Note: Descriptions are shown in the official language in which they were submitted.
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31629-2DL
DESCRIPTION
BASE STATION, MOBILE STATION, COMMUNICATION SYSTEM, AND
REORDERING METHOD THEREOF
This application is a divisional of Canadian
Patent Application No. 2,681,127 filed March 22, 2007.
TECHNICAL FIELD
[0001]
The present invention relates to a base station,
mobile station, communication system.and reordering
method thereof, and more particularly to a base station,
mobile station, communication system and reordering
method where packets, to which numbers indicating
sequence are attached, are sent from a base station to a
mobile station, and the packets are rearranged in order
=
of the sequence number in the mobile station.
BACKGROUND ART
[00021
CDMA service based on the third generation method
has begun in mobile communication systems, but a next
generation mobile communication system (LTE: Long Term
Evolution) which allows even faster communication is now
under consideration at 3GPP (Third Generation Partnership
Project) (see Non-patent Document 1). Here a decrease in
transmission delay is a major issue, in addition to an
increase in transmission rate.
In order to increase the transmission rate and
decrease the transmission delay, an attempt to speed up
the handover processing in comparison with the
conventional systems, is being made in the LTE
communication system. In the case of mobile
communication, a base station that communicates with a
mobile station is switched to another base station
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according to the receive state when the mobile station is
moving during communication. This is referred to as
handover and a base station in communication before
handover is called a "handover source base station", and
= a base station to be in communication after handover is
called a handover target base station. Therefore speeding
up the handover is absolutely necessary to implement
high-speed/low delay communication. In the LTE
communication system, which is based on a packet exchange
system, hard handover is used for the handover. In the
case of hard handover, a line between a mobile station
and a handover target base station is connected after a
line between the mobile station and a handover source
base station is disconnected. Hard handover can be
performed quickly by obtaining system information of the
handover target base station immediately before executing
handover, but transmission of the user data is
interrupted during handover.
This means that in order to decrease transmission
delay, it is important to decrease the transmission
interruption state and to prevent loss of packets during
the transmission interruption state. If packets are
dropped during the transmission interruption state, the
dropped packets are recovered by end-to-end packet
retransmission, so transmission delay increases.
[0003]
Therefore in the handover of the LTE communication
system, standardized is a method in which a handover
source base station transfers at least packets, among the
data including control information and packets addressed
to the mobile station, to a handover target base station
(see Non-patent Document 2). However, whether the data
is actually transferred or not depends on whether this
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function is installed.
[0004]
Fig. 19 is a diagram depicting packet transference
during handover. In (A) of Fig. 19, two base stations la
and lb are connected to a host station (e.g. access
gateway) 2. A mobile station 4 exists in a cell 3a of
the base station la, and is currently communicating with
the base station la. In this state, if the mobile
station 4 moves toward the base station lb and enters a
cell 3b, as shown in (B) of Fig. 19, handover is executed,
and the communication base station of the mobile station
switches from base station la to base station lb. A base
station in communication before handover is called a
"handover source base station" (source base station), and
a base station to be in communication after handover is
called a "handover target base station" (target base
station).
The handover source base station la stores packets,
received from the host station 2, in an internal buffer,
and sequentially sends the packets stored in the buffer
to the mobile station 4. Because of this, when handover
occurs, some stored packets remain in the buffer without
being sent to the mobile station. In (B) of Fig. 19,
packets n-2 to n, which were received before handover and
are not yet sent to the mobile station, exist in the
buffer, and these packets must be sent from the handover
target base station lb to the mobile station 4 after
handover. Therefore when the handover sequence is
executed, the handover source base station la transfers
(forwards) the packets n-2 to n to the handover target
base station lb (this is referred to as forwarding). By
using this forwarding method, in which the handover
target base station lb sends these packets to the mobile
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station 4 immediately after handover, packet transmission
is not interrupted. Hence end-to-end packet
retransmission is not required, and high-speed handover
can be executed. The above mentioned n-2 to n are
numbers which indicate a sequence of packets (sequence
number).
[0005]
Fig. 20 is a diagram depicting a handover of an LTE
communication system, and Fig. 21 is a diagram depicting
a handover procedure which is currently assumed in the
LTE communication system.
The mobile station (UE)4 notifies the handover
source base station la that handover HO is necessary,
using the Measurement Report (1. Measurement control).
The handover source base station la decides a target
base station lb based on the content of the Measurement
Report (2. HO decision), and sends the handover request
to this handover target base station lb (3. HO request).
HO means handover. At this time, the handover source
base station la also sends information on the mobile
station (e.g. mobile station ID and QoS (Quality of
Service) information to the handover target base station).
The handover target base station lb executes call
acceptance control based on this information (4. Call
acceptance control).
If the handover target base station lb admits
acceptance of the mobile station, it returns handover
response to the handover source base station (5. HO
response). Then, the handover source base station la
instructs handover to the mobile station 4 (6. HO
instruction), thereafter starts transfer of data
(packets) before or after this step (packet transfer:
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forwarding).
The mobile station 4 which received the handover
instruction insures synchronization with the handover
target base station lb by Ll/L2 signaling (7.
Synchronization insuring), and when the synchronization
is insured, the mobile station 4 sends the handover
completion report to the handover target base station lb
(8. HO completion).
Thereby the handover target base station lb sends
the handover completion report to the host station 2 (9.
HO completion). The host station 2 which received the
handover completion report switches the packet
transmission path from the handover source base station
la to the handover target base station lb (10. Path
switching), and returns the HO completion response to the
handover target base station lb (11. HO completion
response). By the HO completion response, the handover
target base station lb notifies the handover source base
station la that the handover HO is completed (12.
Resource release). Then the path between the handover
source base station la and the host station 2 is cleared
(13. Resource release).
[0006]
If packet transference (forwarding) is generated
during the execution of the above mentioned handover
sequence, the transferred packets may be jumped over by
packets which flow into the handover target base station
lb from the host station 2, and the sequence numbers may
be out of order. If the handover target base station lb
transfers the packets to the mobile station 4 without
correcting the order, the mobile station cannot receive
the packets in correct order, whereby communication
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quality deteriorates and high quality communication
before and after the handover cannot be implemented as a
result.
Therefore in the LTE communication system, the
packet sequence consistency between the base station and
the mobile station is maintained by the following method.
Fig. 22 is a diagram depicting the packet sequence
consistency, where the handover target base station lb
maintains packet sequence consistency by transmitting the
packets transferred from the handover source base station
la with priority over the packets received from the host
station. In other words, packets n-5 to n have been
stored in the handover source base station la before
handover, and handover is then generated, so the packets
n-5 to n-3 are transferred to the handover target base
station lb and stored in the buffer BF. In the buffer BF
of the handover target base station lb, packets n+1 and
n+2, received from the host station, have also been
stored.
The handover target base station lb, which stores
the transferred packets n-5 to n-3 and the packets n+1 to
n+2 that flowed into in the buffer from the host station,
sends the packets n-5 to n-3 transferred from the
handover source base station la first to the mobile
station. Then if a delay exists in the transfer of the
packets n-2 to n from the handover source base station la,
the handover target base station lb sends the packets n+1
to n+2 to the mobile station. The mobile station 4
executes processing to rearrange the received packets in
the order of sequence numbers (reordering).
[0007]
Fig. 23 is a diagram depicting the reordering
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processing of the mobile station. In Fig. 22, the mobile
station 4 received the packets n-5 to n-3 in the order of
sequence numbers, so the packets are sequentially
transferred to the upper layer. At the point of
receiving the packets n+1 to n+2, however, packets n-2 to
n have not yet arrived. Therefore the mobile station 4
stores the packets n+1 to n+2 in the buffer BF1 until
receiving these packets n-2 to n which have not yet
arrived, and does not transfer these packets n+1 to n+2
to the upper layer. When the packets n-2 to n are
received, the mobile station 4 transfers these packets
and packets n+1 to n+2 sequentially to the upper layer.
An upper limit is normally set for the packet wait time,
and is measured by a timer of the mobile station, for
example.
As mentioned above, in the case of handover in the
LTE communication system, the essential technologies are
the packet transfer (packet forwarding) from the handover
source base station to the handover target base station
and the packet reordering processing at the mobile
station. The relationship of these functions will now be
described in detail.
[0008]
Fig. 24 is a diagram depicting a protocol
configuration between the mobile station and the network.
Between the mobile station and the network, at least a
PDCP (Packet Data Convergence Protocol) layer, RLC (Radio
Link Control) layer and lower layer (MAC layer/physical
layer MAC/PHY) are installed. These layers are all
installed in the mobile station, but are not always
installed in a station at the network side. In the case
of the example in Fig. 25, the PDCP layer is installed in
the host station aGW2, and the RLC layer and the lower
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layer are installed in the base station 1. The system
may be constructed such that all of the PDCP layer, RLC
layer and lower layer are installed in the base station 1,
and only simple functions, such as the packet routing
function and the sequence number attaching function, are
provided to aGW2.
[0009]
In the case of the example in Fig. 25, data in the
PDCP layer is exchanged between the mobile station 4 and
aGW2, which is the host station, and data in the RLC
layer is exchanged between the user terminal 4 and the
base station 1.
In other words, data addressed to the mobile station
flows from the upper layer (e.g. IP layer) to the PDCP
layer first, and becomes PDCP SDU (Service Data Unit),
and then header information (e.g. sequence numbers in
PDCP layer) is added, and the PDCP PDU (Protocol Data
Unit) is created.
The PDCP PDU is routed to the RLC layer, and becomes
RLC SDU, and then header information (e.g. sequence
number of RLC layer) is added, and RLC PDU is created.
The RLC PDU arrives at the RLC layer of the mobile
station via the processing in the lower layer. In the
RLC layer, the header is removed and RLC SDU is
reconstructed, then in the PDCP layer, the header of the
PDCP PDU is removed, and PDCP SDU is created and routed
to the upper layer of the mobile station.
In this protocol configuration, in the LTE
communication system, packet transfer is executed in RLC
SDU units or in PDCP SDU units, and reordering is
executed in PDCP PDU units. Since RLC SDU and PDCP PDU
are substantially the same data, they are simply referred
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to as "packets" in the present description, and it is
assumed that a number of a packet described here
indicates a sequence number of a PDCP PDU, unless
otherwise specified.
(0010]
Fig. 26 is a flow chart depicting an operation of
the handover source base station device during handover.
When the handover source base station la receives
the field strength of reception from the mobile station 4
via Measurement Report (step 101), the handover source
base station la judges whether handover HO is necessary
(step 102), and returns to the beginning if handover is
unnecessary.
If it is decided that handover is necessary, the
handover source base station la decides the handover
target base station lb based on the content of
Measurement Report, and sends a handover request to the
handover target base station lb (step 103).
Then the handover source base station la receives a
handover response which is sent from the handover target
base station lb (step 104), and judges whether data
transference is executed (step 105). If the transference
of the packets which are not sent to the mobile station
and remain in the buffer is not executed, the handover
source base station la sends HO instruction to the mobile
station, and erases these packets (step 106). If the
transference of the packets which are not sent to the
mobile station and remain in the buffer is executed, on
the other hand, the handover source base station la sends
HO instruction to the mobile station, and forwards these
packets to the handover target base station (step 107).
The transference of the packets for a service which
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requires real-time processing, such as VoIP calling, is
not executed, but is discarded. This is because
discarding packets insures voice transmission and
reception without delays. The transference of the
= packets for a service which requires high QoS is executed.
Then the handover source station la receives a
resource release message which is sent from the handover
target base station lb (step 108), and executes a
resource release (step 109).
[0011]
Fig. 27 is a flow chart depicting operation of the
handover target base station during handover.
When the handover target base station lb receives an
HO request (including mobile station ID and QoS
information) from the handover source base station la
(step 121), the handover target base station lb performs
call acceptance control based on this information, and
judges whether acceptance of the mobile station is
admitted or not (step 122). If not admitted, the
handover target base station lb performs post-processing
(step 130), and ends handover control.
If acceptance of the mobile station, on the other
hand, is admitted, the handover target base station lb
returns an HO response to the handover source base
station la (step 123). Then the handover target base
station lb stores packets transferred from the handover
source base station la in a buffer (step 124), and
receives an HO completion report from the mobile station
4 (step 125). When the HO completion report is received,
the handover target base station lb sends the HO
completion report to the host station 2 (step 126). When
the handover completion report is received, the host
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station 2 switches the packet transmission path from the
handover source base station la to the handover target
base station lb, and returns with the HO completion
response to the handover target base station lb(step 127).
When the HO completion response is received from the host
* station 2, the handover target base station lb starts
sending packets forwarded from the handover target base
station lb preferentially to the mobile station, and
starts sending packets received from the host station 2
to the mobile station after the above packets are sent
(scheduling: step 128). The mobile target base station
lb also sends the resource release to the handover source
base station la in parallel with step 128 (step 129), and
performs post-processing (step 130), and ends handover
control.
[0012]
Fig. 28 is a flow chart depicting an operation of
the mobile station during handover.
The mobile station 4 notifies the field strength of
reception to the handover source base station using
Measurement Report (step 151). The mobile station 4 then
waits for an HO instruction from the handover source base
station la, and if received (step 152), the mobile
station 4 insures synchronization with the handover
target base station lb by Ll/L2 signaling (step 153), and
sends the handover completion report to the handover
target base station lb when synchronization is insured
(step 154), then if packets are received from the
handover target base station lb, the mobile station
executes reordering processing (steps 155 to 160).
In other words, when the lower layer packets are
received from the handover target base station lb, the
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control unit of the mobile station constructs RLC SDU,
and transfers this RLC SDU to the reorder unit (step 155).
The reorder unit checks whether the sequence number is
continuous (step 156), and transfers this RLC SDU to the
upper layer as PDCP SDU if the sequence numbers are
=
continuous without missing any numbers (step 160). If
the continuity of the sequence number of a RLC SDU ceases,
on the other hand, the reorder unit stores RLC SDU(=PDC
PDU)(step 157), and then checks whether the continuity of
the sequence number is resumed by the received RLC SDU or
not (step 158). If the continuity of the sequence
numbers is resumed by the received RLC SDU, the reorder
unit transfers this RLC SDU to the upper layer as PDCP
SDU, and then transfers the stored RSC SDU(=PDCP PDU) to
the upper layer (step 160).
In step 158, if the sequence numbers of the received
RLC SDU are not continuous, the mobile station monitors
whether a predetermined time has elapsed (step 159), and
repeats the processing after step 157 if not, or
transfers the stored PDCP PDU to the upper layer if
elapsed, even if the sequence numbers are not continuous
(step 160).
[0013]
To execute packet transfer during handover in the
LTE communication system, the following problem exists.
That is, when handover is executed in the LTE
communication system, the transference of the packets
destined for the mobile station remaining in the handover
source base station la is executed as mentioned above,
thereby the packets are transferred to the handover
target base station (forwarding). However, whether the
transference of the packets executed during handover
depends on whether this transference function is
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installed in the handover source base station.
As a result, even whether the handover source base
station la did not execute packet transfer (packet
forwarding), the mobile station 4, which was not notified,
may judge that packet transfer was executed, and in such
a case, after the handover, the reorder management unit
of the mobile station must unnecessarily wait for the
arrival of packets of which sequence numbers are
continuous, until a predetermined time elapses. This
results in that communication delays increase, and
throughput deteriorates, and high quality communication
quality cannot be maintained before and after the
handover.
[0014]
Fig. 29 shows an example of packets n-2 to n
remaining in the handover source base station la. If
these packets are not forwarded to the handover target
base station lb, the mobile station 4 must unnecessarily
wait for the arrival of these packets n-2 to n, which
will never be sent for a predetermined time after
receiving packet n+1 from the handover target base
station lb. As a result, a communication delay occurs,
and throughput of the entire system drops.
A first prior art that is available is a
reassembling and reordering device, which restores
packets before fragmentation from fragmented packets, and
corrects reversal of the packet arrival sequence to
recover the original sequence (Patent Document 1).
However, this prior art relates to a reassembling and
reordering device which restores packets before
fragmentation from the packets fragmented in GTP tunnel
(GTP: GPRS Tunneling Protocol) of GPRS (General Packet
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31629-2D1
Radio Service), and corrects the reversal of the packet arrival
sequence generated by the fragmentation and reassembles to the
original sequence.
A second prior art that is available is a mobile
communication system which realizes high-speed packet data
transmission without generating data loss during handover
between base stations in high-speed packet communication
(Patent Document 2). In this mobile communication system, when
a handover is generated between base stations in conformity
with a communication state of a mobile station during high-
speed packet communication between a base station and a mobile
station, the handover source base station transfers the packet
data to the handover target base station (forwarding).
However, neither the first nor the second prior arts
are for suppressing an increase in communication delays or the
deterioration of throughput due to the reordering of packets
received from the handover target base station.
[0015]
In view of the foregoing, it is an object of an
embodiment of the present invention that the mobile station
need not execute reordering at the packets in order of the
sequence numbers even if they are not continuous, if the
packets remaining in the handover source base station are not
forwarded to the handover target base station (transference is
not executed) when handover control is executed.
It is another object of an embodiment of the present
invention that the mobile station executes reordering of the
packets in order of the sequence numbers if the packets
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remaining in the handover source base station were forwarded to
the handover target base station (transference was executed)
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when handover control is executed.
[Patent Document 1] Japanese Patent Application Laid-Open
No. JP2004-135076A
[Patent Document 2] Japanese Patent Application Laid-Open
No. JP2004-282652A
[Non-patent Document 1] 3GPP, "Requirements for Evolved
UTRA (E-UTRA) and Evolved UTRAN (E-UTRAN)," TR25.913
V7.3.0, Release 7, March 2006
[Non-patent Document 2] 3GPP, "Evolved Universal
Terrestrial Radio Access (E-UTRA) and Evolved Universal
Terrestrial Radio Access Network (E-UTRAN)," TS36.300,
Release 8, Vol. 4.0, January 2007
DISCLOSURE OF THE INVENTION
[0016]
= Reordering method
A first aspect of the present invention is a
reordering method for sending packets, to which numbers
indicating sequence are attached, from a base station to
a mobile station, and rearranging the packets in order of
the sequence number in the mobile station. This
reordering method comprises: a first step of sending data
to notify that transference of the packets has been
executed at the execution of handover sequence to the
mobile station when a handover source base station
transfers packets which have not been sent to the mobile
station, out of packets received from a host station, to
a handover target base station, and the packets are sent
from the handover target base station to the mobile
station; a second step of sending data to notify that
transference of the packets is not executed at the
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execution of the handover sequence, to the mobile station when
the packets are not transferred to the handover target base
. station; and a third step of executing reordering of the
receive packets at the mobile station when the transference of
the packets has been executed.
In the third step, the reordering processing ends
when packets having continuous sequence numbers are not
received even if reordering processing of the received packets
is executed for a predetermined time.
The reordering method further comprises a step of
deciding whether the packets, which have not been sent to the
mobile station, are to be transferred to the handover target
base station or to be erased, by referring to communication
state information of the handover target base station that is
received from the handover target base station at the execution
of the handover sequence.
The reordering method further comprises a step of
deciding whether packets, which have not been sent to the
mobile station, are to be transferred to the handover target
base station or to be erased, depending on the type of service.
If numbers to indicate the sequence of the packets
are attached to the packets in the base station, the numbers
attached to the packets, which have not been sent from the
handover source base station to the mobile station, are
notified to the handover target base station when the packets
are transferred to the handover target base station.
There is also provided a method of avoiding an
unnecessary reordering process of packets, to which numbers
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indicating sequence are attached, from a base station to a
mobile station, and rearranging the packets in order of the
. sequence number in the mobile station, comprising steps of:
when a handover source base station transfers packets which
have been received from a host station and have not been sent
to the mobile station, to a handover target base station, and
the handover target base station sends the packets to the
mobile station, sending data from the source base station to
the mobile station to notify that transference of the packets
from the source base station to the target station has been
executed at the execution of handover sequence; sending data
from the source base station to the mobile station to notify
that transference of the packets is not executed at the
execution of the handover sequence, when the packets are not
transferred to the handover target base station; and at the
mobile station judging whether transference of the packets is
executed with reference to said data, and executing reordering
of the packets received from the handover target base station
when the transference of the packets has been executed wherein
the mobile station does not execute reordering of the received
packets when the transference of the packets has not been
executed.
[0017]
= Communication system
A second aspect of the present invention is a
communication system for sending packets to which numbers
indicating sequence are attached, from a base station to a
mobile station, and performing delivery of the packets in order
of the sequence number in the mobile station. This
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communication system comprises a handover source base station,
a handover target base station and a mobile station wherein (1)
. the handover source base station having: a buffer for storing
packets received from a host station; a packet transmission
unit for sending the packets stored in the buffer to the mobile
station; and a control unit which sends data to notify that
transference of the packets has been executed to the mobile
station when the handover source base station transfers the
packets, which have not been sent to the mobile station, to the
handover target base station at the execution of handover
sequence, and sends data to notify that transference of the
packets is not executed to the mobile station when the packets
are not transferred to the handover target base station, (2)
the handover target base station having: a buffer which stores
packets received from the handover source base station and
packets received from the host station at the execution of
handover sequence; a control unit which controls such that the
packets received from the handover source base station are sent
to the mobile station preferentially; and a transmission unit
which sends packets to the mobile station, and (3) the mobile
station having: a buffer which stores packets received from the
base station; and a control unit which executes reordering of
the received packets or does not execute reordering of the
received packets based on the data received from the handover
source base station and indicating whether transference of the
packets has been executed.
The control unit of the handover source base station
decides whether the packets, which have not been sent to the
mobile station, are to be transferred to the handover target
base station or to be erased by referring to the communication
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state information of the handover target base station that is
received from the handover target base station at the execution
of the handover sequence.
The control unit of the handover source base station
decides whether the packets, which have not been sent to the
mobile station, are to be transferred to the handover target
base station or to be erased depending on the type of service.
[0018]
= Base station
A third aspect of the present invention is a base
station in a communication system for sending packets to which
numbers indicating sequence are attached, from a base station
to a mobile station and performing delivery of the packets in
order of the sequence number in the mobile station, comprising:
a buffer for storing packets received from a host station and
packets received from a handover source base station at the
execution of handover sequence; a packet transmission unit
which sends packets stored in the buffer to the mobile station;
a handover control unit which decides whether packets, which
have not been sent to the mobile station, are to be transferred
to a handover target base station at the execution of handover
sequence or not, transfers the packets to the handover target
base station and data to notify that transference of the
packets has been executed to the mobile station if the packets
are to be transferred to the handover target base station, and
sends the data to notify that transference of the packets is
not executed to the mobile station if the packets are not to be
transferred to the handover target base station; and a
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transmission control unit which sends packets received by the
handover source base station to the mobile station with
priority over the packets received from the host station at the
execution of handover sequence.
[0019]
= Mobile station
A fourth aspect of the present invention is a mobile
station in a communication system for sending packets to which
numbers indicating sequence are attached, from a base station
to a mobile station and rearranging the packets in order of the
sequence number in the mobile station, comprising: a buffer for
storing packets received from the base station; and a control
unit which decides whether reordering of the packets received
from a handover target base station is to be executed or not
based on data received from a handover source base station at
the execution of the handover sequence and indicating whether
transference of the packets has been executed. The control
unit ends reordering processing when packets having continuous
numbers are not received even if reordering processing of the
received packets is executed for a predetermined time.
There is also provided a mobile station in a
communication system for sending packets, to which numbers
indicating sequence are attached, from a base station to a
mobile station and performing delivery of the packets in order
of the sequence number in the mobile station, comprising: a
receiver which receives information indicating whether
forwarding function of the packets from a handover source base
station to a handover target base station is configured or not,
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31629-2D1
from the handover source base station; a buffer which stores
packets received from the handover target base station; and a
control unit which controls the delivery of the packets in
order at the handover procedure based on the information
indicating whether the forwarding function of the packets from
the handover source base station to the handover target base
station is configured or not.
A further aspect of the invention relates to a
reordering method in a communication system in which a base
station sends packets, to which numbers indicating order are
attached, to a mobile station, the mobile station performs
delivery of the packets in order, and handover is performed,
the method comprising: at a handover source base station,
deciding whether the handover source base station forwards
packets, which have been received from a host station and have
not been sent to the mobile station, to the handover target
base station or not, controlling the forwarding of the packets
from the handover source base station to the handover target
base station at the handover based on the decision, and sending
the information, indicating whether packet forwarding function
is configured or not, to the mobile station; at the mobile
station, receiving, from the handover source base station, the
information indicating whether the packet forwarding function
is configured or not and receiving packets from the target base
station; and at the mobile station, controlling delivery of the
packets, received from the handover target base station at the
handover, in order, based on the information indicating whether
the packet forwarding function is configured or not.
A further aspect of the invention relates to a
communication system in which a base station sends packets, to
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31629-2D1
which numbers indicating order are attached, to a mobile
station, the mobile station performs delivery of the packets in
order, and handover is performed, comprising: a host station; a
handover source base station; a handover target base station;
and a mobile station; wherein the handover source base station
includes a controller which is configured to decide whether the
handover source base station forwards packets, which have been
received from the host station and have not been sent to the
mobile station, to the handover target base station or not, to
control the forwarding of the packets from the handover source
base station to the handover target base station at the
handover based on the decision, and control the sending of
information, indicating whether the packet forwarding function
is configured or not, from the handover source base station to
the mobile station; the mobile station includes: a receiver
configured to receive the information, indicating whether the
packet forwarding function is configured or not, from the
handover source base station; a buffer which stores packets
received from the handover target base station; and a
controller configured to control delivery of the packets,
received from the handover target base station at the handover,
in order based on the information indicating whether the packet
forwarding function is configured or not.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020]
Fig. 1 is a diagram depicting a first embodiment;
Fig. 2 shows format examples of HO response messages
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including communication state information;
Fig. 3 is a block diagram of a base station;
Fig. 4 is a block diagram of a mobile station;
Fig. 5 is a flow chart depicting an operation of a
handover target base station according to the first
embodiment;
Fig. 6 shows a format example of an HO instruction
message;
Fig. 7 is a flow chart depicting an operation of a
handover source base station according to the first
embodiment;
Fig. 8 is a flow chart depicting an operation of a
mobile station according to the first embodiment;
Fig. 9 is a flow chart depicting a reordering
processing in the mobile station;
Fig. 10 is a diagram depicting a second embodiment;
Fig. 11 is a flow chart depicting an operation of a
handover source base station according to the second
embodiment;
Fig. 12 is a flow chart depicting an operation of a
handover source base station according to a variant form;
Fig. 13 is a flow chart depicting a reordering
processing in a mobile station according to a variant
form;
Fig. 14 is a block diagram of a base station of
which buffer management unit has a simplified
configuration without packet transfer functions;
Fig. 15 is a flow chart depicting an operation of a
CA 02883699 2015-03-04
handover source base station according to the third
embodiment;
Fig. 16 is a system block diagram focusing on
layers;
Fig. 17 is a diagram depicting a fourth embodiment;
Fig. 18 is a diagram depicting a handover procedure
of the fourth embodiment;
Fig. 19 is a diagram depicting transference of the
packets during handover;
Fig. 20 is a diagram depicting handover of an LTE
communication system;
Fig. 21 is a diagram depicting a handover procedure
which is currently assumed in the LTE communication
system;
Fig. 22 is a diagram depicting packet sequence
matching;
Fig. 23 is a diagram depicting reordering processing
of a mobile station;
Fig. 24 is a diagram depicting a protocol
configuration between a mobile station and network;
Fig. 25 is a diagram depicting a case when a PDCP
layer is installed in aGW, which is a host station, and
an RLC layer and a lower layer are installed in a base
station;
Fig. 26 is a flow chart depicting an operation of
the handover source base station device during handover;
Fig. 27 is a flow chart depicting an operation of
the handover target base station during handover;
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Fig. 28 is a flow chart depicting an operation of
the mobile station during handover; and
Fig. 29 is a diagram depicting a problem of prior
art.
BEST MODE FOR CARRYING OUT THE INVENTION
[0021]
(A) Principle of this invention
In the present invention, the problem is solved by
enabling a base station and a mobile station to execute
the following two procedures.
Procedure 1: During handover, a handover source base
station or a handover target base station notifies
transference execution information, on whether data
transference was executed or not, to the mobile station.
Procedure 2: When the transference execution
information is received, the mobile station judges
whether data transference was executed based on this
information, and if data transference was not executed,
the mobile station does not reorder the arrived packets,
and transfers the packets immediately to the upper layer
as received.
In the conventional method, the handover source base
station does not notify the transference execution
information to the mobile station during handover.
Therefore, even when data transference is not executed,
thereby the packets are not forwarded from the handover
source base station to the handover target base station,
the mobile station must wait needlessly for these not-
forwarded packets until a predetermined time elapses,
which generates an increase in communication delays and a
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deterioration of throughput. However if the mobile
station is notified the transference execution
information according to the method of the present
invention, it can know whether the data transference is
executed or not, and if the packets were not forwarded,
reordering can be stopped, whereby unnecessary reordering
attempt of packets can be prevented. As a result,
communication quality before and after handover can be
maintained to be higher than a conventional method.
[0022]
(B) First embodiment
Fig. 1 is a diagram depicting a first embodiment,
where a handover source base station ha judges the
possibility of packet transfer (packet forwarding) based
on the communication state of a handover target base
station llb when the handover sequence is executed, and
notifies the forwarding execution information
(transference execution information) to a mobile station
14.
In Fig. 1, when handover sequence is started,
packets n-2 to n addressed to the mobile station are
stored in a buffer BF of the handover source base station
ha and the packet n-2 is being transmitted to the mobile
station, but the transmission of this packets n-2 does
not end. During execution of the handover sequence, the
handover target base station llb sends information of the
communication state on the handover target base station
to the handover source base station ha along with an HO
response message. When the communication state
information is received, the handover source base station
ha decides whether data transference can be executed
depending on the communication state of the handover
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target base station 11b, and attaches the transference
execution information, which indicates whether data
transference is executed or not, to HO instruction and
sends it to the mobile station 14.
[0023]
Fig. 2 shows format example of HO response messages,
including the communication state information. This
message includes at least an identifier ID and
communication state information CST, as shown in (A) of
Fig. 2. As the identifier, a new identifier which at
least the mobile station uses when it communicates with
the handover target base station, may be included. And
the address of the handover source base station ha may
be included as a destination address of this message and
the address of the handover target base station lib may
be included as the transmission source address of this
message. If the communication state information is
represented by X bits, the number of states that can be
defined is 2.
As (B) of Fig. 2 shows, the communication state
information CST has congestion degree information
according to the degree of congestion of the handover
target base station 11b. For example, if the congestion
degree information is represented by two bits, four
congestion degrees can be represented (serious congestion,
heavy congestion, light congestion, no congestion). On
the other hand, the communication state information CST
may include buffer state information for notifying
residual amount of memory of the handover target base
station, as shown in (C) of Fig. 2. For example, the
buffer state information is represented by 10 bits, and
1024 states can be represented. If the unit of this
value is Kbytes, it is possible to represent that a
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maximum of 1024 Kbytes of memory is secured for this
mobile station. Further the communication state
information CST may include packet transfer function
installation information in the handover target base
station as shown in (D) of Fig. 2. This transfer
function installation information is information to
indicate whether the packet transfer function has been
installed or not. For example, in order to transfer
packets from the handover source base station ha to the
handover target base station 11b, packet transfer
protocol (packet transfer function) is required.
Information on whether such a function has been installed
or not can be represented by 1 bit, and the installation
of the function is notified to the handover source base
station ha by this bit.
After the handover source base station ha receives
the congestion state information message, the possibility
of data transference is judged. For example, if "light
congestion" is notified by the handover target base
station 11b, data transference is executed. If "heavy
congestion" is notified by the handover target base
station 11b, data transference is not executed. On the
other hand, if the residual memory amount of the handover
target base station llb is an amount that can
sufficiently store all the packets to be transferred,
data transference is executed. If it is notified that
the residual memory amount of the handover target base
station llb is "0 Kbyte", then data transference is not
executed. Further, if the handover target base station
llb has installed the packet transfer function, the data
transference is executed. If it is notified that the
packet transfer function is not installed, then data
transference is not executed.
CA 02883699 2015-03-04
[0024]
Fig. 3 is a block diagram of the base station, in
which a buffer unit 21, scheduler unit 22,
transmission/reception unit 23 and control unit 24 are
shown.
The buffer unit 21 is a memory for storing packets
that flow in from a host station, and packets transferred
from an adjacent base station (handover source base
station). In Fig. 3, the base station physically has two
buffers, but may have one physical memory partitioned by
software. The scheduler unit 22 selects a mobile station
with which radio transmission is performed, from among a
plurality of mobile stations in communication, extracts
packets of this mobile station stored in the buffer unit,
and inputs them to the transmission/reception unit 23.
The transmission/reception unit 23 encodes and modulates
packets input from the scheduler, and transmits them by
radio. The transmission/reception unit 23 also receives
and demodulates control signals and various data which
are sent from the mobile station.
The control unit 24 has a buffer management unit 24a,
HO control unit 24b and measurement information control
unit 24c. The buffer management unit 24a manages various
packets stored in the buffer 21. If data transference is
executed during handover, all the packets stored in the
buffer unit 21 are transferred to the handover target
base station. On the other hand, if data transference is
not executed even if handover is generated, the buffer
management unit 24a controls such that all the packets
stored in the buffer unit 21 are erased. The HO control
unit 24b executes the handover control described in Fig.
21, and the measurement control unit 24c collects various
measurement information which is sent from the mobile
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station, such as radio quality CQI (Channel Quality
Information) of the mobile station.
[0025]
Fig. 4 is a block diagram of the mobile station, in
which a transmission/reception unit 31, buffer unit 32,
reorder unit 33 and control unit 34 are shown. The
transmission/reception unit 31 transmits/receives packets
and control information to/from the
transmission/reception unit of the base station. If RLC
PDU cannot be constructed from the received lower layer
packets, the buffer unit 32 holds the packets until the
RLC PDU is constructed, and if RLC PDU can be constructed,
the buffer unit 32 removes the header and transfers the
packets to the reorder unit 33 as RLC SDU (see Fig.24).
The reorder unit 33 has a function to rearrange RLC SDU
(=PDCP PDU) in the order of sequence numbers, and
transfer it to the upper layer. If it is detected that
the continuity of the sequence number of a RLC SDU (=PDCP
PDU) ceases, the reorder unit 33 stores the subsequent
RLC SDU (=PDCP PDU) in the internal memory until the
continuity of the sequence number is resumed by the
received RLC SDU. If such RLC SDU (=PDCP PDU) does not
arrive even if a predetermined time elapses, the reorder
unit stops the reordering processing, and transfer all
the stored PDCP PDU to the upper layer.
The control unit 34 has a measurement control unit
34a, reorder management unit 34b and retransmission
management unit 34c. The measurement control unit 34a
measures various measurement information to be sent to
the base station. For example, radio quality CQI
(Channel Quality Information) of the mobile station is
measured. The reorder management unit 34b controls the
reorder unit 33, and if the continuity of the sequence
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number of a PDCP PDU ceases, the reorder management unit
34b instructs the reorder unit 33 to store the PDCP PDU
and wait for the arrival of PDCP PDU by which the
continuity of the sequence numbers is resumed. When a
predetermined time to wait for the arrival of the packets
elapses, the reorder management unit 34b instructs the
reorder unit 33 to stop reordering, and also removes the
header of all the stored PDCP PDUs, and transfers them to
the upper layer as PDCP SDUs, so that new PDCP PDUs can
be received. During retransmission control time, the
retransmission management unit 34c sends the
retransmission request signals to the base station via
the transmission/reception unit 31 as shown by the dotted
line.
If forwarding is executed in Fig. 1, the
transmission of the packet n-2 is stopped, and the
packets n-2 to n are transferred to the handover target
base station 11b. If forwarding of the packets is not
executed, on the other hand, the transmission of the
packet n-2 is stopped, and the packets n-2 n are erased
from the buffer unit BF. The handover source base
station ha attaches the transference execution
information to indicate whether data transfer (data
forwarding) is executed, to an HO instruction message to
the mobile station 14, and sends the HO instruction
message.
[0026]
Fig. 5 is a flow chart depicting an operation of the
handover target base station llb for executing a series
of above mentioned operations.
In Fig. 5, when the handover control unit 24b of the
handover target base station llb receives an HO request
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(including mobile station ID and QoS information) from
the handover source base station ha (step 201), the
handover control unit 24b performs call acceptance
control based on this information, and judges whether
acceptance of the mobile station is admitted (step 202).
If not admitted, post-processing is performed (step 211),
and handover control ends.
If acceptance of the mobile station is admitted, on
the other hand, the handover control unit 24b judges the
communication state (congested state, buffer use state or
function installed state) of the handover target base
station llb (step 203), and returns the HO request
response message including the communication state
information, which was described in Fig. 2, to the
handover source base station ha (step 204). Then the
handover target base station llb stores the packets
forwarded from the handover source base station ha into
the buffer 21 in a case where the data transference is
executed (step 124), and hereafter, the buffer unit 21
stores the packets forwarded from the handover source
base station ha.
If the handover control unit 24b receives the HO
completion report from the mobile station 4 in this state
(step 206), the handover control unit 24b sends the HO
completion report to the host station 12 (step 207).
When the handover completion report is received, the host
station 2 switches the packet transmission path from the
handover source base station ha to the handover target
base station 11b, and returns with the HO completion
response to the handover target base station llb (step
208). When the HO completion response is received from
the host station 12, the handover control unit 24b of the
handover target base station llb instructs the scheduler
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22 to start transmission of the packets. Thereby the
scheduler 22 starts transmission of the forwarded packets
to the mobile station 14 with priority, and then starts
transmission of the packets received from the host
* station 12 to the mobile station after sending the above
packets (scheduling: step 209). In parallel with step
209, the handover control unit 24b sends a resource
release to the handover source base station ha (step
210), performs post-processing (step 211), and ends
handover control.
[0027]
The handover source base station ha notifies the
mobile station 14 of whether data transference was
executed or not using the HO instruction message, as
mentioned above. Fig. 6 is a format example of the HO
instruction message, and this message includes at least
the identifier ID and transference execution information
PHO. As the identifier, at least a new identifier, which
the mobile station 14 uses when it communicates with the
handover target base station 11b, is included. An
address of the mobile station 14 may be included as the
destination address of this message, and an address of
the handover source base station ha may be included in
the transmission source address of this message. Also,
in order to notify the transference execution information,
at least one bit of information is included. For example,
value "0" of this information indicates that data
transference (packet forwarding) was executed, and value
"1" of this information indicates that data transference
was not executed. On the contrary, value "0" of this
information may indicate that data transfer was not
executed, and value "1" of this information may indicate
that data transference was executed.
CA 02883699 2015-03-04
[0028]
Fig. 7 is a flow chart depicting a device operation
of the handover source base station for executing a
series of the above mentioned operations.
In Fig. 7, when the measurement control unit 24a of
a user of the handover source base station ha receives
the receive state information from the mobile station 14
using Measurement Report (step 251), the measurement
control unit 24a judges whether handover HO is required
based on this receive state information (step 252), and
returns to the beginning if handover is unnecessary.
If it is decided that the handover HO is necessary,
the handover control unit 24b determines the handover
target base station lib based on the content of
Measurement Report, and sends the handover request to
this handover target base station lib (step 253).
Then the handover control unit 24b receives an HO
response message transmitted from the handover target
base station lib (step 254), decides whether transfer of
the packets (packet forwarding) is executed based on the
communication state information CST included in this HO
response message (step 255), and if it is decided that
the transference of the packets is not executed, the HO
control unit 24b enters the transference execution
information PHO (= "1": transference is not executed) in
the HO instruction message, and sends it to the mobile
station (step 256), and instructs the buffer management
unit 24a to erase the packets remaining in the buffer 21
(step 257).
If it is decided that the transference of the
packets is executed in step 255, on the other hand, the
HO control unit 24b enters the transfer execution
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information PHO (= "O": transference is executed) in the
HO instruction message, and sends it to the mobile
station 14 (step 258), and instructs the buffer
management unit 24a to forward the packets remaining in
the buffer 21 to the handover target base station llb
(packet forwarding) (step 259). Thereby the buffer
=
management unit 24a forwards the packets, which have not
been sent to the mobile station 14 and which remain in
the buffer 21, to the handover target base station llb
via the route indicated by the dotted line. Then the HO
control unit 24b receives the resource release message
sent from the handover target base station llb (step 260),
and executes resource release (step 261).
In Fig. 1, the mobile station 14 receives the
transference execution information PHO included in the HO
instruction message, and starts reordering if the
transference was executed. Specifically, in the case
when the mobile station 14 received n+1 and later packets
before the packets n-2 to n, the mobile station 14 waits
for the arrival of the packets n-2 to n until a
predetermined time elapses, without transferring the
packet n+1 to the upper layer. If the transference was
not executed, on the other hand, the mobile station 14
immediately transfers the n+1 and later packets to the
upper layer, and prepares for receiving the next packet
without waiting for the arrival of the packets n-2 to n.
[0029]
Fig. 8 is a flow chart depicting an operation of the
mobile station.
The measurement control unit 34a of the mobile
station 14 notifies the receive state to the handover
source base station ha using Measurement Report (step
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271). Then, the control unit 34 waits for an HO
instruction message which is sent from the handover
source base station 11a, and if the HO instruction
message is received (step 272), the control unit 34
insures synchronization with the handover target base
station llb by Ll/L2 signaling (step 273), and sends the
handover completion report to the handover target base
station llb if synchronization is insured (step 274).
Then the control unit 34 checks whether data transference
(data forwarding) was executed by referring to the
transference execution information PHO of the HO
instruction message received in step 272 (step 275), and
if data transference was not executed, the control unit
34 performs a control to generate PDCP SDU using packets
received from the handover target base station 11b, and
transfer it to the upper layer, without executing
reordering processing (step 276). If it is detected that
data transference was executed in step 275, on the other
hand, the reorder management unit 34b controls the
reorder unit 33, and executes the reordering processing
(step 277).
[0030]
Fig. 9 is a flow chart depicting the reordering
processing of the mobile station.
When the transmission/reception unit 31 receives
lower layer packets from the handover target base station
11b, the reorder management unit 34b checks whether RLC
PDU can be constructed (step 302), checks whether a
predetermined time has elapsed if it cannot be
constructed (step 303), and stores these lower layer
packets in the buffer 32 (step 304) and executes
processing after step 301 if the predetermined time has
not yet elapsed. If RLC PDU cannot be constructed even
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if the predetermined time has elapsed after the lower
layer packets are received, the lower layer packets are
erased from the buffer (step 305).
If RLC PDU can be constructed using the lower layer
packets received in step 302, on the other hand, the
reorder management unit 34b transfers this RLC PDU to the
reorder unit 33 as RLC SDU (step 306). If RLC SDU is
received, the reorder unit 33 checks whether there is any
missing sequence number and confirms the continuity of
the sequence number (step 307), and transfers the RLC SDU
to the upper layer as the RDCP SDU if sequence numbers
are continuous without any missing (step 311). If there
is any missing sequence number, however, the reorder
management unit 34b instructs the reorder unit 33 to
stores RLC SDU (=PDCP PDU) (step 308). Thereby the
reorder unit 33 stores RLC SDU (=PDCP PDU) in the
internal memory and checks whether the continuity of the
sequence numbers is resumed by the received RLC SDU (step
309). If the continuity of the sequence numbers is
resumed by the received RLC SDU, the reorder unit 33
transfers this RLC SDU to the upper layer as PDCP SDU,
and transfers the stored RLC SDU (=PDCP PDU) to the upper
layer (step 311).
If RLC SDU by which the continuity of the sequence
numbers is resumed, is not received in step 309, the
reorder unit 33 monitors whether the predetermined time
has elapsed (step 310), repeats processing after step 308
if not elapsed, or transfers stored PDCP PDU to the upper
layer if elapsed, even if the sequence numbers are not
continuous (step 311).
As described above, according to the first
embodiment, if packets which remain in the handover
source station are not forwarded to the handover target
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base station when handover control is executed
(transference is not executed), the mobile station does
not have to execute reordering, even if the sequence
numbers are not continuous, so unnecessary wait time is
not generated, and delay time of data can be minimized
and throughput of the entire system can be improved.
[0031]
(C) Second embodiment
Fig. 10 is a diagram depicting a second embodiment,
where a handover source base station ha judges whether
packet transfer (packet forwarding) is performed or not
based on the type of communication service when the
handover sequence is executed, and notifies the
forwarding execution information (transference execution
information) to a mobile station 14.
It is assumed that the handover source based station
ha stores packets of non-real-time traffic (NRT traffic)
in FTP (File Transfer Protocol) communication or Web
communication and packets of real-time traffic (RT
traffic) in VoIP communication and streaming respectively
in different buffers BF11 and BR12, with different
sequence numbers attached thereto and performs scheduling
to transmit these packets, as shown in Fig. 10. It is
also assumed that one of the packets m-2 to m
constituting NRT traffic and packets n-2 to n
constituting RT traffic is in-transmission and others are
now stored in the buffers BF1, BF2 without being
transmitted to the mobile station 14. In the second
embodiment, the data transference is executed based on
the policy that the packets of NRT communication service
are forwarded, and the packets of RT communication
service are not forwarded. This is because of the
CA 02883699 2015-03-04
followings. For packets of communication service that
must be processed in high real-time, such as packets of
VoIP calls, it is preferable to discard them without
forwarding in order to transmit and receive voice without
delay. And for packets of low real-time and high QoS
services it is preferable to forwarding them to the
handover target base station in order to receive high
quality data.
If the mobile station 14 which executes handover is
performing RT communication, an HO control unit 24b (see
Fig. 3) of the handover source base station ha decides
not to forward the packet n-2 which is currently being
transmitted, and packets n-1 to n which are currently
stored are not forwarded to the handover target base
station lib when the handover sequence is executed based
on the above mentioned packet transference policy. And
the HO control unit 24b includes a transference execution
information PHO indicating that forwarding was not
performed in the HO instruction message, to notify the
mobile station 14. The message format in this case is
the same as Fig. 6. The mobile station 14, which
received the transference execution information PHO,
performs a similar operation as Fig. 8 and Fig. 9, as
shown in the first embodiment, without executing the
reordering processing.
If the mobile station 14 which executes handover is
performing NRT communication, on the other hand, the HO
control unit 24b of the handover source base station ha
decides to forward the packet m-2 which is currently
being transferred, and packets m-1 to m which are
currently stored are forwarded to the handover target
base station llb when handover sequence is executed.
Then transference execution information PHO to notify
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that forwarding was executed is included in the HO
instruction message, and is sent to the mobile station 14.
The message format in this case is the same as Fig. 6.
Mobile station 14, which received the transference
execution information PHO, performs an operation the same
as Fig. 8 and Fig. 9, and reordering processing is
performed as shown in the first embodiment.
[0032]
Fig. 11 is a flow chart depicting an operation of
the handover source base station ha for executing the
above mentioned series of operations, in which the same
steps as the flow chart of the first embodiment in Fig. 7
are denoted with the same numbers. The difference is
step 255', in which it is determined whether the
transference of the packets (packet forwarding) is
executed or not depending on whether the communication
service is NRT communication service or RT communication
service. If the communication service is RT
communication service, an HO control unit 24b decides
that forwarding is not executed, enters the transference
execution information PHO (= "1": transference is not
executed) in an HO instruction message, and sends it to
the mobile station (step 256), and instructs a buffer
management unit 24b to erase the packets remaining in a
buffer 21 (step 257).
If it is decided that the transference of the
packets is executed in step 255', on the other hand, the
HO control unit 24b enters the transference execution
information PHO (= "O": transference is executed) in the
HO instruction message, and sends it to the mobile
station 14 (step 258), and instructs the buffer
management unit 24a to forward the packets (transfer the
packets) remaining in the buffer 21 to the handover
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target base station lib (step 259).
[0033]
= Variant form
In the second embodiment, transference is not
executed if the communication service is RT communication
service, but in some cases, packets may or may not be
forwarded depending on the setting even if the
communication service is RT communication service (e.g.
VoIP calls). This variant form is for supporting such a
case, and Fig. 12 is a flow chart depicting an operation
of the handover source base station ha of the variant
form, in which the same steps as the processing flow of
the first embodiment in Fig. 11 are denoted with the same
numbers. The difference is the existence of step 265, in
which it is checked whether the setting is to forward
packets or not if the communication service is RT
communication service, and if not, the HO control unit
24b decides that forwarding is not executed, enters the
transference execution information PHO (= "O":
transference is not executed) in the HO instruction
message, and sends it to the mobile station (step 256),
and instructs the buffer management unit 24b to erase the
packets remaining in the buffer 21 (step 257).
If the setting is to forward packets in step 265, on
the other hand, the HO control unit 24b enters the
transference execution information PHO (= "O":
transference is executed) in the HO instruction message,
and sends it to the mobile station 14 (step 258), and
instructs the buffer management unit 24a to forward the
packets (transfers the packets) remaining in the buffer
21 to the handover target base station llb (step 259).
[0034]
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Fig. 13 is a flow chart depicting the reordering
processing in the mobile station of the variant form, in
which the same steps as the processing flow of the first
embodiment in Fig. 9 are denoted with the same numbers,
and the difference is that the time to continue
reordering processing is switched depending on whether
the communication service is VoIP calling or not. In
other words, it is checked whether the call type is a
VoIP call (step 312) if RLC SDU of which sequence numbers
are continuous is not received in step 309, and if not
VoIP calling, the control unit 34 monitors whether the
predetermined first setup time TS1 has elapsed (step 310),
repeats the processing after step 308 if not elapsed, or
transfers the stored PDCP PDU to the upper layer if the
setup time has elapsed, even if the sequence numbers are
not continuous (step 311). If the call type is VoIP
calling in step 312, the control unit 34 monitors whether
a second setup time TS2 (< TS1) has elapsed (step 313),
repeats the processing after step 308 if not elapsed, or
transfers the stored PDCP PDU to the upper layer if the
setup time has elapsed, even if the sequence numbers are
not continuous (step 311).
According to the above mentioned variant form, the
quality of VoIP can be improved by forwarding packets
even in the case of VoIP calling, and delay time due to
reordering processing can be decreased by decreasing the
setup time TS2.
[0035]
(D) Third embodiment
The third embodiment is an embodiment to determine
whether packet transfer (packet forwarding) is possible
depending on whether a handover source base station has a
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packet transfer function or not, notifying this execution
information to a mobile station. Fig. 14 is a block
diagram depicting a base station in which a buffer
management unit has a simplified configuration without a
packet transfer function, and the same portions as the
base station of the first embodiment in Fig. 3 are
denoted with the same symbols. The difference is that
the buffer management unit 24a' has a simplified
configuration, and does not have a function to forward
packets to the handover target base station llb or a
packet transfer scheduler function.
Fig. 15 is a flow chart depicting an operation of
the handover source base station, in which the same steps
as the flow chart of the first embodiment in Fig. 7 are
denoted with the same numbers. The difference is that it
is determined whether the transference of the packets
(packet forwarding) is executed or not depending on
whether the forwarding function and the packet transfer
scheduler function are installed in the handover source
base station ha in step 255". If these functions are
not installed, an HO control unit 24b decides that
forwarding is not executed, enters the transference
execution information PHO (= "1": transference is not
executed) in an HO instruction message, and sends it to
the mobile station (step 256), and instructs a buffer
management unit 24b to erase the packets remaining in a
buffer 21 (step 257).
If the forwarding function and the packet transfer
scheduler function are installed in step 255", on the
other hand, the HO control unit 24b decides to execute
the transfer of the packets, enters the transference
execution information PHO (= "O": transference is
executed) in the HO instruction message, and sends it to
CA 02883699 2015-03-04
the mobile station 14 (step 258), and instructs the
buffer management unit 24a to forward the packets
(transfer the packets) remaining in the buffer 21 to the
handover target base station llb (step 259).
[0036]
(E) Fourth embodiment
In the above embodiments, the PDCP layer is
installed in aGW 12, which is a host station, and the RLC
layer and lower layer are installed in the base station
11 as shown in (A) of Fig. 16, but as (B) of Fig. 16
shows, a system may be constructed such that the entire
PDCP layer, RLC layer and lower layer are installed in
the base station 11, and only simple functions, such as
packet routing function, may be installed in aGW 12. In
the system configuration of (B) of Fig. 16, a sequence
number attaching function may be provided to the base
station. Fig. 17 is a diagram depicting forwarding when
handover is generated in such a system.
Three packets are sent from a host station 12 to a
handover source base station ha, and packet numbers n-2,
n-1 and n are attached in the base station. It is
assumed that handover is started in a state when these
packets n-2, n-1 and n remain in a buffer without being
sent to the mobile station. If these packets n-2, n-1
and n are forwarded during execution of the handover
sequence, these packets are transferred from the handover
source base station ha to the handover target base
station llb as shown in Fig. 17. During this forwarding,
packets may be sent from the host station 12 to the
handover target base station 11b. In such a case, the
handover target base station llb cannot attach correct
sequence numbers to the packets received from the host
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station 12. Therefore when the packets n-2, n-1 and n,
which have not been sent to the mobile station, are
forwarded to the handover target base station 11b, the
handover source base station ha also forwards the
sequence numbers to the handover target base station. In
other words, the sequence number n+1 to be attached to
the packet, which is sent from the host station 12 to the
handover target base station lib is forwarded. Thereby
the control unit 24 of the handover target base station
llb can attach the sequence number n+1 to the packet
exactly, even if packets are sent from the host station
12 to the handover target base station lib during
forwarding.
In the case of the fourth embodiment as well, the
transference execution information PHO, to indicate
whether forwarding was executed or not, can be included
in the HO instruction message and sent to the mobile
station, whereby reordering processing can be omitted
when forwarding is not performed.
[0037]
Fig. 18 is a diagram depicting the handover
procedure of the fourth embodiment, in which the same
procedures as the diagram depicting the handover
procedures in Fig. 21, are denoted with the same numbers.
The difference is that the sequence numbers SN are
transferred from the handover source base station ha to
the handover target base station llb before the packet
transfer (packet forwarding).
According to the fourth embodiment, sequence numbers
are forwarded during handover even if the sequence
numbers are assigned to the packets in the handover
source base station, so correct sequence numbers can be
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attached to the packets in the handover target base
station, and if forwarding is not executed, reordering
processing can be omitted in the mobile station.
[0038]
= Effect of invention
According to the present invention, when packets
remaining in the handover source base station are not
forwarded to the handover target base station (when
transference is not executed) at the execution of
handover control, the mobile station does not have to
execute reordering, even if the sequence numbers are not
continuous, so unnecessary wait time is not generated,
delay time of data is minimized, and throughput of the
entire system can be improved.
Furthermore, according to the present invention, the
mobile station does not have to execute reordering, even
if the forwarding is not executed depending on the
communication state (congested state, buffer empty state,
function installed state) and type of communication
service, so unnecessary wait time is not generated, delay
time of data is minimized, and throughput of the entire
system can be improved.
Furthermore, according to the present invention,
packets are forwarded during handover even in the case of
VoIP calling, so the quality of VoIP can be improved, and
delay time due to reordering processing can be decreased
in the mobile station by decreasing the duration of
reordering processing.
Furthermore, according to the present invention,
sequence numbers are forwarded during handover even if
the sequence numbers are attached to packets in the
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handover source base station, so correct sequence numbers
can be attached to the packets in the handover target
base station, and reordering processing can be omitted in
the mobile station if forwarding is not performed.
44
