U.S. patent number RE47,522 [Application Number 13/684,283] was granted by the patent office on 2019-07-16 for transmitting and receiving systems for increasing service coverage in orthogonal frequency division multiplexing wireless local area network, and method thereof.
This patent grant is currently assigned to ELECTRONICS AND TELECOMMUNICATIONS RESEARCH INSTITUTE. The grantee listed for this patent is ELECTRONICS AND TELECOMMUNICATIONS RESEARCH INSTITUTE. Invention is credited to Seung-Chan Bang, Eun-Young Choi, Seung-Ku Hwang, Tae-hyun Jeon, Il-Gu Lee, Sok-Kyu Lee, Deuk-Su Lyu, Seung-Wook Min, Jung-Bo Son, Chan-Ho Yoon, Hee-Jung Yu.
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United States Patent |
RE47,522 |
Yu , et al. |
July 16, 2019 |
Transmitting and receiving systems for increasing service coverage
in orthogonal frequency division multiplexing wireless local area
network, and method thereof
Abstract
The present invention relates to an orthogonal frequency
division multiplexing wireless local area network (LAN)
transmitting/receiving system for providing expanded service
coverage, and a method thereof. A first OFDM modulation is
performed for an even-numbered time, and a second OFDM modulation
is performed for an odd-numbered time. A transmitting frame
including a plurality of signal fields according to the first and
second OFDM modulation is transmitted. The receiving system
determines whether a signal field is repeatedly generated in the
frame. If the signal field is not repeatedly generated,
corresponding demodulation is performed. If repeatedly performed,
the signal field is demodulated by using first bit allocation
information and second bit allocation information having a 1/2
value of the first bit allocation information. A data field is
demodulated according to the demodulated signal field.
Inventors: |
Yu; Hee-Jung (Daejeon,
KR), Choi; Eun-Young (Daejeon, KR), Yoon;
Chan-Ho (Seoul, KR), Son; Jung-Bo
(Gyeongsangnam-do, KR), Lee; Il-Gu (Seoul,
KR), Lyu; Deuk-Su (Daejeon, KR), Jeon;
Tae-hyun (Kyungki-do, KR), Min; Seung-Wook
(Seoul, KR), Lee; Sok-Kyu (Daejeon, KR),
Bang; Seung-Chan (Daejeon, KR), Hwang; Seung-Ku
(Daejeon, KR) |
Applicant: |
Name |
City |
State |
Country |
Type |
ELECTRONICS AND TELECOMMUNICATIONS RESEARCH INSTITUTE |
Daejeon |
N/A |
KR |
|
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Assignee: |
ELECTRONICS AND TELECOMMUNICATIONS
RESEARCH INSTITUTE (Daejeon, KR)
|
Family
ID: |
1000003744747 |
Appl.
No.: |
13/684,283 |
Filed: |
November 23, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
11635927 |
Dec 8, 2006 |
7839760 |
Nov 23, 2010 |
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Foreign Application Priority Data
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Dec 9, 2005 [KR] |
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10-2005-0120849 |
Jun 2, 2006 [KR] |
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10-2006-0049871 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04W
84/12 (20130101); H04L 27/2627 (20130101); H04L
27/261 (20130101); H04L 27/2602 (20130101); H04L
27/263 (20130101); H04L 27/265 (20130101); H04L
5/0044 (20130101); H04L 5/0046 (20130101) |
Current International
Class: |
H04J
9/00 (20060101); H04L 5/00 (20060101) |
Field of
Search: |
;370/208 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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20040001354 |
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Jan 2004 |
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1020040077567 |
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Apr 2004 |
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1020040001354 |
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Jul 2004 |
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KR |
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2004007567 |
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Sep 2004 |
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KR |
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1020040076710 |
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Sep 2004 |
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KR |
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1020040076710 |
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Sep 2004 |
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KR |
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1020040077301 |
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Sep 2004 |
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KR |
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1020040077301 |
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Sep 2004 |
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KR |
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1020040102292 |
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Dec 2004 |
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KR |
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1020040102292 |
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Dec 2004 |
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KR |
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1020050117363 |
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Dec 2005 |
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KR |
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1020050117363 |
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Dec 2005 |
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KR |
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Other References
"Multiuser OFDM with Adaptive Subcarrier, Bit, and Power
Allocation," authored by Cheong Yui Wong et al., IEEE Journal on
Selected Areas in Communication, vol. 17, No. 10, Oct. 1999, pp.
1747-1758. cited by examiner .
Y.H. You, et al; "Simple construction of OFDM signals with
diversity gain and PAPR", Electronics Letters, Jan. 20, 2005, vol.
41, No. 2, 2 pages. cited by applicant .
USPTO RR dated Jul. 23, 2009 in connection with U.S. Appl. No.
11/635,927. cited by applicant .
USPTO NFOA dated Dec. 17, 2009 in connection with U.S. Appl. No.
11/635,927. cited by applicant .
USPTO NOA dated Jul. 14, 2010 in connection with U.S. Appl. No.
11/635,927. cited by applicant .
USPTO Notice of Allowability dated Aug. 13, 2010 in connection with
U.S. Appl. No. 11/635,927. cited by applicant.
|
Primary Examiner: Pokrzywa; Joseph R
Attorney, Agent or Firm: Ladas & Parry LLP
Claims
What is claimed is:
.[.1. A transmitting system of an orthogonal frequency division
multiplexing (OFDM) wireless local area network (LAN), the
transmitting system comprising: an OFDM modulation controller for
controlling first OFDM modulation for an even-numbered time, and
controlling second OFDM modulation by changing subcarrier
allocation positions of first OFDM modulated symbols for an
odd-numbered time; a frame generation controller for controlling
generation of a frame having a plurality of signal fields generated
according to the first OFDM modulation and the second OFDM
modulation; a buffer unit for storing input data that are first
OFDM modulated and second OFDM modulated according to a control
operation of the OFDM modulation controller; and an OFDM modulation
unit for repeatedly modulating the first and second OFDM modulated
data stored in the buffer unit, forming the repeatedly modulated
OFDM symbol as a frame according to a control operation of the
frame generation controller, and transmitting the frame, wherein a
bit allocation according to the first OFDM modulation is different
from a bit allocation according to the second OFDM
modulation..].
.[.2. The transmitting system of claim 1, wherein the frame
generation controller comprises: a first bit allocation controller
for controlling bit allocation according to the first OFDM
modulation; a second bit allocation controller for controlling bit
allocation according to the second OFDM modulation; and a signal
field generation controller for controlling generation of a
plurality of signal fields according to information of the bit
allocation performed by the first bit allocation controller and the
second bit allocation controller..].
3. A transmitting system of an orthogonal frequency division
multiplexing (OFDM) wireless local area network (LAN), the
transmission system comprising: a first OFDM modulation controller
for controlling first OFDM modulation for an even-numbered time; a
second OFDM modulation controller for controlling second OFDM
modulation performed by cyclically moving a subcarrier allocation
position of each first OFDM symbol by 1/2 of the first OFDM symbol
with reference to an FFT point for an odd-numbered time; a frame
generation controller for controlling generation of a frame having
a plurality of signal fields generated according to the first OFDM
modulation and the second OFDM modulation; a buffer unit for
storing input data that are respectively first OFDM modulated and
second OFDM modulated according to control operations of the first
and second OFDM modulation controllers; and an OFDM modulation unit
for repeatedly modulating the first and second OFDM modulated data,
and forming the repeatedly modulated OFDM symbol as a frame
according to a control operation of the frame generation
controller, wherein a bit allocation according to the first OFDM
modulation is different from a bit allocation according to the
second OFDM modulation.
4. The transmitting system of claim 3, wherein the frame generation
controller comprises: a first bit allocation controller for
controlling bit allocation according to the first OFDM modulation;
a second bit allocation controller for controlling the bit
allocation by 1/2 of bits allocated by the first bit allocation
controller, according to the second OFDM modulation; and a signal
field generation controller for controlling generation of a
plurality of signal fields according to information of the bit
allocation respectively performed by the first bit allocation
controller and the second bit allocation controller.
.[.5. A transmitting method of an orthogonal frequency division
multiplexing (OFDM) wireless local area network (LAN), the
transmitting method comprising: a) generating a signal field
according to a first OFDM modulation for an even-numbered time; b)
generating a signal field according to a second OFDM modulation for
an odd-numbered time, the second OFDM modulation performed by
changing subcarrier allocation position of a first OFDM modulated
symbol; and c) transmitting a transmitting frame having a plurality
of signal fields generated in a) and b), wherein a bit allocation
according to the first OFDM modulation is different from a bit
allocation according to the second OFDM modulation..].
.[.6. The transmitting method of claim 5, wherein the signal field
is generated by using bit allocation information according to the
first OFDM modulation and the second OFDM modulation..].
.[.7. A transmitting method of an orthogonal frequency division
multiplexing (OFDM) wireless local area network (LAN), the
transmitting method comprising: a) generating a signal field by
using first bit allocation information according to first OFDM
modulation for an even-numbered time; b) generating a signal field
by using second bit allocation information according to second OFDM
modulation for an odd-numbered time, the second OFDM modulation
performed by cyclically moving each subcarrier position of first
OFDM modulated symbols by 1/2 of a fast Fourier transform (FFT)
point; and c) transmitting a transmitting frame having a plurality
of signal fields generated in a) and b), wherein a bit allocation
according to the first OFDM modulation is different from a bit
allocation according to the second OFDM modulation..].
.[.8. The transmitting method of claim 7, wherein, in b), the
signal field is generated by using the second bit allocation
information having a 1/2 value of the first bit allocation
information..].
.Iadd.9. The transmitting system of claim 3, wherein the OFDM
modulation unit repeats a same information signal across two OFDM
symbols in different subcarriers. .Iaddend.
Description
CROSS-REFERENCE TO RELATED APPLICATION
This application claims priority to and the benefit of Korean
Patent Application No. 10-2005-0120849 filed on Dec. 9, 2005, and
No. 10-2006-0049871 filed on Jun. 2, 2006, in the Korean
Intellectual Property Office, the entire contents of which are
incorporated herein by reference.
BACKGROUND OF THE INVENTION
(a) Field of the Invention
The present invention relates to an orthogonal frequency division
multiplexing wireless local area network (LAN)
transmitting/receiving system for providing expanded service
coverage, and a method thereof. More particularly, the present
invention relates to a method for expanding service coverage of a
wireless LAN system.
(b) Description of the Related Art
Recently, in addition to providing an Internet service in an indoor
environment, wireless local area network (LAN) techniques have
allowed expansion of its service providing area to a small hot spot
area, and various applications using the wireless LAN have been
rapidly developed.
IEEE 802.11a/b/g are standards for the wireless LAN system. IEEE
802.11b/g are defined in a 2.4 GHz band, and IEEE 802.11a is
defined in a 5 GHz band. The maximum transmission speed is 11 Mbps
in IEEE 802.11b, and 54 Mbps in IEEE 802.11a/g. Such a wireless LAN
system uses an orthogonal frequency division multiplexing (OFDM)
method. In addition, a wireless LAN system of IEEE 802.11 n is now
standardized.
A configuration of the wireless LAN system according to the IEEE
802.11a standard will now be described with reference to FIG.
1.
Data are transmitted from a media access control layer 11 to a
convolutional encoder 15 through a scrambler 13, and the
convolutional encoder 15 performs a channel encoding operation. A
puncturing unit 17 controls data rates of the data, an interleaver
19 rearranges the data, and a mapping unit 21 maps the data as
binary data. A buffering unit 23 stores the binary data, and an
inverse fast Fourier transform (IFFT) unit 25 OFDM modulates the
data. The data is transmitted to a preamble generator 29 through a
multiplex unit 27, and the preamble generator 29 generates a
preamble. The modulated data and the generated preamble form an
entire frame. The data are modulated by a digital to analog (D/A)
converter 31, are amplified to a radio frequency (RF) bandwidth by
an RF transmitting unit 33, and are transmitted through an
antenna.
A signal received through an antenna and attenuated to a baseband
signal by a radio frequency (RF) receiving unit 35 is converted
into a digital signal by an analog to digital ((A/D) converter 37.
A signal detection and synchronization unit 39 detects and
synchronizes time and frequency of the digital signal, and a buffer
unit 41 stores the signal. A fast Fourier transform (FFT) unit 43
transforms the signal, a channel estimation unit 45 estimate a
channel, and an equalizer 47 equalizes the channel. A demapper 49
converts the signal into binary data and soft-decision data. A
deinterleaver 51, a depuncturing unit 53, a Viterbi decoder 55, and
a descrambler 57 respectively performs inverse-processes of the
transmitter (i.e., deinterleaving, depuncturing, Viterbi decoding,
and descrambling processes)
In this case, a configuration of a wireless LAN frame includes a
preamble period P10, a signal field period P20, and data field
period P30, as shown in FIG. 2.
Here, the preamble period P10 includes a short preamble and a long
preamble.
The short preamble is used for performing frame synchronization and
coarse frequency synchronization after performing signal detection
and automatic gain control.
The long preamble is used for performing fine frequency
synchronization and channel estimation of each subcarrier.
A signal field of the signal field period P20 has transmission mode
information (i.e., modulation method and code rate information) and
frame length information.
Accordingly, the signal field is firstly demodulated to extract the
transmission mode and frame length information, and a data field of
the data field P30 is demodulated based on the extracted
transmission mode and frame length information to obtain receiving
data.
Since the demand for wideband for a voice over Internet protocol
(VoIP) service using the wireless LAN has increased, studies for
increasing a service area (i.e., coverage for the conventional
wireless LAN system) have been actively pursued.
However, since the wireless LAN system problematically has narrow
service coverage, the service radius in a wireless LAN of IEEE
802.11a/g is approximately 100 m.
In addition, the service coverage is limited since the transmission
output is low, and therefore the service radius may be increased
when a high gain amplifier and a high gain antenna and sector are
used.
However, this may increase the system manufacturing cost, and power
consumption in a portable terminal may be increased.
The above information disclosed in this Background section is only
for enhancement of understanding of the background of the invention
and therefore it may contain information that does not form the
prior art that is already known in this country to a person of
ordinary skill in the art.
SUMMARY OF THE INVENTION
The present invention has been made in an effort to provide a
transmitting/receiving system of a wireless local area network
(WLAN) having high receiving sensitivity and wider coverage, and a
method thereof.
The present invention has been made in an effort to provide a
transmitting/receiving system of a WLAN for providing compatibility
with a conventional system, and a method thereof.
An exemplary transmitting system of an orthogonal frequency
division multiplexing (OFDM) wireless local area network (LAN)
according to an embodiment of the present invention includes an
OFDM modulation controller, a frame generation controller, a buffer
unit, and an OFDM modulation unit. The OFDM modulation controller
controls first OFDM modulation for an even-numbered time, and
controls second OFDM modulation by changing subcarrier allocation
positions of first OFDM modulated symbols for an odd-numbered time.
The frame generation controller controls generation of a frame
having a plurality of signal fields generated according to the
first OFDM modulation and the second OFDM modulation. The buffer
unit stores input data that are first OFDM modulated and second
OFDM modulated according to a control operation of the OFDM
modulation controller. The OFDM modulation unit repeatedly
modulates the first and second OFDM modulated data stored in the
buffer unit, forms the repeatedly modulated OFDM symbol as a frame
according to a control operation of the frame generation
controller, and transmits the frame.
An exemplary transmitting system of an OFDM wireless LAN according
to another embodiment of the present invention includes a first
OFDM modulation controller, a second OFDM modulation controller, a
frame generation controller, a buffer unit, and an OFDM modulation
unit. The first OFDM modulation controller controls first OFDM
modulation for an even-numbered time. The second OFDM modulation
controller controls second OFDM modulation performed by cyclically
moving a subcarrier allocation position of each first OFDM symbol
by 1/2 of the first OFDM symbol, for an odd-numbered time. The
frame generation controller controls generation of a frame having a
plurality of signal fields generated according to the first OFDM
modulation and the second OFDM modulation. The buffer unit stores
input data that are respectively first OFDM modulated and second
OFDM modulated according to control operations of the first and
second OFDM modulation controllers. The OFDM modulation unit
repeatedly modulates the first and second OFDM modulated data, and
forms the repeatedly modulated OFDM symbol as a frame according to
a control operation of the frame generation controller.
An exemplary receiving system of an OFDM wireless LAN according to
an embodiment of the present invention includes an OFDM
demodulation controller, an equalizer, and an OFDM modulation unit.
The OFDM demodulation controller determines whether OFDM symbol
modulation is repeated in a format configuration of a received
frame, and controls a demodulation mode according to a determined
result. The equalizer performs an equalization operation according
to the demodulation mode. The OFDM modulation unit demodulates a
signal field of the received frame according to the demodulation
mode, and demodulates a data field by using the demodulated signal
field.
In an exemplary transmitting method of an OFDM wireless LAN
according to an embodiment of the present invention, a) a signal
field according to a first OFDM modulation is generated for an
even-numbered time, b) a signal field according to a second OFDM
modulation performed by changing subcarrier allocation position of
a first OFDM modulated symbol is generated for an odd-numbered
time, and c) a transmitting frame having a plurality of signal
fields generated in a) and b) is transmitted.
In an exemplary transmitting method of an OFDM wireless LAN
according to another embodiment of the present invention, a) a
signal field is generated by using first bit allocation information
according to first OFDM modulation for an even-numbered time, b) a
signal field is generated by using second bit allocation
information according to second OFDM modulation performed by
cyclically moving each subcarrier position of first OFDM modulated
symbols by 1/2 of a fast Fourier transform (FFT) point, for an
odd-numbered time, and c) a transmitting frame having a plurality
of signal fields generated in a) and b) is transmitted.
In an exemplary receiving method of an OFDM wireless LAN according
to an embodiment of the present invention, a) a format
configuration of a received frame is determined to determine
whether a signal field of the frame is repeatedly generated, b) a
demodulation mode is selected according to a result determined in
a), c) a frame in which the signal field is not repeatedly
generated is demodulated according to the selected demodulation
mode, and d) a frame in which the signal field is repeatedly
generated is demodulated according to the selected demodulation
mode.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a block diagram of a conventional wireless
transmitting/receiving system.
FIG. 2 shows a diagram of a frame of a conventional wireless local
area network (LAN) configuration.
FIG. 3 shows a block diagram of a wireless LAN
transmitting/receiving system according to an exemplary embodiment
of the present invention.
FIG. 4 shows a detailed block diagram of a configuration of an OFDM
modulation controller and a frame generation controller shown in
FIG. 3.
FIG. 5 shows a detailed diagram of an OFDM demodulation controller
shown in FIG. 3.
FIG. 6 shows a diagram representing repeated OFDM symbols of the
wireless LAN transmitting system according to the exemplary
embodiment of the present invention.
FIG. 7 shows a diagram of a wireless local area network (LAN) frame
configuration according to the exemplary embodiment of the present
invention.
FIG. 8 shows a diagram representing a transmission method of the
wireless LAN transmission system according to the exemplary
embodiment of the present invention.
FIG. 9 shows a diagram representing a receiving method of the
wireless LAN receiving system according to the exemplary embodiment
of the present invention.
DETAILED DESCRIPTION OF THE EMBODIMENTS
In the following detailed description, only certain exemplary
embodiments of the present invention have been shown and described,
simply by way of illustration.
As those skilled in the art would realize, the described
embodiments may be modified in various different ways, all without
departing from the spirit or scope of the present invention.
Accordingly, the drawings and description are to be regarded as
illustrative in nature and not restrictive. Like reference numerals
designate like elements throughout the specification.
Throughout this specification and the claims which follow, unless
explicitly described to the contrary, the word "comprise" and
variations such as "comprises" or "comprising" will be understood
to imply the inclusion of stated elements but not the exclusion of
any other elements.
In addition, the word "module" will be understood to indicate a
unit for processing a predetermined function or operation, which
may be realized by hardware, software, or a combination
thereof.
An orthogonal frequency division multiplexing (OFDM) wireless local
area network (LAN) transmitting/receiving system for providing
expanded service coverage according to an exemplary embodiment of
the present invention, and a method thereof, will now be described
with reference to the figures.
FIG. 3 shows a block diagram of a wireless LAN
transmitting/receiving system according to the exemplary embodiment
of the present invention. The wireless LAN transmitting/receiving
system is based on OFDM-based IEEE 802.11a/g standards, and it may
be applied to the wireless LAN system according to an IEEE 802.11n
standard or IEEE standards to be further provided.
As shown in FIG. 3, the wireless LAN transmitting/receiving system
includes a media access control (MAC) layer 100, an OFDM modulation
controller 200, a frame generation controller 300, a buffer unit
400, an OFDM modulation unit 500, a radio frequency (RF)
transmitting unit 600, an RF receiving unit 700, an OFDM
demodulation controller 800, an equalizer 900, and an OFDM
demodulation unit 1000.
The OFDM modulation controller 200, the frame generation controller
300, the buffer unit 400, the OFDM modulation unit 500, and the RF
transmitting unit 600 form a transmitting system, and the RF
receiving unit 700, the OFDM demodulation controller 800, the
equalizer 900, and the OFDM demodulation unit 1000 form a receiving
system.
The media access control layer 100 generates a signal field
according to a control operation of the frame generation controller
300.
The OFDM modulation controller 200 differently allocates a
subcarrier to control modulating the OFDM symbol.
The frame generation controller 300 controls generation of a frame
including a signal field repeatedly generated according to the OFDM
symbol modulation in control of the OFDM modulation controller 200.
Here, sequential OFDM symbols are repeated to perform the OFDM
symbol modulation, and the subcarrier is differently allocated to
the same signal to achieve a diversity effect.
The buffer unit 400 stores input data including repeated OFDM
symbols according to a control operation of the OFDM modulation
controller 200. That is, mapped symbols are OFDM modulated to be
input to an inverse Fast Fourier transform unit, and the OFDM
symbol that is cyclically repeated for a subsequent time is
input.
According to the control operation of the OFDM modulation
controller 200, the OFDM modulation unit 500 repeatedly modulates
the OFDM symbols input from the buffer unit 400, forms the OFDM
symbols as a transmission frame, and transmits the transmission
frame.
Here, the OFDM modulation unit 500 may further include a
multiplexer MUX (not shown) for generating the transmission frame
by using the signal field generated according to a control
operation of the frame generation controller 300, and the OFDM
symbol is modulated according to control operations of the OFDM
symbol controller 200 and an inverse fast Fourier transform unit
for performing first and second OFDM modulations according to the
control operation of the OFDM symbol controller 200.
The OFDM demodulation controller 800 determines whether a received
frame includes repeatedly modulated OFDM symbols, and controls an
operation of a demodulation mode according to a determination
result.
The equalizer 900 performs an equalization operation for each
demodulation mode according to the determination result on whether
the received frame includes the repeatedly modulated OFDM symbols,
according to a control operation of the OFDM demodulation
controller 800. In this case, the respective OFDM symbols of the
received frame including the repeatedly modulated OFDM symbols may
be detected by using a maximal ratio combining method.
The OFDM demodulation unit 1000 demodulates the signal field of the
received frame for each demodulation mode determined according to
whether the received frame includes the repeatedly modulated OFDM
symbols, according to the control operation of the OFDM
demodulation controller 800.
FIG. 4 shows a detailed block diagram of a configuration of the
OFDM modulation controller 200 and the frame generation controller
300 shown in FIG. 3.
Referring to FIG. 4, the OFDM modulation controller 200 controls
the first OFDM modulation, and the second OFDM modulation for
changing subcarrier allocating positions of the first OFDM
modulated OFDM symbols. In this case, the first OFDM modulation is
performed for an even-numbered time. The second OFDM modulation is
performed for an odd-numbered time.
Here, the OFDM modulation controller 200 may separately include a
first OFDM modulation controller (not shown) and a second OFDM
modulation controller (not shown).
In this case, the first OFDM modulation controller performs the
first OFDM modulation for the even-numbered time.
The second OFDM modulation controller performs the second OFDM
modulation by cyclically moving a subcarrier allocation position by
1/2 of the first OFDM modulated symbol based on an FFT point, so as
to perform the second OFDM modulation. The second OFDM symbol
modulation will be later described in further detail with reference
to FIG. 6.
The frame generation controller 300 controls generation of a frame
including a plurality of signal fields generated according to the
first OFDM modulation and the second OFDM modulation. The frame
generation controller 300 includes a first bit allocation
controller 320, a second bit allocation controller 340, and a
signal field generation controller 360.
The first bit allocation controller 320 controls bit allocation
based on bit allocation information according to the first OFDM
modulation.
The second bit allocation controller 340 controls the bit
allocation based on bit allocation information according to the
second OFDM modulation. At this time, the bit allocation is
controlled by a 1/2 value of the bit allocation information
allocated by the first bit allocation controller 320.
The signal field generation controller 360 controls generation of
the plurality of signal fields according to each bit allocation
performed by the first bit allocation controller 320 and the second
bit allocation controller 340.
FIG. 5 shows a detailed diagram of the OFDM demodulation controller
800 shown in FIG. 3.
As shown in FIG. 5, the OFDM demodulation controller 800 includes a
mode information generating module 810, a first demodulation mode
control module 820, and a second demodulation mode control module
830.
The mode information generating module 810 generates demodulation
mode information according to the determined result on whether the
received frame includes the repeated signal fields.
The first demodulation mode control module 820 controls a
demodulation mode operation of the received frame by using the
demodulation mode information of the mode information generating
module 810 when the signal field is not repeatedly generated in the
received frame.
The second demodulation mode control module 830 controls the
demodulation operation of the received frame having the repeated
signal field by using the demodulation mode information of the mode
information generating module 810. In this case, the second
demodulation mode control module 830 demodulates the signal field
by using first and second bit allocation information. Data fields
are demodulated according to each signal field.
The second bit allocation information is obtained by cyclically
moving the FFT point of the subcarrier allocation by 1/2 of the
OFDM symbol (i.e., a value of the second bit allocation information
is half of that of the first bit allocation information).
The second demodulation mode control module 830 may further include
a 2-1 demodulation mode control module 832, and a 2-2 demodulation
mode control module 834.
The 2-1 demodulation mode control module 832 controls a
demodulation operation of the data field by using one demodulated
signal filed when the one signal field is successfully demodulated.
The data field demodulation may be controlled by demodulating the
signal field once more after the one signal field is
demodulated.
The 2-2 demodulation mode control module 834 controls the data
field demodulation according to the repetitive signal field
demodulation when the one signal field fails to be demodulated.
FIG. 6 shows a diagram representing the repeated OFDM symbols of
the wireless LAN transmitting system according to the exemplary
embodiment of the present invention.
In FIG. 6, the OFDM symbols are repeated to expand the coverage of
the wireless LAN.
In this case, since not only the OFDM symbol is repeated but also
the FFT point (N) is cyclically moved by 1/2 of the OFDM modulated
symbol when allocating the subcarrier of the two repeated symbols,
the diversity effect may be obtained.
A process for repeating the OFDM symbol will be described in
further detail. Firstly, an input OFDM symbol is transmitted for
the even-numbered time to form a first OFDM symbol modulation
sequence. Then, the OFDM symbol transmitted during the
even-numbered time is repeated, and a subcarrier location is
circulated by 1/2 of the FFT point to transmit the OFDM symbol,
which forms a second OFDM symbol modulation sequence. Accordingly,
a total data rate is reduced by half.
That is, data A1 to A52 and a pilot symbol are allocated to
subcarriers -26 to -1 and 1 to 26. Subsequently, in the next
repeated OFDM symbol, data A27 to A52 are allocated to subcarriers
-26 to -1, and data A1 to A26 are allocated to subcarriers 1 to
26.
The first and second OFDM symbol modulation sequences are allocated
to the subcarrier and are transmitted, and a receiving terminal
performs a maximal ratio combining operation to detect the first
and second OFDM symbol modulation sequences.
Accordingly, since a signal to noise ratio (SNR) of 3 dB due to the
repetition of the OFDM symbol and a diversity effect due to the
subcarrier allocation may be achieved, the transmission speed may
be reduced by half, but a service radius may be increased to 50% to
100%.
FIG. 7 shows a diagram of a wireless local area network (LAN) frame
configuration according to the exemplary embodiment of the present
invention.
As shown in FIG. 7, the wireless LAN frame configuration includes a
preamble period P100, a signal field period P200, and a data field
period P300.
A configuration of the preamble period P100 is the same as that of
the conventional wireless LAN frame shown in FIG. 2. However, the
signal field period P200 and the data field period P300 are
repeated. In the signal field period P200, the signal field is
repeated. When the signal field is not repeated, since receiving
sensitivity of the data field is improved but the receiving
sensitivity of the signal field is not improved, the coverage may
not be increased.
Here, data rate information of the signal field (i.e., a modulation
method and a code rate) is given as in Table 1.
TABLE-US-00001 TABLE 1 RATE (Mbps) R1-R4 New RATE (Mbps) R1-R4 6
1101 3 1100 9 1111 4.5 1110 12 0101 6 0100 18 0111 9 0110 24 1001
12 1000 36 1011 18 1010 48 0001 24 0000 54 0011 27 0010
A rate RATE on the left side of Table 1 corresponds to the first
bit allocation information of the second demodulation mode control
module 830, and a rate New RATE on the right side of Table 1
corresponds to the second bit allocation information of the second
demodulation mode control module 830.
Here 6, 9, 12, 18, 24, 36, 48, and 54 (Mbps) modes corresponding to
the rate on the left side of Table 1 correspond to the conventional
bit allocation information.
3, 4.5, 6, 9, 12, 18, 24, and 27 (Mbps) modes of the rate New RATE,
the same bits as the bits of the rate RATE, are allocated to R1 to
R3, and 0 is allocated on R4.
Since the bit allocation is newly defined, compatibility with the
conventional system may be provided.
The compatibility with the conventional system will now be
described.
That is, when receiving the frame having the format configuration
shown in FIG. 7 and obtaining the SNR for demodulating the frame,
the conventional wireless LAN system demodulates the signal field.
However, at this time, the conventional system does not process the
received frame since bit allocation information that is not used in
the conventional system is provided, and it waits until the frame
is completely received. Since the signal field is not demodulated
when receiving power is low, subsequent data may not be
demodulated.
Accordingly, the frame configuration shown in FIG. 7 may not affect
the operation of the conventional wireless LAN system, that is, it
may be compatible with the conventional system.
FIG. 8 shows a diagram representing a transmission method of the
wireless LAN transmission system according to the exemplary
embodiment of the present invention.
As shown in FIG. 8, it is determined in step S101 whether it is an
even-numbered time, and the first OFDM modulation is performed for
the even-numbered time in step S103.
The first bit allocation according to the first OFDM modulation is
performed in step S105.
The signal field according to the first bit allocation is generated
in step S107.
When it is determined in step S101 that it is an odd-numbered time,
the second OFDM modulation is performed for the odd-numbered time
in steps S109 and S111. Here, the second OFDM modulation is
performed by changing subcarrier allocation positions of the symbol
that is first OFDM modulated. In further detail, the second OFDM
modulation is performed by cyclically moving the subcarrier
positions of the first OFDM-modulated symbol by 1/2 of the FFT
point.
The second bit allocation according to the first OFDM modulation is
performed in step S113.
The signal field according to the second bit allocation is
generated in step S115.
A transmission frame including the plurality of signal fields
generated in steps S107 and S115 is formed and transmitted in step
S117.
FIG. 9 shows a diagram representing a receiving method of the
wireless LAN receiving system according to the exemplary embodiment
of the present invention.
As shown in FIG. 9, signal detection, synchronization, and
automatic gain control are performed in step S203 for a frame
received in step S201, and a channel is estimated in step S205.
A format configuration of the received frame is determined in step
S207. A demodulation mode of the frame in which the signal field is
not repeated, or a demodulation mode of the frame in which the
signal field is repeated, is selected according to a determined
result in step S207.
That is, according to the determined result in step S207, when it
is determined in step S209 that the OFDM symbol is not repeatedly
modulated in the frame, the signal field is demodulated in step
S211, and the data field is demodulated in step S213 by using the
demodulated signal field. That is, the demodulation is performed by
using a Legacy ratio format which is the rate RATE on the left side
of Table 1, and the data is transmitted to the MAC 100 in step
S231.
According to the determined result in step S207, when it is
determined in step S209 that the signal field is repeatedly
generated in the frame (i.e., the OFDM symbol is repeatedly
modulated), the signal field is demodulated in step S215.
It is determined in step S215 whether the signal field is
successfully demodulated. In this case, two demodulation methods
may be performed according to the determined result in step
S215.
That is, the signal field is successfully demodulated when the
demodulation is performed by one single signal field, and the
signal field is demodulated in step S219 by using a ratio format
which is the rate NEW RATE on the right side of Table 1. In this
case, the subsequent repeated signal field is ignored, the data
field is demodulated in an optimum ratio method, and the data are
transmitted to the MAC 100 in steps S221, S223, and S231.
To determine the signal field again, demodulation of two signal
fields (a first signal field and a second signal field) is
performed, and the data field is demodulated by using the
demodulated signal fields.
When a failure to demodulate the signal field occurs (i.e., the
demodulation may not be performed by one single signal field), the
repeated signal field is demodulated in step S225 by using the
ratio format which is the rate NEW RATE on the right side of Table
1.
The signal field is demodulated in an optimum ratio detection
method, the data field is demodulated by using the demodulated
signal field, and the demodulated data field is transmitted to the
MAC 100 in steps S227, S229, and S231.
The above-described methods and apparatuses are not only realized
by the exemplary embodiment of the present invention, but, on the
contrary, are intended to be realized by a program for realizing
functions corresponding to the configuration of the exemplary
embodiment of the present invention or a recording medium for
recording the program.
While this invention has been described in connection with what is
presently considered to be practical exemplary embodiments, it is
to be understood that the invention is not limited to the disclosed
embodiments, but, on the contrary, is intended to cover various
modifications and equivalent arrangements included within the
spirit and scope of the appended claims.
According to the exemplary embodiment of the present invention,
service coverage may be increased while maintaining compatibility
with the conventional wireless LAN system
Compared to using a high power amplifier or a high gain sector
antenna, a method for transmitting a signal by repeatedly
modulating the signal according to the exemplary embodiment of the
preset invention has a cost reduction effect, and further, when the
method according to the exemplary embodiment and the high power
amplifier or the high gain sector antenna are used together, the
cost reduction effect is further improved.
* * * * *