Channel Equalization

Abstract

A method for use in an equalization of a channel by means of an equalizer 22, 23 is shown, wherein the channel uses a certain frequency band for a transfer of signals. In order to enable a channel equalization which requires a low complexity and which provides at the same time a good performance, the method determines a channel response for at least one frequency point within the frequency band used by the channel. The method further sets at least one adjustable coefficient (φ0k, bck, brk, a0k, a1k, a2k of the equalizer such that an equalizer response compensates optimally the determined channel response at the at least one selected frequency point. Also shown is a corresponding signal processing device 2, a corresponding signal processing system and a corresponding software program product.

Description

BRIEF DESCRIPTION OF THE FIGURES

Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings.

FIG. 1 is a block diagram of a known 0^th order ASCET equalizer structure;

FIG. 2 is a schematic block diagram of a system according to an embodiment of the invention;

FIG. 3 is a schematic circuit diagram of an exemplary equalizer which can be used in the system of FIG. 2; and

FIG. 4 is a flow chart illustrating the operation of a channel estimation component of the system of FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

The system illustrated in FIG. 1 was already described above. An embodiment of the system according to the invention, which is an enhancement of the system of FIG. 1, will now be described with reference to FIG. 2.

The system of FIG. 2 comprises a transmitter and a receiver between which multicarrier signals are to be transmitted via the radio interface. The system of FIG. 2 utilizes to this end a filter bank structure which is based on sine-modulated and cosine-modulated filter bank sections in a transmultiplexer configuration. The equalization scheme realized in this embodiment is called AP-ASCET (Amplitude-Phase Adaptive sine-modulated/cosine-modulated filter bank equalizers for transmultiplexers).

The transmitter of the system of FIG. 2 includes a synthesis portion 20 with a synthesis bank. The synthesis bank comprises for 2M input low-rate sub-channel signals a dedicated up-conversion section with a conversion factor of M and a processing function f_k(m), which constitutes the impulse response for a sub-channel filtering of a particular sub-channel. The index k of the function f indicates the respective sub-channel for which the function is provided, while the parameter m is a time index. The synthesis bank may, but does not have to be structured and operated exactly like the synthesis bank 10, 11 of FIG. 1.

The receiver of the system of FIG. 2 is part of some signal processing device 2 and includes an analysis portion 21 with an analysis bank. The analysis bank comprises for each of the 2M sub-channels a cosine-based processing function h_k^c(m) followed by a down-conversion section with a conversion factor of M, outputting a respective in-phase signal. The analysis bank further comprises for each of the 2M sub-channels a sine-based processing function h_k^s(m) followed by a down-conversion section with a conversion factor of M, outputting a respective quadrature signal. The indices k indicate again a respective sub-channel, while the parameter m is a time index. The analysis bank in the analysis portion 21 is implemented in the two-times oversampled form by taking the output signals in complex I/Q format. Oversampling makes it possible to perform the channel equalization within each sub-channel independently of the other sub-channels, that is, it enables a per-carrier equalization. A typical case with 100% roll-off, or lower, is assumed in the filter bank design so that the sub-band frequency range is twice the sub-band spacing and that two times oversampling is sufficient to keep all unwanted aliasing signal components below a level determined by the stopband attenuation. The analysis bank may, but does not have to be structured and operated exactly like the analysis bank 12-15 of FIG. 1.

In contrast to the system of FIG. 1, the I and Q outputs of the analysis portion 21 of FIG. 2 for each of the sub-channels are connected to a dedicated filter structure forming an equalizer 22, 23 for the respective sub-channel. The equalizers 22, 23 can be realized by hardware or software. The I and Q outputs of the analysis portion 21 are connected in addition to a channel estimation component 24, which has a controlling access to each of the equalizers 22, 23. For the sake of clarity, only a connection between the channel estimation component and one of the equalizers 22 is shown. The channel estimation component 24 can equally be realized by hardware or software.

Each equalizer 22, 23 comprises an assembly of amplitude and phase equalizers, in order to be able to compensate Inter-Carrier- and Inter-Symbol-Interferences. Non-ideal channels cause phase distortions, resulting in a rotation between real- and imaginary branches, and thus causing Inter-Carrier-Interference, while Inter-Symbol-Interference is caused mainly by amplitude distortion.

The structure of the equalizers 22, 13 is illustrated in more detail in FIG. 3.

Each equalizer 22, 23 comprises connected to the associated I and Q output of the analysis portion 21 a first order complex allpass filter 30. Both inputs to the complex allpass filter 30 are connected to an amplifying element 301 having an adjustable amplification factor of b_ck. The outputs of amplifying element 301 are connected via a multiplication element 302 multiplying the outputs of amplifying element 301 with -j and via a summing element 303 to the outputs of the complex allpass filter 30. The inputs to the complex allpass filter 30 are moreover connected via a delay element 304 to further inputs of summing element 303. The outputs of summing element 303 are moreover connected in a feedback loop via a further delay element 305, a multiplication element 306 multiplying the outputs of delay element 305 with j and an amplifying element 307 having an adjustable amplification factor of -b_ck to further inputs of summing element 303. The transfer function of the complex allpass filter 30 is given by:

$\begin{array}{cc}{H}_c\left(z\right)=\frac{1-{\mathrm{jb}}_cz}{1+{\mathrm{jb}}_cz^{-1}}& \left(1\right)\end{array}$

The complex output of the complex allpass filter 30 is processed by a phase rotator 31. The phase rotator 31 comprises an adjustable complex coefficient e^jφ0k and a multiplication element 311. The multiplication element 311 multiplies the output of the complex allpass filter 30 with the complex coefficient e^jφ0k, which causes a phase rotation of the output of the complex allpass filter 30. A component 32 taking the real part Re{.} calculates the real part of the complex output of the phase rotator 31 and provides it to a first order real allpass filter 33.

The input to the real allpass filter 33 is connected to an amplifying element 331 having an adjustable amplification factor of b_rk. The output of amplifying element 331 is connected via a summing element 333 to the output of the real allpass filter 33. The input to the real allpass filter 33 is moreover connected via a delay element 334 to a further input of summing element 333. The output of summing element 333 is moreover connected in a feedback loop via a further delay element 335 and an amplifying element 337 having an adjustable amplification factor of -b_rk to a further input of summing element 333. The transfer function of the real allpass filter 33 is given by:

$\begin{array}{cc}{H}_r\left(z\right)=\frac{1+b_rz}{1+b_rz^{-1}}& \left(2\right)\end{array}$

In practice, the allpass filters 30, 33 are realized in the causal form as z⁻¹H_x(z), but the above non-causal form simplifies the analysis.

The total phase response of the equalizer for the kth sub-channel is thus given by:

$\begin{array}{cc}\begin{array}{c}\text{arg}\left[H_{\mathrm{peg}}\left({}^{\mathrm{j\omega }}\right)\right]=\text{arg}\left[{}^{{\mathrm{j\omega }}_{0k}}·H_r\left({}^{\mathrm{j\omega }}\right)·H_c\left({}^{\mathrm{j\omega }}\right)\right]\\ ={\varphi }_{0k}+2\arctan \left(\frac{b_{\mathrm{rk}}\sin \omega }{1+b_{\mathrm{rk}}\cos \omega }\right)+2\arctan \left(\frac{-b_{\mathrm{ck}}\cos \omega }{1+b_{\mathrm{ck}}\sin \omega }\right)\end{array}& \left(3\right)\end{array}$

The real allpass filter 33 is followed by a symmetric 5-tap FIR filter 34 as amplitude equalizer, which provides the output of the equalizer 22, 23.

The input of the FIR filter 34 is connected via a series connection of 4 delay elements 341, 342, 343, 344, an amplifying element 355 having an adjustable amplification factor of a_2k and a summing element 364 to the output of the FIR filter 34. The input of the FIR filter 34 is further connected via an amplifying element 351 having an adjustable amplification factor of a_2k and a series connection of summing elements 361, 362, 363, 364 to a further input of summing element 365. The output of delay element 341 is moreover connected via an amplifying element 352 having an adjustable amplification factor of a_1k to a further input of summing element 361. The output of delay element 342 is moreover connected via an amplifying element 353 having an adjustable amplification factor of a_0k to a further input of summing element 362. The output of delay element 343 is moreover connected via an amplifying element 354 having an adjustable amplification factor of a_1k to a further input of summing element 363. The equalizer amplitude response for the k^th sub-channel is given by:

|H_aeq(e^jω)|=a_0k+2a_1k cos ω+2a_2k cos 2ω  (4)

The channel estimation component 24 has a controlling access to each of the equalizers 22, 23 for selecting the structure of the equalizers 22, 23 which is actually to be used by activating/deactivating some of the filter parts 30, 33, 34, as will be explained further below. Moreover, the channel estimation component 24 has a controlling access to each of the equalizers 22, 23 for setting the coefficients φ_0k, b_ck, b_rk, a_0k, a_1k and a_2k required for the equalizer structure selected for the k^th sub-channel.

For a transmission, 2M low-rate symbol sequences I_k(m), I_2M-1-k(m), which are to be transmitted on sub-channels k, 2M-1-k, are fed to the synthesis filter bank of the transmitting end, half of them corresponding to sub-channels between 0 and f_s/2, and the other half corresponding to sub-channels between 0 and -f_s/2, where f_s is the high sampling rate. In the notation I_k(m), I_2M-1-k(m), the indices k, 2M-1-k indicate again a respective sub-channel, while the parameter m is a time index. The 2M sub-channel symbol sequences I_k(m), I_2M-1-k(m) are processed in the synthesis portion 20, transmitted via the radio interface, where they undergo a channel distortion h(m), the parameter m being again a time index, received by the receiver and processed by the analysis portion 21, e.g. as described above with reference to FIG. 1. The sub-channels k and 2M-1-k, which are located symmetrically with respect to the zero-frequency in the baseband model, are equally located symmetrically with respect to the radio frequency carrier frequency in the modulated signals.

The analysis portion outputs for each of the 2M sub-channels an in-phase component and a quadrature component, e.g. like in the system of FIG. 1 signals of a first, second, third and fourth group of low-rate sub-channel signals. The subsequent channel equalization, however, is not realized as in the system of FIG. 1 simply by multiplying the output of each sub-band filter with a fixed complex coefficient c_k, s_k.

The channel equalization which is performed instead under control of the channel estimation component 24 will be described in the following with reference to the flow chart of FIG. 4.

The channel estimation component 24 receives for each of the 2M sub-channels the I and Q signals for one data block output by the analysis portion 21 and determines based on these signals the frequency domain channel estimates for each sub-channel.

The structure of each equalizer 22, 23 is now to be controlled such that it equalizes the associated sub-channel optimally at certain frequency points within the frequency band employed by the sub-channel. More specifically, at these frequency points, the equalizer amplitude response is to be equal to the inverse of the channel amplitude response, and the equalizer phase response is to be equal to the negative of the channel phase response.

The number of the considered frequency points determines the computational complexity and the required power consumption. Therefore, the channel estimation component 24 selects for each sub-channel the minimum number of frequency points which can be expected to result in a sufficient performance of the channel equalization. The selection is carried out data block wise based on the determined frequency domain channel estimates. The channel estimates can be determined for instance based on known pilot signals transmitted in all or some of the sub-channels from the transmitter to the receiver. Alternatively, a so-called blind method could be employed, which would not require pilot signals.

In a first case, the frequency domain channel estimates for a specific sub-channel indicate that a single frequency point located at the center frequency of a specific sub-channel, that is at ω=π/2 at the low sampling rate, can be expected to result in a sufficient channel equalization. In this case, the associated equalizer 22, 23 only has to comprise a complex coefficient e^jφ0k for a phase rotation. The allpass filters 30, 33 are therefore omitted and the amplitude filter 34 of the equalizer structure of FIG. 3 is reduced to just one real coefficient as scaling amplification factor. In above equation (3) describing the equalizer phase response, this means that only the first term originating from the complex component e^jφ0k has to be considered. The equalizer amplitude response is constant.

In a second case, the frequency domain channel estimates for a specific sub-channel indicate that two frequency points located at the edges of the passband of a specific sub-channel, that is at ω=0 and ω=±π, can be expected to result in a sufficient channel equalization. The + sign is valid for odd sub-channels and the − sign is valid for even sub-channels. In this case, the associated equalizer 22, 23 has to comprise in addition to the complex coefficient e^jφ0k the first-order complex allpass filter 30 as phase equalizer, and a symmetric 3-tap FIR filter as amplitude equalizer. That is, compared to the equalizer structure of FIG. 3, the real allpass filter 33 is omitted and the length of the 5-tap FIR filter 34 is reduced from 5 to 3. In above equation (3) describing the equalizer phase response, this means that the middle term is omitted, and in above equation (4) describing the equalizer amplitude response, this means that the last term is omitted.

In a third case, the frequency domain channel estimates for a specific sub-channel indicate that three frequency points are required for a sufficient channel equalization. One frequency point is located at the center of the sub-channel frequency band, that is at ω=±π/2, and two frequency points are located at the passband edges of the sub-channel, that is at ω=0 and ω=±π. The respective+sign is valid for even sub-channels and the respective − sign is valid for odd sub-channels. In this case, the associated equalizer 22, 23 has to comprise all components of the equalizer structure depicted in FIG. 3.

Optionally, further cases could be considered, in which the frequency domain channel estimates for a specific sub-channel indicate that additional frequency points at multiples of π/4 are expected to result in a better performance with a somewhat increased complexity. For such cases, the equalizer structure of FIG. 3 has to be adapted accordingly.

Once suitable frequency points have been selected for each sub-channel, the channel estimation component 24 determines for each sub-channel the coefficients which are required for the equalizer structure corresponding to the respectively selected frequency points.

For even sub-channels, the phase response values for up to three selected frequency points ω=0, ω=π/2 and ω=π are determined by the channel estimation component 24 to be:

arg[H_ch(e^jω)]_ω=0=ζ₀

arg[H_ch(e^jω)]_ω=π/2=ζ₁

arg[H_ch(e^jω)]_ω=πζ₂  (2)(5)

For even sub-channels, moreover the inverse of the amplitude response values for up to three selected frequency points ω32 0, ω=π/2 and ω=π are determined by the channel estimation component 24 to be:

$\begin{array}{cc}\frac{1}{{\left[H_{\mathrm{ch}}\left({}^{\mathrm{j\omega }}\right)\right]}_{\omega =0}}={\varepsilon }_0\frac{1}{{\left[H_{\mathrm{ch}}\left({}^{\mathrm{j\omega }}\right)\right]}_{\omega =\pi /2}}={\varepsilon }_1\frac{1}{{\left[H_{\mathrm{ch}}\left({}^{\mathrm{j\omega }}\right)\right]}_{\omega =\pi }}={\varepsilon }_2& \left(6\right)\end{array}$

For odd sub-channels, the phase response values for up to three selected frequency points at ω=−π, ω=-−π/2 and ω=0 are determined by the channel estimation component 24 to be:

arg└H_ch(e^jω)┘_ω=−π=ζ₀

arg[H_ch(e^jω)]_ω=−π/2=ζ₁

arg[H_ch(e^jω)]_ω=0ζ₂  (7)

For odd sub-channels, the inverse of the amplitude response values for three selected frequency points at ω=−π, ω=−π/2 and ω=0 are determined by the channel estimation component 24 to be:

$\begin{array}{cc}\frac{1}{{\left[H_{\mathrm{ch}}\left({}^{\mathrm{j\omega }}\right)\right]}_{\omega =-\pi }}={\varepsilon }_0\frac{1}{{\left[H_{\mathrm{ch}}\left({}^{\mathrm{j\omega }}\right)\right]}_{\omega =-\pi /2}}={\varepsilon }_1\frac{1}{{\left[H_{\mathrm{ch}}\left({}^{\mathrm{j\omega }}\right)\right]}_{\omega =0}}={\varepsilon }_2& \left(8\right)\end{array}$

If the right hand term of equation (3) is set equal for each frequency point to the negative value of the right hand term of the corresponding one of equations (5) and (7), and if the right hand term of equation (4) is set equal for each frequency point to the right hand term of the corresponding one of equations (6) and (8), the coefficients φ_0k, β_ck, β_rk, α_0k, α_1k, α_2k of the filter structure of FIG. 3 can be calculated as:

$\begin{array}{cc}\begin{array}{cc}{\varphi }_{0k}=-\frac{{\zeta }_{0k}+{\zeta }_{2k}}{2}& a_{0k}=\frac{1}{8}\left(2{\varepsilon }_{0k}+4{\varepsilon }_{1k}+2{\varepsilon }_{2k}\right)\\ b_{\mathrm{ck}}=\pm \tan \left(\frac{{\zeta }_{0k}-{\zeta }_{2k}}{4}\right)& a_{1k}=\pm \frac{1}{8}\left(2{\varepsilon }_{0k}-2{\varepsilon }_{2k}\right)\\ b_{\mathrm{rk}}=\pm \tan \left(\frac{-{\zeta }_{1k}-{\varphi }_{0k}}{2}\right)& a_{2k}=\frac{1}{8}\left({\varepsilon }_{0k}-2{\varepsilon }_{1k}+{\varepsilon }_{2k}\right)\end{array}& \left(9\right)\end{array}$

In these coefficients, the + signs apply again for the even sub-channels and the − signs for the odd sub-channels.

In the case of only two frequency points, the part for the real allpass filter in equation (9) has to be omitted, while coefficients for the phase rotator and for the complex allpass filter can be determined as in equations (9). The amplitude equalizer coefficients can be calculated in this case as:

$\begin{array}{cc}{a}_{0k}=\frac{1}{2}\left({\varepsilon }_{0k}+{\varepsilon }_{2k}\right)a_{1k}=\frac{1}{4}\left({\varepsilon }_{0k}-{\varepsilon }_{2k}\right)& \left(10\right)\end{array}$

In the case of one frequency point, for the phase only the coefficient for the phase rotator in equations (9) is relevant. For the amplitude equalizer, a_0k is set in this case to ε_1k.

The channel estimation component 24 calculates for each sub-channel according to equations (9) and/or (10) the coefficients required for the equalizer structure corresponding to the frequency points selected for the current data block for the respective sub-channel.

The channel estimation component 24 then selects for each sub-channel a structure for the equalizers 22, 23 in accordance with the selected frequency points. The selection may consist for each sub-channel in activating the required filter parts in a single comprehensive equalizer structure as depicted in FIG. 3, or in choosing one of several equalizer structures available for each equalizer 22, 23. Finally, the channel estimation component 24 sets all required coefficients in the selected equalizer structures as determined.

As long as further data blocks are provided by the analysis portion 21, the procedure of determining frequency domain channel estimates, determining required frequency points, calculating required coefficients, selecting equalizer structures, and setting the required coefficients is repeated.

The equalizers 22, 23 having the selected structure compensate in each signal output by the analysis portion 21 the effects of fading and frequency selectivity in the respective sub-channel on the radio interface.

After this channel equalization, the filtered signals are subjected to a respective slicer (not shown), in order to obtain the restored 2M sub-channel symbol sequences Î_k(m), Î_2M-1-k(m). In the notation Î_k(m) Î_2M-1-k(m) , the indices k, 2M-1-k indicate again the respective sub-channel, while the parameter m is again a time index.

Compared to the 0^th order ASCET of FIG. 1, the proposed system has a better performance for a given number of sub-channels, or enables a reduction of sub-channels for a given performance, since the channel response of a sub-channel is not assumed to be a constant value. Compared to known higher-order ASCETs or to an approach using a polynomial frequency response model, the proposed system is less complex, since no modeling step is required.

It has to be noted that there are various possibilities to order the components of the equalizers 22, 23 without effecting the overall response.

It has moreover to be noted that instead of the presented first-order phase equalizer, equally higher order phase equalizers may be used. The phase equalizer may include for example several real allpass filters and complex allpass filters in cascade, possibly including second-order filters. Also the length of the amplitude equalizer can be selected arbitrarily.

Further, it is to be understood that the described embodiment constitutes only one of a variety of possible embodiments of the invention.

Claims

1. Method for use in an equalization of a channel by means of an equalizer, wherein said channel uses a certain frequency band for a transfer of signals, said method comprising: determining a channel response for at least one frequency point within said frequency band used by said channel; andsetting at least one adjustable coefficient of said equalizer such that an equalizer response compensates optimally the determined channel response at said at least one selected frequency point.

2. Method according to claim 1, wherein determining said channel response comprises determining a channel phase response and a channel amplitude response for said channel, and wherein said at least one adjustable coefficient of said equalizer is set such that an equalizer amplitude response approaches optimally an inverse of a determined channel amplitude response for all considered frequency points and that an equalizer phase response approaches optimally a negative of a determined channel phase response for all considered frequency points.

3. Method according to claim 1, further comprising selecting a number of said at least one frequency point for said channel to correspond to a minimum number which can be expected to result in a sufficient channel equalization.

4. Method according to claim 3, wherein said number of said at least one frequency point is selected for said channel data block-wise based on frequency domain channel estimates for said channel.

5. Method according to claim 1, wherein in case said at least one frequency point comprises one frequency point, setting said at least one adjustable coefficients comprises for an equalization of phase of said channel setting a complex coefficient of a phase rotator part of said equalizers.

6. Method according to claim 1, wherein in case said at least one frequency point comprises one frequency point, setting said at least one adjustable coefficients comprises for an equalization of amplitude of said channel setting a real scaling amplification factor.

7. Method according to claim 1, wherein in case said at least one frequency point comprises two frequency points, setting said at least one adjustable coefficients comprises for an equalization of phase of said channel setting a complex coefficient as a phase rotator part of said equalizer and setting at least one coefficient of a complex allpass filter part of said equalizers.

8. Method according to claim 1, wherein in case said at least one frequency point comprises two frequency points, setting said at lest one adjustable coefficients comprises for an equalization of amplitude of said channel setting at least one coefficient of a symmetric 3-tap Finite Impulse Response filter part of said equalizer.

9. Method according to claim 1, wherein in case said at least one frequency point comprises three frequency points, setting said at least one adjustable coefficients comprises for an equalization of phase of said channel setting a complex coefficient as a phase rotator part of said equalizer, setting at least one coefficient of a complex allpass filter part of said equalizer, and setting at least one coefficient of a real allpass filter part of said equalizer.

10. Method according to claim 1, wherein in case said at least one frequency point comprises three frequency points, setting said at least one adjustable coefficients comprises for an equalization of amplitude of said channel setting at least one coefficient of a symmetric 5-tap Finite Impulse Response filter part of said equalizer.

11. Use of the method according to claim 1 for a single channel of a single carrier system.

12. Use of the method according to claim 1 for each of a plurality of sub-channels of a filter bank based multicarrier system or of a transform based multicarrier system.

13. Use of the method according to claim 1 for each of a plurality of sub-channels of a filter bank based multiantenna system or of a transform based multiantenna system in a Multiple Input Multiple Output configuration.

14. Use of the method according to claim 1 for channels which are to be processed in an analysis-synthesis filter bank configuration.

15. Signal processing device comprising: at least one equalizer associated to a channel using a certain frequency band for a transfer of signals, which at least one equalizer comprises at least one adjustable coefficient; anda channel estimation component adapted to determine for at least one channel to which said at least one equalizer is associated a channel response for at least one frequency point within a frequency band used by said at least one channel, and adapted to set at least one adjustable coefficient of said at least one equalizer such that an equalizer response compensates optimally a determined channel response at said at least one frequency point.

16. Signal processing device according to claim 15, wherein said channel estimation component is adapted to determine as said channel response for said at least one channel a channel phase response and a channel amplitude response, and to set said coefficients of said equalizer such that an equalizer amplitude response approaches optimally inverse of a determined channel amplitude response for all considered frequency points and that an equalizer phase response approaches optimally negative of a determined channel phase response for all considered frequency points.

17. Signal processing device according to claim 15, wherein said channel estimation component is further adapted to select a number of said at least one frequency point for said at least one channel such that it corresponds to a minimum number which can be expected to result in a sufficient channel equalization.

18. Signal processing device according to claim 17, wherein said channel estimation component is adapted to select said number of said at least one frequency point for said at least one channel data block-wise based on frequency domain channel estimates for said at least one channel.

19. Signal processing device claim 15, wherein in case said at least one frequency point comprises one frequency point, said at least one equalizer comprises for an equalization of the phase of said at least one channel a phase rotator part with an adjustable complex coefficient which is adapted to be set by said channel estimation component.

20. Signal processing device according to claim 15, wherein in case said at least one frequency point comprises one frequency point, said at least one equalizer comprises for an equalization of amplitude of said at least one channel an adjustable real scaling amplification factor.

21. Signal processing device according to claim 15, wherein in case said at least one frequency point comprises two frequency points, said at least one equalizer comprises for an equalization of phase of said at least one channel a phase rotator part with an adjustable complex coefficient which is adapted to be set by said channel estimation component and a complex allpass filter part with at least one coefficient which is adapted to be set by said channel estimation component.

22. Signal processing device according to claim 15, wherein in case said at least one frequency point comprises two frequency points, said at least one equalizer comprises for an equalization of amplitude of said at least one channel a symmetric 3-tap Finite Impulse Response filter part with at least one coefficient which is adapted to be set by said channel estimation component.

23. Signal processing device according to claim 15, wherein in case said at least one frequency point comprises three frequency points, said at least one equalizer comprises for an equalization of phase of said at least one channel a phase rotator part with an adjustable complex coefficient which is adapted to be set by said channel estimation component, a complex allpass filter part with at least one coefficient which is adapted to be set by said channel estimation component, and a real allpass filter part with at least one coefficient which is adapted to be set by said channel estimation component.

24. Signal processing device according to claim 15, wherein in case said at least one frequency point comprises three frequency points, said at least one equalizer comprises for an equalization of amplitude of said at least one channel a symmetric 5-tap Finite Impulse Response filter part with at least one coefficient which is adapted to be set by said channel estimation component.

25. Signal processing device according to claim 15, wherein said at least one equalizer is a single equalizer adapted to equalize a single channel of a single carrier system.

26. Signal processing device according to claim 15, wherein said at least one equalizer comprises a plurality of equalizers, each adapted to equalize another one of a plurality of sub-channels of a filter bank based multicarrier system or of a transform based multicarrier system.

27. Signal processing device according to claim 15, wherein said at least one equalizer comprises a plurality of equalizers, and wherein a respective matrix of equalizers is adapted to equalize another one of a plurality of sub-channels of a filter bank based multiantenna system or of a transform based multiantenna system in a Multiple Input Multiple Output configuration.

28. Signal processing device according to claim 15 comprising an analysis-synthesis filter bank, wherein said at least one equalizer comprises a plurality of equalizers, each adapted to equalize another one of a plurality of sub-channels which are to be processed by said analysis-synthesis filter bank.

29. Signal processing system comprising a signal processing device with: at least one equalizer associated to a channel using a certain frequency band for a transfer of signals, which at least one equalizer comprises at least one adjustable coefficient; anda channel estimation component adapted to determine for at least one channel to which said at least one equalizer is associated a channel response for at least one frequency point within a frequency band used by said at least one channel, and adapted to set at least one adjustable coefficient of said at least one equalizer such that an equalizer response compensates optimally determined channel response at said at least one selected frequency point.

30. Signal processing system according to claim 29, wherein said channel estimation component is adapted to determine as said channel response for said at least one channel a channel phase response and a channel amplitude response, and to set said coefficients of said equalizer such that an equalizer amplitude response approaches optimally thean inverse of a determined channel amplitude response for all considered frequency points and that an equalizer phase response approaches optimally a negative of a determined channel phase response for all considered frequency points.

31. Signal processing system according to claim 29, wherein said channel estimation component is further adapted to select a number of said at least one frequency point for said at least one channel such that it corresponds to a minimum number which can be expected to result in a sufficient channel equalization.

32. Signal processing system according to claim 31, wherein said channel estimation component is adapted to select said number of said at least one frequency point for said at least one channel data block-wise based on frequency domain channel estimates for said at least one channel.

33. Signal processing system according to claim 29, wherein in case said at least one frequency point comprises one frequency point, said at least one equalizer comprises for an equalization of the phase of said at least one channel a phase rotator part with an adjustable complex coefficient which is adapted to be set by said channel estimation component.

34. Signal processing system according to claim 29, wherein in case said at least one frequency point comprises one frequency point, said at least one equalizer comprises for an equalization of amplitude of said at least one channel an adjustable real scaling amplification factor.

35. Signal processing system according to claim 29, wherein in case said at least one frequency point comprises two frequency points, said at least one equalizer comprises for an equalization of the phase of said at least one channel a phase rotator part with an adjustable complex coefficient which is adapted to be set by said channel estimation component and a complex allpass filter part with at least one coefficient which is adapted to be set by said channel estimation component.

36. Signal processing system according to claim 29, wherein in case said at least one frequency point comprises two frequency points, said at least one equalizer comprises for an equalization of the amplitude of said at least one channel a symmetric 3-tap Finite Impulse Response filter part with at least one coefficient which is adapted to be set by said channel estimation component.

37. Signal processing system according to claim 29, wherein in case said at least one frequency point comprises three frequency points, said at least one equalizer comprises for an equalization of phase of said at least one channel a phase rotator part with an adjustable complex coefficient which is adapted to be set by said channel estimation components, a complex allpass filter part with at least one coefficient which is adapted to be set by said channel estimation component, and a real allpass filter part with at least one coefficient which is adapted to be set by said channel estimation component.

38. Signal processing system according to claim 29, wherein in case said at least one frequency point comprises three frequency points, said at least one equalizer comprises for an equalization of amplitude of said at least one channel a symmetric 5-tap Finite Impulse Response filter part with at least one coefficient which is adapted to be set by said channel estimation component.

39. Signal processing system according to claim 29, wherein said system is a single carrier system and wherein said at least one equalizer is a single equalizer adapted to equalize a single channel.

40. Signal processing system according to claim 29, wherein said system is a filter bank based multicarrier system and wherein said at least one equalizer comprises a plurality of equalizers, each adapted to equalize another one of a plurality of sub-channels of said filter bank based multicarrier system.

41. Signal processing system according to claim 29, wherein said system is a filter bank based or transform based multiantenna system in a Multiple Input Multiple Output configuration, wherein said at least one equalizer comprises a plurality of equalizers, and wherein a respective matrix of equalizers is adapted to equalize another one of a plurality of sub-channels of said filter bank based or transform based multiantenna system.

42. Signal processing system according to claim 29, wherein said system is an analysis-synthesis filter bank system, wherein said at least one equalizer comprises a plurality of equalizers, each adapted to equalize another one of a plurality of sub-channels which are to be processed by said analysis-synthesis filter bank system.

43. A software program product in which a software code for use in an equalization of a channel by means of an equalizer is stored, wherein said channel uses a certain frequency band for a transfer of signals, said software code for execution when running in a signal processing device comprising said equalizer: determining a channel response for at least one frequency point within said frequency band used by said channel; andsetting at least one adjustable coefficient of said equalizer such that an equalizer response compensates optimally the determined channel response at said at least one selected frequency point.