U.S. patent application number 14/168320 was filed with the patent office on 2014-05-29 for scanning and handover operation in multi-carrier wireless communications systems.
This patent application is currently assigned to MEDIATEK, INC.. The applicant listed for this patent is MEDIATEK, INC.. Invention is credited to Yih-Shen Chen, Chao-Chin Chou, I-Kang Fu.
Application Number | 20140146789 14/168320 |
Document ID | / |
Family ID | 41416381 |
Filed Date | 2014-05-29 |
United States Patent
Application |
20140146789 |
Kind Code |
A1 |
Chou; Chao-Chin ; et
al. |
May 29, 2014 |
Scanning and Handover Operation in Multi-Carrier Wireless
Communications Systems
Abstract
A comprehensive solution is provided for multi-carrier scanning
and handover operations in OFDM wireless systems. A multi-carrier
scanning is any scanning operation that involves multi-carrier
radio frequency carriers. In one embodiment, a mobile station
communicates with a serving base station over a primary carrier,
and performs scanning over one or more determined carriers. A
multi-carrier handover is any handover operation that involves
multiple radio frequency carriers. In a first embodiment, a
break-before-entry (BBE) handover procedure with fast
synchronization is provided. In a second embodiment, an
entry-before-break (EBB) handover procedure through unavailable
intervals is provided. In a third embodiment, EBB handover
procedures for both inter-FA and intra-FA using multiple carriers
are provided. Finally, in a fourth embodiment, intra-BS handover
procedures are provided. The multi-carrier handover procedures may
be applied to 2-to-2 or N-to-N carriers handover situation. The
overall scanning time and handover interruption time may be reduced
through the provided procedures.
Inventors: |
Chou; Chao-Chin; (Taipei
City, TW) ; Fu; I-Kang; (Taipei City, TW) ;
Chen; Yih-Shen; (Hsinchu City, TW) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
MEDIATEK, INC. |
Hsin-Chu |
|
TW |
|
|
Assignee: |
MEDIATEK, INC.
Hsin-Chu
TW
|
Family ID: |
41416381 |
Appl. No.: |
14/168320 |
Filed: |
January 30, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12456006 |
Jun 9, 2009 |
8676208 |
|
|
14168320 |
|
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|
61060563 |
Jun 11, 2008 |
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61078558 |
Jul 7, 2008 |
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Current U.S.
Class: |
370/331 |
Current CPC
Class: |
H04L 27/2655 20130101;
H04W 36/08 20130101; H04L 27/0006 20130101; H04L 5/0007 20130101;
H04W 36/12 20130101; H04W 36/0027 20130101; H04W 36/18 20130101;
H04L 27/2618 20130101; H04W 36/0088 20130101; H04W 48/16 20130101;
H04W 36/0072 20130101 |
Class at
Publication: |
370/331 |
International
Class: |
H04W 36/12 20060101
H04W036/12 |
Claims
1-29. (canceled)
30. A method of operating a mobile station to handover from a
serving base station to a target base station in a multi-carrier
wireless communications system, the method comprising: (a)
receiving a handover command from the serving base station via an
original primary radio frequency carrier; (b) disconnecting
connections on the original primary radio frequency carrier from
the serving base station; (c) performing a ranging procedure with
the target base station after the connections with the serving base
station on the original primary radio frequency carrier are
disconnected; and (d) performing network reentry and thereby
establishing data path with the target base station through a new
primary carrier, and establishing data connections with the target
base station over the new primary carrier and a secondary
carrier.
31. The method of claim 30, wherein the network reentry is
performed using the original primary carrier.
32. The method of claim 31, wherein the original primary carrier
becomes the new primary carrier.
33. A method of operating a mobile station to handover from a
serving base station to a target base station in a multi-carrier
wireless communications system, the method comprising: (a)
receiving a handover command from the serving base station via an
original primary radio frequency carrier; (b) acquiring network
reentry related parameters; (c) disconnecting connections on the
original primary radio frequency carrier from the serving base
station; (d) performing a ranging procedure with the target base
station after the connections with the serving base station on the
original primary radio frequency carrier are disconnected; and (e)
performing network reentry and thereby establishing data path with
the target base station through a new primary carrier, wherein the
network reentry related parameters is acquired before the
connection with the serving base station is disconnected.
34. The method of claim 33, wherein the network reentry in (e) is
performed using the original primary carrier, wherein the downlink
or uplink adjustments of the secondary carrier are reused by the
original primary carrier for the network reentry, and wherein the
original primary carrier becomes the new primary carrier.
35. The method of claim 33, wherein the network reentry in (e) is
performed using an original secondary carrier, and the original
secondary carrier becomes the new primary carrier.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation, and claims priority
under 35 U.S.C. .sctn.120 from nonprovisional U.S. patent
application Ser. No. 12/456,006, entitled "Scanning and handover
operation in multi-carrier wireless communications systems," filed
on Jun. 9, 2009, the subject matter of which is incorporated herein
by reference. application Ser. No. 12/456,006, in turn, claims
priority under 35 U.S.C. .sctn.119 from U.S. Provisional
Application No. 61/060,563, entitled "Scanning and Hard Handover
Design for Multicarrier OFDMA Systems," filed on Jun. 11, 2008;
U.S. Provisional Application Number 61/078,558, entitled "Soft
Handover Design for Multi-Band OFDMA Systems," filed on Jul. 7,
2008, the subject matter of which is incorporated herein by
reference.
TECHNICAL FIELD
[0002] The disclosed embodiments relate generally to wireless
network communications, and, more particularly, to scanning and
handover in multi-carrier wireless systems.
BACKGROUND
[0003] In current wireless communications systems, 5 MHz-20 MHz
radio bandwidths are typically used for up to 100 Mbps peak
transmission rate. Much higher peak transmission rate is required
for next generation wireless systems. For example, 1 Gbps peak
transmission rate is required by ITU-R for IMT-Advanced systems
such as the 4.sup.th generation ("4G") mobile communications
systems. The current transmission technologies, however, are very
difficult to perform 100 bps/Hz transmission spectrum efficiency.
In the foreseeable next few years, only up to 15 bps/Hz
transmission spectrum efficiency can be anticipated. Therefore,
much wider radio bandwidths (i.e., at least 40 MHz) will be
necessary for next generation wireless communications systems to
achieve 1 Gbps peak transmission rate.
[0004] Orthogonal Frequency Division Multiplexing (OFDM) is an
efficient multiplexing protocol to perform high transmission rate
over frequency selective channel without the disturbance from
inter-carrier interference. There are two typical architectures to
utilize much wider radio bandwidth for OFDM system. In a
traditional OFDM system, a single radio frequency (RF) carrier is
used to carry one wideband radio signal, and in an OFDM
multi-carrier system, multiple RF carriers are used to carry
multiple narrower band radio signals. The multi-carrier operation
is also known as carrier aggregation. An OFDM multi-carrier system
has various advantages as compared to a traditional OFDM system
such as lower Peak to Average Power Ratio, easier backward
compatibility, and more flexibility. Thus, OFDM multi-carrier
wireless systems have become the baseline system architecture in
IEEE 802.16m and LTE-Advanced draft standards to fulfill system
requirements.
[0005] Scanning and handover are critical operations in wireless
communications systems. FIG. 1 (Prior Art) is a message sequence
diagram of a normal scanning procedure in a single-carrier wireless
system. Before the initiation of the scanning procedure, a mobile
station (MS) may receive parameters for neighbor base stations
(BS#2 and BS#3) from serving base station BS#1. The MS then sends a
scanning request to BS#1 and receives a scanning response back from
BS#1. The MS then scans the neighbor BSs within the scheduled
scanning period. Optionally, the MS may also perform initial
ranging with the neighbor BSs. During the scanning operation, data
communication is interrupted because of interleaved scanning
intervals. In an autonomous scanning procedure, the MS simply
performs scanning whenever it does not communicate data with its
serving BS.
[0006] FIG. 2 (Prior Art) is a message sequence diagram of a normal
handover procedure in a single-carrier wireless system. In either a
BS-initiated or an MS-initiated handover operation, existing data
path is disconnected from the serving base station (S-BS) after the
MS transmits a handover indication message, and data communication
remains interrupted while the MS performs network reentry to the
target base station (T-BS) until a new data path is established
with the T-BS. In a seamless handover procedure, if the T-BS is
fully synchronized with the S-BS in both time and frequency domain,
then the MS may proceed to data transmission immediately without
downlink synchronization and initial ranging.
[0007] In OFDM multi-carrier wireless systems, it is desirable to
have a comprehensive solution to facilitate multi-carrier scanning
and handover operations such that data interruption caused by
scanning and handover can be reduced.
SUMMARY
[0008] A comprehensive solution is provided for multi-carrier
scanning and handover operations in OFDM wireless systems. As a
general design concept, one radio frequency carrier is established
as a primary carrier for control message exchange and data
communication between a mobile station and its serving base
station, while another radio frequency carrier is established as a
secondary carrier between the mobile station and the serving base
station for data communication. The secondary carrier can also be
used for scanning, initial ranging, and network reentry between the
mobile station and a target base station.
[0009] A multi-carrier scanning is any scanning operation that
involves multi-carrier radio frequency carriers. In one embodiment,
a mobile station communicates with its serving base station over a
primary radio frequency carrier, and performs scanning over one or
more determined radio frequency carriers. The determined carriers
may include the primary carrier, a secondary carrier, or multiple
carriers that include both the primary carrier and one or more
secondary carriers. When scanning operation is performed using
multiple carriers simultaneously, the overall scanning time can be
reduced.
[0010] A multi-carrier handover is any handover operation that
involves multiple radio frequency carriers. In a first embodiment,
a break-before-entry (BBE) handover procedure for a mobile station
with fast synchronization is provided. The MS receives a handover
command from its serving BS via a primary carrier, the MS then
performs DL and optional UL synchronization with a target BS using
a secondary carrier. After the synchronization is completed, the MS
disconnects all carriers from the serving BS and then performs
network reentry with the target BS via either the primary carrier
or the secondary carrier to establish new data path with the target
BS. Because full or part of the UL/DL parameters acquired during
synchronization using the secondary carrier can be used for network
reentry, handover interruption time is reduced. The multi-carrier
BBE handover procedure may be applied to 2-to-2 or N-to-N carriers
handover situation.
[0011] In a second embodiment, an entry-before-break (EBB) handover
procedure for a mobile station through unavailable intervals is
provided. During handover operation, the MS requests unavailable
intervals and then performs network reentry with a target BS.
Because network reentry is performed within the requested
unavailable intervals, any existing connection between the MS and
its serving BS remains until a new primary carrier is established
between the MS and the target BS.
[0012] In a third embodiment, EBB handover procedures for a mobile
station for both inter-FA handover and intra-FA handover using
multiple radio frequency carriers are provided. The MS receives a
handover command from its serving BS via a primary carrier. The MS
then performs network reentry with a target BS using either the
primary carrier or a secondary carrier. After network reentry is
completed, the MS establishes a new primary carrier with the target
BS. Finally, the MS disconnects the original primary carrier from
the serving BS. The multi-carrier EBB handover procedure may be
applied to 2-to-2 or N-to-N carriers handover situation.
[0013] In a fourth embodiment, intra-BS handover procedures for a
mobile station are provided. The MS requests or is requested by its
serving BS to relocated its primary carrier to another carrier of
the same serving BS through intra-BS handover request (optional)
and command message exchange. After intra-BS handover, the primary
carrier is switched from one carrier frequency to another carrier
frequency within the same serving BS.
[0014] Other embodiments and advantages are described in the
detailed description below. This summary does not purport to define
the invention. The invention is defined by the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] The accompanying drawings, where like numerals indicate like
components, illustrate embodiments of the invention.
[0016] FIG. 1 (Prior Art) is a message sequence diagram of a normal
scanning procedure in a single-carrier wireless system.
[0017] FIG. 2 (Prior Art) is a message sequence diagram of a normal
handover procedure in a single-carrier wireless system.
[0018] FIG. 3 illustrates a high-level design of scanning and
handover operation in a multi-carrier wireless system in accordance
with one novel aspect.
[0019] FIG. 4 is a flow chart of a method of multi-carrier scanning
operation in accordance with one novel aspect.
[0020] FIG. 5 illustrates a scanning procedure using primary
carrier in a multi-carrier wireless system.
[0021] FIG. 6 is a message sequence chart of a scanning procedure
using primary carrier in a multi-carrier wireless system.
[0022] FIG. 7 illustrates a scanning procedure using secondary
carrier in a multi-carrier wireless system.
[0023] FIG. 8 is a message sequence chart of a scanning procedure
using secondary carrier in a multi-carrier wireless system.
[0024] FIG. 9 illustrates a scanning procedure using multiple
carriers in a multi-carrier wireless system.
[0025] FIG. 10 is a message sequence chart of a scanning procedure
using multiple carriers in a multi-carrier wireless system.
[0026] FIG. 11 is a flow chart of a method of multi-carrier
break-before-entry (BBE) handover operation in accordance with one
novel aspect.
[0027] FIG. 12 illustrates a BBE handover procedure with fast
synchronization using secondary carrier.
[0028] FIG. 13A is a message sequence chart of one embodiment of a
multi-carrier BBE handover procedure with fast synchronization
using secondary carrier.
[0029] FIG. 13B is a message sequence chart of another embodiment
of a multi-carrier BBE handover procedure with fast synchronization
using secondary carrier.
[0030] FIG. 14 is a message sequence chart of 2-to-2 carriers BBE
handover procedure.
[0031] FIG. 15 is a message sequence chart of N-to-N carriers BBE
handover procedure.
[0032] FIG. 16 illustrates an entry-before-break (EBB) handover
procedure through unavailable intervals.
[0033] FIG. 17A is a message sequence chart of one embodiment of
EBB handover procedure through unavailable intervals.
[0034] FIG. 17B is a message sequence chart of another embodiment
of EBB handover procedure through unavailable intervals.
[0035] FIG. 18 is a flow chart of a method of multi-carrier EBB
handover operation in accordance with one novel aspect.
[0036] FIG. 19 illustrates an EBB handover procedure using multiple
radio frequency carriers.
[0037] FIG. 20A is a message sequence chart of one embodiment of a
multi-carrier inter-FA EBB handover procedure.
[0038] FIG. 20B is a message sequence chart of another embodiment
of a multi-carrier intra-FA EBB handover procedure.
[0039] FIG. 21 is a message sequence chart of 2-to-2 carriers
intra-FA EBB handover procedure.
[0040] FIG. 22 is a message sequence chart of 2-to-2 carriers
inter-FA EBB handover procedure.
[0041] FIG. 23 is a message sequence chart of N-to-N carriers
intra-FA EBB handover procedure.
[0042] FIG. 24 is a message sequence chart of N-to-N carriers
inter-FA EBB handover procedure.
[0043] FIG. 25-27 are message sequence charts of different
embodiments of intra-BS handover procedure in a multi-carrier
wireless system.
DETAILED DESCRIPTION
[0044] Reference will now be made in detail to some embodiments of
the invention, examples of which are illustrated in the
accompanying drawings.
[0045] FIG. 3 illustrates a high-level design of scanning and
handover operation in a multi-carrier wireless communications
system 30 in accordance with one novel aspect. Multi-carrier
wireless system 30 comprises a serving base station S-BS31, a
target base station T-BS32, and a mobile station MS33. Mobile
station MS33 supports two radio frequency carriers (also referred
as carrier components): RF#1 and RF#2. In the example of FIG. 3, as
a general design concept, RF#1 is established as a primary carrier
(also referred as anchor carrier) for control message exchange and
data communication with serving base station S-BS31, while RF#2 is
used as a secondary carrier (also referred as non-anchor carrier)
for data communication with serving base station S-BS31 and can
also be used for scanning, initial ranging, and network reentry
with target base station T-BS32.
[0046] FIG. 4 is a flow chart of a method of multi-carrier scanning
operation in accordance with one novel aspect. A multi-carrier
scanning operation is any scanning operation that involves multiple
radio frequency carriers. In a multi-carrier wireless system, a
multi-carrier MS supports multiple radio frequency (RF) carriers,
and uses one of the RF carriers as a primary carrier to communicate
data with its serving BS (step 41). To initiating a normal scanning
procedure, the mobile station transmits a scanning request to the
serving BS (step 42), and then receives a scanning response from
the serving BS (step 43). In an autonomous scanning procedure, step
42 and 43 are not required. In step 44, the mobile station
determines which radio frequency carrier is used for scanning. The
determined carrier can be a primary carrier, a secondary carrier,
or both. Finally, in step 45, the mobile station performs scanning
over the determined one or more radio frequency carriers.
[0047] FIG. 5 illustrates a scanning procedure using primary
carrier in a multi-carrier wireless system 50. Multi-carrier
wireless system 50 comprises a serving base station S-BS51,
neighbor base stations BS52 and BS53, and a mobile station MS54.
MS54 supports RF#1 as its primary carrier and RF#2 as its secondary
carrier. As illustrated in FIG. 5, MS54 scans neighbor BSs while
maintaining normal operation with S-BS51 on primary carrier RF#1.
Because scanning is performed during interleaved scanning
intervals, normal data communications is interrupted periodically
by the scanning operation.
[0048] FIG. 6 is a more detailed message sequence chart corresponds
to the scanning procedure using primary carrier in multi-carrier
wireless system 50. In the example of FIG. 6, mobile station MS54
initiates a normal scanning operation by transmitting a scanning
request to serving base station S-BS51 for scheduled scanning
intervals. S-BS51 responds by transmitting a scanning response back
to MS54 with scheduled start frame (M frame) and duration frame (N
frame) for scanning. During the scanning interval, MS54 starts to
measure carrier#1 (RF#1) of neighbor base station BS52, and then
optionally performs downlink (DL) synchronization procedure with
RF#1 of BS52 using the primary carrier RF#1 of MS54. The
measurement objective can be radio signal strength (RSS),
carrier-to-interference noise ratio (CINR) and round trip delay
(RTD). In addition, MS54 may optionally perform initial ranging
procedure with RF#1 of BS52 during the scanning interval if
possible and needed. Such scanning operation is then repeated with
carrier #2 (RF#2) of another neighbor base station BS53. Additional
scanning may be performed during additional scanning intervals
interleaved with normal operations.
[0049] Similar to a single-carrier scanning operation, the
above-described multi-carrier scanning operation is performed on
the primary carrier RF#1 only and data communications is thus
interrupted on RF#1. Multi-carrier mobile station MS54, however, is
able to maintain data communication with its serving base station
S-BS51 through its secondary carrier RF#2. Another difference
between multi-carrier scanning and single-carrier scanning is the
capability of scanning multiple carriers within a neighbor base
station. In one example (i.e. IEEE 802.16m system), if a neighbor
base station supports multiple RF carriers, then MS54 scans fully
configured carriers of the neighbor BSs during cell reselection.
MS54 may not need to scan partially configured carriers because
they may not be used to perform network reentry.
[0050] FIG. 7 illustrates a scanning procedure using secondary
carrier in a multi-carrier wireless system 70. Multi-carrier
wireless system 70 comprises a serving base station S-BS71,
neighbor base stations BS72 and BS73, and a mobile station MS74.
MS74 supports RF#1 as its primary carrier and RF#2 as its secondary
carrier. As illustrated in FIG. 7, MS74 scans neighbor BSs using
the secondary carrier RF#2 while maintaining normal operation with
S-BS51 on primary carrier RF#1. Because scanning is performed using
a carrier different from the primary carrier, normal data
communications is not interrupted by the scanning operation.
[0051] FIG. 8 is a more detailed message sequence chart corresponds
to the scanning procedure using secondary carrier in multi-carrier
wireless system 70. MS74 communicates with S-BS71 over primary
carrier RF#1. MS74 may also communicate with S-BS71 over secondary
carrier RF#2. As illustrated in FIG. 8, MS74 first exchanges
scanning request and response messages with S-BS71 for scheduled
scanning intervals. The scanning request and response messages may
be exchanged over either the primary carrier or the secondary
carrier. During the scanning interval, MS74 starts to measure
carrier #1 (RF#1) of neighbor base station BS72, and then
optionally performs DL synchronization with RF#1 of BS72 using the
secondary carrier RF#2 of MS74. In addition, MS74 may optionally
perform initial ranging procedure with RF#1 of BS72 during the
scanning interval if possible and needed. Such scanning operation
is then repeated with carrier #2 (RF#2) of another neighbor base
station BS53. Because the multi-carrier scanning operation is
performed using the secondary carrier, it goes in parallel with
normal operation on the primary carrier without interruption to the
normal data communications with the serving BS.
[0052] FIG. 9 illustrates a scanning procedure using multiple
carriers including primary carrier and secondary carriers in a
multi-carrier wireless system 90. Multi-carrier wireless system 90
comprises neighbor base stations BS91, BS92, BS93 and BS94, and a
mobile station MS95. MS95 supports RF#1 as its primary carrier and
RF#2 as its secondary carrier. As illustrated in FIG. 9, MS95 scans
neighbor base stations BS91 and BS93 using the primary carrier RF#1
while scans neighbor base stations BS92 and BS94 using the
secondary carrier RF#2.
[0053] FIG. 10 is a more detailed message sequence chart
corresponds to the scanning procedure using both primary carrier
and secondary carrier in multi-carrier wireless system 90. As
illustrated in FIG. 10, during the scheduled scanning interval,
MS95 starts to perform measurement and DL synchronization with BS91
using the primary carrier RF#1. In addition, MS95 also starts to
perform measurement and DL synchronization with BS92 using the
secondary carrier RF#2. After the scanning and the synchronization
with BS91 and BS92 are completed, MS95 starts to scan BS93 and BS94
using the primary carrier RF#1 and the secondary carrier RF#2,
respectively. Because such scanning operation is performed using
multiple carriers simultaneously, the overall scanning time is
reduced and faster cell reselection may be achieved.
[0054] In one embodiment of multi-carrier scanning, a mobile
station may not be connected to its serving base station when
performing the scanning operation. In such a situation, the mobile
station simply uses multiple carriers simultaneously to reduce
scanning time.
[0055] Similar to multi-carrier scanning operation, a multi-carrier
handover operation is any handover operation that involves multiple
radio frequency carriers. There are various types of multi-carrier
handover operations: break-before-entry (BBE) handover with fast
synchronization, entry-before-break (EBB) handover through
unavailable intervals, EBB handover through multiple carriers, and
intra-BS primary carrier switching. Each of the handover operations
is described below with more detail.
[0056] FIG. 11 is a flow chart of a method of multi-carrier BBE
handover operation with fast synchronization in accordance with one
novel aspect. In step 111, a multi-carrier mobile station (MS)
receives a handover command from a serving BS via a primary
carrier. The MS then performs downlink (DL) and optional uplink
(UL) synchronization with a target BS using a secondary carrier in
step 112. After synchronization is completed, the MS sends an
optional handover indication to the serving BS and disconnects all
carriers from the serving BS (step 113). Finally, the MS performs
network reentry with the target BS via either the primary carrier
or the secondary carrier to establish new data path with the target
BS.
[0057] FIG. 12 illustrates a BBE handover procedure with fast
synchronization using secondary carrier in a multi-carrier wireless
system 120. Multi-carrier wireless system 120 comprises a serving
base station S-BS121, a target base station T-BS122, and a mobile
station MS123. MS123 supports carrier#1 as its primary carrier and
carrier#2 as its secondary carrier. As illustrated in FIG. 12,
during handover operation, MS123 uses the secondary carrier to
perform DL synchronization and acquire DL/UL parameters with
T-BS122 and then disconnects all carriers from S-BS121 before
network reentry is performed. Because full or part of the UL/DL
parameters of T-BS122 can be acquired through the synchronization
process to T-BS122 using the secondary carrier of MS123, MS123 can
use these acquired information for its network reentry to T-BS122
afterward. Therefore, handover interruption time is reduced.
[0058] FIG. 13A is a more detailed message sequence chart of one
embodiment of a BBE handover procedure in multi-carrier wireless
system 120. The multi-carrier handover operation is either
initiated by MS123 through a handover request message to its
serving base station S-BS121, or initiated by the serving based
station S-BS121 through a handover command to MS123. After
receiving the handover command, MS123 starts to perform
synchronization procedure with target base station T-BS122 using
its secondary carrier. The synchronization procedure may include
performing downlink physical layer synchronization, obtaining
network reentry related system parameters, and performing ranging
for uplink power/timing/frequency adjustments. After the
synchronization procedure is completed, MS123 may send a handover
indication to S-BS121. MS123 then disconnects all carriers from
S-BS121 and starts to perform network reentry procedure with
T-BS122 using the secondary carrier. After the network reentry, the
secondary carrier (carrier#2) becomes the new primary carrier and a
new data path is established between MS123 and T-BS122.
[0059] FIG. 13B is a more detailed message sequence chart of
another embodiment of a BBE handover procedure in multi-carrier
wireless system 120. The handover procedure is similar to the one
illustrated above with respect to FIG. 13A. However, the acquired
DL/UL physical layer parameters are passed from the secondary
carrier to the primary carrier and network reentry is performed
using the primary carrier. Thus, the original primary carrier
remains as the new primary carrier for the new data path.
[0060] FIG. 14 is a message sequence chart of a 2-to-2 carriers BBE
handover procedure. In a 2-to-2 carriers handover situation, a
mobile station (MS) communicates with its serving base station
(S-BS) over both a primary carrier (carrier#1) and a secondary
carrier (carrier#2), and both serving carriers will be handed over
to two target carriers of a target base station (T-BS) after the
completion of the 2-to-2 carriers handover operation. For
MS-initiated handover, the MS and the S-BS exchanges handover
request and command messages via the primary carrier. For
BS-initiated handover, the MS receives handover command from the
S-BS. Because multi-carrier handover is involved, the S-BS informs
the T-BS for handover of multiple carriers via backend, and
receives a handover response back from the T-BS. The S-BS then
forwards the information of target carrier assignment and
configuration to the MS. The MS then performs handover ranging
(i.e. UL synchronization) on the target primary carrier after
disconnecting all connections from the S-BS. Handover ranging on
the target secondary carrier may either be performed or be skipped
depending on the synchronization status. The MS then performs
network reentry on the target primary carrier. New connections are
thus established on both the target primary carrier and the target
secondary carrier simultaneously.
[0061] FIG. 15 is a message sequence chart of an N-to-N carriers
BBE handover procedure. In an N-to-N carrier handover situation, a
mobile station (MS) communicates with its serving base station
(S-BS) over N multiple carriers (carrier#1-#N), and all N serving
carriers will be handed over to N target carriers of a target base
station (T-BS) after the completion of the N-to-N carriers handover
operation. The N-to-N carriers BBE handover procedure is similar to
the 2-to-2 carriers BBE handover described above with respect to
FIG. 14. It is noted that although ranging to the target primary
carrier has to be performed after disconnecting all existing
connections with the S-BS, additional ranging to other target
secondary carriers may be skipped. Furthermore, all new connections
on the target primary carrier and other target secondary carriers
are established simultaneously after the network reentry on the
target primary carrier.
[0062] FIG. 16 illustrates an EBB handover procedure through
unavailable intervals in a multi-carrier wireless system 160.
Multi-carrier wireless system 160 comprises a serving base station
S-BS161, a target base station T-BS162, and a mobile station MS163.
MS163 supports carrier#1 as its primary carrier and carrier#2 as
its secondary carrier. As illustrated in FIG. 16, during handover
operation, MS163 requests unavailable intervals with S-BS161 and
then performs network reentry. Because network reentry is performed
within the requested unavailable intervals, the existing connection
between MS163 and S-BS161 remains until a new primary carrier is
established with T-BS162.
[0063] FIG. 17A is a more detailed message sequence chart of one
embodiment of EBB handover procedure through unavailable intervals
in multi-carrier wireless system 160. During the handover
preparation phase, the length of each unavailable interval is
negotiated between MS163 and S-BS161. In the example of FIG. 17A,
MS163 performs network reentry procedure with T-BS162 on the
secondary carrier within the scheduled intervals (N frame) while
normal communication with S-BS161 is maintained on the primary
carrier. After the new primary carrier with T-BS162 is established
over the secondary carrier, MS163 immediately disconnects its
primary carry to S-BS161. S-BS161 also stops all DL/UL data
transmission and resource allocation upon expiration of Disconnect
Time or receiving handover complete message from T-BS162, whichever
comes first. In another example (not illustrated in FIG. 17A), the
network reentry is performed on the primary carrier within the
scheduled intervals, and the primary carrier remains as the new
primary carrier after the network reentry is completed.
[0064] FIG. 17B is a sequence chart of another embodiment of EBB
handover procedure through unavailable intervals. In the example of
FIG. 17B, MS173 is a single-carrier mobile station and supports
only one radio frequency carrier. Thus, it uses the same carrier to
perform network reentry with S-BS172 within the scheduled intervals
while maintains normal communication with S-BS171.
[0065] FIG. 18 is a flow chart of a method of multi-carrier EBB
handover operation in accordance with one novel aspect. In an EBB
handover procedure using multiple radio frequency carriers, a
multi-carrier mobile station first receives a handover command from
a serving BS via a primary carrier (step 181). The mobile station
then performs network reentry with a target BS using either the
primary carrier or a secondary carrier (step 182). After network
reentry is completed, the mobile station establishes a new primary
carrier with the target BS (step 183). Finally, the mobile station
disconnects the original primary carrier from the serving BS (step
184).
[0066] FIG. 19 illustrates an EBB handover procedure using multiple
radio frequency carriers in a multi-carrier wireless system 190.
Multi-carrier wireless system 190 comprises a serving base station
S-BS191, a target base station T-BS192, and a mobile station MS193.
MS193 supports carrier#1 as its primary carrier and carrier#2 as
its secondary carrier. As illustrated in FIG. 19, during handover
operation, MS193 first uses either carrier#1 or carrier#2 to
perform network reentry and then establishes a new primary carrier
with T-BS192. MS193 then disconnects the primary carrier from
S-BS191 after network reentry is completed. There are two different
types of multi-carrier EBB handover: an inter-FA handover and an
intra-FA EBB handover, each handover operation is described below
with more details.
[0067] FIG. 20A is a more detailed message sequence chart of an
inter-FA EBB handover procedure in multi-carrier wireless system
190. In an inter-FA EBB handover, the primary carrier frequency
changes after network reentry. As illustrated in FIG. 20A, MS193
receives a handover command from S-BS191 via the primary carrier
(carrier#1). MS193 then starts to perform network reentry with
T-BS192 using the secondary carrier (carrier#2) while maintains
connection with S-BS191 on the original primary carrier
(carrier#1). A new primary carrier data path with T-BS192 is then
established after network reentry and the secondary carrier
(carrier#2) becomes the new primary carrier. S-BS191 also stops all
DL/UL data transmission and resource allocation upon expiration of
Disconnect Time or upon receiving a handover complete message from
T-BS192, whichever comes first.
[0068] FIG. 20B is a more detailed message sequence chart of an
intra-FA EBB handover procedure in multi-carrier wireless system
190. In an intra-FA EBB handover, the primary carrier frequency
remains the same after network reentry. As illustrated in FIG. 20B,
MS193 receives a handover command from S-BS191 via the primary
carrier (carrier#1). Before performing network reentry, MS193
switches its primary carrier to the secondary carrier. MS193 then
starts to perform network reentry with T-BS192 using the original
primary carrier (carrier#1) while maintains connection with S-BS191
on the original secondary carrier (carrier#2). A new primary
carrier data path with T-BS192 is then established after the
network reentry and the original primary carrier (carrier#1)
remains as the new primary carrier. Similar to the inter-FA
handover in FIG. 20A, S-BS191 stops all DL/UL data transmission and
resource allocation upon expiration of Disconnect Time or upon
receiving a handover complete message from T-BS192, whichever comes
first.
[0069] FIG. 21 is a message sequence chart of a 2-to-2 carriers
intra-FA EBB handover procedure. In a 2-to-2 carriers handover
situation, a mobile station (MS) communicates with its serving base
station (S-BS) over both a primary carrier (carrier#1) and a
secondary carrier (carrier#2), and both serving carriers will be
handed over to two target carriers after the completion of the
2-to-2 carriers handover operation. In MS-initiated handover, the
MS and the S-BS exchanges handover request and command messages via
the primary carrier. In BS-initiated handover, the MS receives
handover command from the S-BS. Because multi-carrier handover is
involved, the S-BS informs the T-BS for multiple carriers via
backend, and receives a handover response back from the T-BS. The
S-BS then forwards the information of target carrier assignment and
configuration to the MS. The MS performs handover ranging (i.e. UL
synchronization) with the T-BS on one carrier while maintaining
data connection with the S-BS on the other carrier. If the primary
carrier is used for handover ranging, then primary carrier switch
is conducted optionally before such ranging. The MS then performs
remaining network reentry procedure (i.e. key exchange, capability
negotiation) with the T-BS and establishes a new connection to the
target primary carrier. Optionally, handover ranging to the target
secondary carrier may either be performed or skipped depending on
the synchronization status and a new connection to the target
secondary carrier is established. After the intra-FA handover, the
original primary carrier remains as the new primary carrier.
[0070] FIG. 22 is a message sequence chart of a 2-to-2 carriers
inter-FA EBB handover procedure. The inter-FA EBB handover
procedure is very similar to the intra-FA EBB handover procedure
described above with respect to FIG. 21. The difference is that the
MS maintains connection with the S-BS on the primary carrier while
performing handover ranging with the T-BS on the secondary carrier
and thus no primary carrier switch is needed. After the inter-FA
handover, the secondary carrier becomes the new primary
carrier.
[0071] FIG. 23 is a message sequence chart of an N-to-N carriers
intra-FA EBB handover procedure. In an N-to-N carrier handover
situation, a mobile station (MS) communicates with its serving base
station (S-BS) over N multiple carriers (carrier#1-#N), and all N
serving carriers will be handed over to N target carriers after the
completion of the N-to-N carriers handover operation. The N-to-N
carriers intra-FA EBB handover procedure is similar to the 2-to-2
carriers intra-FA EBB handover described above with respect to FIG.
21, and all carriers connecting to the serving BS are disconnected
right after the target primary carrier is established.
[0072] FIG. 24 is a message sequence chart of an N-to-N carriers
inter-FA EBB handover procedure. The N-to-N carriers inter-FA EBB
handover procedure is similar to the 2-to-2 carriers inter-FA EBB
handover described above with respect to FIG. 22, and all carriers
connecting to the serving BS are disconnected right after the
target primary carrier is established.
[0073] FIG. 25-27 are message sequence charts of different
embodiments of intra-BS handover (sometimes also referred as
primary carrier switching) procedure in a multi-carrier wireless
system. To start the intra-BS handover operation, the MS requests
or is requested by its serving BS to relocated its primary carrier
to another carrier of the same serving BS through intra-BS handover
request and command message exchange. After intra-BS handover, the
primary carrier is switched from one carrier frequency to another
carrier frequency within the same serving BS.
[0074] In the example of FIG. 25, MS251 is a single-carrier mobile
station. After intra-BS handover request (optional for MS-initiated
handover) and command message exchange with S-BS252, MS251
disconnects the old primary carrier first, performs DL/UL
synchronization, and then establishes a new primary carrier. In the
example of FIG. 26, both primary carrier (carrier#1) and secondary
carrier (carrier#2) are established between MS261 and S-BS262
before intra-BS handover. After intra-BS handover request (optional
for MS-initiated handover) and command message exchange with
S-BS262, the primary carrier and the secondary carrier simply
switch (carrier#2 is the new primary carrier and carrier#1 is the
new secondary carrier) without the need to perform any DL/UL
synchronization. In the example of FIG. 27, MS271 supports two
radio frequency carriers (carrier#1 and carrier#2), but only the
primary carrier (carrier#1) is established with S-BS272. After
intra-BS handover request (optional for MS-initiated handover) and
command message exchange, MS271 performs DL/UL synchronization
using a secondary carrier without disconnecting the original
primary carrier. After a new primary carrier (carrier#2) is
established, the original primary carrier (carrier#1) can either be
configured into a new secondary carrier or be disconnected
immediately.
[0075] Although the present invention has been described in
connection with certain specific embodiments for instructional
purposes, the present invention is not limited thereto.
Accordingly, various modifications, adaptations, and combinations
of various features of the described embodiments can be practiced
without departing from the scope of the invention as set forth in
the claims.
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