KR100399008B1 - Apparatus for acquisition for wideband DS/CDMA signal - Google Patents

Abstract

The present invention relates to a code acquisition receiver for acquiring a code phase of a DS / CDMA signal of a DS / CDMA system, comprising: a) a code generator for simultaneously generating at least two phase codes having a phase difference, and b) the code generator. A correlator for correlating each received phase code signal with a received signal; A square unit which squares the output of the correlation unit; And an asynchronous detector including a coupling unit for adding the output of the square unit, c) a discriminator for determining whether to acquire a code for the output of the asynchronous detector, and d) a code generator if it is determined that the code is not acquired by the discriminator. Characterized in that it comprises a code phase update unit for updating the code phase generated in the.

Description

Code acquisition receiver for wideband direct sequence code division multiple access received signal {Apparatus for acquisition for wideband DS / CDMA signal}

The present invention relates to a code acquisition receiver of a direct sequence code division multiple access (DS / CDMA) system.

DS / CDMA is a technology adopted as the standard of next generation mobile communication system and multiplies data by spreading code to transmit data after spreading broadband. To demodulate the data at the receiver, the despreading process of multiplying the transmitted signal by the same code as the spreading code is required. To despread, the receiver must acquire the phase of the spreading code multiplied by the received signal. This process is called acquisition. In the code acquisition process, a pilot channel signal is generally used in which only a spreading code is transmitted without data modulation. In a mobile communication environment, a transmission signal reaches a receiver through several paths. Code acquisition refers to a process of making a phase difference between a spreading code signal received through a path and a spreading code signal generated by a receiver smaller than one chip using a pilot channel signal received through a multipath.

In the code acquisition process, the channel phase cannot be estimated. Therefore, in the code acquisition process, an asynchronous detector that can determine whether the code is acquired regardless of the channel phase is generally used. 1 is a block diagram of a conventional asynchronous detector. The code acquisition receiver according to FIG. 1 includes an antenna 100, a local oscillator LO, 102, a mixer 104, a code generator 106, an integrator 108, and a sampler 110. A correlator 112 and a squarer 114. The operation according to the configuration is as follows. The antenna 100 receives a high frequency signal that undergoes fading and adds noise through a wireless channel. The mixer 104 multiplies the received signal by the signal generated by the local oscillator 102 and converts the received signal into a baseband complex signal. The correlator 112 correlates the real and imaginary components of the complex signal, respectively, and the squarer 114 squares the correlated signals to remove phase components due to the channel.

As the correlator 112, an active correlator shown in FIG. 1 is generally used. The active correlator multiplies the signal generated by the code generator with the received signal, integrates it over the correlation period, and samples it to find the correlation. In the search process, a matched filter correlator may be used instead of an active correlator. Since the matched filter correlator can test different phases on each chip, it has an advantage of faster searching than an active correlator. However, the matched filter correlator has a disadvantage in that it is more complicated than the active correlator and cannot be used in the verification process in which correlation sections should not overlap. In the following description, the active correlator is used for both the searching process and the checking process.

2 (a) to 2 (e) show correlation results for the case where the synchronization of the code phase is achieved and vice versa when the power of the received signal is 1, assuming an ideal channel without noise and fading. It is. r ( t ) shows the received signal, c ( t ) shows the output of the code generator and p ( t ) shows the product of r ( t ) and c ( t ). 2 (a) shows a reception signal. FIG. 2 (b) shows the received signal r ( t ) in case of in-sync, and FIG. 2 (c) is a result of multiplying the values shown in FIGS. 2 (a) and 2 (b). P ( t ) is shown. As shown, the p ( t ) value is always 1 when synchronization is achieved, and the correlator output is 1. FIG. 2 (d) shows the received signal r ′ ( t ) when out-of-sync and FIG. 2 (e) is shown in FIGS. 2 (a) and 2 (d). P ' ( t ) is the result of multiplying the calculated values. As shown, in the case of no synchronization, the p ' ( t ) value is 1 or -1 and the integrated value is much smaller than 1.

The code acquisition process is generally done in two stages. Determination of code acquisition at each step is made by comparing the output of the asynchronous detector with a threshold. The first step is the search mode, which compares the asynchronous detector output with the first threshold. If the asynchronous detector output is larger than the first threshold, it is determined temporarily that the code has been acquired and enters the second mode of verification mode. In the verify mode, for the sake of more reliable testing, the A asynchronous detector output for the code phase determined in the search mode is compared with the second threshold to determine that the code is finally acquired when it is greater than or equal to B times. do. If it is determined that the code acquisition has not been made in the search or confirm mode, the code generator phase in the asynchronous generator After updating by T _c , test for the next code phase. T _c represents chip time Is usually 1 or 1/2, which is assumed to be 1 in the following description. The first threshold value, the second threshold value, and A and B should be set to minimize the average code acquisition time.

The general code acquisition receiver described above is designed on the assumption that there is only one reception path of radio waves, that is, only one code phase that can be code acquisition exists. [A. Polydoros and CL Weber, "A Unified Approach to Serial Search Spread-Spectrum Code Acquisition-Part I: General Theory," IEEE Trans. Commun ., Vol. COM-32, pp. 542-549, May 1984.] However, since DS / CDMA signals are received through multipath and the delay difference of the path that can be distinguished at the receiver is T _c , the delay spread of the channel is divided by T _c . As many paths as values exist in delay diffusion. The presence of multiple paths increases the number of code phases that can be acquired, while reducing the signal-to-noise ratio (SNR) for each path, which can degrade code acquisition performance.

An object of the present invention is to provide a code acquisition receiver for a DS / CDMA received signal that can reduce the code acquisition time by effectively using the multipath in a multipath environment.

1 is a block diagram of a conventional asynchronous detector.

FIG. 2 illustrates a correlation result of a correlator for a case where synchronization of a code phase is performed and vice versa when an ideal channel without noise and fading is assumed and power of a received signal is 1. FIG.

3 is a block diagram of a code acquisition receiver of a DS / CDMA received signal according to the present invention.

4 is an embodiment of a code acquisition receiver for a wideband DS / CDMA received signal according to the present invention.

5 (a) and 5 (b) show a search order of code phases in the code acquisition receiver of FIG.

According to an aspect of the present invention, there is provided a code acquisition receiver for acquiring a code phase of a DS / CDMA signal, comprising: a) a code generator for simultaneously generating at least two phase codes having a phase difference, and b) the code generator. A correlator for correlating each received phase code signal with a received signal; A square unit which squares the output of the correlation unit; And an asynchronous detector including a coupling unit for adding the output of the square unit, c) a discriminator for determining whether to acquire a code for the output of the asynchronous detector, and d) a code generator if it is determined that the code is not acquired by the discriminator. Code acquisition receiver for acquiring the code phase of the DS / CDMA signal, characterized in that it comprises a code phase update unit for updating the code phase generated in the.

The determination unit of the code acquisition receiver according to the present invention is characterized by determining whether to acquire a code by comparing the asynchronous detection unit output with a threshold value.

The code generator of the code acquisition receiver according to the present invention is characterized in that it comprises one code generator and a memory.

The code phase update unit of the code acquisition receiver according to the present invention updates the phase of the code generator by the number of N chips, and if the code acquisition is not performed even after one code period has passed, the second to Nth times from the initial code phase. The code phase is updated by one of the code phases, and the code generator phase is updated by N chips again.If the code is not acquired after another cycle, the code phase is one except the previously selected phase of the 2nd to Nth phases from the initial code phase. Update the code generator phase by N chips again, and repeat this process to perform discrete code updates for the entire code phase until the code is acquired. N can be set to an optimal value by making several measurements.

As another method for achieving the above technical problem, the present invention also provides a code acquisition receiver for acquiring a code phase of a DS / CDMA signal, comprising: a) one or more simultaneously generating at least two phase codes having a phase difference from each other; Code generator, b) one or more asynchronous detectors, each of the asynchronous detectors comprising: a correlator for correlating the received signal with each phase code signal generated at the code generator; A square unit which squares the output of the correlation unit; And a combiner for adding outputs of the squares,-c) a determiner for determining whether to acquire a code for the output of the at least one asynchronous detector, and d) a code generation if it is determined that the code is not acquired at the determiner. And a code phase update unit for updating a code phase generated from the unit, wherein the asynchronous discrimination unit compares the outputs of the asynchronous detectors corresponding to a part of the entire code phase to determine a code phase corresponding to the largest value of the outputs. do.

In the present invention, the code generator comprises one code generator and a memory.

The code phase update unit according to the present invention is characterized in that the asynchronous detection unit updates the code phase so that the asynchronous detector generates output for code phases having a phase difference by N chips. If the code acquisition fails in the determination unit, the code phase is updated to obtain an asynchronous detector output for N code phases that have not been tested previously.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings. 3 is a block diagram of a code acquisition receiver according to the present invention. The code acquisition apparatus according to FIG. 3 includes a determination unit 302 using a asynchronous detection unit 300: a search mode 304, a confirmation mode 306, and a code phase update unit 308. Unlike the general code acquisition apparatus, the asynchronous detector 300 correlates a received signal with an internal code generator signal and a delayed signal, squares each of them, and adds them to each other to obtain a discrimination value. The determination unit 302 is divided into a search mode 304 and a confirmation mode 306. In the search mode 302, the determination value obtained by the asynchronous detector 300 is compared with the first threshold value to make a temporary determination on whether the code is acquired. In the confirmation mode 304, the A output of the asynchronous detector 300 for the code phase determined in the search mode is compared with the second threshold value, and if it is larger than or equal to B than the second threshold value, it is finally determined as code acquisition. If it is determined that the code acquisition is not performed in the search mode or the confirmation mode, the code phase updater 306 updates the code generator phase of the asynchronous detection unit 300 and repeats the above process until the code acquisition is achieved. At this time, unlike a general code acquisition device that updates a code phase by one chip, the chip phase is updated by N chips so as to make a discontinuous search.

4 is an embodiment of a code acquisition receiver for a wideband DS / CDMA received signal according to the present invention. The code acquisition receiver according to FIG. 4 includes asynchronous detection unit 400, a determination unit 403 for a search mode, a determination unit 404 (not shown in detail block) and a code phase updater for a confirmation mode using the asynchronous detector 400. 405. The asynchronous detector 400 includes a code generator 401, two memories 411 and 412, three multipliers 421 to 423, three integrators 431 to 433, three samplers 441 to 443, Three squarers 451-453 and adder 402. The operation according to the above configuration is as follows. Using the code generator 401, the memories 411 and 412, the multipliers 412 to 413, the integrators 431 to 433, the samplers 441 to 443 and the squarers 451 to 453, Find the square of the correlation of the code generator signal. In this case, the three correlations are correlations for adjacent different code phases, and are combined using the adder 402 to generate a discrimination value. By generating the discrimination value in this way, not only a more reliable discrimination value can be obtained, but also multiple code phases can be tested simultaneously. This is because in a wideband CDMA system, since the chip time is small, there is a general possibility that a public path exists on adjacent code phases, thereby obtaining diversity gain through synthesis. In addition, although FIG. 4 combines correlations for three adjacent code phases, correlations for more code phases may be combined in an environment having a large number of paths. The determination value is used by the determination unit 403 of the retrieval mode and the determination unit 404 of the confirmation mode.

5 (a) to 5 (b) show the order in which the code phases are retrieved in the code acquisition receiver of FIG. H ₁ denotes a code phase in which a signal exists, that is, a code phase in which code acquisition can be performed, and H ₀ denotes a reverse code phase. L denotes the period of the code, that is, the code phase number, and L _p denotes the number of multipaths, which corresponds to the number of H ₁ phases. The order in which the code phases are searched in FIGS. 5 (a) and 5 (b). Denotes an operation function of the adder 402 corresponding to the coupling unit for the correlation result of the code phase update unit 405 and the asynchronous detection unit 400 shown in FIG. 4. That is, the code phase update unit 405 causes the code phase to be tested to change by N (for example, 5) chip intervals, thereby allowing the code phases to be tested in a discontinuous order of N chip intervals, and the adder 402 of the coupling unit. Figure 5 (a) shows that the number of multipaths is 5 and the code phases updated in each test in the receiver of Figure 4 are 5 chips, by combining the correlator outputs for three adjacent code phases. , That is, the order in which the code phases are tested for the case of N = 5. _{l j (j = 1, 2} , ..., L p) is [L / N] +1 or [L / N] ([x ] is the integer part of x) inde becomes 1 / N of approximately code period . Description of what is shown is as follows. First, we test the code phases that are multiples of N from the first code phase i 1. if l _i will _first be a code obtained after a test for one code phase starting from the second through the N-th one of the code phase (i 2) from the initial phase for the code phase spaced multiple of N from the phase Perform the test. l _{i 2} If there is no code obtained after a test for one code phase is to, starting at one, except for i 2 of the second through the N-th code phase from the initial phase a phase code phase spaced multiple of N from the phase Perform a test on If the code is not acquired even after performing the test for all L code phases by repeating this process, the above process is repeated until the code acquisition is achieved. FIG. 5A illustrates the case where i 2 = 3, i 3 = 5, i 4 = 2, and i 5 = 4. FIG. FIG. 5 (b) shows the search order of code phases when N = L _p for the general case. It can be seen that for every l _j searches, there is one phase corresponding to one of the L _p paths, that is, a phase where code acquisition can be performed. 5 (a) and 5 (b) show the case where the updating code phase number N is equal to the number of paths L _p , but since the actual number of paths is not known, N is set to an approximate number of expected paths or to the environment. It should be set variable accordingly. N may be set to an optimal value by making several measurements. A dotted line in FIG. 5 (a) shows the operation of the adder 402 of FIG. 4, and several adjacent ones (three in FIGS. 5 (a) and 5 (b)) to obtain a decision variable for each test. According to the present invention, in the absence of multipath, combining the correlation results of adjacent code phases results in only noise increase and inferior discrimination characteristics. If the multi-path, when the combination of matter for this greater potential there is multi-path on because they reach the receiver as a sum of signals having a different code phase transmission signal, the adjacent code phases, adjacent code phase H as _{When the} code phases match as shown in FIG. ₁ , adjacent multipath signals may be combined to increase the magnitude of the signal. In particular, in a fading environment, since the magnitude of the signal changes with time, and the probability of the multipath signal being simultaneously reduced is very small, the diversity gain can be obtained and the detection probability can be increased. This determination can also be used to simultaneously test multiple phases that are combined.

In the present invention, only the serial search method for determining whether to acquire a code by comparing the discrimination value with a threshold value has been described as an example. However, the discrimination value for a code phase corresponding to a part of the overall code phase is determined using a code phase correlator. A full parallel search method that selects the code phases corresponding to the largest value by taking them at the same time, gathering the discriminant values for all code phases with one or several correlators, and then selecting the code phases corresponding to the largest value, or successive It can be applied to the method of selecting the largest of the correlations for a part of code phases and comparing them with a threshold again. That is, by using the method proposed in the present invention, it is possible to determine whether to obtain a code by obtaining only the discriminant values for phases having a phase difference of N chips without having to obtain the discriminant values for all code phases. By combining the correlation of the code phases, the reliability of the decision can be increased and tests for several phases can be performed simultaneously.

According to the present invention, first, the code acquisition time can be reduced by distributing code phases that can be acquired in a multipath environment over the entire code phase region. Second, by combining correlations for adjacent code phases, signals distributed in multiple paths can be combined to increase detection probability and to test multiple code phases simultaneously, thus reducing code acquisition time. Third, the transmission power is reduced to obtain the same code acquisition time, or the service area per base station is expanded. In addition, various modifications, changes, additions, and the like will be possible within the spirit and scope of the present invention. Such modifications, changes, and the like should be regarded as falling within the scope of the following claims.

Claims (7)

A code acquisition receiver for acquiring a code phase of a DS / CDMA signal, a) a code generator for simultaneously generating at least two or more phase codes having a phase difference, b) a correlator for correlating the received signal with each phase code signal generated by the code generator; A square unit which squares the output of the correlation unit; An asynchronous detector including a coupling unit for adding an output of the square unit; c) a judging unit for judging whether to obtain a code for the output of the asynchronous detecting unit, and d) a code phase update unit for updating the code phase generated at the code generation unit when it is determined that the code acquisition has not been made; Code acquisition receiver for acquiring the code phase of the DS / CDMA signal, characterized in that it comprises a. The code acquisition receiver of claim 1, wherein the determination unit determines whether to acquire a code by comparing the output of the asynchronous detection unit with a threshold value. The code phase update unit according to claim 1, wherein the code phase update unit updates the phase of the code generator by the number of N chips, and if the code is not acquired even after one code period has elapsed, the second to N th code phases from the initial code phase. Update the code phase by one N chip to update the code generator phase by N chips, and if the code is not acquired after another cycle, update the code phase to one of the 2 to Nth phases except the previously selected phase from the initial code phase. The code acquisition phase is updated again by N chip, and the code acquisition is performed to obtain the code phase of the DS / CDMA signal, characterized by discontinuous code updating for the entire code phase until the code acquisition is repeated. receiving set. A code acquisition receiver for acquiring a code phase of a DS / CDMA signal, a) one or more code generators for simultaneously generating at least two or more phase codes having a phase difference from each other, b) a correlator for correlating the received signal with each phase code signal generated by the code generator; A square unit which squares the output of the correlation unit; And one or more asynchronous detectors each including a combiner that adds outputs of the squares; c) a discriminating unit for determining whether to obtain a code for the outputs of the at least one asynchronous detecting unit, and d) acquiring the code phase of the DS / CDMA signal, characterized in that it comprises at least one code phase update unit for updating the code phase generated in the code generator so that the asynchronous detection unit obtains an output for the code phase required for determination. Code acquisition receivers. The method of claim 4, wherein the determining unit compares the asynchronous detector outputs for all or part of the code phases obtained from the at least one asynchronous detector to determine a code phase corresponding to the largest value among the outputs. Code Acquisition Receiver for Acquiring Code Phase of DS / CDMA Signal. The code phase update unit of claim 4, wherein the code phase update unit updates the code phase so that the asynchronous detector generates output for code phases having a phase difference of N chips, and if the code acquisition fails in the determination unit, the code not previously tested. A code acquisition receiver for acquiring the code phase of a DS / CDMA signal, characterized in that the code phase is updated to obtain an asynchronous detector output for a code phase with a phase difference of N chips among the phases. The code acquisition receiver according to any one of claims 1 to 6, wherein the code generator comprises one code generator and a memory.