Abstract:
An apparatus and method for detecting the reception timing of a received signal in a mobile communication system are provided. Two time points having the same energy, earlier and later than the received signal, are detected. The energy ratio between other time points spaced from the two time points by the same interval is calculated and it is determined whether the energy ratio falls into a predetermined rage. If the energy ratio is within the range, the received signal is considered to have no effects from an interference signal or a neighboring signal.

Description:
PRIORITY  
       [0001]     This application claims the benefit under 35 U.S.C. § 119(a) of an application entitled “Apparatus and Method for Detecting Timing Error in a Mobile Communication System” filed in the Korean Intellectual Property Office on August 9, 2003 and assigned Serial No. 2003-55198, the entire contents of which are incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates generally to a rake receiver in a mobile communication system. In particular, the present invention relates to an apparatus and method for improving the performance of a time tracker in a rake receiver.  
         [0004]     2. Description of the Related Art  
         [0005]     Due to the rapid development of mobile communication systems and the rapid growth of data traffic serviced in mobile communication systems, 3 rd  generation mobile communication systems have been developed to transmit data at higher rates. Wideband Code Division Multiple Access (WCDMA) and Code Division Multiple Access 2000 (CDMA2000) have been selected as the 3 rd  generation radio access standards in Europe and North America, respectively. WCDMA utilizes an asynchronous base station operation, while CDMA2000 utilizes a synchronous base station operation. The mobile communication systems are typically configured so that a plurality of user equipments (UEs) communicate with a Node B. During high-speed data transmission, fading on a radio channel causes distortion in a received signal. The fading phenomenon reduces the amplitude of the received signal by several to tens of decibels. Without compensating for the distortion at demodulation for the received signal, the distortion leads to information errors in data transmitted from a transmitter, thereby decreasing a quality of service (QoS). Thus, to transmit data at high rates without decreasing the QoS, fading must be overcome. For this purpose, a variety of diversity schemes are used.  
         [0006]     Typically, a CDMA communication system uses a rake receiver that receives a channel signal using diversity, exploiting its delay spread. Receive diversity is applied to the rake receiver, for reception of multipath signals. Each finger of the rake receiver is assigned to one of the signal paths and demodulates data from the assigned signal path.  
         [0007]     However, if a delay spread is below a threshold, the rake receiver does not work.  
         [0008]     As described above, a transmitted signal having different power levels arrives at a UE via different paths that have different time delays. To convert the multipath signals to a signal having sufficient power, the received signals must be combined. Hereinbelow, data transmission and reception in a conventional mobile communication system using a direct spreading scheme will be described.  
         [0009]     User data a n  is spectrum-spread with effective spreading sequences including a spreading code and a scrambling code. The spread signal is transmitted on a radio channel through a pulse-type filter. A baseband model of a transmitted signal for a UE is expressed as  
               s   ⁡     (   t   )       =         ∑     m   =   ∞     ∞     ⁢           ⁢       a   n     ⁢       ∑     k   =   0         N   c     -   1       ⁢           ⁢     d     nN   c             ⁢     +   k     ⁢     g   ⁡     (     t   -   nT   -     kT   c       )                 (   1   )             
 
 where s t  is the transmitted signal, N c  is a spreading component, g(t) is a root-raised cosine pulse with a roll-off factor of 0.22, T is a symbol duration, and T c  is a chip duration, equaling T/N c . The transmitted signal arrives at a receiver from L paths on a multipath channel in the mobile communication system. The following equation represents the impulse response of the channel.  
               h   ⁡     (   τ   )       =       ∑     l   =   0       L   -   1       ⁢           ⁢       C   l     ⁢     δ   ⁡     (     τ   -     τ   1       )                   (   2   )             
 
 where t i  is the time delay of each path and C 1  is a complex attenuation component. C of C 1  is a complex value. 
 
         [0012]     Additive White Gaussian Noise (AWGN) is added to the received transmitted signal which in the form that  
               r   ⁡     (   l   )       =         ∑     i   =   0       L   -   1       ⁢           ⁢       C   l     ⁢       ∑     m   =     -   ∞       ∞     ⁢           ⁢       a   n     ⁢       ∑     k   =   0       N   -   1       ⁢           ⁢     d     nN   c                 ⁢     +   k     ⁢     g   ⁡     (     t   -   nT   -     kT   o     -     τ   1       )       +     n   ⁡     (   t   )                 (   3   )             
 
         [0013]     The received signal is filtered in the same root-raised cosine filter as used in the transmitter. The filter output is  
               z   ⁡     (   t   )       =         ∑     l   =   0       L   -   1       ⁢           ⁢       C   l     ⁢       ∑     m   =     -   ∞       ∞     ⁢           ⁢       a   n     ⁢       ∑     k   =   0         N   c     -   1       ⁢           ⁢       d       nN   c     +   k       ⁢       R   g     ⁡     (     t   -   nT   -     kT   c     -     τ   1       )                   +       n   ′     ⁡     (   t   )                 (   4   )             
 
 where R g (t) is an auto-correlation function of g(t) and n′(t) is noise and interference signals from other users that have passed through the filter, equaling n(t)·p*(t)·R g (t) is determined by  
                 R   g     ⁡     (   t   )       =       ∫     -   ∞     ∞     ⁢         g   M     ⁡     (   τ   )       ⁢     g   ⁡     (     t   +   τ     )       ⁢           ⁢     ⅆ   τ                 (   5   )             
 
         [0015]     As in a conventional mobile communication system, it is assumed that the receiver is aware that a known pilot symbol is transmitted on a pilot channel. Let the pilot symbol on the pilot channel be denoted by A. Then,  
               s   ⁡     (   t   )       =     A   ⁢       ∑     k   =     -   ∞       ∞     ⁢           ⁢       d   k     ⁢     g   ⁡     (     t   -     k   ⁢           ⁢     T   c         )                     (   6   )             
 
         [0016]     In the mobile communication system, multiple paths vary with time or the position of a UE and relative time differences between the multiple paths vary with the mobile velocity and radio environment of the receiver. The number of multiple paths involved in the communication of the UE is not fixed. Because of the receiver&#39;s limited time resolution ability and the nature of the radio channel, a reduced number of multiple paths may be used.  
         [0017]     Traditionally, if a received signal is simple in structure, an early late timing error detector (EL TED) is used to thereby increase the efficiency. The EL TED detects a timing by applying the energy difference between signals spaced at a 1/2 chip interval to the input of a filter.  
         [0018]     Referring to  FIG. 1 , a conventional TED will be described in detail. A multiplexer (MUX)  100  multiplexes a received signal. A scrambler  110  receives a signal 1/2 chip earlier than the received signal and a scrambler  112  receives a signal 1/2 chip later than the received signal. The 1/2-chip earlier signal and the 1/2-chip later signal are expressed respectively as  
                 r     g   +     (     1   /   2     )         ≈       r   ⁡     [       (     s   +     ɛ   σ     +     1   2       )     ⁢     T   c       ]       -     C   ·       R   g     (       (     s   +     ɛ   s     +     1   2       )     ⁢     T   c       ]       +     n       s   +     (     1   /   2     )       ⁢     
             ⁢     
     ⁢   and           (   7   )                 r     g   -     (     1   /   2     )         ≈       r   ⁡     [       (     s   +     ɛ   s     -     1   2       )     ⁢     T   c       ]       -     C   ·       R   s     (       (     s   +     ɛ   s     -     1   2       )     ⁢     T   c       ]       +     n     g   -     (     1   /   2     )                   (   8   )             
 
 where ε s  is a chip timing error in a chip S and n has the same meaning of n of Eq. (3). Averagers  120  and  122  receive a scrambled signal from the scrambler  110 , and averagers  124  and  126  receive a scrambled signal from the scrambler  112 . The averagers  120  to  126  calculate  
                   z   ~     s   +     =           d   k   2     ·     1   N       ⁢       ∑   1   N     ⁢           ⁢     r     s   +     1   /   2             +       n   ~       s   +     1   /   2             ⁢     
     ⁢   and           (   9   )                   z   ~     s   -     =           d   k   2     ·     1   N       ⁢       ∑   1   N     ⁢           ⁢     r     s   -     1   /   2             +       n   ~       s   -     1   /   2                   (   10   )             
 
         [0020]     The averages output from the averagers  120  to  126  are applied to squarers  130  to  136 , respectively. An adder  140  adds the outputs of the squaers  130  and  132 , and an adder  142  adds the outputs of the squaers  134  and  136 . A subtractor  150  calculates the difference between the outputs of the adders  140  and  142  by 
 
 e   s=   |{tilde over (z)}   s   + | 2   −|{tilde over (z)}   s   − | 2    (11) 
 
 which includes squared noise. 
 
         [0022]     The difference e s  is input to a loop filter  160 . The above equations (7) to (11) are computed on the assumption that the received signal is flat-faded.  FIG. 2  illustrates a transmitted signal from a transmitter received at a receiver. As noted from Eq. (11), the energy of the 1/2-chip earlier signal is compared with that of the 1/2-chip later signal. If they are equal, the receiver detects a signal received at the same time when the transmitter transmits the signal. However, the transmitted signal usually takes some time to arrive at the receiver. Hence, the 1/2-chip later signal has a greater energy than the 1/2-chip earlier signal. In this case, the receiver detects two time points having the same energy value by adjusting chip positions and detects a received signal in the mean of the two time points.  
         [0023]     Yet, an S curve observed using e s  under a multipath environment is very different from a typical S curve. The effects of e s  and multipath-caused changes are demonstrated on the S curve. The operation of the receiver under the multipath environment will be described below.  
         [0024]      FIG. 3  is a graph illustrating reception of a transmitted signal from multiple paths, particularly two paths. Referring to  FIG. 3 , curves  101  and  103  represent two received signals and a curve  102  represents a signal whose energy is the sum of the energies of the two received signals. A problem encountered with the conventional EL TED will be described with reference to  FIG. 3 . According to Eq. (4), the root-raised cosine filter output of a k th  sample is  
               x   k     =       x   ⁡     (   kT   )       =     re   ⁢     {           a   ^     *     k     ⁢         c   ^     *       k   ^       ⁢       ∑     j   =   kN           (     k   +   1     )     ⁢     N   c       -   1       ⁢           ⁢       (       z   ⁡     (       j   ⁢           ⁢     T   c       +       T   c     /   2     +     τ   ^       )       -     z   ⁡     (       j   ⁢           ⁢     T   c       -       T   c     /   2     +     τ   ^       )         )     ⁢     ⅆ   j   *           }                 (   12   )               
 where â k * denotes a common pilot channel and ĉ k * is the channel estimation value of the k th  symbol. Eq. (12) is based on the assumption that the channel coefficient and user data symbols of the k th  sample are known. This equation is viable under a flat-fading environment but results in performance degradation under the multipath environment. The cause of the performance degradation in the multipath environment will be described in connection with the following equations. A signal on an S curve of the EL TED is determined as 
   S(τ−{circumflex over (τ)})=   R   g ( T   c /2+{circumflex over (τ)}−τ)− R   g (− T   c /2+{circumflex over (τ)}−τ)   (13)  
         [0026]     A channel estimation value obtained from the pilot channel under the multipath environment is  
                 E   ⁡     [       x   n     ❘   C     ]       ⁢     E   ⁡     [     ❘     a   ⁢     ❘   2         ]       ⁢   Re   ⁢     {              c   m          2     ⁢     S   ⁡     (       τ   m     -       τ   ^     m       )         }       +         E   ⁡     [        a        ]       2     ⁢   Re   ⁢     {       c   m   *     ⁢       ∑       l   =       0   ⁢           ⁢   …   ⁢           ⁢     N   p       -   1       ,     l   +   m                 ⁢           ⁢       C   l     ⁢     s   ⁡     (       τ   l     -       τ   ^     m       )             }               (   14   )             
 
         [0027]     The first part of the right term in Eq. (14) represents a desired signal component and the last part represents a multipath-incurred low-frequency interference signal. As illustrated in  FIG. 3 , two signals are received. The conventional EL TED has a problem with the last part of Eq. (14). As stated earlier, the last part of Eq. (14) is eliminated in the case of flat fading, allowing a normal operation. On the other hand, if the channel is not flat-faded, that is, a neighboring signal component is received within a predetermined chip range, the neighboring signal component acts as an interference signal to the earlier and later parts of the received signal, as illustrated in  FIG. 3 . In  FIG. 3 , the mean between two time points having the same energy value in the curve  102  is different from the peak of the curve  101 . As a result, multipath signals each serve as interference in energy estimation of earlier and later parts of other signals, thereby decreasing performance. Thus, the conventional EL TED cannot discriminate neighboring paths from one another, thereby decreasing performance.  
         [0028]     In general, a line of sight (LOS) signal having higher energy and reflected signals are received from multiple paths at the same time in a radio environment. Particularly when the received signals differ in energy considerably but not much in path, the above-described problem becomes more serious. The problem leads to system overload on the side of a Node B. That is, a UE requests the Node B to transmit signals at a high power level in order to achieve a target signal-to-interference ratio. Because the interference components are low-frequency components, a slow processing UE is highly likely to experience the interference. Especially when data is received at high rate in an indoor environment, the interference signal affects the resolution of fingers as noted from Eq. (14). Consequently, performance is decreased. In this context, there is a need for a method of accurately estimating multipath signal components with approximate spread delays.  
       SUMMARY OF THE INVENTION  
       [0029]     An object of the present invention is to substantially solve at least the above problems and disadvantages and to provide at least the advantages below. Accordingly, an object of the present invention is to provide an apparatus and method for accurately detecting a reception timing by eliminating the effects of an interference signal or a neighboring signal on a received signal.  
         [0030]     Another object of the present invention is to provide an apparatus and method for when a transmitted signal travels along multiple paths, accurately recovering the transmitted signal by accurately estimating received multipath signals.  
         [0031]     A further object of the present invention is to provide an apparatus and method for detecting initial errors in a received signal and eliminating the initial errors.  
         [0032]     The above objects are achieved by providing a method and apparatus for receiving a transmitted signal by accurately estimating spread delays of multiple paths along which the transmitted signal travels in a mobile communication system using a rake receiver with a plurality of fingers.  
         [0033]     According to one aspect of the present invention, in the receiving method, the energy of a first path earlier than a predetermined path and the energy of a second path later than the predetermined path are calculated. The predetermined path is estimated using time points at which the energy of the first path is equal to the energy of the second path. The accuracy of the estimated path is verified using a ratio between the energy of earlier paths other than the predetermined path and the first path and the energy of later paths other than the predetermined path and the second path. Only a signal from the verified path is output.  
         [0034]     According to another aspect of the present invention, in the receiving apparatus, a timing error detector detects the timing of a predetermined path by calculating the energy of a first path earlier than the predetermined path and calculating the energy of a second path later than the predetermined path, a verifier verifies the accuracy of the estimated path, and a controller controls the timing detection of the timing error detector, determines whether the output of the verifier falls in a predetermined range, and controls the output of the timing error detector to be output according to the determination result. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0035]     The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings in which:  
         [0036]      FIG. 1  is a block diagram of a conventional Timing Error Detector (TED) for detecting a timing error;  
         [0037]      FIG. 2  is a graph illustrating time points set for timing error detection if a signal is received from a single path;  
         [0038]      FIG. 3  is a graph illustrating timing error detection failure if a signal is received from two paths;  
         [0039]      FIG. 4  is a graph illustrating time points set for timing error detection according to an embodiment of the present invention;  
         [0040]      FIG. 5  is a block diagram of a TED according to an embodiment of the present invention;  
         [0041]      FIG. 6  is a flowchart illustrating the operation of the TED according to an embodiment of the present invention;  
         [0042]      FIG. 7  illustrates the structure of a finger having the TED according to an embodiment of the present invention;  
         [0043]      FIG. 8  is a flowchart illustrating the operation of the finger according to an embodiment of the present invention;  
         [0044]      FIG. 9  is a graph illustrating two signals spaced from each other by one chip;  
         [0045]      FIG. 10  is a graph illustrating reception of the signal illustrated in  FIG. 9  in the conventional TED;  
         [0046]      FIG. 11  is a graph illustrating reception of the signal illustrated in  FIG. 9  in the TED according to an embodiment of the present invention;  
         [0047]      FIG. 12  is a graph illustrating elimination of an initial error in two received signals according to an embodiment of the present invention;  
         [0048]      FIG. 13  is a graph illustrating four signals spaced from each other by one chip;  
         [0049]      FIG. 14  is a graph illustrating reception of the signal illustrated in  FIG. 13  in the conventional TED;  
         [0050]      FIG. 15  is a graph illustrating reception of the signal illustrated in  FIG. 13  in the TED according to an embodiment of the present invention; and  
         [0051]      FIG. 16  is a graph illustrating elimination of an initial error in four received signals according to an embodiment of the present invention. 
     
    
       [0052]     Throughout the drawings, it should be noted that the same or similar elements are denoted by like reference numerals.  
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0053]     An embodiment of the present invention will be described herein below with reference to the accompanying drawings. In the following description, well-known functions or constructions are not described in detail for conciseness.  
         [0054]      FIG. 4  is a graph illustrating time points at which the energy of a received signal is measured. Referring to  FIG. 4 , the energy of the received signal is measured at six time points. Consideration is given to only time points having the same energy value, earlier and later than a predetermined time point in a conventional Early Late Timing Error Detector (EL-TED) method. However, if a signal received within several chips from the received signal serves as interference, the reception time of the received signal cannot be detected accurately due to the interference signal, as described before with reference to  FIG. 3 .  
         [0055]     In accordance with an embodiment of the present invention, once the time points having the same energy value, earlier and later than the predetermined time point are detected, additional time points are taken for energy detection. If the detected energy is below a threshold, it is determined that interference has no effect on the received signal.  
         [0056]     To detect the interference signal in the received signal, a multipath searcher (MPS) can be used. However, the embodiment of the present invention detects a neighboring signal or an interference signal without using the MPS. The following equation represents an energy ratio of the received signal between particular time points.  
               ∑   M     ⁢                   E   ⁡     (     t   +       3   2     ⁢     T   c         )            -          E   ⁡     (     t   +     T   c       )                       E   ⁡     (     t   -       3   2     ⁢     T   c         )            -          E   ⁡     (     t   -     T   c       )                             (   15   )             
 
 where M is a predetermined time period. As noted from Eq. (15), the energy of the received signal is detected at four time points. A ratio of the energy difference between two earlier time points to the energy difference between two later time points is calculated. While the energy is measured at 1-chip and 3/2-chip earlier time points and at 1-chip and 3/2-chip later time points in the case illustrated by Eq. (15), the time points are freely determined according to user selection. In general, when neither a neighboring signal nor an interference signal is present, Eq. (15) results in a value approximate to 1. 
 
         [0058]     If the value of Eq. (15) is within a predetermined range, it is determined that the received signal is not influenced by either the neighboring signal or the interference signal. The S curve of the received signal is symmetrical with respect to the predetermined time point. Thus, neither the neighboring signal nor the interference signal affects the received signal. The predetermined range is given as  
               δ   i     ⁢     ,   1     ⁢     ≤       ∑   M     ⁢                   E   ⁡     (     t   +       3   2     ⁢     T   c         )            -          E   ⁡     (     t   +     T   c       )                       E   ⁡     (     t   -       3   2     ⁢     T   c         )            -          E   ⁡     (     t   -     T   c       )                       ≤     δ   i       ⁢     ,   2             (   16   )             
 
 where δ i  is derived from the nature of the root-raised cosine filter, I denoting a finger index. How δ i  is achieved will be described. Typically, the MPS provides information with +1/2 and −1/2 chip errors to the TED all the time. For example, if an initial error is +1/2 chip in  FIG. 3 , the time points for energy detection are changed in Eq. (4) and the resulting value of Eq. (4) is used as a determinant of δ i . In the presence of Additive White Gaussian Noise (AWGN) and a radio channel, the determinant may vary greatly. Therefore, δ i  is selected to be less than the determinant. e s  is easily obtained through sufficient simulations. Also, it can be changed in software. 
 
         [0060]     If the value of Eq. (15) falls into the range of Eq. (16), which indicates that there are no effect from a neighboring signal or an interference signal, the TED operates in a conventional manner. On the contrary, if it is beyond the range, this indicates a timing error other than a timing error expected from a normal S curve has been generated by the neighboring signal or the interference signal. Therefore, a value resulting from the normal TED operation cannot be still used. In the case where the value of Eq. (15) is within the predetermined range defined by Eq. (16), a non-coherent TED error is detected by  
                   TE   NC     =         E   ⁡     [        a        ]       2     ⁢       ∑       j   =   1     ,   2       ⁢     ·       (     -   1     )       j   +   1       ·            C   ·       R   g     ⁡     (         T   c     H     +     τ   ^     -   τ     )              2                    H   =         -   2     ⁢           ⁢   for   ⁢           ⁢   j     =   2           H   =   2     ,       for   ⁢           ⁢   j     =   1               (   17   )             
 
 and a coherent TED error is detected by  
                   TE   C     =         E   ⁡     [        a        ]       2     ⁢       ∑       j   =   1     ,   2       ⁢           (     -   1     )       j   +   1       ·       C   ^     m       *     C   ·              R   g     ⁡     (         T   c     H     +     τ   ^     -   τ     )            2                        H   =     -   2       ,           ⁢       for   ⁢           ⁢   j     =   2           H   =   2     ,       for   ⁢           ⁢   j     =   1               (   18   )             
 
         [0062]      FIG. 5  is a block diagram of a TED according to an embodiment of the present invention. Referring to  FIG. 5 , the TED comprises a MUX  500 , scramblers  510  to  515 , averagers  520  to  525 , squarers  530  to  535 , a subtractor  540 , a switch  550 , a filter  560 , a controller  542 , and a calculator  544 . Only components related to the embodiment of the present invention are illustrated in  FIG. 5 , although the TED may further comprise components other than those illustrated.  
         [0063]     The MUX  500  multiplexes a received signal and outputs signals earlier and later than a predetermined time point. The scrambler  510  receives a  1 / 2 -chip earlier signal and the scrambler  511  receives a 1/2-chip later signal. The scramblers  510  and  511  scramble the input signals with a predetermined scrambling code. While the 1/2-chip earlier signal and the 1/2-chip later signal each are branched into an I signal and a Q signal, they are illustrated to include the I and Q signals in  FIG. 5 , for conciseness. The scrambled signals are applied to the input of the squarers  530  and  531  through the averagers  520  and  521 . The subtractor  540  calculates the difference between the square values output from the squarers  530  and  531 . The switch  550  switches the difference to the filter  560  under the control of the controller  542 .  
         [0064]     In the mean time, the MUX  500  outputs 1-chip and 3/2-chip earlier signals and 1-chip and 3/2-chip later signals to the scrambles  512  to  515 . That is, the scrambler  512  receives the 3/2-chip earlier signal, the scramble  513  receives the 1-chip earlier signal, the scrambler  514  receives the 1-chip later signal, and the scrambler  515  receives the 3/2-chip later signal. The scramblers  512  to  515  operate in the same manner as the scramblers  510  and  511 . The scrambled signals are fed to the squarers  532  to  535  through the averagers  522  to  525 .  
         [0065]     The calculator  544  calculates Eq. (15). The controller  542  determines whether the value of Eq. (15) falls into the range defined by Eq. (16). Alternatively, a verifier determines whether the value of Eq. (15) falls into the range and notifies the controller  542  of the determination result.  
         [0066]     If the value falls in the range, the controller  542  turns on the switch  550  so that the difference output from the subtractor  540  is fed to the filter  560 , and the filter  560  detects the reception time of the received signal.  
         [0067]     On the contrary, if the value of Eq. (15) is beyond the range, the controller  542  turns off the switch  550 .  
         [0068]      FIG. 6  is a flowchart illustrating the operation of the EL-TED according to an embodiment of the present invention. Referring to  FIG. 6 , the EL-TED detects two time points having the same energy levels with respect to a predetermined time point, as described with reference to  FIG. 5 , in step  600 . In step  602 , the EL-TED calculates Eq. (15) using the detected two time points. The mean time point between the two time points is calculated and four time points spaced from the mean time point by a predetermined value are detected. Using the energy levels of the four time points, Eq. (16) is calculated. The predetermined value can be adjusted according to user selection. In step  604 , the EL TED determines if the value of Eq. (15) falls into a predetermined range. If the value falls into the predetermined range, the EL TED proceeds to step  606 . Otherwise, it returns to step  600 . In step  606 , the EL TED detects a time point having the highest energy value using the conventional time error detection operation and recovers the received signal using a signal at the detected time point. By repeating this procedure, the receiver can detect an accurate reception timing of the received signal.  
         [0069]      FIG. 7  illustrates the structure of a finger including the TED in a rake receiver according to an embodiment of the present invention. Referring to FIG.  7 , the rake receiver comprises a squared root-raised cosine filter (SRRC)  700 , a preprocessor &amp; multipath detector  702 , and a plurality of fingers  710 ,  730  and  732 . The finger  710  includes a scrambler  712 , a conventional timing error detector (CTED)  714 , a switch  716 , a filter  718 , a position controller  720 , and a controller  722 . The SRRC  700  provides a received signal to the preprocessor &amp; multipath detector  702 . The preprocessor &amp; multipath detector  702  assign one path to each finger. In the case illustrated in  FIG. 7 , N paths exist. Hereinbelow, the operation of the finger  710  (finger # 1) will be described.  
         [0070]     The scrambler  712  multiplies the received signal by a predetermined scrambling code, for scrambling. The controller  722  determines whether the scrambled signal satisfies the condition of Eq. (16). When the condition is satisfied, the controller  722  turns on the switch  716 . As the switch  716  turns on, the filter  718  filters the output of the CTED  714  and the position controller  720  adjusts a reception timing according to the filter output.  
         [0071]      FIG. 8  is a flowchart illustrating the operation of the finger having the TED according to an embodiment of the present invention.  
         [0072]     Referring to  FIG. 8 , the finger determines whether to use MPS information or not in step  800 . If the MPS information is used, the finger proceeds to step  802 . Otherwise, it goes to step  804 . In step  802 , the finger determines whether there is a Common Signaling Mode (CSM) signal for the received signal using the MPS information. In the presence of the CSM signal, the finger goes to step  804 . In the absence of the CSM signal, the finger returns to step  800 .  
         [0073]     In step  804 , the finger determines whether the received signal satisfies the condition of Eq. (16). If the condition is satisfied, the finger proceeds to step  808 . If it is not, the finger goes to step  806 . The TED performs a timing error detection operation and the position controller updates a reception timing according to the output of the TED in step  808 . On the other hand, the finger maintains the reception timing in step  806 . Steps  804  through  810  are performed for a predetermined time period. Upon detection of a new path for the time period, the finger returns to step  800 .  
         [0074]      FIG. 9  is a graph illustrating signals spaced from each other at one chip interval and  FIG. 10  is a graph illustrating reception of the signals illustrated in  FIG. 9  in the conventional EL TED. As noted from  FIG. 10 , input signals for the fingers are converged to one signal after a predetermined time point because the 1-chip spaced signals each interfere with the other signals, as interference or neighboring signals.  
         [0075]      FIG. 11  is a graph illustrating reception of the 1-chip spaced signals illustrated in  FIG. 9  in the EL TED according to an embodiment of the present invention. Unlike the conventional EL TED, the EL TED in an embodiment of the present invention accurately tracks the received two signals.  FIG. 12  is a graph illustrating the operation of the EL TED when the received signals have initial errors according to an embodiment of the present invention. Referring to  FIG. 12 , the EL TED eliminates the initial errors over time.  
         [0076]      FIG. 13  is a graph illustrating four signals spaced from each other at one chip interval and  FIG. 14  is a graph illustrating reception of the signals illustrated in  FIG. 13  in the conventional EL TED. As noted from  FIG. 14 , input signals for the fingers converge to one signal after a predetermined time point because the 1-chip spaced signals each interfere with the other signals, as interference or neighboring signals.  
         [0077]      FIG. 15  is a graph illustrating reception of the 1-chip spaced signals illustrated in  FIG. 13  in the EL TED according an embodiment of the present invention. Unlike the conventional EL TED, the EL TED according to an embodiment of the present invention accurately tracks the received two signals.  FIG. 16  is a graph illustrating the operation of the EL TED when the received signals have initial errors according to an embodiment of the present invention. Referring to  FIG. 16 , the EL TED eliminates the initial errors over time.  
         [0078]     In accordance with an embodiment of the present invention as described above, signals received from neighboring paths are accurately estimated and the phenomenon of convergence of finger signals corresponding to the multiple paths is prevented. Also, initial errors are eliminated from the received signals.  
         [0079]     While the invention has been shown and described with reference to a certain preferred embodiment thereof, it should be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.