the present invention now will be described more fully hereinafter with reference to the accompanying drawings , in which illustrative embodiments of the invention are shown . however , this invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein . rather , these embodiments are provided so that this disclosure will be thorough and complete , and will fully convey the scope of the invention to those skilled in the art . it will be understood that when an element is referred to as being “ coupled ”, “ connected ” or “ responsive ” to another element , it can be directly coupled , connected or responsive to the other element or intervening elements may also be present . in contrast , when an element is referred to as being “ directly coupled ”, “ directly connected ” or “ directly responsive ” to another element , there are no intervening elements present . like numbers refer to like elements throughout . as used herein the term “ and / or ” includes any and all combinations of one or more of the associated listed items and may be abbreviated by “/”. it will also be understood that , although the terms first , second , etc . may be used herein to describe various elements , these elements should not be limited by these terms . these terms are only used to distinguish one element from another element . the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention . as used herein , the singular forms “ a ”, “ an ” and “ the ” are intended to include the plural forms as well , unless the context clearly indicates otherwise . it will be further understood that the terms “ comprises ,” “ comprising ,” “ includes ” and / or “ including ” when used herein , specify the presence of stated features , steps , operations , elements , and / or components , but do not preclude the presence or addition of one or more other features , steps , operations , elements , components , and / or groups thereof . unless otherwise defined , all terms ( including technical and scientific terms ) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs . it will be further understood that terms , such as those defined in commonly used dictionaries , should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein . the present invention is described in part below with reference to block diagrams of methods , systems and computer program products according to embodiments of the invention . it will be understood that a block of the block diagrams , and combinations of blocks in the block diagrams , may be implemented at least in part by computer program instructions . these computer program instructions may be provided to one or more enterprise , application , personal , pervasive and / or embedded computer systems , such that the instructions , which execute via the computer system ( s ) create means , modules , devices or methods for implementing the functions / acts specified in the block diagram block or blocks . combinations of general purpose computer systems and / or special purpose hardware also may be used in other embodiments . these computer program instructions may also be stored in memory of the computer system ( s ) that can direct the computer system ( s ) to function in a particular manner , such that the instructions stored in the memory produce an article of manufacture including computer - readable program code which implements the functions / acts specified in block or blocks . the computer program instructions may also be loaded into the computer system ( s ) to cause a series of operational steps to be performed by the computer system ( s ) to produce a computer implemented process such that the instructions which execute on the processor provide steps for implementing the functions / acts specified in the block or blocks . accordingly , a given block or blocks of the block diagrams provides support for methods , computer program products and / or systems ( structural and / or means - plus - function ). finally , the functionality of one or more blocks may be separated and / or combined with that of other blocks . a dvb - t receiver according to exemplary embodiments of the present invention includes a plurality of channels for processing a plurality of input path signals and selects a channel , such as an optimum channel , which can demodulate the multipath signals from the plurality of channels . the optimum channel and an optimum range of a fast fourier transform ( fft ) window are selected , according to exemplary embodiments of the invention , by measuring channel impulse responses of a multipath channel while changing the range of the fft window for each of the channels . fig4 is a block diagram of a dvb - t receiver 400 according to exemplary embodiments of the present invention . referring to fig4 , the dvb - t receiver 400 includes an analog - to - digital converter ( adc ) 401 , a demodulator 402 , a coarse symbol timing recovery ( str ) & amp ; carrier recovery ( cr ) block 403 , an fft block 404 , a fine cr block 405 , an adder ( summer node ) 406 , a number controlled oscillator ( nco ) 407 , a fine str block 408 , an equalizer 409 , a viterbi decoder 410 , a reed - solomon decoder 411 , a bit error rate ( ber ) calculator 412 , and an str controller 413 . in fig4 , bold arrows indicate lines carrying complex signals , and fine arrows indicate lines carrying real signals . the adc 401 samples an analog signal γ ( t ) transmitted from a dvb - t transmitter ( not shown ). the demodulator 402 demodulates the analog signal γ ( t ) sampled by the adc 401 and outputs a complex signal γ ( n ) in response to a precise frequency offset signal fos 1 offset from of a sampling signal and complex carrier signals sin (*) and cos (*). the coarse str & amp ; cr block 403 receives the complex signal γ ( n ), and generates a coarse offset signal cos 1 indicating the starting point of the fft block 404 and a coarse frequency offset signal cos 2 containing frequency offset information regarding the complex carrier signals sin (*) and cos (*). when the coarse offset signal cos 1 , a precise offset signal fos 2 indicating the starting point of the fft , and a window movement indication signal fwm are input to the fft block 404 , the fft block 404 generates a frequency domain complex signal r k ( m ), at least in part by subtracting a guard interval ( gi ) from the complex signal γ ( n ). the frequency domain complex signal r k ( m ) is a complex signal of an m th subcarrier in a k th orthogonal frequency division multiplexing ( ofdm ) symbol ( where k and m are integers ). the fine cr block 405 generates a precise frequency offset signal fos 3 containing frequency offset information regarding the complex carrier signals sin (*) and cos (*) from the frequency domain complex signal r k ( m ) output from the fft block 404 . the adder 406 combines the coarse frequency offset signal cos 2 and the precise frequency offset signal fos 3 . the nco 407 generates the complex carrier signals sin (*) and cos (*) in response to a signal output from the adder 406 . the fine str block 408 creates the precise frequency offset signal fos 1 containing the frequency offset information regarding the complex carrier signals sin (*) and cos (*) and the precise offset signal fos 2 indicating a starting point of the fft , which are included in the frequency domain complex signal r k ( m ) output from the fft block 404 . the equalizer 409 performs channel estimation and compensation by performing a predetermined operation on the frequency domain complex signal r k ( m ) output from the fft block 404 , in response to a channel selection signal cs . the viterbi decoder 410 viterbi decodes the compensated frequency domain complex signal r k ( m ) output from the equalizer 409 , and outputs a real signal . the reed - solomon decoder 411 generates a transport stream ( ts ) from the real signal output from the viterbi decoder 410 . the ber calculator 412 computes a ber value by comparing the real signal output from the viterbi decoder 410 with a signal output from the reed - solomon decoder 411 . using the ber value output from the ber calculator 412 , the str controller 413 generates the channel selection signal cs for channel selection and the window movement indication signal fwm indicating adjustment of the range of a window to be used during an fft operation . when a system is initialized or power ( e . g ., power - on reset ) is initially supplied to the system , both the window movement indication signal fwm and the channel selection signal cs are reset . fig5 is a block diagram of an equalizer 409 of fig4 according to exemplary embodiments of the invention . referring to fig5 , the equalizer 409 includes a time domain interpolator 501 , a frequency domain interpolator 502 , and a compensator 503 . the time domain interpolator 501 interpolates the frequency domain complex signal r k ( m ) in the time domain . the frequency domain interpolator 502 includes a finite impulse response ( fir ) filter 502 - 1 and a filter coefficient storage unit 502 - 2 . the frequency domain interpolator 502 interpolates a signal output from the time domain interpolator 502 in the frequency domain in response to the channel selection signal cs . the fir filter 502 - 1 filters the signal output from the time domain interpolator 501 using coefficients received from the filter coefficient storage unit 502 - 2 . the filter coefficient storage unit 502 - 2 stores two different types of filter coefficients and outputs filter coefficients corresponding to the channel selection signal cs . the band characteristics of the fir filter 502 - 1 are determined by the coefficients output from the filter coefficient storage unit 502 - 2 . for instance , the band characteristics of the fir filter 502 - 1 are set to correspond to a first channel when the channel selection signal cs has a logic value of 0 , and set to correspond to a second channel when the channel selection signal cs has a logic value of 1 . the compensator 503 performs compensation by dividing the complex signal r k ( m ) with a signal output from the frequency domain interpolator 502 . the construction and operation of a dvb - t receiver according to an embodiment of the present invention will now be described briefly . although the dvb - t receiver can include more than two channels , it is assumed herein that there are two channels in the dvb - t receiver and that the two channels process two path signals , for convenience . hereinafter , the two channels will be referred to as echo channels so that they can be differentiated from general channels . compared to the conventional dvb - t receiver of fig1 , a dvb - t receiver of fig4 further includes the str controller 413 and its interaction with other blocks of fig4 . also , the equalizer 409 of fig5 is different from the equalizer 9 , shown in fig2 , of the conventional dvb - t receiver . the str controller 413 stores the value of the channel selection signal cs and the value of the window movement indication signal fwm , and stores a first ber value generated by the ber calculator 412 . the str controller 413 changes the values of the channel selection signal cs and the window movement indication signal fwm , and outputs the changed channel selection signal cs and window movement indication signal fwm . the str controller 413 compares the first ber value with a second ber value generated by the ber calculator 412 in response to the changed channel selection signal cs and window movement indication signal fwm . then , the str controller 413 selects and outputs the channel selection signal cs and the window movement indication signal fwm , or the changed channel selection signal cs and the changed window movement indication signal fwm , according to the result of comparison . in some embodiments , the str controller 413 selects and outputs the channel selection signal cs and the window movement indication signal fwm , or the changed channel selection signal cs and window movement indication signal fwm , according to the combination that results in a smaller ber value . to determine a desired ( e . g ., optimum ) echo channel and the range of an fft window for the optimum echo channel , the range of an optimum fft window for a first kind of echo channel is determined by performing a predetermined operation . next , a predetermined operation is performed on an input path signal to obtain a ts and a ber value , and the ber value and information regarding the first echo channel and the determined fft window range are stored in the str controller 413 . next , the str controller 413 sets a current channel to a second kind of echo channel , changes the fft window range and cs value , and obtains a ts and a ber value . the range of the fft window is changed by forwarding the fft window by a gi of the received signal . next , the str controller 413 compares a ber value in the first kind of echo channel with that in the second kind of echo channel , and the first or second kind of echo channel having a smaller ber value is selected . operations of a dvb - t receiver according to exemplary embodiments of the present invention receiving signals via the first or second kind of echo channels will now be described in greater detail . first , demodulating the received signals in the first kind echo channel will be described . next , selecting an optimum cs value and the range of an fft window by determining whether the two path signals can be more exactly demodulated using the second kind of echo channel or the first kind of echo channel will be described . before describing the operations of a dvb - t receiver according to exemplary embodiments of the present invention , three preconditions to be satisfied will be described , according to some embodiments of the invention . first , the bandwidth b of the fir filter 502 - 1 corresponding to the first and second kind of echo channels should satisfy the following : wherein t u denotes the duration of an ofdm symbol . second , a time spread τ of the echo channels should satisfy the following : when the time spread τ is greater than the gi and less than the bandwidth b , thus satisfying equation ( 2 ), it is possible to effectively select an optimum cs value and the range of the fft window by moving the fft window by the gi only once . third , carrier - to - noise ratios ( cnrs ) of the echo channels should be large enough for the dvb - t receiver to normally operate . if the cnrs are too small , the dvb - t receiver may not operate in both the echo channels . in addition , it is assumed that the str controller 413 sets the values of the window movement indication signal fwm and the channel selection signal cs to 0 . fig6 illustrates details of a two - ray multipath channel with channel profile path 1 and path 2 and four fft windows therefor according to exemplary embodiments of the present invention . specifically , ( a ) of fig6 illustrates the channel profiles of the path signals path 1 and path 2 . ( b ) of fig6 illustrates the data structures of the received ofdm signal via the two - ray multipath channel . ( c ) of fig6 illustrates the ranges of the four fft windows . ( d ) of fig6 illustrates a process of estimating a channel using a first fft window . ( e ) of fig6 illustrates a process of estimating a channel using a second fft window . ( f ) of fig6 illustrates a process of estimating a channel after moving the second fft window forward by a gi . ( g ) of fig6 illustrates a process of estimating a channel after moving the first fft window forward by the gi . referring to ( a ) of fig6 , the amplitude of the first path signal path 1 is greater than that of the second path signal path 2 . referring to ( b ) of fig6 , a k th ofdm symbol is activated for a symbol duration t u , and a time spread τ of the two - ray channel , i . e ., time interval between the first and second path signals path 1 and path 2 , is greater than the gi of the received ofdm signal . referring to ( c ) of fig6 , the durations of the first through fourth fft windows are equal to one another , but they start at different times . it is possible to detect an optimum window from the first through fourth fft windows by performing an operation . referring to fig6 , it is assumed that the first fft window begins at the interface between the gi and the k th ofdm symbol of the first path signal path 1 , and the second fft window begins at the interface between the gi and the k th ofdm symbol of the second path signal path 2 . referring to ( d ) and ( g ) of fig6 , the first fft window of ( d ) of fig6 can best demodulate the symbols of the first and second path signals path 1 and path 2 . referring to ( d ) of fig6 , the first and second path signals path 1 and path 2 are generated at the both edges of the first fft window , thereby minimizing aliasing between the path signals path 1 and path 2 . in contrast , referring to ( g ) of fig6 , when a current channel is reset to a second echo channel and the first fft window is moved forward by the gi , aliasing between the first and second path signals path 1 and path 2 happens , which may prevent the path signals path 1 and path 2 from being exactly demodulated . referring to ( d ) through ( g ) of fig6 , the symbol duration t u is divided into three parts , and the channel impulse responses of the path signals path 1 and path 2 are divided according to the division of the symbol duration t u . here , long , dashed arrows indicate the channel impulse responses path 1 - 1 , path 1 - 2 , and path 1 - 3 of the first path signal path 1 . short , solid arrows indicate the channel impulse responses path 2 - 1 , path 2 - 2 , and path 2 - 3 of the second path signal path 2 . the channel impulse responses path 1 - 1 through path 2 - 3 may be rgb signals . fig6 illustrates that use of the first fft window in the first kind of echo channel may be the most desirable in these embodiments . accordingly , when exemplary embodiments of the present invention are actually used , whether the first or the second kind of echo channel is better may be determined . it is assumed that an fft window shown in ( e ) of fig6 is used to process path signals . referring to ( e ) of fig6 , the path signals path 1 and path 2 do not appear to be exactly demodulated using the fft window set for the first kind of echo channel . however , when the coefficients of the frequency domain interpolation corresponding to a current echo channel are reset to those corresponding to the second kind of echo channel and the fft window is moved forward by a gi , it is possible to more precisely demodulate the path signals path 1 and path 2 as shown in ( f ) of fig6 . referring again to fig4 , after the input signal γ ( t ) is synchronized by the coarse str & amp ; cr block 403 , the fine cr block 405 , and the fine str block 408 , the ber calculator 412 compares the signal output from the viterbi decoder 410 with the signal output from the reed - solomon decoder 411 to obtain a quasi ber value . when the dvb - t receiver 400 operates normally , the ber value output from the ber calculator 412 can be less than 10 − 3 ˜ 10 − 4 . when an output of the ber calculator 412 is stable for a predetermined length of time , the ber value is stored in the str controller 413 . it is assumed that the values of the window movement indication signal fwm and the channel selection signal cs are set to 0 according to the stored ber value . next , the str controller 413 resets the value of the window movement indication signal fwm according to the gi so that the fft block 404 moves a current fft window forward by the gi , and resets the value of the channel selection signal cs to 1 to operate the equalizer 409 for the second kind of echo channel . when the value of the channel selection signal cs is set to 1 , the equalizer 409 performs channel estimation and compensation of the frequency domain complex signal r k ( m ) using the fir filter 502 - 1 with the band characteristics corresponding to the second kind of echo channel . when the value of the window movement indication signal fwm is set according to the gi , the channel selection signal cs has a value of 1 , and a predetermined length of time passes , the ber calculator 412 outputs a stable output . the str controller 413 compares a ber value computed when fwin_move = gi and cs = 1 with a ber value computed when fwin_move = 0 and cs = 0 . if the ber value computed when fwin_move = 0 and cs = 0 is much less than the ber value computed when fwin_move = gi and cs = 1 , the str controller 413 resets fwin_move and cs to 0 . otherwise , fwin_move = gi and cs = 1 are maintained . referring again to ( g ) of fig6 , the cir estimation that is obtained in a channel by using the fourth fft window obtained by moving the first fft window forward by the gi is incorrect . in this case , the ber calculator 412 outputs a large ber value of about 0 . 5 . the str controller 413 compares the current ber value with a previously stored ber value , and a channel selection signal cs and a window movement indication signal fwm corresponding to the smaller of the current and previous ber values is output . therefore , the values of the window movement indication signal fwm and the channel selection signal cs are set to 0 . as described above , dvb - t receivers , methods and computer program products according to exemplary embodiments of the present invention can use a plurality of echo channels and can change the range of an fft window to be used in each of the echo channels in order to demodulate a multipath signal . therefore , it is possible to select an optimum echo channel and fft window for the multipath signal . in the drawings and specification , there have been disclosed embodiments of the invention and , although specific terms are employed , they are used in a generic and descriptive sense only and not for purposes of limitation , the scope of the invention being set forth in the following claims .