BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to an Orthogonal Frequency
Division Multiple Access (OFDMA) communication system, and in particular, to
a system and method for managing a band AMC (Adaptive Modulation and
Coding) channel in a communication system using a Time Division Duplex
(TDD)-based OFDMA scheme (hereinafter referred to as a "TDD-OFDMA
communication system").
2. Description of the Related Art
Research into a 4th generation (4G) communication system, which is the
next generation communication system, is currently being conducted to provide
users with differing services having various Qualities of Service (QoSs) and
supporting a data rate of about 100 Mbps. Compared with the 4G communication
system, a 3rd generation (3G) communication system generally supports a data
rate of about 384 Kbps in an outdoor channel environment having poorer channel
conditions, and supports a data rate of a maximum of 2 Mbps in an indoor
channel environment having better channel conditions.
A wireless Local Area Network (LAN) system and a wireless
Metropolitan Area Network (MAN) system generally support a data rate of 20 to
50 Mbps. Currently,, therefore, active research into the 4G communication system
is being carried out to develop a new communication system guaranteeing
mobility and QoS in the wireless LAN system, and in order to develop the
wireless MAN system guaranteeing a higher data rate, in order to support a high-
speed service provided in the 4G communication, system.
Accordingly, a great deal of research is being conducted on an
Orthogonal Frequency Division Multiplexing (OFDM) scheme for high-speed
data transmission through wired/wireless channels in the 4G communication
system. The OFDM scheme is to a scheme of transmitting data using multiple
carriers, and is a kind of a Multi-Carrier Modulation (MCM) scheme, which
parallel-converts a serial input symbol stream into parallel symbols and
modulates the parallel symbols with a plurality of orthogonal subcarriers, i.e.. a

plurality of subcarrier channels, before transmission.
A multiple access scheme based on the OFDM scheme is the OFDMA
scheme. In the OFDMA scheme, subcarriers in one OFDMA symbol are divided
for a plurality of users, i.e., subscriber stations (SSs). Communication systems
using the OFDM/OFDMA scheme include an Institute of Electrical and
Electronics Engineers (IEEE) 802.16a communication system, an IEEE 802.16d
communication system, and an IEEE 802.16e communication system. The IEEE
802.16d communication system is a system to which the OFDMA scheme is
applied to support a broadband transmission network to a physical channel for the
wireless MAN system. Further, the IEEE 802.16d communication system is a
Broadband Wireless Access (BWA) communication system using a TDD-
OFDMA scheme. Therefore, the IEEE 802.16d communication system, in which
the OFDM/OFDMA scheme is applied to the wireless MAN system, transmits a
physical channel signal using a plurality of subcarriers, thereby enabling high-
speed, high-quality data transmission.
FIG. 1 is a diagran schematically illustrating a frame structure used in a
conventional TDD-OFDMA communication system. Referring to FIG. 1, a frame
used in the TDD-OFDMA scheme is divided into a downlink (DL) interval 149
and an uplink (UL) interval 153. A Transmit/receive Transition Gap (TTG) 151 is
formed in an interval where transition occurs from the DL 149 to the UL 153, as a
guard time, and a Receive/transmit Transition Gap (RTG) is formed in an interval
where transition occurs from the UL 153 back to the DL 149, as a guard time. The
TDD-OFDMA frame has a vertical axis including a plurality of subchannels 147
and a horizontal axis including a plurality of OFDMA symbols 145.
Describing the DL 149, a preamble 111 for synchronization acquisition is
located in a kth OFDMA symbol, and broadcast data information that SSs will
receive in common, such as a frame control header (FCH) 113, DL-MAP 115, and
UL-MAP 117, is located in a (K+l)th or (K+2)th OFDMA symbol. The FCH 113
includes two subchannels, and transmits basic information on subchannels, i.e.,
ranging and modulation schemes. DL bursts 121, 123, 125, 127, and 129 are located between the (K+2)th OFMDA symbol exclusive of a UL-MAP 119 and
a (K+8)th OFDMA symbol.
Describing the UL 153, preambles 131. 133. and 135 are located in a
(K+9)lh OFDMA symbol, and UL bursts 137, 139. and 141 are located between a
(K+10)th OFDMA symbol and a (K+12)th OFDMA symbol. In addition, a ranging

subchannel 143 is located between the (K+9)th OFDM A symbol and the (K+12)th
OFDMA symbol.
Information on positions and allocation of the UL bursts 137, 139, and
141 and the DL bursts 121, 123, 125, 127, and 129 is provided from a base station
(BS) controlling a particular cell to SSs, which are located in the cell, through the
DL-MAP 115 and the UL-MAP 117. The SSs are variably allocated subchannels,
each of which a combination of frequencies and symbols, through the information
every frame, and perform communication using the allocated subchannels. That is,
the SSs can use different subchannels every frame, instead of fixed subchannels.
Also, in a neighbor cell, SSs perform communication using the same frequency
band. Therefore, for an SS located in a cell boundary, if different cells use the
same subchannels, the subchannels may significantly interfere with each other.
As described above, the conventional OFDMA communication system
performs data communication with SSs regardless of channel states. That is, a
scheme that enables SSs having good channel states to perform high-speed, high-
capacity communication is not presented in the frame structure for the
conventional OFDMA communication system. Therefore, the conventional
technology cannot perform a flexible modulation and coding method for the SSs
having high subchannel quality.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide a system and
method for performing high-speed, high-capacity communication in a Broadband
Wireless Access communication system.
It is another object of the present invention to provide a band AMC
channel allocation method for providing a high data rate to SSs having low
mobility in a TDD-OFDMA communication system.
It is further another object of the present invention to provide a system
and method for managing band AMC subchannels in a TDD-OFDMA
communication system.
It is yet another object of the present invention to provide a BS and SS
management scheme for enabling high-speed, high-capacity data transmission
through a band AMC channel state report in a TDD-OFDMA communication

system.
It is still another object of the present invention to provide a BS and SS
management scheme for releasing band AMC channels in a TDD-OFDMA
communication system.
It is still another object of the present invention to provide a system and method
for allocating band AMC subchannels such that based on channel states of SSs,
wherein a BS enables SSs having a good channel state to enable high-speed,
high-capacity data transmission, in a TDD-OFDMA communication system.
It is still another object of the present invention to provide a new frame structure
for enabling high-speed, high-capacity data transmission according to channel
states in a TDD-OFDMA communication system.
It is still another object of the present invention to provide a system and method
for enabling high-speed, high-capacity data transmission by applying high-
efficiency modulation and coding schemes to SSs having high channel quality
through band AMC subchannels and their associated messages.
Accordingly, the present invention provides a method for transmitting data
through a channel set up between a subscriber station (SS) and a base station
(BS) in a wireless communication system, the method comprising the steps of
transmitting, by the BS, a channel state request (CH_STA_REQ) message to the
SS for a state report request of the band AMC channel allocated to the SS;
measuring, by the SS, reception quality of each band; generating, by the SS, a
list of bands having high reception quality according to the reception quality
measurements; transmitting, by the SS, a channel state response (CH_STA_RSP)
message including the generated list in response to the CH_ST_REQ message to

the BS; receiving, by the BS, the CH_STA_RSP message; determining, by the BS,
whether the BS can allocate a band AMC channel to the SS in response to the
CH_STA_RSP message; transmitting, by the BS, a band AMC indication
(BAND_AMC_IND) message including information indicating whether the BS
allocates the band AMC channel to the SS; receiving, by the SS, the
BAND_AMC_IND message; and transmitting, by the SS, data to the BS using at
least one of a diversity channel and the band AMC channel according to the
received BAND_AMC_IND message; wherein the CH_STA_RSP message includes
information on at least one band index and a Carrier-to-interference ratio (C/I)
of the band AMC channel corresponding to the at least one band index; wherein
the band AMC channel comprises a plurality of bands, and each band is applied
by a different modulation order and coding rate; wherein the CH_STA_RSP
message comprises a reported channel type field comprising information on a
type of a channel, a state of which the SS will report to the BS, information on a
list of channels, a measured quality of each of which the SS reports to the BS,
and state information of each channel included in the list; and wherein the
information on the type of the channel indicates a channel used when the SS
communicates with the BS, if the channel is the diversity channel the
CH_STA_RSP message comprises information on a Downlink Channel ID of the
diversity channel and a C/I of the diversity channel, if the channel is the band
AMC channel the CH_STA_RSP message comprises information on each Band
Index of the band AMC channel and a C/I of the band AMC channel, the band
AMC channel is allocated based on a band comprising 6 bins, the diversity
channel is allocated based on a subchannel including three tiles spread over the
full subcarrier band, the band AMC channel is larger than the diversity channel in
terms of areas allocated therefor, and when reception quality is high the band

AMC channel can be used for transmitting or receiving large-volume data at a
high speed by applying a modulation scheme having a high coding efficiency.
In accordance with another aspect of the present invention, there is provided a
method for allocating a band Adaptive Modulation and Coding (AMC) channel by
a base station (BS), in a wireless communication system that divides a full
frequency band into a plurality of subcarrier band, each of which is a set of a
predetermined number of subbands, each of which is a set of a
predetermined

number of contiguous subcarriers, the method comprising the steps of: receiving a
band AMC channel request from a predetermined subscriber station (SS) in a
state in which the BS does not use a band AMC channel; determining to allocate a
band AMC channel to the SS in response to the request; and transmitting band
AMC channel allocation information corresponding to the determination result to
the SS.
In accordance with further another aspect of the present invention, there
is provided a method for requesting allocation of a band Adaptive Modulation and
Coding (AMC) channel by a subscriber station (SS), in a wireless communication
system that divides a full frequency band into a plurality of subcarrier bands, each
of which is a set of a predetermined number of subbands, each of which is a set of
a predetermined number of contiguous subcarriers. The method comprises the
steps of: sending a report on a state of a AMC channel to a base station (BS);
receiving a response to the report on the state of the band AMC channel from the
BS; and determining to use the band AMC channel according to the response.
In accordance with still another aspect of the present invention, there is
provided a method for allocating a band Adaptive Modulation and Coding (AMC)
channel by a base station (BS), in a wireless communication system that divides a
full frequency band into a plurality of subcarrier bands, each of which is a set of a
predetermined number of subbands, each of which is a set of a predetermined
number of contiguous subcarriers. The method comprises the steps of:receiving
band AMC channel information from a subscriber station (SS); and determining
to allocate a band AMC channel according to the received channel information.
In accordance with still another aspect of the present invention, there is
provided a method for transmitting data through a channel set up between a
subscriber station (SS) and a base station (BS), in a wireless communication
system that divides a full frequency band into a plurality of subcarrier bands, each
of which is a set of a predetermined number of subbands, each of which is a set of
a predetermined number of contiguous subcarriers. The method comprises the
steps of detecting a change in state of a current band Adaptive Modulation and
Coding (AMC) channel allocated from the BS in the SS; transmitting a channel
state response (CH_STA_RSP) message to report the change to the BS; receiving
the CH_STA_RSP message; determining, by the BS, if the BS can allocate a band
AMC channel to the SS through the CH_STA_RSP message; transmitting a band
AMC indication (BAND_AMC_IND) message including information indicating
whether the BS allocates the band AMC channel to the SS; receiving the

BAND_AMC_IND message; transmitting, by the SS, data to the BS using one of a
diversity channel and the band AMC channel according to the received
BAND_AMC_IND message.
In accordance with still another aspect of the present invention, there is provided
a system for allocating a band Adaptive Modulation and Coding (AMC) channel in
a wireless communication system, the system comprising: a subscriber station
(SS) for receiving a channel state request (CH_STA_REQ) message for a state
report request of the band AMC channel allocated to the SS from a base station
(BS), measuring reception quality of each band, generating a list of bands having
high reception quality according to the reception quality measurements,
transmitting a channel state response (CH_STA_RSP) message comprising the
generated list in response to the CH_STA_REQ message to the BS, receiving a
response to the CH_STA_RSP message from the BS, and transitioning to a state
in which the SS uses a band AMC channel, according to the response; and the BS
for transmitting, the CH_STA_REQ message to the SS for a state report request
of the band AMC channel allocated to the SS, receiving the CH_STA_RSP
message, and transmitting a band AMC indication (BAND_AMC_IND) message
comprising band AMC channel allocation information to the SS in response to the
received CH_STA_RSP message; wherein the CH__STA_RSP message comprises
information on at least one band index and a Carrier-to-interference ratio (C/I)
of the band AMC channel corresponding to the at least one band index; wherein
the band AMC channel comprises a plurality of bands, and each band is applied
by a different modulation order and coding rate; wherein the CH_STA_RSP
message comprises a channel type field representing information on a type of a
channel, a state of which the SS will report to the BS, information on a list of

channels, a measured quality of each of which the SS reports to the BS, and
state information of each channel included in the list; and wherein the
information on the type of the channel indicates a channel used when the SS
communicates with the BS, if the channel is the diversity channel the
CH_STA_RSP message comprises information on a Downlink Channel ID of the
diversity channel and a C/I of the diversity channel, if the channel is the band
AMC channel the CH_STA_RSP message includes information on each Band
Index of the band AMC channel and a C/I of the band AMC channel, the band
AMC channel is allocated based on a band including 6 bins, the diversity channel
is allocated based on a subchannel comprising three tiles spread over the full
subcarrier band, the band AMC channel is larger than the diversity channel in
terms of areas allocated therefor, and when reception quality is high the band
AMC channel can be used for transmitting or receiving large-volume data at a
high speed by applying a modulation scheme having a high coding efficiency.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The above and other objects, features, and advantages of the present invention
will become more apparent from the following detailed description when taken in
conjunction with the accompanying drawings in which:
Figure 1 is a diagram schematically illustrating a frame structure used in a
conventional TDD-OFDMA communication system;
Figure 2 is a diagram schematically illustrating a frame structure used in a TDD-
OFDMA communication system according to an embodiment of the present
invention;

Figure 3 is a flowchart illustrating an SS band AMC channel allocation request
operation in a TDD-OFDMA communication system according to an embodiment
of the present invention;
Figure 4 is a flowchart illustrating a BS operation in response to a band AMC
channel allocation request from an SS in a TDD-OFDMA communication system
according to an embodiment of the present invention;
Figure 5 is a flowchart illustrating a BS operation of receiving a report on a state
of a band AMC channel from an SS in a TDD-OFDMA communication system
according to an embodiment of the present invention;
Figure 6 is a flowchart illustrating an SS operation of transmitting a report on a
state of a band AMC channel in a TDD-OFDMA communication system according
to an embodiment of the present invention; and

FIG. 7 is a signaling diagram illustrating a process of performing
transmission/reception of band AMC channel-related messages between an SS
and a BS in a TDD-OFDMA communication system according to an embodiment
of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Preferred embodiments of the present invention will now be described in
detail herein below with reference to the annexed drawings. In the following
description, a detailed description of known functions and configurations
incorporated herein has been omitted for conciseness.
Generally, the present invention proposes a system and method for
enabling a base station (BS) to transmit high-speed, high-capacity data to
subscriber stations (SSs) having a good channel state in an Orthogonal Frequency
Division Multiplexing (OFDM) communication system. In particular, the present
invention proposes a system and method for allocating and managing band AMC
(Adaptive Modulation and Coding) subchannels for enabling high-speed, high-
capacity data transmission to SSs having a good channel state, according to
channel states of SSs.
That is, the present invention proposes a band AMC channel allocation
scheme for providing a higher data rate to users, i.e., SSs, having lower mobility,
a BS and SS operation scheme according to a band AMC channel state report, and
a BS and SS operation scheme for releasing band AMC channels in a TDD-
OFDMA communication system.
More specifically, the present invention proposes a system and method in
which an SS measures a reception signal level of each band and selects a
modulation scheme having high coding efficiency through a particular band
having high reception quality based on the measured reception signal level,
thereby enabling high-speed data transmission/reception between a BS and an SS
in a TDD-OFDMA communication system.
In addition, the present invention proposes a new TDD-OFDMA frame
structure for enabling data transmission/reception according to channel states. In
particular, the present invention proposes a band AMC channel and a new
message according thereto, and applies high-efficiency modulation and coding
schemes to SSs having high channel quality, thereby enabling high-speed, high-

capacity data transmission.
FIG. 2 is a diagram schematically illustrating a frame structure used in a
TDD-OFDMA communication system according to an embodiment of the present
invention. Referring to FIG. 2, in the frame structure, a full subcarrier band is
divided into a plurality of bands, for example, Band#0 to Band#23, and the band
includes a plurality of bins or tiles. The bin or tile includes a plurality of
subcarriers. Herein, the bin includes 9 consecutive subcarriers in one OFDM
symbol, and there are 1 pilot tone and 8 data tones. The tile includes 3 to 6
consecutive subcarriers, and there are 2 pilot tones and 16 data tones.
Referring to FIG. 2, in the frame, the first three OFDM symbols are used
for a ranging channel, an acknowledge (ACK) channel, and a channel quality
information (CQI) channel, respectively. The other OFDM symbols are allocated
for band AMC channels, diversity channels, and safety channels. Herein, the band
AMC channels at the front of the frame are allocated based on a band including 6
bins, and the diversity channels at the rear of the frame are allocated based on a
subchannel including three tiles spread over the full subcarrier band.
As the band AMC channels are larger than the diversity channels in terms
of areas allocated therefor, i.e., when reception quality is high, the band AMC
channels can be used for transmitting/receiving large-volume data at high speed
by applying a modulation scheme having high coding efficiency.
For the safety channel, a part which is laid over all OFDM symbols, one
bin is allocated. The safety channel is allocated all symbols in one bin. An SS is
allocated a safety channel among safety channels unused in a neighbor cell with a
frequency band available in a BS, i.e., an unallocated frequency band.
FIG. 3 is a flowchart illustrating an SS band AMC channel allocation
request operation in a TDD-OFDMA communication system according to an
embodiment of the present invention. Referring to FIG. 3, if an SS in a band AMC
disabled state in step 311 recognizes the need for a band AMC channel in step 313.
it proceeds to step 315. In step 315, the SS measures reception qualities of all
bands.
In step 317, the SS compares the measured reception qualities with a
reference value defined in the system, and makes a list of bands including higher
reception qualities than the reference value, i.e., bands having high reception

qualities. In step 319, the SS transmits a Channel State Response (CH_STA_RSP)
message to a BS. The CHSTARSP message includes the list of bands having
high reception quality, information on CQI of each band included in the list, and
band AMC channel allocation request information. A format of the CH_STA_RSP
message will be described later.
After transmitting the CH_STA_RSP message, the SS waits for a
response from the BS in step 321. In step 323, when the SS receives a Band AMC
Indication (BAND_AMCIND) message from the BS in response to the
CH_STA_RSP message, the SS proceeds to step 325. A format of the
BANDAMCIND message will be described later.
In step 325, the SS determines if the BS can allocate a band AMC channel to the
SS itself, based on the received BAND_AMC_IND message. If the SS can be
allocated a band AMC channel from the BS, the SS transitions to a band AMC
enabled state in step 327. However, if the SS cannot be allocated a band AMC
channel from the BS, the SS returns to step 311 to repeat the foregoing process.
The CHSTARSP message transmitted in step 319 from the SS to the
BS is used by the SS to report channel quality of a band to the BS, or request the
BS for allocation of a band AMC channel. A format of the CH_STA_RSP
message is shown in Table 1 below.



As shown in Table 1, the CH_STA_RSP message includes a plurality of
information elements (IEs), i.e., a Management Message Type indicating a type of
a transmission message, and a Reported Channel Type indicating type
information of a channel, a state of which the SS will report to the BS,
information on a list of channels, measured quality of each of which the SS
reports to the BS, and state information of each channel included in the list.
The channel type information corresponds to a channel used when the SS
communicates with the BS. For example, if the channel in use is a diversity
channel, the Reported Channel Type represents a value '00'. If the channel in use
is a band AMC channel, the Reported Channel Type represents a value '01'. If the
channel in use is a safety channel, the Reported Channel Type represents a value
'10'.
If the channel type is a diversity channel (Reported Channel Type = 00),
the CH_STA_RSP message includes information on a Downlink Channel ID of
each diversity channel and a carrier-to-interference ratio (C/I) of the channel. If
the channel type is a band AMC channel (Reported Channel Type = 01), the
CH_STA_RSP message includes information on each Band Index of a band AMC
channel and a C/l of the band. If the channel type is a safety channel (Reported
Channel Type = 10), the CH_STA_RSP message includes information on a Bin
ID of the safety channel and a C/I of the bin.
The BAND_AMC_IND message transmitted in step 323 from the BS to
the SS is a response to the CH_STA_RSP message shown in Table 1, and is used
by the BS to inform the SS of allocation/non-allocation of a band AMC channel.


As shown in Table 2, the BAND_AMC_IND message includes a plurality
of IEs, i.e., a Management Message Type indicating a type a transmission
message, and a Band AMC Indicator indicating approval/disapproval for a band
AMC channel allocation request transmitted from the SS to the BS. For example,
if a value of the Band AMC Indicator is ' 1' (Enable), allocation of the band AMC
channel requested by the SS is approved. If a value of the Band AMC Indicator is
'0? (D'sable), allocation of the band AMC channel requested by the SS is
disapproved.
FIG. 4 is a flowchart illustrating a BS operation in response to a band
AMC channel allocation request from an SS in a TDD-OFDMA communication
system according to an embodiment of the present invention. Referring to FIG. 4,
if a BS in a band AMC disabled state in step 411 receives a CHSTARSP
message from an SS in step 413, the BS determines if it can allocate a band AMC
channel requested by the SS in step 415, considering its resource state.
If the BS can allocate a band AMC channel to the SS, the BS transmits a
BAND_AMC_IND message with Band AMC Indicator^ (Enable), shown in
Table 2, to the SS in step 417. Thereafter, in step 421, the BS transitions to a band
AMC enabled state.
However, if the BS cannot allocate a band AMC channel to the SS, the
BS transmits a BANDAMCIND message with Band AMC lndicator=0
(Disable), shown in Table 2, to the SS in step 419, and then returns to step 411
where it transitions to a band AMC disabled state.
FIG. 5 is a flowchart illustrating a BS operation of requesting a report on
a state of a band AMC channel allocated to an SS in a TDD-OFDMA
communication system according to an embodiment of the present invention.

Referring to FIG. 5, if a BS in a band AMC enabled state in step 511 detects
occurrence of a specific effect, for example, if the BS recognizes the need for
receiving a report on a state of a band AMC channel allocated to the SS, in step
513 or if the BS receives a CH_STA_RSP message from the SS in step 517, the
BS performs an operation according to the corresponding state.
In step 513, the BS recognizes the need for receiving a report on a state of
a band AMC channel allocated to the SS. In step 515, the BS transmits a Channel
State Request (CH_STA_REQ) message for an information report request for a
state of the band AMC channel allocated to the SS, and then returns to step 511
where it stays in the band AMC enabled state. A format of the CHSTAREQ
message will be described later.
The BS recognizes the need for receiving a report on a state of a band
AMC channel from the SS in step 513, for example, (1) when it is determined that
the reception quality of data transmitted by the SS with a band AMC channel is
low, (2) when it is determined that it is necessary to change allocation of the
currently scheduled band AMC channels in the course of allocating a band AMC
channel to each SS, or (3) when the BS checks a current state of a band AMC
channel used by each SS and desires to perform an operation according thereto.
If the BS in the band AMC enabled state in step 511 receives, in step 517,
a CHSTARSP message from the SS in response to the CHSTAREQ message
transmitted in step 515, the BS proceeds to step 519.
It is assumed in FIG. 5 that after transmitting a CH_STA_REQ message
to the SS, the BS receives a CH_STA_RSP message in response to the
CHSTAREQ message. However, the present invention is not limited to the
assumption.
For example, the CHSTARSP message received in step 517 can be
transmitted by the SS itself upon detecting the need for reporting a state on a band
AMC channel even when the BS does not transmit in step 515 the CHSTAREQ
message for requesting a report on a state of a band AMC channel to the SS. Then
the BS receives the CH_STA_RSP message transmitted from the SS, and
performs a procedure according to the received CHSTARSP message.
The SS transmits the CH STARSP message in step 517, when the SS
desires to determine if it can be allocated another band AMC channel because of

the low quality of its current band AMC channel. The CH_STA_RSP message
received in step 517, as shown in Table 1, includes quality information of the
band AMC channel allocated to the SS.
After receiving a report on the state of the band AMC channel allocated
to the SS through the CHSTARSP message received from the SS in step 517,
the BS determines if a new band AMC is required from the received
CH_STA_RSP message in step 519.
If the BS can no longer allocate a band AMC channel to the SS or the BS
is not required to allocate a band AMC channel to the SS, the BS transmits a
BANDAMCJND message with Band AMC lndicator=0 to the SS in step 521.
Thereafter, in step 523, the BS transitions to a band AMC disabled state.
However, if it is possible to continuously allocate a band AMC channel to
the SS or it is not necessary to allocate a band AMC channel to the SS, the BS
transmits the BAND_AMC_IND message with Band AMC Indicator=T to the SS
in step 525, and then returns to step 511 where it stays in the band AMC enabled
state.
The CHSTAREQ message transmitted in step 515 from the BS to the
SS is transmitted to request a report on a state of the band AMC channel allocated
to the SS. A format of the CH_STA_REQ message is shown in Table 3 below.

As shown in Table 3, the CHSTAREQ message includes a plurality of
IEs, i.e., a Management Message Type indicating a type of a transmission
message, and a Requested Channel Type indicating type information of a channel,

a report on a state of which the BS desires to receive from an SS.
The channel type information corresponds to a channel used when the BS
communicates with the SS. For example, if the channel in use is a diversity
channel, the R-epeftedRequested Channel Type represents a value '00'. If the
channel in use is a band AMC channel, the ReportedRequested Channel Type
represents a value '01'. If the channel in use is a safety channel, the
ReportedRequested Channel Type represents a value '10'.
FIG. 6 is a flowchart illustrating an SS operation of reporting a state of its
current band AMC channel to a BS in a TDD-OFDMA communication system
according to an embodiment of the present invention. Referring to FIG. 6, if an SS
in a band AMC enabled state in step 611 detects occurrence of a specific effect,
for example, if the SS recognizes the need for transmitting a report on a state of a
band AMC channel allocated from the BS in step 613 or if the SS receives a
CHSTAREQ message from the BS in step 625, the B&SS proceeds to step 615.
In step 613, the SS recognizes the need for transmitting a report on a state
of the band AMC channel (1) when it is determined that the SS can no longer use
a band AMC channel due to the low quality of its current band AMC channel, or
(2) when the SS inquires of the BS about whether it can change its band AMC
channel to antheranother band AMC channel. |
Thereafter, in step 615, the SS transmits a CH_STA_RSP message to the
BS in order to make a report on a state of its current band AMC channel.
It is assumed herein that the SS determines the need for transmitting a
report on a satestate of the band AMC channel. However, the present invention is |
not limited to the assumption. For example, upon receiving the CHSTAREQ
message for requesting a report on a state of a band AMC channel from the BS in
step 625, the SS can transmit the CHSTARSP message in step 615 in order to
make a report on a state of its current band AMC channel.
After transmitting the CH_STA_RSP message in step 615, if the SS in a
waiting state in step 617 receives a BAND_AMC_TND message from the BS in
step 619, the SS determines if it can use a band AMC channel in step 621, by
checking a set value of a Band AMC Indicator included in the received
BAND_AMC_IND message.

For example, as illustrated in Table 2, if a value of the Band AMC
Indicator is ' 1' (Enable), it indicates that the SS can use the band AMC channel. If
a value of the Band AMC Indicator is '0' (Disable), it indicates that the SS cannot
use the band AMC channel.
If the SS can no longer use the band AMC channel, the SS transitions to a
band AMC disabled state in step 623. However, if the SS can continue to use the
band AMC channel, the SS returns to step 611, where it stays in the band AMC
enabled state.
FIG. 7 is a signaling diagram illustrating a process of setting up and
releasing a band AMC channel between an SS and a BS in a TDD-OFDMA
communication system according to an embodiment of the present invention.
Referring to FIG. 7, an SS 710 and a BS 750 exchange data with each other, using
a diversity channel in Step 711. If the SS 710 desires to use a band AMC channel,
the SS 710 transmits a CH_STA_RSP message to the BS 750 to request allocation
of the band AMC channel in Step 713. Thereafter, if the BS 750 determines that it
can allocate a band AMC channel to the SS 710 in Step 715, the BS 750 informs
the SS 710 of the possibility of allocating the band AMC channel through a
BANDAMCJND message in Step 717.
Upon receiving the BANDAMCJND message from the BS 750, the SS
710 performs data transmission/reception according to information included in
the BAND_AMC_IND message. Because the BAND_AMC_IND message, as
described above, includes information indicating the possibility of allocating a
band AMC channel to the SS 710, the SS 710 exchanges data with the BS 750
through a diversity channel or the allocated band AMC channel in Step 719.
For example, assuming that the BS 750 transmits downlink data to the SS
710 in the data transmission/reception process of step 719, if a size of the data is
not large, the data can be transmitted using a diversity channel, and if a size of the
data to be transmitted by the BS 750 is large, the data can be transmitted using the
allocated band AMC channel. In addition, when the SS 710 transmits uplink data
to the BS 750, the data can be transmitted using only the allocated band AMC
channel.
In the band AMC enabled state of the SS 710, the BS 750 can transmit a
CHSTARJEQ message to the SS 710 in order to receive a report on a state of the
allocated band AMC channel in Step 721. The SS 710 transmits a CH_STA_RSP

message including state information of its current band AMC channel to the BS
750 in response to the CH_STA_REQ message in Step 723.
Alternatively, the SS 710 can periodically report its own C/I information
to the BS 750 irrespective of a request of the BS 750 in Step 725.
The BS 750 transmits a BAND_AMC_IND message to the SS 710
according to information included in the CHSTARSP message transmitted from
the SS 710. The SS 710 receives the BANDAMCIND message, and exchanges
data with the BS 750 through a diversity channel or a band AMC channel
according to information included in the received BANDAMCIND message in
Step 727. Whether a diversity channel or a band AMC channel is used for the data
exchange between the SS 710 and the BS 750 in Step 727 is determined in the
method of Step 719.
If a state of the current band AMC channel allocated from the BS 750
suffers a change, the SS 710 transmits a CH STARSP message to report the
change to the BS 750 in Step 729. The BS 750 receives the transmitted
CHSTARSP message, and determines if it is necessary to allocate a band AMC
channel to the SS 710, based on the received CH_STA_RSP message in Step 731.
If it is determined in Step 731 that the SS 710 is no longer required to use a band
AMC channel, the BS 750 transmits a BANDAMCIND message including
information indicating that the SS 710 cannot use the band AMC channel, to
instruct the SS 710 to release the band AMC channel in use in Step 733.
Thereafter, in Step 735, the SS 710 exchanges data with the BS 750 using only
the diversity channel.
With the use of a band AMC channel allocation scheme proposed in the
present invention, the OFDMA communication system allocates, if reception
signal quality is high, a high-capacity band channel to an SS, and reports channel
quality information of the allocated band channel to select a band channel having
high reception quality, thereby enabling high-speed, high-capacity data
transmission/reception between a BS and an SS using a high coding efficiency
modulation scheme through the selected high-quality band channel.
While the present 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 as defined by the appended

WE CLAIM:
1. A method for transmitting data through a channel set up between a subscriber
station (SS) and a base station (BS) in a wireless communication system, the
method comprising the steps of:
transmitting, by the BS, a channel state request (CH_STA_REQ) message to the
SS for a state report request of the band AMC channel allocated to the SS;
measuring, by the SS, reception quality of each band; generating, by the SS, a
list of bands having high reception quality according to the reception quality
measurements; transmitting, by the SS, a channel state response (CH_STA_RSP)
message including the generated list in response to the CH_ST_REQ message to
the BS; receiving, by the BS, the CH_STA_RSP message;
determining, by the BS, whether the BS can allocate a band AMC channel to the
SS in response to the CH_STA_RSP message; transmitting, by the BS, a band
AMC indication (BAND_AMC_IND) message including information indicating
whether the BS allocates the band AMC channel to the SS;
receiving, by the SS, the BAND_AMC_IND message; and

transmitting, by the SS, data to the BS using at least one of a diversity channel
and the band AMC channel according to the received BAND_AMC_IND message;
wherein the CH_STA_RSP message includes information on at least one band
index and a Carrier-to-interference ratio (C/I) of the band AMC channel
corresponding to the at least one band index;
wherein the band AMC channel comprises a plurality of bands, and each band is
applied by a different modulation order and coding rate;
wherein the CH_STA_RSP message comprises a reported channel type field
comprising information on a type of a channel, a state of which the SS will report
to the BS, information on a list of channels, a measured quality of each of which
the SS reports to the BS, and state information of each channel included in the
list; and
wherein the information on the type of the channel indicates a channel used
when the SS communicates with the BS, if the channel is the diversity channel
the CH_STA_RSP message comprises information on a Downlink Channel ID of
the diversity channel and a C/I of the diversity channel, if the channel is the
band AMC channel the CH_STA_RSP message comprises information on each
Band Index of the band AMC channel and a C/I of the band AMC channel, the
band AMC channel is allocated based on a band comprising 6 bins, the diversity
channel is allocated based on a subchannel including three tiles spread over the

full subcarrier band, the band AMC channel is larger than the diversity channel in
terms of areas allocated therefor, and when reception quality is high the band
AMC channel can be used for transmitting or receiving large-volume data at a
high speed by applying a modulation scheme having a high coding efficiency.
2. The method as claimed in claim 1, comprising the steps of:
when it is determined that the SS no longer needs to use the band AMC channel,
transmitting, by the BS, the BAND_AMC_IND message comprising information
indicating no possibility of using a band AMC channel to the SS, and releasing
the band AMC channel in use; and
upon receiving the BAND_AMC_IND message, transmitting, by the SS, data to
the BS using a diversity channel.
3. The method as claimed in claim 1, wherein the CH_STA_REQ message
comprises a channel type field comprising type information of a channel, a report
on a state of which the BS desires to receive from the SS.
4. The method as claimed in claim 1, wherein for downlink data transmission
from the BS to the SS, the BS transmits the data using a diversity channel when
a size of the data is not greater than a predetermined threshold, and transmits
the data using the band AMC channel when the size of the data is greater than
the predetermined threshold.

5. The method as claimed in claim 1, wherein the reported channel type field
comprises information on a channel used when the SS communicates with the
BS; and
wherein the reported channel type comprises a diversity channel, a band AMC
channel, and a safety channel.
6. The method as claimed in claim 1, wherein the BAND_AMC_IND message
comprises an information field indicating one of approval and disapproval for the
band AMC channel allocation request from the SS.
7. A system for allocating a band Adaptive Modulation and Coding (AMC) channel
in a wireless communication system, the system comprising:
a subscriber station (SS) for receiving a channel state request (CH_STA_REQ)
message for a state report request of the band AMC channel allocated to the SS
from a base station (BS), measuring reception quality of each band, generating a
list of bands having high reception quality according to the reception quality
measurements, transmitting a channel state response (CH_STA_RSP) message
comprising the generated list in response to the CH_STA_REQ message to the
BS, receiving a response to the CH_STA_RSP message from the BS, and

transitioning to a state in which the SS uses a band AMC channel, according to
the response; and
the BS for transmitting the CH_STA_REQ message to the SS for a state report
request of the band AMC channel allocated to the SS, receiving the CH_STA_RSP
message, and transmitting a band AMC indication (BAND_AMC_IND) message
comprising band AMC channel allocation information to the SS in response to the
received CH_STA_RSP message;
wherein the CH_STA_RSP message comprises information on at least one band
index and a Carrier-to-interference ratio (C/I) of the band AMC channel
corresponding to the at least one band index;
wherein the band AMC channel comprises a plurality of bands, and each band is
applied by a different modulation order and coding rate;
wherein the CH_STA_RSP message comprises a channel type field representing
information on a type of a channel, a state of which the SS will report to the BS,
information on a list of channels, a measured quality of each of which the SS
reports to the BS, and state information of each channel included in the list; and
wherein the information on the type of the channel indicates a channel used
when the SS communicates with the BS, if the channel is the diversity channel
the CH_STA_RSP message comprises information on a Downlink Channel ID of
the diversity channel and a C/I of the diversity channel, if the channel is the

band AMC channel the CH_STA_RSP message includes information on each Band
Index of the band AMC channel and a C/I of the band AMC channel, the band
AMC channel is allocated based on a band including 6 bins, the diversity channel
is allocated based on a subchannel comprising three tiles spread over the full
subcarrier band, the band AMC channel is larger than the diversity channel in
terms of areas allocated therefor, and when reception quality is high the band
AMC channel can be used for transmitting or receiving large-volume data at a
high speed by applying a modulation scheme having a high coding efficiency.
8. The system as claimed in claim 7, wherein when it is determined that the SS
no longer needs to use the band AMC channel allocated to the SS, the BS
transmits the BAND_AMC_IND message comprising information indicating no
possibility of using the band AMC channel to the SS, and releases the band AMC
channel used by the SS; and
wherein upon receiving the BAND_AMC_IND message, the SS transmits data to
the BS using a diversity channel.

9. The system as claimed in claim 7, wherein when it is determined that the SS
no longer needs to use the band AMC channel allocated to the SS, the BS
transmits the BAND_AMC_IND message comprising information indicating no
possibility of using the band AMC channel to the SS, and releases the band AMC
channel used by the SS; and
wherein upon receiving the BAND_AMC_IND message, the SS receives data from
the BS using a diversity channel.
10. The system as claimed in claim 7, wherein the CH_STA_REQ message
comprises a requested channel type field including type information of a channel,
a report on a state of which the BS desires to receive from the SS.
11. The system as claimed in claim 10, wherein the channel type information
comprises information on a channel used when the BS communicates with the
SS; and
wherein the channel type information represents a diversity channel, a band AMC
channel, and a safety channel.

12. The system as claimed in claim 7, wherein the SS and the BS exchange data
between each other using at least one of a band AMC channel and a diversity
channel according to information included in the BAND_AMC_IND message.
13. The system as claimed in claim 12, wherein for downlink data transmission
from the BS to the SS, the BS transmits the data using the diversity channel
when a size of the data is not greater than a predetermined threshold, and
transmits the data using the band AMC channel when the size of the data is
greater than the predetermined threshold.
14. The system as claimed in claim 12, wherein for uplink data transmission from
the SS to the BS, the SS transmits the data using the band AMC channel.
15. The system as claimed in claim 7, wherein the BAND_AMC_IND message
comprises an information field indicating one of approval and disapproval for the
band AMC channel allocation.

ABSTRACT

TITLE : "A METHOD AND A SYSTEM FOR ALLOCATING A BAND
ADAPTIVE MODULATION AND CODING CHANNEL IN A WIRELESS
COMMUNICATION SYSTEM"
The invention relates to a method for transmitting data through a channel set up
between a subscriber station (SS) and a base station (BS) in a wireless
communication system, the method comprising the steps of transmitting, by the
BS, a channel state request (CH_STA_REQ) message to the SS for a state report
request of the band AMC channel allocated to the SS; measuring, by the SS,
reception quality of each band; generating, by the SS, a list of bands having high
reception quality according to the reception quality measurements; transmitting,
by the SS, a channel state response (CH_STA_RSP) message including the
generated list in response to the CH_ST_REQ message to the BS; receiving, by
the BS, the CH_STA_RSP message; determining, by the BS, whether the BS can
allocate a band AMC channel to the SS in response to the CH_STA_RSP
message; transmitting, by the BS, a band AMC indication (BAND_AMC_IND)
message including information indicating whether the BS allocates the band AMC
channel to the SS; receiving, by the SS, the BAND_AMC_IND message; and
transmitting, by the SS, data to the BS using at least one of a diversity channel
and the band AMC channel according to the received BAND_AMC_IND message;
wherein the CH_STA_RSP message includes information on at least one band

index and a Carrier-to-interference ratio (C/I) of the band AMC channel
corresponding to the at least one band index; wherein the band AMC channel
comprises a plurality of bands, and each band is applied by a different
modulation order and coding rate; wherein the CH_STA_RSP message comprises
a reported channel type field comprising information on a type of a channel, a
state of which the SS will report to the BS, information on a list of channels, a
measured quality of each of which the SS reports to the BS, and state
information of each channel included in the list; and wherein the information on
the type of the channel indicates a channel used when the SS communicates
with the BS, if the channel is the diversity channel the CH_STA_RSP message
comprises information on a Downlink Channel ID of the diversity channel and a
C/I of the diversity channel, if the channel is the band AMC channel the
CH_STA_RSP message comprises information on each Band Index of the band
AMC channel and a C/I of the band AMC channel, the band AMC channel is
allocated based on a band comprising 6 bins, the diversity channel is allocated
based on a subchannel including three tiles spread over the full subcarrier band,
the band AMC channel is larger than the diversity channel in terms of areas
allocated therefor, and when reception quality is high the band AMC channel can
be used for transmitting or receiving large-volume data at a high speed by
applying a modulation scheme having a high coding efficiency.