USOO701.2882B2
`
`(12) United States Patent
`Wang et al.
`
`(10) Patent No.:
`(45) Date of Patent:
`
`US 7,012,882 B2
`Mar. 14, 2006
`
`(*) Notice:
`
`(54) CHANNEL ESTIMATOR FOR OFDM
`SYSTEM
`(75) Inventors: Zhaocheng Wang, Stuttgart (DE);
`Richard Stirling-Gallacher, Stuttgart
`(DE); Thomas Dölle, Haar (DE)
`(73) Assignee: Sony International (Europe) GmbH,
`Berlin (DE)
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 928 days.
`(21) Appl. No.: 09/919,040
`(22) Filed:
`Jul. 30, 2001
`(65)
`Prior Publication Data
`US 2002/0034213 A1
`Mar. 21, 2002
`Foreign Application Priority Data
`(30)
`Aug. 1, 2000
`(EP) .................................. OO116635
`(51) Int. Cl.
`(2006.01)
`H04J II/00
`(52) U.S. Cl. ....................... 370/208; 370/203; 370/206
`(58) Field of Classification Search ................ 370/203,
`370/206,343, 480,491; 375/147
`See application file for complete Search history.
`
`(56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`5,519,730 A *
`5/1996 Jasper et al. ................ 375/260
`5,828,650 A * 10/1998 Malkamaki et al. ........ 370/203
`5,867.478 A * 2/1999 Baum et al. ................ 370/203
`6,240,146 B1* 5/2001 Stott et al. .................. 375/344
`6,310,926 B1 * 10/2001 Tore ........................... 375/355
`
`6,370,131 B1* 4/2002 Miya.......................... 370/335
`6.424,678 B1* 7/2002 Doberstein et al. ......... 375/260
`6,470,030 B1 * 10/2002 Park et al. .................. 370/480
`6,545,997 B1 * 4/2003 Bohnke et al. ............. 370/347
`6,549,753 B1
`4/2003 Rinne ........................ 455/3.02
`6,807,147 B1 * 10/2004 Heinonen et al. .....
`... 370/208
`455/63
`2002/0065047 A1
`5/2002 Moose .............
`- - -
`2002/01764.83 A1 11/2002 Crawford .................... 375/137
`
`FOREIGN PATENT DOCUMENTS
`
`11/1998
`5/1998
`
`EP
`O 877526
`WO
`WO 98 1941O
`* cited by examiner
`Primary Examiner-Ajit Patel
`ASSistant Examiner-Steven A Blount
`(74) Attorney, Agent, or Firm-Oblon, Spivak, McClelland,
`Maier & Neustadt, P.C.
`(57)
`ABSTRACT
`
`The present invention relates to a device (10) for receiving
`Signals in a wireleSS Orthogonal frequency division multi
`plex (OFDM) system and to a channel estimation method in
`Such a System. The data Symbols and pilot Symbols are
`transmitted in frequency Subcarriers and timeslots, whereby
`pilot Symbols are transmitted in a continuous Stream within
`at least one frequency Subcarrier. A channel estimation for a
`data symbol is performed on the basis of received pilot
`Symbols using a filter including a common phase error
`correction value from the continuous Stream pilot Symbol in
`the Same timeslot as the data Symbol to be channel esti
`mated.
`
`The present invention thereby enables a correct and efficient
`channel estimation including a common phase error correc
`tion to be performed.
`
`4 Claims, 2 Drawing Sheets
`
`Modified foctors based
`linear interpolation
`chonnel estimotion
`
`Modified foctors
`Calculation
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`
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`frequency
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`from other continuol pilots
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`time
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`Ford Motor Co.
`Exhibit 1031
`Page 001
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`

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`U.S. Patent
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`Mar. 14, 2006
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`Sheet 1 of 2
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`US 7,012,882 B2
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`| 613
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`uM00
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`UOISIQAu0)
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`Ford Motor Co.
`Exhibit 1031
`Page 002
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`U.S. Patent
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`Mar. 14, 2006
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`Sheet 2 of 2
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`US 7,012,882 B2
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`TWO pilot symbols bosed
`linear interpolotion
`chonnel estimotion
`
`
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`frequency
`
`Fig. 2
`
`
`
`Modified foctors bosed
`linear interpolation
`chonnel estimotion
`
`Modified foctors
`Calculation
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`53
`|| T. 1524
`D
`O
`(77. C.
`HT 144.
`214
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`from other continuol pilots
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`Fig. 3
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`a-A
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`all
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`Ala
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`sala
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`time
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`Ford Motor Co.
`Exhibit 1031
`Page 003
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`

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`1
`CHANNEL ESTMATOR FOR OFDM
`SYSTEM
`
`US 7,012,882 B2
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`The present invention relates to the channel estimation in
`a wireless orthogonal frequency division multiplex (OFDM)
`System. Particularly, the present invention relates to a device
`for receiving signals in a wireless OFDM system and to a
`channel estimation method in a wireless OFDM system.
`Wireless OFDM communication systems are systems, in
`which communication devices, as e.g. base Stations, com
`municate with other devices, as e.g. mobile terminals, over
`a wireless communication link. In an OFDM system, the
`entire frequency bandwidth used for the transmission of
`Signals is Subdivided into a plurality of frequency Subcarri
`erS. Adjacent frequency Subcarriers are respectively
`15
`orthogonal to each other. Thus, very high data rate commu
`nication can be achieved in OFDM systems.
`A transmission channel of an OFDM system can be
`characterised by a specific frequency Subcarrier and a spe
`cific timeslot. A piece of information, Such as a data Symbol,
`to be transmitted in that specific transmission channel is
`mapped onto the frequency Subcarrier in the Specific
`timeslot. The data transmission in an OFDM system can
`therefore be represented by a time/frequency grid. In the
`frequency domain, adjacent transmission channels have
`respectively orthogonal frequency Subcarriers.
`On the receiving side of an OFDM communication link,
`as e.g. a mobile terminal receiving Signals from a base
`Station, a channel estimation is performed for each trans
`mission channel or data Symbol in order to optimise the
`demodulation in the receiver in view of the estimated
`channel quality. Hereby, a specific pilot Symbol pattern is
`transmitted in the time/frequency grid of the OFDM com
`munication link. The time/frequency location (frequency
`35
`subcarrier and timeslot) of the pilot symbols as well as the
`pilot symbol itself are known to the receiver, so that the
`receiver is able to perform a channel estimation for data
`Symbols transmitted in transmission channels different from
`the pilot Symbols. A typical pilot Symbol pattern with a
`plurality of pilot Symbols placed in the frequency Subcarrier/
`time grid of an OFDM system is shown in FIG. 2. The
`frequency domain is Subdivided into a plurality of frequency
`Subcarriers and the time domain is Subdivided into a plu
`rality of timeslots. Each frequency Subcarrier and each
`timeslot define a transmission channel for the transmission
`of a data symbol or a pilot symbol. Pilot symbols are
`indicated by circles. In the example shown in FIG. 2, pilot
`Symbols are transmitted in the frequency Subcarrier f and
`in the frequency Subcarrier f
`in respectively equidistant
`timepoints. For example, in the timeslots t
`,
`2, pilot
`Symbols are transmitted on both frequency Subcarriers f
`and f2.
`In the following, the principle of a Standard channel
`estimation method in an OFDM communication system is
`described. An OFDM signal received in a receiving device
`of the OFDM system after a fast Fourier transformation for
`a frequency Subcarrier X and a timeslot i can be represented
`by
`
`45
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`50
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`55
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`25
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`40
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`risix hy. +n.
`whereby S
`is the transmitted data symbol, he is the
`complex channel response and n is the adaptive White
`Gaussian noise for the frequency Subcarrier X and the
`timeslot i.
`For almost all channel estimation Schemes, the first Step
`is to use the knowledge of the transmitted pilot Symbols and
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`60
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`65
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`2
`the received signals to perform a channel estimation at the
`frequency Subcarrier/timeslot location of the pilot Symbol.
`ASSuming that the pilot Symbols are located at the frequency
`carrier position X and the timeslot position i', an initial
`channel estimation can be formed by
`
`x,
`
`Sa'i
`
`In order to obtain the channel estimation values for the
`frequency Subcarriers and the timeslots located between the
`pilot Symbols (in frequency and/or in time dimension), a
`filter is usually used. This filter can have Several general
`forms, which include a one-dimensional form (in frequency
`or time), a two-dimensional form (in frequency and time),a
`two-one-dimensional form (first frequency and then time or
`vice versa) and the like. Further, the filter itself can have
`fixed or variable coefficients. A very simple example of an
`one-dimensional time filter based e.g. on a linear interpola
`tion Scheme is explained in FIG. 2. In this case, the channel
`estimation for the transmission channel 20, which is char
`acterised by the frequency Subcarrier f and the timeslot t,
`is performed on the basis of the two pilot symbols 21 and 22
`in the frequency Subcarrier f and timepoints t and t,
`respectively. Therefore, transmission channel 20 to be esti
`mated is transmitted on the same frequency Subcarrier f as
`the pilot Symbols 21, 22, So that only a one-dimensional time
`filter is necessary. Thus, the channel estimation for the
`transmission channel 20 can e.g. very simply be performed
`on the basis of a linear interpolation of the channel trans
`mission properties of the received pilot Symbols 21 and 22.
`However, all channel estimation algorithms proposed and
`used for OFDM communication systems as described above,
`do not take into account the effect of phase noise on the
`result of the channel estimation using received pilot Sym
`bols. The phase noise stems from the local oscillator in the
`receiver, which is a random pertubation of the phase of the
`steady sinusoidal waveform. There are two different kinds of
`phase noise. The first kind rotates the received signals by an
`amount, which is the same for all frequency Subcarriers
`within one OFDM symbol (within one timeslot), but varies
`randomly from symbol to symbol, i.e. from timeslot to
`timeslot. This first kind of phase noise is called common
`phase error (CPE) and primarily results from the lower
`frequency components of the phase noise Spectrum of the
`local oscillator. The Second kind of phase noise is called
`intercarrier interference (ICI) which works like additive
`thermal noise and primarily results from the higher fre
`quency components of the phase noise Spectrum of the local
`oscillator. The CPE component caused by the phase noise is
`eliminated in known receiving devices by inserting a com
`plex CPE correction module in an OFDM demodulator.
`Alternatively, the effect of the phase noise can be reduced by
`adapting a stable but expensive local oscillator. However,
`using a complex CPE correction module as an additional
`element or a stable and expensive local oscillator raises the
`entire costs and the constructional complexity.
`The object of the present invention is therefore to provide
`a device for receiving signals in a wireless OFDM system
`and a channel estimation method in a wireless OFDM
`System, which allow the implementation of a simple but
`effective channel estimation algorithm with a simple con
`Struction.
`The above object is achieved by a device for receiving
`Signals in a wireleSS OFDM System according to claim 1, in
`
`Ford Motor Co.
`Exhibit 1031
`Page 004
`
`

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`US 7,012,882 B2
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`3
`which data Symbols and pilot Symbols are transmitted in
`frequency Subcarriers and timeslots. The device according to
`the present invention comprises receiving means for receiv
`ing pilot Symbols transmitted in a continuous Stream within
`at least one frequency Subcarrier and channel estimation
`means for performing a channel estimation for a data Symbol
`on the basis of received pilot symbols using a filter including
`a common phase error correction value from the continuous
`Stream pilot Symbol in the same timeslot as the data Symbol
`to be channel estimated.
`Further, the above object is achieved by a channel esti
`mation method in a wireless OFDM system according to
`claim 6, in which data Symbols and pilot Symbols are
`transmitted in frequency Subcarriers and timeslots and in
`which pilot Symbols are transmitted in a continuous Stream
`within at least one frequency Subcarrier, whereby a channel
`estimation for a data Symbol is performed on the basis of
`received pilot Symbols using a filter including a common
`phase error correction value from the continuous Stream
`pilot symbol in the same timeslot as the data symbol to be
`channel estimated.
`Thus, the present invention proposes a channel estimation
`on the basis of received pilot symbols using a filter including
`a common phase error correction value. The filter can be any
`kind of filter. The common phase error correction value is
`obtained on the basis of the continuous Stream pilot Symbol
`in the same timeslot as the data Symbol to be channel
`estimated. Thus, the wireless OFDM communication system
`of the present invention necessarily requires at least one
`continuous Stream of pilot Symbols in one of the plurality of
`frequency Subcarriers. Some OFDM systems used in wire
`less communication or telecommunication scenarios have a
`high number of frequency Subcarriers, So that using at least
`one entire frequency Subcarrier for the transmission of a
`continuous Stream of pilot Symbols does not effect the data
`transmission capacity too much. It has to be noted that the
`term continuous Stream of pilot Symbols means that each of
`the consecutive Symbols or timeslots of a respective fre
`quency Subcarrier carries a pilot Symbol, So that a continu
`ous Stream of respectively Succeeding pilot Symbols is
`40
`transmitted in that frequency Subcarrier. Further, the com
`mon phase error is the same for all frequency Subcarriers
`within one symbol or timeslot, So that using a phase error
`correction value from the pilot symbol of the continuous
`Stream in the same timeslot as the data Symbol to be channel
`estimated ensures that the phase error can be Sufficiently
`reduced or even eliminated. Further, the present invention
`allows the integration of the common phase error correction
`into the channel estimation algorithm So that the overall
`processing complexity is reduced.
`Advantageous features are claimed in the respective Sub
`claims.
`Advantageously, the receiving means is further adapted to
`receive distributed or scattered pilot symbols distributed or
`Scattered among Said frequency Subcarriers and timeslots,
`whereby Said channel estimation means performs said chan
`nel estimation on the basis of at least two of Said distributed
`pilot Symbols. In other words, besides the continuous Stream
`of pilot Symbols in at least one frequency Subcarrier, further
`distributed pilot symbols are used. These distributed pilot
`Symbols do not need to be in adjacent transmission channels
`and can have a regular or an irregular pattern, as long as the
`pattern is known to the receiving device performing the
`channel estimation. Additionally using pilot Symbols from
`the pattern of distributed pilot symbols makes the channel
`estimation on the receiving Side more accurate and reliable
`and therefore further increases the receiving quality. Hereby,
`
`4
`the channel estimation means may perform the channel
`estimation on the basis of at least two of Said distributed
`pilot symbols in different timeslots using a time filter. Thus,
`a time filter on the basis of at least two pilot Symbols having
`different timeslots is used together with the common phase
`error correction value from the continuous Stream pilot
`symbol of the same timeslot as the data symbol to be channel
`estimated. Hereby, a very accurate and efficient channel
`estimation can be performed.
`The channel estimation means advantageously calculates
`the common phase error correction value on the basis of the
`continuous Stream pilot Symbol in the same timeslot as the
`data symbol to be channel estimated and on the basis of the
`continuous Stream pilot Symbols respectively in the same
`timeslots as said at least two distributed pilot symbols. The
`at least two distributed pilot symbols are located in different
`timeslots So that a respective continuous Stream pilot Symbol
`can be found in the respective same timeslots. Then, the
`common phase error correction value is calculated on the
`basis of the continuous Stream pilot Symbol in the same
`timeslot as the data Symbol to be channel estimated and on
`the basis of the at least two continuous Stream pilot Symbols
`in the same timeslots as the distributed pilot symbols. In this
`case, the common phase error correction value is advanta
`geously calculated on the basis of common phase error ratioS
`between Said continuous Stream pilot Symbol in the same
`timeslot as the data Symbol to be channel estimated and each
`of Said continuous Stream pilot Symbols respectively in the
`Same timeslot as Said at least two distributed pilot Symbols.
`Hereby, the common phase error ratioS are implemented in
`the algorithm for calculating the channel estimation for the
`respective data symbol so that a simple and effective imple
`mentation of the entire channel estimation algorithm includ
`ing a common phase error Suppression is enabled.
`The present invention is explained in more detail in the
`following description in relation to the enclosed drawings, in
`which
`FIG. 1 shows a wireless OFDM communication system
`including a transmitting device and a receiving device,
`FIG. 2 shows a Subcarrier frequency and timeslot grid of
`a wireless OFDM communication system with a known pilot
`Symbol pattern, and
`FIG. 3 shows an example of a Subcarrier frequency and
`timeslot grid of an OFDM communication System according
`to the present invention having at least one continuous
`Stream of pilot Symbols within one frequency Subcarrier.
`A wireleSS communication System comprising a transmit
`ting device 1, Such as a base Station, and a receiving device
`10, Such as a mobile terminal, are shown in FIG. 1. The
`wireless communication system is an OFDM system, in
`which data Symbols are transmitted in frequency Subcarriers
`and timeslots. The entire frequency range is Subdivided into
`a plurality of frequency Subcarriers. The transmitting device
`1 comprises all necessary and known elements for the
`operation in a wireleSS OFDM communication System, Such
`as a voice codec 2, a channel encoder 3, an interleaver 4, a
`modulation means 5, an upconversion means 6, a power
`amplifier 7 and an antenna 8. In case that the transmitting
`device 1 is part of a base Station or a mobile terminal of the
`OFDM system, it further comprises all necessary elements
`for receiving Signals and for processing the received signals.
`Signals transmitted via the antenna 8 of the transmitting
`device 1 are wirelessly transmitted to a receiving device 10
`of the wireless OFDM communication system, optionally
`with the Support of an intermediate amplifying radio tower
`as shown. The receiving device 10 of the wireless OFDM
`communication System is a receiving device according to the
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`Exhibit 1031
`Page 005
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`S
`present invention and comprises all necessary elements for
`the operation in the wireless OFDM communication system,
`Such as an antenna 11, a low-noise amplifier 12, a down
`conversion means 13, an A/D-converter 14, a demodulation
`means 15, a channel estimation means 16, a deinterleaver
`17, a channel decoder 18 and a voice codec 19. In case that
`the receiving device 10 is part of a mobile terminal of the
`wireless OFDM communication system, it further comprises
`all necessary elements for transmitting Signals and proceSS
`ing to be transmitted Signals in the communication System.
`The channel estimation means 16 performs the channel
`estimation for the transmission channels or data Symbols
`received from the transmitting device 1 and Supplies the
`correspondingly calculated channel estimation values to the
`demodulation means 15, which correspondingly demodu
`lates the received data Symbols So that a good receiving
`quality is ensured.
`AS Stated in the introduction, the channel estimation in
`OFDM systems using coherent modulation as in the present
`case, the channel estimation is performed on the basis of
`filters or algorithms operating in the frequency and/or the
`time domain. The channel estimation means 16 of the
`receiving device 10 according to the present invention also
`performs a channel estimation on the basis of a filter.
`However, the used filter includes a common phase error
`correction value to reduce the common phase error Stem
`ming from the local oscillator (not shown) used in the
`receiving device 10. In order to provide a common phase
`error correction value which can be included into the filter
`ing and thus into the channel estimation of a data Symbol, a
`pilot Symbol pattern is necessary, in which at least one
`frequency subcarrier a continuous stream of pilot symbols is
`transmitted and received by the receiving device 10 accord
`ing to the present invention. A continuous Stream of pilot
`Symbols means here that each timeslot or Symbol of at least
`one frequency Subcarrier carries a pilot Symbol, as e.g. the
`Subcarriers f and f shown in the frequency Subcarrier and
`timeslot grid of a wireless OFDM system according to the
`present invention shown as an example in FIG. 3.
`According to the present invention, a common phase error
`correction value from the continuous Stream pilot Symbol in
`the same timeslot as the data Symbol to be channel estimated
`is used in the filter for the channel estimation. If, e.g. the data
`symbol 30 of the frequency/time grid shown in FIG. 3 is to
`be channel estimated in the receiving device 10 shown in
`FIG. 1, a common phase error correction value from the pilot
`symbol 33 which has the same timeslott as the data symbol
`30 is used in the filter for the channel estimation. The general
`construction of the filter can be of any type.
`However, better channel estimation can be performed if
`the filter is applied in more than one dimension (time and/or
`frequency). An example is shown in and explained in
`relation to FIG. 3. Here, the time/frequency grid shows two
`frequency Subcarriers f and f having a continuous stream
`of pilot symbols transmitted therein. Further, distributed
`pilot Symbols are transmitted in distributed transmission
`channels between the frequency Subcarriers with the con
`tinuous Stream of pilot Symbols. In the shown example,
`distributed pilot Symbols are transmitted in the frequency
`Subcarriers f and f
`in an equidistant fashion and at the
`Same timepoints. For example, the pilot Symbol 31 is
`transmitted in the frequency Subcarrier f
`in the same
`timeslott as the pilot symbol 38 in the frequency Subcarrier
`f. Hereby, if the transmission channel of the data Symbol
`30 is to be channel estimated, a one-dimensional filter in the
`time domain on the basis of the pilot symbols 31 and 32
`transmitted in the same frequency Subcarrier f can be used
`
`6
`as a filter for the channel estimation. Hereby, the common
`phase error correction value from the pilot symbol 33 can be
`included in the one-dimensional time filter. The pilot symbol
`33 has the same timeslot t, as the data symbol 30 to be
`channel estimated and therefore a similar or even the same
`phase error.
`In the following, an example of a channel estimation
`according to the present invention using a time domain
`filtering is explained. A convention channel estimation algo
`rithm using exclusively time domain filtering (without com
`mon phase error correction) yields the channel estimation
`h at the data Symbol locations (frequency Subcarrier X and
`timeslot i):
`h. XWhy
`whereby w is a transpose of the filter column vector for the
`timeslot i and h' is a column vector which contains a Subset
`of size N of the initial estimates at the pilot symbol locations
`hi, N being an integer number. In the present case, which
`is explained as an example, a time domain filtering is
`performed by using two pilot Symbols 31, 32, Spaced in time
`(N=2) and whereby the pilot symbols are separated by Y
`timeslots. Further, the wanted channel estimation is located
`at the timeslot i which is V timeslots from the first pilot
`Symbol. For Simple linear interpolation, this gives
`
`F.
`
`whereby C and C are the real channel transfer functions for
`the two pilot symbols 31 and 32 and P and P are their
`respective common phase errors caused by the phase noise
`of the local oscillator. For a coherent detection as necessary
`for the coherent demodulation, CXP is required, whereby
`C is the real channel transfer function and P is the common
`phase error caused by the phase noise of the data Symbol to
`be channel estimated. Since the common phase error is the
`same for all frequency Subcarriers within any one OFDM
`symbol or timeslot, but varies randomly from symbol to
`Symbol, PzPzP is valid. ASSuming that the channel trans
`fer function stays constant between the two consecutive pilot
`symbols 31 and 32, C=C=C is valid. This gives for the
`channel estimation:
`
`It can be seen that he is not equal to CXP. Therefore,
`with a non-negligible common phase error, the conventional
`linear interpolation algorithm does not work for coherent
`OFDM systems. According to the present invention, the
`effects of the phase noise are compensated by using a
`common phase error correction value in the filter algorithm.
`For example, a modified diagonal matrix R can be used in
`the channel estimation algorithm in order to compensate for
`the effects of the phase noise:
`
`The diagonal elements of the diagonal matrix R contain
`the modification factors or common phase error correction
`values. For example, in case that N=2,
`
`In relation to the example shown in FIG. 3, the pilot
`symbols 31 and 32 are used for the time filter but a common
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`Page 006
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`7
`phase error correction value from the pilot symbol 33 of the
`continuous Scheme of pilot Symbols of the frequency Sub
`carrier f
`is included. The pilot symbol 33 has the same
`timeslot t, as the data Symbol to be channel estimated. In
`relation to the above given equations, R can then be the
`common phase error ratio between the pilot symbol 34
`having the same timeslot d, as the first distributed pilot
`symbol 31. R can be the common phase error ratio between
`the pilot symbol 33 and the pilot symbol 35 having the same
`timeslot t as the second distributed pilot symbol 32. Both
`pilot symbols 34 and 35 are also part of the continuous
`Stream of pilot Symbols of the frequency Subcarrier f. In
`this way, a common phase error correction can be included
`in a simple and effective way into the channel estimation
`algorithm. Using the diagonal matrix R, the channel esti
`mation can be given by
`
`In the example given above, R is given as
`
`P
`R = ,
`P
`
`and R2 is given as
`
`ASSuming that the channel transfer function stays constant,
`i.e. C=C=C, between these consecutive pilot Symbols 34
`and 35, this equation can be modified to:
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`and therefore a reliable and correct channel estimation for
`coherent OFDM systems is achieved.
`In case that a Second or more frequency Subcarriers are
`provided having a continuous Stream of pilot Symbols, as
`e.g. frequency Subcarrier f of the example shown in FIG.
`3, further continuous Stream pilot Symbols can be used for
`the calculation of the common phase error correction value
`for the data symbol 30 to be channel estimated. For example,
`the pilot symbols 36 and 37 of the frequency Subcarrier f.
`in the same timeslots as the pilot symbols 34 and 35 of the
`frequency Subcarrier f. could be used and integrated in the
`matrix R. Hereby, a very accurate common phase error
`correction within the channel estimation algorithm is poS
`sible.
`The invention claimed is:
`1. Device (10) for receiving Signals in a wireless orthogo
`nal frequency division multiplex (OFDM) system, in which
`data Symbols and pilot Symbols are transmitted in frequency
`Subcarriers and timeslots, comprising
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`receiving means (11) for receiving pilot Symbols trans
`mitted in a continuous Stream within at least one
`frequency Subcarrier and receiving distributed pilot
`Symbols distributed among Said frequency Subcarriers
`and timeslots,
`channel estimation means (16) for performing a channel
`estimation for a data Symbol on the basis of received
`pilot Symbols using a filter including a common phase
`error correction value from the continuous Stream pilot
`symbol in the same timeslot as the data symbol to be
`channel estimated; Said channel estimation means per
`forming Said channel estimation on the basis of at least
`two of said distributed pilot symbols in different
`timeslots using a time filter; Said channel estimation
`means calculating Said common phase error correction
`value on the basis of the continuous Stream pilot
`symbol in the same timeslot as the data symbol to be
`channel estimated and on the basis of the continuous
`Stream pilot Symbols respectively in the Same timeslot
`as Said at least two distributed pilot Symbols.
`2. Device (10) according to claim 1, characterized in, that
`Said common phase error correction value is calculated on
`the basis of common phase error ratios between Said con
`tinuous Stream pilot Symbol in the same timeslot as the data
`Symbol to be channel estimated and each of Said continuous
`Stream pilot Symbols respectively in the same timeslot as
`said at least two distributed pilot symbols.
`3. Channel estimation method in a wireleSS orthogonal
`frequency division multiplex (OFDM) system, in which data
`symbols and pilot symbols are transmitted in frequency
`Subcarriers and timeslots and in which pilot Symbols are
`transmitted in a continuous Stream within at least one
`frequency Subcarrier, whereby a channel estimation for a
`data symbol is performed on the basis of received pilot
`Symbols using a filter including a common phase error
`correction value from the continuous Stream pilot Symbol in
`the Same timeslot as the data Symbol to be channel esti
`mated;
`wherein distributed pilot symbols are distributed among
`Said frequency Subcarriers and timeslots, whereby Said
`channel estimation is performed on the basis of at least
`two of said distributed pilot symbols in different
`timeslots using a time filter, and
`wherein Said common phase error correction value is
`calculated on the basis of the continuous Stream pilot
`symbol in the same timeslot as the data symbol to be
`channel estimated and on the basis of the continuous
`Stream pilot Symbols respectively in the Same timeslot
`as Said at least two distributed pilot Symbols.
`4. Channel estimation method according to claim 3,
`characterized in, that Said common phase error correction
`value is calculated on the basis of common phase error ratioS
`between Said continuous Stream pilot Symbol in the same
`timeslot as the data Symbol to be channel estimated and each
`of Said continuous Stream pilot Symbols respectively in the
`Same timeslot as Said at least two distributed pilot Symbols.
`
`Ford Motor Co.
`Exhibit 1031
`Page 007
`
`