U.S. patent application number 15/135620 was filed with the patent office on 2016-08-18 for method and apparatus for cell reselection.
This patent application is currently assigned to Signal Trust for Wireless Innovation. The applicant listed for this patent is Signal Trust for Wireless Innovation. Invention is credited to Christopher R. Cave, Rocco DiGirolamo, Paul Marinier, Diana Pani, Benoit Pelletier.
Application Number | 20160242094 15/135620 |
Document ID | / |
Family ID | 40720067 |
Filed Date | 2016-08-18 |
United States Patent
Application |
20160242094 |
Kind Code |
A1 |
Pani; Diana ; et
al. |
August 18, 2016 |
METHOD AND APPARATUS FOR CELL RESELECTION
Abstract
A method and wireless transmit receive unit (WTRU) are disclosed
that is configured to perform cell reselection to another cell when
the WTRU is in a CELL_FACH state using an Enhanced-Dedicated
Channel (E-DCH). The cell reselection is based on internal
measurements by the WTRU. Alternatively, the cell reselection can
be WTRU based on the WTRU measurements reported to the network.
Inventors: |
Pani; Diana; (Montreal,
CA) ; DiGirolamo; Rocco; (Laval, CA) ; Cave;
Christopher R.; (Dollard-des-Ormeaux, CA) ; Marinier;
Paul; (Brossard, CA) ; Pelletier; Benoit;
(Roxboro, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Signal Trust for Wireless Innovation |
Wilmington |
DE |
US |
|
|
Assignee: |
Signal Trust for Wireless
Innovation
Wilmington
DE
|
Family ID: |
40720067 |
Appl. No.: |
15/135620 |
Filed: |
April 22, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14875059 |
Oct 5, 2015 |
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15135620 |
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13665734 |
Oct 31, 2012 |
9161285 |
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14875059 |
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12346631 |
Dec 30, 2008 |
8325684 |
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13665734 |
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61018567 |
Jan 2, 2008 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04W 24/10 20130101;
H04W 88/08 20130101; H04W 36/0072 20130101; H04W 8/26 20130101;
H04W 36/0088 20130101; H04W 36/04 20130101; H04W 36/08 20130101;
H04W 36/36 20130101; H04W 74/0833 20130101; H04W 36/30 20130101;
H04W 36/165 20130101 |
International
Class: |
H04W 36/30 20060101
H04W036/30; H04W 36/00 20060101 H04W036/00; H04W 8/26 20060101
H04W008/26; H04W 36/36 20060101 H04W036/36; H04W 24/10 20060101
H04W024/10; H04W 36/16 20060101 H04W036/16 |
Claims
1. A method performed by a wireless transmit/receive unit (WTRU),
the method comprising: communicating with a source cell; performing
measurements on a plurality of neighboring cells; transmitting, via
the source cell, information from the measurements; receiving, via
the source cell, a message indicating that the WTRU is to
communicate via a target cell, the target cell being one of the
plurality of neighboring cells; and after receiving the message:
ceasing using an enhanced radio network terminal identifier
(E-RNTI) associated with the source cell; resetting a medium access
control; receiving, via the source cell, an E-RNTI associated with
the target cell; and communicating, via the target cell, using the
received E-RNTI.
2. The method of claim 1, further comprising receiving resource
allocation information via the target cell.
3. The method of claim 2, wherein the communicating via the target
cell includes communicating over an enhanced dedicated channel in
accordance with the resource allocation information.
4. The method of claim 1, further comprising: initiating a timer in
response to the received message.
5. The method of claim 1, wherein the received message is a
handover message.
6. The method of claim 1, wherein the received message includes an
identification of the target cell.
7. The method of claim 1, wherein the resetting of the medium
access control includes flushing a hybrid automatic retransmission
request buffer in the WTRU.
8. The method of claim 1, wherein the resetting of the medium
access control includes resetting a transmission sequence number in
the WTRU.
9. The method of claim 1, further comprising: transmitting, in
response to the received message, a random access preamble via the
target cell.
10. The method of claim 1, wherein the received E-RNTI is assigned
to the WTRU by a radio network controller.
11. A wireless transmit/receive unit (WTRU) comprising: a
transmitter; a receiver; and a processor to: perform measurements
by the receiver on signals received from a plurality of neighboring
cells; cause the transmitter to transmit, via a source cell,
information from the measurements; process a message received by
the receiver via the source cell, the message indicating that the
WTRU is to communicate via a target cell, the target cell being one
of the plurality of neighboring cells; and after processing the
message, reset a medium access control, cease using an E-RNTI
associated with the source cell, and cause the WTRU to communicate,
via the target cell, using an enhanced radio network temporary
identifier (E-RNTI) associated with the target cell and received by
the receiver via the source cell.
12. The WTRU of claim 11, wherein the processor processes resource
allocation information received by the receiver via the target
cell.
13. The WTRU of claim 12, wherein the WTRU communicates, via the
target cell, over an enhanced dedicated channel in accordance with
the resource allocation information.
14. The WTRU of claim 11, wherein the processor initiates a timer
in response to the message received by the receiver.
15. The WTRU of claim 11, wherein the message received by the
receiver is a handover message.
16. The WTRU of claim 11, wherein the message received by the
receiver includes an identification of the target cell.
17. The WTRU of claim 11, wherein the resetting of the medium
access control by the processor includes the processor flushing a
hybrid automatic retransmission request buffer in the WTRU.
18. The WTRU of claim 17, wherein resetting of the medium access
control by the processor includes the processor resetting a
transmission sequence number in the WTRU.
19. The WTRU of claim 11, wherein the received E-RNTI is assigned
to the WTRU by a radio network controller.
20. The WTRU of claim 11, wherein the processor, in response to the
message received by the receiver, causes the transmitter to
transmit a random access preamble via the target cell.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 14/875,059 filed Oct. 5, 2015, which is a
continuation of U.S. patent application Ser. No. 13/665,734 filed
Oct. 31, 2012, which issued as U.S. Pat. No. 9,161,285 on Oct. 13,
2015, which is a continuation of U.S. patent application no.
12/346,631 filed Dec. 30, 2008; which issued as U.S. Pat. No.
8,325,684 on Dec. 4, 2012, which claims the benefit of U.S.
provisional Application Ser. No. 61/018,567, filed on Jan. 2, 2008,
which are incorporated by reference as if fully set forth.
BACKGROUND
[0002] Wireless communication systems are well known in the art.
Communications standards are developed in order to provide global
connectivity for wireless systems and to achieve performance goals
in terms of, for example, throughput, latency and coverage. One
current standard in widespread use, called Universal Mobile
Telecommunications Systems (UMTS), was developed as part of Third
Generation (3G) Radio Systems, and is maintained by the Third
Generation Partnership Project (3GPP).
[0003] An example UMTS system architecture in accordance with
current 3GPP specifications is depicted in FIG. 1. The UMTS network
architecture includes a Core Network (CN) interconnected with a
UMTS Terrestrial Radio Access Network (UTRAN) via an Iu interface.
The UTRAN is configured to provide wireless telecommunication
services to users through wireless transmit receive units (WTRUs),
referred to as user equipments (UEs) in the 3GPP standard, via a Uu
radio interface. A commonly employed air interface defined in the
UMTS standard is wideband code division multiple access (W-CDMA).
The UTRAN has one or more radio network controllers (RNCs) and base
stations, referred to as Node Bs by 3GPP, which collectively
provide for the geographic coverage for wireless communications
with WTRUs. One or more Node Bs is connected to each RNC via an Iub
interface; RNCs within a UTRAN communicate via an Iur
interface.
[0004] WTRUs in a UMTS Terrestrial Radio Access Network (UTRAN) can
be in either of two modes: Idle or Connected. Based on WTRU
mobility and activity while in connected mode, the UTRAN can direct
the WTRU to transition between a number of sub-states, e.g.,
CELL_PCH, URA_PCH, CELL_FACH, and CELL_DCH. User Plane
communication between the WTRU and the UTRAN is only permitted
while in CELL FACH and CELL DCH state. The Cell DCH state is
characterized by dedicated channels (DCHs) in both the uplink (UL)
and the downlink (DL). On the WTRU side, this corresponds to
continuous transmission and reception and can be demanding on user
power requirements. The CELL_FACH state does not use DCHs and thus
allows better power consumption, at the expense of a lower uplink
and downlink throughput.
[0005] The CELL_FACH is well-suited for signaling traffic (for
example, the transmission of CELL/URA UPDATE messages), and for
applications requiring very low uplink throughput. In CELL_FACH,
uplink communication is achieved through a random access transport
channel (RACH) mapped to a packet random access channel (PRACH)
physical channel. The RACH is a contention based protocol with a
power ramp-up procedure to acquire the channel and to adjust
transmit power.
[0006] Downlink communication is through a shared Forward Access
Transport Channel (FACH) mapped to a secondary common control
physical channel (S-CCPCH) or through the high speed downlink
channel.
[0007] Mobility is handled autonomously by the WTRU in CELL_FACH.
The currently soft handover does not (as of Release 6 of the
standard) exist within CELL_FACH. As such, the WTRU independently
takes measurements, and determines when to make cell
reselections.
[0008] System information during CELL_FACH is read from a broadcast
channel (BCH). This information includes the setup details for the
uplink RACH, the downlink FACH and the high speed downlink shared
channel (HS-DSCH)) channels to be used in CELL_FACH.
[0009] Recent work by the standardization bodies has identified
reuse of an Enhanced-DCH (E-DCH) in the CELL_FACH state.
Enhanced-DCH is a feature that was introduced to increase uplink
throughput. The E-DCH operates on a request/grant principle. WTRUs
send an indication of the requested capacity they require through a
combination of mechanisms, while the network responds with grants
to these requests. These grants are generally generated by a Node B
scheduler.
[0010] At the same time, Hybrid Automatic Repeat Requests (HARQs)
are used in connection with the physical layer transmissions. To
facilitate the above mechanisms, two new UL physical channels have
been introduced, an Enhanced-Dedicated Physical Control Channel
(E-DPCCH) for control, and an Enhanced-Dedicated Physical Data
Channel (E-DPDCH) for data. Three new downlink (DL) physical
channels, two for transmission of grants and one for fast physical
layer acknowledgements (Layer 1 ACK/NACK), were also introduced.
The Node B, therefore, is permitted to issue both absolute grants
and relative grants. Grants are signaled in terms of a power ratio.
Each WTRU maintains a serving grant, which it can convert to a
payload size. For Release 6 WTRUs, mobility is handled by the
network through soft handover and active sets.
[0011] In addition to the new channels at the physical layer, E-DCH
is also required at the Medium Access Control (MAC) layer, with the
introduction of new MAC-e/es protocol entities to handle the
Enhanced Dedicated Transport Channel (E-DCH).
[0012] One of the concerns with the use of E-DCH in CELL_FACH is
the interaction of the uplink procedure with the mobility
procedure, in particular, the cell reselection procedure. This
procedure can either remain WTRU autonomous or could be network
assisted in some way. In both cases, the network and WTRU actions
upon a cell reselection need to be defined. On the WTRU side,
actions have to be specified to deal with the medium access control
entities (MAC-e/es), hybrid automatic repeat request (HARQ)
buffers, MAC Transmission Sequence Numbers (TSN), and the like.
With respect to the network, a serving radio network controller
(SRNC) may need to be made aware when a new enhanced radio network
temporary identifier (E-RNTI) has been assigned by a controlling
radio network controller (CRNC). The network may also have to deal
with releasing the resources in the source cell.
[0013] Accordingly, there exists a need for a method and apparatus
to address reselection for WTRUs capable of using the E-DCH while
in Cell_FACH state.
SUMMARY
[0014] A method and wireless transmit receive unit (WTRU) are
disclosed that is configured to perform cell reselection to another
cell. When the WTRU is in a CELL_FACH state using an
Enhanced-Dedicated Channel (E-DCH). The cell reselection can be
network assisted based on WTRU measurements reported to the
network. Alternatively, the cell reselection can be WTRU based.
BRIEF DESCRIPTION OF THE DRAWING
[0015] A more detailed understanding of the method may be had from
the following description, given by way of example and to be
understood in conjunction with the accompanying drawing.
[0016] FIG. 1 is a block diagram of an overview of the system
architecture of a conventional UMTS network;
[0017] FIG. 2 is a block diagram of a wireless communication
system; and
[0018] FIG. 3 is a timing diagram illustrating a CELL_UPDATE
procedure with a MAC-es included in the controlling radio network
controller (CRNC).
DETAILED DESCRIPTION
[0019] When referred to hereafter, the terminology "wireless
transmit/receive unit" ("WTRU") 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 device capable of
operating in a wireless environment. When referred to hereafter,
the terminology "base station" 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. When referred to hereafter, the terminology "E-DCH
system information" includes but is not limited to E_DCH
information that is broadcast by the Node B as part of its system
information. This may include information for a set of shared E-DCH
resources that are assigned by the NodeB and shared by WTRUs in
CELL_FACH state. The terminology enhanced random access channel
(E-RACH) refers to the enhanced uplink mechanism used in CELL_FACH
state, including, but not limited to the use of Enhanced-DCH
resources.
[0020] A Medium Access Control (MAC) layer is divided into several
entities; MAC-e/es protocol entities are preferably provided to
handle an Enhanced Dedicated Transport Channel (E-DCH). Generally,
the expression "MAC-is", "MAC-i", and "MAC-is/i" may be substituted
for "MAC-es", "MAC-e" and "MAC-es/e" respectively. "MAC-es/e reset"
procedure may be replaced by "MAC-is/i reset" procedure where the
"MAC-is/i reset" procedure refers to a procedure similar to
"MAC-es/e reset" with the possible additional step that
segmentation buffers are flushed.
[0021] Referring to FIG. 2, a HSPA wireless communication network
(NW) 10 comprises a WTRU 20, one or more Node Bs 30, and one or
more cells 40. Each cell 40 comprises one or more Node Bs (NB or
eNB) 30. WTRU 20 comprises a processor 9 configured to implement
the cell reselection method disclosed hereafter.
[0022] In accordance with a disclosed method, WTRU 20 performs
autonomous cell reselection, with the MAC-es, used for common
control channel (CCCH) data or common traffic, terminated at a
Controlling RNC (CRNC). Accordingly, the MAC-es entity is
associated with a common E-DCH resource set used by WTRU 20, or a
common Enhanced-Radio Network Temporary Identifier (E-RNTI) that is
selected by WTRU 20. Preferably, the MAC-es for dedicated traffic
(i.e., DCCH or DTCH) is terminated in a serving RNC (SRNC) and is
associated with a WTRU 20. Alternatively, the MAC-es for dedicated
traffic is also terminated in the CRNC.
[0023] According to this disclosed method, WTRU 20 uses internal
measurements to make cell reselection decisions. FIG. 3 is a signal
diagram of the method that may be used by WTRU 20 when a target
cell is selected in the CELL_FACH state. Upon determining to
perform a cell reselection, WTRU 20 ceases transmitting and
receiving from source Node B 22, and clears the variable enhanced
radio network temporary identifier (E-RNTI) that was assigned to
WTRU 20 by controlling radio network controller 26.
[0024] If WTRU 20 is transmitting in the uplink (UL) when it
determines that a cell reselection is to be performed, then prior
to moving to the target cell, the WTRU 20 completes transmission
for all hybrid access request (HARQ) processes that are active.
WTRU 20 may also stop monitoring the downlink (DL) E-DCH channels
in the source cell (and, if applicable, in the neighboring cells as
well).
[0025] In an alternative, WTRU 20 may reset Transmission Sequence
Numbers (TSNs) associated with the common control channel (CCCH)
logical channel in the MAC-es and flush the HARQ processes if UL
data is present in the HARQ processes. Alternatively, WTRU 20 can
autonomously perform a complete reset of the MAC-es/e entity (i.e.,
reset TSN, flush HARQ processes, and discard any remaining segments
if applicable).
[0026] WTRU 20 then receives system information blocks from target
Node B 22 in the broadcast control channel 202. If the E-DCH
information element (IE) (referred to herein as E-DCH system
information) is broadcasted in the target cell system information
blocks (SIBs), WTRU 20 starts a new preamble ramp-up phase in
target cell using the broadcasted E-DCH RACH preamble sequences.
The presence of this E-DCH system information indicates to WTRU 20
that the cell supports E-DCH in CELL_FACH. E-RACH access,
therefore, can be achieved using a common, shared, or randomly
chosen WTRU ID.
[0027] After a successful acquisition, WTRU 20 is assigned a set of
E-DCH resources for use in the target cell. WTRU 20 then sends a
CELL_UPDATE message 203 in the target cell over the assigned E-DCH
resource, to controlling RNC 26 (CRNC). Since the MAC-es for CCCH
ends in CRNC 26, the CELL_UPDATE message can be read and decoded by
CRNC 26. WTRU 20 may include an information element (IE) indicating
the E-DCH in CELL_FACH capability in CELL_UPDATE message 203 (e.g.,
IE "E-DCH in CELL_FACH"). This IE may be an enumerated IE. If the
E-DCH in CELL_FACH IE is present, the WTRU supports E-DCH in
CELL_FACH. The absence of the IE indicates that the WTRU 20 does
not support E-DCH in CELL_FACH. Alternatively, the E-DCH in CELL
FACH IE can be set to TRUE or FALSE to indicate whether the WTRU
has E-DCH in CELL_FACH capable.
[0028] Alternatively, the E-DCH capability is implicitly detected
by CRNC 26. If CRNC 26 receives the CELL_UPDATE 203 message via an
E-RACH Iub frame protocol, CRNC 26 implicitly determines that WTRU
20 supports E-DCH in CELL_FACH.
[0029] CRNC 26 may alternatively check the sub-layer from which the
packet was received. If delivered from the MAC-es entity, CRNC 26
determines that WTRU 20 supports E-DCH in CELL_FACH. Otherwise,
WTRU 20 does not support E-DCH in CELL FACH.
[0030] In another alternative, source Node B 24 notifies CRNC 26
that the packet was received over E-DCH. This alternative requires
signaling over the Iub. As such, a new Iub message can be defined
or the Node B can include the indication with the message over the
Iub frame
[0031] Accordingly, when CRNC 26 receives the CELL_UPDATE message
203 and determines that E-DCH in CELL_FACH is supported by WTRU 20,
and also supported by CRNC 26, CRNC 26 allocates a new E-RNTI to
WTRU 20. CRNC 26 then forwards the message to Serving RNC (SRNC) 28
via radio network subsystem application part (RNSAP) UL Signaling
Transfer 205, including the variable E-RNTI.
[0032] Alternatively, CRNC 26 does not send an indication that WTRU
20 supports E-DCH in CELL_FACH, but relies on SRNC 28, which is
aware of the WTRU 20 capabilities. As such, SRNC 28 requests CRNC
26 to allocate a "new E-RNTI" for WTRU 20, which may be
accomplished, for example, via the common transport channel
request.
[0033] SRNC 28 can tell source Node B that the E-DCH resources of
the WTRU can be released. In the case where a MAC-e is dedicated
per WTRU, the MAC-e entity may be fully released. If the MAC-e
entity is present per set of E-DCH resources, the HARQ soft buffers
in the source Node B are flushed, but not necessarily released. If
a MAC-e/es reset is autonomously performed every time a cell
reselection is performed, the MAC-es entity in the SRNC, associated
with the WTRU performing the reselection, also has to be reset.
[0034] SRNC 28, upon receiving the message from CRNC 26, generates
a CELL UPDATE CONFIRM message 206, 207, including a new E-RNTI for
use in CELL_FACH state. This message may be used by the network to
assign E-DCH resources. Alternatively, any E-DCH resources are
allocated by target Node B 22 after a preamble power ramp-up
performed when WTRU 20 needs to transmit additional traffic.
[0035] Upon receiving the CELL_UPDATE CONFIRM message 207, WTRU 20
stores the new E-RNTI for use in future uplink access.
[0036] Alternatively, if WTRU 20 does not autonomously perform a
MAC-e/es reset as disclosed above, the network may explicitly
request a MAC-e/es reset to be performed by WTRU 20. The network
may request a reset of the MAC-e/es entity in WTRU 20 following
SRNS relocation, every time a cell reselection is performed, when a
reconfiguration occurs, or when the dedicated MAC-es needs to be
released or reset.
[0037] In accordance with this method, a MAC-e/es reset may be
performed by adding a new IE "MAC-e/es reset" indicator in the
CELL_UPDATE CONFIRM message. Upon reception of the indicator by
WTRU 20, WTRU 20 performs a full reset of the MAC-e/es (i.e., reset
TSN and flush HARQ processes). If applicable, WTRU 20 may discard
any remaining segments in the MAC. The MAC-e/es may also be reset
by WTRU 20 autonomously resetting the MAC-e/es when WTRU 20
receives a CELL_UPDATE CONFIRM and at least one of the following
conditions are true: a SRNS relocation has been performed, which
may be detected when the IE "new U-RNTI" is present in the
CELL_UPDATE CONFIRM; a reconfiguration of MAC protocol occurs
within the CELL_UPDATE CONFIRM; or a reconfiguration of the radio
link control (RLC) protocol occurs.
[0038] Each of the above mentioned methods of resetting the
MAC-e/es may be performed alone or in combination with one another.
WTRU 20 may also perform a partial MAC-e/es reset, where the TSN
number is set to zero for the logical channel CCCH when the
CELL_UPDATE CONFIRM message is received.
[0039] In accordance with an alternative method of autonomous cell
reselection, the UTRAN MAC-e and MAC-es entities are both at the
Node B. As a result, the E-DCH transmission for CELL_FACH WTRUs
terminates at the Node B. A WTRU, therefore, is configured to make
a cell reselection decision based on internal measurements with
respect to a new target cell selected as part of cell
reselection.
[0040] WTRU 20 ceases transmitting to and receiving from the source
cell and stops monitoring the downlink (DL) E-DCH channels in
source cell. If the WTRU is transmitting in the UL, prior to moving
to the target cell, WTRU 20 may complete transmission of all HARQ
processes that are active at the time it is determined that WTRU 20
is to perform a cell reselection.
[0041] WTRU 20 then performs a reset of the MAC-es/e entity (i.e.,
flushes HARQ buffers and resets TSN to 0 and, if applicable, may
discard any remaining segments in the MAC-e/es entity). The
variable E-RNTI is then cleared by WTRU 20. The target Node B
transmits SIB information in the broadcast control channel to WTRU
20. If the E-DCH system information IEs are broadcasted in the
target cell SIBs, WTRU 20 starts a new preamble ramp-up phase in
the target cell using the E-DCH preamble sequences.
[0042] After a successful acquisition, WTRU 20 is assigned a set of
E-DCH resources to use in the target cell. For collision
resolution, WTRU 20 may use a common E-RNTI or a random ID chosen
in the MAC header. WTRU 20 then sends a CELL UPDATE message
including the E-DCH in CELL_FACH capability indication, over the
target cell to the controlling RNC. The target cell CRNC receives
the CELL_UPDATE message, and when E-DCH in CELL_FACH is supported,
the CRNC allocates an E-RNTI. The CRNC then forwards the message to
the SRNC via Radio Network Subsystem Application Part (RNSAP) UL
Signaling Transfer including the variable E-RNTI.
[0043] Alternatively, WTRU 20 does not send E-DCH in CELL_FACH
capability in the CELL_UPDATE message. The SRNC, though, is aware
of the WTRU capability, and therefore, requests the CRNC to
allocate a new E-RNTI for WTRU 20. This may be done via the common
transport channel request. The CRNC provides the new E-RNTI in the
response message. Alternatively, the E-DCH capability can be
implicitly detected by the CRNC. If the CRNC receives the
CELL_UPDATE via an E-RACH Iub frame protocol, the CRNC can
implicitly determine that the WTRU supports E-DCH in CELL_FACH.
Optionally, the CRNC can check what sub-layer the packet was
received from. If delivered from the MAC-es entity, the WTRU
supports E-DCH in CELL_FACH, otherwise the WTRU does not.
[0044] Alternatively, the Node B can notify the CRNC that the
packet was received over E-DCH. This requires signaling over the
Iub. A new Iub message can be defined, or alternatively, the Node B
can include the indication with the message over the Iub frame.
[0045] Optionally, the SRNC tells source Node B that the E-DCH
resources from the WTRU can be released. The source Node B can also
reset the UTRAN MAC-e and MAC-es and flush the HARQ soft memory
buffers in the source cell.
[0046] SRNC preferably generates a CELL_UPDATE CONFIRM message,
where it optionally includes the "new E-RNTI" to be used in
CELL_FACH state. The network may optionally use this message to
assign a different set of E-DCH resources.
[0047] Upon reception of CELL_UPDATE CONFIRM the WTRU stores the
"new E-RNTI" and uses it for future uplink access.
[0048] Alternatively, the network can include a MAC-es/e reset
indicator in the CELL_UPDATE_CONFIRM message.
[0049] In accordance with another alternative method for autonomous
cell reselection, the E-DCH for a CELL_FACH WTRU terminates at a
SRNC but CELL_UPDATE message is sent over a legacy (release 99)
RACH.
[0050] The UTRAN MAC-es entity, in accordance with this method, is
located at the SRNC and associated with a particular WTRU. The WTRU
is configured to perform cell reselection using a legacy RACH
procedure to transmit the CELL_UPDATE message, instead of sending
the CELL_UPDATE message over an enhanced RACH in the target cell.
This allows the WTRU to undergo a cell reselection without
resetting the MAC-e/es entity (i.e. the WTRU does not need to flush
the HARQ buffers and reset the TSN number to 0), allowing the
incrementing of the TSN to continue after a cell reselection.
Furthermore, this allows the WTRU to temporarily suspend E-DCH
transmission while the cell reselection is being performed and to
resume transmission after the reselection.
[0051] As disclosed above, the WTRU makes cell reselection
decisions based on internal measurements. If, as a result of the
internal measurements, a new target cell is selected, the WTRU
stops transmitting in a source cell. If data is available in the
HARQ processes, the WTRU stops the transmission of the HARQ
processes such that the WTRU can continue with the same HARQ
processes in the target cell. Alternatively, the data in the HARQ
processes is flushed.
[0052] If the WTRU is transmitting in the UL, then prior to moving
to the target cell, the WTRU may complete transmission of all HARQ
processes that are active at the time it determines that it is to
perform a cell reselection.
[0053] The WTRU then ceases monitoring the DL E-DCH channels and
other downlink resources in the source cell and clears the variable
E-RNTI.
[0054] The WTRU then receives the target cell PRACH information and
DL information from the SIBs and transmits the CELL_UPDATE message.
The CELL_UPDATE message may include the E-DCH in CELL_FACH
capability indication over the Release 99 RACH of the target cell.
The CELL_UPDATE message is received by the CRNC and forwarded to
the SRNC. The CRNC receives the CELL_UPDATE, and allocates an
E-RNTI when the WTRU is E-DCH in CELL_FACH capable. The CRNC then
forwards the message, including the variable E-RNTI, to the SRNC
via RNSAP UL Signaling Transfer. In the alternative, the WTRU does
not send E-DCH in CELL_FACH capability in the CELL_UPDATE. Since
the SRNC is aware of the WTRU capability, it requests the CRNC to
allocate a new E-RNTI for the WTRU, which may be accomplished via
the common transport channel request. The CRNC, therefore, provides
the new E-RNTI in the response message and the SRNC includes the
E-RNTI in the CELL UPDATE CONFIRM.
[0055] The SRNC generates the CELL_UPDATE CONFIRM message, which
can be used by the network to assign dedicated E-DCH resources.
Alternatively, any E-DCH resources can be allocated by the target
Node B after a preamble power ramp-up is performed when the WTRU
needs to transmit additional traffic. The CELL_UPDATE_CONFIRM
message may include the "new E-RNTI" for the WTRU.
[0056] The SRNC then informs the source Node B that the E-DCH
resources of the WTRU can be released. In the case where a MAC-e is
dedicated per WTRU, the MAC-e entity is also fully released. If the
MAC-e entity is present per set of E-DCH resource, the HARQ soft
buffers in the source Node B are flushed.
[0057] Upon reception of the CELL_UPDATE_CONFIRM message, the WTRU
stores the new E-RNTI for future uplink access.
[0058] The network may explicitly request a MAC-e/es reset to be
performed by the WTRU. The network may request a reset of the
MAC-e/es entity in the WTRU following the occurrence of SRNS
relocation, the performance of cell reselection, and the occurrence
of a reconfiguration.
[0059] In accordance with this method, a MAC-e/es reset may be
performed by adding a new IE "MAC-e/es reset" indicator in the
CELL_UPDATE_CONFIRM message. Upon reception of the indicator by the
WTRU, the WTRU performs a full reset of the MAC-e/es (i.e., reset
TSN, flush HARQ processes). If applicable, WTRU 20 may discard any
remaining segments in the MAC. The MAC-e/es may also be reset by
sending a special reset that only flushes the HARQ buffers without
altering the TSN used for reordering. The MAC-e protocol data units
(PDUs) that are in the HARQ buffers would require retransmission
from some higher layer protocol.
[0060] Alternatively SRNC can send a special reset signal telling
the WTRU to restart all currently active HARQ processes in the
target cell. The network then informs the source Node B that E-DCH
resources in the source cell can be released. The network can also
prepare the E-DCH resources in the target cell.
[0061] Alternatively, the WTRU can autonomously perform a reset
after completing transmission of all HARQ processes (using any of
the reset options highlighted above).
[0062] In accordance with another alternative method for autonomous
cell reselection, the E-DCH for CELL_FACH terminates at a Serving
RNC (SRNC) for all data. In accordance with this method, the MAC-es
terminates in the SRNC for all types of data traffic, including
CCCH, and the CELL_UPDATE message is received and decoded in the
MAC-es in the SRNC. As disclosed in above methods, the initial
steps prior to sending the CELL_UPDATE message by the WTRU are the
same.
[0063] Once the CELL_UPDATE message is received by the SRNC, the
SRNC sends a request to the CRNC to allocate at least the C-RNTI;
H-RNTI (if HS-DSCH in CELL_FACH/PCH is supported); E-RNTI (if E-DCH
in CELL_FACH is supported); and other information provided by the
CRNC in the UL signaling transfer. The request may be signaled by
introducing a new RNSAP message, or by using an existing RNSAP
procedure, such as Common Transport Channel Request.
[0064] The CRNC responds to the SRNC with the requested
information, which may be sent using the UL Signaling Transfer
Indication or via the Common Transport Channel Response message.
The SRNC then transmits the CELL_UPDATE_CONFIRM message to the
WTRU. The procedures following the CELL_UPDATE_CONFIRM are similar
to the ones described in the methods disclosed above.
[0065] For all of the methods disclosed above for autonomous cell
reselection, the SRNC has the option to allocate E-DCH resources to
the WTRU. The set of E-DCH resources can be signaled and provided
in the CELL_UPDATE_CONFIRM message, or signaled as an index to one
of the broadcasted set of resources in the SIBs using the
CELL_UPDATE_CONFIRM. The WTRU may then use that set of resources to
transmit uplink data in CELL_FACH.
[0066] The SRNC may chose to give these resources to the WTRU every
time a cell reselection is performed, or when the WTRU has
additional data to send. In accordance with the latter scenario,
the WTRU may include with the CELL_UPDATE message an indication of
the amount of other additional data and the logical channel to
which they belong. Alternatively, it can signal just an indication
that it has other data to transmit. The RNC can then use this
information to decide whether the WTRU requires E-DCH uplink
resources. If no additional data are to be sent by the WTRU, the
RNC sets up the transport channel and physical channel resources in
the target Node B. The RNC does not signal to the WTRU any E-DCH
resources.
[0067] An alternative network assisted cell reselection method is
disclosed wherein the network preferably has control of cell
reselection. In accordance with this method, the WTRU measures the
channel quality and provides these measurements to the network via
measurement reports. Triggering criteria is defined for CELL_FACH
WTRUs to transmit these measurement reports. The network then
controls cell reselection, based on the received measurements.
[0068] The network may initiate cell reselection based on
measurements taken from Node Bs in the alternative. If the
conditions for a cell reselection are met, the network may decide
to move the WTRU to CELL_DCH in the target cell, or keep the WTRU
in CELL_FACH in the target cell. In this alternative, the WTRU is
kept in CELL_FACH. The network transmits an RRC message through a
source cell to the WTRU. The WTRU, in response to the receipt of
the RRC message, stops transmitting in the source cell and ceases
monitoring the DL E-DCH channels in the source cell. E-DCH
resources are then re-acquired in the target cell using, for
example, a power ramp up procedure. The WTRU then resets the MAC
es/e entities and/or HARQ processes by sending a MAC-es/e reset
indicator in the RRC message and perform a full MAC-e/es reset
procedure (i.e., flush HARQ and reset TSN to 0).
[0069] The MAC-e/es entities may also be reset by performing a
special reset that only flushes the HARQ buffers without altering
the TSN used for reordering. The MAC-e PDUs that are in the HARQ
buffers would require retransmission from some higher layer
protocol. The special reset can be indicated as a special bit in
one of the RRC messages ordering the handover, or it can be
specified in the cell reselection procedure for WTRUs using E-DCH
in CELL_FACH. For example, the WTRU using E-DCH performs a special
reset every time a cell reselection occurs while it is in CELL_FACH
or CELL_PCH. In the case where SRNS relocation occurs together with
a cell reselection, the WTRU needs to perform a full MAC-e/es
reset.
[0070] Another method for resetting the MAC entities sends a
special reset signal to the WTRU informing the WTRU to restart all
active HARQ processes in the target cell. The RNC tells the source
Node B that the old connection is ending and informs the target
Node B to set up for the upcoming connection.
[0071] Alternatively, the network could pre-allocate E-DCH
resources in the target cell and provide this allocation
information in the RRC message.
[0072] The source Node B, alternatively, can signal the WTRU to
stop transmission (i.e. through a zero grant). The WTRU then
initiates cell reselection upon reception of this signal.
[0073] In an alternative method for mixed autonomous/network cell
reselection, the WTRU decides to perform a handover to the target
cell using the cell reselection criteria. Instead of acquiring the
system information of the target cell and sending the CELL_UPDATE
message to the target cell, as disclosed above, the WTRU sends the
CELL_UPDATE to the source cell with an indication of a desired
target cell. The CELL_UPDATE message includes the cell ID of the
target cell.
[0074] Upon reception of CELL_UPDATE by the source Node B, the
message is forwarded to the RNC. The RNC then sets up the E-DCH
resources in the target cell, which can be resources that are
specified in the CELL_UPDATE_CONFIRM or an index to one of the
broadcasted set of E-DCH resources. After sending the CELL_UPDATE
message, the WTRU reads the System Information broadcast and
connects to the target cell to receive the CELL_UPDATE_CONFIRM
message. If the confirm message is not received by the WTRU and the
CELL_UPDATE timer expires, the WTRU reattempts to send the
CELL_UPDATE over the target cell by initiating a RACH access.
[0075] The WTRU may have the option to choose to send the initial
CELL_UPDATE over the source Node B or over the target Node B. The
WTRU may use one or more of the following conditions for choosing
to send the CELL_UPDATE over the source Node B: the WTRU has
dedicated E-DCH resources allocated in CELL_FACH in the source Node
B; the WTRU has been given RACH access for an UL transmission prior
to initiating the cell reselection, and thus the WTRU can still use
the given resources for the remaining time; the WTRU always sends
CELL_UPDATE over the source cell; or the WTRU has data to send
other than the CELL_UPDATE.
[0076] Upon reception of the CELL_UPDATE message, the SRNC has the
option of giving the WTRU a set of resources or an index to the set
of resources broadcasted in the SIBs. The RNC may choose to give
these resources to the WTRU every time a cell reselection is
performed, or when the WTRU has additional data to send. The WTRU
may include in the CELL_UPDATE an indication of the amount of other
additional data and the logical channel to which they belong.
Alternatively, the WTRU signals an indication that it has other
data to transmit.
[0077] The RNC can then use this information to decide whether the
WTRU requires E-DCH uplink resources. If no additional data are to
be sent by the WTRU, the RNC sets up the transport channel, and
physical channel resources in the target Node B but does not signal
to the WTRU any E-DCH resources.
[0078] Alternatively, the network responds with CELL_UPDATE_CONFIRM
(or other RRC message) in source cell, providing the resources to
use in target cell. The WTRU may respond with a message informing
network that the physical channel reconfiguration has been
completed. The network should use this message as indication to
stop transmitting in source cell and to release all MAC e/es
resources in that cell/NodeB.
[0079] A timer is preferably started upon sending the cell update
message. If unsuccessful or if the network responds with a R7-like
CELL_UPDATE CONFIRM, the WTRU should abort its attempts to
communicate with the source cell and attempt to transmit the
CELL_UPDATE over the target cell using one or a combination of the
procedures described in the first embodiment.
[0080] Although the features and elements are described in
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 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 computer-readable storage mediums include a read only
memory (ROM), a random access memory (RAM), a register, cache
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).
[0081] Suitable processors include, by way of example, 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, Application Specific
Integrated Circuits (ASICs), Field Programmable Gate Arrays (FPGAs)
circuits, any other type of integrated circuit (IC), and/or a state
machine.
[0082] 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 videophone, a speakerphone, a vibration device, a speaker, a
microphone, a television transceiver, a hands free headset, a
keyboard, a Bluetooth.RTM. module, a frequency modulated (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.
* * * * *