JPH01161933A - Pn code acquisition device - Google Patents

Abstract

PURPOSE:To improve the detection probability of a PN code by devising the device such that the phase of a reference carrier is arranged to the phase of a carrier of a reception signal. CONSTITUTION:The device is provided with a control voltage generator 23 generating a control voltage based on an output of a soft decision circuit 22 applying soft decision to an output of a sample and hold circuit S/H 3(21) sampling a level of a square device 2(13), a voltage controlled oscillator 24 controlling the oscillated frequency based on the control voltage, a comparator whose threshold level is lower than the comparator 15, a comparator 1(26) comparing the output of the square device 1(12) with the preset threshold level and an acquisition circuit outputting the output of the comparator 1(26) externally and an output terminal 27. Then a control signal is generated based on the output of the 2nd correlation device 11, the oscillated frequency of the reference carrier is controlled based on the control signal to compensate the phase difference between the reception signal and the reception carrier. Moreover, the output of the 1st correlation device 10 is used to apply the decision of the acquisition of the PN code. Thus, the acquisition probability of the PN code is improved.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a PN code capture device that captures a bit string consisting of a fixed pattern, and particularly to a PN code capture device that performs initial capture used in a spread spectrum communication device. be.

[Conventional technology]

Figure 3 shows, for example, the document rGLOBEcOM 83.1.
This shows the conventional PNN code acquisition device shown on pages 315 to 1319. In the figure, (1) is the input terminal for the received signal, and (2) is the base! ! A carrier wave oscillator, (3) and (4) are mixers 1 and 2 that multiply the received signal and the reference carrier wave, and (5) is a multiplier for multiplying the reference carrier wave by π/2 (ra
d) The changing π/2 phase shifters (6) and (7) remove high frequency components from the outputs of each of the above mixers 1 (3) and 2 (4).
LPF2, (8), (9) are each of the above LPFIs (6),
S/H (hereinafter referred to as sample hold circuit) 11S/H2, (lO), (11) that samples the output of LPF2 (7)
are correlator 1 and correlator 2 that take the correlation of PN codes, (12)
, (13) is each of the above correlator 1 (lO), correlator 2 (
11) The amount of two bundles that squares the output! , 2 bundle amount 2, (14)
is an adder that adds the outputs of the double squarer 1 (12) and the two bundle quantity 2 (13), and (15) compares the output level of the adder (14) with a preset threshold level. The comparator (16) is a capture circuit output terminal for outputting the output of the comparator (15) to the outside.

Figure 4 shows each of the above correlators 1 (10) and 2 (11).
), in which (17) is a shift register that stores the received PN code, (18) is a shift register that stores the PN code to be received, and (19) is a shift register that stores the PN code to be received.
is a multiplier that multiplies the received PN code by a PN code prepared in advance in the shift register (18), and (20) is an adder that adds the results from the multiplier (19).

A conventional PN code acquisition device is constructed as described above, - The received signal inputted to the input terminal (1) is branched, and one is inputted to mixer 1 (3) and the other to mixer 2 (4). . The signal input to the mixer 1 (3) is multiplied by the output of the reference carrier wave oscillator (2) and converted into a baseband signal. On the other hand, the signal input to mixer 2 (4) is π/
It is multiplied by a reference carrier wave whose phase is shifted by π/2 (rad) by a two-phase shifter (5) and converted into a baseband signal.

After unnecessary high frequency components are removed from the output signals from mixer 1 (3) and mixer 2 (4), S/)II (8) and S/H2 (
9) and correlator 1 (10), correlator 2
(11) is input. In each correlator 1 (10) and correlator 2 (11), a PN code to be received is prepared in advance and correlated with the received PN code.

That is, the received PN code is stored in the shift register (17), and the PN code to be received is prepared in advance in the shift register (18). Both of these PN codes are multiplied by a multiplier (19), and the output is multiplied by an adder (2) over the number of stages of shift registers (17) and (18).
0) is added. The output of this adder (20) becomes the correlator output.

Next, the outputs of each correlator 1 (10) and correlator 2 (11) are expressed as
The results are multiplied by an adder (14).

The output of the adder (14) is input to the comparator (15).

Next, the operations described above will be specifically explained.

Now, let's assume that the received signal input to the input terminal (1) is (1
) expression.

r (t) = A-d (t) −PN (t) −
cos (Wot 10) (1) It is assumed that the output of the reference carrier wave oscillator (2) is CO5Wot. In addition, in equation (1), A is the amplitude, d(tLpN(t)
are data and PN code, each taking a value of ±1.

Further, WO is the carrier wave angular frequency, and θ is the phase difference between the carrier wave of the received signal and the reference carrier wave.

From the above formula (1), LPFI (8), LPF2 (7)
Let the outputs of be Wl(t) and Wo(t) respectively, then w,(t) = P N (t)cosθ
・(2) Wo(L) = −P N (t)s
inθ ・(3). However, data d(t
) only complicates the explanation of the operation, so it is set to 1 here, and the amplitudes of the outputs L(t) and Wo(t) are set to 1 for simplicity. Output L(t), Wo
(t) are S/)It(8) and S/H2(9), respectively.
), correlator 1 (10), correlator 2 (1
1) and is correlated with the PN code of the shift register (18).

Here, the PN signals in the first stage of the shift register (17) are assumed to be Wl(t) and Wo(t), and the shift register (
17), (18), the number of stages is M, and the width of 1 bit of the PN code (chip width) is T. Then, L (t) = P N (t −1T() ・cos
θ ・(4)W, (t) = −P N (t −
1Tc) ・sin θ −(5). Correlator 1
(10) and the output of correlator 2 (11) as XI(t)
, Xo(t)tort, L(t) = '%:'oP N (t-1Tc)
・PN (ζTc-1Tc)・cosθ
...(6)Xo(t)"-'2:,: P
N (t −1Tc) ・PN(ζTc−1T(,)
・5ino...(7).

However, ζTc represents the initial phase difference between the received PN code and the PN code prepared in advance.

Therefore, each of the above outputs X+(t) and Xo(t) are t
= ζ ding, + nLTc ea+ (
8) becomes the maximum correlation output value (where n: integer, L: PN code length), and the outputs X+ and Xo at this time are XI(ζT
c+nLTc) = M-cosθ-(9)
XO(ζTc+nLTc) = -M-cosθ ・
(10).

Each of these outputs X, ,
) is added. Therefore, if the output of the adder (14) is y(t), then y(t)=X+(t)2+Xo(t)2= (%:2 P N (t −1Tc) ・PN(ζ Tc−
1Tc))2...(11) It becomes. Then, when the PN codes match, y (t)
takes the maximum value. At this time, y (t) is given in (9) above.
From equation (10), the following equation is obtained.

y(ζT(+ nLT□ = M2”・(12) The output y (t) of the adder (14) is input to the comparator (15) and is set at a preset level (temporarily assume this is RTH). When y (t) exceeds RT□, the comparator (15) outputs “1”, for example, and y
When (t) does not reach RTH, it outputs "0".

Therefore, if the output of the comparator (15) is 2 (1), then it is expressed as 2 (1).

The output Z (t) of the comparator (15) is output from the output terminal (16), and it is determined that the PN code has been captured when this output is 0.1°.

[Problem that the invention seeks to solve]

In the conventional PN code acquisition device as described above, if θ=0
Considering the case where the PN codes match in the state, correlator 1' (10) (7) output
) output Xo(t) is obtained from the above equations (9) and (lO) as follows.

XI (t) = M at θ=0, t=ζ7(
, + nLTc...(14) Xo(t)=Oat θ = 0, t =
ζ7c+nLdc...(15) That is, all the correlation information is included in the output X+(t) of correlator 1 (10), and the output Xo of correlator 2 (11)
No correlation information appears in (t). Input terminal (
If the received signal input to 1) is accompanied by noise,
The output X, (t) of correlator 2 (11) contains only noise components. Therefore, the adder (1
In 4), there is a problem in that an extra noise component that does not include any correlation information is added, and the comparison result in the comparator (15) is likely to be erroneous, making it easy to fail in capturing the PN code.

This invention was made to solve this problem, and is a PN code that can reliably capture the PN code.
The purpose is to obtain a code capture device.

[Means for solving problems]

The PN code acquisition device according to the present invention includes a first mixer that multiplies a received signal and a reference carrier wave, and the base '! J-
a phase shifter that shifts the phase of the carrier wave, a second mixer that multiplies the phase-shifted reference carrier wave and the received signal, and a first correlation that correlates the PN code based on the signal from the first mixer. a second correlator that correlates the PN code based on the signal from the second mixer; and means for determining PN code acquisition based on the output of the first correlator;
a control means that generates a control signal based on the output of the second correlator; a control voltage generator that generates a control voltage based on the control signal; and a control voltage generator that controls the oscillation frequency of the reference carrier based on the control voltage. A voltage controlled oscillator is provided.

[Effect]

In this invention, a control signal is generated based on the output of the second correlator, and the oscillation frequency of the reference carrier is controlled based on this control signal, thereby eliminating the phase shift difference between the received signal and the received carrier. Then, the output of the first correlator is used to determine whether the PN code is captured. Therefore, it is possible to increase the probability of capturing the PN code.

〔Example〕

FIG. 1 shows an embodiment of the present invention.
The same reference numerals as those in the figures and FIG. 4 indicate the same or corresponding parts.

(21) is the S/H3 that samples the level of the two-bundle quantity 2 (13), (22) is a soft decision circuit that makes a soft decision on the output of S/H3 (21), and (23) is the soft decision circuit (22) ), a control voltage generator that generates a control voltage based on the output of (
24) is a voltage controlled oscillator that controls the oscillation frequency based on this control voltage, (25) is a comparator with a lower threshold level than the comparator (15) in Figure 3, and (26) is a two-bundle quantity 1 (12) A comparator 1 (27) that compares the output of the comparator 1 (27) with a preset threshold level outputs the output of the comparator 1 (26) to the outside.

This is the output terminal of the capture circuit.

In the PN code acquisition device configured as above,
When the PN codes match, the output of the comparator (25) becomes “1”.
”. Therefore, using this output, the amount of two bundles 2 (
By sampling the output of 13) at S/H3 (21), it is possible to monitor the output level of one of the two correlators, specifically, correlator 2 (11). The pulse sampled by the S/83 (21) is soft-determined by the soft-decision circuit (22), and then sent to the control voltage generator (23).
) will be sent to. The control voltage generator (23) uses a voltage controlled oscillator (24) so that this pulse level is always O.
supply voltage to.

In the output of the correlator 2 (11), the correlation information multiplied by sin θ appears in accordance with the carrier wave phase difference θ, as shown in equation (10). Therefore, controlling this output so that it is always 0 means setting this phase difference θ to 0 (rad) or π (rad). When θ becomes 0 or π, all the correlation information appears in the output of the other correlator 1 (10) as shown in equation (9), so it is difficult to judge whether the PN code has been captured or not. Correlator 1 without adding the output of Correlator 2 (11)
This can be done using only the output of (10).

Note that since the threshold level of the comparator (25) in FIG. 1 is set lower than the threshold level of the comparator (15) shown in FIG. 3, the probability of erroneously capturing noise increases. However, the role of the comparator (25) is to obtain the timing to monitor the level of the output of the correlator 2 (11), and the role of the comparator (25)
It is not a final acquisition circuit judge like . and,
By lowering the threshold level of the comparator (25), it becomes possible to control the phase difference θ for each PN frame.

FIG. 2 shows another embodiment of this invention, in which the same reference numerals as in FIG. 1 indicate the same or corresponding parts. (28) is an integral discharge circuit that integrates and discharges one cycle of the PN code, (2
9) is a comparator 2 that compares the output of the correlator 1 (10) with a preset threshold level, and the integrated discharge voltage of the output of the correlator 2 (11) is used as the control voltage. ing.

By configuring in this way, the amount of two bundles 1 shown in FIG.
(12), the two-bundle quantity 2 (13), the adder (14), the comparator (25), and the S/) 13 (21) circuits are not required, so the structure can be simplified.

In addition, in each of the above embodiments, the correlator 2 (
11) is used for control, but conversely, the output of correlator 1 (10) is used for control, and the output of correlator 2 is used for control.
A correlation pulse may be obtained from the output of (11).

〔Effect of the invention〕

As explained above, this invention allows the phase of the reference carrier wave to be aligned with the phase of the carrier wave of the received signal.
This has effects such as being able to improve the detection probability of N codes.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a PN code acquisition device showing one embodiment of the present invention, and FIG. 2 is a block diagram of a PN code acquisition device showing another embodiment of the invention.
Fig. 3 is a first diagram showing a conventional PN code acquisition device.
FIG. 4 is a block diagram showing the configuration of the correlator. (3)...Mixer 1, (4)...Mixer 2
, (5)...π/2 phase shifter, (lO)...correlator 1, (11)...correlator 2, (12)...
...squared 1, (13)...squared 2, (14
)...Adder, (21)...S/H3, (22)...
... Soft decision circuit, (23) ... Control voltage generator, (24) ... Voltage control oscillator, (25) ... Comparison,
(26)...Comparator 1, (28)...Integrator discharge circuit, (29)...Comparator 2. In each figure, the same reference numerals indicate the same or equivalent parts.

Claims (3)

[Claims] (1) A first mixer that multiplies the received signal and a reference carrier wave, a phase shifter that shifts the phase of the reference carrier wave, and a second mixer that multiplies the received signal and the reference carrier wave from the phase shifter.
mixer, and PN based on the signal from the first mixer.
a first correlator that correlates the codes; a second correlator that correlates the PN codes based on the signal from the second mixer; and a determination of PN code capture based on the output of the first correlator. a control means for generating a control signal based on the output of the second correlator, a control voltage generator for generating a control voltage based on the control signal, and oscillation of the reference carrier wave based on the control voltage. 1. A PN code acquisition device comprising: a voltage controlled oscillator that controls frequency. (2) The control means includes a comparator that detects timing based on the sum of the squares of both correlators, a sample hold circuit that samples the output of the second correlator at that timing, and an output of this sample hold circuit. 2. The PN code acquisition device according to claim 1, further comprising a soft decision circuit that makes a soft decision and outputs a control signal. (3) The PN code acquisition according to claim 1, wherein the control means has an integral discharge circuit that integrates and discharges the output of the second correlator and outputs a control signal. Device.