HK1151411A - Timing and cell specific system information handling for handover in evolved utra - Google Patents

Description

Timing and cell specific system information handling for handover in evolved UTRA

Technical Field

The present application relates to wireless communications.

Background

In order to provide improved spectral efficiency and faster user experience, the third generation partnership project (3GPP) has proposed a Long Term Evolution (LTE) project to bring new technologies, new network architectures, new configurations, and new applications and services to wireless networks.

A Wireless Transmit Receive Unit (WTRU) may not be continuously communicating with a single enodeb (enb) in a cell. The process of transitioning (switch) between a first cell and a second cell when a WTRU moves from communicating with the two cells is referred to as "handover". In an LTE network, a WTRU should be able to undergo a handover from a source eNB, which refers to an eNB in the cell to which the WTRU is transitioning, to a target eNB, which refers to an eNB in the cell to which the WTRU is transitioning, with little impact on the performance of the communication link.

At some stage of the handover procedure in LTE networks, in order for handover to proceed smoothly, the WTRU must obtain information about the target eNB. One way for a WTRU to obtain information about a target eNB is for the WTRU to read a Broadcast Channel (BCH), a common downlink control channel that carries information about the eNB that is sending the BCH. The information may be located on a primary broadcast channel (P-BCH) or on a dedicated broadcast channel (D-BCH). More specifically, a Master Information Block (MIB) including specific information related to the target eNB is transmitted on the P-BCH. A plurality of System Information Blocks (SIBs) including other information are transmitted on the D-BCH. Since each channel is allocated a relatively long Transmission Time Interval (TTI), the WTRU may take a significant amount of time to read these downlink channels.

In a third generation partnership project (3GPP) Long Term Evolution (LTE) synchronous network, a Wireless Transmit Receive Unit (WTRU) may handover to a target cell without having to read a primary broadcast channel (P-BCH) to obtain a System Frame Number (SFN) before it sends a dedicated preamble in the target cell. However, the WTRU may need to know the SFN after handover for it to operate normally in the target cell. In particular, Discontinuous Reception (DRX) and reception of a dynamic broadcast channel (D-BCH) both require that the WTRU know the SFN.

Disclosure of Invention

A method and apparatus for reducing handover time is disclosed. This may include sending cell specific information in the handover command.

Drawings

A more detailed understanding can be obtained from the following exemplary description taken in conjunction with the accompanying drawings, in which:

figure 1 illustrates an exemplary wireless communication system including an eNB and a plurality of WTRUs in accordance with one embodiment;

figure 2 shows a functional block diagram of one WTRU and the eNB of figure 1 according to one embodiment;

FIG. 3 shows a signal diagram of a handover according to an embodiment;

fig. 4 shows a signal diagram of a handover procedure according to another embodiment; and

fig. 5 shows a signal diagram of a handover procedure according to an alternative embodiment.

Detailed Description

The term "wireless transmit/receive unit (WTRU)" as referred to below 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 below includes, but is not limited to, a node B, a site controller, an Access Point (AP), or any other type of interfacing device capable of operating in a wireless environment.

Fig. 1 shows a wireless communication system 100 including an eNB 120 and a plurality of WTRUs 110. As shown in fig. 1, the WTRU 110 communicates with the eNB 120. Although fig. 1 shows three WTRUs 110 and one eNB 120, it should be noted that any combination of wireless and wired devices may be included in the wireless communication system 100.

Figure 2 is a functional block diagram of a WTRU 110 and a base station 120 of the wireless communication system 100 of figure 1. As shown in fig. 1, the WTRU 110 communicates with the eNB 120. The WTRU 110 is configured to receive messages on a downlink communication channel, such as a broadcast channel. The eNB 120 may be configured to send signals on the Broadcast Channel (BCH), and the WTRU 110 is configured to receive and monitor signals on the BCH. The WTRU 110 may transmit on an uplink channel such as a Random Access Channel (RACH). The WTRU 110 may be configured to transmit and receive Radio Resource Control (RRC) messages and layer 1(L1) messages.

In addition to the components that may be found in a typical WTRU, the WTRU 110 includes a processor 215, a receiver 216, a transmitter 217, and an antenna 218. The WTRU 110 may also include a user interface 221. the user interface 221 may include, but is not limited to, an LCD or LED screen, a touch screen, a keyboard, an electronic stylus, or any other typical input/output device. The WTRU 110 may also include volatile and non-volatile memory 219, and an interface 220 to other devices, such as a Universal Serial Bus (USB) port, serial port, etc. The receiver 216 and the transmitter 217 are in communication with the processor 215. The antenna 218 is in communication with both the receiver 216 and the transmitter 217 to facilitate the transmission and reception of wireless data.

In addition to the components that can be found in a typical eNB, the eNB 120 includes a processor 225, a receiver 226, a transmitter 227, and an antenna 228. The receiver 226 and the transmitter 227 are in communication with the processor 225. The antenna 228 is in communication with both the receiver 226 and the transmitter 227 to facilitate the transmission and reception of wireless data.

The handover interruption time is defined as the time difference between when the WTRU receives the handover command and the time when the WTRU completes Radio Resource Control (RRC) reconfiguration with the target cell (i.e., when the WTRU resumes data transmission and reception in the target cell). To enable the WTRU to perform normal operations such as data transmission and Discontinuous Reception (DRX) in the target cell, the WTRU may obtain cell-specific system information carried on the P-BCH and D-BCH of the target cell. However, reading the P-BCH with a 40ms Transmission Time Interval (TTI) repeated 4 times and the D-BCH with scheduling units of 80, 160, and 320ms increases the handover interruption time.

The format of the signals received by the WTRU during the handover procedure may help reduce the handover interruption time. Cell-specific system information for the target cell, which is typically carried on the P-BCH and D-BCH, may be sent to the WTRU in other downlink signals that are part of the handover procedure. This may avoid handover interruptions.

The target cell specific information received by the WTRU during the handover procedure may include:

a. a downlink system bandwidth;

b. physical Control Format Indicator Channel (PCFICH) information;

c. physical hybrid ARQ indicator channel (PHICH) information such as PHICH duration and PHICH resource size;

d. signaling of reference signal transmit power and power scaling (scaling) of the reference signal to other data/control subcarriers;

e. random Access Channel (RACH) configuration:

i. information on a dedicated preamble reserved for a handover WTRU in a target cell; and

a validity timer for dedicated preambles for synchronized and unsynchronized networks;

f. contention-based RACH information (optional);

g. information for uplink reference signals (frequency hopping);

h. information (location) for detecting (sounding) reference signals;

i. physical Uplink Control Channel (PUCCH) Reference Signal (RS) sequence hopping (sequence hopping);

j. physical Uplink Shared Channel (PUSCH) hopping, i.e., semi-static configuration of two hopping modes (inter-subframe and intra-subframe or inter-subframe) on a cell-specific basis;

k. an uplink power control parameter;

DRX related parameters in the target cell;

m. start time of new DRX cycle in target cell;

n. System Frame Number (SFN);

o. the full SFN of the target cell;

p. SFN difference of source cell and target cell;

q. number of transmit antennas at eNB that the WTRU may blindly detect during cell search.

Multiple broadcast/multicast service (MBMS) single frequency number (MBSFN) related parameters; and

s. neighbor cell list.

The target cell may provide the information to the source cell in a handover request reply message. The WTRU may obtain this information from the source eNB in a downlink signal.

Alternatively, the network or eNB may define handover parameters with one or more sets of "default" values for intra-evolved universal terrestrial radio access (E-UTRA) handover. In handover, the target cell eNB may determine which of the set of values the WTRU uses for handover and may send an index of the set of handover parameter values with no actual values. This may result in compact signaling.

Also, a specific System Information Block (SIB) format may be defined for predefined handover parameter values, which include the above-mentioned properties. These values may relate to a particular Public Land Mobile Network (PLMN). The network/service provider may pre-define the required handover values that the WTRU will obtain prior to handover, which may be in one or more sets of values. The PLMN may be carried on the eNB broadcasting the SIBs. The handover command may convey an index (one per group) to the WTRU for handover parameters to the target cell.

The WTRU may indicate or report to the network that it obtained the handover parameters or the SIB including the handover parameters in an uplink message, such as an RRC reconfiguration complete message or an RRC measurement report message. For example, the obtained acknowledgement may be a single bit in the message.

The network may determine in what manner to send the handover parameter values to the WTRU in the handover command. A full set of values may be used, or an index to a default set of values may be used. Alternatively, an index to a set of predefined value sets (predefined value sets) may be sent by the eNB in a SIB broadcast.

Fig. 3 shows a signal diagram of a handover 300 according to an embodiment. The WTRU 302 sends the measurement results 308 to the source eNB 304. Based on the measurements, the source eNB 304 sends a handover request 310 to the target eNB 306. The target eNB 306 returns a handover request reply message 312 to the source eNB 304. As described above, the handover request reply message 312 includes specific information for the target eNB 306.

The handover procedure 300 continues with the source eNB 304 sending a handover command 314 to the WTRU 302, where the handover command 314 carries the target cell specific information. The WTRU 302 communicates directly with the target eNB 306 by exchanging a RACH preamble 316, a RACH response 318, and a handover complete command 320. Normal operation 322 may then take place between the WTRU 302 and the target eNB 306.

Fig. 4 shows a signal diagram of a handover procedure 400 according to another embodiment. Similar to the process 300 in fig. 3, the WTRU 402 sends the measurement result 408 to the source eNB 404. Based on the measurements, the source eNB 404 sends a handover request 410 to the target eNB 406. The target eNB 406 returns a handover request acknowledgement message 412 to the source eNB 404. As described above, the handover request reply message 412 includes specific information for the target eNB 406.

The WTRU may now begin receiving and processing signals on P-BCH and D-BCH (416). Reception and processing (416) of the P-BCH and D-BCH signals may begin before the WTRU sends a RACH preamble 418. The physical resources used by the WTRU for reception of the P-BCH and D-BCH (416) are different from the physical resources that the WTRU may use to receive eNB messages such as RACH response 420. The WTRU 402 may receive and process both P-BCH and D-BCH (416) as well as RACH messages (not shown). The WTRU 402 sends a handover complete message to the target eNB 406.

The target eNB 406 may conclude that: the WTRU 402 has obtained the target eNB SFN, P-BCH, and D-BCH after K subframes 426. K is equal to M + N, where M is the number of P-BCH TTIs and N is the number of D-BCH cycles. For example, M-4 corresponds to 160ms after the target eNB 406 receives the first RACH dedicated preamble from the WTRU 402 and is equal to the time after the WTRU 402 starts normal operation after the WTRU 402 receives the handover command 414.

The time period for the WTRU 402 to acquire the target eNB SFN may be less than the P-BCH and D-BCH information periods (K subframes). However, until K subframes have been received by the WTRU 402, the eNB 406 does not initiate normal operation 424 for the WTRU 402 even though the WTRU 402 has acquired the SFN. These normal operations 424 include, but are not limited to:

a.DRX cycle;

b. layer 1(L1) feedback;

c. dynamic and semi-persistent data transmission/reception; and

d. time alignment (alignment).

If the WTRU obtains the target eNB SFN before K subframes, a default mode of operation will be used in the target eNB 406 until the WTRU 402 obtains the SFN and/or BCH information. For example, DRX operation may be disabled and L1 feedback may be ignored or not generated. The WTRU 402 may provide implicit or explicit signaling to inform the target eNB 406 that SFN and/or BCH information has been obtained and normal operation may resume.

Alternatively, if the WTRU 402 fails to successfully receive the target eNBFN and P-BCH after K subframes 426 and fails to successfully detect P-BCH timing (timing), the WTRU 402 may determine that a radio link failure has occurred. The WTRU 402 may then begin a radio link recovery process (not shown).

Fig. 5 shows a signal diagram of a handover procedure 500 according to an alternative embodiment. Similar to process 300 in fig. 3 and process 400 in fig. 4, the WTRU 502 sends a measurement result 508 to the source eNB 504. Based on the measurements, the source eNB 504 sends a handover request 510 to the target eNB 506. The target eNB 506 returns a handover request acknowledgement message 512 to the source eNB 504. As described above, the handover request reply message 512 includes specific information for the target eNB 506.

The WTRU 502 sends a RACH preamble 516 to the target eNB 506. The target eNB 506 sends a RACH response message 518. The WTRU 502 then sends a handover complete message 520 to the target eNB 524. The WTRU 502 may now begin receiving and processing signals 522 on the P-BCH and D-BCH. The reception of the P-BCH and D-BCH signals 522 begins after the WTRU 502 sends a handover complete message 520. Once the WTRU 502 has acquired the P-BCH and D-BCH signals 522, the WTRU 502 may resume normal operations 524.

Examples

1. A method of handover in a Wireless Transmit Receive Unit (WTRU), the method comprising:

sending a handover request, and receiving one of a set of handover signals, wherein the one of the set of handover signals further comprises specific configuration information of a target eNodeB (eNB) only if the one of the set of handover signals is part of a handover procedure.

2. The method of embodiment 1, wherein the target eNB specific information comprises a System Frame Number (SFN) of the target eNB.

3. The method of embodiment 1 or 2, further comprising:

the WTRU determines a post-handover Discontinuous Reception (DRX) cycle based on the SFN.

4. The method of any of the preceding embodiments, further comprising:

the WTRU performs a Random Access Channel (RACH) procedure and simultaneously receives and processes a broadcast channel.

5. The method of any of embodiments 2-4, further comprising:

the WTRU performs a Random Access Channel (RACH) procedure and receives and processes a broadcast channel.

6. A method of handover in a Wireless Transmit Receive Unit (WTRU), the method comprising:

transmitting a measurement result, receiving a handover command based on the measurement result, performing a random access procedure while receiving and processing a broadcast channel, and completing a handover, wherein the handover command includes specific information on a target enode B, the specific information including a system frame number of the target enode B.

7. The method of embodiment 6, wherein the particular information is a complete set of values.

8. The method of embodiment 6, wherein the particular information comprises an index to a set of values.

9. The method of embodiment 6, wherein the specific information is a set of predefined values.

10. A method of handover in a Wireless Transmit Receive Unit (WTRU), the method comprising:

the method includes transmitting a measurement result, receiving a handover command based on the measurement result, performing a random access procedure, completing a handover, and receiving and processing a broadcast channel, wherein the handover command includes specific information on a target enode B, the specific information including a system frame number of the target enode B.

11. The method of embodiment 10, wherein the particular information is a complete set of values.

12. The method of embodiment 10, wherein the particular information comprises an index to a set of values.

13. The method of embodiment 10, wherein the specific information is a set of predefined values.

14. A Wireless Transmit Receive Unit (WTRU) configured to perform a handover, the WTRU comprising:

a transmitter configured to transmit a handover request, and a receiver configured to receive a handover command, wherein the handover command further includes specific configuration information of a target eNodeB (eNB).

15. The WTRU of embodiment 14 wherein the target eNB specific information includes a System Frame Number (SFN) of the target eNB.

16. The WTRU of embodiment 14 or 15, further comprising a processor configured to determine a post-handover Discontinuous Reception (DRX) cycle based on the SFN.

17. The WTRU as in embodiment 15 or 16 wherein the WTRU is further configured to perform a Random Access Channel (RACH) procedure while simultaneously receiving and processing a broadcast channel.

18. A Wireless Transmit Receive Unit (WTRU), comprising:

a transmitter configured to transmit measurement results, a receiver configured to receive a handover command based on the measurement results, a processor configured to perform a random access procedure when the receiver is receiving a broadcast channel and the processor is further processing the broadcast channel, and wherein the processor is further configured to complete a handover, the handover command comprising specific information about a target enodeb including a system frame number of the target enodeb.

19. The WTRU of embodiment 18 wherein the specific information is a complete set of values.

20. The WTRU of embodiment 18 wherein the specific information includes an index to a set of values.

21. The WTRU of embodiment 18 wherein the specific information is a set of predefined values.

Although the features and elements of the present invention are described in the particular combinations, each feature or element can be used alone without the other features and elements or in various combinations with or without other features and elements. The methods or flow charts provided herein may be implemented in a computer program, software, or firmware executed 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 disks and Digital Versatile Disks (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) or Ultra Wideband (UWB) module.

Claims (21)

1. A method of handover in a Wireless Transmit Receive Unit (WTRU), the method comprising:

sending a switching request; and

receiving a handover signal of a set of handover signals, wherein in case the handover signal of the set of handover signals is part of a handover procedure, the handover signal of the set of handover signals further comprises specific configuration information of a target eNodeB (eNB).

2. The method of claim 1, wherein the target eNB specific information includes a System Frame Number (SFN) of the target eNB.

3. The method of claim 2, further comprising:

the WTRU determines a post-handover Discontinuous Reception (DRX) cycle based on the SFN.

4. The method of claim 2, further comprising:

the WTRU:

performing a Random Access Channel (RACH) procedure; and

while receiving and processing the broadcast channel.

5. The method of claim 2, further comprising:

the WTRU:

performing a random access channel procedure; and

a broadcast channel is received and processed.

6. A method of handover in a Wireless Transmit Receive Unit (WTRU), the method comprising:

sending the measurement result;

receiving a handover command based on the measurement result;

performing a random access procedure while receiving and processing a broadcast channel; and

completing handover, wherein the handover command includes specific information about a target eNodeB, the specific information including a system frame number of the target eNodeB.

7. The method of claim 6, wherein the particular information is a complete set of values.

8. The method of claim 6, wherein the specific information comprises an index to a set of values.

9. The method of claim 6, wherein the specific information is a set of predefined values.

10. A method of handover in a Wireless Transmit Receive Unit (WTRU), the method comprising:

sending the measurement result;

receiving a handover command based on the measurement result;

performing a random access procedure;

completing the switching; and

receiving and processing a broadcast channel, wherein the handover command includes specific information about a target eNodeB, the specific information including a system frame number of the target eNodeB.

11. The method of claim 10, wherein the particular information is a complete set of values.

12. The method of claim 10, wherein the specific information comprises an index to a set of values.

13. The method of claim 10, wherein the specific information is a set of predefined values.

14. A Wireless Transmit Receive Unit (WTRU) configured to perform a handover, the WTRU comprising:

a transmitter configured to transmit a handover request; and

a receiver configured to receive a handover command, wherein the handover command further includes specific configuration information of a target eNodeB (eNB).

15. The WTRU of claim 14 wherein the target eNB specific information includes a System Frame Number (SFN) of the target eNB.

16. The WTRU of claim 15, further comprising:

a processor configured to determine a post-handover Discontinuous Reception (DRX) cycle based on the SFN.

17. The WTRU as in claim 15 wherein the WTRU is further configured to perform a Random Access Channel (RACH) procedure while simultaneously receiving and processing a broadcast channel.

18. A Wireless Transmit Receive Unit (WTRU), comprising:

a transmitter configured to transmit the measurement result;

a receiver configured to receive a handover command based on the measurement result;

a processor configured to perform a random access procedure when the receiver is receiving a broadcast channel and the processor is further processing the broadcast channel; and

wherein the processor is further configured to complete a handover, the handover command including specific information about a target eNodeB, the specific information including a system frame number of the target eNodeB.

19. The WTRU of claim 18, wherein the specific information is a complete set of values.

20. The WTRU of claim 18, wherein the specific information includes an index to a set of values.

21. The WTRU of claim 18, wherein the specific information is a set of predefined values.