JP2000078429A - Spread spectrum communications system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the manufacturing cost of a receiver and to miniaturize the receiver without necessitating a correlation unit to detect quantity of deviation by constituting the receiver to track the synchronization of a correlation peak position by shifting the correlation peak position in the direction to correct the deviation by a predetermined quantity when a deviation of the correlation peak position is detected. SOLUTION: A receiver R of a spread spectrum communications system is constituted of a receiving part 19 consisting of a reception antenna 18, an RF amplifier (reproduced signal amplifier) and an 1F amplifier, etc., a correlation device 20 consisting of a correlation unit and a memory, etc., and a control part 22 consisting of a demodulation part 21 and a CPU, etc. A specified signal to be transmitted from a transmitter of the system is received by the reception antenna 18 of the receiver R, the received signal is inputted in the correlation device 20 via the receiving part 19, is inversely spread by using a PN code for reference which is stored in the memory by the correlation device 20 and is demodulated to original data by the demodulating part 21.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spread spectrum communication system, and more particularly to a spread spectrum communication system for performing synchronous tracking of a signal received by a receiving apparatus.

[0002]

2. Description of the Related Art Conventionally, as a system for performing wireless data communication, for example, a system in which a personal computer and a printer are connected via a wireless line, and print data created by the personal computer is transmitted to the printer to perform a printing operation. Widely known. In this type of system, a spread spectrum (Spread Spread) method is used as a radio wave modulation method for information to be transmitted in order to eliminate the influence of fading and secure a desired communication distance.
spectrum: SS) spread spectrum communication system (Spread Spectrum C)
communication (SSC) is often used.

In this spread spectrum communication system, the PN (P) is much faster than the information signal to be transmitted.
Spread spectrum (frequency component) of information signal using pseudo noise (pseudo noise) code (wideband)
The transmitted signal is sent from the transmitting device to the receiving device.

[0004] The PN code is a kind of encryption in which digital signals of "1" and "0" are combined, and a PN code having a long period is used.
In the code, the patterns of "1" and "0" are irregular, appearing as noise and cannot be intercepted by a third party.

[0005]

However, according to the data communication method described above, unless data is demodulated,
There is a problem that the destination (Destination) cannot be determined.

That is, in such a data communication system, the data described above generally has an 8-bit configuration, and address information of a transmission destination to which information is to be transmitted is also included in the data portion. On the receiving side, it is possible to know if the data is addressed to the own station only after confirming the address information in the data portion demodulated after the synchronization acquisition. In this case, the efficiency of information access is low. Further, since the data has an 8-bit configuration, the number of destinations that can be set, that is, the number of channels, can be set to only 256.

In order to solve such a problem, Japanese Patent Application No. 6-308293 has been proposed as a technique for detecting a destination at high speed without using data demodulation.

[0008] In this technique, a code related to a transmission destination is inserted in a preamble set before data to be transmitted, so that data is demodulated prior to data demodulation.
It becomes possible to identify the destination using code synchronization.

In this case, it is necessary to set a threshold level in order to detect a correlation peak between a signal on the transmitting side and a signal on the receiving side. However, there is a problem that it is difficult to set the threshold level in a poorly changing radio wave environment, and there is a high possibility of malfunction. When detecting the correlation peak between the signal on the transmitting side and the signal on the receiving side at the threshold level, the level setting is complicated.For example, even if the signal is correct, the threshold level is not exceeded. I do.

Further, in the above-mentioned technique, a code for synchronization acquisition is included in the preamble in addition to the transmission destination identification code, and since a plurality of codes are present, spurious is generated at the time of code switching. is there.

Further, in the above spread spectrum communication system, the PN code in the received signal and the P
Synchronization acquisition for establishing synchronization by making the phase relationship with the N code (same as the PN code of the signal) coincide is generally performed.

After the acquisition of the synchronization, when the demodulation of the data is started, the synchronization tracking is continuously performed so that the synchronization state is not lost by the influence of the modulation or the noise.

[0013] Conventionally, in order to perform the synchronization tracking, in addition to the despreading correlator in the correlation device of the receiving device,
A correlator for inputting the phase shifted reference PN code was required. For example, in addition to a correlator for inputting a reference PN code for despreading, a correlator for inputting a reference PN code with an advanced phase and a correlator for inputting a reference PN code with a delayed phase are provided. I was Thus, the synchronous tracking was performed by calculating the direction of the phase shift of each PN code and the amount of the phase shift, and controlling the phase of the reference PN code or clock input to these correlators. .

However, in the conventional spread spectrum communication system, since a plurality of correlators are provided in the receiving apparatus for performing synchronous tracking, there is a problem that the manufacturing cost of the receiving apparatus increases by that much. .

Accordingly, an object of the present invention is to use a transmission signal configured to enable a high-speed media access capable of specifying a destination and communicating before demodulating data even under conditions where the radio wave environment is not very good. SUMMARY OF THE INVENTION It is an object of the present invention to provide a spread spectrum communication system that can solve the above-mentioned conventional problems, reduce the manufacturing cost of the receiving device, and realize the downsizing of the receiving device.

[0016]

According to the first aspect of the present invention,
A transmitting apparatus for transmitting a transmission signal by performing spread spectrum modulation using a pseudo noise code, and receiving the spread spectrum modulated signal, and detecting a correlation peak between the pseudo noise code of the received signal and a reference pseudo noise code. In a spread spectrum communication system including a receiving device including a correlator, when a shift occurs in a correlation peak position detected by the correlator, means for detecting the direction of the shift of the correlation peak position, Means for shifting the correlation peak position by a predetermined amount in a direction to correct the shift when the shift of the correlation peak position is detected, and the means for tracking the synchronization of the correlation peak position by each means. It is characterized by the following.

According to the present invention, there is no need to calculate the amount of shift of the correlation peak position, and only the direction of the shift is detected.
Synchronous tracking is performed by shifting the correlation peak position in the direction of the shift by a predetermined fixed amount, so that a correlator for calculating the amount of shift is not required, and the manufacturing cost of the receiving apparatus can be reduced, and the reception can be reduced. The size of the device can be reduced.

According to a second aspect of the present invention, in the first aspect of the present invention, a memory for storing the correlation peak position is provided, and the correlation peak position calculated for each cycle of the pseudo noise code is stored in the memory. The detected correlation peak position is compared to detect the direction of the shift of the correlation peak position.

According to the present invention, the direction of the shift of the correlation peak position is detected by simply comparing the calculated correlation peak position with the correlation peak position stored in the memory. The direction of the displacement can be easily detected.

According to a third aspect of the present invention, in the first aspect of the present invention, there is provided a counter for counting the number of times the correlation peak position shifts in the same direction. In this case, the correlation peak position is shifted by a predetermined amount in a direction in which the shift is corrected when the shift is performed.

According to the present invention, it is determined that the correlation peak position has shifted when it has shifted by a predetermined number of times in the same direction, so that a sudden shift in the correlation peak position can be ignored, and the true correlation peak can be ignored. The displacement can be detected.

According to a fourth aspect of the present invention, in the first aspect of the present invention, the correlation device includes a digital matched filter.

According to the present invention, the cost of the digital matched filter is lower than that of the analog correlator, and the size of the digital matched filter is easily reduced, so that the manufacturing cost and the size of the receiving apparatus can be reduced.

According to a fifth aspect of the present invention, in the invention of the fourth aspect, when the correlation peak position is shifted by a predetermined amount, one cycle of the sampling clock output from the sampling clock generator is shifted. It is a feature.

According to the present invention, since the correlation peak position is shifted by one period of the sampling clock, fine control becomes possible, and accurate synchronization tracking becomes possible.

According to a sixth aspect of the present invention, there is provided a transmitting apparatus for transmitting a transmission signal by performing spread spectrum modulation using a pseudo noise code, receiving the spread spectrum modulated signal, and transmitting the pseudo noise code of the received signal to a reference signal. And a receiving device including a correlation device that detects a correlation peak with a pseudo-noise code of a spread spectrum communication system, the correlation device includes a digital matched filter that detects a correlation peak position, and the correlation peak position is determined by the digital matched filter. Means for storing the correlation peak position in a memory when detected, and generating windows at desired intervals before and after based on the correlation peak position information stored in the memory; and calculating for each period of the pseudo noise code Means for comparing the obtained correlation peak position information with the correlation peak position information stored in the memory; Means for shifting windows generated at desired intervals before and after according to the result of the comparison by a predetermined amount in any of the front and rear directions, and configured to synchronously track the correlation peak position by each means. It is characterized by the following.

According to the present invention, since the digital matched filter is used, the cost is lower than that of the analog correlator, and the size is easily reduced. Therefore, the manufacturing cost and the size of the receiving apparatus can be reduced. Become. Further, since the correlation peak position is synchronously tracked by shifting the window, control becomes easy.

According to a seventh aspect of the present invention, when the window is shifted by a predetermined amount, one window of the sampling clock output from the sampling clock generator is shifted. It is assumed that.

According to the present invention, since the window is shifted by one period of the sampling clock, fine control can be performed, and accurate synchronous tracking can be performed.

[0030] The invention according to claim 8 is a transmitting apparatus for transmitting a frame-structured transmission signal in which data on information to be transmitted following a preamble is arranged by using spread spectrum modulation using a pseudo noise code, and A correlation device that receives a spread-modulated transmission signal and detects a correlation peak between a pseudo-noise code of the received signal and a pseudo-noise code for reference, and a correlation peak detected by the correlation device, wherein the transmission signal A receiving device including a means for calculating the number of peaks of the correlation peak that appears with a periodicity of the pseudo-noise code in the preamble and the pseudo-noise code for reference,
Means for detecting the direction of the shift of the correlation peak position when the correlation peak position detected by the correlator is shifted, and shifting the correlation peak position by a predetermined amount in the detected direction. Means for tracking synchronization of the correlation peak position by each means.

According to the present invention, the periodicity of the correlation peak between the pseudo noise code in the preamble of the transmission signal and the pseudo noise code for reference is detected without setting the threshold level, and Since a means for calculating the number of correlation peaks is provided, it is possible to identify and communicate with a transmission destination only by calculating the number of correlation peaks prior to demodulating the data portion, and in a condition where the radio wave environment is not very good. However, high-speed media access can be performed almost certainly.

Further, since the correlation device performs synchronization tracking by detecting only the direction of the phase shift, a correlator for calculating the amount of the shift is not required, so that the manufacturing cost of the receiving device can be reduced and the reception cost can be reduced. The size of the device can be reduced.

According to a ninth aspect of the present invention, in the eighth aspect of the present invention, a plurality of preambles of the transmission signal are provided.

The tenth aspect of the present invention is characterized in that the pseudo noise codes in the respective preambles are the same but are shifted in phase.

According to these inventions, since a plurality of preambles are provided in the transmission signal, the periodicity of the correlation peak between the pseudo-noise code in each preamble and the pseudo-noise code for reference is detected to determine the predetermined period. Calculate the number of correlation peaks,
In addition, by calculating the difference between the correlation peak positions in each preamble, for example, even if the jamming radio wave has periodicity, it is possible to identify and communicate with a transmission destination prior to demodulating the data portion, Even under conditions where the radio wave environment is not so good, high-speed media access can be reliably performed.

[0036]

Embodiments of the present invention will be described below with reference to the drawings.

In FIG. 1, T indicates a transmitting apparatus of the spread spectrum communication system according to the present embodiment. The transmission device T includes a transmission signal output unit 11, a DPSK modulator 12,
PN code generator (Pseudo Noise Gene)
rator: pseudo-noise generator (hereinafter, referred to as PNG) 1
3, a multiplier 14, a carrier wave oscillator 15, and a multiplier 16
And a transmission antenna 17.

The signal output from the transmission signal output section 11 is multiplied by a multiplier 14 with a PN code from a PN code generator 13, and further multiplied by a carrier from a carrier oscillator 15, and transmitted from a transmission antenna 17. Sent.

FIG. 3 shows the frame structure of the signal S transmitted from the transmitting device T. In the present embodiment, this frame configuration is, for example, an AGC (Auto
Gain Control settling 51 and a plurality of preambles PR1 to PR4
, Guard 53, frame pattern 55, data 5
7 are provided. In the present embodiment, each preamble P
R1 to PR4 pseudo noise codes (hereinafter referred to as PN codes)
Are the same PN code and their phases are different.

In FIG. 2, R indicates a receiving device of the spread spectrum communication system according to the present embodiment. The receiving device R includes a receiving antenna 18, a receiving unit 19 including an RF amplifier (reproduced signal amplifier) and an IF amplifier, a correlating device 20 including a correlator and a memory, a demodulating unit 21, a CPU
And a control unit 22 composed of the above.

The received signal S received by the receiving antenna 18
Is input to the correlator 20 via the receiver 19, and the correlator 20 stores the reference P stored in a memory (not shown).
The data is despread using the N code and demodulated by the demodulation unit 21 into the original data.

FIG. 4 shows a configuration of the correlation device 20 and the demodulation unit 21 of the receiving device R.

The correlation device 20 uses a reference P used for despreading.
Digital matched filter (hereinafter referred to as DMF) 31 for inputting an N code (reference pattern), weighting unit 32, amplitude conversion unit 33, and window generation unit 34
And a vector synthesis / peak hold unit 35.

The demodulation section 21 has a periodicity / phase difference judging section 36
, A timing generator 37 including synchronization tracking, a data demodulator 38, and a frame detector 39.

In this embodiment, as described above, the DMF 31 which is a digital correlator is used as the correlator, and the DMF 31 passes through the RF / IF section of the receiving section 19 and is subjected to a quadrature-detected baseband signal (Inphase Phase). And Q
Digital signals (COS component, SIN component) obtained by converting an analog component into a digital component by using an A / D converter (not shown) for both the ud component and the spread spectrum frequency band component are input. Here, the reference pattern (PN
Code), the same PN code as the input signal is used.
An autocorrelation output peak (hereinafter simply referred to as a correlation peak) can be obtained.

In the present embodiment, a digital correlator (DMF31) is used as a correlator. This digital correlator is lower in cost and easier to miniaturize than an analog correlator. The manufacturing cost can be reduced and the size can be reduced.

In the processing after the DMF 31, the correlation peak position is detected (stored in the vector synthesis / peak hold unit 35), and the periodicity, phase difference, and the like of the correlation peak position are calculated from the correlation peak position information.

The maximum processing time for digital signal processing after the A / D converter in the receiving device R is A / D
This is the sampling frequency of the converter. In this embodiment, the sampling frequency is twice the chip rate of the PN code.

FIG. 5 is a flowchart showing signal processing relating to the synchronization acquisition operation. Here, “synchronization acquisition” and “code synchronization” described later are used separately, but “code synchronization” is data modulation in which data is superimposed by one symbol (corresponding to one bit) in one cycle of a PN code. In the case of (1), in order to realize data demodulation by the DMF 31, one cycle length of the PN code received on the correlator (in the data modulation, a phase relationship of a certain PN code) is changed to a phase relationship with a reference PN code. It is to match.
The number of PN code chips to be used can be set arbitrarily. In the following, the word “position” indicates a temporal position with respect to a predetermined absolute time in the receiving device R. The absolute time is a time determined in advance by the receiving device R. For example, as shown in FIG. 7, one cycle of the PN code is represented by 1 count to 23 counts.

When the receiving apparatus R receives a received signal, first, necessary parameters are set (S1), and a timer or the like (not shown) is initialized (reset) (S1).
2).

Next, the vector synthesis / peak hold unit 35 (FIG. 4) outputs the PNs of the preambles PR1 to PR4.
A position having a maximum peak level (corresponding to the peak amplitude value) within one cycle of the code, that is, a maximum correlation peak point (hereinafter, referred to as MPP) is detected (S3). Then, the periodicity / phase difference determination unit 36 (FIG. 4) determines an arbitrary continuous PN code n (eg, n = 8) cycle of the PN code m (eg, m = 16) cycle of each of the preambles PR1 to PR4. The correlation peak is detected, and the maximum value (MAX) and the minimum value (MIN) of the MPP within the n periods of the continuous PN code.
Is calculated (S4). Steps S3 and S4 are a detection and calculation process for the portion (a) of FIG. Then, whether or not the difference between the maximum value and the minimum value of the MPP in the PN code n period of all the preambles PR1 to PR4 is within a predetermined peak point variation range, that is, (MAX)
(MIN) ≦ (variation range of peak points) is determined (S5). If the condition of S5 is satisfied, the process proceeds to step S6. However, if it is not within the range of the variation of the peak points, that is, if the continuity of the correlation peak is poor, the process returns to step S4 and executes step S4 again.

The periodicity / phase difference judging section 36 detects a phase difference between adjacent preambles. First, a representative value of each preamble PR1 to PR4: (MAX + MIN)
/ 2 is calculated (S6). (The representative values are t1 to
This corresponds to t4. ) It is determined whether or not the difference between representative values between adjacent preambles is within a range of a phase difference ± a variation (S7). (The difference between the representative values corresponds to Δ1 to Δ4 in FIG. 6.) If the condition of S6 is not satisfied, the process returns to step S4 and repeats steps S4 to S7 again.

As described above, in the present embodiment, the continuity of the correlation peaks in the preamble (the number of correlation peak positions in the same period) and the peak positions (phase differences) between adjacent preambles are calculated to obtain noise and noise. The resistance to interference waves is improved, and the synchronization acquisition performance described later is improved.

Even when periodic noise (jamming radio waves) is mixed in the PN codes of the preambles PR1 to PR4, if the variation of the phase difference is within the range determined by the equation in S7. Goes to step S8. That is, if the variation range of the continuous correlation peak is suppressed only within the predetermined range in S5, periodic noise may be included. When such periodic noise is included, it occurs, for example, when another spread spectrum communication system using the same frequency band operates at a short distance.

Steps S8 and subsequent steps are steps that are adopted assuming that periodic noise is included, and focus on the phase difference between adjacent preambles. Steps S6 and S7 are processing relating to the portion (b) of FIG. Steps S4 to S7 always operate so that they can operate immediately after the timeout.

Synchronous acquisition is performed based on the representative value of the final preamble PR4 (S8), and code detection (Code d) is performed.
eject: CD) (S9). That is, steps S8 and S9 are processing for shifting to synchronous acquisition if the phase difference between the preambles is also OK following the continuity of the preambles. The “code detection” includes both code synchronization and synchronization acquisition.

The timer (T) of step S2 is started (S10), and if the frame detection unit 39 (FIG. 4) can perform pattern matching of the frame of step S11, the process proceeds to step S13. If the frame pattern cannot be matched in step S11, it is determined whether or not a timeout has occurred (S12). If it is not time-out, the process returns to step S11. If it is time-out, the process returns to step S2, and all the processes after step S2 are redone. The timer in step S10 is a timer during which a frame is detected. Even if it is OK until the synchronization acquisition in S8, depending on the radio wave environment, the timeout situation in step S12 is quite possible.

The frame detector 39 detects a frame (Fl
a. Detect: FD) is output (S13), and the data demodulation unit 38 (FIG. 4) synchronizes with a receive timing clock (Receive timing: RT) (S14) to receive data (Receive data).
a: RD) is output and the processing ends. In this step S11,
Steps S13 and S14 are the transition stages to data demodulation.

A. Range of phase difference variation between preambles A register is used to set the range of phase difference variation between adjacent preambles in step S7. For example, a range of 0 to 15 (4 bits) is set. Then, it is calculated whether or not the predicted correlation peak position calculated based on the phase difference data between the preambles set in another register is within a set range in a plus or minus direction within a set range. If the phase difference between adjacent preambles is simultaneously detected in the set variation range, a certain output terminal goes to “H” level (asynchronous output). As a result, since the continuous periodicity of the maximum correlation peak position and the phase difference between the preambles are detected within the set range, the communication system (MDM2) using the DMF in step S9 shown in FIG. /
The CD is output, and the process proceeds from the initial synchronization process to the data demodulation process after step S10.

B. FIG. 7 shows how to determine the range of variation in determining the continuous periodicity of the peak position, and the range of variation in determining the periodicity of the maximum correlation peak position. In the case of determining the above, if the data exists over the start bit (hereinafter referred to as STB) which is the start point of the absolute time, the variation (maximum-minimum) cannot be simply calculated, and special processing is performed. Must be applied. Therefore, it is the threshold value set here that gives a selection condition for determining which process to calculate the variation range. It is set in the range of 0 to 15 (4 bits) (the resolution depends on the system clock), and two thresholds are provided based on the STB. As an example, as shown in FIG. 7, when the set threshold value is “2”, (1 + 2 = 3) and (23−2 = 2)
Threshold values are provided at the two positions of 1). If continuity is detected and all the maximum correlation peak positions are within the set threshold range, S as shown in FIG.
A process in the vicinity of TB is performed to obtain a variation range.

C. STB delay setting value In step S9 in FIG. 5, after / CD output,
In the data demodulation process, the communication system generates a window. A window is created for the STB based on the set position and width information, but a window that straddles the STB cannot be created. Therefore, in order to correspond to the maximum correlation peak that straddles between STBs, a normal STB (No.
rmal-STB), a tentative STB delayed by several chips.
By preparing (Variable-STB),
In the data demodulation process in FIG.
Since the position of the maximum correlation peak is shifted so as not to span between (V-STB), a window can be generated at an appropriate position.

If the synchronization acquisition operation is performed normally, the peak position in the data demodulation process is uniquely determined. Therefore, once the optimum V-STB delay value is determined, it is not necessary to change this register thereafter. Absent. If the maximum correlation peak position does not straddle the STB (N-STB) after synchronization acquisition, "0" may be left as it is. Note that the reference PN code for the DMF 31 is always synchronized with the N-STB,
After synchronization acquisition only inside the IC, V-STB is regarded as a normal STB and signal processing is performed.

In this embodiment, the detection of the correlation peak of the PN code is not performed by using the conventional threshold level.

The reason is that even if the signal is correct, the signal may not exceed the threshold value. When the noise exceeds the threshold, it shifts to code synchronization, and theoretically goes forever after channel identification.
It is conceivable to shorten the timer, but some cycles are necessary, so there is a limit. NG before timeout (trigger by code synchronization)
Since the position of the correct correlation peak is determined, there is a possibility that a malfunction occurs in the middle of the frame pattern (identification 2) after the preamble.

In the present embodiment, one or more preambles are repeated without setting a threshold level, so that a high-speed communication can be performed by specifying a communication partner before demodulating the data part. Media access can be reliably performed even under conditions where the radio wave environment is not very good. The present embodiment is useful for communication in a place where the radio wave environment is poor. For example, wireless communication between a command device and an unmanned carrier in a factory, and point-of-sale information management (P
OS) system and the like.

FIG. 8 is a flowchart showing the synchronous tracking operation. This synchronous tracking operation is related to the timing generator 37 including synchronous tracking.

The vector synthesis / peak hold unit 35 (FIG. 4) is provided with a memory for storing the peak hold value of the correlation peak. It should be noted that in the processing steps, there is a place where a lower frequency is handled (for example, the peak hold value in the memory is updated at a frequency corresponding to the PN code cycle length). The control uses the maximum frequency (the sampling frequency of the A / D converter).

As described in the synchronization acquisition operation, the periodicity and the phase difference of a series of correlation peaks are calculated, and the periodicity and the phase difference are determined using preset values (S4 to S4 in FIG. 5). S7) If the periodicity and the phase difference are OK, the flag (/ CD) is output assuming that the synchronization has been established (S9 in FIG. 5). At the same time, the final preamble P
The correlation peak position obtained in R4 is stored in the memory of the vector synthesis / peak hold unit 35 (S21).

The window generator 34 (FIG. 4) samples a desired interval before and after the window width information and the correlation peak position information stored in the memory (for example, sampling in the front-back direction with the correlation peak position information as the center). Clock n
The window is generated at intervals of a cycle. This sampling clock is output from a sampling clock generator provided in the control unit 22 (FIG. 2).

Before the output of the flag (/ CD), the detection range of the correlation peak by the window is not set (S2).
2).

The timing generator 37 including the synchronization tracking
The correlation peak position information (Ta) calculated for each period of the PN code is stored in the peak position information (T
c) (S23).

The timing generator 37 including synchronous tracking has an up / down counter.

As a result of the comparison in S23, the timing generator 37 including the synchronization tracking changes the counter value of the up / down counter under the following conditions.

If the calculated correlation peak position is smaller than the correlation peak position in the memory (Ta <Tc), the counter value is counted down (−1).

If the calculated correlation peak position is larger than the correlation peak position in the memory (Ta> Tc), the counter value is counted up (+1).

When the calculated correlation peak position is equal to the correlation peak position in the memory (Ta = Tc), the counter value is not changed.

At the start, the counter range of the up / down counter is set to 0 to N, and the initial value of the up / down counter is set to N / 2. N of this counter range is set at the initial stage and can be arbitrarily changed, but is not changed during the operation (S24). As described above, the direction of the shift of the correlation peak position is detected by simply comparing the calculated correlation peak position with the correlation peak position stored in the memory. Can be detected.

Next, when the up / down counter satisfies the following conditions, the window is controlled. Specifically, the window is shifted in a direction to correct the shift of the correlation peak position.

When the up / down counter value becomes 0, the position of the window is shifted forward by one sampling clock cycle (a predetermined fixed amount) from the position up to now.

When the up / down counter value becomes N, the position of the window is shifted backward by one sampling clock cycle (a predetermined fixed amount) from the previous position. (S25). As described above, since the correlation peak position is shifted by one period of the sampling clock,
Fine control becomes possible, and accurate synchronous tracking becomes possible.

At the same time as the control in S25, the latest correlation peak position is input (updated) to the memory, and the counter value of the up / down counter is set to N / 2 (S2).
6). Then, the process returns to S23 and the control of S23 to S26 is repeated.

The value of the counter range N depends on the difference in the moving speed of the correlation peak position (for example, the amount of deviation of the system frequency between the transmitting side and the receiving side) and the control amount (here, the sampling frequency is the resolution). Just set it.

According to the synchronous tracking method of this embodiment, there is no need to calculate the amount of deviation of the correlation peak position.
Since only the direction of the shift of the correlation peak position is detected and the correlation peak position is shifted in the direction of the shift by one period of the sampling clock, the correlator 20 is not required in the correlator 20.

Accordingly, the circuit configuration of the correlation device 20 is simplified, the manufacturing cost of the receiver R can be reduced, and the size of the receiver R can be reduced.

It should be noted that the latest correlation peak position for updating may not be changed depending on the situation. For example, a correlation peak position at the time when the up / down counter value becomes 0 or N may be adopted, or an average value of correlation peak positions for several cycles in the past may be used.

The present invention is not limited to the above-described embodiment, but can be variously modified without departing from the scope of the claims.

In this embodiment, the synchronous tracking is performed by shifting the window. However, the present invention is not limited to this. The synchronous tracking may be performed by shifting the correlation peak position.

Although four preambles PR1 to PR4 are described, the number of preambles may be one, two, three, or five or more. In this embodiment, a digital matched filter (correlator) is used.
An analog correlator (for example, a convolver) may be used. Also,
In the present embodiment, the PN of each preamble PR1 to PR4 is
The phases of the codes may be the same.

[0089]

According to the first aspect of the present invention, only the direction of the shift of the correlation peak position is detected, and the synchronous tracking is performed by shifting the correlation peak position in the direction of the shift by a predetermined amount. A correlator for detecting the amount of deviation is not required, so that the manufacturing cost of the receiving device can be reduced and the receiving device can be downsized.

According to the second aspect of the present invention, the direction of the shift of the correlation peak position is detected by simply comparing the calculated correlation peak position with the correlation peak position stored in the memory. The direction of the shift of the correlation peak position can be easily detected.

According to the third aspect of the present invention, it is determined that the correlation peak position is shifted when the counter is shifted by a predetermined number of times in the same direction using the counter. Therefore, a sudden shift of the correlation peak position is ignored. , The deviation of the true correlation peak position can be detected. Therefore, accurate synchronization tracking can be performed.

According to the fourth aspect of the present invention, since the correlator includes the digital correlator which is lower in cost and easier to miniaturize than the analog correlator, the manufacturing cost and the miniaturization of the receiver can be reduced. Become.

According to the fifth aspect of the present invention, when the correlation peak position is shifted by a predetermined amount, the correlation peak position is shifted by one period of the sampling clock, so that fine control can be performed and accurate synchronization can be achieved. Tracking becomes possible.

According to the sixth aspect of the present invention, since a digital matched filter is used, the cost is lower than that of an analog correlator, and the size can be easily reduced. Is possible. Further, since the correlation peak position is synchronously tracked by shifting the window, control becomes easy.

According to the seventh aspect of the present invention, since the window is shifted by one period of the sampling clock, fine control becomes possible, and accurate synchronous tracking becomes possible.

According to the present invention, the periodicity of the correlation peak between the pseudo-noise code in the preamble of the transmission signal and the reference pseudo-noise code is detected without setting the threshold level. Therefore, since a means for calculating a predetermined number of correlation peaks is provided, prior to demodulating the data portion,
Only by calculating the number of correlation peaks, it is possible to specify the communication destination and perform communication, and it is possible to almost certainly perform high-speed media access even under conditions where the radio wave environment is not very good.

Further, since the correlation device performs synchronization tracking by detecting only the direction of the phase shift, a correlator for detecting the amount of the shift is not required, so that the manufacturing cost of the receiver can be reduced, and the reception cost can be reduced. The size of the device can be reduced.

According to the ninth and tenth aspects of the present invention, since a plurality of preambles are provided in a transmission signal, the period of the correlation peak between the pseudo-noise code in each preamble and the pseudo-noise code for reference is provided. By calculating the predetermined number of correlation peaks by detecting the characteristic and calculating the difference between the positions of the correlation peaks in the respective preambles, the data part is demodulated even if the jamming radio wave has periodicity, for example. Can identify and communicate with the recipient prior to
Even under conditions where the radio wave environment is not so good, high-speed media access can be reliably performed.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a schematic configuration of a transmission device of a spread spectrum communication system according to an embodiment.

FIG. 2 is a block diagram illustrating a schematic configuration of a receiving device of the spread spectrum communication system according to the present embodiment.

FIG. 3 is a diagram illustrating a frame configuration of a signal transmitted from a transmission device.

FIG. 4 is a block diagram illustrating a configuration of a correlation device and a demodulation unit of FIG. 2;

FIG. 5 is a flowchart illustrating signal processing related to a synchronization acquisition operation.

FIG. 6 is a diagram illustrating an example of a PN code in a signal frame.

FIG. 7 is a diagram illustrating a method of obtaining a variation range in determining the continuous periodicity of the maximum correlation peak position.

FIG. 8 is a flowchart illustrating signal processing related to a synchronous tracking operation.

[Explanation of symbols]

 T transmitter R receiver 20 correlator 31 digital matched filter (correlator)

Claims (10)

[Claims] 1. A transmitting apparatus for transmitting a transmission signal by performing spread spectrum modulation using a pseudo noise code, and receiving the spread spectrum modulated signal, and comparing a pseudo noise code of the received signal with a pseudo noise code for reference. In a spread spectrum communication system comprising a receiving device including a correlator for detecting a correlation peak, a means for detecting the direction of the deviation of the correlation peak position when a deviation occurs in the correlation peak position detected by the correlator. And means for shifting the correlation peak position by a predetermined amount in a direction to correct the shift when the shift of the correlation peak position is detected by this means, and synchronously tracking the correlation peak position by each means. A spread spectrum communication system having a configuration. 2. A memory for storing the correlation peak position, wherein the correlation peak position calculated for each cycle of the pseudo-noise code is compared with the correlation peak position stored in the memory, and the correlation peak position is calculated. 2. The spread spectrum communication system according to claim 1, wherein the direction of the shift is detected. 3. A counter for counting the number of times the correlation peak position shifts in the same direction, wherein when the detected correlation peak position shifts a predetermined number of times in the same direction, the correlation peak is corrected in a direction to correct the shift. The spread spectrum communication system according to claim 1, wherein the position is shifted by a preset amount. 4. The spread spectrum communication system according to claim 1, wherein said correlation device includes a digital matched filter. 5. The spread spectrum communication system according to claim 4, wherein when the correlation peak position is shifted by a predetermined amount, one cycle of the sampling clock output from the sampling clock generator is shifted. 6. A transmitting apparatus for transmitting a transmission signal by performing spread spectrum modulation using a pseudo noise code, and receiving the spread spectrum modulated signal and generating a pseudo noise code of the received signal and a pseudo noise code for reference. A spread spectrum communication system comprising: a correlation device that detects a correlation peak; and a reception device that includes a correlation device that detects a correlation peak. Means for storing the correlation peak position in a memory and generating windows at desired intervals before and after based on the correlation peak position information stored in the memory; and a correlation calculated for each cycle of the pseudo-noise code. Means for comparing the peak position information with the correlation peak position information stored in the memory; Means for shifting the window generated at a desired interval back and forth according to the result of the comparison by a predetermined amount in any of the front and rear directions, and the means for synchronously tracking the correlation peak position by each means. A spread spectrum communication system, comprising: 7. The spread spectrum communication system according to claim 6, wherein when the window is shifted by a preset amount, one cycle of the sampling clock output from the sampling clock generator is shifted. 8. A transmitting apparatus for transmitting a transmission signal having a frame configuration in which data on information to be transmitted following a preamble is arranged by using a pseudo noise code and transmitting the transmission signal, and a transmission signal subjected to the spread spectrum modulation. And a correlation device for detecting a correlation peak between a pseudo-noise code of the received signal and a pseudo-noise code for reference, and a correlation peak detected by the correlation device, wherein the pseudo-noise is included in a preamble of the transmission signal. A receiver including means for calculating the number of peaks of correlation peaks appearing with a periodicity between the code and the reference pseudo-noise code, and when the correlation peak position detected by the correlation device is shifted Means for detecting the direction of the shift of the correlation peak position, and a direction for correcting the shift when the shift of the correlation peak position is detected by the means. Means for shifting the correlation peak position by a predetermined amount, and tracking the synchronization of the correlation peak position by each means. 9. The spread spectrum communication system according to claim 8, wherein a plurality of preambles of the transmission signal are provided. 10. The spread spectrum communication system according to claim 8, wherein the pseudo noise codes in each preamble are the same but are shifted in phase.