PCT
`
`WORLD INTELLECTUAL PROPERTY ORGANIZATION
`International Bureau
`
`
`
`INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY (PCT)
`
`
`(51) International Patent Classification6: (11) International Publication Number: WO 97/30531
`
`HO4L 5/06‘
`(43) International Publication Date:
`21 August 1997 (21.08.97)
`
`
`
`(21) International Application Number: PCT/SE97/00109|(81) Designated States: NO, European patent (AT, BE, CH, DE,
`DK, ES, FI, FR, GB, GR, IE, IT, LU, MC, NL,PT, SE).
`
`(22) International Filing Date:
`
`23 January 1997 (23.01.97)
`
`(30) Priority Data:
`9600537-6
`
`14 February 1996 (14.02.96)
`
`SE
`
`Published
`With international search report.
`
`(71) Applicant; TELIA AB [SE/SE]; Marbackagatan 11, S-123 86
`Farsta (SE).
`
`(72) Inventor: LARSSON, Roger; Blidvagen 53, S-951 48 Luled
`(SE).
`
`Telia Research AB,
`KARLSSON, Berne;
`(74) Agent:
`Rudsjéterrassen 2, S-136 80 Haninge (SE).
`
`(54) Title)
`
`IMPROVEMENTSIN OR RELATING TO OFDM SYSTEMS
`
`(57) Abstract
`
`amplitude
`
`To ensure that the performance of an OFDM system
`is adequate,
`it
`is necessary to provide a guard space
`between symbols so that the effects of mutual interference
`between adjacent symbols is avoided.
`In a conventional
`OFDM system the length of this guard space must be
`equal to, or greater than, the maximum delay spread in the
`system. Bearing in mind that under some conditions the
`delay spread in a mobile system maybe large, while under
`other conditions the delay spread may be low, the use of
`a fixed guard space corresponding to the longest delay
`spread, imposes an overhead on the transmission capacity
`of a communications channel. This conflict between
`channeltraffic capacity and the need for long guard spaces
`between symbols can be overcome by using a variable
`length guard space, ie. a guard space of variable duration.
`A receiver is able to instruct a transmitter to increase the
`duration of the guard space if the system performanceis
`degraded.
`
`08
`07
`
`0.6
`as
`0. 4
`0.3
`02
`0. 1
`°
`0
`
`0
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`2
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`3
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`L
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`7 -5
`6
`5
`time (s)x 10
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`

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`FOR THE PURPOSES OF INFORMATION ONLY
`
`Codes used to identify States party to the PCT on the front pages of pamphlets publishing international
`applications under the PCT.
`
`Viet Nam
`
`United Kingdom
`Georgia
`Guinea
`Greece
`Hungary
`Ireland
`Italy
`Japan
`Kenya
`Kyrgystan
`Democratic People’s Republic
`of Korea
`Republic of Korea
`Kazakhstan
`Liechtenstein
`Sri Lanka
`Liberia
`Lithuania
`Luxembourg
`Latvia
`Monaco
`Republic of Moldova
`Madagascar
`Mali
`Mongolia
`Mauritania
`
`AM
`AT
`AU
`BB
`BE
`BF
`BG
`BJ
`BR
`BY
`CA
`CF
`CG
`CH
`cl
`CM
`CN
`cs
`CZ
`DE
`DK
`EE
`ES
`FI
`FR
`GA
`
`Armenia
`Austria
`Australia
`Barbados
`Belgium
`Burkina Faso
`Bulgaria
`Benin
`Brazil
`Belarus
`Canada
`Central African Republic
`Congo
`Switzerland
`Cite d'Ivoire
`Cameroon
`China
`Czechoslovakia
`Czech Republic
`Germany
`Denmark
`Estonia
`Spain
`Finland
`France
`Gabon
`
`Malawi
`Mexico
`Niger
`Netherlands
`Norway
`New Zealand
`Poland
`Portugal
`Romania
`Russian Federation
`Sudan
`Sweden
`Singapore
`Slovenia
`Slovakia
`Senegal
`Swaziland
`Chad
`Togo
`Tajikistan
`Trinidad and Tobago
`Ukraine
`Uganda
`United States of America
`Uzbekistan
`
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`W097/30531
`
`PCT/SE97/00109
`
`-
`
`1 -
`
`Improvements in or Relating to OFDM Systems
`
`The present invention relates to OFDM (orthogonal
`frequency
`division multiplex)
`telecommunications
`systems, and methods of operating such systems, more
`particularly to the use of variable guard spaces in such
`systems.
`
`a
`is modulated onto
`system data
`In an OFDM
`broadband signal comprising a large number of individual
`frequency carriers which
`form a
`frequency division
`multiplex. The bandwidths of the individual frequency
`channels, are small and arranged so that the maximum of
`the sinc(x), (sinc(x) = sin(x)/x), power spectrum, of
`one channel, corresponds with the first minimum in the
`sinc(x) power spectrum of the adjacent channels.
`In
`other words,
`the channel separation equals 1/ (symbol
`length), for rectangular symbols. It is for this reason
`that adjacent channels are described as "orthogonal".
`OFDM systems normally use a FFT (fast fourier transform)
`process
`to demodulate
`the data
`signal
`from
`the
`transmitted signal. Convolution error coding and FFT
`may be employed at the modulator (transmitter) stage.
`In
`the
`receiver,
`complementary FFT processing
`is
`combined with Viterbi decoding, at
`the demodulator
`stage. This ensures that the overall bit error rate is
`very low. This particular variant of OFDM is known as
`COFDM (Coded Orthogonal Frequency Division Multiplex).
`In recent years, COFDM systems have been developed for
`a variety of broadcasting applications, e.g. for digital
`audio broadcasting
`and high definition TV.
`For
`convenience, in this specification the term OFDM is used
`to refer to both OFDM and COFDM.
`
`communications
`The next generation of mobile
`systems may, with advantage, employ OFDM. However,
`in
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`wo 97/30531
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`-
`
`2 -
`
`PCT/SE97/00109
`
`the distance between a
`mobile communications systems
`receiver and tra~smitter is not constant and,
`in
`addition, the terrain between receiver. and transmitter
`may vary.
`This results in signal dispersion in
`the
`frequency domain, or delay spread in the time domain, in
`a communications channel employing OFDM.
`
`To ensure that the performance of an OFDM system is
`adequate, it is necessary
`to provide a guard space
`between
`symbols
`so
`that
`the · effects of mutual
`interference between adjacent symbols is avoided.
`In a
`conventional OFDM system, the length of this guard space
`must be equal to, or greater than,
`the maximum delay
`spread in the system. Bearing in mind that under some
`conditions the delay spread in a mobile system may be
`large, while under other conditions the delay spread may
`be low, the use of a fixed guard space corresponding to
`the longest delay spread,
`imposes an overhead on the
`transmission capacity of a communications channel. Any
`compromise in the selection of the length of guard space
`will, in some circumstances, cause a loss of transmitted
`data.
`
`to
`invention
`the present
`is an object of
`It
`the overhead
`imposed on
`channel
`traffic
`minimise
`capacity in an OFDM system by the use of a guard space
`between symbols, without degrading system performance.
`
`mobile
`in
`spaces
`guard
`of
`use
`The
`European
`telecommunications systems is well known.
`Patent Application EP 0,295,227 describes a digital TDMA
`(time division multiple access) mobile telephone system
`in which time slot assignment is made in dependence on
`the propagation time between different mobile stations
`and a base station. Each time frame includes a guard
`space used to avoid overlap between transmissions to, or
`from, different mobile stations.
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`W097/30531
`
`PCT/SE97/00109
`
`-
`
`3 -
`
`US Patent 5,371,548 discloses the use of guard
`spaces with OFDM systems.
`
`0,589,709 A2
`European Patent Application EP
`discloses an OFDM system employing quadrature amplitude
`modulation, or modified phase shift keying,
`in which
`long guard
`times and/or wider channel spacings are
`employed.
`
`system in
`US Patent 4, 937,819 discloses a TDMA
`which ranging, with respect to time, is employed
`to
`reduce guard times between successive transmissions.
`
`the conflict
`invention overcomes
`The present
`between channel traffic capacity and the need for long
`guard spaces between symbols by using a variable length
`guard space, i.e. a guard space of variable duration.
`A receiver is able to instruct a transmitter to increase
`the duration of
`the guard
`space
`if
`the
`system
`performance is degraded.
`
`The use of variable duration guard spaces in OFDM
`systems is not disclosed in the prior art.
`
`the present
`first aspect of
`a
`to
`According
`invention, there is provided an OFDM system comprising
`a receiver and a
`transmitter, said transmitter being
`adapted to transmit data in OFDM symbol bursts in which,
`in the
`time domain, a portion of a symbol burst is
`repeated within said symbol burst as a guard space, said
`receiver having
`a
`time window with which, after
`demultiplexing, said symbol burst must be aligned,
`characterised in that said repeated portion of a symbol
`burst has a duration which is variable and which is
`adjusted, during system operation, to a minimum duration
`necessary to prevent data loss caused by delay spread.
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`W097/30531
`
`- 4 -
`
`PCT/SE97 /00109
`
`Preferably said receiver is adapted to vary said
`time window to produce, on demultiplexing, a guard space
`of a minimum duration necessary to prevent data loss
`caused by delay spread.
`
`The portion of said symbol burst which is repeated
`may be copied from a leading edge of said symbol burst.
`
`Said repeated portion of said symbol burst may be
`repeated at a trailing edge of said symbol burst.
`
`Said receiver may be adapted to transmit a signal
`to said
`transmitter indicative of a
`level of delay
`spread in a received signal, and said transmitter is
`adapted to adjust said guard space duration to a minimum
`value necessary to prevent data loss caused by delay
`spread.
`
`Preferably said receiver is adapted to detect a
`transmitted signal when said time window is incorrectly
`adjusted.
`
`Said OFDM system may be adapted to operate as a
`mobile telecommunications system.
`
`the present
`second aspect of
`a
`to
`According
`invention there is provided a receiver, for use with an
`OFDM system including a transmitter adapted to transmit
`data in OFDM
`symbol bursts,
`in which,
`in
`the
`time
`domain, a portion of a symbol burst is repeated within
`said symbol burst as a guard space, said receiver having
`a
`time window with which, after demul tiplexing, said
`symbol burst must be aligned, characterised in that said
`repeated portion of a symbol burst has a duration which
`is variable and said receiver is adapted to vary said
`time window to produce, on demultiplexing, a guard space
`of a minimum duration necessary to prevent data loss
`
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`wo 97130531
`
`-
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`5 -
`
`PCT/SE97/00109
`
`caused by delay spread.
`
`includes performance
`receiver
`said
`Preferably
`measuring means for measuring received signal quality
`and reception window adjusting means for adjusting said
`time window duration in response to a signal from said
`performance measuring means.
`
`Preferably said receiver is adapted to transmit a
`signal to said transmitter indicative of a
`level of
`delay spread in a received signal, and said transmitter
`is adapted to adjust said guard space duration to a
`minimum value necessary to prevent data loss caused by
`delay spread.
`
`a
`to detect
`adapted
`be
`receiver may
`Said
`transmitted signal when said time window is incorrectly
`adjusted.
`
`the present
`third aspect of
`a
`to
`According
`invention there is provided a method of operating an
`OFDM system comprising a receiver and a transmitter, by
`transmitting data as a series of OFDM symbol bursts,
`each symbol burst, in the time domain, having a portion
`thereof repeated therein as a guard space, said receiver
`having a
`time window with which, after demultiplexing,
`said symbol burst must be aligned, characterised by the
`repeated portion of a symbol burst having a variable
`duration, and adjusting said variable duration
`to
`produce a guard space of a minimum duration necessary to
`prevent data loss caused by delay spread.
`
`Preferably said receiver time window is adjusted to
`produce, on demultiplexing, a guard space of a minimum
`duration necessary to prevent data loss caused by delay
`spread.
`
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`wo 97130531
`
`- 6 -
`
`PCT/SE97/00109
`
`The repeated portion of said symbol burst may be
`copied from a leading edge thereof.
`
`The repeated portion of said symbol burst may be
`repeated at a trailing edge of said symbol burst.
`
`Said receiver may measure received signal quality
`and may adjust said time window duration so that said
`received
`signal quality
`exceeds
`a
`predetermined
`threshold.
`
`Embodiments of the invention will now be described,
`by way of example, with reference to the accompanying
`drawings, in which:
`
`Figure 1 shows a typical impulse response for hilly
`rural terrain.
`
`Figure 2 shows a typical impulse response for urban
`terrain.
`
`Figure 3 shows a typical impulse response for the
`interior of a building.
`
`typical impulse response for a
`Figure 4 shows a
`micro cell in a cellular digital mobile telephone
`system.
`
`Figure 5 is a diagrammatic illustration of an OFDM
`transmission burst.
`
`the
`there is shown
`to 4,
`Referring to Figure 1
`effect of terrain on delay spread, in an OFDM system.
`As can be seen from the drawings delay spread can vary
`from 0. 2).ls
`to 50J.1S.
`If a guard space is to be used
`which wi 11 avoid inter-symbol interference, caused by
`delay spread, in all of the different environments for
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`W097/30531
`
`PCT/SE97/00109
`
`- 7 -
`
`which impulse responses are illustrated in Figures 1 to
`4, it will need to be equal, or greater than, SO~s. In
`the case where delay spread is equal
`to 0. 2~s this
`imposes an unnecessary loss of channel capacity.
`It
`should be noted that the delay spread in the time domain
`transforms
`to
`frequency dispersion in
`the
`frequency
`domain. Whether the effect is viewed as a
`frequency
`time dispersion,
`dispersion, or a
`the effect is the
`same, i.e. loss of channel capacity.
`
`to
`The use of a guard space in an OFDM sys tern,
`overcome the effect of delay spread, is illustrated in
`Figure 5. The guard space takes the form of a cyclic
`repetition of the first part of an OFDM burst, i.e. the
`beginning of the OFDM burst is copied and repeated at
`the end of the burst.
`The OFDM symbol duration is
`denoted by T5 and the duration of the guard Space is
`denoted by Tg.
`An OFDM receiver has a
`time window in
`which it can receive an OFDM symbol.
`The minimum
`duration of
`this
`time window is equal
`The
`to T5
`•
`receiver can,
`therefore, only see that part of
`the
`signal which is not destroyed by delay spread in the
`communications channel.
`A receiver must,
`therefore,
`time window which corresponds to T5 + Tg.
`have a
`The
`loss of performance imposed by the use of a guard space
`Tg is /J., where: !J. = 10log(Tg;T5 )dB. By using a variable
`guard space, as opposed to a fixed guard space having a
`duration corresponding to the maximum needed to overcome
`the effects of delay spread,
`the
`loss of
`system
`performance is reduced to the minimum extent necessary
`to avoid loss of data.
`In order to take account of
`known delay spread in different environments, Tg must be
`capable of being varied from 0.2ps to SOps.
`
`the
`The concept of the present invention, namely
`use of a variable guard space can be implemented in an
`OFDM system as explained below.
`The guard space is
`
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`W097/30531
`
`PCT/SE97/00109
`
`-
`
`8 -
`
`the
`transmitted data
`into
`inserted
`stream after
`modulation and before multiplexing by the transmitter.
`In
`the multiplexed OFDM signal,
`the guard space is
`transformed into an
`increase in the carrier spacing
`present in the OFDM burst, in the frequency domain. At
`the receiver, the guard space is regenerated when the
`OFDM burst
`is demultiplexed by FFT
`(fast
`fourier
`transform} processing. The receiver can detect the OFDM
`burst even if its time window is incorrectly set, and
`can adjust its time window to the correct value for
`proper reception of subsequent OFDM bursts.
`
`two way
`the
`for
`is adapted
`system
`the
`When
`transmission of data, i.e. when
`the receiver has a
`transmission capability,
`the receiver may measure
`the
`delay spread present in a received signal and transmit
`a control signal to the transmitter which causes the
`transmitter to adjust the duration of Tg to the minimum
`value needed
`to overcome loss of data
`through delay
`spread.
`In this way, the system uses the minimum guard
`space necessary to overcome the effects of delay spread,
`thereby maximising the channel traffic capacity without
`signal degradation in the receiver.
`
`A transmitter for use in the present invention must
`be able to insert a guard space in the transmitted data
`bursts and be able to adjust the duration of the guard
`space, so that it is just sufficient to eliminate signal
`degradation by delay
`spread.
`In addition,
`the
`transmitter may be adapted to receive a control signal,
`from a
`receiver,
`indicative of the amount of delay
`spread present in a received signal, and to use this
`signal to adjust the duration of the guard space, on a
`continuous basis. This ability to continuously vary the
`duration of the guard space, during system operation, is
`particularly valuable where the system is used in mobile
`telephony.
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`PCT/SE97/00109
`
`-
`
`9 -
`
`A receiver for use in the present invention must be
`able to adjust the reception window for OFDM bursts to
`match the size of the transmitted burstt as received.
`In particulart the FFT frame must be synchronised with
`the received OFDM burstt if the received signal is to be
`demultiplexed correctly. Howevert a receiver can still
`detect a received burstt even if its reception window is
`incorrectly sett and can adjust the reception window to
`match the correct value for the received signal.
`In
`addition, the receiver may measure the amount of delay
`spread present in the received signal and transmit a
`control
`signalt
`to
`the
`transmittert
`causing
`the
`transmitter to adjust the duration of the guard space
`employed.
`
`The present invention has particular application in
`mobile telephonyt in which a plurality of base stations
`transmit data to a plurality of mobile stations.
`In
`such systems, delay spread may vary during the course of
`transmissiont between a given base station and a given
`mobilet as the mobile's position continuously changes.
`Furthermore, in such systems, traffic capacity is at a
`premium. The ability to continuously measure the delay
`spread present and adjust guard spaces, in OFDM bursts,
`to ensure undegraded transmission with a minimum guard
`space duration t
`conserves
`traffic capacity
`in
`a
`transmission channel.
`
`The design and implementation of OFDM systems
`are
`known
`to
`those
`skilled
`in
`the
`art
`well
`of
`telecommunications t and
`the manner
`in which an
`OFDM
`system,
`implementing
`the present
`invention, can be
`realised will be readily apparent to those skilled in
`the art, from the foregoing description.
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`W097130531
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`CLAIMS
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`- 10 -
`
`PCT/SE97100109
`
`a
`receiver and
`a
`system comprising
`An OFDM
`1.
`transmitter, said transmitter being adapted to transmit
`data in OFDM symbol bursts in which, in the time domain,
`a portion of a symbol burst is repeated within said
`symbol burst as a guard space, said receiver having a
`time window with which, after demultiplexing, said
`symbol burst must be aligned, characterised in that said
`repeated portion of a symbol burst has a duration which
`is variable and which
`is adjusted, during
`system
`operation, to a minimum duration necessary to prevent
`data loss caused by delay spread.
`
`An OFDM system as claimed in claim 1, char~cterised
`2.
`in that said receiver is adapted
`to vary said
`time
`window to produce, on demultiplexing, a guard space of
`a minimum duration necessary to prevent data loss caused
`by delay spread.
`
`An OFDM sys tern as claimed in either claim 1, or
`3.
`claim 2, characterised in
`that the portion of said
`symbol burst which is repeated is copied from a leading
`edge of said symbol burst.
`
`An OFDM system as claimed in any previous claim
`4.
`characterised in that said repeated portion of said
`symbol burst is repeated at a
`trailing edge of said
`symbol burst.
`
`An OFDM system as claimed in any previous claim,
`5.
`characterised in that said receiver includes performance
`measuring means for measuring received signal quality
`and reception window adjusting means for adjusting said
`time window duration.
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`W097/30S31
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`PCT/SE97/00109
`
`- 11 -
`
`An OFDM system as claimed in claim 5, characterised
`6.
`in that said receiver is adapted to transmit a signal to
`said transmitter indicative of a level of delay spread
`in a received signal, and said transmitter is adapted to
`adjust said guard space duration to a minimum value
`necessary to prevent data loss caused by delay spread.
`
`An OFDM system as claimed in any previous claim,
`7.
`characterised in that said guard space can be adjusted
`to a duration of between 0.2ps and SOps.
`
`An OFDM system as claimed in any previous claim,
`8.
`characterised in that said receiver is adapted to detect
`a
`transmitted
`signal when
`said
`time window
`is
`incorrectly adjusted.
`
`An OFDM system as claimed in any previous claim,
`9.
`characterised in that said system includes a plurality
`of mobile stations and a plurality of base stations, and
`is adapted to operate as a mobile
`telecommunications
`system.
`
`10. A receiver, for use with an OFDM system including
`a transmitter adapted to transmit data in OFDM symbol
`bursts, in which, in the time domain, a portion of a
`symbol burst is repeated within said symbol burst as a
`guard space, said receiver having a
`time window with
`which, after demultiplexing, said symbol burst must be
`aligned, characterised in that said repeated portion of
`a symbol burst has a duration which is variable and said
`receiver is adapted to vary said time window to produce,
`on demultiplexing, a guard space of a minimum duration
`necessary to prevent data loss caused by delay spread.
`
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`11. A receiver as claimed in claim 10, characterised in
`that said receiver includes performance measuring means
`for measuring received signal quality and reception
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`PCT/SE97/00109
`
`window adjusting means for adjusting said time window
`duration in respon~e to a signal from said performance
`measuring means.
`
`12. A receiver as claimed in claim 11, characterised in
`that said receiver is adapted to transmit a signal to
`said transmitter indicative of a level of delay spread
`in a received signal, and said transmitter is adapted to
`adjust said guard space duration to a minimum va 1 ue
`necessary to prevent data loss caused by delay spread.
`
`13. A receiver as claimed in any of claims 10 to 12,
`characterised in that said guard space can be adjusted
`to a duration of between 0.2ps and SOps.
`
`14. A receiver as claimed in any of claims 10 to 13,
`characterised in that said receiver is adapted to detect
`time window
`transmitted
`signal when
`said
`is
`a
`incorrectly adjusted.
`
`15. A receiver as claimed in any of claims 10 to 14,
`characterised in that said receiver is a mobile radio
`telephony transceiver adapted for use with a mobile
`telecommunications system.
`
`16. A method of operating an OFDM system comprising a
`receiver and a transmitter, by transmitting data as a
`series of OFDM symbol bursts, each symbol burst, in the
`time domain, having a portion thereof repeated therein
`as a guard space, said receiver having a
`time window
`with which, after demultip1exing, said symbol burst must
`be aligned, characterised by the repeated portion of a
`symbol burst having a variable duration, and adjusting
`said variable duration to produce a guard space of a
`minimum duration necessary to prevent data loss caused
`by delay spread.
`
`5
`
`10
`
`15
`
`20
`
`25
`
`30
`
`Facebook's Exhibit No. 1024
`Page 14
`
`

`

`W097/30531
`
`- 13 -
`
`PCT/SE97/00109
`
`17. A method as claimed in claim 16 characterised in
`that said receiver time window is adjusted to produce,
`on demultiplexing, a guard space of a minimum duration
`necessary to prevent data loss caused by delay spread.
`
`18. A method as claimed in either claim 16, or claim
`17, characterised by copying the repeated portion of
`said symbol burst from a leading edge thereof.
`
`19. A method as claimed in any of claims 16 to 18,
`characterised by repeating the repeated portion of said
`symbol burst at a trailing edge of said symbol burst.
`
`20. A method as claimed in any of claims 16 to 19,
`characterised by said receiver measuring received signal
`quality and adjusting said time window duration so that
`said received signal quality exceeds a predetermined
`threshold.
`
`to 20,
`21. A method as claimed in any of claims 16
`characterised in that said guard space can be adjusted
`to a duration of between 0.2ps and 50ps.
`
`A method as claimed in any of claims 16 to 21,
`22.
`characterised by said receiver detecting a transmitted
`signal when said time window is incorrectly adjusted.
`
`5
`
`10
`
`15
`
`20
`
`Facebook's Exhibit No. 1024
`Page 15
`
`

`

`wo 97/30531
`
`PCT/SE97/00109
`
`112
`
`0.8
`0.7
`0.6
`~
`::::, 0.5
`
`...._ ·- 0.4
`-~
`E: 0.3
`c::s
`0.2
`0.1
`0
`
`0
`
`I
`
`1 2
`
`I
`
`3
`
`I
`
`4
`
`II
`
`~I
`
`l
`
`7
`5 6
`fime(s)x 70-5
`
`045T·----------~------~
`0.40
`0.35
`(!J 0. 30
`-g 0.25
`~ 0.20
`~ 0.15
`CJ 0. 70
`0.05
`0
`
`0
`
`Q5
`
`7
`
`1.5
`
`25
`2
`fime(s)x70-6
`
`0.8.-----------------~
`07
`~ 06-
`~ 0.5-
`.....
`~ 0.4-
`E:
`CJ 0.3-
`0.2-
`0.7-
`0 as
`
`0
`
`15
`
`1
`
`~
`2
`time(s)x70-6
`
`Facebook's Exhibit No. 1024
`Page 16
`
`

`

`WO 97/30531
`
`PCT/SE97/00109
`
`2/2
`
`05
`
`amplitude S wy
`
`0.4
`
`0.2
`
`0
`
`05
`
`~«6f)~(O1S DOS
`time (s)x 107
`
`OFDM symbol time (Ts)
`
`Tg
`
`Facebook's Exhibit No. 1024
`Page 17
`
`Facebook's Exhibit No. 1024
`Page 17
`
`

`

`1
`INTERNATIONAL SEARCH REPORT
`
`International application No.
`PCT/SE 97/00109
`
`A. CLASSIFICATION OF SUBJECT MATTER
`
`IPC6: HO4L 5/06
`According to International Patent Classification (IPC) or to both national classification and IPC
`B. FIELDS SEARCHED
`
`Minimum documentation searched (classification system followed byclassification symbols)
`
`IPC6: HO4L
`
`Documentation searched other than minimum documentation to the extent that such documents are included in the fields searched
`
`SE,DK,FI,NO classes as above
`
`Hlectronic data base consulted during the international search (name of data base and, where practicable, search terms used)
`
`C. DOCUMENTS CONSIDERED TO BE RELEVANT
`
`Category*|tationofdocument,withindication,appropriate,oftherelevantpassages|ofdocument, with indication, where|tationofdocument,withindication,whereappropriate,oftherelevantpassages|ofthe relevant passageswhere Relevantto claim No.
`
`
`
`
`
`
`
`
`
`
`
`DE 4425713 C1 (INSTITUT FiiR RUNDFUNKTECHNIK GMBH),
`1-22
`20 April 1995 (20.04.95),
`claims 1-3,
`abstract
`
`(BRITISH BROADCASTING CORPORATION),
`WO 9406231 Al
`17 March 1994 (17.03.94), page 7,
`line 37 - page 8,
`line 9, abstract
`
`IEEE TRANSACTIONS ON BROADCASTING, Volume 41, No 1,
`March
`1995, William Y. Zou et al,
`"COFDM: AN
`OVERVIEW", see especially abstract and chapter 3.3.
`
`1-22
`
`
`
`[] Further documents arelisted in the continuation of Box C.
`*
`Special categories of cited documents:
`“T”
`“A*
`A”
`document defining the general state of the art which is not considered
`to be of particular relevance
`“E”
` erlier documentbut published on orafter the internationalfiling date
`Ts
`L”
`document which may throw doubts on priority claim(s) or which is
`cited to establish the publication date of another citation or other
`special reason(as specified)
`documentreferring to an oral disclosure, use, exhibition or other
`means
`documentpublishedprior to the international filing date but Later than
`the priority date claimed
`Date of the actual completion of the international search
`
`“©”
`
`“P*
`
`Nameand mailing address of the ISA/
`Swedish Patent Office
`Box 5055, S-102 42 STOCKHOLM
`Facsimile No. +46 8 666 02 86
`Form PCT/ISA/210 (second sheet) (July 1992)
`
`[x See patent family annex.
`tater document published after the international filing date or priority
`date and not in conflict with the application but cited to understan
`the
`iple or theory
`underlying the invention
`“X* document of particular relevance: the claimed invention cannot be
`be considered to involve an inventive
`considered novel or cannot
`step when the document is taken alone
`“Y" document ofparticular relevance: the claimed invention cannot be
`considered to involve an inventive step when the document is
`combined with one or more other such documents, such combination
`being obvious to a personsidlled in the art
`“&*° document member ofthe same patent family
`Date of mailing of the international search report
`
`30 -05- 1997
`Authorized officer
`
`MIKAEL SOLLERHED
`Telephone No.
`+46 8 782 25 00
`
`Facebook's Exhibit No. 1024
`Page 18
`
`Facebook's Exhibit No. 1024
`Page 18
`
`

`

`INTERNATIONAL SEARCH REPORT
`
`International application No.
`Information on patent family members
`02/04/97|PCT/SE 97/00109
`
`
`
`
`
`cited in search report
`DE
`4425713 Cl
`
`date
`
`
`20/04/95
`
`member(s)
`3162795 A
`9602989 A
`
`AU
`WO
`
`
`
`
`
`
`date
`
`16/02/96
`
`
`01/02/96
`
`
`WO
`9406231 Al
`17/03/94
`AU
`4975493 A
`29/03/94
`EP
`0658295 A
`21/06/95
`
`
`GB
`2270819 A,B
`23/03/94
`
`
`JP
`8501195 T
`06/02/96
`US
`5610908 A
`
`11/03/97 SSeSLSASYSSNSSSehSs As mS SS SDSeeSSG ecyDus tecee ee ewe
`
`
`
`Form PCT/ISA/210 (patent family annex) (July 1992)
`
`
`
`Facebook's Exhibit No. 1024
`Page 19
`
`Facebook's Exhibit No. 1024
`Page 19
`
`