JPH03181238A - Data transmission system applying spectrum diffusion communication - Google Patents

Abstract

PURPOSE:To secure the reliability of communication to the increase of the transmitting distance by transmitting two pseudo random code series which are shifted to each other so as to largely increase the mutual correlative function toward the minus side in accordance with the data bit. CONSTITUTION:Both M1 and M0 series signals which are shifted to each other so that the mutual correlation phi10 between both series signals is largely increased toward the minus side are transmitted by the M series generators 56 and 60 provided to a data carrier 12. That is, the process gain can be increased as long as the self-correlative function phi11 is satisfactorily increased at the plus side and at the same time the correlation phi10 is increased at the minus side respectively in terms of the correlative value phi calculated by the correlative calculation at the side of a reader/writer.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a data transmission system using spread spectrum communication in which data is transmitted in a non-contact manner between units arranged separately using spread spectrum communication technology.

[Prior Art] In recent years, so-called data carriers have been developed in which a data carrier equipped with a non-volatile memory and short-range communication function is attached to a moving "object" and information is read from and written to the "object" without contact. Technology is showing remarkable progress.

Specifically, expansion of applications to the FA field, logistics field, and security field is being considered, and further miniaturization of data carriers is desired.

Under these trends, due to constraints in terms of operating environment, shape, lifespan, etc., methods of incorporating batteries into data carriers have been avoided, and instead of batteries, magnetic coupling of coils wound around ferrite cores has been used. A method is used to receive energy electromagnetically from the outside through electromagnetic induction.

[Problem to be solved by the invention] However, since the inductively coupled coil that can be used in a miniaturized data carrier is small and the induced electromotive force generated in the coil is small, the communication power from the data carrier is inevitably small. turn into.

Furthermore, when data carriers are used in factories, the radio wave environment is quite poor, and the influence of noise and interference is large, resulting in deterioration of communication reliability, which is a major problem.

In other words, since inductively coupled coils are so-called coupled transformers, the magnetic force decreases in inverse proportion to the cube of the distance.As a result, unless the coil spacing is kept to a few millimeters or less, it will be difficult to operate in a factory with a lot of external noise. stable communication cannot be guaranteed.

Therefore, the inventor of the present application has proposed a method that dramatically expands the transmission gap interval by applying spread spectrum communication technology to the electromagnetic inductive coupling method (Japanese Patent Application No. 63-2
No. 15472, etc.).

For example, two types of M-sequence generators are prepared on the transmitting side, and different M-sequence signals are transmitted depending on data bits 0 and 1. On the receiving side, the two M-sequence signals from the transmitting side are stored in memory as reference values, and after sampling the received signal at a predetermined period, correlation calculations are performed in parallel with each of the two M-sequence reference values. When comparing the respective correlation values, the correlation value when the received signal and reference value sequences match and the peak value due to autocorrelation is obtained is larger, so the data bit 0 corresponding to that reference value is Or it outputs 1.

In such a data transmission method that calculates the presence or absence of autocorrelation using two types of M-sequence signals, the signal arrangement is 1 for the autocorrelation value when the arrangements match between the two M-sequence signals. The cross-correlation value becomes extremely small when there is a deviation (
For an M sequence with a word length of 2N-1, the S/N ratio for a received signal of an M sequence that is the same as the reference value is extremely high.

However, as the transmission distance between the coils increases to 8 mm, 10 mm, etc., the S/N error rate drops significantly, causing the problem that communication reliability cannot be guaranteed.

The present invention was made in view of these problems, and
It is an object of the present invention to provide a data transmission method using spread spectrum communication that further improves communication reliability as the transmission distance increases and further simplifies correlation calculation processing.

[Means for Solving the Problems] First, the present invention is directed to a data transmission system in which bit data is transmitted bit by bit from the transmitting unit 12 to the receiving unit 10 in response to a bit transfer request. In addition, the reference numerals in the drawings of the embodiments are also shown.

In this data transmission method, the sending unit 12 has the following:
generating a first pseudo-random sequence signal corresponding to one logic of the data bits, for example data bit 1, and
An M sequence generator (52, 54, 56, 511, 60) is provided which generates a second pseudo-random sequence signal in response to the other logic of the data bits, for example data bit O. is a correlation circuit (TO
, 72, 74) and a determination circuit (7678, 80) that compares the output value φ of the correlation circuit with a predetermined threshold value δ to determine the logical value of the data bit.

In the present invention for a data transmission system using such spread spectrum communication, the pseudo-random generator is configured to generate a value of a cross-correlation function φ10 between the first pseudo-random sequence signal and the second pseudo-random sequence signal. It is designed to generate two pseudo-random sequence signals in which the value is largely on the negative side.

Specifically, M-sequence signals or GOLD-sequence signals are generated that are mutually shifted so that the cross-correlation function φ10 is largely on the negative side.

Further, the random sequence signal generator generates a Manchesterized pseudo-random sequence code waveform.

Furthermore, the threshold value δ of the discriminator provided in the receiving unit IO is
It is made to change according to the magnitude of received energy.

[Operation] In the data transmission system using spread spectrum communication of the present invention having such a configuration, two pseudo-random sequences that are shifted from each other such that the cross-correlation function φlO appears largely on the negative side are Since the code sequence is transmitted according to data bits 1 and 0, the process gain Pc given as the difference between the autocorrelation function φ11 and the cross-correlation function φ10 of the transmission sequence code can be increased, and the S/N error can be reduced as the transmission distance increases. You can improve your rate.

In addition, by Manchester-izing the code waveform of the pseudo-random series and inverting the waveform even in a continuous state of bits 1 and 0, it is possible to improve energy loss due to distortion of the received waveform due to electromagnetic inductive coupling and obtain a large process gain Pc.

Furthermore, the transmission distance is increased by determining the transmission distance based on the amplitude of the received waveform, etc., and changing the threshold δ for determining data bits 1 and 0 from the output value φ of the correlation circuit according to the transmission distance. communication reliability can be further improved.

[Embodiment] FIG. 1 is a block diagram showing an embodiment of the present invention.

In FIG. 1, 10 is a reader/writer connected to the host side, and a data carrier 12 as a portable unit is prepared for this reader/writer 10, and as shown in the figure, when reading and writing, reader writer 10
It is placed with a transmission distance of several millimeters between the two.

The reader/writer 10 is provided with a CPU-based control unit 16, and the control unit 16 accesses the data carrier 12 for data writing or data succession with the host CPU via the interface 14.

If we take the communication directed to the data carrier 12 as an example,
For example, data transferred from the host CPU to the control unit 16 via the interface 14 is converted into serial data by the P/S converter 18 and provided to the FSX modulation circuit 20. An oscillator 22 is connected to the FSX modulation circuit 20, and FSK modulation is performed using a frequency F1 for data bit 1 and a frequency FO for data bit O, for example. The FSK modulated signal is power amplified by a power amplifier 24, and then passed through a transmission/reception changeover switch 26 to a coil 3 wound around a core 28.
0. The transmission/reception changeover switch 26 is controlled by the control unit 16 to be turned on when transmitting to the data carrier 12 and turned off when receiving from the data carrier 12.

Electric power is induced in the coil 34 of the data carrier 12 in response to the high frequency magnetic field generated by supplying the FSK modulated signal to the coil 30. The electric power induced in the coil 34 is supplied to a DC power supply voltage by a power rectifier circuit 36 to supply power to the internal circuit. Further, the signal induced in the coil 34 is input to the frequency discrimination circuit 38, which demodulates the FSK modulated signal consisting of frequencies Fl and FO to restore the original data bits 0. Outputs 1.

The data bits output from the frequency discrimination circuit 38 are S/
It is converted into parallel data by the P conversion circuit 40 and sent to the control unit 4.
2, the control unit 42 determines the command or data from the received data, and if it is a write command, the EEP
Write data to the non-volatile memory 44 using ROM, and if it is a read command, the specified non-volatile memory 4
Read data from address 4.

Next, communication from the data carrier 12 to the reader/writer 10 will be explained.

Read data read from the nonvolatile memory 44 by read access by the control unit 42 is converted into serial data by the P/S conversion circuit 46 and provided to the signal generator 48 .

The signal generator 48 generates different pseudo-random sequence signals based on the oscillation output of the oscillator 50 according to the data bit 0.1, as will be explained later. For example, data bit 0 generates an MO sequence signal of a predetermined word length, and data bit 1 generates an M1 sequence signal of the same word length. The pseudorandom sequence signal generated by the signal generator 48 is supplied to the coil 34 to induce a high frequency magnetic field, and electric power is induced in the coil 30 on the reader/writer 10 side. At this time,
The transmission/reception selector switch 26 is turned off as shown in the figure.
The signal induced in the coil 30 is amplified by a preamplifier 82 and then applied to a correlator 84 . The correlator 84 has one of the two pseudo-random sequence signals of the 12 data carriers, for example, a replica of the M1 sequence signal, the M1=sequence signal, as a reference value, and the correlator 84 calculates the correlation with the received signal. The correlation value φ is obtained, and compared with a predetermined threshold value δ set in advance, data bit 0.1 is determined and output.

The data bits obtained based on the correlation calculation of the correlator 54 are converted into parallel data by the S/P conversion circuit 56 and output to the control section 16. Note that the control unit 16 is provided with a data buffer 58, which stores data from the host CPU in the data buffer 58 and then transfers it to the data carrier 12 side, and stores received data from the data carrier 12 side in the data buffer 58. After that, it is transmitted to the host CPU side. Non-volatile memory 44 of normal data carrier 12
When writing and reading data to, for example, taking communication from the reader/writer 10 to the data carrier 12, the reader/writer 10 transmits data one bit at a time each time a bit transfer request is received from the data carrier 12.

FIG. 2 is a block diagram of an embodiment of a data transmission method using spectrum communication of the present invention, which is used when transmitting data from the data carrier 12 to the data writer 10 in FIG. 1.

First, the data carrier 12 is connected to the signal generator 48 shown in FIG.
This shows a modulation circuit section consisting of.

That is, in the data carrier 12, data d(t) having a value of bit 1°0 is provided to a discriminator 52, which determines whether the value of data d(t) is 1 or O.

If d(t)=O, an output is generated in the multiplier 54, and an MO sequence signal is generated from the M sequence generator 56 as a first pseudo-random sequence signal. On the other hand, d(t)=
If it is 1, it is output to the multiplier 58, and the M sequence generator 60 outputs M
1 series signal is generated.

The Ml and MO sequence signals generated by the M sequence generators 56 and 60 have a length of, for example, 63 words (=26-1), and are specifically composed of a six-stage shift register consisting of shift bits bO to b5 and a shift register. It can be constituted by an EX-OR gate that inputs two inputs, the output and the output of an arbitrary shift stage, calculates an exclusive OR, and inputs the result to the input shift stage.

The M1 sequence signal or MO sequence signal obtained via the multiplier 54 or 58 is applied to the multiplier 62, which spread spectrum modulates the IMHz frequency signal from the signal generator 64. For example, the code waveform of the Ml, MO sequence signal is
The generated signal from the signal generator 64 is multiplied by +1 for bit 1 and -1 for bit 0, and spread spectrum modulation is applied. The spread spectrum modulation signal from the multiplier 62 is supplied to the coil 34 to generate a high frequency magnetic field on the reader/writer 10 side.

The league writer 10 is the coil 34 of the data carrier 12.
A signal induced in the coil 30 by the high frequency magnetic field is inputted via an attenuator 66 and converted into digital data by an A/D converter 68. This A/D converter 68 uses, for example, a 20 MHz sampling clock.
Output bit data. The output of the A/D converter 68 is given to a shift register 70, and the shift register 70 receives 6 of the Ml and MO sequence signals generated on the data carrier 12 side.
It has a number of shift stages to store sampling data for three words. The 63-word length sampling data stored in the shift register 70 is given to the multiplier 72, and M1' as a correlation replica stored in the reference value memory 74 is applied to the multiplier 72.
A coded sequence, that is, an Ml'' sequence signal which is a copy of the M1 sequence signal generated by the M sequence generator 56 on the data carrier 12 side is generated.The number of Ml'' sequence signal data stored in this reference value memory 74 is also The data is stored as data having the same resolution as the number of shift stages of the shift register 70, and a multiplier 72 multiplies the output of each shift stage of the parallel sampling data of the shift register 70 by the output of each memory stage of the reference value memory. Let's do it.

The output of the multiplier 72 is given to an adder 75 to calculate the sum, and the output of the adder 75 becomes the correlator output φ. That is, A/D converter 68, shift register 70 . By the multiplier 72, reference value memory 74 and adder 75, φ=ΣS (n) ・R(n) ... (1)
However, S (n) performs a correlation calculation in which sampling data R(n) becomes reference value data.

The correlation value φ output from the adder 75 is given to the discrimination circuit 76 and compared with a predetermined threshold δ, and if the correlation value φ is larger than the threshold δ, the output circuit 78 outputs data d (t)=1. is output, and on the other hand, the correlation value φ is output from the threshold δ
If d(t)=O is small, the output circuit 80 outputs data d(t)=O.

Regarding the data transmission method using spread spectrum communication shown in FIG. 2, in the present invention, data carrier 1
The M sequence generators 56 and 60 provided in 2 transmit Ml and MO sequence signals shifted from each other so that the cross-correlation φ10 between the M1 sequence signal and the MO sequence signal appears largely on the negative side.

That is, the process gain P in the data transmission system of the present invention. Then, P6=φ11Cτ)−φ10(τ) is defined.

Here, φ11 represents an autocorrelation function when the transmission pattern is Ml and the correlation replica is Ml'', and φ10 represents a cross-correlation function when the transmission pattern is MO and the correlation replica is Ml-.

That is, in the data transmission method of the present invention, in order to extend the transmission distance and ensure communication reliability, the autocorrelation function φ11 must be sufficiently large on the plus side as the correlation value φ calculated by the correlation calculation on the league writer 10 side. Moreover, if the cross-correlation function φ10 is large on the negative side, the process gain P given by the above-mentioned equation (2). can be made larger. In this way, the process gain P. If you can make it larger, +
By setting the threshold value δ to be located between φ11 and −φlO, communication reliability can be improved as the transmission distance increases.

Also, process gain P. If is large, change the sign to 2
It is also effective when assigning multiple values greater than the value.

Next, in the second embodiment of the present invention, GOLD codes are used instead of the Ml and MO sequence signals shown in FIG. That is, in order to increase the process gain, the present invention
This method transmits two code sequences shifted so that the correlation function φ10 is largely on the negative side, depending on the data bit, but since the number of M sequences is limited, the negative side value of φ10 that is so large is transmitted. You can't get it. Therefore, in the second embodiment of the present invention, a GOLD code with a large degree of freedom is introduced to obtain a larger value of the cross-correlation function φ10 on the negative side.

Next, as a third embodiment of the present invention, Ml, M generated in the M sequence generator 56, 60 on the data carrier 12 side in FIG.
Manchesterize the O series code waveform.

That is, as shown in FIG. 3(a), for example, a code waveform in which data bits invert to 0 after three consecutive data bits from the league writer 10 side in FIG.
data carrier 12
In the coil 34 on the side, a received waveform which is considerably distorted compared to the transmitted rectangular wave shown on the right side of FIG. 3(a) is obtained. This distortion of the received waveform is not so great when the transmitted waveform is inverted bit by bit, but as shown in Figure 3(a), for example, when data bits 1 are continuous, the received waveform becomes considerably distorted. , the energy loss becomes large, and therefore the positive value of the autocorrelation function φ11 obtained on the receiving side cannot be set very large.

Therefore, in the third embodiment of the present invention, for example, when data bits 1 are consecutive as shown in FIG. 3(b),
Manchesterization is performed to create a code waveform that is inverted in the middle for each data bit, and this Manchesterization prevents continuous transmission of bits 1 and 0 and reduces distortion as shown in the received waveform on the right side of Figure 3(b). The energy loss is minimized and the energy loss is improved to obtain a large positive value of the autocorrelation function.

By Manchester-izing (bit expansion) the code waveform of the pseudo-random sequence signal generated on the transmitting side, it is possible to reduce energy loss and increase the process gain P6 itself, further improving communication reliability over extended transmission distances. It can be improved.

Specifically, instead of the 63 word length (=26-1) generated by the M sequence generator 56.60 in FIG.
=2'-1) is generated, Manchester-ized with 2 bits per code, and finally a 63-word Manchesterized code sequence is generated.

This Manchesterization is applied to G in the second embodiment of the present invention.
The same procedure can be applied to the OLD code.

According to experiments conducted by the inventor of the present invention, the Manchester GOLD code has the largest process gain with respect to the transmission distance, followed by the Manchester M-sequence code, then the GOLD code, and then the Manchester GOLD code.
Furthermore, it was confirmed that the order is the M-sequence code.

It has been confirmed that such Manchesterization significantly improves the process gain when the Manchester GOLD code is used in the present invention. In addition, in the Manchester GOLD code, the cross-correlation function φ10 is quite large and goes on the negative side, so it can be brought close to the same absolute value as the autocorrelation function φ11, which goes on the positive side. Therefore, when determining data bits from correlation values, The value of the threshold value δ can be set considerably small, which can greatly contribute to expanding the transmission distance.

Next, as a fourth embodiment of the present invention, if there is a relationship in which the process gain decreases as the transmission distance increases, and the threshold δ for determining data bit 1.0 from the correlation value φ is a fixed value, The threshold value is determined to be the optimum value at a transmission distance of, for example, 6 mm, so if the transmission distance is 8 mm,
When enlarged to 10 mm, the characteristics deteriorate considerably. Therefore,
In the fourth embodiment of the present invention, the transmission distance is determined based on the received energy, such as the amplitude of the received waveform, and the optimal threshold value δ is determined according to the transmission distance by changing the threshold value δ according to the transmission distance. By setting this, communication reliability can be ensured even as the transmission distance increases.

In the embodiment shown in FIG. 2, one system of correlation calculation circuit is provided on the reader/writer 10 side, which is the receiving side, and the correlation value is determined based on the threshold value δ, and data bits 1 and 0 are demodulated. However, the M of the data carrier 12 is on the reader/writer 10 side.
Regarding the O series signal, two systems are provided with the same correlation circuit using MO= as a correlation replica, and data bit 1.0 is determined by comparing the magnitude relationship of the correlation values of the two systems of correlation circuits. You can also do this.

In addition, although the above embodiment takes as an example a case where spread spectrum communication is used for communication from the data carrier 12 to the reader/writer 10, conversely, when the reader/writer 10
Of course, spread spectrum communication may be used for communication from the data carrier 12 to the data carrier 12 and in both directions.

Furthermore, although the above embodiments take the M sequence and the GOLD code as examples, the present invention is not limited thereto, and any suitable pseudorandom sequence can be used as is.

[Effects of the Invention] As explained above, according to the present invention, two pseudo-random code sequences shifted from each other so that the cross-correlation function appears largely on the negative side are transmitted in accordance with data bit 1.0. By increasing the process gain given as the difference between the autocorrelation function and the cross-correlation function, communication reliability can be guaranteed even as the transmission distance increases.

In addition, by transmitting the code waveform of the pseudo-random sequence in Manchester format, it is possible to improve energy loss due to distortion of the received waveform due to electromagnetic inductive coupling and obtain a large process gain.

Furthermore, by determining the transmission distance based on the amplitude of the received waveform, etc., and setting the optimal threshold for determining data bits from the correlation calculation output value according to the transmission distance, communication reliability can be improved as the transmission distance increases. It is possible to further guarantee the quality of the product. Furthermore, the amount of correlation calculation processing is halved, and the number of correlation calculators is reduced.

[Brief explanation of drawings]

Figure 1 is an overall configuration diagram of the present invention; Figure 2 is an embodiment configuration diagram showing one embodiment of the present invention;
The figure is an explanatory diagram of the transmission and reception waveforms of the present invention according to Manchester. In the figure, 10: Reader/writer 12: Data carrier 14: Interface 16.42: Control unit (CPU) (Sending side unit) (Receiving side unit) 18.46: P/S conversion circuit 20: FSK modulation circuit 22. 50 Oscillator 24: Power amplifier 26: Transmission/reception selector switch 28.32: Core 30.34: Coil 36: Power supply rectifier circuit 38: Frequency discriminator 40.56: S/P conversion circuit 44: Non-volatile memory (EEPROM) 48: Signal generator 52.76: Discrimination circuit 54.58.62.72: Multiplier 56.60: M-sequence generator 54.56: Reference value memory 64: Signal generator 66: Attenuator 68: A/D converter 70 :Shift register 74:Reference value memory 75:Adder 78.80:Output circuit 82:Preamplifier 84:Correlator 88:Data buffer

Claims (4)

[Claims] (1) Transmit bit data one bit at a time from the transmitting unit to the receiving unit in response to a bit transfer request, and transmit a first pseudo-random sequence signal to the transmitting unit corresponding to one logical value of the data bits. and a pseudo-random sequence generator that generates a second pseudo-random sequence signal corresponding to the other logical value of the data bits, and the receiving unit stores the received signal and a reference value in a memory. a correlation circuit that performs correlation calculation with either the first or second pseudo-random sequence signal;
In a data transmission system using spread spectrum communication, which is provided with a discrimination circuit that compares the output value of the correlation circuit with a predetermined threshold value and discriminates the logical value of the data bit, as the pseudorandom sequence generator, Data using spread spectrum communication, characterized in that two pseudo-random sequence signals are generated in which the value of the cross-correlation function between the first random sequence signal and the second pseudo-random sequence signal becomes large on the negative side. Transmission method. (2) The pseudo-random sequence generator generates M-sequence signals or GOLD-sequence signals that are mutually shifted so that the cross-correlation function of the two pseudo-random sequence signals appears largely on the negative side. A data transmission method using spread spectrum communication described above. (3) The data transmission system using spread spectrum communication according to claim 1, wherein the pseudo-random sequence generator generates a waveform pattern of a Manchester-ized pseudo-random sequence signal. (4) The data transmission method using spread spectrum communication according to claim 1, characterized in that a threshold value of a discriminator provided in the receiving side unit is changed according to the magnitude of received energy.