KR20070020469A - A method for signal processing and a signal processor in an ofdm system - Google Patents

Abstract

)를 추정하는 단계와, 상기 채널 전달 함수(

)와 수신된 신호(y₀)로부터 데이터 추정 방식에 의한 데이터(

)의 추정 단계를 포함한다. 그후, 각 서브-캐리어에서 상기 채널 함수의 도함수(

)가 시간 필터링에 의해 추정되고, 인터-캐리어 간섭(ICI)은 순정된 수신된 신호(y₁)를 얻기 위해 상기 추정된 데이터(

)와 상기 채널 전달 함수의 상기 추정된 도함수(

)를 사용해서 상기 수신된 신호로부터 제거된다.A method for processing a signal for a receiver for an OFDM encoded digital signal, the method for neutralizing inter-carrier interference (ICI) caused by Doppler extension. OFDM encoded digital signals are transmitted as sub-carriers in multiple channels forming an OFDM block. This method is based on the channel estimation method in each sub-carrier.

Estimating) and the channel transfer function (

) And data by the data estimating method from the received signal y ₀

Estimating step). Then, the derivative of the channel function at each sub-carrier (

) Is estimated by temporal filtering, and inter-carrier interference (ICI) is estimated by the estimated data ( _i ) to obtain a pure received signal y ₁ .

) And the estimated derivative of the channel transfer function (

Is removed from the received signal.

Description

A method and signal processor for processing signals in an OPM system {A METHOD FOR SIGNAL PROCESSING AND A SIGNAL PROCESSOR IN AN OFDM SYSTEM}

The present invention relates to a signal processor corresponding to a method for processing a signal for a receiver for an encoded digital signal in a wireless communication system.

The invention also relates to a receiver for receiving an OFDM encoded signal and a mobile device comprising such a receiver. The invention also relates to a communication system comprising a mobile device. This method can be used to mitigate inter-carrier interference (ICI) caused by Doppler expansion, for example in terrestrial video broadcast systems (DVB-T) using OFDM techniques.

The mobile device may be, for example, a portable computer such as a portable television, cell phone, PDA or laptop or any combination thereof.

In wireless systems for the transmission of digital information such as voice and video signals, orthogonal frequency division multiplexing technology (OFDM) has been widely used. OFDM can be used to cope with a frequency selective fading radio channel. Interleaving of data can be used for effective data recovery and use of data error correction schemes.

Today, OFDM is used, for example, in the digital audio broadcasting (DAB) system Eureka 147 and the terrestrial digital video broadcasting system (DVB-T). DVB-T supports 5-30 Mbps net bit rates, depending on modulation and coding mode, over 8 MHz bandwidth. For the 8K mode 6817 sub-carriers (of 8192 total) are used for sub-carrier spacing of 1116 Hz. The OFDM symbol valid time duration is 896 ms and the OFDM guard interval is a period of 1/4, 1/8, 1/16 or 1/32.

However, in a mobile environment such as a car or a train, the channel transfer function perceived by the receiver is changed as a function of time. This change in transfer function within an OFDM symbol can cause inter-carrier interference (ICI) between OFDM sub-carriers, such as Doppler extension of the received signal. Inter-carrier interference increases with the increasing speed of the vehicle and makes it impossible to reliably detect above the threshold speed without countermeasures.

Signal processing methods are previously known from WO 02/067525, WO 02/067526 and WO 02/067527, where not only the data signal a but also the channel transfer function H of the OFDM symbol and the time derivative H of this function ') Is calculated for the particular OFDM symbol under consideration.

In addition, US Pat. No. 6,654,429 discloses a method for channel estimation using a pilot, where a pilot symbol is inserted into each data packet at a known position, thus occupying a predetermined position in time-frequency space. The received signal is two-dimensional inverse Fourier transform, two-dimensional filtering and two-dimensional Fourier transform to recover the pilot symbols to estimate the channel transfer function.

It is an object of the present invention to provide a less complex signal processing method.

Another object of the present invention is to provide a signal processing method in which the time correlation of the channel transfer function H is used.

Another object of the present invention is to provide a signal processing method for an OFDM receiver in which inter-carrier interference (ICI) is mitigated.

)는 상기 채널 전달 함수(

)와 신호(y ₀)로부터의 데이터 추정 방식에 의한 데이터(

) 추정에 의해 후속되는 각 서브-캐리어에서 채널 추정 방식에 의해 추정된다. 또한, 서브-캐리어의 서브세트에서 상기 채널 전달 함수의 도함수(

)는 시간 필터링에 의해 추정된다. 인터-캐리어 간섭(ICI)은 순정된 수신된 신호(y ₁)를 얻기 위해, 상기 추정된 데이터(

)와 상기 채널 전달 함수의 상기 추정된 도함수(

)를 사용해서 상기 신호로부터 제거된다.This and other objects are achieved by a method for processing for an OFDM encoded digital signal. OFDM encoded digital signals are transmitted as sub-carriers in multiple frequency channels. Channel transfer function (

) Is the channel transfer function (

) And data by the data estimation method from the signal y ₀

Is estimated by the channel estimation scheme at each sub-carrier subsequent to the estimation. Furthermore, the derivative of the channel transfer function in a subset of sub-carriers (

) Is estimated by time filtering. Inter-carrier interference (ICI) is calculated by the estimated data (I ₁ ) to obtain a genuine received signal y ₁ .

) And the estimated derivative of the channel transfer function (

) Is removed from the signal.

)를 계산하기 위해 상기 획득된 도함수(H_I')로부터 스펙트럼 보간에 의해 후속된다. 가상 파일롯 채널은 예를 들면, 3개와 12개의 채널 사이에서 이격된 모든 채널의 서브세트일 수 있다. 따라서, 충분한 정밀도로 가상 파일롯 채널로부터 중간 채널로 보간하는 것이 가능하다.Temporal filtering may be performed in the virtual pilot channel to obtain the derivative H _I ′ for the pilot channel _I , which is derived for the residual channel within the OFDM symbol (

Is followed by spectral interpolation from the obtained derivative (H _I ′). The virtual pilot channel may be, for example, a subset of all channels spaced between three and twelve channels. Thus, it is possible to interpolate from the virtual pilot channel to the intermediate channel with sufficient precision.

Time and spectral filtering can be performed by using a finite impulse transfer function (FIR) with precalculated filter coefficients. Thus, signal processing becomes less complicated.

Estimation of the channel transfer function from at least one other OFDM symbol may be used. This other OFDM symbol may be a previous or subsequent OFDM symbol.

Inter-carrier interference (ICI) can be removed using an initial estimate of the derivative H 'of the channel transfer function and an initial soft estimate of the data. Further estimation of the channel transfer function H may be performed at least after the removal of the inter-carrier interference (ICI) in the virtual pilot channel, so that more accurate data estimation is achieved.

Inter-carrier interference (ICI) can be eliminated by repetition of data estimation steps and removal steps.

Another aspect of the invention involves the use of a temporal binner filtering followed by a signal processor for performing the indicated method steps and spectral binner filtering according to the aforementioned method steps for reducing inter-carrier interference. do.

Further objects, features and advantages of the present invention will become apparent by reading the description of exemplary embodiments of the present invention with reference to the accompanying drawings.

1 is a graph depicting a channel transfer function as a function of frequency and time.

2 shows a signal required as a function of (sub-carrier) frequency.

3 is a schematic diagram of an OFDM symbol.

4 is a flow chart of an embodiment of the invention.

5 shows SINR before and after ICI removal for various rates.

6 shows the average MSA of H for various velocities.

FIG. 7 shows the bit error rate (BER) before and after ICI removal for various rates. FIG.

1 is a graph illustrating the variation of the sub-carrier channel transfer function H (f)} as perceived by the receiver as a function of frequency and time in a mobile environment. Variation of H (f) within an OFDM symbol results in inter-carrier interference between OFDM sub-carriers, called so-called Doppler extension of the received signal.

2 shows the variation of the desired signal indicated by the upper solid line 1 on the frequency. The sum of ICI and noise is indicated by the dotted line (2). The difference between the curves is the signal-interference-noise ratio (SINR). However, ICI increases with increasing vehicle speeds, which makes it impossible to reliably detect above threshold speeds without countermeasures.

In accordance with the present invention, for all reasonable vehicle speeds and sub-carrier frequencies, it is observed that the channel transfer function H for a given frequency varies almost linearly as a function of time for one OFDM symbol period. In this case, the received signal y is:

ICI noise signal required

here,

H is the complex transfer function of the channel,

H 'is the time derivative of H ,

Ξ is the ICI spreading matrix,

a is the transmitted data vector,

n is a complex circular white Gaussian noise vector.

The present invention is based on the discovery that this equation can be used as a basis for a signal processing method and uses the spectral and temporal correlation of H (f) to obtain an estimate of H and H 'in each channel of each OFDM symbol. have. This method can use a non-energy filter and a minimum mean square error (MSE) non-energy data estimator in both the frequency and time domains to obtain reliable estimates of H and H ', with continuous or iterative data estimation, ICI cancellation H estimation can be used. This result is a signal processing method that can be used for effective DVB-T reception in the presence of Doppler extension of medium to low complexity.

The DVB-T signal is characterized by the temporal concatenation of OFDM symbols, where each OFDM symbol 6 comprises a data carrier 3, a pilot carrier 4 and an empty carrier 5 schematically shown in FIG. 3. .

For a given OFDM symbol, the pilot 7 in the sub-carrier i with a known transmitted value allows estimation of H _I within this OFDM symbol.

Using a spectral correlation of H (f) in accordance with the delay spread of the channel and the SINR characteristic, a non-ener filter is designed to provide a minimum mean square error (MMSE) estimate of H _j in all channels of a given OFDM symbol. It works in the domain. This binner filter is called a spectral binner filter.

Other non-ener filters are designed that use the temporal correlation of H _j in each channel, depending on the multipath Doppler frequency distribution and SINR characteristics. This temporal non-enter filter provides an MMSE estimate of the temporal derivative H ' _j and H _j in a given OFDM symbol.

The filters mentioned above are designed to track and predict H _j and H ' _j in a given OFDM symbol.

The temporal binner filter may operate on a pre-selected set of channels I called "virtual pilot channels", and the spectral binner filter provides an estimate of H _I for each OFDM symbol. These virtual pilot channels are spaced between three to twelve channels.

In the virtual pilot channel, for a given OFDM symbol H ' _i is calculated from H _i obtained using the corresponding temporal binner filter. Thus, the MMSE estimates of H ' _j and H _j in all sub-carriers of each OFDM symbol are calculated from the results in the virtual pilot channel using a spectral binner filter.

The data estimation portion of this algorithm is based on the initial estimation of the unknown data on the data carrier using the signal received on each channel and the calculated H _j . The estimated ICI is then subtracted using H ' _j , initial data estimation and pilots, in the sub-carriers involved to obtain a genuine data carrier. Finally, reestimation of unknown data is performed on the genuine data carrier.

Since an accurate estimate of H is considered very important for data estimation, the channel transfer function H can also be recalculated or filtered from the original pilot carrier.

Thus, the basic scheme of the present invention basically uses temporal non-energy filtering in the virtual pilot sub-carrier to obtain estimates of H ' ₁ and H ₁ in this pilot sub-carrier, thus providing the basic computational flow required for Doppler compensation. Use. Then, spectral binner filtering is used for noise averaging and interpolation to get H ' _j and H _j in all subcarriers.

In terrestrial digital video broadcasting (DVB-T), orthogonal frequency division multiplexing (OFDM) is used to transmit digital information over a frequency-selective broadcast channel.

If all objects, such as transmitters, receivers and other distributed objects, are fixed, the use of OFDM with guard lengths of appropriate length, including cyclic prefix, can cause orthogonal sub-carriers, i.e., FFT Simultaneous demodulation of all sub-carriers using s results in no inter-carrier interference. If the object moves so fast that the channel can no longer be considered fixed for OFDM symbol time, the orthogonality between the sub-carriers is lost and the received signal is altered by the ICI, i.e. certain sub-carriers The signal used to modulate 또한 also disturbs other sub-carriers after demodulation. In the frequency domain, this Doppler extension of a frequency-selective Rayleigh fading channel is as if the channel's frequency response {H (f)} develops as a function of time, but quite far for frequencies farther apart than the coherence bandwidth. It can be understood as independent. The above-mentioned ICI levels for OFDM systems using 8k FFT have been found to preclude the use of 64-QAM at slow vehicle speeds.

In the present invention, non-energy filtering is used to take advantage of the spectrum and temporal correlation that exist within and between OFDM symbols for estimation of H (f) and H '(f).

It is assumed that the linear moving multipath propagation channel consists of uncorrelated paths, each of which has a complex attenuation (h _l ), a delay (τ _l ) and a grouping of angles of arrival (θ _l ). . Complex attenuation h _l is a circular Gaussian random variable with an average value of zero. The channel impulse response has an exponentially dissipated power profile and is characterized by the root mean square delay spread (τ _rms ). The receiver travels at a certain speed (v) resulting in each path with a Doppler shift of f ₁ = f _d cosθ _l , so that at time t the complex attenuation of path l is h _l (t) = It is further assumed that h _l exp (j2πf _l t). The maximum Doppler shift (f _d ) is related to the vehicle speed of f _d = f _c (v / c) (assuming this is the same for all sub-carriers), where

m/s이고 f_c는 캐리어 주파수이다.

m / s and f _c is the carrier frequency.

In an OFDM system, the N "QAM-type" symbols denoted by s = [s ₀ , ....., s _N-1 ] ^T (in DVB-T systems, N is 2048 or 8192) period T _u ) is modulated onto the N orthogonal sub-carriers by an N-point IFFT to form an OFDM symbol with _u ). This symbol is also extended with a cyclic prefix and then transmitted. The transmitted signal passes through a time-varying selective fading channel. Cyclic prefix extension is longer than the duration of the channel impulse response, so that the received signal is assumed to be unaffected by inter-symbol interference. At the receiver side, the received signal is sampled at the ratio 1 / T (where T = T _u / N) and the cyclic prefix is removed. The N-point FFT is then used to demodulate all sub-carriers of the composite signal simultaneously.

The baseband received signal in the time domain is denoted as r (t), as follows:

Where H _n (t) is the channel frequency response of the sub-carrier n at time t, f _s = 1 / T _u is the sub-carrier spacing, and v (t) is N ₀ / AWGN with a two-faced spectral density of two.

Taylor expansion of H _n (t) is taken around t ₀ and approximated to the first order term:

Using Equations 1 and 2, after the sampling operation and the FFT, the signal y _m received at the mth sub-carrier can be approximated as follows:

Where v _m is the mth noise sample after the FFT. Substituting T = 1 / (Nf _s ) and using Equation 3 can be rewritten as:

Where t ₀ = ΔT. In matrix description, the following approximation is a channel model:

Used for, where H = diag (H ₀ (t ₀ ), ...., H _N-1 (t ₀ )), and H '= diag (H' ₀ (t ₀ ), ...., H ' _N-1 (t ₀ )). t ₀ is chosen so that the error of the channel approximation is the smallest, ie in the middle of the effective part of the OFDM symbol.

In Equation 6, the first term is equivalent to a distorted desired signal in a stationary environment with no movement. The corresponding channel frequency response H has the following second order statistics in time and frequency:

Where J _n is the Bessel function of the first type of order n. The ICI described in the second term of Equation 6 is the result of the spreading of symbols transmitted on all other sub-carriers by a fixed spreading matrix Ξ weighted by the derivative H ' _m . Ξ is a fixed matrix, and the channel model is completely characterized by H _m and H ' _m . The knowledge of this structure is beneficial for channel estimation because the number of parameters to be estimated is 2N rather than N ² .

Equation 6 also forms the basis of the ICI suppression scheme, since ICI is first approximated using an estimate of H 'and s, which is then subtracted from the received signal y.

The linear minimum mean squared error (MMSE) of the channel parameters H _m and H ' _m and the transmitted data are obtained by applying discrete-time or discrete-frequency non-energy filtering. A set of noise observations y _k , k ∈ {1, ..., L) is available, from which it is assumed that a random variable x _l is to be estimated. A linear MMSE estimate of x _l is obtained using an L-tap FIR filter:

Here, minimization of the mean squared error is such that α _k is the so-called normal equation:

Satisfies

The mean squared error (MSE) of the estimate using these filter coefficients is MSE = E [| x _l | ² ]-E [| x ^ _l | ² ].

The matrix H is estimated per OFDM symbol basis using the normal structure of the pilot distributed in the OFDM symbols defined by the DVB-T standard. The pilot symbol provides a noisy initial estimate of H at the pilot position, where the noise consists of both AWGN and ICI caused by the Doppler spread. The FIR filter is applied in the frequency and / or temporal domain to obtain an MMSE estimate of H in the pilot symbol, using the spectral correlation of H. This result is then interpolated to obtain H in the residual data sub-carrier between pilot sub-carriers.

The approach is to estimate H _'m using the temporal correlation of H _m given in equation (8). It can be seen that a random process {H ' _m (t)} exists because R _HH (t) is bandwidth limited, where R _HH (t) means the time correlation of H at a fixed frequency. Given a set of noise measurements y (t) = H _m (t) + n (t) from many consecutive OFDM symbols, if the second order statistics E [y (t) y ^* (s)] and E [ H ' _m (t) y ^* (s)] is known, a temporal binner filter can be designed to provide an MMSE estimate of H' _m (t) using this noise measure. Using noise and the independence between H and Equation 8, Equation 11 is obtained:

Similarly, equation 12 is obtained:

Here, lim means "limit in mean". Using this correlation function, a binner filter is obtained that estimates H ' _m (t) in the middle of the OFDM symbol using a noise estimate of H _m (t) from the surrounding OFDM symbols. In practice, the temporal binner filter can only be used for equally spaced subsets of sub-carriers called virtual pilot sub-carriers. In the remaining sub-carriers, H ' _m is equal to H' _m It can be obtained by interpolation in the frequency domain using spectral correlation, which has been found to be the same as that of H _m (Equation 7).

Finally, R _{H'H '} (0) is required, and the power of the WSS derivation process for the performance evaluation of the non- _energy filter for H' _m is:

to be.

Data estimation is performed per subcarrier using a standard MMSE equalizer. If low complexity resolution is required, the 1-tap MMSE equalizer may be selected.

Using the derivation as given above, the estimated symbol in the sub-carrier m is given by:

here,

Is the ICI power in the sub-carrier m, and σ ² _{^ H} is the MSE of the H estimate.

Since the signal power to interference plus noise power ratio (SINR) of the received signal is low in a high speed environment due to ICI, the estimated data may not have sufficient quality for symbol detection. However, the soft-estimated data can still be used to regenerate the ICI sufficiently precisely to be used to mostly cancel the ICI from the received signal. Because of the ICI removal operation, the SINR is improved and therefore better estimated data can be obtained by performing data re-estimation. However, as SINR increases, the MSE of H _m needs to be lower, so that the inaccuracy in the estimated H _m is not a critical source of error in the data reestimation process. Therefore, reestimation of H is also performed.

을 얻기 위해, 제1 시간적/스펙트럼 H' 비엔너 필터(13)에 공급된다.4 illustrates a complete iterative channel and data estimation scheme in accordance with the present invention. At the distributed pilot position, the channel transfer function H _m is estimated from the received signal y ₀ with the aid of the known pilot symbol a _p at block 11. The result H ₀ is provided following the first spectral H binner filter 12. The output H ₁ is an estimate of H ' _m at the sub-carrier m, i.e.

To obtain a first temporal / spectrum H 'binner filter 13.

}은 제1 데이터 추정기(14)에 공급된다. 추정된 데이터(

)와

는 수학식 15에서와 유사한 방식으로 y ₀로부터의 ICI를 상쇄하기 위해 후속적으로 사용된다{블록(15) 참조}.Output { y ₀ (or y ₁ )

} Is supplied to the first data estimator 14. Estimated data (

)Wow

Is subsequently used to cancel the ICI from y _{0 in a} similar manner as in Equation 15 (see block 15).

를 얻기 위해 블록(16)내의 파일롯 위치에서 수행되고,

는 그후 모든 서브-캐리어에서

를 얻기 위해 제2 스펙트럼 H 비엔너 필터(17)에서 필터링되고,

는

를 얻기 위해 블록(18)에서 제2 데이터 추정을 위해 사용된다.Reestimation of H and data is then performed on the reduced ICI received signal y ₁ using a similar procedure to estimate H and data, but using a filter and equalizer adapted to the reduced ICI condition. Thus, the second channel estimate is

Is performed at the pilot position in block 16 to obtain

Then on all sub-carriers

Filtered in a second spectral H binner filter 17 to obtain

Is

Is used for second data estimation in block 18 to obtain.

와 알려진 파일롯 심볼(a_p)을 사용하고, 그후 y ₀로부터 ICI를 상쇄한다.Additional operations may be performed prior to the first data estimation to ensure whiteness of residual ICI and noise processes at the input of the second H filter, i.e., to remove pilot-induced ICI from the received signal ( Reference is made to a patent application co- filed with the agent management number ID696812, the contents of which are hereby incorporated by reference). In order to regenerate the ICI caused by the pilot symbol on all sub-carriers, this operation

And known pilot symbol (a _p ) and then cancel ICI from y ₀ .

The performance of the DVB-T system according to the present invention using the proposed iteration scheme is discussed below. 8k mode is used in the simulation. However, to shorten the simulation time, about 1000 sub-carriers are used. Modulated 64-QAM symbols in the data sub-carrier are randomly generated. Distributed pilots are inserted according to the DVB-T standard. After the IFFT, the signal is extended with a cyclic prefix of ratio (1/8). The carrier frequency f _c is selected at approximately 600 MHz in the center of the spectrum for analog TV in the UHF band. The channel model used is a frequency selective delay fading channel with a normalized exponentially dissipating power profile of τ _rms = 1 kHz and a maximum delay spread of 10 kHz. On the receiving side, Gaussian noise with E _s / N ₀ of 30 dB is added. For non-energy filtering operations, a symmetric non-casual filter with a length of L = 11 and an asymmetric transient filter with a length of L = 10 are used for H and H 'filtering, respectively. All filters are optimized for their speed.

5, 6 and 7 show the mean MSE and bit error rate (BER) of SINR, H for various steps of processing in an iterative manner from stationary conditions to the speed of the vehicle of 250 km / h.

의 BER이 200 km/h의 속도에서 획득된다. 보다 느린 운송 수단 속도에 대해, ICI가 덜 심각하므로, 가우스 잡음이 보다 우세하게 된다. 이것이 ICI 제거 때문에 얻어진 이득이 감소하는 이유이다.The average MSE is normalized to the average power of H (E [| H] ² ] = 1. Without any treatment, both the SINR and the average MSE of H decreases rapidly as the speed of the vehicle increases. At 200 km / h, with an SINR of approximately 18 dB, it is clear that reliable detection for 64-QAM on the Ralay fading channel is impossible. First H filtering 12 reduces the MSE approximately 6.5 dB. At this stage, BER is measured prior to ICI removal. Because of ICI rejection, SINR increases approximately 8 dB for faster speeds. It is noted that the reduced SINR approximates the accuracy of H. Using the second filtering 17, the MSE is lowered back by approximately 7 dB. With reestimated H and reduced ICI received signals,

BER is obtained at a speed of 200 km / h. For slower vehicle speeds, Gaussian noise becomes more prevalent because the ICI is less severe. This is why the gain obtained due to ICI removal is reduced.

For practical implementation, a fixed filter designed for the worst case situation (eg speed of 200 km / h) may be used. Although for slower speeds the performance is sub-optimum, the performance degradation is not significant.

As an example, the design of a temporal filter for T _OFDM with f _{d, max at} 112 Hz and 0.001 s (period between successive OFDM symbols) is:

To calculate.

Spectral filters for the same conditions are:

Can be.

Other filters and operations may be performed in dedicated digital signal processors (DSPs) and software. Alternatively, all or some of the steps of the method may be performed in hardware or a combination of hardware and software, such as, for example, Application Specific Integrated Circuit (ASIC) and Programmable Gate Array (PGA).

The expression “comprising” does not exclude other elements or steps, and it is mentioned that a singular element does not exclude a plurality of elements. Also, reference signs in the claims should not be construed as limiting the scope of the claims.

In the foregoing, a number of embodiments of the invention have been described with reference to the drawings. Those skilled in the art upon reading this disclosure will contemplate many other alternatives, which are intended to be within the scope of the present invention. Also, combinations other than those specifically mentioned herein are intended to be within the scope of the present invention. The invention is only limited by the appended patent claims.

The invention is applicable to a signal processor corresponding to a method for processing a signal for a receiver for an encoded digital signal in a wireless communication system.

Claims (16)

A method of processing an OFDM encoded digital signal, the OFDM encoded digital signal being transmitted as a sub-carrier in multiple frequency channels, A channel transfer function (by channel estimation method in each sub-carrier)

Estimating step; The channel transfer function (

) And data by the data estimation method from the received signal y ₀

Estimating step; A derivative of the channel transfer function in the subset of sub-carriers by time filtering (

Estimating step; And The estimated data to obtain a pure received signal y ₁ ,

) And the estimated derivative of the channel transfer function (

Removing inter-carrier interference (ICI) from the received signal. The method of claim 1, wherein the temporal filtering comprises the derivative of the pilot channel (

Is performed in the virtual pilot channel to obtain; Derivative (for residual channel within OFDM symbol)

To obtain the derivative (

Further comprising spectral interpolation. 3. The method of claim 2, wherein the pilot channel is a subset of all channels spaced apart, for example between three and twelve channels. 4. A method according to any one of the preceding claims, wherein said temporal filtering is performed using a finite impulse transfer function (FIR) with pre-computed filter coefficients. The method of claim 1, wherein the spectral filtering is performed by using a finite impulse transfer function (FIR) filter having pre-calculated filter coefficients. 5. The method of claim 4, wherein the finite impulse transfer function filter uses an estimate of the channel transfer function (H) from at least one other OFDM symbol. 7. The method of claim 6, wherein the other OFDM symbol is a subsequent OFDM symbol. 8. A method according to any one of the preceding claims, wherein subtracting inter-carrier interference (ICI) calculated using an initial estimate of the derivative (H ') of the channel transfer function and an initial soft estimate of data. The method of claim 1, further comprising an OFDM encoded digital signal. 9. A further estimate of the channel transfer function (H) after removal of the inter-carrier interference (ICI) at least in the virtual pilot channel, wherein a more accurate data estimate is obtained by this estimate. A method for processing an OFDM encoded digital signal. 10. The method of any one of the preceding claims, further comprising canceling the inter-carrier interference (ICI) by repetition of data estimation and elimination steps. . A signal processor arranged to process an OFDM encoded digital signal to neutralize inter-carrier interference (ICI) caused by Doppler expansion, The OFDM encoded digital signal is transmitted as a sub-carrier in multiple channels forming an OFDM block, A channel transfer function (by channel estimation method in each sub-carrier)

A channel estimator arranged to estimate; The channel transfer function (

) By the data estimation method from the received signal y ₀

A data estimator arranged to estimate; A derivative of the channel transfer function at each sub-carrier by time filtering (

A derivative estimator arranged to estimate; And The estimated data to obtain a pure signal y ₁ ,

) And the estimated derivative of the channel transfer function (

And an inter-carrier interference canceller arranged to remove inter-carrier interference (ICI) from the signal using < RTI ID = 0.0 >).≪ / RTI > Use of temporal binner filtering for channel estimation followed by spectral binner filtering according to the method of claims 1 to 10 to neutralize inter-carrier interference (ICI). A receiver arranged to receive an OFDM encoded digital signal, transmitted as a sub-carrier in multiple channels forming an OFDM block, A channel transfer function (by channel estimation method in each sub-carrier)

A channel estimator arranged to estimate; The channel transfer function (

) By the data estimation method from the received signal y ₀

A data estimator arranged to estimate; A derivative of the channel transfer function at each sub-carrier by time filtering (

A derivative estimator arranged to estimate; And The estimated data to obtain a pure signal y ₁ ,

) And the estimated derivative of the channel transfer function (

And an inter-carrier interference canceller arranged to remove inter-carrier interference (ICI) from the signal using < RTI ID = 0.0 > A mobile device comprising the receiver according to claim 13. A mobile device arranged for carrying out the method according to claim 1. A telecommunications system comprising a mobile device according to claim 13 or 14.

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