(19) United States
`(12) Patent Application Publication (10) Pub. No.: US 2004/0037215 Al
`
`
`US 20040037215A1
`
`(54) ORTHOGONAL FREQUENCY DIVISION
`MULTIPLEXING COMMUNICATION
`METHOD AND APPARATUS ADAPTED TO
`CHANNEL CHARACTERISTICS
`
`(75) Inventors: Chan-Soo Hwang, Yongin-city (KR);
`Yung-Soo Kim, Seongnam-city (KR)
`
`Correspondence Address:
`Paul J. Farrell, Esq.
`DILWORTH & BARRESE, LLP
`333 Earle Ovington Blvd.
`Uniondale, NY 11553 (US)
`
`(73) Assignee: SAMSUNG ELECTRONICS CO.,
`LTD., KYUNGKI-DO (KR)
`
`(21) Appl. No. (cid:9)
`
`10/606,430
`
`(22) Filed:
`
`Jun. 25, 2003
`
`(30) (cid:9)
`
`Foreign Application Priority Data
`
`Jul. 29, 2002 (cid:9)
`
`(KR) .................................. 2002-0044630
`
`Publication Classification
`
`Int. Cl.. ...................................................... H04J 11/00
`(51)
`(52) U.S. Cl . (cid:9)
`.............................................................. 370/203
`
`(57) (cid:9)
`
`ABSTRACT
`
`An orthogonal frequency division multiplexing (OFDM)
`communication method and apparatus adapted to channel
`characteristics are provided. The OFDM communication
`method includes changing at least one of a length of a
`transmission symbol, a format of a frame, and a format of
`the transmission symbol depending on a type of the trans-
`mission symbol and a radius of a cell, in which communi-
`cation is performed. The OFDM communication apparatus
`includes a symbol inspector, for inspecting a type of a
`transmission symbol and outputting the result of the inspec-
`tion as a first control signal, and a symbol and format
`converter, for changing at least one of a length of a trans-
`mission symbol, a format of a frame, and a format of the
`transmission symbol in response to the first control signal
`and a radius of a cell, in which communication is performed.
`
`START
`
`0
`
`YES
`
`IS TRANSMISSION ;
`A SYMBOL USED FOR
`~CHANNEL?
`
`IS CELL (cid:9)
`RADIUS GREATER
`THAN FIRST PREDETERMINE
`VALUE?
`
`14
`
`YES
`
`NO
`
`1 B
`
`IS CELL (cid:9)
`RADIUS GREATER
`THAN SECOND PREDETERMINED
`VALUE?
`
`YES
`
`12 (cid:9)
`
`22
`
`NO
`
`20
`
`16
`
`DETERMINE FIRST SYMBOL (cid:9)
`AS TRANSMISSION SYMBOL (cid:9)
`
`DETERMINE FIFTH SYMBOL
`AS TRANSMISSION SYMBOL
`
`DETERMINE FOURTH SYMBOL I I DETERMINE SECOND OR THIRD
`AS TRANSMISSION SYMBOL (cid:9)
`SYMBOL AS TRANSMISSION SYMBi
`
`END
`
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`(cid:9)
`(cid:9)
`

`

`00
`
`b
`
`SYMBOL AS TRANSMISSION SYMBOL
`
`DETERMINE SECOND OR THIRD
`
`AS TRANSMISSION SYMBOL
`DETERMINE FOURTH SYMBOL
`
`AS TRANSMISSION SYMBOL
`DETERMINE FIFTH SYMBOL
`
`AS TRANSMISSION SYMBOL
`DETERMINE FIRST SYMBOL
`
`END
`
`16
`
`20
`
`YES
`
`YES
`
`NO
`
`22
`
`12
`
`THAN SECOND PREDETERMINED
`
`VALUE?
`
`1 B
`
`RADIUS GREATER (cid:9)
`
`IS CELL (cid:9)
`
`NO
`
`THAN FIRST PREDETERMINE
`
`VALUE?
`
`14
`
`RADIUS GREATER
`
`IS CELL (cid:9)
`
`NO
`
`A SYMBOL USED FOR CONTROL
`
`CHANNEL?
`
`IS TRANSMISSION SYMBOL—
`10
`
`
`
`YES
`
`START
`
`FIG. 1
`
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`Patent Application Publication Feb. 26, 2004 Sheet 2 of 8
`
`US 2004/0037215 Al
`
`FIG. 2
`
`40
`
`42 44 46
`
`48
`
`50 (cid:9)
`
`52
`
`54 56 58
`
`A E D (cid:9)
`
`B
`
`L
`
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`(cid:9)
`(cid:9)
`(cid:9)
`(cid:9)
`(cid:9)
`

`

`END
`
`INTO PICO FORMAT
`
`INTO MICRO FORMAT
`
`CONVERT FORMAT OF FRAME
`
`CONVERT FORMAT OF FRAME
`
`INTO MACRO FORMAT
`
`CONVERT FORMAT OF FRAME
`
`FA
`
`NO
`
`~
`76
`
`YES (cid:9)
`
`VLUE?
`
`ECOND PREDETERMINED
`RADIUS GREATER THAN
`
`IS CELL \~
`
`74
`
`70
`
`NO
`
`VALUE?
`
`FRIST PREDETERMINED
`RADIUS GREATER THAN
`IS CELL —<
`
`START
`
`FIG. 3
`
`72
`
`YES (cid:9)
`
`b
`
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`Patent Application Publication Feb. 26, 2004 Sheet 4 of 8
`
`US 2004/0037215 Al
`
`FIG. 4
`
`90
`
`FIRST (cid:9)
`
`THIRD (cid:9)
`
`SYMBOL I SYMBOL I SYMBOL I SYMBOL
`
`THIRD
`
`FIRST
`SECOND (cid:9)
`SYMBOL ISYMBOLI
`
`FIG. 5
`
`92
`
`I SYMBOLI SYMBOL I
`
`SYMBOL I
`
`FOURTH FIRST
`FOURTH (cid:9)
`SYMBOL SYMBO ISYMBOLI
`
`FIG. 6
`
`94
`
`FIRST (cid:9)
`
`FIFTH (cid:9)
`
`SYMBOL( SYMBOL I SYMBOL I (cid:9)
`
`FIFTH (cid:9)
`
`FIFTH (cid:9)
`
`I SYMBOL I SYMBOL
`
`FIFTH (cid:9)
`
`I
`
`FIRST
`SYMBOL
`
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`Patent Application Publication Feb. 26, 2004 Sheet 5 of 8 (cid:9)
`
`US 2004/0037215 Al
`
`FIG. 7
`
`START
`
`IS CHANNEL
`CHANGE SPEED FASTER (cid:9)
`THAN PREDETERMINED
`SPEED?
`
`114 (cid:9)
`
`YES
`
`110
`
`NO
`
`112
`
`DETERMINE SECOND SYMBOL
`AS TRANSMISSION SYMBOL
`
`DETERMINE THIRD SYMBOL (cid:9)
`AS TRANSMISSION SYMBOL (cid:9)
`
`I..' (cid:9)
`
`END
`
`FIG. 8
`
`I
`
`34
`
`32
`
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`(cid:9)
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`

`Patent Application Publication Feb. 26, 2004 Sheet 6 of 8 (cid:9)
`
`US 2004/0037215 Al
`
`FIG. 9
`
`CP
`
`TRANSMISSION DATA
`
`(cid:9) CS
`
`-1- (cid:9)
`150 156 (cid:9)
`
`L.
`152 154
`
`FIG. 10
`
`170 (cid:9)
`
`172 (cid:9)
`
`174 (cid:9)
`
`176
`
`FIG. 11
`
`190 (cid:9)
`
`192 (cid:9)
`
`194 (cid:9)
`
`196
`
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`Patent Application Publication Feb. 26, 2004 Sheet 7 of 8 (cid:9)
`
`US 2004/0037215 Al
`
`FIG. 12
`
`210 (cid:9)
`
`212
`
`SYMBOL (cid:9)
`INSPECTOR (cid:9)
`
`Cl SYMBOL AND
`FORMAT (cid:9)
`CONVERTER
`
`OUT1
`
`Ni (cid:9)
`
`IN2
`
`FIG. 13
`
`212A
`
`230 (cid:9)
`
`1 (cid:9)
`
`234
`
`OUT2
`C1
`FR 1ST (cid:9)
`SECOND (cid:9)
`C2 (cid:9)
`FIRST (cid:9)
`IN3 COMPARATOR COMPARATOR CONVERTER
`C3
`
`232-
`
`FIG. 14
`
`212B
`
`250 (cid:9)
`
`I (cid:9)
`
`252 (cid:9)
`
`254
`
`L (cid:9)
`THIRD (cid:9)
`IN4-~
`COMPARATOR C4
`
`FOURTH (cid:9)
`COMPARATOR (cid:9)
`
`C5
`
`
`ER UTS
`CONVERTER O
`
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`(cid:9)
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`(cid:9)
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`

`Patent Application Publication Feb. 26, 2004 Sheet 8 of 8 (cid:9)
`
`US 2004/0037215 Al
`
`FIG. 15
`
`270 (cid:9)
`
`272
`
`C2_
`C2
`H
`
`FIFTH C6
`COMPARATOR (cid:9)
`
`FORMAT
`CONVERTER (cid:9)
`
`OUT2
`
`FIG. 16
`
`1
`
`7 (cid:9)
`
`12 (cid:9)
`
`17 (cid:9)
`
`22
`
`Li1~
`
`---------------------------------------------------------------
`
`m
`w
`
`0.01
`
`0.001
`
`1
`
`Eb/NO
`
`FIG. 17
`
`7 (cid:9)
`
`12 (cid:9)
`
`17 (cid:9)
`
`22
`
`0.1
`
`---------------------------------------------------------------
`
`Ir
`w m
`
`0.01
`
`0.001
`
`Eb/NO
`
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`

`US 2004/0037215 Al
`
`Feb. 26, 2004
`
`ORTHOGONAL FREQUENCY DIVISION
`MULTIPLEXING COMMUNICATION METHOD
`AND APPARATUS ADAPTED TO CHANNEL
`CHARACTERISTICS
`
`CROSS-REFERENCE TO RELATED
`APPLICATIONS
`[0001] This application claims the priority of Korean
`Patent Application No. 2002-44630, filed on Jul. 29, 2002,
`which is incorporated herein in its entirety by reference.
`
`BACKGROUND OF THE INVENTION
`[0002] 1. Field of the Invention
`[0003] The present invention relates to orthogonal fre-
`quency division multiplexing (OFDM) communication, and
`more particularly, to an OFDM communication method and
`apparatus adapted to channel characteristics.
`[0004] 2. Description of the Related Art
`[0005] With a variety of environments in which a com-
`munication method is used, the communication method is
`required to be effective even if Doppler frequency or delay
`spread changes. However, since an optimum physical layer
`varies with channel change speed and delay spread, it is
`difficult to efficiently support a communication method
`using a single physical layer. Accordingly, a hierarchical cell
`including a variety of cells is used in a single communication
`method.
`[0006] When using such a hierarchical cell, channels for
`users corresponding to different layers have different char-
`acteristics. For example, when a cell has a large radius, delay
`spread is long, and a channel change speed is fast. Accord-
`ingly, if the same modulation method is applied to different
`layers, a communication method cannot be adapted to the
`channel characteristics. In order to overcome this problem,
`a conventional communication method uses OFDM when
`the channel change speed is slow and uses code division
`multiple access (CDMA) when the channel change speed is
`fast. As described above, when using the conventional
`communication method, two modems of different types need
`to be provided for a terminal. Accordingly, the conventional
`communication method increases the complexity of trans-
`mitter and receiver of a terminal. In addition, since signals
`having different spectrum characteristics are used, the con-
`ventional communication method is difficult to develop, and
`radio resource management such as handover and associa-
`tion is difficult.
`
`SUMMARY OF THE INVENTION
`
`[0007] The present invention provides an orthogonal fre-
`quency division multiplexing (OFDM) communication
`method through which at least one of the length of a
`transmission symbol, the format of a transmission symbol,
`and the format of a frame is changed to adapt to channel
`characteristics such as channel change speed and channel
`spread.
`[0008] The present invention also provides an OFDM
`communication apparatus for performing the OFDM com-
`munication method adapted to the channel characteristics.
`[0009] According to an aspect of the present invention,
`there is provided an OFDM communication method adapted
`
`to channel characteristics, including changing at least one of
`a length of a transmission symbol, a format of a frame, and
`a format of the transmission symbol depending on a type of
`the transmission symbol and a radius of a cell, in which
`communication is performed.
`[0010] According to another aspect of the present inven-
`tion, there is provided an OFDM communication apparatus
`adapted to channel characteristics, including a symbol
`inspector, which inspects a type of a transmission symbol
`and outputs the result of the inspection as a first control
`signal; and a symbol and format converter, which changes at
`least one of a length of a transmission symbol, a format of
`a frame, and a format of the transmission symbol in response
`to the first control signal and a radius of a cell, in which
`communication is performed.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`[0011] The above and other features and advantages of the
`present invention will become more apparent by describing
`in detail preferred embodiments thereof with reference to the
`attached drawings in which:
`[0012] FIG. 1 is a flowchart of an orthogonal frequency
`division multiplexing (OFDM) communication method
`adapted to channel characteristics according to a first
`embodiment of the present invention;
`[0013] FIG. 2 is a diagram showing an example of a single
`frame including symbols having various lengths;
`[0014] FIG. 3 is a flowchart of an OFDM communication
`method adapted to channel characteristics according to a
`second embodiment of the present invention;
`[0015] FIG. 4 is a diagram showing an example of a
`macro format;
`[0016] FIG. 5 is a diagram showing an example of a micro
`format;
`[0017] FIG. 6 is a diagram showing an example of a pico
`format;
`[0018] FIG. 7 is a flowchart of an embodiment of step 16
`shown in FIG. 1 according to the present invention;
`[0019] FIG. 8 is a diagram showing a hierarchical cell
`structure;
`[0020] FIG. 9 is a diagram showing an example of a usual
`multiplex carrier wave transmission symbol;
`[0021] FIG. 10 is a diagram showing another example of
`a usual multiplex carrier wave transmission symbol;
`[0022] FIG. 11 is a diagram showing still another example
`of a usual multiplex carrier wave transmission symbol;
`[0023] FIG. 12 is a block diagram of an OFDM commu-
`nication apparatus for performing an OFDM communication
`method of the present invention, according to an embodi-
`ment of the present invention;
`[0024] FIG. 13 is a block diagram of an embodiment of a
`symbol and format converter shown in FIG. 12;
`[0025] FIG. 14 is a block diagram of another embodiment
`of the symbol and format converter shown in FIG. 12;
`[0026] FIG. 15 is a block diagram of a first converter
`shown in FIG. 13;
`
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`US 2004/0037215 Al
`
`Feb. 26, 2004
`
`2
`
`[0027] FIG. 16 is a graph showing changes in a bit error
`rate with respect to changes in Doppler frequency; and
`
`[0028] FIG. 17 is a graph showing changes in a bit error
`rate with respect to changes in the number of carrier waves.
`
`DETAILED DESCRIPTION OF THE
`INVENTION
`
`[0029] Hereinafter, preferred embodiments of an orthogo-
`nal frequency division multiplexing (OFDM) communica-
`tion method to adapt to channel characteristics according to
`the present invention will be described in detail with refer-
`ence to the attached drawings. In an OFDM communication
`method to adapt to channel characteristics according to the
`present invention, at least one of the length of a transmission
`symbol, the format of a frame, and the format of a trans-
`mission symbol is changed depending on a type of trans-
`mission symbol and the radius of a cell, in which commu-
`nication is performed.
`
`[0030] Channel variation is usually measured in terms of
`Doppler frequency multiplied by the length of an OFDM
`symbol, denoted as fdTs (fd: Doppler frequency in Hz, Ts;
`symbol duration in seconds). When fdTs is less than 0.01,
`the effect of channel variation on the detection performance
`is negligible. However, when fdTs becomes greater than
`0.01, the effect becomes noticeable. Generally speaking, a
`fast channel change speed is when fdTs is greater than 0.01,
`though this is not a hard and fast rule.
`
`[0031] Likewise, the channel length is measured by the
`delay spread of a channel, which is the time delay incurred
`from when the first signal components arrive at the receiver
`to when the last signal components arrive at the receiver. For
`example, if the last signal arrives at the receiver 0.01
`seconds after the first signal arrived at the receiver, the
`length of the channel is 0.01 seconds. A long, medium or
`short channel is a relative measure utilized in the industry to
`describe this relative channel length. For example, if the
`default symbol length is 0.1 msec, a 0.1-msec channel is
`considered to be a long channel, a 0.01-msec channel is
`considered to be a medium channel, and a 0.001-msec is
`considered to be a short channel. In other words, when the
`length of a channel, divided by the length of the default
`OFDM symbol, is more than 10%, it is considered to be a
`long channel.
`
`[0032] FIG. 1 is a flowchart of an OFDM communication
`method to adapt to channel characteristics according to a
`first embodiment of the present invention. The OFDM
`communication method according to the first embodiment
`includes determining the length of a transmission symbol
`depending on a type of transmission symbol and a cell radius
`(steps 10 through 22).
`
`[0033] FIG. 2 is a diagram showing an example of a single
`frame 40, in which symbols having various lengths are
`mixed. The single frame 40 includes first symbols 42 and 44,
`second symbols 50 and 52, third symbols 54, 56, 58, and 60,
`a fourth symbol 48, and a fifth symbol 46.
`
`[0034] In the OFDM communication method according to
`the first embodiment of the present invention shown in FIG.
`1, the length of a transmission symbol is changed depending
`on a type of transmission symbol and the radius of a cell, in
`which communication is performed.
`
`[0035] More specifically, it is determined whether a trans-
`mission symbol is a symbol that is used for a control channel
`in step 10. If it is determined that the transmission symbol
`is the symbol that is used for the control channel, the first
`symbol 42 or 44 shown in FIG. 2 is determined as the
`transmission symbol in step 12. The first symbol 42 or 44
`contains control information and has a length A. In other
`words, if it is determined that the transmission symbol is the
`symbol that is used for the control channel, the length of the
`transmission symbol is set to A. As described above, when
`a large amount of data is not necessary or when it is
`necessary to finely divide time, as in random access or
`control, the relatively short length A is determined as the
`length of a transmission symbol.
`
`[0036]
`If it is determined that the transmission symbol is
`not the symbol that is used for the control channel, it is
`determined whether a cell radius is greater than a first
`predetermined value in step 14. If it is determined that the
`cell radius is greater than the first predetermined value, the
`second symbol 50 or 52 or the third symbol 54, 56, 58, or
`60 shown in FIG. 2 is determined as the transmission
`symbol in step 16. The second symbol 50 or 52 has a length
`B and is suitable to channel characteristics, in which a
`channel change speed is slow and the length of a channel is
`long. The third symbol 54, 56, 58, or 60 has a length C and
`is suitable to channel characteristics, in which a channel
`change speed is fast and the length of a channel is long or
`short. In other words, if it is determined that the cell radius
`is greater than the first predetermined value, the length of the
`transmission symbol is set to B or C.
`
`[0037] However, if it is determined that the cell radius is
`not greater than the first predetermined value, it is deter-
`mined whether the cell radius is greater than a second
`predetermined value in step 18. Here, the second predeter-
`mined value is less than the first predetermined value. If it
`is determined that the cell radius is greater than the second
`predetermined value, the fourth symbol 48 shown in FIG. 2
`is determined as the transmission symbol in step 20. The
`fourth symbol 48 has a length D and is suitable to channel
`characteristics, in which a channel change speed and the
`length of a channel are medium. In other words, if it is
`determined that the cell radius is not greater than the first
`predetermined value but greater than the second predeter-
`mined value, the length of the transmission symbol is set to
`D.
`
`[0038] However, if it is determined that the cell radius is
`not greater than the second predetermined value, the fifth
`symbol 46 shown in FIG. 2 is determined as the transmis-
`sion symbol in step 22. The fifth symbol 46 has a length E
`and is suitable to channel characteristics, in which a channel
`change speed is slow and the length of a channel is short. In
`other words, if it is determined that the cell radius is not
`greater than the second predetermined value, the length of
`the transmission symbol is set to E.
`
`[0039] According to the present invention, the length D of
`the fourth symbol 48 is shorter than the length B of the
`second symbol 50, and each of the lengths A, C, and E of the
`respective first, third, and fifth symbols 42, 54, and 46 is
`shorter than the length D of the fourth symbol 48. In
`addition, according to the present invention, each of the
`lengths B, C, D, and E of the respective second, third, fourth,
`and fifth symbols 50, 54, 48, and 46 may be an integer
`
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`US 2004/0037215 Al
`
`Feb. 26, 2004
`
`3
`
`multiple of the length A of the first symbol 42, and each of
`the lengths B, C, and D of the respective second, third, and
`fourth symbols 50, 54, and 48 may be an integer multiple of
`the length E of the fifth symbol 46.
`
`[0040] In order to change the length of a transmission
`symbol, as shown in FIG. 1, the present invention changes
`the number of carrier waves while fixing an entire signal
`bandwidth. The entire signal bandwidth indicates the result
`of dividing an interval between carrier waves by the length
`of a transmission symbol. For example, when increasing the
`number of carrier waves while fixing an entire signal band-
`width, a distance between carrier waves is long and the
`length of a transmission symbol increases. Conversely, when
`decreasing the number of carrier waves while fixing an
`entire signal bandwidth, a distance between carrier waves is
`short and the length of a transmission symbol decreases. As
`described above, the length of a transmission symbol can be
`changed by adjusting the number of carrier waves, in step
`12, 16, 20 or 22.
`
`[0041] FIG. 3 is a flowchart of an OFDM communication
`method to adapt to channel characteristics according to a
`second embodiment of the present invention. The OFDM
`communication method includes converting the format of a
`frame depending on a cell radius in steps 70 through 78.
`
`[0042] FIG. 4 is a diagram showing an example of a
`macro format. A single frame 90 is composed of a single first
`symbol and a plurality of second symbols, and a plurality of
`third symbols.
`
`[0043] FIG. 5 is a diagram showing an example of a micro
`format. A single frame 92 is composed of a single first
`symbol and a plurality of fourth symbols.
`
`[0044] FIG. 6 is a diagram showing an example of a pico
`format. A single frame 94 is composed of a single first
`symbol and a plurality of fifth symbols.
`
`[0045] In the OFDM communication method according to
`the second embodiment of the present invention shown in
`FIG. 3, the format of a frame is converted depending on the
`radius of a cell, in which communication is performed.
`
`[0046] For this operation, it is determined weather a cell
`radius is greater than a first predetermined value in step 70.
`If it is determined that the cell radius is greater than the first
`predetermined value, the format of a frame is converted into
`a macro format, as shown in FIG. 4, in step 72. Referring to
`FIG. 4, the macro format is composed of a single first
`symbol, a plurality of second symbols, and a plurality of
`third symbols. In other words, when a channel change speed
`is fast or slow and the length of a channel is long due to a
`large cell radius, the format of the frame is converted into the
`macro format shown in FIG. 4.
`
`[0047] However, if it is determined that the cell radius is
`not greater than the first predetermined value, it is deter-
`mined weather the cell radius is greater than a second
`predetermined value in step 74. The second predetermined
`value is smaller than the first predetermined value. If it is
`determined that the cell radius is greater than the second
`predetermined value, the format of a frame is converted into
`a micro format, as shown in FIG. 5, in step 76. Referring to
`FIG. 5, the micro format is composed of a single first
`symbol and a plurality of fourth symbols. In other words,
`
`when a channel change speed and the length of a channel are
`medium, the format of the frame is converted into the micro
`format.
`[0048] However, if it is determined that the cell radius is
`not greater than the second predetermined value, the format
`of a frame is converted into a pico format, as shown in FIG.
`6, in step 78. Referring to FIG. 6, the pico format is
`composed of a single first symbol and a plurality of fifth
`symbols. In other words, when a channel change speed is
`slow and the length of a channel is short due to a small cell
`radius, the format of the frame is converted into the pico
`format.
`[0049] FIG. 7 is a flowchart of an embodiment of step 16
`shown in FIG. 1 according to the present invention. The
`embodiment of step 16 includes determining a second or
`third symbol as a transmission symbol depending on a
`channel change speed in steps 110 through 114.
`[0050] Referring to FIG. 7, if it is determined that the cell
`radius is greater than the first predetermined value (step 14
`of FIG. 1), it is determined whether a channel change speed
`is greater than a predetermined speed in step 110.
`[0051]
`If it is determined that the channel change speed is
`not greater than the predetermined speed, the second symbol
`50 shown in FIG. 2 is determined as the transmission
`symbol in step 112. In other words, the length of the
`transmission symbol is set to B. However, if it is determined
`that the channel change speed is greater than the predeter-
`mined speed, the third symbol 54 is determined as the
`transmission symbol in step 114. In other words, the length
`of the transmission symbol is set to C.
`[0052] According to a third embodiment of the present
`invention, the length of a transmission symbol and the
`format of a frame are changed depending on a type of
`transmission symbol and a cell radius. For this operation,
`referring to FIG. 1, if it is determined that the cell radius is
`greater than the first predetermined value, the second or third
`symbol is determined as the transmission symbol, and
`simultaneously the format of the frame is converted into the
`macro format shown in FIG. 4, in step 16. However, if it is
`determined that the cell radius is not greater than the first
`predetermined value but is greater than the second prede-
`termined value, the fourth symbol is determined as the
`transmission symbol, and simultaneously the format of the
`frame is converted into the micro format shown in FIG. 5,
`in step 20. In addition, if it is determined that the cell radius
`is not greater than the second predetermined value, the fifth
`symbol is determined as the transmission symbol, and
`simultaneously the format of the frame is converted into the
`pico format shown in FIG. 6, in step 22.
`
`[0053] FIG. 8 is a diagram showing a hierarchical cell
`structure, which is composed of macro cells 130, micro cells
`132, and pico cells 134.
`[0054] Referring to FIG. 8, the macro cells 130 repre-
`sented by dotted lines correspond to cells having a radius
`that is greater than the first predetermined value. The micro
`cells 132 represented by bold sold lines correspond to cells
`having a radius that is not greater than the first predeter-
`mined value but greater than the second predetermined
`value. The pico cells 134 represented by thin solid lines
`correspond to cells having a radius that is not greater than
`the second predetermined value. The hierarchical cell struc-
`
`Intel Corporation Ex. 1026
`Intel Corp v. UNM Rainforest Innovations - IPR2020-01576
`Page 12 of 18
`
`(cid:9)
`

`

`US 2004/0037215 Al
`
`Feb. 26, 2004
`
`0
`
`ture shown in FIG. 8 is used in order to increase frequency
`efficiency when frequency resources are limited. As shown
`in FIG. 8, a plurality of micro cells 132 exist within each
`macro cell 130, and a plurality of pico cells 134 exist within
`each micro cell 132. Usually, the hierarchical cell structure
`is designed such that users with a fast channel change speed
`are gathered at the macro cells 130 and users with a slow
`channel change speed are gathered in the micro cells 132 or
`the pico cells 134. This is disclosed in pages 301-304 of a
`book entitled "Radio Resource Management for Wireless
`Networks", written by Jens Zander and Seong-Lyun Kim,
`and published by Artech Houser in 2001.
`[0055] FIG. 9 is a diagram showing an example of a
`multiplex carrier wave transmission symbol. In this
`example, the transmission symbol is composed of a first
`cyclic prefix (CP) 150, a first transmission signal 158, and a
`first cyclic suffix (CS) 154.
`[0056] According to the fourth embodiment of the present
`invention, the format of a symbol as well as the length of the
`symbol can be changed depending on a cell radius and a
`channel change speed.
`[0057] For example, if it is determined that the channel
`change speed is not greater than the predetermined speed,
`the second symbol is determined as the transmission symbol
`and the format of the second symbol is converted into a
`format shown in FIG. 9 in step 112 of FIG. 7. In FIG. 9, the
`first CP 150 of the transmission symbol is the result of
`copying an end portion 152 of the first transmission signal
`158 to the front of the first transmission signal 158 and is
`used to eliminate the interference of a previous symbol. The
`first CS 154 of the transmission symbol is the result of
`copying a beginning portion 156 of the first transmission
`signal 158 to the back of the first transmission signal 158 and
`is used to mitigate the alignment condition of transmission
`time when a carrier wave is divided and used by multiple
`users usually in an upward channel. Here, the first transmis-
`sion signal 158 contains transmission data. As described
`above, since the end portion 152 of the transmission data
`158 is copied to the first CP 150 and the beginning portion
`156 of the transmission data 158 is copied to the first CS
`154, the transmission symbol shown in FIG. 9 has a cyclic
`structure.
`[0058] FIG. 10 is a diagram showing another example of
`a multiplex carrier wave transmission symbol. In this
`example, the transmission symbol is composed of a second
`CP 170, second and third transmission signals 172 and 174,
`and a second CS 176.
`[0059] FIG. 11 is a diagram showing still another example
`of a multiplex carrier wave transmission symbol. In this
`example, the transmission symbol is composed of a third CP
`190, fourth and fifth transmission signals 192 and 194, and
`a third CS 196.
`[0060] However, if it is determined that the channel
`change speed is greater than the predetermined speed, the
`third symbol is determined as the transmission symbol and
`the format of the third symbol is converted into a format
`shown in FIG. 10 or 11 in step 114 of FIG. 7.
`[0061] According to the present invention, the second CP
`170 of the third symbol shown in FIG. 10 includes the end
`portion of transmission data stored in each of the second and
`third transmission signals 172 and 174 and the beginning
`
`portion of the transmission data. In other words, the second
`CP 170 is composed of two first CPs 150 and one first CS
`154 shown in FIG. 9. In addition, each of the second and
`third transmission signals 172 and 174 shown in FIG. 10
`contains the same transmission data as that contained in the
`first transmission signal 158 shown in FIG. 9. Unlike the
`transmission symbol shown in FIG. 9, the transmission
`symbol shown in FIG. 10 includes repeated transmission
`data following the second CP 170. Here, the second CS 176
`includes the beginning portion of the transmission data. In
`other words, the second CS 176 is composed of one first CS
`154 shown in FIG. 9.
`[0062] According to the present invention, the third CP
`190 of the third symbol shown in FIG. 11 includes the end
`portions of transmission data stored in each of the fourth and
`fifth transmission signals 192 and 194. In other words, the
`third CP 190 is composed of only two first CPs 150. In
`addition, each of the fourth and fifth transmission signals
`192 and 194 shown in FIG. 11 contains the same transmis-
`sion data as that contained in the first transmission signal
`158 shown in FIG. 9. Unlike the transmission symbol
`shown in FIG. 9, the transmission symbol shown in FIG. 11
`includes repeated transmission data following the third CP
`190. Here, the third CS 196 includes the beginning portions
`of the transmission data. In other words, the third CS 196 is
`composed of two first CSs 154 shown in FIG. 9. The
`transmission symbol shown in FIG. 11 can be used when
`timing does not agree well as a whole as in random access.
`[0063] Consequently, in an OFDM communication
`method, the length of the first CP 150 is required to be longer
`than a channel length. However, since duplicate information
`is contained in the first CP 150, communication efficiency is
`decreased when the result of dividing the length of the first
`CP 150 by the transmission data contained in the first
`transmission signal 158 is too large. Accordingly, in order to
`maintain the communication efficiency, the length of the
`transmission data needs to be 5-10 times longer than the
`length of the first CP 150. In other words, in the transmission
`symbol, the length of the first CP 150 needs to be as short
`as possible. Here, if the length of the transmission symbol is
`long in a state in which a channel change speed is fast, a
`channel may change within the transmission data, and thus
`communication performance may be degraded. As described
`above, it is necessary to increase the length of the first CP
`150 as a channel length increases, but there is a limitation in
`increasing the length of the first CP 150. In order to solve
`this problem, an OFDM communication method according
`to the present invention described above adaptively changes
`the length of a transmission symbol depending on a channel
`change speed and a cell radius, as shown in FIG. 1. As
`described above, influence of inter symbol interference (ISI)
`can be overco