U.S. patent application number 14/527397 was filed with the patent office on 2015-03-05 for handover control method in a wireless access system, relay station and base station.
This patent application is currently assigned to ALCATEL LUCENT. The applicant listed for this patent is ALCATEL LUCENT. Invention is credited to Shan Jin, Wei Ni, Gang Shen, Wei Zou.
Application Number | 20150065139 14/527397 |
Document ID | / |
Family ID | 38655082 |
Filed Date | 2015-03-05 |
United States Patent
Application |
20150065139 |
Kind Code |
A1 |
Shen; Gang ; et al. |
March 5, 2015 |
HANDOVER CONTROL METHOD IN A WIRELESS ACCESS SYSTEM, RELAY STATION
AND BASE STATION
Abstract
The present invention provides a handover control method in a
wireless access system, a relay station and a base station for
performing handover control in a mobile multi-hop relay wireless
access system such that the wireless access system is enabled to
cover a wider area. To achieve the above object, the present
invention provides a handover control method in a wireless access
system, wherein the wireless access system comprises a mobile
station and a base station, which receive and send message via a
wireless channel, and further comprises a relay station for
forwarding message from the mobile station and the base station
under control of the base station, characterized in that the method
comprising a relay station measure and arbitration step in which
the relay station measures the message and arbitrates whether to
relay the message, and a base station measure and handover step in
which the base station measures the message and arbitrates whether
to perform handover.
Inventors: |
Shen; Gang; (Shanghai,
CN) ; Ni; Wei; (Shanghai, CN) ; Zou; Wei;
(Shanghai, CN) ; Jin; Shan; (Shanghai,
CN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ALCATEL LUCENT |
Paris |
|
FR |
|
|
Assignee: |
ALCATEL LUCENT
Paris
FR
|
Family ID: |
38655082 |
Appl. No.: |
14/527397 |
Filed: |
October 29, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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12298645 |
Oct 27, 2008 |
8903394 |
|
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PCT/CN2007/001448 |
Apr 28, 2007 |
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14527397 |
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Current U.S.
Class: |
455/436 |
Current CPC
Class: |
H04W 36/30 20130101;
H04B 7/155 20130101; H04B 7/2606 20130101; H04W 36/0009 20180801;
H04W 16/26 20130101 |
Class at
Publication: |
455/436 |
International
Class: |
H04W 36/30 20060101
H04W036/30 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 28, 2006 |
CN |
200610026180.6 |
Apr 28, 2007 |
CN |
PCT/CN2007/001448 |
Claims
1. (canceled)
2. A method for control of a handover of a mobile station in a
wireless access system, comprising: receiving an uplink message
from a mobile station at a relay station via a wireless channel;
forwarding the uplink message from the relay station to the base
station when it is determined that the signal quality of the uplink
message measured at the relay station exceeds a predetermined
value; receiving the uplink message via the wireless channel at the
base station from at least one of the mobile station and the relay
station; and at the base station, causing initiation of a handover
of the mobile station involving the relay station based at least in
part on a measured signal quality of the uplink message as received
at the base station.
3. The method according to claim 2 wherein the uplink message
includes at least one of (i) a ranging request message or (ii) an
uplink data burst.
4. The method according to claim 2 wherein the wireless channel
includes an uplink channel and a downlink channel.
5. The method according to claim 2, further comprising: measuring
signal quality of the uplink message at the relay station; and
comparing the measured signal quality of the uplink message to the
predetermined value at the relay station.
6. The method according to claim 2 wherein the uplink message is
forwarded from the relay station to the base station via the
wireless channel through a dedicated control information relay zone
reserved for forwarding uplink control information.
7. The method according to claim 2 wherein involving the relay
station in the handover of the mobile station means said handover
is at least one of (i) from the relay station and (ii) to the relay
station.
8. The method according to claim 2, further comprising: measuring
signal quality of the uplink message(s) received at the base
station; comparing the measured signal quality (qualities) and link
budgets at the base station; and at the base station, determining
whether to initiate the handover based at least in part on the
comparing.
9. The method according to claim 8 wherein the determining whether
to initiate the handover is based at least in part on one or more
of channel load, multi-hop bandwidth efficiency, and transmission
power.
10. A relay station configured to operate in a wireless access
system, comprising: a receiver configured to receive an uplink
message from a mobile station via a wireless channel; and a
transmitter configured to forward the uplink message to the base
station via the wireless channel when it is determined that the
signal quality of the uplink message exceeds a predetermined
value.
11. The relay station according to claim 10 wherein the transmitter
is configured to forward the uplink message via the wireless
channel through a dedicated control information relay zone reserved
for forwarding uplink control information.
12. The relay station according to claim 10 wherein the uplink
message includes at least one of (i) a ranging request message or
(ii) an uplink data burst.
13. The relay station according to claim 10 wherein the wireless
channel includes an uplink channel and a downlink channel.
14. The relay station according to claim 10, further comprising: a
measurement circuit configured to measure signal quality of the
uplink message; and at least one processor configured to compare
the measured signal quality of the uplink message to the
predetermined value.
15. A base station configured to operate in a wireless access
system, comprising: a receiver configured to receive an uplink
message generated by a mobile station from at least one of the
mobile station and a relay station forwarding the uplink message
via a wireless channel; a measurement circuit configured to measure
signal quality of the uplink message; and at least one processor
configured to cause initiation of a handover of the mobile station
involving the relay station based at least in part on the measured
signal quality of the uplink message as received at the base
station.
16. The base station according to claim 15 wherein the receiver is
configured to receive the uplink message via the wireless channel
through a dedicated control information relay zone reserved for
forwarding uplink control information.
17. The base station according to claim 15 wherein the uplink
message is received from the relay station after the relay station
received the uplink message from the mobile station and determined
the signal quality exceeded a predetermined value.
18. The base station according to claim 15 wherein the uplink
message includes at least one of (i) a ranging request message or
(ii) an uplink data burst.
19. The base station according to claim 15 wherein the wireless
channel includes an uplink channel and a downlink channel.
20. The base station according to claim 15 wherein involving the
relay station in the handover of the mobile station means said
handover is at least one of (i) from the relay station and (ii) to
the relay station.
21. The base station according to claim 15 wherein the at least one
processor is configured to compare the measured signal quality
(qualities) and link budgets and to determine whether to initiate
the handover based at least in part on the comparing.
22. The base station according to claim 21 wherein the at least one
processor is configured to determine whether to initiate the
handover based at least in part on one or more of channel load,
multi-hop bandwidth efficiency, and transmission power.
23. A method for control of a handover of a mobile station in a
wireless access system, comprising: at a current base station,
receiving a mobile handover request generated by a mobile station,
wherein the mobile station and current base station are associated
with a wireless access system and the mobile station is currently
within coverage of the current base station; sending a pre-handover
notification request message from the current base station to at
least one neighboring base station, each neighboring base station
associated with the wireless access system; and receiving a
pre-handover notification response message at the current base
station from one or more neighboring base stations to which the
pre-handover notification request message was sent, wherein the
pre-handover notification response message from at least one of the
one or more neighboring base stations includes signal quality
information relating to the corresponding ranging request message
or uplink data burst received by a relay station within coverage of
the corresponding neighboring base station.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation application of co-pending
U.S. patent application Ser. No. 12/298,645, filed Oct. 27, 2008,
which is a national stage entry of PCT Patent Application No.
PCT/CN2007/001448, filed Apr. 28, 2007, which claims the benefit of
Chinese Patent Application No. 200610026180.6, filed Apr. 28, 2006.
The entire contents of each of the above-identified patent
applications are fully incorporated herein by reference.
TECHNICAL FIELD
[0002] The present invention relates to a wireless access system,
and more specifically to a method for performing handover control
in a mobile multi-hop relay wideband wireless access system, and a
relay station and a base station therefor.
BACKGROUND OF THE INVENTION
[0003] The IEEE802.16-based Wireless Metropolitan Area Network
(WiMAX) provides a wireless access solution for wideband access
service, and the WiMAX standards adopts an Orthogonal Frequency
Division Multiple Access (OFDMA) technology. But its coverage is
limited by power and transmission technique, especially in
metropolitan areas. At the edge of a cell or in regions which are
shadowed, data throughput of a user drops dramatically and complex
wireless environment may also result in coverage blind areas. In
view of the above problems, the solution of simply increasing the
density of base stations will only result in increase of facilities
and network wiring costs.
[0004] Therefore, there is provided a wireless access system with a
lower cost, comprising a mobile station, a base station, and a
relay station for receiving and forwarding message between the
mobile station and the base station under the base station control.
After the relay capability is integrated into a wireless access
network system, the system may expand coverage and enhance data
throughput.
[0005] However, in the current wireless access system, there is not
specified a method of how to implement roaming handover control. It
is well known that handover control is an important issue in the
wireless access technology. To expand coverage, the relay station
must supports roaming and handover of the mobile station. The
handover includes handover of the mobile station between the base
station and the relay station as well as between a relay station
and another relay station, and handover of the mobile station cross
base stations. The mobility of the relay station per se is also an
important issue.
[0006] In view of the above problems, a feasible solution for
handover control in a mobile multi-hop relay wireless access system
is desired.
SUMMARY OF THE INVENTION
[0007] The object of the present invention is to provide a handover
control method in a wireless access system, a relay station and a
base station for performing handover control in a mobile multi-hop
relay wireless access system such that the wireless access system
is enabled to cover a wider area.
[0008] To achieve the above object, the present invention provides
a handover control method in a wireless access system including a
base station and a relay station, characterized in that the method
comprising a relay station measure and arbitration step in which
the relay station measures the message and arbitrates whether to
relay the message, and a base station measure and handover step in
which the base station measures the message and arbitrates whether
to perform handover,
[0009] wherein the relay station measure and arbitration step
comprises: at least one relay station receiving the message sent by
the mobile station; the relay station measuring signal strength of
the message sent by the mobile station; the relay station analyzing
and arbitrating signal strength of the message; if the message has
a strong signal, the relay station forwarding the message or
sending a measure report to the base station, and if the message
has a weak signal, the relay station ignores the mobile station
message,
[0010] and wherein the base station measure and handover step
comprises: the base station receiving message sent directly by the
mobile station or forwarded by the relay station; the base station
measuring signal strength of the message; the base station
analyzing and arbitrating signal strength of the message received
directly from the mobile station or the message forwarded by the
relay station, and then determining whether relay handover is
required, and the base station sending to the relay station message
as to whether to provide relay service; andif the message is
ranging request message, the base station sends ranging response
message comprising adjustment to radio frequency power level and
time offset.
[0011] If the base station determines that a relay service is
required while the mobile station is in a state of not using the
relay service, the base station sends providing relay service
message to the relay station, and then handover of the mobile
station from the base station to the relay station is performed;
and
[0012] if the base station determines that no relay service is
required while the mobile station is in a state of already using
the relay service, the base station sends cancelling relay service
message to the relay station, and then handover of the mobile
station from the relay station to the base station is
performed.
[0013] The base station determining the relay station with strong
signal as the target relay station through analysis and
arbitration, the base station sending cancelling relay service
notification to the current relay station, and the base station
sending providing relay service notification to the target relay
station, thereby handover of the mobile station from the current
relay station to the target relay station is performed.
[0014] To achieve the object of cross-base station handover of the
mobile station, the present invention provides a mobile station
cross-base station handover preparation step in the handover
control method, comprising: the mobile station sending a mobile
handover request to the current base station directly or via the
relay station; the current base station receiving the mobile
handover request; the current base station sends a pre-handover
notification request to the target base station; the target base
station sending a pre-handover request response to the current base
station; the current base station sending the mobile handover
response to the mobile station; the mobile station sending a mobile
handover instruction to the current base station directly or via
the relay station; the current base station receiving the mobile
handover instruction; the target base station sending an uplink MAP
to the mobile station; and the mobile station changing its preamble
so as to be synchronized with the target base station preamble.
[0015] According to another aspect of the present invention, there
is provided a relay station for implementing the handover control
method in the above wireless access system, comprising: relay
control means for controlling operation of a relay station; relay
receiving means for receiving message from a mobile station and a
base station via a wireless channel; relay sending means for
sending message to a mobile station and a base station via a
wireless channel; relay measure means for measuring signal strength
of message sent by the mobile station and for ranging the mobile
station; and relay arbitration means for analyzing, arbitrating and
determining whether it is required to relay received message,
wherein the base station allocates a special connection identifier
to the relay station. Under the control of the relay control means,
the relay receiving means receives message, the relay measure means
measure signal strength of the message, and the relay arbitration
means analyzes and arbitrates the measure result of the message to
determine whether to forward the message by the relay sending
means. Further, the relay receiving means receives a special
connection identifier sent by the base station.
[0016] According to another aspect of the present invention, there
is provided a base station for implementing the above handover
control method in a wireless access system, comprising: base
station control means for controlling operation of a base station;
base station receiving means for receiving message from a mobile
station and a relay station via a wireless channel; base station
sending means for sending message to a mobile station and a relay
station via a wireless channel; base station measure means for
measuring signal strength of the message sent by the mobile
station; and base station arbitration means for arbitrating and
determining whether relay handover is required, wherein under
control of the base station control means, message received by the
base station receiving means is sent to the base station measure
means for measure, and after being analyzed and arbitrated by the
base station arbitration means, the message is sent by the base
station sending means to the relay station and the mobile station,
and the base station sending means sending a special connection
identifier to the relay station.
[0017] By virtue of the method and devices provided by the present
invention and with the introduction of the handover control method,
the present invention realizes handover functionality in a mobile
multi-hop wireless relay system, which enables the base station to
allocate resources in a centralized way to the mobile station and
the relay station within the its coverage. Thus, the present
invention not only enhances data throughput, but also expands the
coverage.
[0018] The present invention provides a simple and ingenious
solution for IEEE 802.16, and meanwhile it is completely backward
compatible with the current standards, thereby the traditional
mobile station without any change is supported for relay and
handover. By virtue of the present invention, handover of mobile
station within the same base station or relay-involved cross-base
station handover are enabled. Furthermore, the handover needs no
extra response time. Since the base station bears the
responsibility for all control functionality in all handover
processes while the relay station is only responsible for sending
data based on the instruction of the base station, the relay
station becomes simpler and much cheaper.
[0019] The other features and advantages of the present invention
will be more apparent from the following detailed description taken
in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 shows a networking state of a mobile station handover
within a same base station in a wireless access system according to
a preferred embodiment of the present invention;
[0021] FIG. 2 shows a structural diagram of an OFDMA relay frame
according to a preferred embodiment of the present invention;
[0022] FIG. 3 shows a flow chart of handover of a mobile station
within a same base station according to a preferred embodiment of
the present invention;
[0023] FIG. 4 shows a diagram of a handover process of a mobile
station from a relay station to a base station within a same base
station according to a preferred embodiment of the present
invention;
[0024] FIG. 5 shows a diagram of a handover process of a mobile
station from a relay station RS1 to a relay station RS2 within a
same base station according to a preferred embodiment of the
present invention;
[0025] FIG. 6 shows a diagram of a handover process of a mobile
station from a base station to a relay station within a same base
station according to a preferred embodiment of the present
invention;
[0026] FIG. 7 shows a networking state of a mobile station
cross-base handover in a wireless access system according to a
preferred embodiment of the present invention;
[0027] FIG. 8 shows a flow chart of a mobile station cross-base
station handover preparation process according to a preferred
embodiment of the present invention;
[0028] FIG. 9 shows a diagram of a cross-base station handover
process of a mobile station from a relay station of a current base
station to an neighboring target base station according to a
preferred embodiment of the present invention;
[0029] FIG. 10 shows a diagram of a cross-base station handover
process of a mobile station from a current base station to a relay
station of an neighboring target base station according to a
preferred embodiment of the present invention;
[0030] FIG. 11 shows a networking state of a relay station
cross-base station handover in a wireless access system according
to a preferred embodiment of the present invention;
[0031] FIG. 12 shows a structural diagram of a relay station
according to a preferred embodiment of the present invention;
[0032] FIG. 13 shows a structural diagram of a base station
according to a preferred embodiment of the present invention;
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0033] Hereinafter, references will be made to the figures to
describe in detail working principles of a wireless access handover
control method, and a relay station and a base station of the
present invention.
[0034] The wireless access system according to a preferred
embodiment of the present invention comprises a base station for
receiving and sending message via a wireless channel and a relay
station for forwarding message under the control of the base
station. The wireless channel includes an uplink channel and a
downlink channel, and the message includes ranging request message
or an uplink data burst.
[0035] As to roaming handover in a mobile relay wireless access
system, relay handover of a mobile station is classified into two
types, i.e. handover within a same base station and cross-base
station handover of a mobile station. A control method for the
mobile station handover with a same base station comprises a relay
station measure and arbitration step, in which the relay station
measures message and arbitrates whether to relay the message; and a
base station measure and handover step, in which the base station
measures the message and arbitrates whether to perform
handover.
[0036] The relay station measure and arbitration step comprises at
least one relay station receiving the message sent by the mobile
station; measuring signal strength of the message sent by the
mobile station, analyzing and arbitrating the signal strength,
forwarding the message with strong signal to the base station or
sends a measure report to the base station, and if the message has
a weak signal, the relay station ignores the mobile station
message.
[0037] The base station measure and handover step comprises: the
base station receiving message, measuring signal strength of the
message, analyzing and arbitrating whether to perform relay
handover, sending to the relay station message as to whether to
provide relay service. If the message is ranging request message,
the base station sending a ranging response message, and the
ranging response message comprising adjustment to radio frequency
power level and time offset.
[0038] For the sake of a clearer description, the implementation
process of the handover control method is illustrated and analyzed
through a concrete relay handover process.
[0039] I. Handover of Mobile Station within a Same Base Station
[0040] Within coverage of the same base station, there are three
types of relay-involved handovers: [0041] Handover from a base
station to a relay station within coverage of the same base station
[0042] Handover from a relay station to a base station within
coverage of the same base station [0043] Handover from a relay
station to another relay station within coverage of the same base
station
[0044] FIG. 1 shows a networking state of a mobile station handover
in the same base station in a wireless access system according to a
preferred embodiment of the present invention, wherein a mobile
station 110 is located at position A which might be at at the edge
of a cell or in a shadowed area or within a building, and message
from the mobile station and the base station is forwarded via a
relay station 120. When the mobile station roams to position B
closer to the base station, its connection with a base station 130
may not need a relay to forward message, thus it is required to
process handover from the relay station to the base station.
Besides, when the mobile station 110 moves from position B to
position A, it is required to process handover from the base
station to the relay station.
[0045] The wireless access system in a preferred embodiment of the
present invention utilizes a control and scheduling system centered
at the base station 130. The mobile station 110, the relay station
120 and the base station 130 receive and send message therebetween
through a full-duplex wireless channel, the wireless channel
comprising a downlink frequency (shortly as DL) and an uplink
frequency (shortly as UL). The message includes control message and
bearer data. Though allocating control message and arbitrating
access request, the base station 130 coordinates the resources of
the mobile station 110 and the relay station 120 in the cell. The
relay station 120 only has a function of forwarding uplink message
to the base station 130 and forwarding the downlink message to the
mobile station 110. Besides, the control message from the base
station 130 down to the mobile station 110 is directly sent, which
required no relay. For further detailed description, the uplink
bearer data and control message from the mobile station 110 are
sent through the following path: firstly received by the relay 120
and then forwarded to the mobile station 130. It is the same for
the step of transmitting downlink bearer data, just in a reverse
direction; the direct control connection of the downlink between
the mobile station 130 and the mobile station 110 facilitates
lessening latency for relaying.
[0046] A preferred embodiment of the present invention employs an
OFDMA relay frame structure, as shown in FIG. 2. The relay frame
structure is defined the same as the OFDMA frame structure in the
traditional standard, wherein the OFDMA frame is of a
time-frequency two-dimensional structure, the longitudinal axis
unit being sub-channel, and the horizontal axis unit being symbol.
The minimal units scheduled by the Media Access Control (MAC) layer
are a sub-channel and a time slot comprising one or more symbols,
the specific number of symbols being determined by the sub-carrier
mapping pattern. Each frame is divided into an uplink frame and a
downlink frame in time domain. The boarders between uplink and
downlink are Tansmit/Receive Transition Gap (TTG) and
Receive/Transmit Transition Gap (RTG). The start of each downlink
frame is Preamble, and then Frame Control Header (FCH), Downlink
MAP (DL-MAP) and Uplink MAP (UL-MAP). The DL-MAP immediately
follows the FCH, and the UL-MAP immediately follows the DL-MAP.
Following are DL burst blocks and UL burst blocks. The arrangement
pattern and encoding modulation manner of DL burst blocks are
designated by DL-MAP, and the corresponding arrangement patterns
and encoding modulation manners of UL burst blocks are designated
by UL-MAP.
[0047] As shown in FIG. 2, in the OFDMA relay frame structure
employed in the embodiment of the present invention, a dedicated
control information relay zone is reserved for forwarding uplink
control information, for example, ranging request relay. The relay
zone is located at or adjacent to the end of an uplink frame. A
ranging sub-channel information is located in front of the control
information, thereby the ranging request of the mobile station 110
received by the relay station 120 is able to be transmitted in the
same frame through the relay zone, which thus has the following
advantages: in the process of forwarding the ranging request or in
the relay process of other uplink control signal, no extra latency
is increased.
[0048] In the preferred embodiment of the present invention, the
entry and initialization process of the relay station is completely
identical to a traditional mobile station, except that the relay
station has a special relay connection identifier. It is the base
station that assigns a special connection identifier (CID) to the
relay. Next, the base station 130 handles the relay through such
CID in a way different from the traditional mobile station. Thus,
the present invention makes some improvement and updating to the
base station 130 so as to enable the base station to identify the
relay station.
[0049] As to the present invention, to guarantee a backward
compatibility, there is no change to the mobile station 110. The
mobile station 110 only processes in accordance with a traditional
flow. In other wards, the relay station 120 is transparent to the
mobile station, which is one of the major advantages of the present
invention. Besides, the scanning and synchronization process of the
downlink channel is completely identical to the traditional
process, and in this way, the base station may broadcast
synchronization and MAP message without the necessity of any
modification, and the mobile station 110 is synchronized to the
downlink to obtain the downlink and uplink parameters. During the
process of the mobile station accessing the base station, the relay
station 120 participates in the ranging process. During the ranging
process, firstly, the mobile station 110 should be synchronized
with the downlink and understand the features of the uplink through
uplink channel descriptor (UCD) MAC management information. The
mobile station 110 scans the UL-MAP message to find the Initial
Ranging Interval (IRI).
[0050] Hereinafter, reference is made to FIG. 3 to describe a flow
chart of handover of the mobile station within a same base station
according to a preferred embodiment of the present invention,
comprising handover of the mobile station from a relay station to a
base station within the same base station, handover from the base
station to the relay station, and handover from the current relay
station RS1 to the target relay station RS2. The flow of FIG. 3
starts at step S301; at step S305, a mobile station sends message;
during the process, each mobile station sends message, thus there
might be several mobile stations sending message, and such message
will be detected by the relay station. At step S310, at least one
relay station receives the message sent from the mobile station. At
step S313, signal strength is measured. At step S315, the relay
station arbitrates and selects those mobile stations better for
relay based on signal strength, and then determines whether to
forward message. It forwards the message through a reserved
dedicated control information relay zone to the base station only
when the relay station detects message with a strong signal. If the
signal is weak, the flow turns to step S316, and the relay station
ignores the message sent from the mobile station , which requires
no relaying. The arbitration criterion may be that the signal power
is larger than a predetermined value, but the present invention is
not limited thereto. If it is arbitrated that the signal is strong,
the flow turns to step S318, and the message is forwarded to the
base station and reports signal strength. At step S318, the base
station receives message. At step S320, the base station measures
signal strength of the message. At step S330, the base station
analyzes and compares the signal strength. The base station may
receive multiple pieces of message from the same mobile station.
Through arbitrating the signal strength, the base station compares
the signal strength and link budgets, and then determines whether
it is required to perform relay handover to the mobile station.
Upon determining whether to perform relay handover, the base
station may consider channel load, multi-hop bandwidth efficiency
and transmission power, etc. If it is required to perform handover
from the relay station to the base station, the flow turns to step
S340. If it is required to perform handover from the current relay
station RS1 to the target relay station RS2, the flow turns to step
S350. If it is required to handover from the base station to the
relay station, the flow turns to step S360. At step S340, if the
mobile station is in a state of already using the relay station
service while the communication signal between the mobile station
and the base station is quite good, the base station returns the
ranging response message to the mobile station and notifies the
relay station to cancel the relay service, thereby realizing
handover from the relay station to the base station, and the flow
ends at step S370. At step S350, if the comparative analysis turns
out that the signal quality of the current relay station RS1 is
weaker than the message strength of the target relay station RS2,
the base station sends cancelling relay service message to the
current relay station RS1, sends providing relay service message to
the target relay station RS2, and sends ranging response message to
the mobile station, and thereby handover between relay stations is
realized and the flow ends at S370. At step 360, if the mobile
station is in a state of not using the relay station service, the
base station sends preparing to provide relay service message to
the relay station, and returns the ranging response message to the
mobile station. If the direct connection quality is not
satisfactory due to rather long distance between the base station
110 and the relay station 120 or there is shadowing while the
signal quality between the mobile station 110 and the relay station
120 is good and may facilitate increasing data throughput,
providing relay is required. In some worse cases, if the connection
signal between the mobile station and the base station is too weak
that the base station can not detect the mobile station message
directly, the base station can only receive message forwarded by
the relay station through the dedicated control information relay
zone. In this scenario, the base station also requires providing
relay to the mobile station. The ranging response message returned
by the base station to the mobile station comprises adjustment to
the radio frequency power level and time offset so as to adapt to
the connection between the relay station and the mobile station.
Since all the uplink transmission from these mobile stations are
firstly received by the relay station and then forwarded to the
base station, the power level of the base station needs to be
adjusted to be adapted to the transmission distance of the
connection between the mobile station 110 and the relay station
120. Likewise, time synchronization offset correction in the mobile
station also needs to be adjusted. From the perspective of the
mobile station, the relay station is deemed as a base station, and
all uplink message passes through the virtual base station. At step
370, the operation ends. The following operation process is
identical to the prior art wireless access process.
[0051] FIG. 4 shows in detail the process of handover of a mobile
station from a relay station to a base station within a same base
station, FIG. 5 shows in detail the process of handover of a mobile
station between relay stations within a same base station, and FIG.
6 describes in detail the process of handover from a base station
to a relay station within a same base station. The main steps and
contents thereof have been explained in the description of above
flow charts.
[0052] II. Cross-Base Station Handover of a Mobile Station
[0053] During handover of a mobile station within a same base
station, the mobile station before and after handover is
synchronized to the preamble of the same base station. Whereas
during the cross-base station handover, the mobile station after
handover is synchronized to the preamble of a target base station,
characterized in that the preambles before and after the handover
are different. Both of the scenarios comprise handover process of a
mobile station within the same base station.
[0054] FIG. 7 shows a networking state of cross-base station
handover of a mobile station in a wireless access system according
to a preferred embodiment of the present invention. Similarly,
roaming of the mobile station 110 from position A to position B
requires to process cross-base station handover from base station
130 to the relay station 120 within coverage of base station 131.
Contrarily, roaming of the mobile station 110 from position B to
position A requires to process handover from base station 131 to
the relay station 120 within coverage of base station 130.
[0055] The cross-base station relay handover of a mobile station is
an extension of the handover step of the mobile station within a
same base station. The message communication between the current
base station and the neighboring target base station is identical
to the message communication in the current standards. The
cross-base station handover of a mobile station has three
relay-involved scenarios: [0056] handover from the current base
station to a relay station within the coverage of the target base
station [0057] handover from a relay station within the coverage of
the current base station to the target base station [0058] handover
from a relay station within the coverage of the current base
station to a relay station within the coverage of a target base
station
[0059] In the wireless access system according to the preferred
embodiment of the present invention, the cross-base station
handover method of a mobile station further comprises a mobile
station cross-base station preparation process, wherein the
wireless access system comprises at least two base stations, and
the base station which controls the mobile station is the current
base station. FIG. 8 describes a flow chart of a mobile station
cross-base station handover preparation process. The flow starts at
step S805. At step S810, the mobile station sends a mobile handover
request. If it arbitrated to have relay service at step S815, the
mobile handover request is relayed to the current base station at
step S820. If it is arbitrated to have no relay service, the mobile
station directly sends the request to the current base station. At
step S825, the current base station receives the mobile handover
request message. At step 830, the current base station sends
pre-handover notification request message to at least one
neighboring base station. At step 835, the at least one neighboring
base station returns re-handover notification response message to
the current base station. At step S840, the current base station
arbitrates and determines a target base station and returns mobile
handover response message to the mobile station. At step S845, the
mobile station sends mobile handover instruction message. If it is
arbitrated to have relay service at step S850, the relay station
forwards the mobile handover instruction to the current relay
station at step S855. At step S860, the current base station
receives the mobile handover instruction message. At step S865, the
target base station sends UL-MAP message to the mobile station. At
step S870, the mobile station changes its preamble so as to be
synchronized with the preamble of the target base station. At step
S880, this time of cross-base station preparation process ends.
Hereinafter, within the coverage of the target base station, the
handover process of the mobile station from the base station to the
relay station is similar to the handover process within the same
base station as described above. Combining the cross-base station
preparation step of the mobile station and the step of handover
within the same base station, the cross-base station handover from
the current base station to the target base station can be
implemented.
[0060] With a purpose of better illustration of the mobile station
cross-base station process, FIG. 9 shows in detail the handover
process from a relay station within the coverage of current base
station to the target base station according to an embodiment of
the present invention. Before the handover, the mobile station is
located within the coverage of a relay station of the current base
station, and all the message communication except the downlink
control message is forwarded by the relay station. Thus, in the
handover preparation period, all handover message communication
such as Mobile Handover Request (MOB_HO_REQ) and Mobile Handover
Instruction (MOB_HO_IND) is firstly received by the relay station
and then forwarded to the current base station through the reserved
relay zone. And all the downlink control signals directly arrive at
the mobile station. In the following process, the mobile station
performs CDMA ranging and is associated with the target base
station, and the process is completely identical to a standard
process. Thus the description thereof is omitted. FIG. 10 shows in
detail the cross-base station handover process from a current base
station to a relay station within coverage of a target base
station. What's different is that during the handover preparation
period, the mobile station transmits some handover preparation
messages to the current base station, which ignores the existence
of the relay station. The real handover starts with the re-ranging
of the target base station, and meanwhile the relay station starts
to participate in the handover. Besides, in the network entry and
initialization, the relay station plays a similar role as in the
handover process within the same base station. Through comparing
the measure results, the target base station determines whether to
use relay and returns the ranging response message to the mobile
station so as to adjust the power level and time offset. Further,
another scenario is a handover from a relay station to another
relay station within coverage of an neighboring base station, which
is a combination of the above two scenarios, thus further
description thereof is omitted.
[0061] In addition, in an embodiment, the mobile station cross-base
station handover preparation step may further comprise: at least
one base station providing signal strength information of a relay
station within its own coverage to the current base station; the
current base station determining a target base station based on the
information provided by the mobile station and the relay station
information provided by at least one base station.
[0062] III. Mobility of a Relay Station
[0063] FIG. 11 shows a networking state of a relay station
cross-base station handover in a wireless access system according
to a preferred embodiment of the present invention, wherein the
relay station 120 moves from position A to position B, which
requires processing handover of the relay station from the base
station 130 and the base station 131, vice versa.
[0064] A mobile relay station can get support from the standard
IEEE802.16j. Thus, the mobility of a relay station and its
influence on the mobile station service needs to be considered. In
roaming, a relay station has the same process as a mobile station,
except that the base station allocates a special identifier CID for
identifying the relay station and the target base station also
identifies the relay station through the CID.
[0065] As to a mobile station within the coverage of a relay
station, there have the following cases: the mobile station within
the coverage of the relay station moves with the relay station; the
mobile station does not move with the relay station; and with the
moving of the relay station, some new mobile stations may enter the
coverage of the relay station.
[0066] As to the mobile station moving with the relay station, the
mobile station handover shall be considered as well as the relay
station handover. Thus, in this case, all mobile stations are
required to follow the cross-base station handover process, and
such process is implemented after the relay station handover. When
the relay station handover is completed, all mobile stations within
the relay station coverage will perform cross-base station handover
process and manage to be synchronized with the relay station. The
handover may result in delay of some services. At this point, we
see that the relay station and all mobile stations follow the
standard handover process. The base station and the relay station
do not require additional functionality. To save time, some
functionalities of mobile station handover are simplified or
ignored. For example, since the relay station-mobile station
channel condition is unchangeable, re-ranging may be set as
optional. Before the relay station completes its handover, the
mobile station is configured to start handover process so as to
save time. In other words, the relay station handover process and
the mobile station handover process overlap partially in some
cases. To save time, some mobile stations are configured to
implement the cross-base station handover process
simultaneously.
[0067] The present invention realizes handover functionality in a
mobile multi-hop wireless relay system, comprising moving and
handover of a mobile station between relay stations, or moving and
handover of mobile station between a base station and a relay
station, or moving and handover of a relay station between base
stations. The centralization resource allocation and control
solution enables the base station to allocate resources to a mobile
station and a relay station within the coverage and to completely
control the handover process, wherein the selection and
determination of a relay station is determined under the control of
the base station. The handover control method of the present
invention has no relationship with the frame structure definition,
which is adapted to different relay frame structure definitions,
comprising a corresponding throughput enhancement relay frame
structure and coverage extension relay frame structure. The
throughput enhancement relay is defined as: a mobile station is
located within coverage of a base station, the downlink control
message of the base station may arrive directly at the mobile
station without passing through a relay station, and the main
function of the relay station is to enhance the throughput of the
mobile station. The coverage extension relay is defined as: a
mobile station is located beyond coverage of a base station, the
downlink control message of the base station can not arrive
directly at the mobile station, all message interaction (including
bearer data and control message) between the mobile station and the
base station must be relayed by a relay station, and the main
function of the relay station is to enhance base station
coverage.
[0068] Based on what is described above, to implement the above
method for control wireless access, the present invention provides
a relay station 120 as shown in FIG. 12, comprising: relay control
means 1205 for controlling operation of a relay station; relay
receiving means 1201 for receiving mobile station and base station
message via a wireless channel; relay sending means 1204 for
sending message to the mobile station and the base station via the
wireless channel; measure means 1203 for measuring signal strength
of message sent from the mobile station and ranging the mobile
station; relay arbitration means 1202 for analyzing and arbitrating
signal strength of the message sent by the mobile station. If the
message signal is strong, the relay station forwards the message or
sends a measure report to the base station; if the message signal
is weak, the relay station ignores the message sent by the mobile
station. Under the control of the relay control means, the relay
receiving means receives the message, the relay measure means
measures signal strength of the message, the relay arbitration
means analyzes and arbitrates the signal measure result and then
determines whether to forward the message by the relay sending
means, and the relay receiving means receives the special
connection identifier sent from the base station. The relay station
and the wireless channel uses an Orthogonal frequency-division
multiplexing (OFDM) frame structure including an uplink frame where
a dedicated control information relay zone is provided.
[0069] Further, to achieve the object of the present invention,
there is also provided an improved base station 130, as shown in
FIG. 13, comprising: a base station control means 1305 for
controlling operation of a base station; a base station receiving
means 1301 for receiving message from the mobile station and the
relay station via a wireless channel; a base station sending means
1304 for sending message to the mobile station and the relay
station via the wireless channel; a base station measure means 1306
for measuring signal strength of the message sent by the mobile
station; a base station arbitration means 1303 for comparing signal
strength measured by the relay station and the signal strength of
the message sent by the mobile station measured by the base station
measure means 1306, so as to arbitrate whether relay handover is
required; a base station control means 1305 instructes the base
station sending means 1304 to return a ranging response message
back to the mobile station, the ranging response message comprising
radio frequency power level and synchronization offset correction
adjusted based on the relay station signal measure information.
Under the control of the base station control means, the message
received by the base station receiving means is sent to the base
station measure means to measure. Through the analysis and
arbitration by the base station arbitration means, the base station
sending means sends message to the relay station and the mobile
station, and the base station sending means sends a special
connection identifier to the relay station. The relay station and
the wireless channel uses an Orthogonal Frequency-Division
Multiplexing (OFDM) frame structure including an uplink frame where
a dedicated control information relay zone is provided.
[0070] Although the embodiments of the present invention have been
described with reference to the drawings, various variations or
modifications can be made by those skilled in the art within the
scope of the accompanying claims.
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