Abstract:
A synchronization acquisition apparatus and a method thereof are disclosed. The apparatus includes a local code generator coupled to a plurality of delayers, a plurality of multipliers commonly coupled between the delayers and a plurality of integrators, and a plurality of switches coupled between the multipliers of an integrator. The plurality of integrators are coupled to a detector that detects the maximum integrator output. A plurality of comparators form a feedback loop for obtaining a reliable signal level under any environment and implementing a quick synchronization acquisition without checking all PN code offsets.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an improved synchronization acquisition apparatus and an implementation a method thereof applicable for wireless communications systems, and more particularly, Code Division Multiple Access (CDMA) wireless telephones or receivers. 
     2. Background of the Related Art 
     A Double Dwell, Maximum Likelihood, Serial Sliding Acquisition (DDMLSSA) may be implemented by discrete circuit elements, or a software routine performed by a digital data processor such as a high-speed signal processor, or a combination of the circuit device and the software routine. FIG. 1 shows the DDMLSSA of the related art. The DDMLSSA is a part of a remote communication apparatus receiver such as a Code Division Multiple Access (CDMA) wireless phone in accordance with the mobile telephone station-base station compatibility standard of the TIA/EIA/IS-95(July, 1993), which is the dual mode wide band diffusion spectrum cellular system. 
     When a wireless telephone is energized, one or more guide channel (i.e., pilot channels) are received from one or more neighboring base stations. Each guide channel transmits a psuedorandom noise (PN) code sequence which differs in phase (e.g., offset of the GPS time) from the PN code sequences of other base stations of the system. The DDMLSSA synchronizes the local PN generator of the receiver to the PN sequence of the guide channel with a signal intensity that exceeds the noise level. While the DDMLSSA need not synchronize to the guide channel of the base station nearest to the receiver at the initial stage, it should synchronize to the guide channel having a sufficiently intense signal strength to initiate communication between the base station and the receiver. 
     A high frequency receiver  1  and a frequency demodulator  2  receive a PN code signal from the guide channel of more than one transmission base station BS. The DDMLSSA is also coupled to a controller such as a data processor  3 , which may input an integration time and a predetermined threshold value. The data processor  3  reads the adaptively obtained threshold value, as discussed in further detail below. 
     The related art DDMLSSA also contains a multiplier  11 , first and second integrators  13 ,  14 , a local PN code generator  12 , a first, second, third, fourth, fifth, sixth, and seventh comparison block  21 ,  22 ,  23 ,  24 ,  25 ,  25 ,  26 ,  27 , a noise sample count index initialization and incrementing blocks  31 ,  33 , local phase incrementing block  32 , and first and second threshold value initialization block  34 ,  35 . 
     In the related art DDMLSSA, the received PN code signal (including noise) is applied to the multiplier  11 . The received PN code signal is then multiplied by the PN code outputted from the local PN generator  12  of the wireless phone. The multiplier  11  output is applied to the first integrator  13  and the second integrator  14 . The first integrator  13  is a trial integrator having an integration period of T D1 , seconds, and an output Zi 1  of that integrator  13  is transmitted to the first comparator  21 . 
     The first comparator  21  performs an operation to compare the first integrator  13  output Zi 1  with a first threshold value (1-y) Z 1  at time t. That first threshold value is a function of the maximum first integrator  13  output from past history until time (t-1), and provides a confidence interval greater than 50% for the relatively short correlation length. Initially, the first threshold value Z 1  is set to ‘0’, and y is between {fraction (1/16)} and ⅛ for the present comparison. 
     When the first integrator  13  output Zi 1  is greater than or equal to the first threshold value (1-y) Z 1 , the fifth comparator  25  performs a test and updates the first threshold value Z 1 , as discussed in greater detail below. When the first integrator  13  output Zi 1  is less than the first threshold value, the second comparator  22  performs an operation to compare the first integrator  13  output Zi 1  with a threshold likelihood value Z 1 / 2 , which is less than the historical value of the output of the first integrator  13 . The predetermined threshold value is 6 dB less than the maximum signal energy or the maximum likelihood threshold value Z 1 / 2 , plus or minus (x), where (x) varies between about 0 and 3 dB. 
     If the first integrator  13  output Zi 1  is greater than or equal to the first threshold likelihood value Z 1 / 2 ±X based on the test performed by the second comparator  22 , the system resets the value of the noise sample count index m to 0 at the index initialization block  31 . Next, the third comparator  23  compares the phase i of the locally generated code signal with q, where q is the total number PN phases to be searched in the PN space. Here, q represents the total number of PN chips in the code region and has a value of 2 15 , or 32,768 chips. 
     The third comparator  23  determines whether the signal is at the end portion of the PN code region. If the phase i has a different value from the total number of PN chips q, the phase i is incremented by the local phase incrementing block  32  and the PN code generator  12  is updated, and the interrelationship is checked again. If the locally generated phase i equals the total number of PN chips q in a third comparator  23 , the acquisition process is terminated, as an exhaustive search of the PN code region has been conducted, and the correct PN code phase has been determined. 
     If the first integrator  13  output Zi is less than the first threshold likelihood value Z 1 / 2 ±X based on the test performed by the second comparator  22 , the noise sample count index m is incremented by a value of 1 by the index incrementing block  33 . The resulting value of the noise sample index m is then compared with a threshold value M in the fourth comparator  24 . 
     If the noise sample index m is greater than the threshold value M, the checking process of the acquisition process is terminated, as a correct PN code phase determination has been completed, the acquisition apparatus has obtained a proper signal, and a predetermined number of the noise samples has been evaluated. For example, a suitable threshold value M between about 70 and about 150 provides a detection probability that exceeds 90%. 
     If the noise sample index m is less than or equal to the threshold value M, the phase of the locally generated PN code signal is incremented by the local incrementing block  32 , and the interrelationship is checked again. The entire acquisition operation is performed until the first integrator  13  output (1-y)Zi 1  exceeds the first threshold value Z 1  in the first comparator  21 , for the relatively short correlation interval. The output Zi 1  of the first integrator  13  is then compared with Z 1  by a fifth comparator  25 . If the value of the first integrator  13  output Zi 1  exceeds the threshold value Z 1 , the first threshold value is updated to equal the current output value Zi 1  of the first integrator  13  in the first threshold value initialization block  34 . 
     If the output Zi 1  of the first integrator  13  is smaller than the first threshold value Z 1  based on the test performed by the fifth comparison block  25 , the first threshold value Z 1  is not updated. Since the initial value Z 1  is set at ‘0’, the initial comparison result of the first comparison block  21  is followed by the operation of the fifth comparator  25 , and the value of the first threshold value Z 1  is initialized to the first integrator  13  output Zi 1  by the first threshold value initialization block  34 . 
     Next, the integration (i.e., dwell) time is increased to T D2  seconds without changing the locally generated PN code phase. The second dwell time provides a higher detection probability and a lower false alarm probability. The integration time of the second integrator  14  is equivalent to about 128 to 2,048 chips, preferably 128 chips (104 msec). The integration time of the second integrator  14  is selected to exceed the integration time of the first integrator  13 . 
     The sixth comparator  26  determines whether the second integrator  14  output Zi 2  exceeds the second threshold value Z 2 . If the second integrator  14  output Zi 2  exceeds the second threshold value Z 2 , then the second threshold value initialization block  35  updates the second threshold value Z 2  to equal the current output value Zi 2  of the second integrator  14 . Since the second threshold value initially equals ‘0’, the result of the sixth comparison block leads to the operation of the second threshold value initialization block, where the second threshold value Z 2  is set to the second integrator  14  output Zi 2 . Next, the index initialization block  31  sets the noise sample count index m to an initial value of ‘0’. The phase of the internally generated code signal is varied by the decimal unit of the chip at the local phase incrementing block  32 , and the interrelationship is rechecked until the condition in the third comparison block  23  has been satisfied. 
     If the output Zi 2  of the second integrator  14  is less than the second threshold value Z 2  as determined by the test performed in the sixth comparison block, the seventh comparison block  27  compares the output value Zi 2  of the second integrator  14  with the second threshold likelihood value Z 2 / 2 , which is smaller by about 6 dB than the energy level of the maximum signal. If the output value Zi 2  of the second integrator  14  is greater than or equal to the second threshold likelihood value Z 2 / 2 , the index initialization block  31  resets the noise sample counter index m to equal ‘0’, and the phase of the PN code signal is varied by the decimal unit of the chip in the local phase incrementing block  32 , and the interrelationship is checked again. 
     If the output Zi 2  of the second integrator  14  is less than the second threshold prediction value Z 2 / 2 , the index incrementing block  33  increments noise sample counter index m by a value of 1, and the fourth comparator  24  compares the index m with the threshold value M. If the noise sample index m is greater than the threshold value M, the acquisition apparatus terminates the acquisition process as discussed above. If the noise sample counter index m is less than or equal the threshold value M, the entire acquisition process is continuously performed, as described above. 
     When the acquisition process of the related art is performed in a noisy communication environment, the output of the first integrator  13  fluctuates rapidly. Accordingly, the second integrator  14  is frequently used. However, because the first integrator  13  increasingly discards the false PN phases, the second integrator  13  is used less frequently. Since the second integrator  14  has a longer dwell time, the acquisition time is decreased when the second integrator  14  is used less frequently. 
     In the index initialization block  31 , the noise sample counter index m is set to equal ‘0’, and the next locally generated PN code phase is set in the local phase incrementing block  32 . As a result, once the first locally generated PN code phase of the PN code space has been sampled, the acquisition apparatus automatically self-initializes. 
     The input PN signal is serially correlated with all possible code positions of the locally generated PN code replica. Whenever the output of the first and second integrators  13 , 14  exceeds the first and second threshold values, Z 1 , Z 2  a corresponding threshold value is updated. The above-described operation continues until the correlated output satisfies the acquisition process. After the acquisition process terminates, the correct PN alignment is selected as the local PN code phase position, which generates the maximum detection output. 
     However, as described above, the related art synchronization acquisition apparatus has various disadvantages. Synchronization acquisition speed and reliability are decreased because all the PN code offsets are checked, and there is substantial noise. 
     The above description of the related art is incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a synchronization acquisition apparatus and an implementation method thereof that substantially obviates one or more of the problems caused by limitations and disadvantages of the related art. 
     Another object of the present invention is to provide a synchronization acquisition apparatus and a method thereof that obtains a reliable signal level in an environment where there is much noise and implements a quick synchronization acquisition without checking all PN code offsets. 
     To achieve the above objects, there is provided a synchronization acquisition apparatus which includes a PN code generator for generating a PN code signal by an initial PN code offset, a plurality of delay units for sequentially delaying the PN code signals, a plurality of multipliers for multiplying the received PN code signal and the PN code signals delayed by the delay units, a plurality of integrators for integrating the outputs of the multipliers over a first integration interval, a plurality of switches for selectively outputting one among the outputs of the multipliers, a variable integrator for varying an output of the multiplier selected by the switches, a detector for detecting a maximum value among the variable integrator and the integrators, a first comparator for comparing the maximum value detected by the detector and a first threshold value, a second comparator for comparing the maximum detected value and a first maximum value, a first block for updating the first maximum value among the values integrated over the first integration interval to the maximum detected value, a third comparator for comparing the maximum detected value and a first likelihood value, a second block for initializing the count, a fourth comparator for comparing the PN code offset and the PN code period, a third block for increasing the count, a fifth comparator for comparing the count and a post detection search time(PDT), a fourth block for increasing the PN code offset, a sixth comparator for comparing a second integration value integrated over the second integration interval and a second maximum value, a seventh comparator for comparing the second integration value and a second likelihood value, a fifth block for updating the second maximum value among the values integrated over the second integration interval to a second integration result value, and a plurality of switches for selectively outputting the output of the variable integrator to the detector or the sixth comparator. 
     To achieve the above objects, there is provided a synchronization acquisition method which includes the steps of a first step for delaying sequential code signals by a plurality of delay ratios, multiplying a received code signal by each of the delayed code signals, and integrating each of the multiplied code signals over a first integration interval; a second step of detecting the maximum value among the multiplied code signals integrated over the first integration interval; a third step of comparing the maximum detected value with a first threshold value; a fourth step of comparing the maximum detected value with a second threshold value when the maximum detected value is smaller than the first threshold value; a fifth step of initializing a first counter value when the maximum detected value is larger than or equal to a second threshold value, changing a first code delay with a second code delay when an end signal of the generated code signal is reached, repeating the first through fourth steps, increasing the counter value when the maximum detected value is smaller than the second threshold value, changing the first code delay with the second code delay when the counter value is smaller than the post detection search time (PDT), and the end signal of the generated code signal is not reached by comparing the counter value and the post detection search time and repeating the first step through the fourth step; a sixth step of comparing the maximum detected value and a third threshold value, when the maximum detected value is larger than or equal to the first threshold value, wherein the third threshold value is set equal to the maximum detected value when the maximum detected value is larger than the third threshold value; wherein the sixth step comprises; a seventh step of integrating a value obtained by multiplying the received code signal by a second delayed code signal, over a second integration interval; an eighth step of comparing the second integration value with a fourth threshold value; a ninth step of comparing the second integration value with a fifth threshold value when the second integration value is smaller than the fourth threshold value; and a tenth step of initializing the counter value when one of the second integration values is not less than the fifth threshold value, changing a current code delay with another code delay by adding a predetermined number to the current code delay when the end of the generated code signal is not reached and repeating the first through the fourth steps, increasing the counter value when the second integration value is smaller than the fifth threshold value, comparing the counter value and the PDT, completing the acquisition when the counter value is not less than the PDT as a result of the comparison, changing the current code delay with another code delay when the counter value is smaller than the post detection search time and repeating the fourth through tenth steps. 
     To achieve the above objects, there is provided an apparatus for detecting and acquiring reliable synchronization in a communications system, comprising: a plurality of multipliers that receive an input code signal; a local code generator coupled to the plurality of multipliers to provide a corresponding plurality of local codes from a set of local codes; a plurality of integrators, wherein each of the said integrators receives and concurrently integrates over a first integration interval an output from a corresponding one of the multipliers; a detector coupled to receive outputs of the integrators, wherein the detector outputs a maximum value of the integrator outputs corresponding to a selected one of the local codes; and a first comparator that compares the detector output with a first threshold value and selectively resets a first maximum value. 
     To achieve the above objects, there is also provided a method for detecting and acquiring reliable synchronization, comprising the steps of: multiplying a received code signal by a first group of codes generated from a set of codes; concurrently integrating the plurality of multiplication products over a first integration interval; detecting the maximum value of the integrated values that corresponds to a selected code of the first group; comparing the maximum detected value with a first threshold value; integrating the selected code over a second integration interval when the maximum detected value is greater than the first threshold value; and comparing the output of the second integration interval with a second maximum value. 
     Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objects and advantages of the invention may be realized and attained as particularly pointed out in the appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be described in detail with reference to the following drawings in which like reference numerals refer to like elements wherein: 
     FIG. 1 is a block diagram illustrating a related art synchronization acquisition apparatus; and 
     FIG. 2 is a block diagram illustrating a synchronization acquisition apparatus according to a preferred embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 2 illustrates a preferred embodiment of a synchronization acquisition apparatus according to the present invention. The preferred embodiment of a synchronization acquisition apparatus includes a pair of integrators  132 ,  133  with identical integration intervals, and a variable integrator  131  that varies the integration interval to produce a synchronization acquisition time three times faster than the related art. 
     A PN input code signal (including noises) received by the synchronization acquisition apparatus is applied to first, second, and third multipliers  121 ,  122 ,  123 . A first PN code signal from a PN code generator  100  is multiplied by a first delay PN code signal PNCSD 1  and a second delay PN code signal PNCSD 2  as first and second delay units  111 ,  112  sequentially delay the PN code signal. Since the PN code offset (K) of the PN code generator  100  equals 1 at an initial stage, the PN code generator  100  generates a PN code signal. The first and second delay units  111 ,  112  sequentially delay the locally generated PN code signal when the PN code offset (K) equals 1, such that first and second delay PN code signals are generated for PN code offset values (K) equal to 2 and 3, respectively 
     The outputs of the second and third multipliers  122 ,  123  are applied to the second and third integrators  132 ,  133  having identical integration intervals. The outputs of the multipliers  121 ,  122 ,  123  are selectively applied to the variable integrator  131  by first, second and third switches SW 1 , SW 2 , SW 3  for varying the integration interval. Initially, the first switch SW 1  is transited to the “ON” position, so that the output of the first multiplier  121  is applied to the variable integrator  131 . Additionally, the first ‘delta’ value of the variable integrator  131  is initially equals the integration value t 1  of the second and third integrators  132 ,  133 . As a result, the variable first integrator  131  and the non-variable second and third integrators  132 ,  133  integrate the outputs of the first through third multipliers  121 ,  122 ,  123  over an identical integration interval. 
     The output of the variable integrator  131  is selectively outputted to the detector  110  or the sixth comparator  146  based on the position of fourth and fifth switches SW 4 , SW 5 . Initially, the fourth switch SW 4  is transited to the ‘ON’ position, and the output of the variable integrator  131  is applied to the detector  110 . 
     The detector  110  selects a maximum value MAXt 1  from the outputs of the integrators  131 ,  132 ,  133 , which is outputted to a first comparator  141 . The first comparator  141  then performs an operation to compare the output MAXt 1  of the detector  110  with the first threshold value X*Z 1 . In the present embodiment, Z 1  represents a first maximum value, which is the largest historical integration value, and X represents a value of about 0.85˜0.94. If the output MAXt 1  of the detector  110  is greater than or equal to the first threshold value X*Z 1 , the first maximum value Z 1  is compared with the output MAXt 1  of the detector  110  by a second comparator  142 . 
     If the second comparator  142  determines that the maximum output MAXt 1  of the detector  110  is greater than or equal to the first maximum value Z 1 , the first maximum value Z 1  among the first integration values is updated to equal the output value MAXt 1  of the detector  110  by the first threshold value initialization block  210 . The second delta value t 2  of the variable integrator  131  is updated for the second integration to a value greater than a first delta value. If the detector  110  maximum output value MAXt 1  equals the output of the variable integrator  131 , the first switch SW 1  is transited to the ‘ON’ position. Correspondingly, the maximum output value MAXt 1  equals the output of the second integrator  132 , the second switch SW 2  is transited to the ‘ON’ position, and if the maximum output value MAXt 1  equals the output of the third integrator  133 , the third switch SW 3  is transited to the ‘ON’ position. If either the second switch SW 2  or the third switch SW 3  is in the ‘ON’ position, the fourth switch SW 4  is transited to the ‘OFF’ position, and the fifth switch SW 5  is transited to the ‘ON’ position. 
     If the output MAXt 1  of the detector  110  is less than the first maximum value Z 1  among the former first integration values, the first maximum value Z 1  among the former first integration values is not updated to equal the maximum output MAXt 1  value of the detector. The condition for the second integration is set as described above. 
     If the maximum value MAXt 1  is less than the first threshold value X*Z 1  based on the operation performed by the first comparator  141 , a third comparator  143  compares the maximum output value MAXt 1  with a first likelihood value Z 1 / 2 , which is less than the first maximum threshold value Z 1 . If the maximum output value MAXt 1  is greater or equal to the first likelihood value Z 1 / 2 , the count CNT is set to 0 by a counter initialization block  220 , and the PN code offset K and the PN code period F are compared by a fourth comparator  144 . If the PN code offset K is less than the PN code period F, the PN code offset K is incremented by 3 by a local phase incrementing block  240 , so the PN code generator  100  generates a PN code signal by the offset K. 
     The local phase incrementing block  240  increases the number added to the offset K by the number of integrators. In the preferred embodiment of synchronization acquisition apparatus according to the present invention, three integrators are used. If the PN code offset K is greater than the PN code period F, the PN code phase has been correctly determined, and the synchronization acquisition operation is terminated. 
     If the maximum output value MAXt 1  is less than the first likelihood value Z 1 / 2 , a count incrementing block  230  increments the count CNT by a value of 1. The count CNT and a post detection search time (PDT) are compared by a fifth comparator  145 . The post detection search (PDT) is the time required to evaluate the noise sample or non-related signals, based on the number determined by the synchronization apparatus after a reliable signal is obtained. A detection probability of about 99% is obtained based on the PDT. If the count CNT is less than or equal to the post detection search time PDT, the PN code offset K and the PN code period F are compared by the fourth comparator  144 . If the count CNT is greater than the post detection search time PDT, the PN code phase has been correctly determined, and the synchronization acquisition operation is terminated. 
     When the variable integrator  131  integrates with respect to integration intervals determined by the second delta value based on the condition for the second integration, the fifth switch SW 5  is transited to the ‘ON’ position and a second integration value MAXt 2  of the variable integrator  131  is compared with a second maximum value Z 2  by a sixth comparator  146 . The second maximum value Z 2  is the maximum value among the second integration values. 
     If the second integration value MAXt 2  is greater than or equal to the second maximum value Z 2 , based on the operation of the sixth comparator  146 , the second maximum value Z 2  is updated to the second integration value MAXt 2  by a second maximum value initialization block  250 . The counter initialization block  220  resets the count CNT to a value of ‘0’, and the fourth comparator  144  compares the PN code offset K and the PN code period F as discussed above. If the PN code offset K is less than the PN code period F, the local phase incrementing block  240  increments the PN code offset K by a value of 3, and the PN code generator  100  generates a PN code signal by the PN code offset K. If the PN code offset K is greater than the PN code period F, the PN code phase is correctly determined, and the synchronization acquisition operation is terminated. 
     If the second integration value MAXt 2  is less than the second maximum value Z 2  based on the operation of the sixth comparator  146 , a seventh comparator  147  compares the second integration value MAXt 2  to a second likelihood value Z 2 / 2 , which is less than the second maximum value Z 2 . If the second integration value MAXt 2  is greater than or equal to the second likelihood value Z 2 / 2 , the count CNT is set to a value of 0 by the count initialization block  220 . The PN code offset K and the PN code period F are compared by the fourth comparator  144  as described above. If the PN code offset K is less than the PN code period F, the local phase incrementing block  240  increases the PN code offset K by a value of 3, and the PN code generator  100  generates a PN code signal by the PN code offset K. If the PN code offset K is greater than the PN code period F, the PN code phase is correctly determined, and the synchronization acquisition operation is terminated. 
     If the second integration value MAXt 2  is less than the second likelihood value Z 2 / 2 , the count CNT is incremented by a value of 1 by the count incrementing block  230 , and the count CNT and the post detection search time PDT are compared by the fifth comparator  145  as described above. If the count CNT is less than or equal to the post detection search time PDT, the PN code offset K and the PN code period F are compared by the fourth comparator  144  as described above. If the count CNT is greater than the post detection search time PDT, the PN code phase is correctly determined, and the synchronization acquisition operation is terminated. 
     In the synchronization acquisition apparatus, the likelihood values are automatically determined in real time under an environment having a high noise level, for obtaining a reliable signal level. After the reliable signal is obtained, the synchronization acquisition process is terminated without a need to detect all remaining PN code offsets. Since a plurality of code offsets are concurrently searched, it is possible to implement a faster synchronization acquisition. 
     The foregoing embodiments are merely exemplary and are not to be construed as limiting the present invention. The present teaching can be readily applied to other types of apparatuses. The description of the present invention is intended to be illustrative, and not to limit the scope of the claims. Many alternatives, modifications, and variations will be apparent to those skilled in the art. In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents but also equivalent structures.