Enhancement to the Recovery Mechanism for Cell Update Procedure in CELLJDCH State Cross Reference Application
[0001] This application claims priority from U.S. Provisional Patent Application No.
60/377,567 filed on May 3, 2002.
Background
[0002] Once a mobile device is turned on, the mobile device searches, finds and selects a cell of the
chosen public land mobile network (PLMN), turns to its control channel and camps on it. As long
as the mobile device is power on, this cell selection and reselection is a continuous process.
Especially, when the mobile device moves among cells. Inevitably, the mobile device has to
disconnect its communication with the fading cell coverage and reconnect with a new suitable cell
that the mobile device can have a better signal. Based on connected mode radio measurements and
cell reselection criteria, the cell reselection process of a mobile device includes selecting a more suitable cell and associated radio access technology (RAT). When a mobile device is in idle mode,
URA_PCH, CELL_PCH or CELLJFACH state, it regularly performs cell reselection procedures
to search for and camp on a better cell (i.e. cell has higher signal level) according to the cell
reselection criteria.
[0003] Figure 1 shows the states and procedures for cell reselection process in URA_PCH,
CELLJPCH and CELL_FACH states of connected mode. Assume that the mobile device is in the
Universal Mobile Telecommunication System (UMTS) Terrestrial Radio Access (UTRA) Radio
Resource Control (RRC) connected mode 5, when a cell reselection is triggered 10, the mobile device starts to evaluate the cell reselection criteria based on radio measurements. And if a better cell using the same RAT is found, then that cell is selected. The mobile device goes back to the
UTRA RRC connected mode 5. If the change of cell implies a change of RAT, the existing Radio
Resource Control (RRC) connection is released, and the mobile device enters idle mode of the
other RAT 20. If no suitable cell is found in the cell reselection procedure, the mobile device will
go into the Cell Selection when leaving connected mode 25 and eventually enters an idle mode.
Meanwhile when the radio link failure is triggered, the mobile device shall trigger the initial cell
reselection procedure 15 in order to request re-establishment of the RRC connection. If the mobile
device is unable to find a suitable cell for a period, the mobile device eventually enters an idle
mode. If the mobile device finds a suitable cell, the mobile device goes back to the UTRA RRC
connected mode 5.
[0004] On the other hand, when the mobile device successfully selects a suitable Universal Terrestrial Radio Access (UTRA) cell, the mobile device performs a cell re-selection procedure
and submits the CELL UPDATE message for transmission on the Uplink Common Control Channel (CCCH) of the selected cell.
[0005] According to the prior art, two timers, T314 and T315, are relevant to track either the radio
link failure process or the Radio Link Control (RLC) unrecoverable error process in CELLJDCH
state of connected mode. The value of timers T314 and T315 are broadcasted in the system
information by network, and all the broadcasted timers value shall be store at mobile device. All
the established Radio Access Bearers (RABs), except signalling Radio Access Bearers (RABs) that used to transfer signalling messages, shall be associated with one of the timers T314 or T315
by network, depending on how long the disconnection can be tolerated by the application/service
using this RAB. For only signalling Radio Access Bearers (RABs) are established, i.e. only RRC
connection exists, these signalling RABs are associated with one of the timer T314 and T315. A
radio link failure happens when the mobile device receives a plurality of consecutive "out of
sync" signals from the physical layer, the mobile device starts the timer T313. If the mobile
device receives successive "in sync" signals from its physical layer before the T313 expires,
then the mobile device will stop and reset the T313 timer. If the T313 expires, then the mobile device enters a "Radio link failure" state, which the mobile device will clear the dedicated
physical channel configuration and perform a cell update procedure. On the other hand, a Radio
Link Control (RLC) unrecoverable error happens when the retransmission of a message has
exceeded the maximum retries that invokes the RLC unrecoverable error procedure. Upon the triggering of the radio link failure or the unrecoverable error occurrence, either or both timers T314
or T315 will start to count. While both timers T314 and T315 expire, the mobile device will enter
an idle mode.
[0006] However, according to the prior art, when the mobile device initiates a Cell Update
procedure in CELLJDCH state due to a radio link failure or a RLC unrecoverable error, the mobile
device of the prior art shall (1) start timer T314, if a Radio Access Bearer (RAB) associated with
T314 is established and if the stored value of the timer T314 is greater than zero; or (2) start timer
T315,' if a RAB associated with T315 is established and if the stored value of the timer T315 is
greater than zero; or (3) start timer T314, if there are no RAB associated with T314 nor any RAB associated with T315 is established, i.e. only signalling radio bearers are established, and if the
stored value of the timer T314 is greater than zero. When the invoked timer(s) T314 and/or T315
are expired, the mobile device enters an idle mode. Before the invoked timer(s) T314 and/or T315
are expired, the mobile device shall perform Cell Update procedure to try to re-establish the failed
radio link or the unrecoverable RLC connection. In addition, when the mobile device initials a Cell
Update procedure in CELLJDCH state, if the stored value of both timers are equal to zero, the Cell
Update procedure will release all its radio resources, inform the released connections and bearers
to upper layers, clear a plurality of variables and enter an idle mode. Moreover, if the stored value
of the timer T314 is equal to zero, the Cell Update procedure will release all radio access bearers
associated with T314. Similarly, if the stored value of the timer T315 is equal to zero, the Cell
Update procedure will release all radio access bearers associated with T315.
[0007] Nevertheless, several undefined or not clear defined scenarios exist during the mobile
device' s Cell Update operation in the CELLJDCH state if a radio link failure or a RLC
unrecoverable error happens. First, when the timer T314 is greater than zero (T314>0) with no
associated RAB is established and the timer T315 is equal to zero (T315=0) with at least one associated RAB is established. Second, when T315 is greater than zero (T315>0) with no
associated RAB is established and T314 is equal to zero (T314=0) but with at least one associated
RAB is established. And last, when T315>0 with no associated RAB is established and T314=0
with no associated RAB is established, hi the above three situations, if a radio link failure happens
or a RLC unrecoverable error occurs, neither timer T314 nor T315 will be started when the mobile
device initiates a Cell Update procedure in the CELLJDCH state. Therefore, if no suitable cell can
be found, the mobile device will keep searching a suitable cell until the battery power is exhausted,
since there exists no timer started to make the mobile device enters idle mode while expiring.
Summary
[0008] Because the requirements of cell re-selection operations in other modes are more strictly than it does in an idle mode, it makes a mobile device keep searching for a suitable cell more
frequently and consume more power in these modes during the cell re-selection procedure than it
does in an idle mode. Instead of continuous operating in the cell reselection procedure in these
modes during the above-identified situations, the mobile device should be able to enter the idle
mode until the environment changes to save more power.
[0009] Following drawings with reference numbers and exemplary embodiments are referenced
for explanation purpose.
[0010] Figure 1 illustrates the mobile device UTRA RRC connected mode cell reselection process
for URAJPCH, CELL_PCH and CELL_FACH state;
[0011] Figures 2a and 2b illustrates the brief logical flowchart of how the mobile device initials a
Cell updated procedure in CELLJDCH state.
Detail Description of the Invention
[0012] This invention develops an enhanced process for a mobile device to handle the failure of the
radio link or the occurrence of a RLC unrecoverable error in CELLJDCH state. Figures 2a and 2b
illustrates the logical flow of this invention. Once the mobile device initials a Cell Update
procedure in CELLJDCH state 50, the invented process checks if both timers, T314 and T315, are
not running by examining the stored value for both timers (T314=T315=0) 52, if the condition
T314=T315=0 is true, then the mobile device releas.es all its radio resources and enter an idle mode
54. Next, the process checks if there is only one timer running at Step 58. When it is, then the
process assigns the running timer as the first timer and the non-running timer as the second timer
Step 59a. On the other hand, if both timers are running, then the process will randomly assign one timer as the first timer and the other as the second timer as specified in Step 59b. Under the only
one timer is running situation, the process further checks if the second timer has any radio access
bearer (RAB) associated with it as specified in Steps 60. If there is no RAB associated with the
second timer, then the mobile device goes to logical step 64. If the second timer has at least one
RAB associated then the mobile device shall release all RABs associated with the second timer
Step 62. Next, at Step 64 the process further checks if any RAB associates with the first timer, if
there is, the process starts the first timer then exits Steps 66 and 74. Of course, if there is no RAB
associates with the first timer, the process will check if the timer, used for only RRC connection
exists (i.e. only signalling radio bearers are established), is the second timer Step 68, if it isn' t,
then starts the first timer Step 72. Otherwise, the process shall either start the first timer or release
all radio resources and enter an idle mode Step 70.
[0013] Refer back to the logical Step 59b while both timers are running, for example T314 > 0 and T315 >0, then the process will go to Step 76, at this stage, the mobile device already randomly
assigned one of the two timers as the first timer and the other as the second timer, h Step 76, the
mobile device checks if the first timer has any RAB associated with it, if it is, the mobile device
starts the first timer 78. Step 78 will lead to Step 80. Meanwhile, if the first timer doesn' thave
any RAB associated with it, then the process will go to Step 80. At Step 80 the process checks if
the second timer has any RAB associated with it, if it has, then the process starts the second timer
and exits Steps 82 and 86. Otherwise, if the second timer does not have any RAB associated with
it, the mobile device will start the timer used for only RRC connection and exits Steps 84 and 86.
[0014] This new invention will cover the situations covered by the prior art and it also covers few situations undefined or not clear defined by the prior art. For example, first, if the timer T314 has
stored value larger than zero (T314>0) without any associated Radio Access Bearer (RAB) is
established and the timer T315 is equal to zero (T315=0) with at least one associated RAB is
established, according to the new process referring to Figures 2a and 2b, the condition of logical
Step 58 of Figures 2a and 2b is true, which leads to the Step 60. Since the second timer T315 has
RAB(s) associated with it, the mobile device will release all T315 associated RABs in Step 62 and
start the first timer T314 Steps 64 and 66.
[0015] Next, if T315>0 without any associated RAB is established and T314=0 with at least one
associated RAB is established. Follows the logical flow of Figures 2a and 2b, at the step 58,
because the first timer T315 >0 and the second timer T314=0, the process will check if the second
timer has any RAB associated with it in Step 60. Because the second timer (T314) has associated RAB(s) established that results in Step 62, the process release all RABs associated with the second
timer T314 Step 62 and then goes to Step 64. At this point, the process will check if any RAB
associates with the first timer T315 Step 64, because the answer is no, the process further checks if
the timer, used for only RRC connection exists, is the second timer T314 (i.e. equal to zero). If no,
then starts the first timer T315 Step 72. Otherwise, the process shall either start first timer T315, or
releases all radio resources and enter directly the idle mode.
[0016] Last, in the case of T315>0 without any associated RAB is established at the same time
T314=0 without any associated RAB is established, the invented process also provides a clear
solution for the undefined state. After the step 58, because the first timer T315 >0 and the second timer T314=0, the process will check if the second timer has any RAB associated with it in Step 60.
Because the second timer (T314) has no associated RAB(s) established that results in Step 64. At this point, the process will check if any RAB associates with the first timer T315 Step 64, because
the answer is no, the process further checks if the timer, used for only RRC connection exists, is the second timer T314 (i.e. equal to zero). If no, then starts the first timer T315 Step 72. Otherwise, the process starts first timer T315, or releases all radio resources and enters an idle mode Step 70.