(19) United States
`(12) Patent Application Publication (10) Pub. No.: US 2007/0115802 A1
`(43) Pub. Date:
`May 24, 2007
`Yu et al.
`
`US 200701 15802A1
`
`(54) TRANSMITTING AND RECEIVING
`SYSTEMIS FOR INCREASING SERVICE
`COVERAGE IN ORTHOGONAL
`FREQUENCY DIVISION MULTIPLEXING
`WIRELESS LOCAL AREA NETWORK, AND
`METHOD THEREOF
`
`(76) Inventors: Hee-Jung Yu, Daejeon-city (KR):
`Eun-Young Choi, Daejeon-city (KR);
`Chan-Ho Yoon, Seoul (KR); Jung-Bo
`Son, Masan-city (KR); Il-Gu Lee,
`Seoul (KR); Deuk-Su Lyu,
`Daejeon-city (KR); Tae-hyun Jeon,
`Sungnam-city (KR); Seung-Wook Min,
`Seoul (KR); Sok-Kyu Lee,
`Daejeon-city (KR); Seung-Chan Bang,
`Daejeon-city (KR); Seung-Ku Hwang,
`Daejeon-city (KR)
`Correspondence Address:
`LADAS & PARRY LLP
`224 SOUTH MICHGANAVENUE
`SUTE 16OO
`CHICAGO, IL 60604 (US)
`(21) Appl. No.:
`11/635,927
`
`(22) Filed:
`(30)
`
`Dec. 8, 2006
`Foreign Application Priority Data
`
`Sep. 12, 2005 (KR)............................ 10-2005-0120849
`Feb. 6, 2006 (KR)............................ 10-2006-0049871
`
`Publication Classification
`
`(51) Int. Cl.
`(2006.01)
`H04 II/00
`(52) U.S. Cl. .............................................................. 370/208
`
`(57)
`
`ABSTRACT
`
`The present invention relates to an orthogonal frequency
`division multiplexing wireless local area network (LAN)
`transmitting/receiving system for providing expanded Ser
`Vice coverage, and a method thereof. According to the
`present invention, first OFDM modulation is performed for
`an even-numbered time, and second OFDM modulation is
`performed by changing Subcarrier allocation positions of
`first OFDM modulated symbols for an odd-numbered time.
`In addition, a transmitting frame including a plurality of
`signal fields according to the first and second OFDM modu
`lation is transmitted. The receiving system determines a
`format configuration of the received frame to determine
`whether a signal field is repeatedly generated in the frame.
`When it is determined that the signal field is not repeatedly
`generated, corresponding demodulation is performed. When
`it is determined that the signal field is repeatedly performed,
`the signal field is demodulated by using first bit allocation
`information and is demodulated by using second bit alloca
`tion information having a 1/2 value of the first bit allocation
`information. A data field is demodulated according to the
`demodulated signal field.
`
`200
`
`assassessessessed
`
`OFDM modulation controller
`
`
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`300
`
`First bit allocation
`controller
`
`Second bit allocation
`controle
`
`Frame
`generation
`controster
`
`Signal field generation
`controller
`
`INTEL-1014
`10,079,707
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`Patent Application Publication May 24, 2007 Sheet 1 of 9
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`Patent Application Publication May 24, 2007 Sheet 6 of 9
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`Patent Application Publication May 24, 2007 Sheet 7 of 9
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`Patent Application Publication May 24, 2007 Sheet 9 of 9
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`US 2007/0115802 A1
`
`May 24, 2007
`
`TRANSMITTING AND RECEIVING SYSTEMIS FOR
`INCREASING SERVICE COVERAGE IN
`ORTHOGONAL FREQUENCY DIVISION
`MULTIPLEXING WIRELESS LOCAL AREA
`NETWORK, AND METHOD THEREOF
`
`CROSS-REFERENCE TO RELATED
`APPLICATION
`0001. 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
`0002) (a) Field of the Invention
`0003. 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.
`0004 (b) Description of the Related Art
`0005 Recently, in addition to providing an Internet ser
`Vice 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 appli
`cations using the wireless LAN have been rapidly devel
`oped.
`0006 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.
`0007. A configuration of the wireless LAN system
`according to the IEEE 802.11a standard will now be
`described with reference to FIG. 1.
`0008 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 fre
`quency (RF) bandwidth by an RF transmitting unit 33, and
`are transmitted through an antenna.
`0009. A signal received through an antenna and attenu
`ated to a baseband signal by a radio frequency (RF) receiv
`ing unit 35 is converted into a digital signal by an analog to
`digital ((A/D) converter 37. A signal detection and synchro
`nization unit 39 detects and synchronizes time and fre
`
`quency 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, depunctur
`ing, Viterbi decoding, and descrambling processes)
`0010. 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.
`0011. Here, the preamble period P10 includes a short
`preamble and a long preamble.
`0012. The short preamble is used for performing frame
`synchronization and coarse frequency synchronization after
`performing signal detection and automatic gain control.
`0013 The long preamble is used for performing fine
`frequency synchronization and channel estimation of each
`subcarrier.
`0014) 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.
`00.15
`Accordingly, the signal field is firstly demodulated
`to extract the transmission mode and frame length informa
`tion, 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.
`0016 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., cover
`age for the conventional wireless LAN system) have been
`actively pursued.
`0017. However, since the wireless LAN system problem
`atically has narrow service coverage, the service radius in a
`wireless LAN of IEEE 802.11a/g is approximately 100 m.
`0018. 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.
`0019 However, this may increase the system manufac
`turing cost, and power consumption in a portable terminal
`may be increased.
`0020. The above information disclosed in this Back
`ground 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
`0021. 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.
`0022. 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.
`
`

`

`US 2007/0115802 A1
`
`May 24, 2007
`
`0023. An exemplary transmitting system of an orthogo
`nal 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 modu
`lated OFDM symbol as a frame according to a control
`operation of the frame generation controller, and transmits
`the frame.
`0024. An exemplary transmitting system of an OFDM
`wireless LAN according to another embodiment of the
`present invention includes a first OFDM modulation con
`troller, a second OFDM modulation controller, a frame
`generation controller, a buffer unit, and an OFDM modula
`tion 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 sub
`carrier allocation position of each first OFDM symbol by /
`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 modu
`lation 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.
`0025. An exemplary receiving system of an OFDM wire
`less LAN according to an embodiment of the present inven
`tion includes an OFDM demodulation controller, an equal
`izer, 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 accord
`ing 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
`0026.
`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 per
`formed 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.
`0027. 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 modu
`lation for an even-numbered time, b) a signal field is
`generated by using second bit allocation information accord
`ing to second OFDM modulation performed by cyclically
`moving each subcarrier position of first OFDM modulated
`symbols by % 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.
`0028. 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 demodu
`lated according to the selected demodulation mode.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`0029 FIG. 1 shows a block diagram of a conventional
`wireless transmitting/receiving system.
`0030 FIG. 2 shows a diagram of a frame of a conven
`tional wireless local area network (LAN) configuration.
`0031
`FIG. 3 shows a block diagram of a wireless LAN
`transmitting/receiving system according to an exemplary
`embodiment of the present invention.
`0032 FIG. 4 shows a detailed block diagram of a con
`figuration of an OFDM modulation controller and a frame
`generation controller shown in FIG. 3.
`0033 FIG. 5 shows a detailed diagram of an OFDM
`demodulation controller shown in FIG. 3.
`0034 FIG. 6 shows a diagram representing repeated
`OFDM symbols of the wireless LAN transmitting system
`according to the exemplary embodiment of the present
`invention.
`0035 FIG. 7 shows a diagram of a wireless local area
`network (LAN) frame configuration according to the exem
`plary embodiment of the present invention.
`0036 FIG. 8 shows a diagram representing a transmis
`sion method of the wireless LAN transmission system
`according to the exemplary embodiment of the present
`invention.
`0037 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
`0038. In the following detailed description, only certain
`exemplary embodiments of the present invention have been
`shown and described, simply by way of illustration.
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`US 2007/0115802 A1
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`May 24, 2007
`
`0039. 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.
`0040 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.
`0041. Throughout this specification and the claims which
`follow, unless explicitly described to the contrary, the word
`“comprise' and variations such as "comprises' or “compris
`ing will be understood to imply the inclusion of stated
`elements but not the exclusion of any other elements.
`0042. 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.
`0043. 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.
`0044 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 stan
`dard or IEEE standards to be further provided.
`0045. As shown in FIG. 3, the wireless LAN transmit
`ting/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 demodula
`tion unit 1000.
`0046) 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.
`0047 The media access control layer 100 generates a
`signal field according to a control operation of the frame
`generation controller 300.
`0048. The OFDM modulation controller 200 differently
`allocates a subcarrier to control modulating the OFDM
`symbol.
`0049. The frame generation controller 300 controls gen
`eration of a frame including a signal field repeatedly gen
`erated 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.
`0050. 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.
`0051. 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.
`0.052
`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 accord
`ing to control operations of the OFDM symbol controller
`200 and an inverse fast Fourier transform unit for perform
`ing first and second OFDM modulations according to the
`control operation of the OFDM symbol controller 200.
`0053) The OFDM demodulation controller 800 deter
`mines whether a received frame includes repeatedly modu
`lated OFDM symbols, and controls an operation of a
`demodulation mode according to a determination result.
`0054 The equalizer 900 performs an equalization opera
`tion for each demodulation mode according to the determi
`nation result on whether the received frame includes the
`repeatedly modulated OFDM symbols, according to a con
`trol 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.
`0055. 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, accord
`ing to the control operation of the OFDM demodulation
`controller 800.
`0056 FIG. 4 shows a detailed block diagram of a con
`figuration of the OFDM modulation controller 200 and the
`frame generation controller 300 shown in FIG. 3.
`0057 Referring to FIG. 4, the OFDM modulation con
`troller 200 controls the first OFDM modulation, and the
`second OFDM modulation for changing subcarrier allocat
`ing 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.
`0.058
`Here, the OFDM modulation controller 200 may
`separately include a first OFDM modulation controller (not
`shown) and a second OFDM modulation controller (not
`shown).
`0059. In this case, the first OFDM modulation controller
`performs the first OFDM modulation for the even-numbered
`time.
`0060. The second OFDM modulation controller performs
`the second OFDM modulation by cyclically moving a
`subcarrier allocation position by % of the first OFDM
`modulated symbol based on an FFT point, so as to perform
`
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`

`US 2007/0115802 A1
`
`May 24, 2007
`
`the second OFDM modulation. The second OFDM symbol
`modulation will be later described in further detail with
`reference to FIG. 6.
`0061 The frame generation controller 300 controls gen
`eration 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.
`0062) The first bit allocation controller 320 controls bit
`allocation based on bit allocation information according to
`the first OFDM modulation.
`0063. The second bit allocation controller 340 controls
`the bit allocation based on bit allocation information accord
`ing to the second OFDM modulation. At this time, the bit
`allocation is controlled by a /2 value of the bit allocation
`information allocated by the first bit allocation controller
`32O.
`0064. 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.
`0065 FIG. 5 shows a detailed diagram of the OFDM
`demodulation controller 800 shown in FIG. 3.
`0066. As shown in FIG. 5, the OFDM demodulation
`controller 800 includes a mode information generating mod
`ule 810, a first demodulation mode control module 820, and
`a second demodulation mode control module 830.
`0067. The mode information generating module 810 gen
`erates demodulation mode information according to the
`determined result on whether the received frame includes
`the repeated signal fields.
`0068 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.
`0069. The second demodulation mode control module
`830 controls the demodulation operation of the received
`frame having the repeated signal field by using the demodu
`lation 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.
`0070 The second bit allocation information is obtained
`by cyclically moving the FFT point of the subcarrier allo
`cation by /3 of the OFDM symbol (i.e., a value of the second
`bit allocation information is half of that of the first bit
`allocation information).
`0071. 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.
`0072 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.
`0073. The 2-2 demodulation mode control module 834
`controls the data field demodulation according to the repeti
`tive signal field demodulation when the one signal field fails
`to be demodulated.
`0074 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.
`0075). In FIG. 6, the OFDM symbols are repeated to
`expand the coverage of the wireless LAN.
`0076.
`In this case, since not only the OFDM symbol is
`repeated but also the FFT point (N) is cyclically moved by
`% of the OFDM modulated symbol when allocating the
`subcarrier of the two repeated symbols, the diversity effect
`may be obtained.
`0077. 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 /3 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.
`0078 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.
`0079. The first and second OFDM symbol modulation
`sequences are allocated to the Subcarrier and are transmitted,
`and a receiving terminal performs a maximal ratio combin
`ing operation to detect the first and second OFDM symbol
`modulation sequences.
`0080 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%.
`0081
`FIG. 7 shows a diagram of a wireless local area
`network (LAN) frame configuration according to the exem
`plary embodiment of the present invention.
`0082) 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.
`0083) 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.
`0084. Here, data rate information of the signal field (i.e.,
`a modulation method and a code rate) is given as in Table 1.
`
`

`

`US 2007/0115802 A1
`
`May 24, 2007
`
`TABLE 1.
`
`RATE (Mbps)
`
`R1-R4
`
`New
`RATE (Mbps)
`
`R1-R4
`
`6
`9
`12
`18
`24
`36
`48
`S4
`
`1101
`1111
`O101
`O111
`1001
`1011
`OOO1
`OO11
`
`3
`4.5
`6
`9
`12
`18
`24
`27
`
`1100
`1110
`O1 OO
`O110
`1OOO
`1010
`OOOO
`OO10
`
`0085. A rate RATE on the left side of Table 1 corresponds
`to the first bit allocation information of the second demodu
`lation 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.
`0086). Here 6, 9, 12, 18, 24, 36,48, and 54 (Mbps) modes
`corresponding to the rate on the left side of Table 1 corre
`spond to the conventional bit allocation information.
`0087 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.
`0088 Since the bit allocation is newly defined, compat
`ibility with the conventional system may be provided.
`0089. The compatibility with the conventional system
`will now be described.
`0090 That is, when receiving the frame having the for
`mat 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 demodu
`lated when receiving power is low, Subsequent data may not
`be demodulated.
`0091. 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.
`0092 FIG. 8 shows a diagram representing a transmis
`sion method of the wireless LAN transmission system
`according to the exemplary embodiment of the present
`invention.
`0093. 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.
`0094) The first bit allocation according to the first OFDM
`modulation is performed in step S105.
`0.095 The signal field according to the first bit allocation
`is generated in step S107.
`0096] When it is determined in step S101 that it is an
`odd-numbered time, the second OFDM modulation is per
`formed for the odd-numbered time in steps S109 and S111.
`
`Here, the second OFDM modulation is performed by chang
`ing 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 /3 of the
`FFT point.
`0097. The second bit allocation according to the first
`OFDM modulation is performed in step S113.
`0098. The signal field according to the second bit allo
`cation is generated in step S115.
`0099. A transmission frame including the plurality of
`signal fields generated in steps S107 and S115 is formed and
`transmitted in step S117.
`0.100
`FIG. 9 shows a diagram representing a receiving
`method of the wireless LAN receiving system according to
`the exemplary embodiment of the present invention.
`0101. As shown in FIG. 9, signal detection, synchroni
`Zation, and automatic gain control are performed in step
`S203 for a frame received in step S201, and a channel is
`estimated in step S205.
`0102) 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.
`0103) 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.
`0104. According to the determined result in step S207,
`when it is determined in step S