U.S. patent number RE44,447 [Application Number 13/333,718] was granted by the patent office on 2013-08-20 for method and system for forward link cell switching approach without abis traffic flooding.
This patent grant is currently assigned to Nokia Corporation. The grantee listed for this patent is Mark W. Cheng, Liangchi (Alan) Hsu. Invention is credited to Mark W. Cheng, Liangchi (Alan) Hsu.
United States Patent |
RE44,447 |
Cheng , et al. |
August 20, 2013 |
Method and system for forward link cell switching approach without
ABIS traffic flooding
Abstract
A method in a system including a mobile station, a group of
active cells including a first serving cell and a second target
cell and a controller of the active cells which switches forward
link transmissions of data packets from the controller through the
first serving cell to the mobile station to forward link
transmission of data packets from the controller through a second
cell to the mobile station. The method determines at the mobile
station that switching of forward link transmissions should occur
from the first serving cell to the second target cell while forward
link transmission of data packets through the first serving cell to
the mobile station are occurring; transmitting an indication to
switch the forward link transmission of data packets to the second
target cell from the mobile station to the controller; the
controller in response to the indication switches the transmission
of data packets from the first serving cell to the second target
cell; and the second target cell transmits the data packets to the
mobile station.
Inventors: |
Cheng; Mark W. (San Diego,
CA), Hsu; Liangchi (Alan) (San Diego, CA) |
Applicant: |
Name |
City |
State |
Country |
Type |
Cheng; Mark W.
Hsu; Liangchi (Alan) |
San Diego
San Diego |
CA
CA |
US
US |
|
|
Assignee: |
Nokia Corporation (Espoo,
FI)
|
Family
ID: |
23096781 |
Appl.
No.: |
13/333,718 |
Filed: |
April 24, 2002 |
PCT
Filed: |
April 24, 2002 |
PCT No.: |
PCT/IB02/01357 |
371(c)(1),(2),(4) Date: |
July 30, 2004 |
PCT
Pub. No.: |
WO02/101966 |
PCT
Pub. Date: |
December 19, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
10311893 |
Jul 30, 2004 |
7848290 |
Dec 7, 2010 |
|
|
Current U.S.
Class: |
370/331; 370/332;
370/328; 455/437; 455/436; 370/338 |
Current CPC
Class: |
H04L
1/0026 (20130101); H04W 36/02 (20130101); H04L
1/0003 (20130101); H04L 1/1812 (20130101); H04L
1/0009 (20130101); H04L 1/1874 (20130101) |
Current International
Class: |
H04W
4/00 (20090101); H04W 36/00 (20090101); H04W
72/00 (20090101) |
Field of
Search: |
;370/328,329,331,332,333,338 ;455/432.1-453 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Kim; Wesley
Attorney, Agent or Firm: Alston & Bird LLP
Claims
What is claimed is:
1. A method comprising: in response to a mobile station initiated
determination that switching of transmission of data packets should
occur from a first site to a second site, the second site being
selected by the mobile station via serving sector selection from an
active set, receiving an invocation initiating a switching process
from the mobile station, the invocation including an indication to
a controller to indicate a desire to switch the transmission of
data packets from the first site to the second site and maintaining
the transmission of data packets through the first site during the
switching process, the switching process having a duration that is
network configured as a delay time period and having a start
.[.that is initiated by the mobile station.]. upon receipt of the
indication .Iadd.from the mobile station.Iaddend.; and switching
the transmission of data packets from the first site to the second
site once the switching process is completed, as determined by the
controller in response to the indication, such that data packets
are only transmitted from the first site during the switching
process and from the second site when the switching process is
completed.
2. A method in accordance with claim 1 wherein: the first site
continues transmission of data packets for the delay time period,
until the completion of the switching.
3. A method in accordance with claim 2 wherein: the mobile station
transmits the indication to the controller on a reverse link.
4. A method in accordance with claim 3 wherein: the mobile station
transmits a quality indicator to only the first site during the
delay time period which is used by the first site to control at
least one of a power level of transmission or selection of
modulation and coding type used by the forward link during the
delay time period in transmitting data packets to the mobile
station.
5. A method in accordance with claims 3 wherein: the mobile station
transmits acknowledgment information to the first site during the
delay time period; and the first site retransmits data packets
which were negatively acknowledged during the delay time
period.
6. A method in accordance with claim 5 wherein: the acknowledgment
information is either an acknowledgment or a negative
acknowledgment that data packets of the forward link have been
received by the mobile station.
7. A method in accordance with claims 3 wherein: the second site
transmits the data packets to the mobile station after expiration
of a delay time period which represents the completion of the
switching.
8. A method in accordance with claims 7 wherein: the second site
switches transmission of data packets to the mobile station at an
end of a time including an additional delay from the expiration of
the delay time period.
9. A method in accordance with claim 2 wherein: the delay time
period is one of zero or an integer multiple of a time frame
interval required to transmit a single data packet on a forward
link.
10. A method in accordance with claim 2 wherein: the delay time
period is determined or configured dependent upon the first and
second site in an active set being between sectors or being in
different base transceiver stations or cells.
11. A method in accordance with claim 1 wherein: the first site and
the second site are both in an active set.
12. A method in accordance with claims 1 wherein: the indication is
transmitted to sites in an active set and a quality indicator is
sent to the first site.
13. A method in accordance with claim 1 wherein: the indication to
switch is a cover of the second site.
14. An apparatus comprising: a receiver that is configured to
receive pilot signals and a processor that is configured to
determine that switching of transmission of data packets should
occur from a first site to a second site, the second site being
selected by the mobile station via serving sector selection from an
active set, the processor configured for initiating a switching
process, responsive to a determination made by a mobile station, by
invoking transmitting an indication to a network to indicate a
desire to switch the transmission of data packets from the first
site to the second site and maintaining the transmission of data
packets through the first site during the switching process, such
that data packets are only transmitted from the first site during
the switching process and from the second site when the switching
process is completed, wherein the indication is a cover pointing to
the second site, and wherein the switching process has a duration
that is network configured as a delay time period and has a start
.[.that is initiated by the mobile station.]. upon receipt of the
indication .Iadd.from the mobile station.Iaddend..
15. The apparatus of claim 14 wherein: the receiver continues the
reception of data packets from the first site for the delay time
period, until the completion of the switching.
16. The apparatus of claim 14 wherein: the apparatus transmits the
indication to a controller on a reverse link.
17. The apparatus of claim 14 wherein: the first site and the
second site are both in an active set.
18. The apparatus of claim 14 wherein: the apparatus transmits
acknowledgement information to the first site during a delay time
period.
19. The apparatus of claim 18 wherein: the acknowledgement
information is either an acknowledgement or a negative
acknowledgement that data packets of a forward link have been
received by the receiver.
20. The apparatus of claim 18 wherein: the delay time period is one
of zero or an integer multiple of a time frame interval required to
transmit a single data packet on a forward link.
21. The apparatus of claim 14 wherein: the indication is
transmitted to the sites in an active set and a quality indicator
is sent to the first site.
22. An apparatus comprising: a mobile station configured to process
an input signal to determine that switching of transmission of data
packets should occur from a first site to a second site, the second
site being selected by the mobile station via serving sector
selection from an active set, the mobile station being further
configured to initiate a switching process by generating an
indication to indicate a desire for switching the transmission of
data packets from the first site to the second site and maintaining
the transmission of data packets through the first site during the
switching process, such that data packets are only transmitted from
the first site during the switching process and from the second
site when the switching process is completed, wherein the
indication is a cover pointing to the second site, wherein the
switching process has a duration that is network configured as a
delay time period and has a start .[.that is initiated by the
mobile station.]. upon receipt of the indication .Iadd.from the
mobile station.Iaddend..
23. The apparatus of claim 22 wherein: the mobile station is
configured to utilize the delay time period to control switching of
data packets from the first site to the second site.
24. An apparatus comprising: a receiver configured to receive an
indication to indicate a desire to switch transmission of data
packets from a first site to a second site, the indication being
received from a mobile station that determined that the switch
should occur, wherein the indication is a cover pointing to the
second site, the second site being selected by the mobile station
via serving sector selection from an active set; and a controller
configured to control switching of transmission of data packets
from the first site to the second site and maintain the
transmission of data packets through the first site during a
switching process, such that data packets are only transmitted from
the first site during the switching process and from the second
site when the switching process is completed, wherein the switching
is in response to the indication, and wherein the switching process
has a duration that is network configured as a delay time period
and has a start .[.that is initiated by the mobile station.]. upon
receipt of the indication .Iadd.from the mobile
station.Iaddend..
25. The apparatus of claim 24 wherein: the first site and the
second site are both in an active set.
26. The apparatus of claim 24 wherein: the first site retransmits
data packets which were negatively acknowledged during the delay
time period.
27. The apparatus of claim 24 wherein: the second site transmits
the data packet to a mobile .Iadd.station .Iaddend.after expiration
of the delay time period which represents completion of
switching.
28. The apparatus of claim 24 wherein: the first site continues
transmission of data packets for the delay time period until
completion of switching and the delay time period is one of zero or
an integer multiple of a time frame interval required to transmit a
single data packet on a forward link.
29. The apparatus of claim 24 wherein: the first site continues
transmission of data packets for the delay period until completion
of switching and the delay time period is determined or configured
dependent upon the first and second sites in an active set being
between sectors or being in different base transceiver stations or
cells.
30. The apparatus of claim 24 wherein: the second site switches
transmission of data packets to a mobile .Iadd.station .Iaddend.at
an end of a time including an additional delay from expiration of
the delay time period until completion of switching.
31. A method comprising: receiving pilot signals; determining, at a
mobile station, that switching of transmission of data packets
should occur from a first site to a second site, the second site
being selected by the mobile station via serving sector selection
from an active set; and initiating a switching process by
transmitting an indication to a network to indicate a desire to
switch transmission of data packets from the first site to the
second site and maintain the transmission of data packets through
the first site during the switching process, such that data packets
are only transmitted from the first site during the switching
process and from the second site when the switching process is
completed, wherein the indication is a cover pointing to the second
site, and wherein the switching process has a duration that is
network configured as a delay time period and has a start .[.that
is initiated by the mobile station.]. upon receipt of the
indication .Iadd.from the mobile station.Iaddend..
32. A method in accordance with claim 31 wherein: the delay time
period is provided to control switching of .[.a.]. data packets
from the first site to the second site.
33. An apparatus comprising: means for receiving pilot signals;
means for determining, at a mobile station, that switching of
transmission of data packets should occur from a first site to a
second site, the second site being selected by the mobile station
via serving sector selection from an active set; and means for
initiating a switching process by transmitting an indication to a
network to indicate a desire to switch transmission of data packets
from the first site to the second site and maintain the
transmission of data packets through the first site during the
switching process, such that data packets are only transmitted from
the first site during the switching process and from the second
site when the switching process is completed, wherein the
indication is a cover pointing to the second site, and wherein the
switching process has a duration that is network configured as a
delay time period and has a start .[.that is initiated by the
mobile station.]. upon receipt of the indication .Iadd.from the
mobile station.Iaddend..
34. The apparatus of claim 33 comprising: means for providing the
delay time period to control switching of data packets from the
first site to the second site.
.Iadd.35. The apparatus of claim 18 wherein: the acknowledgement
information is either an acknowledgement or a negative
acknowledgement that data packets of a forward link have been
received by the receiver..Iaddend.
.Iadd.36. The apparatus of claim 18 wherein: the delay time period
is one of zero or an integer multiple of a time frame interval
required to transmit a single data packet on a forward
link..Iaddend.
.Iadd.37. The apparatus of claim 36 wherein: the indication is
transmitted to the sites in an active set and a quality indicator
is sent to the first site..Iaddend.
.Iadd.38. A method comprising: in response to a mobile station
initiated determination that switching of transmission of data
packets should occur from a first site to a second site, the second
site being selected by the mobile station via serving sector
selection from an active set, receiving an invocation initiating a
switching process from the mobile station, the invocation including
an indication to a controller to indicate a desire to switch the
transmission of data packets from the first site to the second site
and maintaining the transmission of data packets through the first
site during the switching process, the switching process having a
duration that is network configured as a delay time period and
having a start that is initiated in an instance in which an
indication is received from the mobile station; and switching the
transmission of data packets from the first site to the second site
once the switching process is completed, as determined by the
controller in response to the indication, such that data packets
are only transmitted from the first site during the switching
process and from the second site when the switching process is
completed..Iaddend.
.Iadd.39. A method in accordance with claim 38 wherein: the first
site continues transmission of data packets for the delay time
period, until the completion of the switching..Iaddend.
.Iadd.40. A method in accordance with claim 39 wherein: the mobile
station transmits the indication to the controller on a reverse
link..Iaddend.
.Iadd.41. A method in accordance with claim 40 wherein: the mobile
station transmits a quality indicator to only the first site during
the delay time period which is used by the first site to control at
least one of a power level of transmission or selection of
modulation and coding type used by the forward link during the
delay time period in transmitting data packets to the mobile
station..Iaddend.
.Iadd.42. A method in accordance with claims 40 wherein: the mobile
station transmits acknowledgment information to the first site
during the delay time period; and the first site retransmits data
packets which were negatively acknowledged during the delay time
period..Iaddend.
.Iadd.43. A method in accordance with claim 42 wherein: the
acknowledgment information is either an acknowledgment or a
negative acknowledgment that data packets of the forward link have
been received by the mobile station..Iaddend.
.Iadd.44. A method in accordance with claims 40 wherein: the second
site transmits the data packets to the mobile station after
expiration of a delay time period which represents the completion
of the switching..Iaddend.
.Iadd.45. A method in accordance with claims 44 wherein: the second
site switches transmission of data packets to the mobile station at
an end of a time including an additional delay from the expiration
of the delay time period..Iaddend.
.Iadd.46. A method in accordance with claim 39 wherein: the delay
time period is one of zero or an integer multiple of a time frame
interval required to transmit a single data packet on a forward
link..Iaddend.
.Iadd.47. A method in accordance with claim 39 wherein: the delay
time period is determined or configured dependent upon the first
and second site in an active set being between sectors or being in
different base transceiver stations or cells..Iaddend.
.Iadd.48. A method in accordance with claim 38 wherein: the first
site and the second site are both in an active set..Iaddend.
.Iadd.49. A method in accordance with claims 38 wherein: the
indication is transmitted to sites in an active set and a quality
indicator is sent to the first site..Iaddend.
.Iadd.50. A method in accordance with claim 38 wherein: the
indication to switch is a cover of the second site..Iaddend.
.Iadd.51. An apparatus comprising: a receiver that is configured to
receive pilot signals and a processor that is configured to
determine that switching of transmission of data packets should
occur from a first site to a second site, the second site being
selected by the mobile station via serving sector selection from an
active set, the processor configured for initiating a switching
process, responsive to a determination made by a mobile station, by
invoking transmitting an indication to a network to indicate a
desire to switch the transmission of data packets from the first
site to the second site and maintaining the transmission of data
packets through the first site during the switching process, such
that data packets are only transmitted from the first site during
the switching process and from the second site when the switching
process is completed, wherein the indication is a cover pointing to
the second site, and wherein the switching process has a duration
that is network configured as a delay time period and has a start
that is initiated in an instance in which an indication is received
from the mobile station..Iaddend.
.Iadd.52. The apparatus of claim 51 wherein: the receiver continues
the reception of data packets from the first site for the delay
time period, until the completion of the switching..Iaddend.
.Iadd.53. The apparatus of claim 51 wherein: the apparatus
transmits the indication to a controller on a reverse
link..Iaddend.
.Iadd.54. The apparatus of claim 51 wherein: the first site and the
second site are both in an active set..Iaddend.
.Iadd.55. The apparatus of claim 51 wherein: the apparatus
transmits acknowledgement information to the first site during a
delay time period..Iaddend.
.Iadd.56. An apparatus comprising: a mobile station configured to
process an input signal to determine that switching of transmission
of data packets should occur from a first site to a second site,
the second site being selected by the mobile station via serving
sector selection from an active set, the mobile station being
further configured to initiate a switching process by generating an
indication to indicate a desire for switching the transmission of
data packets from the first site to the second site and maintaining
the transmission of data packets through the first site during the
switching process, such that data packets are only transmitted from
the first site during the switching process and from the second
site when the switching process is completed, wherein the
indication is a cover pointing to the second site, wherein the
switching process has a duration that is network configured as a
delay time period and has a start that is initiated in an instance
in which an indication is received from the mobile
station..Iaddend.
.Iadd.57. The apparatus of claim 56 wherein: the mobile station is
configured to utilize the delay time period to control switching of
data packets from the first site to the second site..Iaddend.
.Iadd.58. An apparatus comprising: a receiver configured to receive
an indication to indicate a desire to switch transmission of data
packets from a first site to a second site, the indication being
received from a mobile station that determined that the switch
should occur, wherein the indication is a cover pointing to the
second site, the second site being selected by the mobile station
via serving sector selection from an active set; and a controller
configured to control switching of transmission of data packets
from the first site to the second site and maintain the
transmission of data packets through the first site during a
switching process, such that data packets are only transmitted from
the first site during the switching process and from the second
site when the switching process is completed, wherein the switching
is in response to the indication, and wherein the switching process
has a duration that is network configured as a delay time period
and has a start that is initiated in an instance in which an
indication is received from the mobile station..Iaddend.
.Iadd.59. The apparatus of claim 58 wherein: the first site and the
second site are both in an active set..Iaddend.
.Iadd.60. The apparatus of claim 58 wherein: the first site
retransmits data packets which were negatively acknowledged during
the delay time period..Iaddend.
.Iadd.61. The apparatus of claim 58 wherein: the second site
transmits the data packet to a mobile station after expiration of
the delay time period which represents completion of
switching..Iaddend.
.Iadd.62. The apparatus of claim 58 wherein: the first site
continues transmission of data packets for the delay time period
until completion of switching and the delay time period is one of
zero or an integer multiple of a time frame interval required to
transmit a single data packet on a forward link..Iaddend.
.Iadd.63. The apparatus of claim 58 wherein: the first site
continues transmission of data packets for the delay period until
completion of switching and the delay time period is determined or
configured dependent upon the first and second sites in an active
set being between sectors or being in different base transceiver
stations or cells..Iaddend.
.Iadd.64. The apparatus of claim 58 wherein: the second site
switches transmission of data packets to a mobile station at an end
of a time including an additional delay from expiration of the
delay time period until completion of switching..Iaddend.
.Iadd.65. A method comprising: receiving pilot signals;
determining, at a mobile station, that switching of transmission of
data packets should occur from a first site to a second site, the
second site being selected by the mobile station via serving sector
selection from an active set; and initiating a switching process by
transmitting an indication to a network to indicate a desire to
switch transmission of data packets from the first site to the
second site and maintain the transmission of data packets through
the first site during the switching process, such that data packets
are only transmitted from the first site during the switching
process and from the second site when the switching process is
completed, wherein the indication is a cover pointing to the second
site, and wherein the switching process has a duration that is
network configured as a delay time period and has a start that is
initiated in an instance in which an indication is received from
the mobile station..Iaddend.
.Iadd.66. A method in accordance with claim 65 wherein: the delay
time period is provided to control switching of data packets from
the first site to the second site..Iaddend.
.Iadd.67. An apparatus comprising: means for receiving pilot
signals; means for determining, at a mobile station, that switching
of transmission of data packets should occur from a first site to a
second site, the second site being selected by the mobile station
via serving sector selection from an active set; and means for
initiating a switching process by transmitting an indication to a
network to indicate a desire to switch transmission of data packets
from the first site to the second site and maintain the
transmission of data packets through the first site during the
switching process, such that data packets are only transmitted from
the first site during the switching process and from the second
site when the switching process is completed, wherein the
indication is a cover pointing to the second site, and wherein the
switching process has a duration that is network configured as a
delay time period and has a start that is initiated in an instance
in which an indication is received from the mobile
station..Iaddend.
.Iadd.68. The apparatus of claim 67 comprising: means for providing
the delay time period to control switching of data packets from the
first site to the second site..Iaddend.
Description
TECHNICAL FIELD
This invention relates to wireless high-speed packet data
technology, e.g. in CDMA2000 1xEV-DV and 3GPP HSDPA and more
specifically, to improving the cell switching techniques for
forward radio channels.
BACKGROUND ART
Physical Layer ARQ (HARQ) and cell switching are two
link-adaptation techniques that are employed by the 1xEV-DV forward
link standard. Cells are comprised of base transceiver stations
(BTS) in wireless environments which have lower traffic and
sectors, which subtend an angular portion of a full periphery, such
as 120.degree., in wireless environments having higher traffic.
The hybrid automatic repeat request (HARQ) protocol uses an
adaptive automatic repeat request (ARQ) technique for
retransmission combining.
Cell switching is a handoff technique that allows the mobile
terminal (MS) to identify an optimal serving cell pilot channel
based on measurement with C/I being a strength ratio of the carrier
signal to the interference.
In the 1XTREME/1xEV-DV proposal, fast cell site selection (FCSS) is
proposed to ensure mobility. When a mobile moves from one cell to
another cell, a central entity Network Convergence Function (NCF)
is used to coordinate multiple cells in the active set. During soft
handoff, a NCF provides the same data units (PDUs) to all of the
cells in the active set (flooding). However, only one cell delivers
the PDUs to the MS. When the MS moves from one cell to another in
the active set, the MS echoes the most recently received NCF
sequence number so that the new cell can resume the data transfer
without delay. 1. FIG. 1 shows an example of a prior art cell
switching operation. Cell a and cell b both are in the MS's active
set. Prior to switching cell a sends the data frames to the MS by
the Forward Shared Channel (F-SHCH). Upon a measurement threshold,
the MS may decide to request new cell switching by sending a
request on R-CCH to request cell switching to cell b. The serving
cell a serves the MS, before the cell switching, with the forward
and reverse link channels. The target cell b is the cell chosen for
the transmission after the cell switching is completed. An active
set for the Forward Packet Data Channel is updated to cell a based
on the pilot strength feedback from the MS. All cells in the active
set (only two have been illustrated for convenience purposes) are
eligible for forward link cell switching.
In FIG. 1, the Abis interface (the Abis interface is between the
base station controller (BSC) and the cells) flooding occurs
during, for example, the soft handoff of 1XTREME/1xEV-DV FCSS
procedure. This problem significantly affects the BSC and cell
performance. During soft handoff, both Abis links between the BSC
and cell a and cell b are active as indicated by the bidirectional
arrows therebetween. Flooding involves substantial transmission
overhead, memory requirement inside the cells and a centralized
management entity which manages the large sequence frame
numbering.
After the MS has signalled the BSC with an indication on R-CCH as
indicated in FIG. 1 that the MS wants to switch receiving forward
link transmissions from cell a to cell be, the BSC transmits the
data packets simultaneously to both the serving and target cells
until handoff is complete. The simultaneous use of the Abis
resources by the BSC for the serving and target cells and the radio
resources from the serving and target cells is wasteful especially
when data rates are high such as for 1 xEV-DV (around 4 Mbps).
DISCLOSURE OF INVENTION
This invention is to a cell switching technique which avoids the
prior art flooding of the forward link soft-handoff of FIG. 1. The
avoidance of soft handoff provides the benefits of reducing the
Abis interface overhead and quick resumption of data transfer and
saves the radio resource from being loaded with unnecessary
information. The cell-switching technique of the present invention
permits base stations including 1xEV-DV cells to provide data users
with better network resource utilization and quick resumption of
data transfer after switching.
In a system including a mobile station, cells in an active set
including first serving and second target cells and a controller of
the active cells, a method of switching forward link transmissions
of data packets from the controller through the first serving cell
to the mobile station to forward link transmission of data packets
from the controller through the second target cell to the mobile
station in accordance with the invention includes determining at
the mobile station that switching of the forward link transmission
should occur from the first serving cell to the second target cell
while the forward link transmission of the data packets through the
first serving cell to the mobile station is occurring; transmitting
an indication to switch the forward link transmission of the data
packets from the mobile station to the controller; the controller,
in response to the indication, switches the transmission of data
packets from the first serving cell to the second target cell; and
the second target cell transmits the data packets to the mobile
station. The first cell may continue transmission of data packets
on the forward link to the mobile station for a cell switch delay
time period measured from the indication to switch until the
completion of the switching. The mobile station may transmit a
quality indicator to only the first serving cell during the cell
switch delay which is used by the first serving cell to control at
least one of a power level of transmission or selection of
modulation and a coding type used by the forward link during the
cell switch delay in transmitting data packets to the mobile
station. The mobile station may transmit acknowledgment information
to the first serving cell during the cell switch delay; and the
first serving cell may retransmit on the forward link during the
cell switch delay packets which were negatively acknowledged. The
acknowledgment information may be either an acknowledgment or a
negative acknowledgment that data packets of the forward link has
been received by the mobile station. The second cell may transmit
the data packets to the mobile station after expiration of a cell
switch delay period measured from the indication to switch until
the completion of the cell switching. The data packets may be
transmitted from the cells to the mobile station on a forward
shared channel (F-SHCH); and the indication to switch may be
transmitted from the mobile station to the group of active cells on
the reverse control channel (R-CCH) and a quality indicator may be
sent on the reverse control channel to the first serving cell.
F-SHCH may be mapped to a forward packet data channel (F-PDCH); and
R-CCH may be mapped to a reverse acknowledgment channel (R-ACKCH)
and a reverse channel quality indicator channel (R-CQICH). The cell
switch delay may be one of zero or an integer multiple of a time
frame interval required to transmit a data packet on the forward
link. The cell switch delay may be determined or configured by the
network dependent upon the servicing and target cells in the active
set being between sectors or being in different base transceiver
stations. The indication to switch may be a Walsh code cover of the
second target cell base transceiver stations. The second target
cell switches transmission of data packets to the mobile station at
an end of a time including an additional time delay measured from
an end of the cell switch delay period.
A system in accordance with the invention includes a mobile
station, cells in an active set including first serving and second
target cells, and a controller of the active cells, and wherein
switching of forward link transmission of data packets from the
controller through the first serving cell to the mobile station to
forward link transmission of data packets from the controller
through the second target cell to the mobile station occurs by
determining at the mobile station that switching of forward link
transmission should occur from the first serving cell to the second
target cell while forward link transmission of the data packets
through the first serving cell to the mobile station is occurring,
transmitting an indication to switch the forward link transmission
of the data packets from the mobile station to the controller, the
controller in response to the indication switches the transmission
of data packets from the first serving cell to the second target
cell and the second target cell transmits the data packets to the
mobile station. The first serving cell may continue transmission of
data packets on the forward link to the mobile station for a cell
switch delay time period measured from the indication to switch
until the completion of the switching. The mobile station may
transmit a quality indicator to only the first serving cell during
the cell switch delay which is used by the first serving cell to
control at least one of a power level of transmission or selection
of modulation and coding type used by the forward link to the
mobile station during the cell switch delay. The mobile station may
transmit acknowledgment information to the first serving cell
during the cell switch delay; and the first serving cell may
retransmit on the forward link during the cell switch delay packets
which were negatively acknowledged. The acknowledgment information
may be either an acknowledgement or a negative acknowledgment that
data packets of the forward link have been received by the mobile
station. The second target cell may transmit the data packets to
the mobile station after expiration of a cell switch delay period
measured from the indication to switch until the completion of the
switch. The data packets may be transmitted from the cells to the
mobile station on a forward shared channel (F-SHCH); and the
indication to switch may be transmitted from the mobile station to
the second target cell on the reverse control channel (R-CCH) and a
quality indicator may be sent on the reverse control channel to the
first serving cell. The cell switch delay may be one of zero or an
integer multiple of a time frame interval required to transmit a
data packet on the forward link. The cell switch delay may be
determined or configured by the network dependent upon the source
and target pilots in the active set being between sectors within
the same BTS or being in different base transceiver stations. The
indication to switch may be a Walsh code cover of the second target
cell. The second target cell switches transmission of data packets
to the mobile station at an end of a time including an additional
time delay measured from an end of the cell switch delay
period.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagram of a prior art forward link cell switching
operation which floods the Abis interface;
FIG. 2 is a diagram of forward link data transmission and reverse
link feedback during the cell switching according to an embodiment
of the present invention;
FIG. 3 is a diagram of communications between a base station
controller, a first serving and a second target cell and a mobile
station in accordance with the invention.
FIG. 4 is a flowchart of a cell processing according to an
embodiment of the present invention; and
FIG. 5 is a flowchart of a MS processing according to an embodiment
of the present invention.
Like parts are identified by like identifications throughout the
drawings.
BEST MODE FOR CARRYING OUT THE INVENTION
Forward Link Cell Switching
To reduce the Abis interface overhead during cell switching the
invention: 1. Limits the data transfer from the BSC to only one
cell at a time. 2. Moves buffered data from the serving (first)
cell to the target (second) cell for fast data recovery during the
switching period. 3. Optionally uses a new sequence numbering
format with a bit field of fewer bits than the prior art or an
existing radio link protocol (RLP) sequence number optionally may
be utilized. The present invention is useful for 1xEV-DV cell and
MS implementation and is also related to 1xEV-DV
standardization.
MS switching of data reception from cell to cell in accordance with
the invention is described as follows. Each MS is assigned an
active set of cells dynamically by the network. Data packets are
sent on the forward shared channel (F-SHCH) and acknowledgements
are sent on the reverse control channel (R-CCH). The indication to
switch cells is sent on the R-CCH. For 1XTREME, R-CCH is mapped to
the "Reverse Acknowledgement Indication Channel" (R-AISCH) and
"Transmit Sector Indicator Channel" (R-TSICH). For 1xEV-DV, F-SHCH
is mapped to the "Forward Packet Data Channel" (F-PDCH); R-CCH is
mapped to "Reverse Acknowledgement Channel" (R-ACKCH); and "Reverse
Channel Quality Indicator Channel" (R-CQICH).
The table below defines the timing relationships between T1 and T2
shown in FIG. 2 and described with reference to FIG. 3.
TABLE-US-00001 T1 The MS indicates cell switching to target cell b
to invoke a cell switching procedure. T2 T1 + CSD where CSD is the
cell switching delay required to ready target cell b for the packet
data transmission when the R-CQICH transmissions are directed to
target cell b after T2.
FIGS. 2 and 3 illustrates the transmission of data packets and
acknowledgements during cell switching in accordance with the
invention. There are three phases during the transition period: 1.
Phase 1--Time duration before T1. 2. Phase 2--Time duration between
T1 and T2. 3. Phase 3--Time duration after T2.
The table below describes three significant types of transmissions
which head three columns entitled "BSC Sends Data to", "MS Receives
Data from & Sends CQI" and "CELL that Decodes ACK/NAK" during
the phases 1, 2 and 3 as defined above which row identifications
therein.
TABLE-US-00002 BSC Sends MS Receives Data CELL that Decodes Data to
from & Sends CQI to ACK/NAK Responses Phase 1 CELL a CELL a
CELL a Phase 2 CELL b CELL a CELL a Phase 3 CELL b CELL b CELL
b
Data transmission up to the end of phase 1 at time T1 when
transmission of data packets occurs only to the first serving cell
a. At the beginning of phase 2, the invention switches data packet
transmission to second target cell b thus eliminating the flooding
of the prior art in FIG. 1 when both Abis resources between the BSC
and the first serving and second target cell are active. During the
remainder of phase 2 and through phase 3, the data transmission
continues from the BSC to target cell b. The MS receives data from
and sends CQI to cell a all the way up to the end of phase 2 which
is also the end of the CSD described below at which transmission is
switched to target cell b. The transmission of CQI up to the end of
phase 2 enables cell a to adjust power level on the forward link to
continue to change signal strength in response to changing
conditions or to select modulation and a coding type used on the
forward link. Decoding of ACK/NAK transmissions occurs at serving
cell a until the end of phase 2 at which time decoding of ACK/NAK
transmissions switches to target cell b. The MS also receives any
pending retransmitted frames from serving cell a up to the end of
the CSD as described below. The unified sequence number or RLP
Sequence Number may be used by target cell b to continue the new
frame transmission after switching occurs. The frames sent during
phase 1 cannot be retransmitted after entry into phase 3. In that
case, the upper layer (e.g. RLP in the BSC) handles the
retransmission of the erroneous frames.
The data packets are transmitted by the target (second) cell to the
MS after the CSD. The CSD is required for the target cell to
allocate network and radio resources and for the serving (first)
cell to complete any pending data packet retransmissions and their
acknowledgements. The CSD equals M*Xms where M is zero or a
positive integer and X is a time duration of transmission of a data
frame. The CSD time duration is between when the MS generates an
indication for cell switching from target cell a to serving cell b
is to occur and the time when the forward link packet data
transmission is ready or occurs from the target cell (for example,
cell b). If the target cell is not ready after the expiration of
the CSD due to signaling delay or time latency, additional handoff
delay time may be needed in addition to the CSD to complete the
handoff to the target cell. However, in this circumstance, the data
transmission between the serving cell and the MS indicated at time
T2 at the end of phase 2 in FIG. 2 is dropped after expiration of
the CSD regardless of whether the handoff is complete. The value of
CSD can be determined or configured by the network depending upon
the serving and target cells in the active set being between
sectors or being in different base transceiver stations. The
additional handoff delay is determined by the traffic load of the
target cell and the transport capacity of the cells. The indication
to switch may be a Walsh code cover of the second target cell.
FIG. 3 illustrates the sequence of transmissions between the BSC,
serving cell a and target cell b and the MS. The forward link and
reverse link transmissions occur between the BSC and the MS through
serving cell a throughout phase 1. The reverse link transmission
between the serving cell a and the BSC are only generally discussed
to the extent necessary to understand the invention. The switch
indication is transmitted from the MS to the active group of cells
indicating that target cell b has been determined by the MS to be
the target cell. The switch indication is represented by a Walsh
cover of the target cell b. A Walsh cover is an identification of
the cell b in the wireless system. Phase 1 ends when the indication
to switch to target cell b is received by the BSC. At the beginning
of phase 2, as indicated in the column of FIG. 2 entitled, "BSC
Sends Data to", the transmission of forward link data to serving
cell a switches to target cell b without the flooding of the Abis
interface of the prior art. Data packet transmission on the forward
link from serving cell a to the MS and CQI on the reverse link
between the MS and the serving cell a occurs until the CSD time out
at which time all transmissions between serving cell a and the MS
stop. Transmission of the data from target cell b to the MS should
begin at the end of the CSD which is normally the time for target
cell b to be set up as the new serving cell and to acquire the
necessary radio resources. If the CSD is not sufficient to complete
the switch over to target cell b, nevertheless the MS ceases to
receive data packets from serving cell a and the aforementioned
additional time delay may be necessary to complete switching.
A New Sequence Numbering Format
In 1XTREME MAC layer, a sequence number is defined for the MuxPDU
(Multiplex Sublayer Protocol Data Unit). This sequence number is
used to synchronize buffer management and package retransmission
during a fast cell site selection (FCSS). In the prior art 12 bits
are defined for the sequence number. The length of the sequence
number is coincidentally the same as the Radio Link Protocol (RLP)
ARQ sequence length. The use of 12 bits may be an over
specification for the purpose of HARQ. If RLP is used for the data
transmission, the RLP sequence number can also be used for this
purpose.
Since the main purpose of sequence numbering is to synchronize the
serving cell and the target during switching, the switching period
should be fast and completed within a few frames duration (e.g. 2
frames or Xms). For a worst case (e.g. 4 HARQ channels and 4
transmissions), 6 bits of sequence number length is sufficient with
the switching sequence of the invention. This length reduction
reduces traffic overhead over the air. Hence, the sequence number
length may be reduced from 12 bits to 6 bits in the 1XEV-DV
specifications if the RLP sequence number is not used.
The following procedures are used by the cells and MS according to
the present invention.
Forward Link Cell Switching and Cell Procedures
The cell defines and initializes the following data structures. The
cell is considered active for a MS when the cell has the MAC
Identifier (MAC_ID) assigned for the MS and is decoding the signal
quality CQI feedback received from the MS. For example, target cell
b in FIGS. 2 and 3 is active in phase 3 and serving cell a is in
transition in phase 2 and active in phase 1.
With reference to FIG. 4, the serving cell a performs the
operations therein every Transmission Time Interval (TTI) ms as
long as there are packets to transmit. The cell operation starts at
initialization point 20 wherein N=number of H-ARQ channels,
mob_seq_un=unified sequence number (initialized by BSC), n=current
H-ARQ channel being processed (initialized to 0) and int
s[N]=one-bit H-ARQ channel sequence number (initialized to
`0`).
The cell operation proceeds to point 22 where a determination is
made if the cell is active for the MS. If the answer is "no" at
point 22, operation proceeds to point 24, where decoding the CQI
and ACK/NAK sent on R-CCH by the MS occurs and operation proceeds
back to point 22. If the cell is active at point 22, operation
proceeds to point 26 wherein a determination is made if an
ACK/NAK=1' was received from the previous transmission to the H-ARQ
channel n, or if the maximum number of retransmissions has been
exhausted. If the determination is "yes" at point 26, operation
proceeds to point 28 where incrementing of the H-ARQ channel
sequence number s(n) mod 2 and advance mob_seq_un occurs. If the
determination is "no" at point 26, operation proceeds to point 30
where retransmission of the buffered frame associated with the
current H-ARQ channel on the F-SHCH occurs. Operation proceeds from
point 28 to point 32 wherein transmission of the encoded and
modulated frame with the sequence number mob_seq_un occurs on
F-SHCH. Operation proceeds from point 32 to point 34, from either
of points 30 or 32 depending upon the previous determinations made
at point 26, where transmission of the current H-ARQ sequence
number s(n) on F-CCH occurs; decoding the ACK/NAK sent on the
Reverse Control Channel from the MS occurs and incrementing of the
H-ARQ channel n=n+1 mod N occurs.
Forward Link CSS MS Station Procedures
The MS runs the operations of FIG. 5 every TTI ms. The following
data structures are defined at initialization point 50: n=current
H-ARQ channel, int s[N]=one-bit H-ARQ channel sequence number
(initialized to `1`); float b[N][Interleaver Size]=H-ARQ channel
soft-symbol buffer (initialized to `0`I and d=delay measured in
units of TTI ms, between transmission of a H-ARQ channel on the
Forward Link and the associated acknowledgement on the Reverse
Link. The operation proceeds from initialization at point 50 to
point 52 where decoding of the H-ARQ channel n and the associated
sequence numbers [n] received on the Forward Control Channel
(F-CCH) from the active cell occurs. The operation proceeds from
point 52 to point 54 where determination is made if the H-ARQ
channel sequence number s(n) is the same as the previous
transmission. If the answer is "yes" at point 54, operation
proceeds to point 56 where the received soft-symbols are added with
the soft-symbols stored in b(n). If the answer is "no" at point 54,
operation proceeds to point 58 where the new soft-symbols are
stored into b(n). Operation proceeds form point 56 to point 60
where decoding the frame occurs. Operation proceeds to point 62
where a determination is made if the cyclic redundancy code is OK.
If the answer is "yes" at point 62, operation proceeds to point 64
where the decoded frame is passed up to the selection and
distributed unit in the BSC and scheduling of an ACK/NAK="1" occurs
on the Reverse Control Channel (R-CCH)k*TTI ms frames later where k
is a positive integer. If the answer is "no" at point 62, operation
proceeds to point 66 where the decoded frame and scheduling an
ACK/NAK=`0` on the R-CCH k*TTI ms frames later occurs. Operation
proceeds from points 64 and 66 to point 68 where any scheduled
ACK/NAK is sent on the R-CCH; if the MS desires a cell switch,
indication of the cell switching on the R-CCH for the target cell b
occurs; if the MS indicates cell switching, the cells in the active
set monitor of the R-CQICH transmissions for the target cell Walsh
cover; and setting the target cell b to active after CSD, which is
Xms, occurs. Operation then returns to point 52.
While the invention has been described in terms of its preferred
embodiments, it should be understood that numerous modifications
may be made thereto. It is intended that all such modifications
fall within the scope of the appended claims.
* * * * *