WO2009020326A1

WO2009020326A1 - Interference cancellation repeater and method for using feedforward/feedback signal search and feedback cancellation window division

Info

Publication number: WO2009020326A1
Application number: PCT/KR2008/004519
Authority: WO
Inventors: Wi Sang Rho; Hee Jun Lee; Hyung Sik Cho; Sung Sang You
Original assignee: Kt Corporation
Priority date: 2007-08-03
Filing date: 2008-08-04
Publication date: 2009-02-12
Also published as: CN101983483B; JP2010536198A; CN101983483A; JP4939653B2

Abstract

The present invention relates to a method of searching for feedforward signals and feedback signals and dividing a feedback cancellation window and an interference cancellation repeater using the method, in which only feedback signals other than feedforward signals are cancelled by an interference cancellation repeater, thus preventing the degradation in the quality of a source signal. A repeater for canceling interference attributable to a feedback signal according to the present invention includes a window setting unit (40) for searching an RF signal, which is received through a reception antenna and includes the intra-repeater feedback signal and an inter-repeater feedback signal, for a feedback signal by moving a feedback cancellation window, and dividing a feedback cancellation window (Xtot) on a basis of the feedback signal. A feedback signal cancellation unit (48) cancels the feedback signal from the received RF signal on a basis of the feedback cancellation window.

Description

[DESCRIPTION]

[invention Title]

INTERFERENCE CANCELLATION REPEATER AND METHOD FOR USING FEEDFORWARD/FEEDBACK SIGNAL SEARCH AND FEEDBACK CANCELLATION WINDOW DIVISION

[Technical Field]

The present invention relates, in general, to a method of dividing a feedback cancellation window in consideration of both feedforward signals and feedback signals, and an interference cancellation repeater using the method, and, more particularly, to a method of searching for feedforward signals and feedback signals and dividing a feedback cancellation window, and an interference cancellation repeater using the method, in which only feedback signals other than feedforward signals are cancelled by the interference cancellation repeater, thus preventing the degradation in the quality of a source signal.

[Background Art]

Domestic mobile communication has been rapidly developed as a mobile communication service based on a Code

Division Multiple Access (CDMA) system has become commercialized for the first time ever since a cellular system based on an Advanced Mobile Phone System (AMPS) was introduced. In particular, an International Mobile Telecommunications (IMT) -2000 system, which is the next- generation mobile communication system, provides various types of multimedia services, such as high-speed and high- quality video services, which have been developed from current voice service and low-speed data service, and thus it is forecasted that a market for the IMT-2000 system will be further increased. However, since the IMT-2000 system uses a frequency band higher than a current cellular band or a Personal Communication System (PCS) band, the radius of a service cell covered by a single base station is reduced. Further, even if a base station is installed based on the radius of each small cell in places such as downtown areas, a Radio Frequency (RF) shadow area attributable to obstacles to propagation remains. In order to solve this problem, it is economical to use a relatively inexpensive repeater rather than to install a plurality of expensive base station devices.

Repeaters can be mainly classified into an optical repeater, a microwave terrestrial repeater, a frequency- shifting repeater using frequency conversion, and a non- frequency-shifting repeater (typical RF repeater) according to a repeating scheme.

An optical repeater employs a scheme in which a Radio Frequency (RF) signal received from a base station is converted into an optical signal, and the optical signal is transmitted through a previously embedded optical line, and in which the optical repeater converts an optical signal into an RF signal and transmits the RF signal. However, such an optical repeater can be installed in any of the places to which optical lines can be introduced, but there is a disadvantage in that the costs required to lease optical lines are high, and service can be provided only in places to which optical lines are capable of being introduced. A microwave terrestrial repeater employs a scheme in which a donor unit (hereinafter referred to as a "DU") converts a signal received from a base station into a high- frequency wave, and thereafter transmits the high-frequency wave. The microwave terrestrial repeater is advantageous in that the installation of equipment is facilitated, but is disadvantageous in that the repeater is greatly influenced by weather conditions and must be installed in places at which visible rays can be ensured.

A frequency-shifting repeater employs a scheme in which a transmission signal is converted into one of the allowable frequencies, which are not currently being used, and the converted signal is relayed. Unlike an existing repeater which depends only on the characteristics of an RF signal, the frequency-shifting repeater is configured to use the characteristics of a base station currently being used after the characteristics of the base station have been modified. Such a frequency-shifting repeater is advantageous in that it can be easily installed and implemented and does not cause oscillation, but is disadvantageous in that it additionally requires frequency conversion equipment and must be inevitably operated only at a 1/2 frequency utilization efficiency. In particular, when only four carriers (FA) per service provider must be used, as in the case of Wideband CDMA (WCDMA) , only a maximum of two carriers can be provided, and thus the use of the frequency-shifting repeater is limited under actual working conditions .

Meanwhile, since a non-frequency-shifting repeater uses the same frequency between transmission and reception, unlike a frequency-shifting repeater, it is a typical RF repeating scheme that can be most easily implemented. However, such a scheme has a disadvantage in that there is a high probability that a signal amplified by the repeater is fed back, and thus oscillation occurs. Therefore, a current non-frequency-shifting repeater employs a method of ensuring isolation between antennas by causing the transmission antenna and the reception antenna of the non- frequency-shifting repeater to be placed far apart from each other, as shown in FIG. 1, and a method of limiting power to a range in which oscillation does not occur, as a method of preventing the oscillation of a repeated signal. However, in the environment in which transmission and reception antennas cannot be placed sufficiently far apart from each other by a desired distance, or in which a high gain of an amplifier is required, several problems may occur in the use of the non-frequency-shifting repeater. In order to solve this problem, a repeater using an

Interference Cancellation System (ICS) (interference cancellation repeater) for detecting and canceling a feedback signal, which is the cause of oscillation, is used. FIG. 2 is a diagram schematically showing the construction of a conventional interference cancellation repeater.

In the present specification, the following description will be made on the basis of a forward link, but those skilled in the art will appreciate that the present invention can also be equally applied to a reverse link.

As shown in FIG. 2, the conventional interference cancellation repeater includes a reception antenna 12 (hereinafter also referred to as a ^Λlink antenna' ) for receiving both a transmission signal r_in(t), transmitted from a base station 11, and a feedback signal fmtra(t), input through a feedback channel which is a time-varying multi-path fading channel, an Analog/Digital (A/D) converter 13 for converting the signal received from the link antenna 12 into a digital signal r'_in(n), a digital signal processing unit 14 for canceling the feedback signal fin_tra(t) from the RF signal received through the link antenna 12, a D/A converter 15 for converting the feedback- cancelled signal into an analog signal r_o(n), an amplifier 16 for amplifying the analog signal provided by the D/A converter 15 to a predetermined system gain (G) and outputting the amplified signal, and a transmission antenna 17 (hereinafter also referred to as a ^Λ service antenna' ) for transmitting the signal received from the base station to a subscriber or another repeater.

The digital signal processing unit 14 includes a feedback signal detection unit 19 for estimating the time delay, amplitude and phase of a feedback signal using the correlation of the received RF input signal, and a feedback signal cancellation filter 18 for adaptively estimating and canceling a time-varying feedback signal, thus canceling the feedback signal which is the cause of oscillation. Since hardware which can be implemented as the feedback signal cancellation filter is limited, the delay time of a cancelable feedback signal, that is, the distance of a feedback signal, is limited. For example, in the case of a WCDMA system, the size of a feedback cancellation window corresponding to the distance of a cancelable feedback signal is the time (μsec) shown in the following Table 1. Generally, after passing through a path having a length of from 2 to 3Km or greater, the level of the feedback signal scarcely causes oscillation attributable to a path loss, and thus the size of the feedback cancellation window is designed in consideration of this. [Table 1]

Delay time(μsec) 1 1. 67 3.33 4 6 8 time Chip 3 84 6 .4 12.8 15. 38 23.04 30 .72

Distance Round-trip 0 .3 0 .5 1 1. 2 1.8 2 .4

(Km) One-way 0 15 0. 25 0.5 0. 6 0.9 1 .2 FIG. 3 is a diagram showing a scheme for setting/operating a feedback cancellation window in a conventional interference cancellation repeater. Generally, a feedback signal leading to X_tot(μsec) based on the equipment delay time of a repeater itself is located in the area of a feedback cancellation window, and can be cancelled, but a feedback signal, received after the time X_tot (μsec) , cannot be cancelled. For example, referring to Table 1, when time X_tot is designed to be 8 μsec, only a feedback signal leading up to about 2.4Km can be cancelled. The detection of a feedback signal is performed by connecting unit windows, each having a size of X_ste_pr to each other in a sequential or parallel manner, and searching for an entire cancellation window. That is, the size of an entire window X_tot enabling cancellation can be represented by the sum of the sizes X_step of M unit windows (where M is a natural number), as shown in the following Equation 1. Hereinafter, such a unit window will be designated as a bank.

[Equation 1] X,_ol = M - X_Uψ

Meanwhile, the interference cancellation repeater is a kind of RF repeater, and the exchange of signals with other surrounding RF repeaters may occur in the repeater. In particular, according to the configuration of the current mobile communication network of Korea, there are many environments in which the distance between installed repeaters is short. When the distance between repeaters is short as in this case, a relevant repeater' s own delay time is included in a feedback path if a feedback loop attributable to the transmission/reception of signals between repeaters is formed, thus resulting in a phenomenon in which an inter-repeater feedback signal is formed outside the area of the feedback cancellation window X_to_t- FIG. 4 is a diagram showing the case where an inter- interference cancellation repeater feedback signal is formed when the interference cancellation repeaters are used. When the interference cancellation repeaters are operated in a specific manner, for example, in a cascade manner, an upstream repeater is called a Donor unit (DU) , and a downstream repeater is called a Remote unit (RU) . When the distance d_DR between DU and RU is less than the distance d_Bo between a base station and the DU, the loss of a path in the level of a signal, input again from RU to DU, is low, and thus an inter-repeater feedback signal fmter(t) cannot be ignored. Although the front/back ratio of an antenna is considered, an inter-repeater feedback signal is formed in an environment in which the influence of a path loss corresponding to a distance is relatively decreased. Such an inter-repeater feedback signal may be located outside the area of a feedback cancellation window required to cancel an intra-repeater feedback signal, which has been described with reference to FIG. 3, thus becoming the cause of oscillation.

In cases other than the case of a cascade manner, as shown in FIG. 5, in environmental conditions in which a plurality of interference cancellation repeaters is located close to each other, an inter-repeater feedback signal, which is similar to that of FIG. 4, may be formed.

[Disclosure] [Technical Problem]

Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a method of searching for feedforward signals and feedback signals, a method of dividing a feedback cancellation window, and an interference cancellation repeater using the methods, in which the interference cancellation repeater cancels only feedback signals other than feedforward signals and feedforward image signals, thus preventing the degradation of the quality of a received signal. [Technical Solution]

The features of the present invention to accomplish the above object are summarized below. In accordance with an aspect of the present invention, there is provided a repeater for canceling interference attributable to a feedback signal, comprising a window setting unit for searching a Radio Frequency (RF) signal, which is received through a reception antenna and includes an intra-repeater feedback signal and an inter-repeater feedback signal, for a feedback signal by moving a feedback cancellation window

(Xtot) , and for dividing the feedback cancellation window on a basis of the feedback signal; and a feedback signal cancellation unit for canceling the feedback signal from the received RF signal on a basis of the feedback cancellation window divided by the window setting unit.

In accordance with another aspect of the present invention, there is provided a method of canceling interference attributable to a feedback signal in a repeater, comprising a window setting step of searching a Radio Frequency (RF) signal, which is received through a reception antenna and can include an intra-repeater feedback signal and an inter-repeater feedback signal, for a feedback signal by moving a feedback cancellation window (X_tot) i and of dividing the feedback cancellation window on a basis of the feedback signal; and a step of canceling the feedback signal from the received RF signal on a basis of the feedback cancellation window divided at the window setting step.

In accordance with a further aspect of the present invention, there is provided a method of canceling interference, comprising the steps of receiving a Radio Frequency (RF) signal, including a feedback signal and a feedforward signal, through a link antenna of an interference cancellation repeater, which cancels the feedback signal using a feedback cancellation window; detecting the feedforward signal; and resetting the feedback cancellation window so that the detected feedforward signal is not included in the feedback cancellation window, thus canceling the feedback signal. In accordance with yet another aspect of the present invention, there is provided an interference cancellation repeater for canceling a feedback signal using a feedback cancellation window, comprising a link antenna for receiving a Radio Frequency (RF) signal, including a feedback signal and a feedforward signal; a feedforward signal searching unit for searching the RF signal, received through the link antenna, for the feedforward signal; and a system delay unit for adding a system delay for the interference cancellation repeater so that the detected feedforward signal is not included in the feedback cancellation window. [Advantageous Effects]

According to the present invention, there is an advantage in that an interference cancellation repeater separates feedforward signals and feedback signals, and cancels only the feedback signals and not the feedforward signals, thus preventing the degradation of the quality of a received signal.

Further, according to the present invention, there is an advantage in that only feedback signals and not feedforward signals can be canceled while existing components of a conventional interference cancellation repeater are used without additionally requiring any separate components.

[Description of Drawings] FIG. 1 is a diagram schematically showing the construction of a conventional RF repeater;

FIG. 2 is a diagram schematically showing the construction of a conventional interference cancellation repeater for detecting/canceling a feedback signal, this being the cause of oscillation;

FIG. 3 is a diagram showing a scheme for setting/operating a feedback cancellation window in a conventional interference cancellation repeater;

FIG. 4 is a diagram showing an example of the case where a conventional inter-interference cancellation repeater feedback signal is formed;

FIG. 5 is a diagram showing another example of the case where a conventional inter-interference cancellation repeater feedback signal is formed;

FIG. 6 is a diagram showing the construction of an interference cancellation repeater according to an embodiment of the present invention;

FIG. 7 is a diagram showing the operation of the feedback signal searching unit of FIG. 6;

FIG. 8 is a diagram showing an example in which a feedback cancellation window is divided;

FIG. 9 is a flowchart showing the operating process of an interference cancellation repeater having a feedback cancellation window division function according to an embodiment of the present invention;

FIG. 10 is a diagram showing an example of an external input signal irrelevant to the gain of a repeater itself for receiving an RF signal, the external input signal being received through another repeater;

FIG. 11 is a diagram showing the relationship between the signals of FIG. 10;

FIG. 12 is a diagram schematically showing a feedforward image signal generated as a result of the measurement of the correlation of an input signal when a feedforward signal is present; FIG. 13 is a diagram schematically showing a method of processing a feedforward signal in an interference cancellation repeater according to an embodiment of the present invention; FIG. 14 is a diagram schematically showing a method of processing a feedforward signal in an interference cancellation repeater according to another embodiment of the present invention;

FIG. 15 is a flowchart showing a method of processing a feedforward signal in an interference cancellation repeater according to a further embodiment of the present invention;

FIG. 16 is a flowchart showing a method of processing a feedforward signal in an interference cancellation repeater according to yet another embodiment of the present invention;

FIG. 17 is a flowchart showing a method of processing a feedforward signal in an interference cancellation repeater according to still another embodiment of the present invention;

FIG. 18 is a flowchart showing a method of processing a feedback forward signal in an interference cancellation repeater according to still another embodiment of the present invention; and FIG. 19 is a diagram schematically showing the construction of an interference cancellation repeater according to an embodiment of the present invention.

[Best Mode]

Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings. In the following description, only the case of a forward link is described, but it should be noted that the case of a reverse link may be applied in the same manner as that of the forward link or may be used separately from that of the forward link. Further, the embodiments, which will be described later, may be implemented in real time, or may be implemented in an on-demand manner at the time of initially installing the repeater or at the request of a user.

FIG. 6 is a diagram showing the construction of an interference cancellation repeater according to an embodiment of the present invention.

An interference cancellation repeater (hereinafter referred to as a "repeater") according to an embodiment of the present invention includes a reception antenna 12, an A/D converter 13, a feedback signal cancellation unit 48, a window setting unit 40, a D/A converter 15, an amplification unit 16, and a transmission antenna 17. Further, the feedback signal cancellation unit 48 includes a feedback signal cancellation filter 46 and a feedback signal detection unit 47, and the window setting unit 40 includes a window division unit 41 and a feedback signal searching unit 42.

The repeater is configured to support a bidirectional link, that is, a forward link and a reverse link. The forward link is configured to receive a signal from a base station through the reception antenna 12 and to transmit the signal, received from the base station, to a shadow area, which the signal from the base station does not reach, through the transmission antenna 17. The reverse link is configured to receive a signal provided by a terminal through the transmission antenna 17 and to transmit the signal to the base station through the reception antenna 12.

Hereinafter, a description will be made on the basis of the forward link, and the reverse link can be thought of as being the reverse of the forward link.

The reception antenna 12 is an antenna for receiving a source reception signal r_in(t) from the base station, wherein the source reception signal r_in(t) typically includes signals from a plurality of base stations. Further, the reception antenna 12 according to an embodiment of the present invention also receives an intra- repeater feedback signal f_mtra(t), which is received from the transmission antenna 17 of the relevant repeater through a radio channel, and an inter-repeater feedback signal f_mter(t), which is received from the transmission antenna of another surrounding repeater through a radio channel, together with the source reception signal. That is, the total input signal r'_in(t) received through the reception antenna 12 is the sum of the source reception signal r_in(t), the intra-repeater feedback signal f_mtra(t) and the inter-repeater feedback signal f_mter(t) . Here, the total input signal is an analog signal.

The A/D converter 13 converts the total input signal r'_in(t), which is an analog signal received through the reception antenna 12, into a digital signal. The generated digital signal may be indicated by r'_in(n), where n is a chip index.

The feedback signal cancellation unit 48 includes the feedback signal cancellation filter 46 and the feedback signal detection unit 47, and cancels feedback signals from the total input signal r'_in(n) in steps of a unit window.

The feedback signal detection unit 47 calculates exact correlation using the correlation between the total input signal r'_in(n) and the previously generated signal, from which feedback has been cancelled, in steps of a unit window X_stepr and estimates the time delays, amplitudes and phases of varying feedback signals on the basis of the calculated correlation. The range of the calculation of the correlation corresponds to the size of the feedback cancellation window, and the feedback signal detection unit according to an embodiment of the present invention detects feedback signals in the feedback window set by the window setting unit.

The feedback signal cancellation filter 46 generates the reverse-phase signals of the feedback signals using the time delays, amplitudes and phases estimated by the feedback signal detection unit 47, and applies the generated reverse-phase signals to the total input signal, and thus cancels the feedback signals from the total input signal. That is, through the use of a subtractor 20, the feedback signals detected by the feedback signal cancellation filter 46 are subtracted from the total input signal r'_in(n), and thus the feedback signal-canceled output signal r_out(n) is generated.

The window setting unit 40 includes the window division unit 41 and the feedback signal searching unit 42, and is configured to detect the characteristics of feedback signals and to divide and set a feedback cancellation window.

The feedback signal searching unit 42 sequentially and additionally performs a unit window search function, thus searching for a window having a size of about N*X_tOf FIG. 7 is a diagram showing the operation of the feedback signal searching unit 42.

Referring to FIG. 7, the feedback signal searching unit 42 sequentially moves a feedback cancellation window X-_totr which is the range of the calculation of correlation, and searches the feedback cancellation window X_tot of Equation 1 for feedback signals in steps of a unit window X_step- That is, the feedback cancellation window X_tot is sequentially moved up to N*X_totf and feedback signals are searched for in each feedback cancellation window in steps of a unit window X_step- Through this process, a number of feedback signals can be detected in a detection area that is N times or more as large as that of a conventional window, using just the sequential window search function without adding search hardware resources. Here, the feedback cancellation window X_tot is the size of the feedback cancellation window defined by the restriction of hardware resources .

The window division unit 41 divides the entire feedback cancellation window X_tot so that a corresponding division feedback cancellation window is allocated to the area of feedback signals exceeding a certain limit among feedback signals found by the feedback signal searching unit 42. Further, each of the division windows is divided into unit windows X_step- The entire window X_tot is divided, as given by the following Equation 2, [Equation 2]

K Xlot ~χ__! ^ak ^'Xstep where a^ is a natural number, and is a value indicating the number of unit windows constituting a k-th division window, and M = ∑a_k is satisfied. t=i

FIG. 8 is a diagram showing an example in which a feedback cancellation window is divided. Referring to FIG. 8, the area of feedback signals exceeding a certain limit among the feedback signals found by the feedback signal searching unit 42, forms three groups. Further, each of division window groups is divided into unit windows X_step-

That is, a value ^λK' based on the division of the feedback cancellation window is set to 3. Further, ai, a_∑, and a₃ are set to 3, 3, and 2, respectively.

The interference cancellation repeater according to an embodiment of the present invention includes the window setting unit 40, and searches an area having a size of N*X_tot_/- which is N times as large as the size X_tot of the feedback cancellation window, for feedback signals. Thereafter, the entire feedback cancellation window having the size X_tot is divided depending on the found feedback signals. Through this operation, a feedback cancellation window is set in a portion greatly influenced by feedback signals, and thus the feedback signals can be effectively cancelled. In particular, an inter-interference cancellation repeater feedback signal, generated outside the area of the feedback cancellation window, can be effectively eliminated. The D/A converter 15 converts the signal r_out(n), which is a signal from which the feedback signals are cancelled by the feedback signal cancellation unit 48, into an analog signal r_out(t) . The amplification unit 16 amplifies the analog output signal r_out(t), provided by the D/A converter 15, by a gain G. At this time, the signal amplified by the amplification unit 16 can be designated as G ^• r_out(t) . The transmission antenna 17 is an antenna for transmitting the amplified signal G - r_out(t), amplified by the amplification unit 16, to another terminal.

FIG. 9 is a flowchart showing the operating process of an interference cancellation repeater having a feedback cancellation window division function according to an embodiment of the present invention.

First, the total input signal r'_in(t) is received through the reception antenna 12 at step SIl, and is converted into a digital signal at step S12. In this case, the total input signal r'_in(t) is the sum of the source reception signal r_in(t), the intra-repeater feedback signal f_mtra(t), and the inter-repeater feedback signal f_mter(t) .

Thereafter, a window setting step Pl is performed, in which feedback signals are searched for at step S13, and a feedback cancellation window is divided at step S14.

At the feedback signal searching step S13, a unit window search function is sequentially and additionally performed, so that a window having a size of N*X_tot is searched, and feedback signals are detected in the area of N*X_tot« At the feedback cancellation window division step S14, the entire feedback cancellation window X_tot is divided so that a corresponding division feedback cancellation window is allocated to an area of feedback signals exceeding a certain limit, among the feedback signals found at the feedback signal searching step S13. Further, each division window is divided into respective unit windows

Y

^Λstep •

Thereafter, on the basis of the division windows, feedback signals are detected in each unit window at step S15, and the detected feedback signals are cancelled at step Sl6.

The feedback signal-cancelled output signal is converted into an analog signal at step S17, and the analog output signal is amplified at step S18. The amplified signal is transmitted to another terminal at step S19.

In the above description, the case where the interference cancellation repeater always performs the window setting step Pl has been described. Generally, however, the location of each feedback signal is not a parameter, the value of which frequently changes over time. The location of the feedback signal is defined by surrounding installation environments in most cases . That is, the location of the feedback cancellation window is a semi-static parameter which does not need to be frequently updated. Therefore, the window setting step Pl may be performed only once when power is supplied to equipment, or may be performed at regular periods .

In this way, the feedback signal searching unit 42 sequentially moves the feedback cancellation window Xtot_r which is the range of the correlation calculation, up to N*Xtot_r and searches each feedback cancellation window X_tot for feedback signals in steps of a unit window X_step- The window division unit 41 divides the feedback cancellation window into a predetermined number of division banks, each composed of a number of unit windows (for example, when the feedback cancellation window is 8 μsec, and a unit window is 1 μsec, the feedback cancellation window is divided into three division banks, respectively having 3, 3, and 2 unit windows) . Therefore, feedback signals can be detected in the area, the size of which is a maximum of N times or more as large as the size X_tot of the existing feedback cancellation window, only through a sequential window search function without adding search hardware resources.

In addition, a problem, which may occur when a feedforward signal input to the reception antenna of an interference cancellation repeater through multiple paths or another repeater is taken into consideration, and a method of solving this problem will be described below. An intra-repeater feedback signal alone, or an inter-repeater feedback signal, together with the intra-repeater feedback signal, can be efficiently cancelled. However, it may happen that signals having a correlation with signals other than the intra-repeater feedback signal or the inter- repeater feedback signal may be regarded as feedback signals and may be cancelled. That is, the reception antenna of the interference cancellation repeater not only receives the intra-repeater feedback signal or the inter- repeater feedback signal, as shown in FIG. 3 or 7, but also may be occasionally influenced by delay signals received from a base station through another path, or signals received from other repeaters (which may include an optical repeater and a microwave repeater, as well as the interference cancellation repeater) . A signal obtained in such a way that a multi-path signal or a single-source signal from the base station is input to the reception antenna of the interference cancellation repeater through other repeaters is an external input signal that is irrelevant to the repeater' s own gain and that exhibits its own correlation value (hereinafter referred to as a λ feedforward signal' ) .

FIG. 10 is a diagram showing an example of an external input signal irrelevant to the gain of a repeater itself for receiving an RF signal, the external input signal being received through another repeater. Referring to FIG. 10, an RF signal input to RUl also includes an input signal 53, which is input to RUl via another repeater RU2 for receiving an input signal from the DU, in addition to an input signal 51 received from DU and an intra-RUl feedback signal 52. The problems attributable to such a feedforward signal are summarized by the two items.

First, as shown in FIG. 11, when the feedforward signal 53, input via another repeater, rather than the intra-repeater feedback signal 52 is included in the feedback cancellation window 54, the feedforward signal 53 may be cancelled without being separated from feedback signals. However, the feedforward signal 53 is a signal for improving reception Signal-to-Noise ratio (SNR) at the time of being combined into the multi-path signal of a reception terminal, and is not the cause of self-oscillation, and thus there is no need to cancel the feedforward signal . Further, in most feedback signal cancellation algorithms, when a feedforward signal is located in an adaptive filter window for feedback cancellation, an operation of converging filter coefficients is not accurately performed, thus deteriorating the performance of the output signal of the repeater .

Second, when an auto-correlation is obtained in the presence of a feedforward signal, image components attributable to the feedforward signal 53 (denoted by reference numerals 521', 521", 522', 522", 523', and 523") (hereinafter referred to as ^Λ feedforward image signals' ) are present in addition to original feedback signals (denoted by reference numerals 521, 522 and 523, and, for convenience of description, only three signals are shown, but may include all feedback signals, such as the intra- repeater feedback signal and an inter-repeater feedback signal), as shown in FIG. 12. Since such signals are image components, there is no need to cancel the signals, but it is impossible to separate feedback signals and feedforward image signals when the auto-correlation of the received signal is used. Accordingly, when feedback signals are cancelled using a conventional window division method, division windows are allocated even to the feedforward image signals. However, for example, since the feedforward image signals 521' and 521" are signals which are automatically cancelled if only a related feedback signal 521 is eliminated, there is no need to allocate separate window resources. Instead, since the size X_tot of an allocated window is smaller than the size N*X_tot of the search window at the time of automatically searching /dividing a window, the case where feedback signals that must be cancelled are not cancelled due to the restriction of resources occurs when unnecessary window hardware (or software) resources are allocated to feedforward image signals, and thus this case becomes the cause of oscillation. The reason for this is that, according to the environmental conditions, feedforward image signals may have larger power than feedback signals. The influence of such a feedforward image signal equally affects the multi- path signal received from the base station, in addition to the feedforward signal 53 received through another repeater.

[Mode for Invention]

Hereinafter, a method of sequentially searching for and processing a feedforward signal according to embodiments of the present invention will be described in detail .

In this section, embodiments of a method of searching for a feedforward signal and preventing a window from being allocated to the feedforward signal are described below.

Among feedforward signals, signals input to the link antenna of an interference cancellation repeater through the multi-path fading of a base station are generally received earlier in time than the feedback signals of the interference cancellation repeater. Therefore, since signals are formed before the feedback cancellation window, a correlation does not appear within the feedback cancellation window, and then does not influence the operation of the interference cancellation repeater (however, in this case, a feedforward image signal may be generated, which will be described later) . However, since the feedforward signal 53, obtained in such a way that the signal from the base station is input through another repeater, as shown in FIG. 10, has a long delay time, it may be directly located in the feedback cancellation window of the interference cancellation repeater. As shown in FIG. 11, according to the technology of the interference cancellation repeater based on a method in which feedforward signals attributable to other repeaters are not considered, an algorithm is operated to cancel feedforward signals, but an interference cancellation algorithm is designed on the assumption that feedback signals are cancelled, and thus there is a problem in that, when feedforward signals are input, filter coefficients do not exactly converge. Due to this problem, the quality of the output signal of the repeater may be greatly degraded. Further, such a feedforward signal is a multi-path signal capable of increasing reception SNR from the standpoint of a terminal, and is not an oscillation-causing signal, the magnitude of which increases according to a repeater gain, and thus the feedforward signal is not a target to be cancelled. Therefore, the interference cancellation repeater needs to reset a feedback cancellation window so that the feedforward signal is not cancelled. For convenience of description, a method of searching for/processing a feedforward signal and a method of searching for/processing a feedback signal in consideration of a feedforward image signal are separately described below. <First method of processing feedforward signal>

FIG. 13 is a diagram schematically showing a method of processing a feedforward signal in an interference cancellation repeater according an embodiment of the present invention. As described above, the interference cancellation repeater has a need to reset a feedback cancellation window so that a feedforward signal is not cancelled. When a feedforward signal is detected, and the output signal of the repeater is delayed so that a feedback cancellation window appears after the time of the detection of the feedforward signal, the feedforward signal is not cancelled.

Both an intra-repeater feedback signal and an inter- repeater feedback signal are related to the transmission signal of the repeater. Accordingly, when the transmission output signal of the repeater is caused to be delayed, the feedback signal is delayed along with the feedback cancellation window. Therefore, as shown in FIG. 13, it is possible to locate the feedforward signal 53 in a portion placed before the feedback cancellation window 61 of the repeater if the output signal of the repeater is caused to be delayed until the feedforward signal 53 appears in the portion placed before the feedback cancellation window 61.

For a method of detecting a feedforward signal, even the detection of the correlation of a signal input to a link antenna by eliminating the output of the repeater is sufficient. The reason for this is that, when the output signal of the repeater disappears, a feedback signal also disappears. Methods of eliminating the output of the repeater may include various methods, such as a method of setting a repeater gain to 0 by switching off the amplifier of the repeater, and a method of setting a digital signal output, which is to be input to the D/A converter, to 0. It is apparent that other methods may be performed as the method of detecting a feedforward signal.

FIG. 14 is a diagram schematically showing a method of processing a feedforward signal in an interference cancellation repeater according to another embodiment of the present invention.

Unlike the above first method, the second method shown in FIG. 14 can prevent a feedforward signal from being cancelled by performing the step of detecting a feedforward signal; storing the location of the feedforward signal; and dividing/setting a feedback cancellation window in such a way as to avoid the stored location of the feedforward signal when dividing the feedback cancellation window. The division/setting of the feedback cancellation window may be performed including a manual division method, as well as an automatic division method.

A method of detecting a feedforward signal 53 is identical to that described in the first method. Further, at the feedback cancellation window division/setting step, the feedback cancellation window is divided into two or more banks 71 and 72 so that the detected feedforward signal 53 is not located in the feedback cancellation window of the repeater itself, as shown in FIG. 14, thus enabling only a feedback signal 52 to be cancelled. The above method has a problem in that, when the location of a feedforward signal overlaps the location of a feedback signal, it is difficult to apply such a method, but this problem can be avoided by using a method of applying a system delay so that the locations of two signals do not overlap each other.

<Third method of processing feedforward signal> FIG. 15 is a diagram schematically showing a method of processing a feedforward signal in an interference cancellation repeater according to a further embodiment of the present invention.

This embodiment includes the step S81 of delaying the output signal of a repeater by a predetermined time; the step S82 of performing the function of automatically dividing a feedback cancellation window, as described above; and the step S83 of recovering the set repeater delay to an original state.

At step S81, since most feedforward signals of significance are signals obtained after passing through one or two other repeaters, the predetermined time is set to a certain time T_c (where T_c may have a magnitude greater than the time, for which the signal input to the link antenna of the repeater is detected when the output of the repeater is eliminated, but there is a maximum available delay time caused by limitations in the application of a delay for the repeater) . Accordingly, if the automatic window division function is performed after the repeater delay has been applied, only the intra-repeater feedback signal and an inter-repeater feedback signal, other than the feedforward signal, can be cancelled using the same method as that of the first method described with reference to FIG. 13. However, when the repeater's own delay is set to the same value for all repeaters, feedforward signals from other repeaters are received as maximally delayed signals, and thus there is no effectiveness unless the repeater' s own delay, which has been previously set to the maximal value, is recovered to an original state, at step S83.

At step S82, feedback signals are searched for by moving the feedback cancellation window so that both the intra-repeater feedback signal and an inter-repeater feedback signal can be cancelled, and then the feedback cancellation window is divided on the basis of the found feedback signals. A search for feedback signals is performed by sequentially moving the feedback cancellation window, and searching the feedback cancellation window for feedback signals in steps of a unit window. The division of the feedback cancellation window is performed to include division banks, each composed of an arbitrary number of unit windows, and is performed using the same method as the above-described method.

However, even in the case of this method, there still remains a problem when the location of a feedforward signal overlaps the location of a feedback signal.

<Fourth method of processing feedforward signal> FIG. 16 is a diagram showing a method of processing a feedforward signal in an interference cancellation repeater according to yet another embodiment of the present invention.

The method of processing a feedforward signal in an interference cancellation repeater according to this embodiment includes the step S91 of setting the output or gain of a repeater to 0; the step S93 of measuring the auto-correlation R_FF(n) of an RF signal input to the repeater; the step S95 of applying a system delay for the repeater; the step of re-measuring the auto-correlation and additionally applying a system delay for the repeater by repeating steps S94 and S95 until a feedforward signal is not detected any more; and the steps S96 and 97 of setting the maximum value of the system delay, thus preventing the delay from being set to a value greater than the maximum value.

First, in the state in which the output or gain of the repeater is set to 0 without additionally delaying the output signal of the repeater at step S91, an operation of searching for feedback signals is performed for a time period ranging from 0 to N*T_tot at step S92. As described above, step S91 may be performed using a method of setting the gain of the repeater to 0 by switching off the repeater amplifier or the like, or a method of setting the digital signal output, which is to be input to the D/A converter, to 0, but is not limited to these methods, and any method can be used as long as an environment enabling measurement only of the influence of a feedforward signal on the RF signal input to the repeater can be configured by preventing feedback signals from flowing into the repeater. In this state, since no feedback signal is present, the presence of a feedforward signal can be detected by measuring the auto-correlation R_FF(Π) of the input signal. Thereafter, whether the correlation value of the input signal, measured at step S93, becomes a level TH_FF is determined through comparison, and thus whether there is any feedforward signal is determined at step S94. If it is determined that a feedforward signal has been input, an additional delay T_d for the repeater is applied at step S95. After the additional delay for the repeater has been applied, the final delay value for the repeater is set by repeatedly detecting the presence of a feedforward signal through the re-measurement of auto-correlation at steps S94, S95 and S99.

During the process for adding a delay value for the repeater, a protection step may be provided so that the delay value does not exceed the maximum value T_d,_max of the set system delay at step S96. The reason for setting the maximum value T_d/max of the additional system delay that can be applied is that the system delay for the repeater may influence the reverse softer combining performance of the base station. When the system delay longer than the combining length of the base station is applied to the repeater, the performance of softer handover may be deteriorated, and thus the maximum delay value is limited. When the system delay for the repeater exceeds the maximum delay value, the additional delay value must be returned to a value between 0 to T_d,_max at step S97. After the additional delay value has been returned, the influence of the remaining feedforward signals remains, and thus a problem may occur. In this case, an additional function of remembering the location of the feedforward signal and preventing a window from being allocated to that location at the time of subsequently dividing a feedback cancellation window is required. Here, when the step of selecting the returned delay value from the range between 0 and Ta,_max to prevent the remaining feedforward signals from overlapping each other is provided by referring again to the feedback signal location search step, which is the subsequent procedure, such an exceptional problem may be solved. The method may include the step S98 of determining whether the RF input signal of the repeater initially enters an oscillation level after the step of measuring the correlation of the input signal of the repeater. If it is determined that the RF input signal of the repeater has already been in the oscillation state, the subsequent signal search procedure is meaningless, so that setting is terminated, and oscillation is prevented from being propagated by switching off the amplifier, thus ensuring the stability of the network. The detection of the oscillation level can be performed by measuring the autocorrelation R_FF(n) of the input signal, and, typically, TH_oscliiation > TH_FF is satisfied.

Through the above-proposed scheme, when the feedforward signals are detected using the correlation value and the output signal of the repeater is delayed, the feedforward signals, directly located in the feedback cancellation window, are cancelled, and thus the process may proceed to the procedure for searching for/separating a feedforward image signal and a feedback signal, which will be described later.

Hereinafter, the influence of a feedforward image signal is described below.

Through this procedure, the correlation value attributable to feedforward signals can be prevented from being located in the feedback cancellation window. However, when feedback signals are present, the influence of the feedforward signals, located outside the window, may be deformed in the shape of images of the feedforward signals and may appear in the window. FIG. 12 illustrates an example of an influence exerted by a feedforward image due to the correlation between a feedforward signal, placed outside a feedback cancellation window, and a feedback signal when the feedforward signal is placed outside the feedback cancellation window. In the example, the condition in which one feedforward signal is generated at a distance of d from a source signal is exemplified and shown. The feedforward signal may be one of multiple paths of the source signal of a base station, or may be a signal obtained in the case where a feedforward signal is located before the window by applying a delay for the repeater (refer to 53 of FIG. 13) . Further, the example of FIG. 12 shows the case where the number of feedback signals is three. Under the above conditions, when the correlation of the input signal of the repeater is obtained, image components (denoted by reference numerals 521', 521", 522', 522", 523' and 523") attributable to the feedforward signal 53 appear in addition to the original feedback signals (denoted by reference numerals 521, 522 and 523), as shown in FIG. 12. Since the feedforward image signals are automatically cancelled if only related feedback signals are eliminated, there is no need to allocate separate window resources.

In the case of automatic window search/division, since the size X_tot of the allocated window is smaller than the size N*N_tot of the search window, the case where feedback signals that must be cancelled are not cancelled due to the restriction of resources occurs when unnecessary window hardware (or software) resources are allocated to feedforward image signals, and thus this case may become the cause of oscillation. Therefore, the processing of feedforward image signals is very important, and an algorithm implemented in consideration of this processing will be described in the subsequent process.

Hereinafter, a process for sequentially searching for a feedback signal and automatically dividing a window in consideration of a feedforward image signal is described below.

In this section, an embodiment of a method of sequentially searching for a feedback signal and automatically dividing a window in consideration of a feedforward image signal is described.

A process for automatically dividing a feedback cancellation window in an interference cancellation repeater in consideration of even the above-described processing of the feedforward signal according to still another embodiment of the present invention is shown in FIG. 17. The steps performed before step S99 of FIG. 17 have been previously described, and thus an automatic search procedure starting from step S99 is described in this embodiment. The procedure for automatically dividing a feedback cancellation window includes the step S99 of turning on the output or gain of the repeater, and thereafter setting a repeater gain to a minimum value; the step SlOO of measuring the correlation R_FB(Π) of the input signal on the basis of a movement and a search after canceling the feedback of the repeater; the step SlOl of determining the effectiveness of resources in relation to whether the division bank of the feedback cancellation window can be allocated to the location at which the maximum value of the measured correlation values is placed; the step S102 of, after the application of re-division of division banks, re- measuring the correlation Rp₆ (n) of the signal obtained after the feedback has been cancelled; the step S103 of dividing/allocating effective banks and repeating steps SlOl and S102 until all the correlation values (V: all) become less than a certain level within the range of search; the step S104 of increasing the gain of the repeater by a unit gain (gain-step) ; the step S105 of repeating steps SlOO to S104 under the condition in which the repeater gain is equal to or less than a certain level P_ref; and the step SlO 6 of dividing and setting the window (bank) , and returning to the user' s set value Atten before the procedure was performed. Further, the procedure may include the step S108 of verifying whether at least one of the correlation values ( 3 : a certain one) enters an oscillation level if it is determined at step SlOl that division bank resources are exhausted and the rearrangement of banks is impossible, and the step S109 of applying effective division and setting performed before oscillation occurs if it is verified that oscillation has been detected.

It should be noted that, at step SlOO, in the situation in which a feedback signal is present, in other words, in the situation in which the output signal of the repeater is delayed to allow the feedback cancellation window to be placed at the location, at which a feedforward signal is not cancelled, when a feedback signal is not present, the auto-correlation R_FB(Π) of the input signal is measured after the feedback signal has been cancelled. In this case, the correlation is a correlation value obtained in the situation in which an operation of canceling the feedback signal is performed through the division of banks of the feedback cancellation window, which are sequentially allocated.

At step SlOl, whether the bank resources of the window remain is determined. If it is determined that the rearrangement of division banks is possible, one of the division banks of the feedback cancellation window is allocated to the location at which the maximum value of correlation values, measured in the search window, is placed, so that a corresponding signal is cancelled, and thereafter correlation is re-measured at step S102.

As described above with reference to FIG. 12, the feedforward image signals are located on both sides of a related feedback signal. The mean power of the correlation values relative to the feedforward image signals is always below 6dB of the mean level of the related feedback signal, and this condition, indicating a difference of 6dB, occurs when a source reception signal is identical to a feedforward signal. Therefore, when one bank is allocated to the location at which the correlation value R_Fβ(n), obtained after the feedback has been cancelled, is the maximum value, at step S102, a window bank is allocated to the location of a feedback signal having the highest power. As a result, feedforward image signals related to the corresponding feedback signal are automatically cancelled. That is, through the repetition of steps SlOl and S102, effective banks may be sequentially allocated only to feedback signals in the order of the power intensities thereof, and resources can be prevented from being allocated to the feedforward image signals. Meanwhile, in the above example, the case where whether any window bank resources remain is determined at step SlOl and the step of rearranging division banks is performed only when window bank resources are found to remain have been described. However, it is also possible to omit step SlOl and rearrange the division bank, allocated at the previous step, at the location at which the maximum value of the re-measured correlation values is placed when the maximum value of the re-measured correlation values is greater than the correlation value, for which the division bank has been allocated at the previous step, even if no window bank resources remain after steps S104 and S105 have been performed.

The above process is repeated until the condition, in which all correlation values (V: all) remaining after cancellation become less than the certain level, is satisfied at steps SlOl to S103. In this embodiment, the condition in which the certain level is TH_G-_20ds in which an Error Vector Magnitude (EVM) becomes less than 10% (that is, the condition in which feedback signals are canceled when isolation, obtained after the cancellation of feedback signals, is in a level less than a repeater gain by 2OdB) has been described for the certain level, but it is apparent to those skilled in the art that operations can be performed by limiting threshold values to comply with respective mobile communication standards. For reference, in the case of a WCDMA system, the standard of EVM is 12.5%, wherein the above condition needs to be limited to TH_G-i8d_B- When correlation values greater than a given threshold value, among re-measured correlation values, are present in the search area, the remaining bank resources are successively and repeatedly allocated to the location at which the maximum value of the re-measured correlation values is present.

Further, when all of the re-measured correlation values are less than the certain level TH_G_₂od_Br the repeater's own gain is increased by a unit gain (Gain-step) at step S104. The procedure for rearranging division banks is repeated until the output of the repeater reaches a predetermined output [output power > min{P_ref, Ps_hutdow_n}] at step S105. Through the procedure for increasing a repeater gain and repeatedly performing measurement, the probability of search can be increased, and the stability of the entire operation can be ensured. The reason for this is that, as the repeater gain increases, the magnitude of a feedback signal intended to be searched for also increases.

Meanwhile, if it is determined at step SlOl that effective division bank resources of the feedback cancellation window are exhausted, and the rearrangement of division banks is not possible, whether at least one ( 3 : a certain one) correlation value greater than an oscillation initiation level THosciiiatioi_v iⁿ which oscillation can be caused, among the remaining correlation values, is present is determined at step S108. If it is determined that a correlation value greater than the oscillation initiation level TH_osciii_ati_on is not present, there is a low probability of oscillation. Therefore, the division bank rearrangement procedure is repeated until the repeater' s own gain reaches the predetermined output [output power > min{P_ref, Pshutdown}] through step S104. If a correlation value greater than the oscillation initiation level TH_OSCiiiatio_n is detected, a repeater gain, obtained immediately before the oscillation initiation level is obtained, is indicated using window division information based on the previously stored information about the arrangement of the feedback cancellation window before oscillation occurs, corresponding window division information is applied, and thereafter an installation procedure is terminated at steps S109 and SIlO.

At step S105, when the repeater's own gain exceeds the predetermined output [output power > min{P_ref, Pshutdown} ]_r the feedback cancellation window is divided and set based on the arrangement of finally set window banks, and then the operation of searching for feedback signals is terminated at steps S106 and S107.

According to the preset embodiment, insufficiency of window resources that may occur due to the image components of feedback signals attributable to the existence of feedforward signals can be overcome, and the efficient utilization of resources can be realized. <Sixth method of processing feedforward signal>

FIG. 18 is a diagram showing an automatic division procedure performed in an interference cancellation repeater according to still another embodiment of the present invention.

This embodiment is almost the same as the above- described fifth method, and thus a description will be made on the basis of the difference therebetween.

In this embodiment, the procedure includes the step SlOO' of measuring convergence coefficient power values Pcoef_f(n) on the basis of the movement and search using the additional feedback cancellation adaptive filter of the repeater; the step S102' of allocating division banks so that one of the division banks is placed at the location at which the maximum value of the measured filter coefficient power values P_COeff(n) is present; the steps S103' , SlOl and S102' of, after division banks have been allocated/applied, re-measuring the convergence coefficient power values Pc_oeff(n) of the feedback cancellation adaptive filter, and dividing/allocating effective banks until all of the re- measured convergence coefficient power values become less than a certain level, thus repeating the third step; and the step S105 of increasing the gain of the repeater by a unit gain and repeating the above steps SlOO', SlOl, S102', S103' , and S104 until the gain of the repeater becomes less than a certain level P_ref- In the fifth method, automatic movement and search for feedback signals are performed based on the correlation of the input signal after feedback has been canceled, but, in the present embodiment, the automatic movement and search procedure is replaced with a movement and search procedure based on the feedback cancellation adaptive filter. After most adaptive filters, including a Least Mean Square (LMS) -series feedback cancellation adaptive filter, are converged, filter coefficients become complex values in which the magnitudes of feedback signals are considered in the locations of the feedback signals. Coefficients are not generated at the locations of feedforward image signals. That is, in the case of the procedure, since feedforward image signals, which must be merely mathematically derived at the time of calculating auto-correlation values, are not generated, the sequential allocation of banks required for the processing of feedforward image signals is not required.

However, for this procedure, an adaptive filter for a movement and search must be provided separately from an original feedback cancellation adaptive filter, thus increasing the complexity of hardware (or software) in implementation. A search for the locations of feedback signals is the basis of the power of complex coefficients of the adaptive filter, and the remaining operations are the same as those of the fifth method, and thus a detailed description thereof is omitted.

FIG. 19 is a diagram schematically showing the construction of an interference cancellation repeater according to an embodiment of the present invention. Referring to FIG. 19, an interference cancellation repeater according to an embodiment of the present invention includes a feedback signal search/division/cancellation unit 400 and a feedforward signal search/system delay unit 406. The remaining components are the same as those of a conventional repeater, and can be suitably adopted to perform respective methods described in the above-described embodiments, and thus a detailed description thereof is omitted for the sake of convenience. The feedforward signal search/system delay unit 406 includes a feedforward signal search unit [R_FF(n)] 404 for searching for a feedforward signal using the correlation of an RF input signal received through a link antenna 12 after the system gain of the repeater has been set to, for example, 0, and a system delay unit 405 for adding a delay for the repeater depending on the time delay of a found feedforward signal .

The feedback signal search/division/cancellation unit 400 includes a feedback signal search unit 403 for searching for a feedback signal using a correlation-based movement and search method, or using an adaptive filter- based movement and search method, a feedback cancellation window division unit 402 for dividing and setting a feedback cancellation window on the basis of the found feedforward signal and feedback signal so that windows are not allocated to the feedforward signal, or the image signal of the feedforward signal, and a feedback signal cancellation filter 401 for canceling the feedback signal from the received RF signal on the basis of respective division windows obtained through the division of the feedback cancellation window.

The respective components of the feedforward signal search/system delay unit 406 and the feedback signal search/division/cancellation unit 400 are configured to perform respective functions described in relation to the above embodiments, and may be easily implemented using hardware, software, or a combination thereof.

Although the preferred embodiments of the present invention have been described in detail, but they are only intended to describe the embodiments of the present invention, and thus it is apparent that the embodiments can be variously modified and implemented by those skilled in the art. Consequently, the scope of the present invention should be defined by the accompanying claims.

Claims

[CLAIMS]

[Claim l]

A repeater for canceling interference attributable to a feedback signal, comprising: a window setting unit for searching a Radio Frequency

(RF) signal, which is received through a reception antenna and includes an intra-repeater feedback signal and an inter-repeater feedback signal, for a feedback signal by moving a feedback cancellation window (X_tot) _/ and for dividing the feedback cancellation window on a basis of the feedback signal; and a feedback signal cancellation unit for canceling the feedback signal from the received RF signal on a basis of the feedback cancellation window divided by the window setting unit.

[Claim 2]

The repeater according to claim 1, wherein the window setting unit comprises : a feedback signal searching unit for receiving the RF signal and searching for the feedback signal while sequentially moving the feedback cancellation window (Xtot) 1 and a window division unit for allocating the feedback cancellation window to an area of feedback signals exceeding a certain limit, among the feedback signal, thus setting each division feedback cancellation window, and dividing the division feedback cancellation window into unit windows (X_step) •

[Claim 3] The repeater according to claim 2, wherein: the feedback signal searching unit sequentially moves the feedback cancellation window (Xtot) i and searches the feedback cancellation window (X_tot) for the feedback signal in steps of a unit window (X_step) ; and the feedback cancellation window (X_tot) is a sum of M unit windows (X_step) i where M is a natural number.

[Claim 4]

The repeater according to claim 3, wherein the window division unit divides the feedback cancellation window (X_tot) as given by the following equation:

K

X tot ^~ Z-_ι ^ak 'Xstep k=\ where a_k is a natural number, and is a value indicating a number of unit windows constituting a k-th division window,

K and M = ∑a_k is satisfied.

[Claim 5]

The repeater according to claim 4, wherein the feedback signal cancellation unit comprises: a feedback signal detection unit for estimating time delays, amplitudes and phases of the feedback signal using correlation between the received RF signal and a previously generated signal, from which feedback has been cancelled, at locations of unit windows (X_step) obtained through division by the window division unit; and a feedback signal cancellation filter for generating a reverse-phase signal of the feedback signal estimated by the feedback signal detection unit, and canceling feedback signals from the RF signal using the generated reverse- phase signal.

[Claim 6]

The repeater according to claim 5, further comprising an amplification unit for amplifying a signal, from which the feedback signals are canceled by the feedback signal cancellation filter, by a preset gain.

[Claim 7]

A method of canceling interference attributable to a feedback signal in a repeater, comprising: a window setting step of searching a Radio Frequency

(RF) signal, which is received through a reception antenna and can include an intra-repeater feedback signal and an inter-repeater feedback signal, for a feedback signal by moving a feedback cancellation window (Xtot) , and of dividing the feedback cancellation window on a basis of the feedback signal; and a step of canceling the feedback signal from the received RF signal on a basis of the feedback cancellation window divided at the window setting step.

[Claim 8]

The method according to claim 7, wherein the window setting step comprises : a feedback signal searching step of receiving the RF signal, and searching for the feedback signal while sequentially moving the feedback cancellation window (X_tot) ; and a window division step of allocating the feedback cancellation window to an area of feedback signals exceeding a certain limit, among the feedback signal, thus setting each division feedback cancellation window, and dividing the division feedback cancellation window into unit windows (X_step) •

[Claim 9] The method according to claim 8, wherein: the feedback signal searching step is performed to sequentially move the feedback cancellation window (X_tot) , and search the feedback cancellation window (X_tot) for the feedback signal in steps of a unit window (X_step) /' and the feedback cancellation window (X_tot) is a sum of unit windows (X_step) , where M is a natural number.

[Claim lθ]

The method according to claim 9, wherein the window division step is performed such that the feedback cancellation window (X_tot) is divided as given by the following equation:

where a_k is a natural number, and is a value indicating a number of unit windows constituting a k-th division window,

K and M = y]a_k is satisfied. k=\

[Claim ll]

The method according to claim 10, further comprising the step of amplifying a signal, from which the feedback signals have been cancelled by a feedback signal cancellation filter, by a preset gain.

[Claim 12]

A method of canceling interference, comprising the steps of: receiving a Radio Frequency (RF) signal, including a feedback signal and a feedforward signal, through a link antenna of an interference cancellation repeater, which cancels the feedback signal using a feedback cancellation window; detecting the feedforward signal; and resetting the feedback cancellation window so that the detected feedforward signal is not included in the feedback cancellation window, thus canceling the feedback signal .

[Claim 13]

The method according to claim 12, wherein the feedback signal include an intra-repeater feedback signal and an inter-repeater feedback signal.

[Claim 14]

The method according to claim 12, wherein the step of detecting the feedforward signal comprises the steps of: setting an output or a gain of the repeater to ^λ0' ; and measuring an auto-correlation of the RF signal, received through the link antenna, on a basis of a movement and a search.

[Claim 15]

The method according to claim 12, wherein the step of resetting the feedback cancellation window and canceling the feedback signal is performed by delaying an output signal of the repeater so that the feedback cancellation window appears after time of detection of the feedforward signal has elapsed.

[Claim 16] The method according to claim 12, wherein the step of resetting the feedback cancellation window and canceling the feedback signal is performed by manually dividing the feedback cancellation window into a predetermined number of windows so that the detected feedforward signal is not included in the feedback cancellation window.

[Claim 17]

The method according to claim 12, wherein the step of resetting the feedback cancellation window and canceling the feedback signal comprises the steps of: delaying an output of the repeater by a certain time greater than a time for which the signal received through the link antenna is detected when the output of the repeater is eliminated; searching the feedback signal while moving the feedback cancellation window; dividing the feedback cancellation window on a basis of the feedback signal; and recovering the delay of the repeater to an original state. [Claim 18]

The method according to claim 17, wherein the step of searching for the feedback signal comprises the step of searching for the feedback signal while sequentially moving the feedback cancellation window.

[Claim 19]

The method according to claim 17, wherein the step of dividing the feedback cancellation window comprises the step of continuously or discontinuously dividing and setting the feedback cancellation window using division banks, each composed of an arbitrary number of unit windows .

[Claim 20]

The method according to claim 12, wherein the step of detecting the feedforward signal comprises: a first step of setting an output or a gain of the repeater to ^λ0' ; a second step of measuring an auto-correlation of the RF signal received through the link antenna on a basis of a movement and a search; a third step of applying an additional system delay for the repeater, and a fourth step of re-measuring the auto-correlation, and applying the additional system delay by repeating the second and third steps until any feedforward signal is not detected any more .

[Claim 2l] The method according to claim 20, wherein the step of detecting the feedforward signal is performed by repeating the fourth step until the system delay reaches a preset maximum value for the system delay.

[Claim 22] The method according to claim 21, wherein the step of detecting the feedforward signal comprises the steps of: recovering the additional system delay to a state before the additional system delay reaches the maximum value when the additional system delay attributable to the feedforward signal becomes greater than the maximum value; and verifying whether the received signal is an oscillation signal in a state in which the recovered system delay is applied.

[Claim 23]

The method according to claim 20, wherein the step of dividing the feedback cancellation window is performed such that window bank resources are not allocated to a feedforward image signal .

[Claim 24]

The method according to claim 23, wherein the step of dividing the feedback cancellation window comprises : a fifthstep of setting a gain of the repeater to a minimum value; a sixth step of measuring a correlation [R_FB(n)] of the received signal on a basis of a movement and a search after feedback of the repeater has been cancelled; an seventh step of allocating division banks so that one of the division banks of the feedback cancellation window is placed at a location at which a maximum value of measured correlation values is present; a eighth step of, after the division banks of the window are allocated, re-measuring a correlation [R_FB(Π)], obtained after feedback has been cancelled, and repeating the seventh step by allocating effective banks until all correlation values become less than a certain level; and a ninth step of repeating the sixth to eighth steps by increasing the gain of the repeater by a unit gain withinthe gain of the repeater less than a certain level

(Pref) •

[Claim 25]

The method according to claim 24, further comprising the step of, if division bank resources to be allocated are exhausted at the seventh step, and rearrangement of division banks is impossible, determining whether remaining correlation values greater than an oscillation initiation level of the repeater are present, wherein, if it is determined that remaining correlation values greater than the oscillation initiation level of the repeater are not present, the gain of the repeater is increased by a unit gain, and thus the sixth to eighth steps are repeated, and wherein, if it is determined that remaining correlation values greater than the oscillation initiation level of the repeater are present, a gain of the repeater, obtained immediately before the oscillation initiation level is obtained, is indicated using window division information based on previously stored information about arrangement of the feedback cancellation window before oscillation occurs, and the feedback signals are cancelled using relevant window division information.

[Claim 26]

The method according to claim 24, wherein, when division bank resources to be allocated are exhausted at the seventh step, and a maximum value of correlation values re-measured at the eighth step is greater than a correlation value for which the division bank is allocated at the seventh step, the division bank allocated at the seventh step is rearranged at a location at which the maximum value of the correlation values re-measured at the eighth step is present.

[Claim 27]

The method according to claim 23, wherein the step of dividing the feedback cancellation window comprises: an tenth step of setting the gain of the repeater to a minimum value; a eleventh step of measuring coefficient power values on a basis of a movement and a search of a feedback cancellation adaptive filter of the repeater; a twelfth step of allocating division banks so that one of the division banks of the feedback cancellation window is placed at a location at which a maximum value of measured coefficient power values of the adaptive filter is present; a thirteenth step of, after the division banks have been allocated/applied, re-measuring coefficient power of the adaptive filter after feedback has been cancelled, and repeating the twelfth step by dividing/allocating effective banks until all of the coefficient power values become less than a certain level; and a fourteenth step of repeating the eleventhto thirteenth steps by increasing the gain of the repeater by a unit gain until the gain of the repeater becomes less than a certain level (P_ref) •

[Claim 28]

The method according to claim 27, further comprising the step of, if division bank resources to be allocated are exhausted at the twelfth step and rearrangement of division banks is impossible, determining whether remaining coefficient power values greater than an oscillation initiation level of the repeater are present, wherein, if it is determined that remaining coefficient power values greater than the oscillation initiation level of the repeater are not present, the gain of the repeater is increased by a unit gain, and thus the eleventh and thirteenth steps are repeated, whereas, if it is determined that remaining coefficient power values greater than the oscillation initiation level of the repeater are present, the gain of the repeater, obtained immediately before the oscillation initiation level is obtained, is indicated using window division information based on previously stored information about arrangement of the feedback cancellation window before oscillation occurs, and the feedback signals are cancelled using relevant window division information.

[Claim 29] The method according to claim 24 or 27, wherein the search using the feedback cancellation window and the division of the feedback cancellation window are performed in real time.

[Claim 30]

The method according to claim 24 or 27, wherein the search using the feedback cancellation window and the division of the feedback cancellation window are performed at a time of initially installing the repeater or at a request of a user.

[Claim 31]

The method according to claim 24 or 27, wherein the search using the feedback cancellation window and the division of the feedback cancellation window are performed separately in a forward direction and in a reverse direction.

[Claim 32]

The method according to claim 24 or 27, wherein the search using the feedback cancellation window and the division of the feedback cancellation window are performed in either forward direction or reverse direction, and the forward and reverse directions are set so that the division information is identical in respective directions. [Claim 33]

An interference cancellation repeater for canceling a feedback signal using a feedback cancellation window, comprising: a link antenna for receiving a Radio Frequency (RF) signal, including a feedback signal and a feedforward signal; a feedforward signal searching unit for searching the RF signal, received through the link antenna, for the feedforward signal; and a system delay unit for adding a system delay for the interference cancellation repeater so that the detected feedforward signal is not included in the feedback cancellation window.

[Claim 34]

The interference cancellation repeater according to claim 33, further comprising: a feedback signal searching unit for searching the RF signal, received through the link antenna, for the feedback signal; a feedback cancellation window division unit for dividing and setting a feedback cancellation window so that division windows are not allocated to the feedforward signal or an image signal of the feedforward signal on a basis of a found feedforward signal and a found feedback signal; and a feedback signal cancellation filter for canceling the feedback signal from the received RF signal on a basis of the feedback cancellation window divided by the feedback cancellation window division unit.