Communication signal receiver for estimating an imaginary-part component of a complex data signal and method thereof

A communication signal receiver includes a feed-forward filter and a coefficient adjusting circuit. The feed-forward filter generates an estimated imaginary-part component signal according to a real-part component of a complex data signal by using tap coefficients of the feed-forward filter. The coefficient adjusting circuit adjusts the tap coefficients of the feed-forward filter according to a control information, wherein the control information comprises a phase error information. The phase error information changes as a phase of the complex data signal changes, wherein the phase is adjusted or not adjusted by the coefficient adjusting circuit.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a communication signal receiver for estimating an imaginary-part component of a complex data signal and a related method, and more particularly, to an apparatus and a related method for adjusting tap coefficients of a feed-forward filter to improve an estimated result of the imaginary-part component at least according to phase error information.

2. Description of the Prior Art

In communication systems, inter-symbol interference (ISI) is a common phenomenon. The primary cause of ISI is multipath propagation. Hence, an equalizer is typically adopted in signal receivers for reducing the effect resulted from multipath propagation during signal transmission.

When processing a complex signal (such as a VSB signal) by using the equalizer, the optimum situation is to respectively process the real-part component and the imaginary-part component of the complex signal by adopting their own equalizers. However, the process is too complicated since the equalizer has too many parameters and tap numbers. A current common approach is to perform a Hilbert transform upon the real-part component of the complex signal to obtain the estimated value of the imaginary-part component, so as to replace the originally required equalizer of the imaginary-part component. Since the Hilbert transform used in the VSB signal is not an ideal Hilbert transform in a conventional signal processing, this approach seems not good enough when the phase error is slightly larger.

SUMMARY OF THE INVENTION

It is therefore one of the objectives of the claimed invention to provide a communication signal receiver for estimating an imaginary-part component of a complex data signal and a related method for solving the above-mentioned problems.

According to one aspect of the present invention, a communication signal receiver for estimating an imaginary-part component of a complex data signal is provided. The communication signal receiver comprises a first feed-forward filter and a first coefficient adjusting circuit. The feed-forward filter generates an estimated imaginary-part component signal according to a real-part component of the complex data signal by using tap coefficients of the feed-forward filter. The first coefficient adjusting circuit is coupled to the feed-forward filter and adjusts the tap coefficients of the feed-forward filter according to a control information, wherein the control information at least comprises a phase error information. The phase error information changes as a phase of the complex data signal adjusted or not adjusted by the first coefficient adjusting circuit changes.

According to another aspect of the present invention, a method for estimating an imaginary-part component of a complex data signal is provided. The method includes the steps of generating an estimated imaginary-part component signal according to a real-part component of the complex data signal together with a group of feed-forward filtering tap coefficients; and adjusting the group of feed-forward filtering tap coefficients according to a control information, wherein the control information at least comprises a phase error information. The phase error information changes as a phase of the complex data signal adjusted or not adjusted by a coefficient adjusting circuit changes. The complex data signal may be a vestigial sideband (VSB) signal.

According to another aspect of the present invention, a communication signal receiver for estimating an imaginary-part component of a complex data signal is provided. The communication signal receiver comprises a feed-forward filter, a feed-back filter, and an operator. The feed-forward filter receives a real-part component of the complex data signal and generates an estimated imaginary-part component signal according to the real-part component of the complex data signal by using tap coefficients of the feed-forward filter. The feed-back filter receives a designated signal and generates a filtered designated signal according to the designated signal by using tap coefficients of the feed-back filter. The operator is coupled to the feed-forward filter and the feed-back filter, and adjusts the estimated imaginary-part component signal according to the filtered designated signal. Both the tap coefficients of the feed-forward filter and the tap coefficients of the feed-back filter are a predetermined value.

DETAILED DESCRIPTION

Please refer toFIG. 1.FIG. 1is a diagram of a communication signal receiver100for estimating an imaginary-part component of a complex data signal according to a first embodiment of the present invention. The communication signal receiver100includes, but is not limited to, a delay unit110, a feed-forward filter130, a first coefficient adjusting circuit140, and a phase error corrector150. The delay unit110delays a real-part component signal yr[n] of a complex data signal to generate a delayed real-part component signal yr′[n]. The first coefficient adjusting circuit140is coupled to the feed-forward filter130, wherein the first coefficient adjusting circuit140receives at least a phase error information Phase′[n] and adjusts tap coefficients f[k] of the feed-forward filter130according to the phase error information Phase′[n]. The phase error information Phase′[n] changes as a phase of the complex data signal changes. The phase of the complex data signal mentioned herein comprises the phase of the complex data signal adjusted or not adjusted by the first coefficient adjusting circuit140. The feed-forward filter130receives the real-part component signal yr[n] and generates an estimated imaginary-part component signal yi′[n] according to the real-part component signal yr[n] by using the tap coefficients f[k] of the feed-forward filter130. The estimated imaginary-part component signal yi′[n] is an estimated value of the imaginary-part component of the complex data signal, and the delayed real-part component signal yr′[n] together with the estimated imaginary-part component signal yi′[n] constitute a first complex signal y′[n]. The phase error corrector150comprises a look-up table160and a complex multiplier170. The look-up table160provides a sine value sin Δθ and a cosine value cos Δθ according to the phase error information Phase′[n]. The complex multiplier170is coupled to the look-up table160, and it adjusts a complex phase corresponding to the delayed real-part component signal yr′[n] and the estimated imaginary-part component signal yi′[n] according to the sine value sin Δθ as well as the cosine value cos Δθ so as to generate an output real-part component signal xr′[n] as well as an output imaginary-part component signal xi′[n], wherein the output real-part component signal xr′[n] together with the output imaginary-part component signal xi′[n] constitute an output complex signal x′[n].

Please note that the aforementioned complex data signal can be a vestigial sideband (VSB) signal and the communication signal receiver100can be a VSB signal receiver, but the present invention is not limited to this only and can be signals and related signal receivers of other types. In addition, the feed-forward filter130can be implemented by a Hilbert Transform circuit or its approximation, but this is not a limitation of the present invention.

Next, a brief expression of the properties of the Hilbert transform circuit is described to help understanding of the technical features disclosed in the present invention. A symbol h[n] represents the Hilbert transform circuit in a time domain, and a symbol H(f) represents the frequency response of the Hilbert transform circuit h[n]. An ideal characteristic of the Hilbert transform circuit h[n] is that: after the Hilbert transforms are performed two times, it is equal to that the input signal multiplied by (−1) and can be expressed by the following equation:
H(f)2=(j)2=−1  (1).

As a result, the aforementioned estimated imaginary-part component signal yi′[n] and the first complex signal y′[n] formed by the estimated imaginary-part component signal yr′[n] together with the delayed real-part component signal yr′[n] can be respectively expressed by the equations below:
yi′[n]=conv(yr[n],h[n])  (2); and
y′[n]=yr′[n]+j*conv(yr[n],h[n])  (3).

In addition, due to the output complex signal x′[n] formed by the output real-part component signal xr′[n] together with the output imaginary-part component signal xi′[n] being the result of rotating the first complex signal y′[n] by an angle Δθ, it can be expressed by the equation below:

Therefore, fit the first complex signal y′[n] listed in the equation (3) into the equation (4), the output real-part component signal xr′[n] and the output imaginary-part component signal xi′[n] can be obtained, as follows:
xr′[n]=yr[n]*cos Δθ−conv(yr[n],h[n])*sin Δθ  (5); and
xi′[n]=yr[n]*sin Δθ+conv(yr[n],h[n])*cos Δθ  (6).

Because of the characteristic of the Hilbert transform circuit h[n], the output imaginary-part component signal xi′[n] can be restored according to the output real-part component signal xr′[n], as follows:

As can be known, the estimated imaginary-part component signal yi′[n] can be generated according to the real-part component signal yr[n] by using the Hilbert transform circuit h[n]. Moreover, the output real-part component signal xr′[n] together with the output imaginary-part component signal xi′[n] calibrated by the phase error corrector150can be mutually transformed according to such characteristic of the Hilbert transform circuit h[n].

As can be seen fromFIG. 1, the tap coefficients f[k] of the feed-forward filter130are adjusted according to the phase error information Phase′[n] and are not predetermined values anymore. Therefore, the estimated imaginary-part component signal yi′[n] generated by the feed-forward filter130is better than that generated by the conventional method. In this embodiment, the tap coefficients f[k] of the feed-forward filter130are adjusted according to the phase error information Phase′[n], but this should not be considered as limitations of the present invention. In other embodiments, other control information CI can be simultaneously referred to adjust the tap coefficients f[k] of the feed-forward filter130, e.g. a signal quality information of the complex data signal or a channel lock status information. Those skilled in the art should appreciate that various modifications to the control information CI for adjusting the tap coefficients f[k] of the feed-forward filter130may be made.

Please also note that the abovementioned embodiment is presented merely as an example for illustrating the present invention, but should not be a limitation of the present invention. Please refer toFIG. 2.FIG. 2is a diagram of a communication signal receiver200for estimating an imaginary-part component of a complex data signal according to a second embodiment of the present invention. The architecture of the communication signal receiver200shown inFIG. 2is similar to that of the communication signal receiver100shown inFIG. 1, and the difference between them is that the communication signal receiver200further comprises a feed-back filter230, a second coefficient adjusting circuit240, and an operator250. The second coefficient adjusting circuit240is coupled to the feed-back filter230for receiving the phase error information Phase′[n], and it adjusts tap coefficients b[k] of the feed-back filter230according to the phase error information Phase′[n]. The feed-back filter230receives a designated signal a[n] and generates a filtered designated signal a′[n] according to the designated signal a[n] by using the tap coefficients b[k] of the feed-back filter230. The operator250is coupled to the feed-forward filter130, the feed-back filter230, and the phase error corrector150, and it adjusts the estimated imaginary-part component signal yi′[n] inputted to the phase error corrector150according to the filtered designated signal a′[n]. In this embodiment, the operator250is implemented by an adder (or a subtractor). Hence, the filtered designated signal a′[n] is subtracted from the estimated imaginary-part component signal yi′[n] of the feed-forward filter130by the adder (or the subtractor). After the estimated imaginary-part component signal yi′[n] is processed, it is then inputted to the phase error corrector150. In other embodiments, other elements can be adopted to implement the operator250, and this should not be a limitation of the present invention.

As can be seen fromFIG. 2, the tap coefficients b[k] of the feed-back filter230are adjusted according to the phase error information Phase′[n] and are not predetermined values anymore. Therefore, the performance of the finally obtained estimated imaginary-part component signal yi′[n] can be further improved. Certainly, in other embodiments, other control information CI can be simultaneously referred to adjust the tap coefficients b[k] of the feed-back filter230, e.g. a signal quality information of the complex data signal or a channel lock status information. Moreover, in another embodiment, the tap coefficients f[k] of the feed-forward filter130as well as the tap coefficients b[k] of the feed-back filter230can be set as a predetermined value at the same time, wherein the predetermined value can be set in advance depending on experiences or by reference to other information so that the cost and complexity of circuits can be reduced. Additionally, the aforementioned designated signal a[n] can be an estimated value of a training sequence, but the present invention is not limited to this only and can be other signals.

Please refer toFIG. 3.FIG. 3is a flowchart illustrating a method for estimating an imaginary-part component of a complex data signal according to an exemplary embodiment of the present invention. Please note that the following steps are not limited to be performed according to the exact sequence shown inFIG. 3if a roughly identical result can be obtained. The method includes, but is not limited to, the following steps:

Step304: Receive a complex data signal having a real-part component signal and an imaginary-part component signal.

Step306: Delay the real-part component signal to generate a delayed real-part component signal.

Step308: Adjust a group of feed-forward filtering tap coefficients according to a control information, wherein the control information at least comprises a phase error information.

Step310: Generate the estimated imaginary-part component signal according to the real-part component signal by using the group of feed-forward filtering tap coefficients.

Step312: Adjust a complex phase corresponding to the delayed real-part component signal together with the estimated imaginary-part component signal according to the phase error information.

How each element operates can be known by collocating the steps shown inFIG. 3and the elements shown inFIG. 1. Further description of the operations of each step shown inFIG. 3is omitted here for brevity.

Please refer toFIG. 4.FIG. 4is a flowchart illustrating a method for estimating an imaginary-part component of a complex data signal according to another exemplary embodiment of the present invention. The method includes, but is not limited to, the following steps:

Step304: Receive a complex data signal having a real-part component signal and an imaginary-part component signal.

Step306: Delay the real-part component signal to generate a delayed real-part component signal.

Step308: Adjust a group of feed-forward filtering tap coefficients according to a control information, wherein the control information at least comprises a phase error information.

Step310: Generate the estimated imaginary-part component signal according to the real-part component signal by using the group of feed-forward filtering tap coefficients.

Step410: Adjust a group of feed-back filtering tap coefficients according to a control information, wherein the control information at least comprises a phase error information.

Step412: Receive a designated signal, and generate a filtered designated signal according to the designated signal by using the group of feed-back filtering tap coefficients.

Step414: Adjust the estimated imaginary-part component signal according to the filtered designated signal.

Step312: Adjust a complex phase corresponding to the delayed real-part component signal together with the estimated imaginary-part component signal according to the phase error information.

The steps shown inFIG. 4are similar to the steps shown inFIG. 3, asFIG. 4is a variation of the embodiment shown inFIG. 3. The difference between them is that the operations and functions of the feed-back filter (i.e., the steps410-414) are added into the flowchart ofFIG. 4, so that the performance of the finally obtained estimated imaginary-part component signal yi′[n] can be further improved. How each element operates can be known by collocating the steps shown inFIG. 4and the elements shown inFIG. 2. Further description of the operations of each step shown inFIG. 4is omitted here for brevity.

Be note that the steps of the flowchart mentioned above are merely a practicable embodiment of the present invention, and should not be considered as limitations of the present invention. The method can include other intermediate steps or can merge several steps into a single step without departing from the spirit of the present invention.

The abovementioned embodiments are presented merely for describing the present invention, and in no way should be considered to be limitations of the scope of the present invention. In summary, the present invention provides a communication signal receiver for estimating an imaginary-part component of a complex data signal and a related method. By making use of the phase error information Phase′[n] to adjust the tap coefficients f[k] of the feed-forward filter130(such as a Hilbert transform circuit), the tap coefficients f[k] are not a predetermined value anymore. Therefore, the performance of the estimated imaginary-part component signal yi′[n] of the complex data signal (such as a VSB signal) generated by the feed-forward filter130can be substantially improved. Especially when the phase error is very large, the imaginary-part component estimation mechanism disclosed in the present invention has a more obvious performance. Furthermore, other control information CI, e.g. a signal quality information of the complex data signal or a channel lock status information, can be simultaneously referred to adjust the tap coefficients f[k] of the feed-forward filter130. The imaginary-part component estimation mechanism disclosed in the present invention can be extensively applied to a feed-back filter, such that the performance of the obtained estimated imaginary-part component signal yi′[n] can be further improved.