KR101876081B1 - Interference cancellation system and method of wireless repeater - Google Patents

Abstract

An apparatus and method for interference cancellation in a wireless repeater are disclosed. The apparatus for canceling interference of a wireless repeater according to an embodiment of the present invention includes an interference canceller for receiving an interference signal generated between transmission and reception antennas of the wireless repeater and a base station signal received by the reception antenna, an interference signal predictor for predicting a size and a delay time of at least one interference signal using a cepstrum; An interference signal generator for generating a predictive interference signal by varying the mixed signal by a magnitude and a delay time of the predicted at least one interference signal; And a subtractor for subtracting the predictive interference signal from the mixed signal.

Description

TECHNICAL FIELD [0001] The present invention relates to an apparatus and a method for removing interference from a wireless repeater,

The present invention relates to an apparatus and method for canceling interference in a wireless repeater, and more particularly, to an apparatus and method for canceling interference in a wireless repeater that effectively removes interference signals without being influenced by autocorrelation according to an input signal.

The mobile communication network repeater is installed in an area where the base station signal is weak and amplifies the base station (or terminal) signal and then retransmits the signal, thereby expanding the cell coverage of the base station.

Such a mobile communication network repeater includes an optical repeater, a microwave repeater, and a wireless repeater.

An optical repeater is a repeater that amplifies a base station signal including a MU (Master Unit) and an RU (Remote Unit) and emits the signal wirelessly to a shadow area. That is, the MU receives the base station signal by wire, converts it into an optical signal, and transmits it to the RU through the optical cable. The RU amplifies the base station signal received via the optical cable and radiates the amplified signal wirelessly to the shaded area.

Microwave repeaters include master and slave devices. The base station receives the base station signal, converts it to a microwave frequency, and transmits it to the sub-device. The receiving unit reconstructs the base station signal converted into the microwave frequency to the original radio frequency, amplifies the amplified base station signal, and radiates the amplified base station signal wirelessly.

A wireless repeater is a repeater that receives a base station signal, amplifies it to a signal of the same frequency, and emits it to a shadow area.

However, the optical repeater can be installed in an area where the optical line is provided, but it is disadvantageous in that it is expensive to install and operate the optical line depending on the use of the optical cable.

 Microwave repeaters are very influenced by the installation environment. Especially, in order to secure the line of site (LOS), the microwave repeater is subject to a lot of installation restrictions.

Although wireless repeaters are relatively low in price compared to optical repeaters and microwave repeaters, they amplify base station signals received by radio waves and radiate them at the same frequency. Therefore, it is difficult to install and operate them due to oscillation and interference according to the degree of isolation between transmitting and receiving antennas .

An ICS wireless repeater including an interference cancellation system (hereinafter referred to as ICS) has been developed to solve the problem of oscillation and interference of such a wireless repeater. The ICS wireless repeater is a system for solving a problem of oscillation due to a feedback signal generated between transmitting and receiving antennas in a general wireless repeater shown in FIG. 1, and is a system in which an interference cancellation technique is applied to a general wireless repeater shown in FIG. It is a wireless repeater that predicts and removes signals.

The interference cancellation technique used in such an ICS radio repeater is mainly based on an adaptive filter algorithm based on correlation. An ICS wireless repeater to which an interference cancellation technique using the adaptive filter algorithm is applied is shown in FIG.

Referring to Fig. 2, the adaptive filter algorithm 1 calculates a correlation (x (n)) between the error signal e (n) from which the interference signal has been removed and the reference signal x And calculates the interference signal removal coefficient w (n). The FIR filter 2 convolutes the interference signal removal coefficient w (n) and the reference signal x (n) to generate a predicted feedback signal y (n) on the same level. The subtractor 3 subtracts the predicted feedback signal y (n) from the original signal d (n) to remove the interference signal.

Most of ICS wireless repeaters using the conventional adaptive filter algorithm use LMS (Least Mean Square) or RLS (Recursive Least Square) adaptive filter algorithm. Since the LMS or RLS adaptive filter algorithm predicts the feedback signal using the correlation between the error signal and the reference signal and generates a feedback signal on the same level, the autocorrelation characteristic of the input signal source greatly affects the interference cancellation performance do.

In particular, when a signal having a small bandwidth and high autocorrelation is input, the ICS repeater using the adaptive filter based on the correlation does not effectively remove the interference signal and causes a problem of distorting the original signal.

A prior art related to the present invention is Korean Patent Laid-Open No. 10-2008-0058870 (published on June 26, 2008).

An interference cancellation apparatus and method of a wireless repeater that effectively removes only interference signals without being influenced by autocorrelation according to an input signal is proposed.

The solution of the present invention is not limited to the above-mentioned solutions, and other solutions not mentioned can be clearly understood by those skilled in the art from the following description.

An apparatus for canceling interference of a wireless repeater according to an aspect of the present invention includes an interference canceller for receiving an interference signal generated between transmission and reception antennas of the wireless repeater and a base station signal received by the reception antenna, an interference signal predictor for predicting a size and a delay time of at least one interference signal using a cepstrum; An interference signal generator for generating a predictive interference signal by varying the mixed signal by a magnitude and a delay time of the predicted at least one interference signal; And a subtractor for subtracting the predictive interference signal from the mixed signal.

Wherein the interference signal predicting unit comprises: a fast Fourier transform unit for performing a fast Fourier transform on the mixed signal to transform the mixed signal into a mixed signal in a frequency domain; A log operation unit for performing a log operation to convert the mixed signal in the frequency domain into a spectrum synthesized by the base station signal and the at least one interference signal; An inverse fast Fourier transform unit for performing inverse fast Fourier transform on the base station signal of the spectrum and the at least one interference signal to convert the base station signal and at least one interference signal into a separated cepstrum in a time domain; And an information extracting unit for extracting a size and a delay time with respect to an interference signal in a time domain which is smaller than the system delay time of the wireless repeater in the cepstrum.

Wherein the interference signal generator comprises: at least one time delay for delaying the mixed signal according to a delay time of the predicted at least one interfering signal; At least one size adjuster for adjusting at least the size of the mixed signal delayed by the size of the predicted interference signal to output at least one mixed signal whose size is adjusted; And an adder for adding the scaled at least one mixed signal to generate the predictive interference signal.

In an interference cancellation method performed by an interference canceller of a wireless repeater according to another aspect of the present invention, interference signals generated between transmission and reception antennas of the wireless repeater and base station signals received by the reception antennas are mixed Predicting a magnitude and a delay time of at least one interfering signal using a cepstrum of the mixed signal; Generating a predictive interference signal by varying the mixed signal to a size and a delay time of the predicted at least one interference signal; And subtracting the predictive interference signal from the mixed signal.

The step of predicting the magnitude and delay time of the at least one interference signal may include performing fast Fourier transform on the mixed signal and converting the mixed signal into a frequency-domain mixed signal;

Performing a log operation to convert the mixed signal in the frequency domain into a spectrum synthesized from the base station signal and the at least one interference signal; Performing inverse fast Fourier transform on the base station signal of the spectrum and at least one interference signal to convert a base station signal and at least one interference signal into separated cepstrum in a time domain; And extracting a magnitude and a delay time for the interference signal in a time domain smaller than the system delay time of the wireless repeater in the cepstrum.

Wherein the generating the predictive interference signal comprises: delaying the mixed signal according to a delay time of the predicted at least one interfering signal; Adjusting at least the magnitude of the delayed mixed signal by the magnitude of the predicted interference signal to output at least one mixed signal whose magnitude is adjusted; And generating the predictive interference signal by adding the at least one mixed signal having the size adjusted.

According to an apparatus and method for canceling interference of a wireless repeater according to an embodiment of the present invention, a cepstrum technique is applied to remove at least one interference signal from a mixed signal in which an input signal (base station signal) and at least one interference signal are mixed It is possible to effectively remove only the interference signal without being affected by the autocorrelation according to the input signal.

1 is a diagram illustrating a typical wireless repeater.
2 is a diagram illustrating an ICS wireless repeater to which an interference cancellation technique using an adaptive filter algorithm is applied.
FIGS. 3 to 6 are diagrams illustrating autocorrelation characteristics according to bandwidths. FIG.
7 is a diagram illustrating a configuration of an interference canceller of a wireless repeater according to an embodiment of the present invention.
8 is a diagram illustrating a detailed configuration of the interference signal predicting unit.
9 is a diagram illustrating a detailed configuration of the interference signal generating unit.
10 is a diagram illustrating a process of deriving a size and a delay time for at least one interference signal in the interference signal predicting unit.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Embodiments of the present invention are provided to more fully describe the present invention to those skilled in the art, and the following embodiments may be modified in various other forms, The present invention is not limited to the following embodiments. Rather, these embodiments are provided so that this disclosure will be more thorough and complete, and will fully convey the concept of the invention to those skilled in the art.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms "a", "an," and "the" include plural forms unless the context clearly dictates otherwise. Also, " comprise "and / or" comprising "when used herein should be interpreted as specifying the presence of stated shapes, numbers, steps, operations, elements, elements, and / And does not preclude the presence or addition of one or more other features, integers, operations, elements, elements, and / or groups. As used herein, the term "and / or" includes any and all combinations of one or more of the listed items.

Although the terms first, second, etc. are used herein to describe various elements, regions and / or regions, it should be understood that these elements, components, regions, layers and / Do. These terms do not imply any particular order, top, bottom, or top row, and are used only to distinguish one member, region, or region from another member, region, or region. Thus, the first member, region or region described below may refer to a second member, region or region without departing from the teachings of the present invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings schematically showing embodiments of the present invention. In the figures, for example, variations in the shape shown may be expected, depending on manufacturing techniques and / or tolerances. Accordingly, embodiments of the present invention should not be construed as limited to any particular shape of the regions illustrated herein, including, for example, variations in shape resulting from manufacturing.

Before describing an apparatus and method for canceling interference in a wireless repeater according to an embodiment of the present invention, an analysis of influence of an autocorrelation and a correlation-based adaptive filter algorithm will be described.

The input signal of a wireless repeater that amplifies and retransmits a base station (or terminal) signal varies in bandwidth from time to time within a maximum bandwidth depending on the radio resource environment of the base station. At this time, the autocorrelation of the input signal is defined by Equation (1) below. The autocorrelation characteristics according to the time delay D of the input signal source according to Equation 1 are as shown in FIGS. 3 to 6 (assuming that the maximum input bandwidth of the repeater is 20 MHz to illustrate the analysis of the autocorrelation characteristic, This change is assumed to be 20 MHz (FIG. 3), 5 MHz (FIG. 4), 1.25 MHz (FIG. 5), and 0.2 MHz (FIG.

In this case, x _n represents the n-th input signal, and x _{n -1} represents the n-1 th input signal.

As can be seen from the autocorrelation characteristics analyzed in FIGS. 3 to 6, the autocorrelation according to the time delay increases as the bandwidth of the input signal source decreases. That is, the autocorrelation with time delay can not be approximated to '0' as the input bandwidth becomes smaller. This characteristic means that the conventional interference cancellation method, which calculates the correlation according to the time delay, (Base station signal) may be distorted regardless of the presence or absence of an interference signal.

When using the conventional adaptive filter algorithm for interference cancellation, the influence of the autocorrelation characteristic according to the bandwidth of the input signal on the interference cancellation performance is explained.

An example of a Least Mean Square (LMS), which is an adaptive filter algorithm typically used in a conventional ICS wireless repeater, is as follows. The LMS algorithm is defined by Equations (2) to (5).

At this time, u is a constant.

The effect analysis according to the correlation of the ICS wireless repeater to which the interference cancellation technique using the conventional adaptive filter algorithm shown in FIG. 2 is applied will be described.

For this, it is assumed that there is no interference signal between the transmission antenna and the reception antenna shown in FIG.

When a signal having a low autocorrelation is input to the input of a conventional ICS wireless repeater using the LMS algorithm defined by Equations (2) to (5), an error signal e (n) Since the correlation degree R between the delayed reference signals x (n) is R? 0, the correlation degree of Equation (5) is also approximated to '0'.

This results in that the coefficient for interference cancellation defined in Equation (4) is also approximated to zero, so that the output of the adaptive filter becomes zero and finally the error signal is output as it is.

On the other hand, when a signal having a high autocorrelation is input to the input of a conventional ICS wireless repeater using the LMS algorithm defined by Equations 2 to 5, an error signal e (n) and an error signal Since the correlation degree R between the reference signals x (n) delayed for a predetermined time is R? 0, the correlation degree of Equation (5) can not be approximated to '0'.

This means that the coefficient for canceling the interference signal defined in Equation (4) also can not be approximated to zero, so that the output of the adaptive filter becomes a non-zero value and finally the error signal is distorted and outputted.

As described above, in the conventional ICS wireless repeater using the adaptive filter algorithm based on the correlation, the interference signal cancellation method according to the autocorrelation of the input signal source, There is a problem that serious distortion occurs in the original signal.

A configuration and operation of an interference canceller of a wireless repeater according to an embodiment of the present invention will be described.

7 is a diagram illustrating a configuration of an interference canceller of a wireless repeater according to an embodiment of the present invention.

Referring to FIG. 7, an apparatus for canceling interference of a wireless repeater according to an embodiment of the present invention includes an interference signal predicting unit 10, an interference signal generating unit 20, and a subtracting unit 30.

The interference signal predicting unit 10 uses a cepstrum of a mixed signal in which an interference signal generated between a transmitting antenna and a receiving antenna of the wireless repeater and a base station signal received by the receiving antenna are mixed Thereby estimating the magnitude and delay time of at least one interference signal.

A detailed configuration of the interference signal prediction unit 10 is shown in Fig.

8, the interference signal predicting unit 10 includes a fast Fourier transform unit 11, a log operation unit 12, an inverse fast Fourier transform unit 13, and an information extraction unit 14.

The fast Fourier transformer 11 performs fast Fourier transform (FFT) on a mixed signal obtained by mixing an interference signal generated between a transmitting antenna and a receiving antenna of the wireless repeater and a base station signal received by the receiving antenna, ) To convert the mixed signal in the frequency domain.

The log operation unit 12 performs a log operation to convert the mixed signal in the frequency domain into a spectrum in which the base station signal and the at least one interference signal are synthesized.

10, the mixed signal in which the base station signal and the at least one interference signal are mixed is passed through the fast Fourier transform unit 11 and the log operation unit 12 of the interference signal prediction unit 10 , And the power spectrum in which the base station signal and the at least one interference signal are combined in the frequency domain.

In FIG. 10, the base station signal corresponds to 'B' in the frequency domain, and at least one interference signal corresponds to 'I'.

The inverse fast Fourier transformer 13 performs inverse fast Fourier transform on the base station signal and the at least one interference signal of the spectrum to convert the base station signal and at least one interference signal into separated cepstrum in the time domain.

That is, as illustrated in FIG. 10, when the base station signal of the base spectrum and the at least one interference signal are transmitted through the reverse Fourier transformer 13, the base station signal B in the time domain QUEFRENCY (SECONDS) The interference signal I is converted into a separated cepstrum.

The information extracting unit 14 extracts the size and delay time of the interference signal in the time domain which is smaller than the system delay time of the wireless repeater in the cepstrum.

That is, the information extracting unit 14 extracts the size and the delay time only for at least one interference signal in a frequency region larger than the system delay frequency, which is an inverse number of the system delay time of the wireless repeater, and generates interference signal prediction information.

At this time, the delay time of the interference signal can be calculated by the following equation (6).

Here, d is the delay time, N is the number of FFT points, and FFT index> = (1 / system delay time (D)).

The magnitude of the interference signal can be calculated by Equation (7) below.

Where Wpresent is the magnitude of the interference signal at the current point in time, Wnext is the magnitude of the interference signal at the next point in time, u is a constant for controlling the convergence speed and may have a value of 0 <u <1, where n> = FFT index .

Referring back to FIG. 7, the interference signal generator 20 generates the predictive interference signal by varying the mixed signal by the magnitude and delay time of the predicted at least one interference signal.

The detailed structure of the interference signal generator 20 is shown in Fig.

9, the interference signal generator 20 includes at least one time delay 21, ..., 22, at least one size adjuster 23, ..., 24, and an adder 25, .

At least one time delay (21, ..., 22) delays the mixed signal according to the delay time of the predicted at least one interfering signal.

At least one size adjuster (23, ..., 24) adjusts at least the size of the mixed signal delayed by the size of the predicted interference signal to output at least one mixed signal whose size is adjusted.

The adder 25 adds the size-adjusted at least one mixed signal to generate the predictive interference signal.

7, the subtractor 30 subtracts the predictive interference signal from the mixed signal, and outputs a signal from which at least one interference signal has been removed.

The interference cancellation process is performed repeatedly and adaptively according to the environment change even after the interference signal completely disappears.

The present invention has been described above with reference to the embodiments. It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. Therefore, the disclosed embodiments should be considered in an illustrative rather than a restrictive sense. Therefore, the scope of the present invention is not limited to the above-described embodiments, but should be construed to include various embodiments within the scope of the claims and equivalents thereof.

10: Interference signal prediction unit
11: Fast Fourier transform unit
12: Log operation unit
13: Inverse fast Fourier transform unit
14: information extracting unit
20: Interference signal generator
21, 22: time delay
23, 24: Size adjuster
25: adder
30:

Claims (6)

An interference canceller of a wireless repeater,
The interference signal generated between the transmitting antenna and the receiving antenna of the wireless repeater and the base station signal received by the receiving antenna are mixed to generate a mixed signal having a cepstrum, And an interference signal predicting unit for predicting a delay time;
An interference signal generator for generating a predictive interference signal by varying the mixed signal by a magnitude and a delay time of the predicted at least one interference signal; And
And a subtractor for subtracting the predictive interference signal from the mixed signal,
Wherein the interference-
A fast Fourier transform unit for performing fast Fourier transform on the mixed signal and converting the mixed signal into a mixed signal in a frequency domain;
A log operation unit for performing a log operation to convert the mixed signal in the frequency domain into a spectrum synthesized by the base station signal and the at least one interference signal;
An inverse fast Fourier transform unit for performing inverse fast Fourier transform on the base station signal of the spectrum and the at least one interference signal to convert the base station signal and at least one interference signal into a separated cepstrum in a time domain; And
And an information extracting unit for extracting a size and a delay time with respect to an interference signal in a time domain smaller than a system delay time of the wireless repeater in the cepstrum,
Wherein the information extracting unit calculates the size and delay time of the interference signal using the following equation.
[Mathematical Expression]

Here, d is the delay time of the interference signal, N is the number of FFT points, FFT index> = (1 / system delay time (D)), Wnext is the magnitude of the interference signal at the next time point, , U is a constant for controlling the convergence speed, and 0 <u <1, and n> = FFT index.
delete The method according to claim 1,
Wherein the interference signal generator comprises:
At least one time delay for delaying the mixed signal according to a delay time of the predicted at least one interference signal;
At least one size adjuster for adjusting at least the size of the mixed signal delayed by the size of the predicted interference signal to output at least one mixed signal whose size is adjusted; And
And an adder for adding the size-adjusted at least one mixed signal to generate the predictive interference signal.
An interference cancellation method performed by an interference canceller of a wireless repeater,
The interference signal generated between the transmitting antenna and the receiving antenna of the wireless repeater and the base station signal received by the receiving antenna are mixed to generate a mixed signal having a cepstrum, And estimating a delay time;
Generating a predictive interference signal by varying the mixed signal to a size and a delay time of the predicted at least one interference signal; And
And subtracting the predictive interference signal from the mixed signal,
Wherein the step of estimating the magnitude and delay time of the at least one interference signal comprises:
Converting the mixed signal into a frequency-domain mixed signal by performing fast Fourier transform;
Performing a log operation to convert the mixed signal in the frequency domain into a spectrum synthesized from the base station signal and the at least one interference signal;
Performing inverse fast Fourier transform on the base station signal of the spectrum and at least one interference signal to convert a base station signal and at least one interference signal into separated cepstrum in a time domain; And
Extracting a size and a delay time for an interference signal in a time domain smaller than a system delay time of the wireless repeater in the cepstrum,
Wherein the size and delay time of the interference signal are calculated using the following equation.
[Mathematical Expression]

Here, d is the delay time of the interference signal, N is the number of FFT points, FFT index> = (1 / system delay time (D)), Wnext is the magnitude of the interference signal at the next time point, , U is a constant for controlling the convergence speed, and 0 <u <1, and n> = FFT index.
delete The method of claim 4,
Wherein the generating the predictive interference signal comprises:
Delaying the mixed signal according to a delay time of the predicted at least one interference signal;
Adjusting at least the magnitude of the delayed mixed signal by the magnitude of the predicted interference signal to output at least one mixed signal whose magnitude is adjusted; And
And adding the scaled at least one mixed signal to generate the predictive interference signal.

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