United States Patent [19J
`Suzuki et al.
`
`[ 54] COMMUNICATION METHOD AND
`RECEIVING APPARATUS
`
`[75)
`
`Inventors: Mitsuhiro Suzuki, Chiba; Kazuyuki
`Sakoda, Tokyo, both of Japan
`
`[73) Assignee: Sony Corporation, Tokyo, Japan
`
`[21) Appl. No.: 08/998,386
`
`[22) Filed:
`
`Dec. 24, 1997
`
`[30)
`
`Foreign Application Priority Data
`
`Dec. 26, 1996
`
`(JP)
`
`Japan .................................... 8-384803
`
`....................................................... H03D 1/00
`Int. Cl.6
`[51)
`[52) U.S. Cl . .......................... 375/340; 375/295; 375/308;
`370/208; 370/210; 370/335
`[58) Field of Search ................................ 342/50, 88, 102,
`342/357; 370/508, 515, 522; 375/200, 202,
`208,210,340, 342-343
`
`[56)
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`I 1111111111111111 11111 111111111111111 111111111111111 lllll 111111111111111111
`US005903614A
`[11) Patent Number:
`[45) Date of Patent:
`
`5,903,614
`May 11, 1999
`
`4,041,391
`4,481,640
`5,541,552
`5,677,927
`5,694,415
`
`8/1977 Deerkoski .... ... ... ... ... .... ... ... ... ... . 325/30
`11/1984 Chow et al. ............................ 375/200
`7/1996 Suzuki et al. .
`10/1997 Fullerton et al. ....................... 375/200
`12/1997 Suzuki et al. .
`
`Primary Examiner-Stephen Chin
`Assistant Examiner-Joseph Roundtree
`Attorney, Agent, or Firm-Jay H. Maioli
`
`[57)
`
`ABSTRACT
`
`A reception method of a multicarrier system is one in which
`a phase-modulated data is transmitted by using each of a
`plurality of subcarriers, and includes a random data gener(cid:173)
`ating step of generating a phase shift data randomly
`changed, a multiplying step for multiplying each of the
`received subcarriers with an output obtained in the random
`data generating step, and a state detection signal generating
`step for monitoring a state of an output obtained in the
`multiplying step and for generating a predetermined state
`detection signal when a predetermined state is detected.
`
`3,742,498
`
`6/1973 Dunn ........................................ 343/7.5
`
`8 Claims, 10 Drawing Sheets
`
`AOC
`
`Windowing
`Circuit
`
`IFFT
`
`Decoder
`
`14
`
`15
`
`20
`
`17
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`16
`Random Phase
`Shift Data
`Generating
`Ckt.
`
`18
`
`Random Phase
`Shift Data
`Storage
`Memory
`
`19
`
`Viterbi
`Decoder
`
`23
`
`22
`
`-Frame
`e interleaving
`Buffer
`
`21
`
`24
`
`Decision
`Circuit
`
`25
`
`Control I er
`
`D1
`
`02
`
`VWGoA EX1009
`U.S. Patent No. 8,467,366
`
`

`

`FIG. I
`
`I""
`21 22 23 24 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 0 2 3
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`
`One Frame (5ms)
`
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`
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`(Subcarrier
`Number)
`
`One Band
`Slot
`(150KHz)
`
`1
`0
`23
`22
`21
`20
`19
`18
`17
`16
`15
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`13
`12
`11
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`FIG. 2F
`FIG. 2£
`FIG. 20
`FIG. 2C
`FIG. 28
`FIG. 2A
`
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`U3 Timing ~A[B] ~A[B] ~A[B] ~A[B] ~A@Jl_
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`rT9°€06'S
`
`

`

`U.S. Patent
`
`May 11, 1999
`
`Sheet 4 of 10
`
`5,903,614
`
`FIG. 4
`(PRIOR ART)
`
`, , ,
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`

`FIG. 5
`
`ADC
`
`Windowing
`Circuit
`
`14
`
`15
`
`Viterbi
`Decoder
`
`23
`
`22
`
`IFFT
`
`Decoder
`
`20
`
`17
`
`16
`Random Phase
`Shift Data
`Generating
`Ckt.
`
`18
`
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`Shift Data
`Storage
`Memory
`
`19
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`uffer
`
`21
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`25
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`

`

`FIG. 6
`
`Number of
`Carriers
`Phase Shift Value
`of Transmission
`Data
`
`Case 1
`
`Case 2
`
`Case 3
`
`-· - - - -
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`
`

`

`U.S. Patent
`U.S. Patent
`
`May11, 1999
`May 11, 1999
`
`Sheet 7 of 10
`Sheet 7 of 10
`
`5,903,614
`5,903,614
`
`FIG. 1
`FIG. 7
`
`#2
`#2
`4
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`“A||
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`
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`I ,
`
`I
`
`I
`
`f
`
`| #5
`---- -----
`#3
`
`

`

`U.S. Patent
`
`May 11, 1999
`
`Sheet 8 of 10
`
`5,903,614
`
`Q
`
`,
`
`,
`
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`--- ---
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`FIG. BA
`(PRIOR ART)
`
`FIG. 88
`(PRIOR ART)
`
`FIG. BC
`(PRIOR ART)
`
`

`

`U.S. Patent
`
`May 11, 1999
`
`Sheet 9 of 10
`
`5,903,614
`
`Q
`
`Q
`
`Q
`
`FIG. 9A
`(PRIOR ART)
`
`FIG. 98
`(PRIOR ART)
`
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`(PRIOR ART)
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`einterleaving
`uffer
`
`21
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`
`14
`
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`Circuit
`15
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`Memory
`
`IFFT
`
`Decoder
`
`16
`
`17
`
`20
`
`Random Phase
`~~Shift Data
`Generating
`Ckt.
`
`31
`
`33
`
`Decoder
`
`18
`
`34 Windowing
`Circuit
`
`Random Phase
`Shift Data
`Storage
`Memory
`D1
`
`19
`
`Control I er
`
`35
`
`D2
`
`

`

`5,903,614
`
`1
`COMMUNICATION METHOD AND
`RECEIVING APPARATUS
`
`BACKGROUND OF THE INVENTION
`
`2
`state of an output obtained in the multiplying step and for
`generating a predetermined state detection signal when a
`predetermined state is detected.
`According to a first aspect of the present invention, a
`5 reception apparatus for a multicarrier system in which a
`phase-modulated data is transmitted by using each of a
`plurality of subcarriers, includes a demodulation unit for
`demodulating a signal of a multicarrier system, a random
`data generating unit for generating phase shift data randomly
`10 changed, a multiplying unit for multiplying an output from
`the demodulation unit with an output from the random data
`generating unit, and a state detection signal generating unit
`for monitoring a state of an output from the multiplying unit
`and for generating a predetermined state detection signal
`15 when a predetermined state is detected.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is an explanatory diagram showing the structure of
`20 slots according to the communication method applied to
`each embodiment of the present invention;
`FIGS. 2A to 2G are explanatory diagrams showing the
`transmission timing according to the communication
`method applied to each embodiment of the present inven-
`2s tion;
`FIGS. 3A and 3B are explanatory diagrams showing the
`band slot according to the communication method applied to
`each embodiment of the present invention;
`FIG. 4 is an explanatory diagram showing the transmis-
`30 sion phase according to the communication method applied
`to each embodiment of the present invention;
`FIG. 5 is a block diagram showing the construction of the
`receiving system according to the first embodiment of the
`present invention;
`FIG. 6 is an explanatory diagram showing the phase shift
`states according to the first embodiment;
`FIG. 7 is a phase characteristic diagram showing an
`example of the phase shift state according to the first
`embodiment;
`FIGS. SA to SC are characteristic diagram showing the
`phase state when assuming that data is zero with the first
`embodiment;
`FIGS. 9A to 9C are characteristic diagrams showing the
`45 phase state when data is scattered with the first embodiment;
`and
`FIG. 10 is a block diagram showing the construction of
`the receiving system according to the second embodiment of
`the present invention.
`
`1. Field of the Invention
`The present invention relates to a communication method
`applicable to the orthogonal frequency division multiplex
`system (OFDM system) and a receiving apparatus for
`receiving a signal according to the communication method.
`2. Description of the Related Art
`For a communication method suitable for a mobile com(cid:173)
`munication such as a wireless telephone system or the like,
`a multicarrier communication method called Orthogonal
`Frequency Division Multiplexing (OFDM system) has been
`proposed. This system is such that a plurality of subcarriers
`are arranged at a predetermined frequency interval within
`one transmission band and data is scattered over the respec(cid:173)
`tive subcarriers to modulate them for transmission. In this
`case, on a transmitting side, transmitting data in the form of
`a time sequence is orthogonal-transformed to a multicarrier
`signal at a predetermined frequency interval by a fast
`Fourier transform or the like. On a receiving side, a received
`multicarrier signal is subjected to the inverse transform of
`that in transmission for obtaining received data.
`The transmitted signal according to the OFDM system has
`an advantage in that even if there is a multipath a good
`transmission characteristic is ensured, so that it is particu(cid:173)
`larly suitable for the mobile communication such as the
`wireless telephone system or the like.
`When such multicarrier signal is received, it is difficult to
`detect a frequency offset of the received signal. Specifically,
`when the multicarrier signal in which subcarriers of a
`predetermined number are provided in one transmission
`band, for example, is transmitted in a plurality of continuous 35
`transmission bands, it is difficult for the reception side to
`easily determine which range of the subcarriers from one
`transmission band. Especially, in order to increase the trans(cid:173)
`mission efficiency, a frequency interval between the adjacent
`subcarriers is very narrow (e.g., an interval of several kHz) 40
`in the communication of this kind, which makes it difficult
`to precisely detect the frequency offset.
`In order to solve this disadvantage, it can be considered
`that the transmission side transmits a specific symbol by
`using a subcarrier at a specific position in one transmission
`band and the reception side corrects an offset of a reception
`frequency with reference to the subcarrier in which the
`reception side receives the specific symbol. However, when
`such a specific symbol is transmitted, the period of data 50
`transmission is reduced to that extent, which reduces the
`transmission capacity.
`
`DESCRIPTION OF THE PREFERRED
`EMBODIMENTS
`
`SUMMARY OF THE INVENTION
`
`In view of such aspects, it is an object of the present
`invention that, when transmitting the multicarrier signal, the
`frame period or a reference timing in a frame can simply be
`detected on a receiving side even if the synchronizing signal
`is not transmitted.
`According to a first aspect of the present invention, a
`reception method of a multicarrier system, in which a
`phase-modulated data is transmitted by using each of a
`plurality of subcarriers, includes a random data generating
`step of generating phase shift data randomly changed, a
`multiplying step for multiplying each of received subcarriers 65
`with an output obtained in the random data generating step,
`and a state detection signal generating step for monitoring a
`
`Embodiments according to the present invention will be
`ss described below with reference to the accompanying draw(cid:173)
`ings.
`In these embodiments, the present invention is applied to
`the wireless telephone system of what is called a cellular
`system in which a base station is arranged in a predeter-
`60 mined condition to form a service area and communicate
`with a portable station (terminal device). First of all, the
`multicarrier transmission system applied to the embodi(cid:173)
`ments will be described in detail with reference to FIG. 1 to
`FIG. 4. A communication system of the present example is
`made to be the orthogonal frequency division multiplex
`system (OFDM system) in which a plurality of subcarriers
`are successively arranged within a preallocated band. And a
`
`

`

`5,903,614
`
`3
`plurality of the subcarriers within one transmission band are
`simultaneously utilized through one transmission path, and
`is further made to modulate collectively a plurality of the
`subcarriers within one band in a band division.
`A structure thereof will be explained. FIG. 1 shows how s
`to construct slots of the transmitting signal in this example,
`in which figure a vertical axis represents frequency and a
`horizontal axis represents time. In case of this example,
`orthogonal bases are provided by dividing the frequency
`axis and the time axis in a grid shape. Particularly, one 10
`transmission band ( one band slot) consists of 150 kHz and
`twenty-four subcarriers are arranged within this one trans(cid:173)
`mission band of 150 kHz. These twenty-four subcarriers are
`successively arranged at an equal interval of 6.25 kHz and
`to each subcarriers are given subcarrier numbers 0 to 23, 15
`respectively. However, really existing subcarriers are
`twenty-two one from subcarriers numbers 1 to 22. Regard(cid:173)
`ing the subcarrier numbers 0 and 23 at both ends within one
`band slot, they are made guard band in which no subcarrier
`is arranged and their powers are made zero.
`Looking over the time axis, one time slot having a time
`period of 200 µs is defined and at every time slot the
`twenty-two subcarriers are modulated by a burst signal for
`transmission. A time section in which twenty-five time slots
`are arranged (i.e. 5 ms) is defined as one frame. To each time 25
`slot within this one frame is given time slot numbers O to 24,
`respectively. An area shown by hatching in FIG. 1 represents
`one time slot section of one band slot. Further, the time slot
`of the slot number 24 is made a time period where no data
`is transmitted.
`Using the orthogonal bases formed by dividing the fre(cid:173)
`quency axis and the time axis in a grid shape, the multiple
`access in which the cell station communicates simulta(cid:173)
`neously with a plurality of the portable stations (terminal
`devices) is carried out. In this case, as to a mode of coupling 35
`to each portable station, it is performed in such a manner as
`shown in FIGS. 2A to 2G. FIGS. 2A to 2G illustrate use of
`the time slots of six portable stations (users) U0, Ul, U2, .
`.. US to be coupled to the cell station through one band slot
`(in practice, the band slot for use is switched by means of a
`frequency hopping described below), in which figure a time
`slot denoted by R is a receiving slot and denoted by T is a
`transmitting slot. The cell station establishes a frame timing
`of twenty-four time slot periods as shown in FIG. 2A (The
`last slot numbered 24 of twenty-five prepared time slots is
`not used.). In this case, the transmitting slot and the receiv(cid:173)
`ing slot are arranged here to use a different band
`transmission, respectively.
`For example, the portable station U0 shown in FIG. 2B
`uses the time slots numbered 0, 6, 12, 18 within one frame so
`as the receiving slot and uses the time slots numbered 3, 9,
`15, 21 as the transmitting slot, through the respective time
`slots the reception or transmission of the burst signal being
`performed. The portable station Ul shown in FIG. 2C uses
`the time slots numbered 1, 7, 13, 19 within one frame as the ss
`receiving slot and uses the time slots numbered 4, 10, 16, 22
`as the transmitting slot. Also, the portable station U2 shown
`in FIG. 2D uses the times slots numbered 2, 8, 14, 20 within
`one frame as the receiving slot and uses the time slots
`numbered 5, 11, 17, 23 as the transmitting slot. Again, the 60
`portable station U3 shown in FIG. 2E uses the time slots
`numbered 3, 9, 15, 21 within one frame as the receiving slot
`and uses the time slots numbered 0, 6, 12, 18 as the
`transmitting slot. Further, the portable station U4 shown in
`FIG. 2F uses the time slots numbered 4, 10, 16, 22 within 65
`one frame as the receiving slot and uses the time slots
`numbered 1, 7, 13, 22 as the transmitting slot. Finally, the
`
`4
`portable station US shown in FIG. 2G uses the time slots
`numbered 5, 11, 16, 22 within one frame as the receiving slot
`and uses the time slots numbered 2, 8, 14, 20 as the
`transmitting slot.
`According such as arrangement as is shown in FIGS. 2A
`to 2G, six TDMA (Time Division Multiple Access) in which
`the six portable stations are coupled to one band slot can be
`performed. Seeing from each portable station side, after the
`reception and transmission during one time slot period had
`been completed, there is a spare time for two time slot
`periods (i.e., 400 µs) until the next transmission or reception
`begins to be performed. Thus, using this spare time, a timing
`process and the process termed the frequency hopping are
`performed. That is, during about 200 µs before each trans(cid:173)
`mitting slot T, a timing process TA in which a transmission
`timing is made to match with a timing of a signal from the
`base station side is performed. After a time passage of about
`200 µs, when each transmitting slot T has been completed,
`the frequency hopping in which a band slot for the trans-
`20 mission and reception is switched over another band slot
`takes place.
`A plurality of the band slots are assigned to one base
`station. For example, in case of the cellular system where
`one cell is comprised of one base station, if a band of 1.2
`MHz is allocated to one cell, eight band slots can be assigned
`to one cell. Likewise, if a band of 2.4 MHz is allocated to
`one cell, sixteen band slots can be assigned to one cell. Also,
`if a band of 4.8 MHz is allocated to one cell, thirty-two band
`slots can be assigned to one cell. Finally, if a band of 9 .6
`30 MHz is allocated to one cell, sixty-four band slots can be
`assigned to one cell. In order to use equality a plurality of the
`band slots assigned to this one cell, the frequency switching
`process called frequency hopping is carried out.
`FIGS. 3A and 3B show an example where eight band slots
`are arranged within one cell. At each of eight band slots
`prepared as shown in FIG. 3A, twenty-two subcarriers are
`arranged as shown in FIG. 3B for data transmission. Data is
`transmitted over each of the respective subcarriers under a
`40 predetermined phase modulation. In this example, QPSK
`(Quadrature Phase Shift Keying) modulation is used, in
`which data is transmitted as data at four points of phase
`position shifted in turn by rt/2 of a circle on an orthogonal
`coordinate (a circle denoted by a broken line in FIG. 4)
`45 which are formed by laying an I component at right angles
`to a Q component, as is shown in FIG. 4.
`Wireless communication takes place in this transmission
`system. However, in case of the present example, the trans(cid:173)
`mitting signal is made of such data as each subcarrier is
`multiplied by respective different random phase shift data.
`That is, at each of the twenty-two subcarriers from the
`subcarrier number 1 to the subcarrier number 22 within one
`band slot, an initial phase shift value of the first data of the
`first time slot of each frame is established and then the phase
`shift value is changed from the initial phase shift value in a
`sequence determined at random sequence which is deter(cid:173)
`mined in advance).
`Next, a construction of a first embodiment according to
`the present invention in which a terminal device (portable
`station) receives the signal transmitted from the base station
`in this way, will be described with reference to FIG. 5. FIG.
`5 shows a receiving system of the terminal device, in which
`a received signal (the signal which is subjected to a receiving
`process in a filter or an amplifier after received by an
`antenna) available at an input terminal 11 is supplied to
`mixer 12, where it is mixed with a frequency signal output
`by a frequency signal generator means 13 comprised of a
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`5,903,614
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`5
`PLL circuit (phase locked loop circuit) for frequency con(cid:173)
`verting the received signal of a predetermined transmission
`band (band slot) into an intermediate frequency signal. In
`this case, this frequency signal generator means 13 has
`basically an output frequency which varies at an interval of 5
`one band slot (i.e. here at a interval of 150 kHz).
`Subsequently, the intermediate frequency signal output by
`the mixer 12 is supplied to an analogue/digital converter 14,
`where it is sampled at a predetermined sampling period. The
`received data sampled in the analogue/digital converter 14 is 10
`supplied to window multiplier circuit 15, wherein it is
`multiplied by window multiplying data (temporal wave
`form) corresponding to a window multiplying data by which
`it was multiplied on the transmitting side.
`The received data multiplied by the window multiplying 15
`data is supplied to an inverse fast Fourier transform circuit
`(IFFT circuit) 16, wherein it is subjected to a transforming
`process between a frequency domain and time domain by
`the inverse fast Fourier transform operation, thereby causing
`the data which modulated the twenty-two subcarriers at an 20
`interval of 6.25 kHz for transmission to be a single sequence
`of continuous data in the time axis.
`The received data transformed into a single sequence is
`supplied to a multiplier 17, wherein it is multiplied by
`random phase shift data output by a random phase shift data
`generator circuit 18. The random phase shift data output by
`the random phase shift data generator circuit 18 is generated
`on the basis of pattern data stored in a random phase shift
`pattern storing memory 19. The random phase shift data is
`data for restoring the data whose phase was shifted and 30
`scattered on every subcarrier in transmission from the trans(cid:173)
`mitting side (base station) to the original data. As to the
`random phase shift data, an initial phase shift value to each
`subcarrier is determined and its value is arranged to change
`the phase to be shifted from the initial phase position at 35
`random (The order in which the phase shift amount is varied
`at random from the initial phase shift value is the same as
`that set up on the transmitting side). A timing to generate the
`random phase shift data by the generator circuit 18 is set up
`under the control of a controller 25 which controls the 40
`receiving operation of this terminal device.
`Thereafter, the data whose phase has been restored to
`original phase is supplied to a decoder 20, where the phase
`modulated data is decoded by the differential demodulation
`or the like. The decoded data is supplied to a four frame
`deinterleave buffer 21, where interleaved data over four
`frames in transmission is restored to data of the original
`sequence. The deinterleaved data is supplied to a Viterbi
`decoder circuit 22 for Viterbi decoding. The Viterbi decoded
`data is then supplied as the received data to a received data 50
`processing circuit (not shown) at subsequent stage from a
`received data output terminal 23.
`Moreover, in this embodiment, the decoded data by the
`decoder 20 is supplied to a decision circuit 24 which decides
`whether or not the data has correctly been decoded and ss
`supplies the decision data to the controller 25. Regarding
`this decision, for example, when accumulating phases of the
`signal over a time period in which data of the twenty-two
`subcarriers forming one band slot time period is acquired, if
`the accumulated phases vary at an angular interval of about 60
`o/2, the decision data is produced that indicates that the
`decoding has been completed correctly. If the accumulated
`phases do not vary at the angular interval of about "/2, the
`decision data is produced that indicates that it is erroneously
`processed data.
`The controller 25 estimates, if it receives the decision data
`indicating that the decoding has been completed correctly,
`
`6
`that there is no frequency offset in the received signal at that
`time. If it receives the decision data indicating that the
`decoding has been performed incorrectly, it estimates that
`there is a frequency offset in the received signal at that time.
`On the basis of a result of the decision, the controller 25
`outputs the frequency offset correction data D1 and makes a
`fine adjustment of a received frequency at intervals of 6.25
`kHz.
`The fine adjustment of the received frequency can be
`implemented by such processings as changing the output
`frequency of the frequency signal generator means 13 at an
`interval of 6.25 kHz, or as establishing the number of
`transform points in the inverse fast Fourier transform by
`IFFT circuit 16 more than the number of the subcarriers
`(twenty-two subcarriers) forming one band slot and then
`changing a position of the twenty-two subcarriers extracted
`from the transform points as a sequence of data or the like.
`Furthermore, the fine adjustment of the received frequency
`may be performed by other processing.
`In addition, the controller 25 in the present embodiment
`outputs a frame position detecting data D2 based on a timing
`when a predetermined condition has been decided by the
`decision circuit 24. On the basis of the frame position
`detecting data D2 , a processing timing at each of the circuits
`25 within the terminal device is set for the timing synchronous
`with the received data.
`Next, an operation when receiving with the terminal
`device according to the present embodiment will be
`described. For example, when the base station transmits, the
`initial phase shift amount by which the first data of each
`frame is multiplied is made a value which is determined for
`every subcarrier and the phase shift amount for each sub(cid:173)
`carrier is arranged to change from the initial phase shift
`amount at a predetermined random manner.
`FIG. 6 shows an example of the initial phase shift
`amounts of respective subcarriers. Phase shift value of
`transmitting data therein shows the initial phase shift amount
`of each of the subcarriers in each frame. Its value is
`determined in turn from the carrier number 0. These phase
`shift values are here set up within a range from -it to 1t so
`that all of them will be different phase shift amounts at
`respective subcarriers within one band slot. FIG. 7 is a
`diagram which shows the initial phase shift values of the
`45 respective carrier numbers by its phase state, in which figure
`the phases of the carrier numbers are represented as #0, #1,
`#2 and so on.
`These initial phase shift values are also stored in the
`random phase shift pattern storing memory 19 of the receiv(cid:173)
`ing side (terminal device). On the basis of data read out of
`the memory 19, a processing to restore the phases of the
`subcarriers by the amount phase shifted by the multiplier 17
`is performed. Case 1, case 2 and case 3 denoted in FIG. 6
`show setting examples of the initial phase shift values by
`which the received signal is multiplied on the receiving side.
`In each case, the initial phase shift values are shifted in turn
`one by one subcarrier. Here, for example, the receiving
`process for the initial phase shift amount set up in each case
`is performed at every one frame. For example, in the first
`frame the initial phase shift amounts are set up according to
`case 1 and in the following frame the initial phase shift
`amounts are set up according to case 2 where they are shifted
`by one subcarrier. In the further following frame, the initial
`phase shift amounts are set up according to case 3 where
`6s they are shifted further by one subcarrier.
`In the example of FIG. 6, since the initial phase shift
`amounts in case 2 correspond with those on the transmitting
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`5,903,614
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`7
`side, in a frame which sets up the initial phase shift amount
`according to case 2 for the receiving process, data can
`correctly be decoded and correct received symbol data can
`be obtained. That is, assuming that the transmitting data
`which is transmitted through the twenty-two subcarriers
`forming one band slot are the same data of all zero data,
`when the initial phase shift of case 1 is set up for the
`receiving process, the phase decoded by the decoder 20 will
`scatter into respective phase states as shown in FIG. SA.
`Also, when the initial phase shift of case 3 is set up for the 10
`receiving process, the phase will scatter into different phase
`states as shown in FIG. SC. In contrast to this, when the
`initial phase shift of case 2 is set up for the receiving process,
`the phase will go into the same phase state as shown in FIG.
`SB. This means that the condition in which the receiving 15
`frequency is set up according to case 2 is the condition in
`which one band slot is correctly received and there is no
`frequency offset.
`In fact, the transmitting data is scattered values and so the
`phase states corresponding to cases 1, 2 and 3 will change
`as shown in FIGS. 9A, 9B and 9C. When the accumulated
`phases in the decision circuit 24 correspond to case 2, it is
`decided that they change at an angular unit of about '½ and
`the decision data indicating that the correct decoding has
`been performed is then supplied to the controller 25. In the
`receiving process corresponding to case 1 and case 3, since
`a change of the accumulated phases is not the change at an
`angular unit of about "/2, the decision data indicating that the
`data has been erroneously processed is supplied to the
`controller 25.
`Therefore, the controller 25 outputs the frequency offset
`correction data D, and makes the initial phase shift to change
`in turn in order to control the receiving frequency to be set
`up correctly, until the state of case 2 is detected.
`By performing a receiving process in such a manner as the
`present embodiment, when a multicarrier signal in which the
`subcarriers are successively arranged at a narrow frequency
`interval is to be received, it is possible to simply detect the
`correct receiving coverage of one band slot and to correct the
`frequency offset by a simple processing in a short period of
`time. In this case, since there is no need to transmit a
`particular symbol for detecting the frequency offset as in the
`past, the data transmission capacity for practical use
`increases by that less need, thereby allowing a correct
`receiving process to be performed without lowering the
`transmission efficiency.
`Also, by performing the receiving process according to
`the present embodiment, it is possible to detect not only the
`frequency offset but also the frame position of the transmit(cid:173)
`ting signal. Further, in this case, it is necessary for the
`random phase shift pattern to be determined beforehand so
`that a different pattern may be used depending on "the slot
`number in a frame given to the relevant slot. "If such an
`arrangement is made in advance, when, after the adjustment
`of the frequency offset has been completed, for example,
`"the random phase shift pattern used for the first slot in a
`frame" is produced by the random phase shift data generator
`means 18 and then the output of the decoder of received
`signal is multiplied by that random phase shift pattern, if it
`is decided that the phases of the respective subcarriers vary
`at an angular unit of about '½, then it can be determined that
`the slot is the first slot in the frame. The timing of the frame
`can be detected by processing in this way.
`In the above-mentioned processing, a slot signal in a
`certain slot is stored in a memory 31 and this signal is
`multiplied by the first shift pattern of the frame, by the
`
`8
`second shift pattern of the frame, by the third shift pattern of
`the frame, etc. Thus, results of the multiplication by the
`respective shift patterns are decided, thereby also allowing
`th