Background Art In general, mobile communication systems are classified into mobile switches, base stations (BS) and mobile terminals. There are several functions in mobile switches. For instance, the mobile switches process incoming and outgoing of each of base stations by connecting with each of a base station controller (BSC) and controls in order that all base station are efficiently used.

In addition, the mobile switches perform a function to connect another network such as Public Switch Telecommunication Network (PSTN).

The base station (BS) comprises a base station controller, a base station transceiver subsystem and a repeater. By the base station (BS) for connecting mobile terminals with mobile switches, users can speak the other party. The repeater is used to extend a cell coverage of the base station and is divided into an optical repeater, a wireless repeater and a laser repeater. The wireless repeater among these repeaters receives a radio signal, which becomes weakened and transferred from the base station to the mobile terminal, or from the mobile terminal to the base station. After that, the repeater amplifies this radio signal

and transfers it.

This repeater generally includes two antennas (e. g. , a link antenna and a service antenna). A forward link signal of the base station received by t he link antenna is amplified to be transmitted to a peripheral mobile terminal by the service antenna. A reverse link signal of the mobile terminal received by the service antenna is amplified to be transmitted to the base station by the service antenna. Accordingly, the respective antenna performs a function to transmit/receive through one antenna.

At this time, since the frequency of the radio signal transmitted/received is equal, a part of signals outputted through transmitting/receiving station may be inputted in an echo signal state through the receiving station. This echo signal is merged with an original signal received from the base station or the mobile terminal and then amplified. Then, this echo signal is outputted by the transmitting station a gain. Through these processes, t here is a possibility o f a n oscillation of the repeater. In addition, now that the echo signal is placed more weight than the original signal, the characteristic of a signal received in the mobile terminal is dramatically decreased.

To overcome these problems due to the echo signal, it is necessary to sufficiently secure the distance between the transmitting station and receiving station o f the repeater to increase an isolation between the transmitting station and receiving station. As a result, the level of the echo signal should be negligible small in comparison with the original signal inputted through the receiving station. However, there are many advantages in aspect of cost, space and repair works.

Therefore, to solve these problems, there is a request of additional echo canceller unit capable of canceling this echo signal. Conventionally, a method for canceling echo signals by Frequency Allocation (FA) has been used in recent

year. That is, echo signals are cancelled by dispreading CDMA signals. In this case, since the echo canceller unit is requested in frequency band, so that the construction of repeaters becomes complex.

Disclosure of Invention An object of the present invention is directed to provide a wireless repeater including an echo canceller unit capable of dividing into an original signal and an echo signal through antennas of the wireless repeater from an input signal to remove an echo signal component and an echo cancellation method. In addition, the present invention provides an echo canceller unit applicable to all signals with complex correlation characteristic as well as to one algorithm irrespective of a frequency band and an echo cancellation method.

In accordance with the present invention, the wireless repeater estimates an amplitude, a phase and a delay time of an echo signal through complex correlation between an input signal including an echo signal component received from the outside and a reference signal outputted from a final output, and thereby generating an echo restore signal equal to the echo signal component and canceling the echo signal component from the input signal. To satisfy this, the wireless repeater includes an echo canceller unit capable of dividing an original signal and an echo signal from an inputted signal using the complex correlation.

Brief Description of Drawings Fig. 1 is a block diagram showing an embodiment of a wireless repeater including an echo canceller unit.

Fig. 2 is a detail block diagram showing an embodiment of the echo canceller unit of Fig. 1.

Fig. 3 is a block diagram showing an internal structure of an ECU finger in the echo canceller unit of Fig. 2.

Fig. 4 is a flowchart illustrating a transmission process by canceling an echo signal from a received signal of the present invention.

Fig. 5 i s a flowchart i llustrating a p rocess o f r eceiving a nd c onverting t he signal of Fig. 4.

Fig. 6 is a flowchart illustrating a process of canceling the echo signal of Fig. 4.

Fig. 7 is a flowchart illustrating a process of generating an echo restore signal of Fig. 6.

Fig. 8 is a flowchart illustrating processes of converting and transmitting a signal where the echo signal is cancelled in Fig. 4.

Best Mode for Carrying out the Invention [Embodiment] Fig. 1 is a block diagram showing an embodiment of a wireless repeater including an echo canceller unit. As shown in Fig. 1, a wireless repeater of the present invention includes a link antenna 100 for transmitting/receiving a signal to Base Station (BS), a first duplexer 101 for bifurcating a sending end and a receiving end so as to transmit/receive a signal through the link antenna 100, a service antenna 120 for transmitting/receiving to a mobile terminal, a second duplexer 115 for bifurcating a sending end and a receiving end so as to transmit/receive a signal through the service antenna 120, a forward link 103 for processing a signal received by the link antenna 100 to output to the service antenna 120, and a reverse link 123 for processing a signal received by the service antenna 120 to output to the link antenna 100. The forward and reverse antennas 103 and 123 include low noise amplifiers (LNA) 102 and 122, down

converters (DNC) 104 and 124, analog/digital converters (ADC) 106 AND 126, echo canceller units (EUC) 108 and 128, digital/analog converters (DAC) 110 and 130, up converters (UPC) 112 and 132, and linear power amplifiers (LPA) 114 and 134, respectively. A signal received through the link antenna 100 of the wireless repeater is inputted to the low noise amplifier 102 by the first duplexer 101. At this time, the signal received by the link antenna 100 is an analog signal of r adio f requency b and a nd a lso i s a signal combining an original signal from the base station and an echo component of a signal outputted before. The low noise amplifier 1 02 minimizes a n oise of an input signal and then amplifies i t.

The amplified signal by the low noise amplifier 102 is converted from the RF band signal to an intermediate frequency signal band signal by the down converter 104. In addition, the IF band signal is converted through the analog/digital c onverter 1 06 t o a d igital s ignal a nd then is inputted to t he e cho canceller unit 108. The echo canceller unit 108 cancels the echo signal component from an input signal using the complex correlation to output an original signal to be emitted. This output signal is converted to an analog signal of the RF band via a reverse signal conversion process to be emitted to the mobile terminal. In other words, this output signal is converted to analog signal through the digital/analog converter 110 and converted to the RF band by he up converter 112, and then it is amplified by the linear power amplifier 114 via the second duplexer 115 to emitted to the mobile terminal by the service antenna 120. In the same way, a signal received through the service antenna 120 is emitted to the base station.

Fig. 2 is a detail block diagram showing an embodiment of the echo canceller unit of Fig. 1.

The echo canceller units 108 and 128 have the same structure and an operation characteristic in the forward link 103 and the reverse link 123, and

hence the description is thus omitted.

As shown in Fig. 2, the echo canceller unit includes an echo signal searcher (EUC) 202, several fingers (hereinafter inclusively referred to as"EUC finger") (210-1, 210-2,..., 210-N), a calculator 206, an auto level controller (ALC) 208, and an automatic gain controller (AGC) 204. As stated above, a signal (SI (t) ) inputted to the echo canceller unit is a digital signal and a signal combining an original signal (S (t) ) to be amplified and an echo signal (SE (t) ) that an output signal (So (t) ) re-inputted via several paths in a delayed state. That is, the input signal (SI (t) ) can be expressed the original signal (S (t) ) plus the echo signal (SE (t) ), this is given by the equation [Mathematical Equation 1] where, Ks, Ps, To represent an amplitude, a phase and a delay time of an output signal obtained via ith path, respectively. In this case, the echo canceller unit is operated in a speed negligible itself relative to a control time of the echo canceller unit.

Referring to Fig. 2, the echo canceller unit is constructed with a circular loop. In addition, the echo canceller unit generates an echo restore signal (S^E (t) ) equal to an echo signal (SE (t) ) component included in an input signal (SI (t) ) using an input signal (SI (t) ) and a predetermined reference signal (SREF (t)), and then cancels the echo signal (SE (t) ) to output. In other words, the echo c anceller unit s earches a d elay t ime o f the e cho s ignal (SE (t) ) included in the an input signal (SI (t) ) to assign a pertinent ECU finger using the input signal (SI (t) ) and the reference signal (SREF (t) ) from the echo signal searcher 202. Each of the ECU finger assigned to cancel the echo signal (SE (t) ) by the echo signal searcher 202 estimates an amplitude K, a phase P and a delay time

T of the echo signal (SE (t) ) using the input signal (SI (t) ) and the reference signal (SREF (t)) to generate each of echo restore signals (SAEz (t), (S^E2 (t)),..., (S^EN (t) ) equal to pertinent echo signal component and then subtracts this from the input signal (S, (t) ) using the calculator. As a result, the echo signal component (SE (t)) is cancelled. This is expressed by the following equation.

[Mathematical Equation 2] SO(t)=SI(t)-#E1(t)-#E2(t)-...-#EN(t) Now, each of hardware blocks of the echo canceller unit is more fully described hereinafter referring to Fig. 2 and Mathematical equation 1. In case that a power So (t) applied to the automatic level controller 208 is under a regular level, the automatic level controller 208 passes a signal in itself. However, in case that the power So (t) applied to the automatic level controller 208 is over a regular level, the auto level controller 208 lessens the signal and then outputs it. Through these processes, it is possible to prevent oscillation of systems in case that an echo cancellation function is abnormally operated by inputting new echo signal due to an initial state of systems or dramatic change of environment. The automatic gain controller 204 controls a gain about a signal inputted so as to always maintain an output power to have a regular value. In addition, the automatic gain controller 204 generates the output the reference signal SREF (t) from the output signal So (t) for searching and canceling the echo signal component included in the system input signal SI (t). The EUC searcher 202 performs a function to search delay time of the echo signal components SE (t) included in the system input signal SI (t). In addition, the EUC searcher 202 searches the number N of echo signal components to be cancelled among the echo signals SE (t) to assign pertinent EUC fingers.

The EUC fingers 210-1, 210-2,..., 210-N perform a function to restore

the echo signal SAEK (t) around a specific delay time assigned by the EUC searcher 202 and is also variably is assigned by the EUC searcher 202 within the number provided from the hardware. Additionally, each of the EUC fingers performs a function to maximally maintain an echo cancellation state through internal adaptation algorithm employing complex correlation even though an amplitude, a phase and a delay time of the present assigned echo signal component are changed by external variation.

Fig. 3 is a block diagram showing an internal structure of an ECU finger in the echo canceller unit of Fig. 2.

In the present invention, the echo cancellation function is performed by the respective EUC fingers of Fig. 3. As previously mentioned, the EUC finger generates an echo restore signal using an input signal and a predetermined reference signal. The reference signal SREF (t) being an output of the automatic gain controller 204 is obtained by multiplying an output signal by the gain of the automatic controller 204. This can be expressed by equation.

[Mathematical Equation 3] Sref (t)=GAGCSO(t) The reference signal of mathematical equation 3 becomes changed via a delay equalizer 302 and a phase equalizer 304, which are shown in Fig. 3 as much as the phase PAK and the delay time T^K. This can be expressed by equation.

[Mathematical Equation 4] #ref (t)=GAGCej#kSO(t-#k) A complex correlator 308 calculates the complex correlation between the input signal SI (t) and the reference signal SAref (t) to generate a final echo restore signal S^EK (t) with respect to kth echo signal SEK (t) expressed by the following

mathematical equation 5.

[Mathematical Equation 5] #Ek (t)=#ej#kSO(t-#k) In the meanwhile, as shown in Fig. 3, each equalizers 302, 3 04 and 3 06 in the EUC finger is controlled by the correlation between the input signal SI (t) and the r eference s ignal S Aref (t) u sing t he c omplex c orrelator 3 08. A t this time, the complex correlation function between two signals can be expressed by equation employing the mathematical equation 1.

[Mathematical Equation 6] where, R (T^k-To) represents an autocorrelation function and is real number. In addition, in case that one or several signals are combined within the same signal band, the autocorrelation function R (T) has a maximum value when T=0. As the absolute value of T becomes large, the autocorrelation function converges 0.

In accordance with these characteristics, if an initial value T^k of the delay equalizer 302 by the EUC searcher 202 is determined to a value Tk similar to a delay time of kth echo signal component S^Ek (t) included in the input signal SI (t), the complex correlation function value of mathematical equation 6 can be expressed by the following mathematical equation 7.

[Mathematical Equation 7]

In the meanwhile, now that a power PREF of the reference signal (SREF (t) ) is always maintained in the same value, it can be expressed by equation.

[Mathematical Equation 8] Employing the results of mathematical equations 7 and 8, the complex correlation function can be expressed by the following mathematical equation 9.

[Mathematical Equation 9] Each of the equalizers in the EUC finger generates a signal SAEk (t) for restoring the k Ih echo signal component using the result of mathematical equation 9. In other words, the delay equalizer 2 02 performs a function to maintain the delay value TAk of the reference signal SRef (t) to be equal to the delay value Tk of the kith echo signal. This function makes use of the characteristic that the autocorrelation function R (r) has a maximum value when T=O. In addition, the phase equalizer 304 makes the phase PAk of the reference signal SRef (t) equal to the phase Pk of the kth echo signal component of the input signal SI (t). To make a phase component (PAk-P^k) zero, there is a request to change the phase of t he reference SRef (t) signal in order that the complex correlation function values (C (TAk, PAk)) are always real number. Moreover, the amplitude equalizer 306 can obtain an amplitude correction value in the complex correlation function where the delay correction and the phase correction are accomplished. If the delay and phase corrections are accomplished, the complex correlation function of the mathematical equation 9 can be expressed by the following mathematical

equation 10.

[Mathematical Equation 10] C (#k,#k)=KkPref/GAGC where. now that GAGC, Pref, C (#k,#k) is determined or can be measured, the amplitude correction value K^k of the kth echo signal can be expressed by the following mathematical equation 11.

[Mathematical Equation 11] Figs. 4 to 8 are flowcharts showing a method for canceling an echo signal component from a signal inputted from the wireless repeater including the above-mentioned echo canceller unit.

Now, the method for canceling an echo signal component of the present invention will be described referring to Figs. 4 to 8.

Referring to Fig. 8, the method comprises the steps of: a first step (S402) for receiving a radio signal from the outside to convert it; a second step (S404) for generating a signal S^E (t) where an echo signal component is restored from a signal S l (t), which i s converted and inputted to the echo canceller unit (108 or 128) and then canceling it from the input signal SI (t); and reconverting a signal So (t) where the echo signal is cancelled by the second step (S404) to transmit it (S406). At this time, as previously mentioned, the radio signal received in the first step is an analog signal including a noise component and an echo signal component.

Fig. 5 is a flowchart illustrating a process of receiving and converting the signal received in the first step (S402) shown in Fig. 4. Referring to Fig. 5, the first

step (S402) comprises the steps of: a receiving step (S502) for receiving a radio signal from the outside; alow noise amplifying step (S504) for amplifying the received radio signal in a low noise.; a down converting step (S506) for converting a radio frequency band signal into an intermediate frequency band signal down; and an analog/digital converting step (S508) for converting an analog signal to a digital signal.

Fig. 6 is a flowchart illustrating a process of canceling the echo signal component from an input signal in the second step (S402) shown in Fig. 4.

Referring to Fig. 6, the second step (S404) comprises the steps of: searching a delay time value of an echo signal component SE (t) included in the input signal SI (t) converted and inputted by the first step (S402) and then assigning pertinent echo cancellation finger (S602) ; generating an echo restore signal S^Ek (t) equal to an echo signal component SEk (t) equivalent to a specific delay time from the input signal SI (t) among each of assigned echo cancellation fingers (S604); and subtracting the echo restore signal S^Ek (t) from the input signal S ; (t) using the calculator 206 to cancel the restore signal S^Ek (t) included in the input signal SI (t) (S606). In this c ase, a s s hown in F ig. 2, the calculator 206 subtracts e cho restore signals, which are respectively restored from the echo cancellation fingers, from the input signal SI (t).

Fig. 7 is a flowchart illustrating a process of generating an echo restore signal in S604 step shown in Fig. 6. As shown in Fig. 7, the method for generating the echo restore signal S^Ek (t) includes the steps of: changing the reference signal S^Ref (t) as much as predetermined delay and phase values to generate a second reference signal S/, ef (t) (S702) ; generating a predetermined delay value TAk, phase value P^k and amplitude correction value K/lk using the complex correlation between the input signal SI (t) and the second reference signal S^ref(t) (S704) ; and generating an echo restore signal S^Ek (t) by applying

the predetermined delay value T^k, phase value P^k and amplitude correction value K^k generated in the S704 step to the reference signal Spree (t) (S706).

In the meanwhile, a signal outputted from the echo canceller unit (108 or 128) via the second step is a digital signal of an intermediate frequency band. This signal is converted through third step shown in Fig. 4 to be transmitted to the outside.

Fig. 8 is a flowchart illustrating processes of converting and transmitting a signal where the echo signal is cancelled in Fig. 4. Referring to Fig. 8, the third step includes the steps of : a digital/analog converting step for converting a digital signal to an analog signal (S802) ; an up converting step for converting an intermediate frequency band signal to a radio frequency band signal (S804) ; an amplifying step for amplifying signal with sufficient power so as to emit to the outside (S806) ; and a transmission step for transmitting a converted signal to the outside (S808).

In accordance with these unit and method, echo restore signals can be generated in each of EUC fingers. In addition, it is possible to cancel an echo signal component SE (t) included in the input signal SI (t) by performing calculation of mathematical equation 2 using the calculator 206 in the echo canceller unit 108.

This echo canceller unit is applicable by one algorithm irrespective of the number of Frequency Allocation (FA). In addition, this echo canceller unit is applicable to Code Division Multiple Access (CDMA) signals as well as all signals having correlation characteristic described in the present invention. For instance, typical examples are CDMA200, WCDMA, Orthogonal Frequency Division Multiplexing (OFDM), DMB, Additive White Gaussian Noise (AWGN) and so forth. Furthermore, the echo canceller unit of the present invention is applicable to a combination of them.

As stated above, the wireless repeater according to the present invention is capable of preventing oscillation of the wireless repeater as well as providing high-quality communication by efficiently canceling an echo signal where an emitted s ignal by a s ending antenna i s r e-inputted t hrough a receiving antenna.

Moreover, the wireless repeater of the present invention is capable of canceling an echo signal irrespective of the number of an assigned frequency, the number of users, or a characteristic of an input signal.

Changes can be made to the invention in light of the above detailed description. In general, in the following claims, the terms used should not be construed to limit the invention to the specific embodiments disclosed in the specification and the claims, but should be construed to include all methods and devices that are in accordance with the claims. Accordingly, the invention is not limited by the disclosure, but instead its scope is to be determined by the following claims.