KR20060130468A - Pseudo noise acquisition apparatus and method for synchronization in a spread spectrum communication system - Google Patents

Abstract

A PN(Pseudo Noise) acquisition device in a spread-spectrum communication system and a method thereof are provided to more improve a detection probability of a correct hypothesis when a search window-based PN acquisition technique is used during synchronization of a receiver, thereby reducing PN acquisition time. Plural accumulators(309,311) output coherent and non-coherent accumulated hypothesis energy values of received signals. An energy detector(321) detects plural time hypotheses among all time hypotheses within a search window, and outputs plural corresponding hypothesis energy values. A threshold value comparator(323) compares the size of the hypothesis energy values with at least one predetermined threshold value, and outputs the compared results. A controller(325) controls accumulating operation of the accumulators(309,311), and decides that PN acquisition is successful if a particular time hypothesis having a hypothesis energy which is more than the threshold value is confirmed among the detected hypothesis energy values.

Description

PSENDO NOISE ACQUISITION APPARATUS AND METHOD FOR SYNCHRONIZATION IN A SPREAD SPECTRUM COMMUNICATION SYSTEM}

1 is a diagram illustrating autocorrelation characteristics of a PN code.

FIG. 2A illustrates a search window based hypothesis test result when the pilot Ec / Io is high. FIG.

2B is a diagram illustrating a search window based hypothesis test result when the pilot Ec / Io is low.

3 is a block diagram showing the configuration of a PN capturing apparatus according to an embodiment of the present invention;

4 is a flowchart illustrating a PN capture process according to an embodiment of the present invention.

5 and 7 illustrate the performance of the PN acquisition method proposed by the present invention in the AWGN channel.

6 and 8 illustrate the performance of the PN acquisition method proposed by the present invention in a fading channel.

The present invention relates to an apparatus and method for synchronizing a receiver in a spread-spectrum communication system, and in particular, a PN (Pseudo) for synchronizing a receiver in a code division multiple access (CDMA) system. Noise) capture device and method.

In general, spread spectrum communication is a transmission method that uses a bandwidth much larger than the minimum bandwidth required for transmitting information. In the transmitter, spread spectrum is performed by using a specific spreading code that is independent of data, and the spread spectrum is synchronized in a synchronized receiver. Data recovery is performed after despreading using code. The spread spectrum communication began to be developed in the mid-1950's, and was mainly applied to military communication. In the 1990's, the spread band communication began to be applied to cellular mobile communication. In addition, spread-band communication using the CDMA scheme is currently adopted and widely used in the third generation mobile communication standard.

In spread spectrum communication, a code used for spread spectrum and despreading is a pseudo-noise (PN) code, and the PN code has an auto-correlation characteristic as shown in FIG. 1. In FIG. 1, reference numeral Tc denotes a chip period, and reference numeral P denotes a period of a PN code. From the autocorrelation property, the receiver synchronizes the PN code of the received signal with the same PN code generated by the receiver within one chip, and then despreads the received signal using the synchronized PN code to recover data. Therefore, the receiver must first acquire PN synchronization for data recovery, and the process of synchronizing the PN synchronization is largely divided into PN acquisition and PN tracking.

In this case, the PN acquisition is a process of roughly synchronizing the PN code of the received signal with the same PN code generated by the receiver within one chip, and the PN tracking is a process of accurately matching the reception after the PN acquisition. The present invention will be described below in more detail the conventional PN acquisition method, for example, CDMA systems such as IS-95, CDMA 2000 as a representative communication system using spread-band communication as a technique for the PN acquisition.

In general, in a CDMA system, a receiver receives a pilot channel signal to perform PN acquisition, and the pilot channel signal is a signal spread with a complex PN code without data modulation for synchronization acquisition or power control of the receiver. Success of the PN acquisition is determined by calculating the energy of the pilot channel signal and comparing the calculated energy intensity with a predetermined threshold. Herein, the energy of the pilot channel signal is divided into an in-phase component and a quadrature component and despread using the PN codes of the I and Q channels, respectively. After accumulating over a period of time, it is obtained by adding squared.

Accumulation of the pilot channel signal energy by a predetermined number of times for comparison with the threshold value is called hypothesis energy, and the hypothesis energy is obtained from an arbitrary time hypothesis and compared with the threshold value. A series of processes will be referred to as hypothesis test. In addition, the time difference between the PN code of the received signal and the PN code generated by the receiver is called a time hypothesis. For example, in the IS-95 and CDMA 2000 systems, a total of 32768 time hypotheses exist when the time difference is changed by one chip interval. do.

In general, when the time difference between the PN code of the received signal and the PN code generated in the receiver is within one chip, the correct hypothesis is called the incorrect hypothesis. As a result of the hypothesis test, if the hypothesis energy is less than the threshold value, the hypothesis test is moved to the next time hypothesis and the hypothesis test is repeated; otherwise, the hypothesis test is performed again for a sufficiently long time to accurately determine whether the capture is successful. In this case, a long enough time is called a penalty time. In the hypothesis test for the correct hypothesis, the case where the hypothesis energy is greater than or equal to the threshold is called detection. In this case, if the hypothesis test is performed again for a penalty time, the hypothesis energy is generally greater than or equal to the threshold and it is determined that the capture is successful.

In the hypothesis test for the wrong hypothesis, the case where the hypothesis energy is greater than or equal to the threshold is called a false alarm. In this case, if the hypothesis test is performed again for a penalty time, the hypothesis energy is generally lower than the threshold, and the receiver hypotheses the next time. Go to and repeat the hypothesis test. PN capture performance is typically evaluated by average capture time, which is determined by detection probability and false probability, which is determined by thresholds and other factors.

However, in order to achieve a sufficiently high detection probability, the conventional receiver sets a threshold value sufficiently lower than the hypothesis energy of the correct hypothesis, so that there are many false hypotheses having hypothesis energy above the threshold value. Therefore, the hypothesis test should be re-run for all false hypotheses with threshold energy above the threshold, and the average capture time can be significantly increased because the penalty time is large enough. In order to solve this problem, a so-called search window based PN capture technique has been proposed.

In the search window-based PN capture, the hypothesis energy is sequentially calculated for all the time hypotheses in the search window, and then the temporal hypothesis having the maximum hypothesis energy is selected, and the maximum hypothesis energy is compared with a threshold to determine the PN capture. Determine success. If the maximum hypothesis energy is less than the threshold value, move to the next search window and repeat the hypothesis test. If the maximum hypothesis energy is more than the threshold value, if the maximum hypothesis energy is greater than or equal to the threshold value, the hypothesis test is repeated for the time hypothesis to determine whether the PN capture is successful. Determine again correctly.

FIG. 2A is a diagram illustrating the search window based hypothesis test result when pilot Ec / Io is high, wherein pilot Ec / Io is the total power (I _O ) of the received signal versus the signal power (E _C ) of the pilot channel. Defined as a ratio, the higher the pilot Ec / Io, the higher the hypothesis energy of the pilot channel signal. In FIG. 2A, the first search window includes a correct hypothesis, and assumes a case where the hypothesis energy of the correct hypothesis is the largest and at the same time the threshold value is larger than the threshold value. Thus in the case of FIG. 2A the PN acquisition will easily succeed. Meanwhile, in FIG. 2A, the second search window includes only false hypotheses, and assumes four false hypotheses that are greater than or equal to a threshold.

Therefore, in the general PN capture technique, the hypothesis test must be re-executed during the penalty time in all four false hypotheses of the search window 2, but the search window-based PN capture technique only performs the hypothesis test during the penalty time in the wrong hypothesis that has the maximum hypothesis energy. By rerunning, the average capture time can be reduced. That is, as shown in FIG. 2A, when the pilot Ec / Io is high, the search window-based PN capture technique reduces the average acquisition time.

Meanwhile, FIG. 2B illustrates the search window-based hypothesis test result when the pilot Ec / Io is low. In FIG. 2B, the search window 1 includes the correct hypothesis, and the hypothesis energy of the correct hypothesis is greater than or equal to the threshold. It is assumed that it is not the maximum hypothesis energy in the search window. Therefore, in the case of FIG. 2B, the PN acquisition is likely to fail. In this case, the receiver can perform hypothesis checking on all remaining search windows in turn, and then return to the search window containing the correct hypothesis, which will take a very long time in this process and increase the average acquisition time.

Therefore, the search window-based PN capture technique can reduce the average acquisition time by preventing excessive misleading when the pilot Ec / Io is high, but the hypothesis energy of the right hypothesis is critical when the pilot Ec / Io is low. Since the value is greater than the value but not the maximum hypothesis energy in the search window, a problem occurs that the probability of detecting the correct hypothesis is reduced, which in turn increases the average capture time.

It is an object of the present invention to provide a PN acquisition device and method that can reduce the average acquisition time when the ratio of the total power of the received signal to the pilot channel signal power is low in a spread band communication system.

The apparatus of the present invention for achieving the above object is a PN acquisition device for the synchronization of the receiver of the spread spectrum communication system, a plurality of accumulators for outputting the synchronous and asynchronous accumulated hypothesis energy value of the received signal, and all in the search window An energy detector for detecting a plurality of time hypotheses among the time hypotheses and outputting corresponding plurality of hypothesis energy values, and comparing the magnitudes of the plurality of hypothesis energy values with at least one predetermined threshold and outputting a comparison result A threshold comparator and controlling the cumulative operation of the plurality of accumulators, and determining that the PN capture is successful when a specific time hypothesis having a hypothesis energy that is greater than or equal to the threshold value of the plurality of detected hypothesis energy values is confirmed. It is characterized by including a controller.

The method of the present invention for achieving the above object in the PN acquisition method for the synchronization of the receiver of the spread spectrum communication system, the process of outputting the hypothesis energy by synchronizing and asynchronously accumulating the energy of the received signal, and all the time in the search window Detecting a plurality of time hypotheses from hypotheses, obtaining a plurality of hypothesis energy values corresponding to the plurality of time hypotheses, and comparing the hypothesis values with at least one predetermined threshold value, and among the plurality of hypothesis energy values. And determining that the PN capture is successful when a specific time hypothesis with a hypothesis energy above the value is identified.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description of the present invention, if it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted.

3 is a block diagram illustrating a configuration of a PN acquisition apparatus according to an exemplary embodiment of the present invention. The PN acquisition apparatus of FIG. 3 is basically provided in a receiver of a spread spectrum communication system to perform PN acquisition based on a search window. It is composed. Preferably, the receiver may be a mobile terminal of a CDMA system, and the PN acquisition device of the present invention may be provided in a pilot channel searcher for synchronization acquisition of the mobile terminal.

Referring to the configuration of FIG. 3, the reception antenna 301 of the PN capturing apparatus receives a radio frequency signal through a wireless channel. In a CDMA system, the radio channel becomes a pilot channel. The receiving module 303 frequency-converts the received signal of the antenna 301 into a baseband signal, filters the signal, and then outputs an analog-to-digital (A / D) conversion into a digital signal. Here, the received signal is a pilot channel signal, and the receiving module 303 separates the pilot channel signal into an in-phase component and a quadrature component and outputs the separated pilot channel signal.

In addition, the PN code generator 305 in FIG. 3, the received signal have the same code and, PN code of I channel according to a predetermined PN offset (PN _I) and PN code (PN _Q) of the Q channel under the control of the controller 325 Is generated and output to the despreader 307. The controller 325 searches for a pilot channel signal having a hypothetical energy greater than a predetermined threshold while changing the PN offset of the generated PN code. The despreader 307 complexly despreads the in-phase and quadrature components of the received pilot channel signal with the PN codes of the generated I and Q channels, respectively.

The accumulator 309 of FIG. 3 coherently accumulates the in-phase component of the despread pilot channel signal for a predetermined time, and the other accumulator 311 maintains the anti-phase component of the despread pilot channel signal constant. Accumulate synchronously over time. The two squarers 313 and 315 square the synchronous accumulation values of the in-phase and anti-phase components, respectively, and the adder 317 adds the synchronous accumulation values output from the two squarers 313 and 315 to the pilot. Calculate the energy value (strength) of the channel signal.

Another accumulator 319 of FIG. 3 accumulates the output of the adder 317 by a predetermined number of times to obtain a hypothetical energy value which is the accumulated energy strength of the pilot channel signal, and converts the calculated hypothetical energy value into the energy detector 321. Output The accumulation operation of the accumulator 317 is referred to as noncoherent accumulation. The energy detector 321 selects K temporal hypotheses in order of increasing energy values among all temporal hypotheses in the search window of a predetermined size, detects hypothetical energy values of the temporal hypotheses, and outputs the hypothetical energy values to the threshold comparator 323. .

The threshold comparator 323 transmits a result of comparing the K hypothesis energies corresponding to the selected K temporal hypotheses with a predetermined threshold value to the controller 325. In the present invention, the comparison process of the threshold value may be performed in two steps for more accurate PN capture. In this case, the threshold value is set to two, and when the threshold value is set to two, the threshold value 1 compared in the first hypothesis test is compared when the hypothesis test is re-executed for the time hypotheses determined to be equal to or greater than the threshold value 1. It is set to a value smaller than the threshold value 2.

In the present invention, the threshold 1 has a value of 0 or a positive value, and is set to 0 in order to increase the detection probability for a correct hypothesis. When the threshold 1 is set to 0, the hypothesis test is re-run in order of magnitude on the detected K time hypotheses, and then compared with the threshold 2. Threshold 2 is set to an experimentally appropriate value so that a false difference in time difference between the PN code of the received signal and the PN code generated at the receiver is, for example, out of one chip.

In FIG. 3, the controller 325 controls the cumulative operations of the accumulators 309, 311, and 319, and when a hypothetical energy value of the threshold values 1 and 2 is detected among K hypothesis energy values, a corresponding time hypothesis. It is determined that PN capture is successful for.

Hereinafter, the PN capturing method of the present invention applied to the configuration of FIG. 3 will be described.

4 is a flowchart illustrating a PN capture process according to an embodiment of the present invention, which is based on a search window-based PN capture technique.

First, when the receiver receives a pilot channel signal transmitted through a wireless network through the antenna 301, the PN acquisition apparatus of FIG. 3 starts PN acquisition. In step 401, the controller 325 of FIG. 3 proceeds to operation 403 immediately after performing a hypothesis check on the first search window, and moves to the next search window when performing a hypothesis test on the second and subsequent search windows. After that, the operation of step 403 is performed.

In operation 403, the energy detector 321 of FIG. 3 detects K temporal hypotheses in order of energy value by performing hypothesis testing on all the time hypotheses in the search window in which the current hypothesis test is performed. The K hypothesis energy values of the detected time hypotheses are output to the threshold comparator 323. In operation 405, the threshold comparator 323 of FIG. 3 transmits a result of sequentially comparing the K hypothesis energy values with a predetermined threshold value to the controller 325.

If the k (k = 1,2, ..., K) th hypothesis energy is greater than or equal to the threshold 1, the controller 325 proceeds to step 407 to perform a hypothesis test on the kth time hypothesis to perform more accurate PN capture. Rerun for a predetermined penalty time. Here, the initial value of k is set to 1. If the k th hypothesis energy value is less than the threshold 1 in step 405, the controller 325 considers that the PN capture for the time hypotheses of the corresponding search window has failed, and performs the PN capture for the time hypotheses of the next search window. In step 401, the operation is repeated.

On the other hand, when the threshold 1 is set to 0 in step 405, the process of step 405 can be omitted. Thereafter, in step 409, when the controller 325 receives the comparison result of the k th hypothesis energy and the threshold value 2 from the threshold comparator 323, and determines that the k th hypothesis energy is smaller than the threshold value 2, the k + 1 th hypothesis energy is determined. In order to perform the operations of steps 405 and 407, the value of k is increased by 1 in step 411. Then, the controller 325 checks if the k value exceeds the predetermined K value in step 413 and considers that the PN capture has failed for the time hypotheses of the corresponding search window, and the PN for the time hypotheses of the next search window. Proceed to step 401 to perform the capture.

When the k value is within the predetermined K value in step 413, the operations of steps 405 and 407 are repeated for the k + 1 th hypothesis energy. If it is determined through the above process that the kth hypothesis energy is greater than or equal to the threshold 2, the controller 325 considers that the PN capture is successful, and then performs the PN tracking process. Since the detailed description of the PN tracking process is irrelevant to the gist of the present invention, the detailed description thereof will be omitted.

According to the present invention, the hypothesis energy is sequentially calculated for all the time hypotheses in the search window, and then K temporal hypotheses are selected in the order of the largest hypothesis energy, and the hypothesis energy is selected in order of the selected K temporal hypotheses. Since success or failure of PN acquisition is determined in comparison with thresholds 1 and 2, the probability of detecting a correct hypothesis can be increased even when the pilot Ec / Io is low as shown in FIG. 2B.

5 to 8 show that the detection probability of the correct hypothesis is improved when the PN capture method of the present invention is performed, thereby reducing the average capture time for PN capture.

First, the experimental conditions of FIGS. 5 to 8 will be described with reference to FIGS. 5 and 6 when threshold 1 has a positive value, and FIGS. 7 and 8 are examples where threshold 1 has a zero value. The system considered in the mathematical analysis of the present invention is as follows. The period for the PN code is 32768, the chip rate is 1.2288Mcps, the pilot Ec / Io is -13dB, the frequency error is 2200Hz, and the number of time hypothesis checkers is 32. Hypothesis tests were performed at half-chip intervals, and the size of the search window was set to 16, 32, 64, 128, 256, 512, 1024, 2048, 4096, and 8192 chips. One, two, four, eight time hypotheses were detected. In addition, the synchronous accumulation interval is 128 chips, the asynchronous accumulation count and the threshold are variable, the penalty time is 3.2ms in the correct hypothesis, and the penalty time is 128ms in the wrong hypothesis. The above experimental conditions assume one condition for demonstrating the effect of the present invention, and it should be noted that the present invention is not necessarily limited to the above-described experimental conditions.

First, FIG. 5 is a diagram illustrating a performance comparison result between a conventional PN acquisition method and an PN acquisition method proposed by the present invention in an AWGN channel.

FIG. 5 shows the average acquisition time of the conventional PN acquisition scheme based on the conventional search window and the PN acquisition scheme proposed by the present invention by the size of the search window when the threshold 1 has a positive value. In this case, K = 1 corresponds to the conventional PN capture technique, and remaining K = 2, 4, and 8 correspond to the PN capture technique of the present invention. In the conventional PN capture technique, the average capture time decreases and then increases again as the size of the search window increases. As the K increases, the PN capturing method proposed by the present invention is superior to the conventional capturing method in terms of the average capturing time, and the average capturing time is reduced by 15.9% at the optimum search window size.

FIG. 6 is a diagram illustrating performance comparison results between a conventional PN acquisition method and a PN acquisition method proposed by the present invention in a fading channel.

FIG. 6 shows the average acquisition time of the conventional search window based PN acquisition technique and the proposed PN acquisition technique in the Rayleigh fading channel when the threshold value 1 has a positive value by the size of the search window. will be. In this case, K = 1 corresponds to the conventional PN capture technique, and the remaining K = 2, 4, and 8 correspond to the PN capture technique of the present invention. In the conventional PN capture technique, the average capture time decreases and then increases again as the size of the search window increases. As the K increases, the PN capture scheme proposed by the present invention is somewhat superior to the conventional capture time in terms of average capture time, and the average capture time is reduced by up to 5.2% at the optimal search window size.

7 is a diagram illustrating the performance of the PN acquisition method proposed by the present invention in the AWGN channel when the threshold value 1 is 0. Referring to FIG. 7, it is shown that the larger the K, the better the performance of the PN acquisition scheme proposed by the present invention. When K = 8, the minimum value of the average acquisition time of the PN acquisition technique of the present invention is a threshold value of 1; It was 15.9% less than it had.

8 is a diagram illustrating the performance of the PN acquisition method proposed by the present invention in a fading channel when threshold 1 is zero. Referring to FIG. 8, the performance of the PN acquisition scheme proposed by the present invention is excellent in the Rayleigh fading channel, and when K = 8, the minimum value of the average acquisition time of the PN acquisition scheme of the present invention is positive. It appeared to be nearly identical to when it had a value.

As described above, according to the present invention, when a search window-based PN acquisition technique is used to synchronize a receiver in a spread spectrum communication system, PN acquisition time can be reduced by further improving the detection probability of a correct hypothesis.

Claims (16)

A PN acquisition device for synchronizing a receiver of a spread spectrum communication system, A plurality of accumulators for outputting synchronous and asynchronous accumulated hypothesis values of the received signal; An energy detector for detecting a plurality of time hypotheses among all time hypotheses in the search window and outputting corresponding plurality of hypothesis energy values; A threshold comparator comparing the magnitudes of the plurality of hypothesis energy values with at least one predetermined threshold and outputting a result of the comparison; And controlling a cumulative operation of the plurality of accumulators and determining that the PN capture is successful when a specific time hypothesis having a hypothesis energy that is greater than or equal to the threshold value of the plurality of detected hypothesis energy values is confirmed. The device, characterized in that. The method of claim 1, Wherein said energy detector detects said plurality of time hypotheses in order of said hypothesis energy value being greater. The method of claim 1, And the threshold comparator compares the plurality of hypothesis energy values with the threshold value in ascending order. The method of claim 1, And when the threshold is set to two or more, the first compared threshold is set to zero. The method of claim 1, And the second threshold compared after the second is set to a positive value within a range where no misinformation occurs for an incorrect hypothesis. The method of claim 1, And when the threshold is set to two or more, the first compared threshold is set to a smaller value than the other threshold. The method of claim 1, And the controller repeats and controls the same hypothesis test for the next search window if the PN capture fails for all time hypotheses of the current search window. The method of claim 1, And the received signal is a pilot channel signal. A PN acquisition method for synchronizing a receiver of a spread spectrum communication system, Outputting hypothesis energy by synchronously and asynchronously accumulating the energy of the received signal; Detecting a plurality of time hypotheses from all time hypotheses in the search window, Obtaining a plurality of hypothesis energy values corresponding to the plurality of time hypotheses and comparing them with at least one predetermined threshold value; And determining that the PN capture is successful when a specific time hypothesis having a hypothesis energy that is equal to or greater than the threshold value among the plurality of hypothesis energy values is confirmed. The method of claim 9, And detecting the plurality of time hypotheses in the order of increasing the hypothesis energy value. The method of claim 9, The comparing method, wherein the plurality of hypothesis energy values are compared with the threshold value in increasing order. The method of claim 9, And if the threshold is set to two or more, the first compared threshold is set to zero. The method of claim 9, And the second threshold compared after the second is set to a positive value within a range in which no misinformation occurs for an incorrect hypothesis. The method of claim 9, And when the threshold is set to two or more, the first compared threshold is set to a smaller value than the other threshold. The method of claim 9, And if the PN capture fails for all time hypotheses of the current search window, repeating the same hypothesis check for the next search window. The method of claim 9, Wherein the received signal is a pilot channel signal.

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