U.S. patent application number 11/773281 was filed with the patent office on 2007-12-06 for system and method for performing soft handover in broadband wireless access communication system.
This patent application is currently assigned to SAMSUNG ELECTRONICS CO., LTD.. Invention is credited to Hong-Sung Chang, Yong Chang, Jung-Won Kim, Geun-Hwi Lim, Jae-Jeong Shim.
Application Number | 20070281702 11/773281 |
Document ID | / |
Family ID | 36647700 |
Filed Date | 2007-12-06 |
United States Patent
Application |
20070281702 |
Kind Code |
A1 |
Lim; Geun-Hwi ; et
al. |
December 6, 2007 |
SYSTEM AND METHOD FOR PERFORMING SOFT HANDOVER IN BROADBAND
WIRELESS ACCESS COMMUNICATION SYSTEM
Abstract
Disclosed is a system and method for performing soft handover in
a broadband wireless access communication system. An anchor base
station transmits first information including channel assignment
information of an active non-anchor base station when it is
determined that a mobile station is to perform the soft handover,
and when there are signals to be transmitted to the mobile station
from the non-anchor base station, the non-anchor base station
transmits second information including channel assignment
information of the anchor base station when it is determined that
the mobile station is to perform the soft handover, and when there
are signals to be transmitted to the mobile station from the anchor
base station, and the mobile station receives signals from the
anchor base station and the non-anchor base station corresponding
to the first information and the second information when it is
determined that the mobile station is to perform the soft
handover.
Inventors: |
Lim; Geun-Hwi; (Seongnam-si,
KR) ; Shim; Jae-Jeong; (Seoul, KR) ; Chang;
Hong-Sung; (Suwon-si, KR) ; Chang; Yong;
(Seongnam-si, KR) ; Kim; Jung-Won; (Seoul,
KR) |
Correspondence
Address: |
THE FARRELL LAW FIRM, P.C.
333 EARLE OVINGTON BOULEVARD
SUITE 701
UNIONDALE
NY
11553
US
|
Assignee: |
SAMSUNG ELECTRONICS CO.,
LTD.
Suwon-si
KR
|
Family ID: |
36647700 |
Appl. No.: |
11/773281 |
Filed: |
July 3, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11166012 |
Jun 24, 2005 |
|
|
|
11773281 |
Jul 3, 2007 |
|
|
|
Current U.S.
Class: |
455/442 |
Current CPC
Class: |
H04W 36/08 20130101;
H04W 48/16 20130101; H04W 36/18 20130101 |
Class at
Publication: |
455/442 |
International
Class: |
H04Q 7/20 20060101
H04Q007/20 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 25, 2004 |
KR |
2004-48566 |
Claims
1. A method for performing a soft handover in a broadband wireless
access communication system which includes a mobile station, an
anchor base station providing communication services to the mobile
station, and an active non-anchor base station different from the
anchor base station, the soft handover of the mobile station
scheduled to be performed toward the active non-anchor base
station, the method comprising the steps of: receiving a first MAP
information which is in the DL-MAP of active non-anchor base
station and indicates at least one burst from anchor base station
or receiving a second MAP information which is in the DL-MAP of the
anchor base station and indicates at least one burst from active
non-anchor base station considering downlink channel state.
2. The method as claimed in claim 1, wherein the first MAP
information includes reference signal information and a connection
identifier in the anchor base station, the reference signal
information indicating a reference signal of the anchor base
station.
3. The method as claimed in claim 1, wherein the second MAP
information includes reference signal information and a connection
identifier in the anchor base station, the reference signal
information indicating a reference signal of the active non-anchor
base station.
Description
PRIORITY
[0001] This application is a continuation of application Ser. No.
11/166,012 filed on Jun. 24, 2005, and claims priority under 35
U.S.C. .sctn.119 to an application entitled "System and Method for
Performing Soft Handover in Broadband Wireless Access Communication
System" filed in the Korean Intellectual Property Office on Jun.
25, 2004 and assigned Serial No. 2004-48566, the contents of which
are incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a broadband wireless access
(BWA) communication system, and more particularly to a system and a
method for performing a soft handover.
[0004] 2. Description of the Related Art
[0005] In the 4.sup.th generation (4G) communication system, which
is the next generation communication system, extensive research is
being conducted to provide users with services having various
Qualities-of-Service (QoSs) at high speeds. In the current 4G
communication system, extensive research is being conducted to
develop a new type of communication system ensuring the mobility of
a mobile station (MS) and a QoS in a BWA communication system such
as a wireless Local Area Network (LAN) system and a wireless
Metropolitan Area Network (MAN) system capable of supporting
relatively high transmission speeds. Representatives of such
communication systems are the Institute of Electrical and
Electronics Engineers (IEEE) 802.16a communication system and he
IEEE 802.16e communication system.
[0006] The IEEE 802.16a/d-based communication system and the IEEE
802.16e-based communication system use an orthogonal frequency
division multiplexing (OFDM)/orthogonal frequency division multiple
access (OFDMA) scheme for a physical channel of the WMAN system in
order to support a broadband transmission network. The IEEE 802.16a
communication system is a single structure system that does not
reflect the mobility of a Subscriber Station (SS) at all, in which
the SS is in a stationary state. In contrast, the IEEE
802.16e-based communication system is a system realized by
supplementing the IEEE 802.16a-based communication system with the
ability to handle the mobility of an SS. Hereinafter, a mobile SS
will be referred to as a MS. Accordingly, in the IEEE 802.16e-based
communication system, the study of handover according to the
mobility of the MS is being activated.
[0007] Handover refers to an operation enabling smooth provision of
services to an MS which is moving between base stations (BSs). Such
handover may have two schemes (a hard handover scheme and a soft
handover scheme). The hard handover scheme and the soft handover
scheme will be described.
[0008] The hard handover scheme denotes a scheme through which,
when an MS moves between base stations, the MS releases a channel
setup with an anchor base station (a serving base station currently
providing a service to the MS) and sets up a channel with an active
non-anchor base station (a target base station) in the shortest
period of time, so that the service may be continuously provided.
The serving base and the target base station will be referred to as
an anchor base station and an active non-anchor base station,
respectively, for the purpose of description. The hard handover
causes a ping-pong phenomenon of continuously alternating channel
release and setup when channel states are continuously inferior,
for example, when the MS moves across a cell boundary region.
[0009] The soft handover scheme denotes a scheme through which,
when an MS moves between base stations, the MS has channels set up
with both an anchor base station and an active non-anchor base
station, is relocated in the non-anchor base station while
simultaneously receiving signals from both the anchor base station
and the non-anchor base station through the setup channel, and then
releases the channel from the anchor base station, so that the
service is continuously provided. Accordingly, when the MS performs
a handover operation through the soft handover scheme, the MS
receives downlink signals from a plurality of base stations (i.e.
the anchor base station and the non-anchor base station) and
improves quality of the received downlink signals by combining the
downlink signals received from the base stations.
[0010] The signal combining scheme may be classified into a soft
combining scheme and a selection diversity scheme.
[0011] The soft combining scheme is a scheme of demodulating each
of the signals received from a plurality of base stations and
combining the signals in a front end of a channel decoder. The
selection diversity scheme is a scheme of de-modulating and
channel-decoding each of the signals received from a plurality of
base stations and then selecting a signal with the best quality
from among the channel-decoded signals.
[0012] The MS performing a handover operation through the soft
handover scheme may obtain a soft combining gain by simultaneously
receiving signals through channels set up with both the anchor base
station and the non-anchor base station. In order to obtain the
combining gain, the MS must receive information regarding channels
(channel allocation information) set up with both the anchor base
station and the non-anchor base station and receive signals from
the anchor base station and the non-anchor base station using the
channel allocation information.
[0013] However, in the typical broadband wireless access system
(e.g., the IEEE 802.16e-based communication system), it is
difficult for the MS to receive channel allocation information of
an active non-anchor base station because an anchor base station
reports only information regarding a channel allocated by the
anchor base station.
SUMMARY OF THE INVENTION
[0014] Accordingly, the present invention has been made to solve at
least the above-mentioned problems occurring in the prior art, and
an object of the present invention is to provide a system and a
method for performing a soft handover in a broadband wireless
access communication system.
[0015] Another object of the present invention is to provide a
system and a method for providing channel allocation information
used for performing a soft handover in a broadband wireless access
communication system.
[0016] Still another object of the present invention is to provide
a system and a method in which an anchor base station informs a
mobile station of channel allocation information of an active
non-anchor base station in a broadband wireless access
communication system.
[0017] Yet another object of the present invention is to provide a
system and a method in which an active non-anchor base station
informs a mobile station of channel allocation information of an
anchor base station in a broadband wireless access communication
system.
[0018] To accomplish the above objects, there is provided a method
for performing a soft handover in a broadband wireless access
communication system which includes a mobile station, an anchor
base station providing communication services to the mobile
station, and an active non-anchor base station different from the
anchor base station, the soft handover of the MS scheduled to be
performed toward the active non-anchor base station. The method
comprises the steps of: receiving first information from the anchor
base station or receiving second information considering channel
state from the active non-anchor base station when it is determined
that the mobile station is to perform the soft handover, the first
information including channel assignment information of the active
non-anchor base station, the second information including channel
assignment information of the anchor base station; and receiving
signals from the anchor base station or the active non-anchor base
station corresponding to the first information and the second
information.
[0019] According to another aspect of the present invention, there
is provided a method for performing a soft handover in a broadband
wireless access communication system which includes a mobile
station, an anchor base station providing communication services to
the mobile station, and an active non-anchor base station different
from the anchor base station, the soft handover of the MS scheduled
to be performed toward the active non-anchor base station. The
method comprises the steps of: determining if there are signals to
be transmitted to the mobile station from the active non-anchor
base station when it is determined that the mobile station is to
perform a soft handover; and transmitting information including
channel assignment information of the active non-anchor base
station when it is determined that there are signals to be
transmitted to the mobile station from the active non-anchor base
station.
[0020] According to still another aspect of the present invention,
there is provided a method for performing a soft handover in a
broadband wireless access communication system which includes a
mobile station, an anchor base station providing communication
services to the mobile station, and an active non-anchor base
station different from the anchor base station, the soft handover
of the MS scheduled to be performed toward the active non-anchor
base station. The method comprises the steps of: determining if
there are signals to be transmitted to the mobile station from the
anchor base station when it is determined that the mobile station
is to perform a soft handover; and transmitting first information
including channel assignment information of the anchor base station
when it is determined that there are signals to be transmitted to
the mobile station from the anchor base station.
[0021] According to still yet another aspect of the present
invention, there is provided a method for performing a soft
handover in a broadband wireless access communication system which
includes a mobile station, an anchor base station providing
communication services to the mobile station, and an active
non-anchor base station different from the anchor base station, the
soft handover of the MS scheduled to be performed toward the active
non-anchor base station. The method comprises the steps of:
transmitting by the anchor base station first information including
channel assignment information of the active non-anchor base
station when it is determined that the mobile station is to perform
the soft handover, and when there are signals to be transmitted to
the mobile station from the active non-anchor base station;
transmitting by the active non-anchor base station second
information including channel assignment information of the anchor
base station when it is determined that the mobile station is to
perform the soft handover, and when there are signals to be
transmitted to the mobile station from the anchor base station; and
receiving by the mobile station signals from the anchor base
station and the active non-anchor base station corresponding to the
first information and the second information when it is determined
that the mobile station is to perform a soft handover.
[0022] According to still yet another aspect of the present
invention, there is provided a system for performing a soft
handover in a broadband wireless access communication system. The
system comprises an anchor base station for transmitting first
information including channel assignment information of an active
non-anchor base station when it is determined that a mobile station
is to perform a soft handover, and when there are signals to be
transmitted to the mobile station from the active non-anchor base
station; an active non-anchor base station for transmitting second
information including channel assignment information of the anchor
base station when it is determined that the mobile station is to
perform a soft handover, and when there are signals to be
transmitted to the mobile station from the anchor base station; and
a mobile station for receiving signals from the anchor base station
and the active non-anchor base station corresponding to the first
information and the second information when it is determined that
the mobile station is to perform the soft handover.
[0023] According to still yet another aspect of the present
invention, there is provided a method for performing a soft
handover in a broadband wireless access communication system which
includes a mobile station, an anchor base station providing
communication services to the mobile station, and an active
non-anchor base station different from the anchor base station, the
soft handover of the MS scheduled to be performed toward the active
non-anchor base station. The method comprises the steps of
receiving a first MAP information which is in the DL-MAP of active
non-anchor base station and indicates at least one burst from
anchor base station or receiving a second MAP information which is
in the DL-MAP of the anchor base station and indicates at least one
burst from active non-anchor base station considering downlink
channel state.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] The above and other objects, features and advantages of the
present invention will be more apparent from the following detailed
description taken in conjunction with the accompanying drawings, in
which:
[0025] FIG. 1 is a block diagram illustrating the structure of an
IEEE 802.16e-based communication system according to an embodiment
of the present invention;
[0026] FIG. 2 is a block diagram illustrating the sector structure
in an IEEE 802.16e-based communication system according to an
embodiment of the present invention;
[0027] FIG. 3 is a block diagram illustrating the frame structure
in an IEEE 802.16e-based communication system according to an
embodiment of the present invention;
[0028] FIG. 4 illustrates the format of a DL-MAP message according
to an embodiment of the present invention;
[0029] FIG. 5 illustrates the format of a UL-MAP message according
to an embodiment of the present invention;
[0030] FIG. 6 illustrates the format of an HO Anchor Active DL MAP
IE according to an embodiment of the present invention;
[0031] FIG. 7 illustrates the format of an HO DL MAP IE in
non-anchor BS according to an embodiment of the present
invention;
[0032] FIG. 8 illustrates the format of an HO CID Translation MAP
IE according to an embodiment of the present invention;
[0033] FIG. 9 illustrates the format of an HO Anchor Active UL MAP
IE according to an embodiment of the present invention;
[0034] FIG. 10 illustrates the format of an HO UL MAP IE in
non-anchor BS according to embodiment of the present invention;
[0035] FIG. 11 is a flowchart illustrating the operation of an MS
performing soft handover by receiving channel assignment
information from an anchor base station according to an embodiment
of the present invention; and
[0036] FIG. 12 is a flowchart illustrating the operation of an MS
performing soft handover by receiving channel assignment
information from an active non-anchor base station according to an
embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0037] Hereinafter, a preferred embodiment of the present invention
will be described in detail with reference to the accompanying
drawings. Note that the same or similar components in drawings are
designated by the same reference numerals as far as possible
although they are shown in different drawings. In the following
description of the present invention, a detailed description of
known functions and configurations incorporated herein will be
omitted when it may make the subject matter of the present
invention rather unclear.
[0038] The present invention proposes a system and a method for
performing a soft handover in a broadband wireless access
communication system (BWA) (e.g., an Institute of Electrical and
Electronics Engineers (IEEE) 802.16e-based communication system).
Particularly, the present invention proposes a system and a method
in which an anchor base station (a serving base station) and an
active non-anchor base station (a target base station) provide
channel allocation information in order to perform a soft handover
in the IEEE 802.16e-based communication system. Hereinafter, the
serving base station and the target base station will be referred
to as an anchor base station and an active non-anchor base station,
respectively. According to the present invention, although the IEEE
802.16e-based communication system is described by way of example
for the purpose of description, it is natural that other
communication systems as well as the IEEE 802.16e-based
communication system can be employed.
[0039] FIG. 1 is a block diagram illustrating a structure of an
IEEE 802.16e-based communication system according to an embodiment
of the present invention.
[0040] The IEEE 802.16e-based communication system having a
multi-cell structure includes a cell 100, a cell 150, a base
station 110 controlling the cell 100, a base station 140
controlling the cell 150, and a plurality of MSs 111, 113, 130,
151, and 153. Although one base station may control several cells,
it is assumed that one base station controls only one cell for the
purpose of description in the embodiment of the present invention.
In addition, the base stations 110 and 140 transmit/receive signals
to/from the MSs 111, 113, 130, 151, and 153 using the OFDM/OFDMA
scheme. Herein, it is assumed that the base stations 110 and 140
have a multi-sector structure, sectors in the same cell use the
same center-frequency, and adjacent sectors are assigned different
sub-channels.
[0041] The above description deals with the structure of the IEEE
802.16e-based communication system according to an embodiment of
the present invention with reference to FIG. 1, and, hereinafter, a
sector structure in the IEEE 802.16e-based communication system
according to an embodiment of the present invention will be
described with reference to FIG. 2.
[0042] FIG. 2 is a block diagram illustrating the sector structure
in the IEEE 802.16e-based communication system according to an
embodiment of the present invention.
[0043] A cell controlled by a base station is divided into several
sectors (e.g., three sectors; a first sector 210, a second sector
220, and a third sector 230). Each of the first sector 210 to the
third sector 230 employs the same center-frequency of F1, and
different sub-channels are used between them. In other words, the
first sector 210 to the third sector 230 use mutually-different
sub-channel sets as shown in FIG. 2. The first sector 210, the
second sector 220, and the third sector 230 use the first
sub-channel set, the second sub-channel set, and the third
sub-channel set, respectively.
[0044] The above description deals with the sector structure in the
IEEE 802.16e-based communication system according to an embodiment
of the present invention with reference to FIG. 2, and,
hereinafter, a frame structure in the IEEE 802.16e-based
communication system according to an embodiment of the present
invention will be described with reference to FIG. 3.
[0045] FIG. 3 is a block diagram illustrating the frame structure
in the IEEE 802.16e-based communication system according to an
embodiment of the present invention.
[0046] The frame structure in the IEEE 802.16e-based communication
system includes a downlink (DL) frame 310 and an uplink (UL) frame
320. The DL frame 310 includes a preamble field 312, a
DL-MAP/UL-MAP field 314, a PUSC (partial usage of sub-channels)
field 316, and an FUSC (full usage of sub-channels) field 318. The
UL frame 320 includes a PUSC field 322.
[0047] The preamble field 312 is a field used for transmitting a
preamble sequence for synchronization between a base station and an
MS. The DL-MAP/UL-MAP field 314 is a field used for transmitting a
DL-MAP message and an UL-MAP message. The base station transmits
the MAP message indicating a channel interval allocated to each MS
before the channel interval, and the MS detects information
included in the MAP message so as to recognize the channel interval
and a coding scheme. Detailed descriptions of the DL-MAP message
and the UL-MAP message will be given later. The PUSC field 316 is a
field used for transmitting DL data burst through a PUSC scheme,
and the FUSC field 318 is a field used for transmitting DL data
burst through an FUSC scheme. In addition, the PUSC field 322 is a
field used for transmitting UL data burst using a PUSC scheme.
[0048] FIG. 4 illustrates the format of the DL-MAP message
according to an embodiment of the present invention.
[0049] The DL-MAP message includes various information elements
(IEs), i.e., `Management Message Type` representing a type of a
transmitted message, `Physical (PHY) Synchronization` set
corresponding to a modulation scheme or a de-modulation scheme
applied to a physical channel in order to acquire synchronization,
`DCD count` representing a count value corresponding to the
configuration change of a downlink channel descriptor message
including downlink burst profile, `Base Station ID` representing a
base station identifier, and n number of DL-MAP IEs. The DL-MAP
message includes information of raging codes assigned for
raging.
[0050] FIG. 5 illustrates the form of the UL-MAP message according
to an embodiment of the present invention.
[0051] The UL-MAP message includes various IEs, i.e. `Management
Message Type` representing a type of a transmitted message, `Uplink
Channel ID` representing a used uplink channel identifier, `UCD
count` representing a count value corresponding to the
configuration change of an uplink channel descript message
including uplink burst profile, `Allocation Start Time`
representing information regarding start time to allocate uplink
resources, and n number of UL-MAP IEs. The Uplink Channel ID is
assigned as a unique value in a Medium Access Control (MAC)-sub
layer.
[0052] A data burst field of the DL-frame 310 shown in FIG. 3
includes time slots assigned according to MSs through a Time
Division Multiplexing (TDM)/Time Division Multiple Access (TDMA)
scheme. A base station broadcasts control information to MSs
(receiving services from the base station) through the
DL-MAP/UP-MAP field 314 by using a preset center-frequency.
[0053] As each of the MSs is powered on, each MS detects a
reference signal having the maximum size (e.g., the maximum Carrier
to Interference and Noise Ratio (CINR)) by monitoring all of the
frequency bands preset in each MS. Herein, the reference signal may
include a pilot signal. Each MS determines a base station having
transmitted the reference signal having the highest CINR as a base
station controlling the MS, analyzes a DL-MAP message and an UL-MAP
message in the DL-MAP/UL-MAP field 314 of the DL frame 310
transmitted from the base station so as to determine channel
allocation information indicating the interval at which real data
burst and control information controlling the DL and the UL of the
MS are transmitted/received, and transmits/receives data burst at
the corresponding data burst transmit/receive interval.
[0054] An IEEE 802.16e communication system in which one base
station uses one center frequency and a plurality of sectors within
the base station use as many sub-bands as the sectors divided from
a frequency band corresponding to the center frequency will now be
described. In such an IEEE 802.16e communication system, when an MS
moves from a current anchor base station to another base station
(an active non-anchor base station), or the MS moves from an anchor
sector (a serving sector) to another sector (an active non-anchor
sector; a target sector) within the same anchor base station, the
MS must perform a handover. In particular, according to an
embodiment of the present invention, the MS must perform a soft
handover. In order to perform the soft handover described above, an
MS must obtain channel allocation information of both an anchor
base station (an anchor sector in the case of handover between
sectors) and an active non-anchor base station (an active
non-anchor sector in the case of handover between sectors). Herein,
the channel allocation information is included in MAP messages
transmitted to the MS (requesting soft handover) from the anchor
base station or the non-anchor base station. In other words, all of
the base stations of the IEEE 802.16e communication system
broadcast channel allocation information of their neighboring base
stations through the MAP messages.
[0055] In the conventional IEEE 802.16e communication system, an
anchor base station inserts the MAP IEs (including channel
allocation information for data burst to be transmitted/received
to/from an MS) into a MAP message to be transmitted, and the MS
transmits/receives data burst through a UL/DL corresponding to the
channel allocation information included in the MAP IEs. However,
according to an embodiment of the present invention, the MS must
receive channel allocation information from the anchor base station
and the non-anchor base station so that the MS may simultaneously
transmit/receive the same data burst from both the anchor base
station and the non-anchor base station in an MS handover area. In
particular, according to an embodiment of the present invention, it
is possible to obtain a soft combining gain by decoding and
buffering data burst from the anchor base station and the
non-anchor base station having the same data burst without taking
into consideration a soft combining scheme employing the same
permutation, the same symbol, and the same sub-channel in a
physical layer.
[0056] Hereinafter, further description about the MAP IEs for the
soft handover newly proposed in the present invention will be
given.
[0057] In the conventional IEEE 802.16e communication system, it is
impossible for an MS to simultaneously receive the MAP IEs from two
or more base stations. Accordingly, in an IEEE 802.16e
communication system according to an embodiment of the present
invention, an anchor base station and an active non-anchor base
station insert the MAP IEs including channel allocation information
of both the anchor base station and the non-anchor base station for
the MS into their own MAP messages. Then, the MS receives the MAP
IEs from one of the anchor base station and the non-anchor base
station, obtains channel information regarding both the anchor base
station and the non-anchor base station from the MAP IEs, and
transmits/receives data burst from/to the anchor base station and
the non-anchor base station corresponding to the obtained channel
information. Hereinafter, a detailed description about the MAP IEs
proposed in the present invention will be given.
[0058] (1) A Handover Anchor Active MAP IE (`HO Anchor Active MAP
IE`).
[0059] The HO Anchor Active MAP IE is a MAP IE transmitted from an
active non-anchor base station that includes channel allocation
information of a DL or a UL of an anchor base station and indicates
that there is data burst transmitted from an anchor base station.
The HO Anchor Active MAP IE including the channel assignment
information of the DL of the anchor base station corresponds to a
HO Anchor Active DL MAP IE, and the HO Anchor Active MAP IE
including the channel assignment information of the UL of the
anchor base station corresponds to a HO Anchor Active UL MAP
IE.
[0060] (2) A Handover MAP IE in a non-anchor base station (`HO MAP
IE in non-anchor BS`).
[0061] The HO MAP IE in non-anchor BS is a MAP IE transmitted from
an anchor base station that includes the channel allocation
information of a DL or a UL of an active non-anchor base station
and indicates that there is data burst transmitted from the
non-anchor base station. The HO MAP IE in non-anchor BS including
the channel assignment information of the DL of the non-anchor base
station corresponds to `HO DL MAP IE in non-anchor BS`, and the HO
MAP IE in non-anchor BS including the channel assignment
information of the UL of the non-anchor base station corresponds to
`HO UL MAP IE in non-anchor BS`.
[0062] (3) A Handover Connection Identifier Translation MAP IE (`HO
CID Translation MAP IE`)
[0063] The HO CID Translation MAP IE is a MAP IE transmitted from
an active non-anchor base station and is transmitted in order to
map a CID of a MS allocated by an anchor base station with a CID of
the MS allocated by an active non-anchor base station. In addition,
the HO CID Translation MAP IE represents that there is data burst
transmitted from the non-anchor base station.
[0064] FIG. 6 illustrates the format of the HO Anchor Active DL MAP
IE according to an embodiment of the present invention.
[0065] The HO Anchor Active DL MAP IE includes `Extended DIUC`
(Downlink Interval Usage Code) field used for distinguishing a
plurality of IEs (i.e., the HO Anchor Active DL MAP IE), `Length`
indicating the length of the HO Anchor Active DL MAP IE, and IEs
for each data burst. As shown in FIG. 6, the IEs for each data
burst include `Anchor Preamble` representing a preamble of the
anchor base station, `Anchor CID` representing a basic CID assigned
to a corresponding MS in the anchor base station, `DIUC`, `OFDMA
Symbol offset` indicating a starting point of a symbol representing
assigned data burst, `Subchannel offset` indicating a starting
point of a sub-channel representing assigned data burst, `Boosting`
representing if transmission power of a sub-carrier for the
assigned data burst is boosted, `No. OFDMA Symbol` representing the
number of symbols of the assigned data burst, `No. Subchannels`
representing the number of sub-channels of the assigned data burst,
and `Repetition Coding Indication` representing a repetition code
used for the assigned data burst.
[0066] FIG. 7 illustrates the format of the HO DL MAP IE in
non-anchor BS according to an embodiment of the present
invention.
[0067] The HO DL MAP IE in non-anchor BS includes `Extended DIUC
(Downlink Interval Usage Code)` used for distinguishing a plurality
of the IEs (i.e., the HO DL MAP IE in non-anchor BS), `Length`
indicating the length of the HO DL MAP IE in non-anchor BS, and IEs
for each data burst. As shown in FIG. 7, the IEs for each data
burst include `Non-Anchor Preamble` representing a preamble of the
active non-anchor base station, `Anchor CID` representing a basic
CID assigned to a corresponding MS in the anchor base station,
`DIUC`, `OFDMA Symbol offset` indicating a starting point of a
symbol representing assigned data burst, `Subchannel offset`
indicating a starting point of a sub-channel used for the assigned
data burst, `Boosting` representing if transmission power of a
sub-carrier for the assigned data burst is boosted, `No. OFDMA
Symbol` representing the number of symbols of the assigned data
burst, `No. Subchannels` representing the number of sub-channels of
the assigned data burst, and `Repetition Coding Indication`
representing a repetition code used for the assigned data
burst.
[0068] FIG. 8 illustrates a format of the HO CID Translation MAP IE
according to an embodiment of the present invention.
[0069] The HO CID Translation MAP IE includes `Extended DIUC
(Downlink Interval Usage Code)` used for distinguishing a plurality
of the IEs (i.e., the HO CID Translation MAP IE), `Length`
indicating the length of the HO CID Translation MAP IE, and IEs for
each data burst. As shown in FIG. 8, the IEs for each data burst
include `Anchor Preamble` representing a preamble of the anchor
base station, `Anchor CID` representing a basic CID assigned to a
corresponding MS in the anchor base station, and `Non-Anchor CID`
representing a basic CID temporally used to represent the channel
assignment information for the data burst to be transmitted to a
corresponding MS in a DL or a UL of the active non-anchor base
station.
[0070] In other words, in an active non-anchor base station, an MS
that is performing a soft handover confirms the HO CID Translation
MAP IE, recognizes the preamble of an anchor base station and
`Non-Anchor CID` mapped with `Anchor CID`, and receives data burst
transmitted from the active non-anchor base station using the
Non-anchor CID assigned to the MS. It is necessary to insert the
Anchor Preamble into the HO CID Translation MAP IE because the MSs
performing soft handover in the active non-anchor base station may
have different anchor base stations. In addition, the anchor base
stations may have the same Anchor CIDs. In this case, the Anchor
Preamble may be used to distinguish the MSs connected to different
anchor base stations. In addition, the MS performing a soft
handover must decode the HO CID Translation MAP IE in every frame
in order to transmit/receive data burst to/from the active
non-anchor base station because the Non-Anchor CID of the active
non-anchor base station may be changed in every frame.
[0071] FIG. 9 illustrates the format of the HO Anchor Active UL MAP
IE according to an embodiment of the present invention. The HO
Anchor Active UL MAP IE includes `Extended UIUC (Uplink Interval
Usage Code)` used for distinguishing a plurality of the IEs (i.e.,
the HO Anchor Active UL MAP IE), `Length` indicating the length of
the HO Anchor Active UL MAP IE, and IEs for each data burst. As
shown in FIG. 9, the IEs for each data burst include `Anchor
Preamble` representing a preamble of the anchor base station,
`Anchor CID` representing a basic CID assigned to a corresponding
MS in the anchor base station, `UIUC` representing an uplink
interval usage code, `Start Subchannel offset` indicating a
starting point of a sub-channel representing assigned data burst,
`Duration` indicating the amount of resource in OFDMA slot, and
`Repetition Coding Indication` representing a repetition code used
for the assigned data burst.
[0072] FIG. 10 illustrates the format of the HO UL MAP IE in
non-anchor BS according to an embodiment of the present
invention.
[0073] The HO UL MAP IE in non-anchor BS includes `Extended UIUC
used for distinguishing a plurality of the IEs (i.e. the HO UL MAP
IE in non-anchor BS), `Length` indicating the length of the HO UL
MAP IE in non-anchor BS, and IEs for each data burst. As shown in
FIG. 10, the IEs for each data burst include `Non-Anchor Preamble`
representing a preamble of the active non-anchor base station,
`Anchor CID` representing a basic CID assigned to a corresponding
MS in the anchor base station, `UIUC`, `Start Subchannel offset`
indicating a starting point of a sub-channel representing the
assigned data burst, `Duration` indicating the amount of resource
in OFDMA, and `Repetition Coding Indication` representing a
repetition code used for the assigned data burst.
[0074] FIG. 11 is a flowchart illustrating the operation of the MS
performing a soft handover by receiving channel assignment
information from an anchor base station according to an embodiment
of the present invention.
[0075] The MS detects a preamble sequence from the anchor base
station so as to obtain synchronization with the anchor base
station in step 1111. In step 1113, the MS determines if it
necessary to perform a soft handover between an anchor base station
and another base station (i.e. an active non-anchor base station).
If it is not necessary for the MS to perform the soft handover, the
MS performs step 1115, wherein the MS demodulates and decodes
typical MAP messages (MAP messages used for the conventional IEEE
802.16e communication system) so as to detect DL-MAP IEs and UL-MAP
IEs. In step 1117, the MS transmits/receives data burst
corresponding to the DL-MAP IE and the UL-MAP IE detected from the
anchor base station and then terminates the operation of performing
the soft handover.
[0076] If the MS must perform a soft handover as the determination
result in step 1113, the MS performs step 1119, wherein the MS
demodulates and decodes MAP messages so as to detect the DL-MAP IE,
the UL-MAP IE, the HO DL MAP IE in non-anchor BS, and the HO UL MAP
IE in non-anchor BS because the MS must perform the soft handover.
In step 1121, the MS detects the Non-Anchor Preamble and the Anchor
CID included in the detected HO DL MAP in non-anchor BS and the
detected HO UL MAP IE in non-anchor BS. It is necessary to detect
the Non-Anchor preamble and the Anchor CID so that the MS may
distinguish data burst transmitted/received from/to the active
non-anchor base station as described above.
[0077] In step 1123, the MS transmits/receives data burst from/to
the anchor base station and the active non-anchor base station
correspondingly to the detected DL-MAP IE, the UL-MAP IE, the HO DL
MAP IE in non-anchor BS, and the HO UL MAP in non-anchor BS and
then terminates the operation of performing the soft handover.
[0078] FIG. 12 is a flowchart illustrating the operation of an MS
performing soft handover by receiving channel assignment
information from an active non-anchor base station according to one
embodiment of the present invention.
[0079] The MS detects a preamble sequence from the active
non-anchor base station so as to obtain synchronization with the
active non-anchor base station in step 1211. The MS determines if a
soft handover operation is currently performed in step 1213. If the
soft handover operation is being performed, the MS demodulates and
decodes MAP messages so as to detect the HO CID Translation MAP IE,
the DL-MAP IE, the UL-MAP IE, the HO Anchor Active DL MAP IE, and
the HO Anchor Active UL MAP IE in step 1215. In step 1217, the MS
detects `Anchor Preamble` and `Anchor CID` included in the HO
Anchor Active DL MAP IE and the HO Anchor Active UL MAP IE. It is
necessary to detect the Anchor preamble and the Anchor CID so that
the MS may distinguish data burst transmitted/received from/to the
anchor base station as described above. However, if the active
non-anchor base station uses a CID identical to the Anchor CID used
in the anchor base station, it is impossible for the MS to
transmit/receive data burst from/to the anchor base station because
CIDs are intrinsically assigned according to base stations.
[0080] Accordingly, in step 1219, the MS detects the Non-Anchor CID
based on the detected HO CID Translation MAP IE. As a result, the
MS detects the Non-Anchor CID from the anchor base station, so that
the MS can transmit/receive data burst having Anchor CID
corresponding to the Non-Anchor CID. In step 1221, the MS
transmits/receives data burst from/to both the anchor base station
and the active non-anchor base station correspondingly to the
detected HO CID Translation MAP IE, the DL-MAP IE, the UL-MAP IE,
the HO Anchor Active DL MAP IE, and the HO Anchor Active UL MAP IE,
and then terminates the operation of performing soft handover.
[0081] As described above, according to the present invention, new
MAP IEs are embodied in the IEEE 802.16e-based communication
system, thereby enabling soft handover of the MS. As a result, the
soft handover of the MS improves signal receiving quality of the MS
and removes the ping-pong phenomenon caused in had handover,
thereby improving the performance of an entire system.
[0082] While the invention has been shown and described with
reference to certain preferred embodiments thereof, it will be
understood by those skilled in the art that various changes in form
and details may be made therein without departing from the spirit
and scope of the invention. Consequently, the scope of the
invention should not be limited to the embodiments, but should be
defined by the appended claims and equivalents thereof.
* * * * *