JPS5936451A - Synchronism catching and holding device for spread spectrum communication - Google Patents

Abstract

PURPOSE:To simplify the circuit constitution and to quicken the acquisition, by using a tracking circuit at the acquisition operation so as to attain the acquisition and to average the side lobe of the correlation peak. CONSTITUTION:A spread spectrum signal enters multipliers 2, 6 from an input terminal 1. In case of the acquisition, a switch 32 is selected to the position (a) and a switch 31-1 is selected to a-c, b-d or a-d, b-c. Thus, the input spread spectrum signal is spread inversely at the multipliers 2, 6. Since the two paths A, B are checked at the same time in the acquisition, the acquisition operating time is reduced to a half.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a synchronization acquisition and holding device in a spread spectrum communication system.

In spread spectrum communication, it is common practice to spread and transmit transmission data using pseudo-noise faster than the transmission speed because it has the advantage of being resistant to interference and providing highly private communication. However, it is not always easy to despread the transmitted spread spectrum signal using known pseudo-noise and obtain the necessary data signal. The data transmission speed is called a bit rate, and the minimum unit of pseudo noise that cannot be spread is called a chip, and the transmission speed is hereinafter called a template. Due to its nature, in spread spectrum communication, communication is sometimes expected to occur in situations with a poor signal-to-noise ratio.In this case, the signal power contained within one chip time is small compared to the noise;
It is impossible to extract the information contained in one chip, and it is necessary to compare or correlate with reference signals of multiple chips. However, the received spread spectrum signal is generally not temporally synchronized with the reference signal.

The time difference TΔ between the received one-word signal and the reference signal is expressed in units of the number of chips. The time for one chip is τ. hip, it can be expressed as TΔ=nτchip+Δτ (1). Here n is an integer, Δτ is 0 and Δτ<τ. hip... (2) shall be satisfied.

In general, a spreading code used as a pseudo noise used in spread spectrum communication is selected to have a small side lobe of autocorrelation and a small cross-correlation. Therefore, in order to achieve synchronization, two steps are required in equation (1): starting n from 0 and trying all integers that do not exceed the spreading code length, and correcting the deviation Δτ within one chip.
Requires one. The first operation here is called acquisition, and in order to realize this on the circuit, the power of the correlation circuit and the side rope for detecting the correlation peak must be used to reduce noise caused by interference waves, etc. The first and second operations, that is, the correction operation of Δτ, which requires a circuit for calculating the average value of the Δτ, are called tracking. In spread spectrum communication, it is desirable to achieve synchronization quickly. The comparison code length is N. omp, the acquisition time Tac, Tacq ”Nco
It can be expressed as mpτchip n' (3). Here, n is the same integer as in formula (1). Furthermore, the maximum time Tagη8 required for acquisition is given by Tacjx=Nco+npτ, where N is the spreading code length.
ch i p N ””” (4).

Since τchip determines the frequency bandwidth of the spread transmission signal, it cannot be made smaller than necessary.

N again. Decreasing omp and N is undesirable because both relatively increase the side lobes of autocorrelation and the cross-correlation, and therefore it becomes impossible to expect the value of the autocorrelation peak to be sufficiently large. Still, T'ac
As a way to reduce q, two or more synchronous circuits (
For example, there is a way to provide N/k chips for one circuit, so Tac
q becomes 1/. Further, the tracking operation ax is an operation for detecting a synchronization deviation of one chip or less and locking the synchronization. Therefore, the 0 detection method, which can only be performed after the acquisition is completed, is as follows.If we intentionally create a synchronization difference Δτt and the correlation output at this time is g(Δτt), then g(Δτt)−g( −Δτt) ・・・・・・(5)
By determining the value, the deviation from the correlation peak can be detected and tracked. Here, Δτt is
Since the purpose is to lock on the correlation peak, generally Δτt〈τchip +++++++++ (
6) Selected.

The circuit configuration for tracking is g(Δτt) and g
(-ΔτI) is required. Also, g(Δτ
There is also a method of time-divisionally finding t) and g(-Δτt) and averaging the differences.

Hereinafter, a conventional circuit configuration for synchronizing spread spectrum signals will be described with reference to FIG.

In the figure, 1 is an input terminal, 2 to 7 are multipliers, and 8 to 10
is a bandpass filter, 11 to 13 are detectors, 14&-
1, low-pass filter, 15.16 is a comparator, 17 is a local oscillator, 18 is a delay circuit, 19°20 is a 1/2 chip delay circuit, 21 is a reference code generator, 22 is a control device, 23 is an output terminal, 24 and 25 are switching devices that operate under the control of the control device 22.0 The received spread spectrum signal is input from the input terminal 1.
〇Meanwhile, the reference code generated by the reference code generator 21 is input to the multiplier 2.4.6 into the delay circuit 18.19.20
The signals generated by the local oscillator 17 are modulated by the multiplication i3.5.7.

The modulated signals each enter a multiplier 2.4.6 which despreads the input signal and drops it to an intermediate frequency. The despread signal dropped to the intermediate frequency is passed through a bandpass filter 8.9.10.
Only the correlated signals are extracted by the detectors 11, 12 .
Envelope detection is performed at 13. Here, the output of 11 is used for correlation peak detection, the output of 12 is used for comparison after correlation peak detection, and is passed through a low-pass filter 14 to average side lobes, and the output of 13 is used for tracking. . The output of the detector 11 and the output of the low-pass filter 14 enter a comparator 15 to detect a correlation peak. The result is the control device 22
If the correlation peak is not detected, the reference code is advanced by one step, and the above operation is repeated until the correlation peak appears. If a correlation peak is detected, the reference code is set to that and tracking begins. On the other hand, the output of the detector 13 is
The switch 24 despreads the signal with a code that is 1/2 chip ahead or behind the delay of the reference code with the correlation peak, and appears as a time-division output. These outputs are separated by a switch 25 operating under the control of the control device 22, compared by a comparator 16, and then input to the control device 22.

A synchronization error of one step or less, which appears as a comparison output, is sent back to the reference code generator 21 by the control device 22.

The spread spectrum signal is synchronized by the acquisition backed up by 2 degrees by the comparator 15 and the tracking fed back by the comparator 16, and the data signal is taken out from the output terminal 23.

As mentioned above, in conventional circuits, each circuit that performs acquisition operation and tracking operation is provided separately, and although acquisition and tracking do not operate at the same time, they partially overlap. There was a waste of having two circuits, and the circuit configuration of the entire device was unnecessarily complicated.

The present invention solves the above-mentioned drawbacks of the prior art.The present invention utilizes a tracking circuit during the acquisition operation to perform the acquisition operation, and mutually calculates the sidelobe average of the correlation peaks used for correlation peak detection. The present invention provides a synchronization acquisition and holding device for spread spectrum communication that has a simplified circuit configuration and speeds up the acquisition operation.

The present invention will be explained in detail below with reference to FIG. 2 showing one embodiment of the present invention. In FIG. 2, the same reference numerals are used for components equivalent to those in FIG. Pass filter, ■1゜131d detector, 14.26 is low pass filter, 15, 27.16 is comparator, 1
9.20.28.29 is a 1/2 chip delay circuit, 3o is a 1/2 code length delay circuit, 24, 25, 31.32 are switches operated by the control device 22, and 17 is a local oscillator. . Next, the operation of the circuit shown in FIG. 2 will be explained.

The received spread spectrum signal is input from input terminal 1 to multiplier 2.
Enter 6. A reference code is generated by a reference code generator 21, and one is generated by a correlation peak detection code and a 1/2-chip lead and lag before and after it by a 1/2-chip delay circuit 19 and 20, as described in FIG. A code is generated.

The other one is delayed by 1/2 code length by the delay circuit 30, and the 1/2 chip delay circuits 28 and 29 generate a correlation peak detection code and codes shifted by 1/2 chip before and after it. Here, the difference between the former and the latter is 1/
There is a time difference of two code lengths. The correlation peak detection code is connected to a switch 31-1, the 1/2 step lead code is connected to a switch 31-2, and the 1/2 chip delay code is connected to a switch 31-3.

In the case of acquisition operation, the switch 32 is connected to a, and the switch 31-1 is connected to a-c, b-d, or a.
-d, connected to b-c. Multipliers 3 and 7
A correlation peak detection code having a time difference of 1/2 code length is input to modulate the signal generated by the local oscillator 17, and the signal is input to multipliers 2 and 6. Therefore, input terminal 1
The input spread spectrum signals inputted from the multipliers 2 and 6 are despread to obtain an intermediate frequency, which is then input to the bandpass filters 8 and 10. Correlation signals are extracted from the despread signals by bandpass filters 8 and 10, detected by detectors 11 and 13, respectively, and input to comparators 15 and 27, and low-frequency filters 14 and 26K.

The rope filter outputs enter comparators 27 and 15 as the other comparison signal, respectively. That is, multipliers 2, 3,
A path constituted by a bandpass filter 8, a detector 11, a low-pass filter 14, and a comparator 15 is connected to the path A1 as well as multipliers 6, 7, If the path configured by the comparator 27 is path B, the average of the side ropes created by path B is used to detect the correlation peak to the path, and the average of path A is used for path B.

The outputs of the comparators 15 and 27 are respectively input to the control device 22, which controls the reference code generator 21 to advance the reference code by one step if the correlation peak is not recognized. Further, if a correlation peak is detected, if it is detected on path A, the switch 31-1 is left as is, and if it is detected on path B, the switch 31-1 is switched.

Note that the switches m31-2 and 31-3 are switched so that the detected correlation code is shifted by 1/2 step before and after the detected correlation code. In addition, the switch 32 is switched to b, and the path B is set to 1.
The switches 24 and 25 are switched at certain time intervals so that the signs of the /2 step lead and lag are detected and compared by time division. Control of these switching devices is performed by control device 2.
This is done by 2. After detecting the correlation peak in this way,
For the path A, the sign added to the multiplier 3 is selected so that the correlation peak occurs. Path B still adds 1/2 chip lead and lag codes to the code sent to path A in a time-division manner to the multiplier 7 in order to perform a tracking operation, and the switch 25 divides both codes in a time-division manner. The reference code generator 21 is controlled and locked by the control device 22 so that the path A takes the maximum value of the correlation peak. Output as a data signal is taken out from the output terminal 23 from the locked path A,
do.

As explained above, during acquisition operation, since the time between two paths is checked, the acquisition operation time is shortened to 1/2. Further, since both paths A and B generate signals that are averages of the side lobes of the other, no additional circuit is required. During the tracking operation, path (1) is used for reproducing data signals, and the other path is used for tracking, and no other tracking circuit is required. The switching circuit for acquisition operation and tracking operation is a digital circuit, and can be implemented using a general-purpose integrated circuit.Also, by integrating each circuit, it is possible to make the device smaller and lighter. possible 0

[Brief explanation of the drawing]

FIG. 1 is a block circuit diagram showing a conventional synchronization acquisition/holding device for a spread spectrum signal, and FIG. 2 is a block circuit diagram showing an embodiment of the present invention. 1... Input terminal 2-7... Multiplier 8-10.
... Band pass filters 11 to 13 ... Detectors 14, 26 ... Low pass filters 15, 16.2
7...Comparator 17...Local oscillator 18...Delay circuit 19, 20
．． 28.29...1/2 step delay circuit 30...1
/2 code length delay circuit 21...Reference code generator 22...Control device 23...Output terminal 24, 25.31-1.31-2.31-3.32...
・Switcher patent applicant Japan Radio Co., Ltd.

Claims (1)

[Claims] (1) In a synchronization acquisition and holding device for spread spectrum communication that performs synchronization using acquisition operation and tracking operation, and spreads and transmits transmission data using pseudo-noise faster than its transmission speed, each multiplier , has two paths consisting of a bandpass filter, a detector, a low-pass filter, and a comparator, and a means for switching between the two paths, and uses an unnecessary tracking circuit during acquisition operation to perform acquisition on the path. 1. A synchronization acquisition and holding device for spread spectrum communication, characterized in that an acquisition operation is performed, and a tracking operation is performed after the acquisition operation is completed by the switching means. (2. The apparatus according to claim 1, wherein a comparison signal for detecting a correlation peak necessary during an acquisition operation is obtained by an acquisition circuit on the other path that simultaneously detects the correlation peak. A synchronization acquisition and holding device for spread spectrum communication, characterized in that: