown in fig. 1 is merely exemplary). A wireless transmit/receive unit (WTRU)110 may communicate with one or more cells 108.

AMC adaptively changes the transmission data rate on the high speed downlink shared channel (HS-DSCH) according to the channel conditions perceived by the WTRU. Specifically, the node B determines the optimal data rate, coding and transport block size by using the following information obtained on the high speed dedicated physical control channel (HS-DPCCH):

1. a Channel Quality Indication (CQI) indicating channel conditions as monitored by the WTRU;

2. acknowledgement/negative acknowledgement (ACK/NACK) feedback for fast retransmission (HARQ).

Handover is the process by which a WTRU switches from one cell to another without service interruption. In HSDPA, the high speed shared channel is monitored by the WTRU in a single cell, referred to as the "serving HS-DSCH cell". When a handover occurs, the WTRU needs to switch to a new serving HS-DSCH cell (target cell/node B) and stop communicating with the old serving HS-DSCH cell (source cell/node B). This procedure is also referred to as serving HS-DSCH cell change.

Fig. 2 shows a flow diagram of a method 200 of performing a handover procedure. The WTRU continuously measures the signal strength of neighboring cells (step 202). The WTRU compares the measured signal strength of the neighboring cell with the signal strength of the serving cell (step 204). Once the signal strength measured on the monitored common pilot channel (CPICH) of the neighboring cell exceeds the signal strength of the serving cell, the WTRU indicates to the RNC that a cell change is required (referred to as a "change of best cell", step 206). The change of best cell is reported from the WTRU to the RNC via RRC measurement report event 1D. The report contains the measured signal strength value and the cell ID. The RNC then makes a final decision whether a serving HS-DSCH cell change will occur. A handover is then performed to handover the WTRU to a new node-B (step 208).

The new serving HS-DSCH cell needs to start downlink transmission to the WTRU when channel configuration occurs (step 210). In order to obtain maximum transmission rate and maximum spectral efficiency, the node B needs to adapt to the new channel conditions as quickly as possible. The target node-B is not aware of the channel quality conditions measured by the WTRU in the new cell and therefore cannot immediately implement the maximum Modulation Coding Scheme (MCS). The node B must wait to receive multiple CQI reports from the WTRU before transmitting at the best data rate.

The target node-B may start transmitting at a lower rate than the WTRU can support before the CQI report is transmitted to the node-B. This would waste HSDPA resources until the node B can adapt to the new channel conditions. It should be noted that the RNC performs a node B handover since the downlink channel conditions are better in the new cell, and the cell change would be a waste of capacity and resources.

On the other hand, before the target node B receives the appropriate number of CQI reports, the target node B may assume that the new channel conditions are better than in the old cell and start transmitting at a higher data rate to avoid wasting HSDPA resources. However, the WTRU may measure bad channel conditions immediately after handover and may have difficulty decoding data on the HS-DSCH. This problem will trigger retransmissions and higher error rates until the node B adapts to the new channel conditions.

The existing 3GPP release 6 specifications do not provide support for optimal MCS selection and scheduling for HS-DSCH in new serving cells after handover occurs.

Disclosure of Invention

A method implemented in a wireless transmit/receive unit (WTRU) for transmitting a Channel Quality Indication (CQI) report or other measurement report begins by receiving a trigger. The CQI report is transmitted to the handover target node B until a stop condition is reached. If the stop condition is reached, the WTRU will stop transmitting CQI reports to the target node B. A WTRU configured to perform a method includes an antenna, a transmitter/receiver coupled to the antenna, and a processor in communication with the transmitter/receiver and configured to transmit a CQI report to a handover target node-B.

Drawings

A more detailed understanding of the present invention will be obtained by way of example and from the following description taken in conjunction with the accompanying drawings, in which:

fig. 1 is a block diagram of a system configured to utilize HSDPA;

FIG. 2 is a flow chart of a method of performing a handover;

FIG. 3 is a block diagram of an HS-DPCCH signal with two embedded CQI reports;

figure 4 is a block diagram of another HS-DPCCH signal with two embedded CQI reports;

FIG. 5 is a flow chart of a method of transmitting CQI reports to a target node B;

figure 6 is a block diagram of a WTRU and a node B configured to transmit and receive CQI reports.

Detailed Description

The term "wireless transmit/receive unit (WTRU)" as referred to herein includes, but is not limited to, a User Equipment (UE), a mobile station, a fixed or mobile subscriber unit, a pager, a cellular telephone, a Personal Digital Assistant (PDA), a computer, or any other type of user equipment capable of operating in a wireless environment. The term "base station" as referred to herein includes, but is not limited to, a node B, a site controller, an Access Point (AP), or any type of interfacing device capable of operating in a wireless environment.

Embodiments disclosed herein relate to transmitting data on a new serving node B after a handover procedure occurs in HSDPA. Specifically, a target node-B method is disclosed that provides CQI feedback information needed to determine the best transmission rate and data scheduling at the time of a cell change (e.g., prior to initiating data transmission to a WTRU on a new HS-DSCH).

Although the embodiments described herein relate to WCDMA systems, the concepts described herein may also be used with other technologies that support mobility and handover (e.g., WiMax, etc.). And the CQI feedback can also relate to other measurement reports used in other technologies.

The first embodiment uses the existing uplink of the WTRU to connect the node-bs in its active set. This active set includes all radio links established with the WTRU and one or more node bs. A Downlink (DL) serving cell change occurs in the active set and the WTRU has existing communication content with the new node-B on the Uplink (UL). Additionally, if a serving cell change occurs with an active set update, UL connections to the newly added neighboring node bs may be established prior to the DL serving cell change.

In this embodiment, the WTRU may send CQI reports to the source node-B and the target node-B during the handover procedure. When the handover is completed, the WTRU sends CQI reports only to the new serving HS-DSCH cell.

During a handover procedure, the WTRU monitors a number of parameters from the target node-B to estimate the pre-perceived channel quality. In this embodiment, the WTRU reports the same CQI measurements as currently defined for the serving node B.

In a second embodiment, measurements on any other downlink reference channel can be used to derive the channel quality criterion.

In a third embodiment, the WTRU uses the same high speed dedicated physical control channel (HS-DPCCH) code to send CQI information to the source node-B and the target node-B during a handover procedure. The CQI of the target node B is appended to the CQI information of the source node B on the HS-DPCCH subframe.

For example, CQI 1 and CQI 2 correspond to CQI information for the source node B and the target node B, respectively. As shown in FIG. 3, one HS-DPCCH sub-frame 300 consists of HARQ-ACK 302, CQI 1 (target NodeB report) 304, and CQI 2 (Source NodeB report) 306. The slot format may be static (e.g., a new slot format is defined and used) or dynamic, where the WTRU can switch formats back and forth during the handover.

Optionally, the feedback mechanism is based on sending information on a different HS-DPCCH. When the node B is added to the active set, it is allocated a new HS-DPCCH code. Thus, the node bs have different HS-DPCCH codes to monitor and the WTRU knows the allocated HS-DPCCH codes of all node bs in its active set.

For example, codes HS-DPCCH 1 and HS-DPCCH 2 are allocated to the source node B and the target node B, respectively. During handover, the WTRU starts sending CQI information on the code HS-DPCCH 2 and continues sending ACK/NACK and CQI information on the code HS-DPCCH 1 to the source node-B. The CQI format in the HS-DPCCH will remain the same.

In a fourth embodiment, the CQI related to a node B is transmitted at every other Transmission Time Interval (TTI) or every multiple TTIs, and the transmission of CQIs related to different node bs is staggered. As shown in fig. 4, the CQI (new)) of the target node B is in a different HS-DPCCH subframe than the CQI (old)) of the source node B. First subframe 400 consists of HARQ-ACK 402 and CQI (old) 404 and second subframe 410 consists of HARQ-ACK 412 and CQI (new) 414.

Under this approach, rules should be established to allow each node B to determine which sub-frame contains the associated CQI. Such a rule can be based on the transmission timing of the HS-DPCCH in relation to the SFN. Alternatively, no pre-established rules are defined and the node B tries to indicate which subframe belongs to its own transmission. Typically, the target node B may assume that the largest CQI is appropriate for its transmission, while the source node B suitably assumes that the smallest CQI is appropriate for its transmission.

Optionally, the WTRU sends only continuous frequent CQI reports to the target node B when handover occurs or at a time interval after measurement report triggering. The frequency of CQI reports is higher than the frequency used in normal operation. More frequent CQI reporting allows the target node B to adapt to the channel conditions quickly. The frequency of fast CQI reporting may be configured by higher layers, predetermined by the WTRU, or transmitted continuously over consecutive TTIs over a period of time.

In a fifth embodiment, CQI reports can be transmitted by using any other existing or new L1, L2, or L3 signaling mechanism/channel.

In a sixth embodiment, CQI reports can be mapped onto the E-DCH channel.

In a seventh embodiment, the CQI to the target node B may be reported using RRC signaling, such as a measurement report message sent from the WTRU based on event 1D. The RNC then forwards the CQI measurements to the target node B when configuring the radio link to the WTRU.

Fig. 5 is a flow diagram of a method 500 of transmitting CQI reports to a target node B and is used with each of the CQI reporting embodiments described above. A determination is made whether the WTRU receives a trigger to begin transmitting CQI reports to the target node-B (step 502). The trigger may be based on one or any combination of the following conditions:

1. once the measurement criteria event 1D is fulfilled.

2. A time interval (Δ t) after sending the event 1D measurement report, where Δ t is a parameter configurable by higher layer signaling. Example values of Δ t are 30ms and 60 ms.

3. When the WTRU receives higher layer signaling (e.g., transport/physical channel or radio bearer reconfiguration) indicating a serving cell change.

4. When the WTRU receives an RRC active set update message indicating a serving cell change. The UL communication to the node B sends CQI information as soon as it is available.

Once the WTRU receives the trigger condition, the WTRU can begin transmitting CQI reports to the target node B using any of the embodiments described above (step 504). The WTRU transmits the CQI report periodically/continuously or transmits the CQI report a preconfigured number of times (e.g., once or twice). In the case of continuous transmission, the periodicity can be configured by higher layer signaling, and in the case where no handover occurs, a mechanism is needed to stop transmitting CQI reports to the target node B.

A determination is made whether a stop condition is reached (step 506). The following mechanisms can be used alone or in combination to determine the stop condition:

1. a timer started based on the triggering of any of the conditions described above may be maintained at the WTRU. The WTRU stops transmission of CQI reports if no indication is received that a handover occurred or will occur within a configured time.

2. Existing handover measurement reporting mechanisms are used. Currently, the WTRU periodically sends RRC measurement report messages to the RNC until the RNC indicates that a handover is occurring or until a pre-configured time. The WTRU stops transmission of CQI reports when the WTRU stops sending measurement reports due to a failed handover.

3. Existing or new L1, L2, or L3 signaling is used to instruct the WTRU to stop transmitting CQI reports to the target node B.

If the stop condition is not met (step 506), the WTRU continues to transmit CQI reports to the target node B (step 508). If the stop condition is reached, the WTRU stops transmitting CQI reports to the target node B (step 510) and the method ends.

The target node-B starts decoding CQI reports from the WTRU if one or a combination of the following conditions occur:

1. upon receiving signaling from the RNC to reconfigure the serving radio link with this WTRU. The target node B can use the message as an internal trigger to start decoding the CQI report.

2. The node B uses blind probing to determine whether a CQI report has been sent.

Figure 6 is a block diagram of a WTRU 602 and a node-B610 configured to transmit and receive CQI reports. The WTRU 602 includes an antenna 604, a transmitter/receiver 606 coupled to the antenna 604, and a processor 608 in communication with the transmitter/receiver 606. The processor 608 is configured to implement the method 500 and any of the described embodiments for transmitting CQI reports to the node B610.

The node B610 includes an antenna 612, a transmitter/receiver 614 coupled to the antenna 612, and a processor 616 in communication with the transmitter/receiver 614.

Although the features and elements of the present invention are described in the preferred embodiments in particular combinations, each feature or element can be used alone without the other features and elements of the preferred embodiments or in various combinations with or without other features and elements of the present invention. The methods or flow charts provided in the present invention may be implemented in a computer program, software, or firmware tangibly embodied in a computer-readable storage medium for execution by a general purpose computer or a processor. Examples of the computer-readable storage medium include read-only memory (ROM), random-access memory (RAM), registers, buffer memory, semiconductor memory devices, magnetic media such as internal hard disks and removable disks, magneto-optical media, and optical media such as CD-ROM discs and Digital Versatile Discs (DVDs).

For example, suitable processors include: a general-purpose processor, a special-purpose processor, a conventional processor, a Digital Signal Processor (DSP), a plurality of microprocessors, one or more microprocessors in association with a DSP core, a controller, a microcontroller, an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA) circuit, any Integrated Circuit (IC), and/or a state machine.

A processor in association with software may be used to implement a radio frequency transceiver for use in a Wireless Transmit Receive Unit (WTRU), User Equipment (UE), terminal, base station, Radio Network Controller (RNC), or any host computer. The WTRU may be used in conjunction with modules, implemented in hardware and/or software, such as a camera, a video camera module, a video phone, a speakerphone, a vibration device, a speaker, a microphone, a television transceiver, a hands free headset, a keyboard, and BluetoothA module, a Frequency Modulation (FM) radio unit, a Liquid Crystal Display (LCD) display unit, an Organic Light Emitting Diode (OLED) display unit, a digital music player, a media player, a video game player module, an Internet browser, and/or any Wireless Local Area Network (WLAN) module.

Examples

1. A method implemented in a wireless transmit/receive unit (WTRU) for transmitting Channel Quality Indication (CQI) reports, the method comprising: receiving a trigger; transmitting a CQI report to the handover target node B; determining whether a stop condition is reached; and stopping transmission of the CQI report if the stop condition has been reached.

2. The method of embodiment 1, wherein the trigger is the execution of a measurement criteria event 1D.

3. The method of embodiment 1, wherein the trigger is a time interval after execution of a measurement criteria event 1D.

4. The method of embodiment 1, wherein the trigger is an indication of a serving cell change.

5. The method of embodiment 4 wherein the indication is received through higher layer signaling.

6. The method of embodiment 4 wherein the indication is received via a radio resource control active set update message.

7. The method as in any one of embodiments 1-6 wherein the CQI report is sent to a handover target node B belonging to an active set of WTRUs during a handover procedure.

8. The method as in any one of embodiments 1-6 wherein the CQI report is sent to a handover target node B using a high speed dedicated physical control channel code used to send the CQI report to a source node B.

9. The method of embodiment 8 wherein the CQI report for the target node B is transmitted in a subframe with the CQI report for the source node B.

10. The method as in any one of embodiments 1-6 wherein the CQI report is sent to the handover target node B by using a high speed dedicated physical control channel (HS-DPCCH) code for the target node B that is different from a HS-DPCCH code for a source node B.

11. The method as in any one of embodiments 1-6 wherein the CQI reports are transmitted to the target node B every other transmission time interval.

12. The method as in any of embodiments 1-6 wherein the CQI report is transmitted to the target node B in a different subframe than a CQI report to a source node B.

13. The method as in any one of embodiments 1-6 wherein the CQI reports are transmitted to the target node B at multiple transmission time intervals.

14. The method as in any of embodiments 1-6, wherein the CQI report is transmitted to the target node B via signaling selected from the group consisting of layer 1 signaling, layer 2 signaling, and layer 3 signaling, the group comprising: .

15. The method as in any of embodiments 1-6 wherein the CQI reports are mapped to an enhanced dedicated channel.

16. The method as in any one of embodiments 1-6 wherein the CQI report is transmitted to a target node B through radio resource control signaling.

17. The method as in any one of embodiments 1-16 wherein the stop condition is a predetermined number of CQI report transmissions.

18. The method as in any one of embodiments 1-17 wherein the CQI reports are transmitted periodically to the target node B; and the stop condition is a timer that is started when the trigger is received.

19. The method as in any one of embodiments 1-17 wherein the CQI reports are transmitted periodically to the target node B; and the stop condition is based on a radio resource control measurement report message transmitted to a radio network controller, such that if the WTRU stops transmitting measurement report messages due to a failed handover, the WTRU stops transmitting CQI reports to the target node B.

20. The method of embodiment 1, wherein the trigger is a handover; and the transmitting step comprises transmitting successive CQI reports to the target node B.

21. The method of embodiment 20 wherein the frequency at which the CQI reports are transmitted is configured by higher layers.

22. The method of embodiment 20 wherein the frequency of transmitting the CQI reports is configured by the WTRU.

23. The method of embodiment 20, wherein the CQI reports are transmitted continuously over consecutive transmission time intervals for a predetermined period of time.

24. The method of embodiment 1, wherein the trigger is a time interval after triggering a measurement report; and the transmitting step comprises transmitting successive CQI reports to the target node B.

25. The method of embodiment 24 wherein the frequency at which the CQI reports are transmitted is configured by higher layers.

26. The method of embodiment 24 wherein the frequency of transmitting the CQI reports is configured by the WTRU.

27. The method of embodiment 24, wherein the CQI reports are transmitted continuously over successive transmission time intervals within a predetermined time period.

28. The method of embodiment 1 wherein the CQI reports are transmitted periodically to the target node B and the stop condition is based on a layer 1 signal received by the WTRU.

29. The method of embodiment 1 wherein the CQI reports are transmitted periodically to the target node B and the stop condition is based on a layer 2 signal received by the WTRU.

30. The method of embodiment 1 wherein the CQI reports are transmitted periodically to the target node B and the stop condition is based on a layer 3 signal received by the WTRU.

31. A wireless transmit/receive unit, comprising: an antenna; a transmitter/receiver connected to the antenna; and a processor in communication with the transmitter/receiver, the processor configured to transmit a channel quality indication report to a handover target node B.

32. A wireless transmit/receive unit configured to perform the method of any of embodiments 1-30.

Claims (4)

1. A method of reporting channel quality information by a wireless transmit/receive unit (WTRU) in a wireless network, the method comprising:

transmitting a plurality of Channel Quality Indication (CQI) reports to a source node B on a high speed dedicated physical control channel (HS-DPCCH);

transmitting at least one CQI report on the HS-DPCCH for a target node B in a further cell, wherein the at least one CQI report is continuously transmitted over consecutive Transmission Time Intervals (TTIs) over a period of time;

determining whether a stop condition is reached; and

stopping transmission of the at least one CQI report if the stop condition is reached.

2. The method of claim 1, wherein transmitting the plurality of CQI reports to the source node B and transmitting the at least one CQI report to a target node B in the other cell are provided during a handover operation.

3. An apparatus configured to report channel quality information by a wireless transmit/receive unit (WTRU) in a wireless network, the apparatus comprising:

means for transmitting a plurality of Channel Quality Indication (CQI) reports to a source node B on a high speed dedicated physical control channel (HS-DPCCH);

means for transmitting at least one CQI report on the HS-DPCCH for a target node B in another cell, wherein the at least one CQI report is continuously transmitted over consecutive Transmission Time Intervals (TTIs) over a period of time;

means for determining whether a stop condition is reached; and

means for stopping transmission of the at least one CQI report if the stop condition is reached.

4. The apparatus of claim 3, wherein transmitting the plurality of CQI reports to the source node B and transmitting the at least one CQI report to a target node B in the other cell are provided during a handover operation.