JP2697935B2 - Data transmission method using spread spectrum communication - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention 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 and separated using spread spectrum communication technology.

[Related Art] In recent years, a so-called data carrier in which a non-volatile memory and a data carrier having a short-distance communication function are attached to a moving “thing” and information is read and written to and from the “thing” in a non-contact manner. Technology is making significant progress.

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

In this trend, due to restrictions on the operating environment, shape, life, etc., avoid the method of incorporating a battery in the data carrier, and use magnetic coupling of a coil wound around a ferrite core instead of the battery A method has been adopted in which energy is supplied electromagnetically from the outside by electromagnetic induction using the communication medium described above.

[Problems to be Solved by the Invention] However, since the inductive coupling coil that can be used in the miniaturized data carrier is small and the induced electromotive force generated in the coil is small, the communication power from the data carrier is necessarily small. turn into.

When a data carrier is used in a factory, the radio wave environment is considerably poor, the influence of noise and interference is large, and the deterioration of communication reliability is a serious problem.

That is, in the inductive coupling coil, since it is a so-called coupling transformer, the magnetic force decreases in inverse proportion to the cube of the distance,
As a result, unless the coil interval is suppressed to several millimeters or less, stable communication in a factory with a lot of external noise cannot be guaranteed.

The inventor of the present application has proposed a method of applying the spread spectrum communication technique to the electromagnetic induction coupling method to greatly increase the transmission gap interval (Japanese Patent Application No. 63-21).
No. 5472).

For example, two types of M-sequence generators are prepared on the transmitting side, and different M-sequence signals are transmitted according to data bits 0 and 1. On the receiving side, the two M-sequence signals on the transmitting side are stored in a memory as reference values, and after the received signal is sampled at a predetermined cycle, the correlation calculation is sequentially performed in parallel with each of the two M-sequence reference values. When the correlation values are compared with each other, the correlation value at the time when the sequence of the received signal matches the reference value and the peak value due to the autocorrelation is obtained is larger, so that the data bit 0 corresponding to the reference value Or 1 is output.

In the data transmission method for calculating the presence / absence of autocorrelation using such two types of M-sequence signals, the signal arrangement is one for the autocorrelation value when the arrangement is identical between the two M-sequence signals. very S / N ratio for the cross-correlation value is very small will (2 ^N -1 word length of -1/2 ^N -1 in M-sequence), reference values and the received signal of the same M-sequence when shifted at any time high.

However, when the transmission distance between the coils increases to 8 mm or 10 mm, the drop in the S / N error rate increases, and there is a problem that communication reliability cannot be guaranteed.

The present invention has been made in view of such problems, and provides a data transmission method using spread spectrum communication that further improves communication reliability with respect to an increase in transmission distance and further simplifies correlation calculation processing. The purpose is to do.

[Means for Solving the Problems] First, the present invention is directed to a data transmission system for transmitting bit data one bit at a time to a transmitting unit 10 in response to a bit transfer request from a transmitting unit 12. The reference numerals in the drawings of the embodiments are also shown.

In this data transmission method, one logic of data bits, for example, data bit 1
And generates a first pseudo-random sequence signal in response to the other logic of the data bit, for example, data bit 0
, An M-sequence generator (52, 54, 56, 58, 60) for generating a second pseudo-random sequence signal is provided, while the receiving unit 10 stores the received signal and a memory as a reference value in a memory. A correlation circuit (70, 72, 74) for performing a correlation calculation with one of the first and second pseudo random sequence signals, and comparing an output value φ of the correlation circuit with a predetermined threshold δ. (76, 78.80) for determining the logical value of the data bit.

According to the present invention, a data transmission method using spread spectrum communication according to the present invention, wherein the pseudo-random generator has a value of a cross-correlation function φ10 between a first pseudo-random sequence signal and a second pseudo-random sequence signal. Are generated to generate two pseudo-random sequence signals that largely appear on the minus side.

Specifically, an M-sequence signal or a GOLD-sequence signal shifted from each other so that the cross-correlation function φ10 largely appears on the negative side is generated.

The random sequence signal generator generates a Manchesterized pseudo random sequence code waveform.

Further, the threshold value δ of the discriminator provided in the receiving unit 10 is
It is changed according to the magnitude of the received energy.

[Operation] In the data transmission system using spread spectrum communication according to the present invention having such a configuration, two mutually shifted random shifts such that the cross-correlation function φ10 largely appears on the negative side as two pseudo-random sequences. from sending code sequence data bits 1 and 0 depending on, you can increase the process gain P _G given as the difference of the autocorrelation function φ11 and cross-correlation function φ10 transmission sequence code, to increase the transmission distance
S / N error rate can be improved.

In addition, by also causing the waveform inversion in a continuous state of bits 1 and 0 Manchester the code waveform of the pseudo random sequence, a large process gain P _G to improve the energy loss due to the distortion of the received waveform caused by electromagnetic induction coupling is obtained .

Further, the extent of the transmission distance is determined based on the amplitude of the received waveform, and the output value φ of the correlation circuit is determined according to the transmission distance.
By changing the threshold δ for discriminating the data bits 1 and 0 from, the communication reliability when the transmission distance is increased can be further improved.

[Embodiment] FIG. 1 is an embodiment configuration diagram showing one embodiment of the present invention.

In FIG. 1, reference numeral 10 denotes a reader / writer connected to the host, and a data carrier 12 as a portable unit is prepared for the reader / writer 10, and as shown in FIG. The reader / writer 10 is disposed at a transmission distance L of about several millimeters.

The reader / writer 10 is provided with a control unit 16 by a CPU. The control unit 16 accesses the data carrier 12 for data writing or data reading with the host CPU via the interface 14.

Here, taking communication toward the data carrier 12 as an example,
For example, the control unit 1 from the host CPU via the interface 14
The data transferred to 6 is converted to serial data by the P / S converter 18 and provided to the FSK modulation circuit 20. FSK modulation circuit 20
Is connected to an oscillator 22, for example, performs FSK modulation with a data bit 1 at a frequency F1 and a data bit 0 with a frequency F0. After the FSK-modulated signal is power-amplified by the power amplifier 24, the signal is supplied to the coil 30 wound around the core 28 via the transmission / reception switch 26. The transmission / reception switch 26
Is turned on during transmission and reception to and from the data carrier 12 under the control of the control unit 16, and turned off when receiving from the data carrier 12.

Upon receiving a high-frequency magnetic field generated by supplying the FSK modulation signal to the coil 30, power is induced in the coil of the data carrier 12. The power induced in the coil 34 is supplied to a DC power supply voltage by a power supply rectifier circuit 36 to supply power to an internal circuit. The signal induced in the coil 34 is input to a frequency discrimination circuit 38, which demodulates the FSK modulation signal having the frequencies F1 and F0 and outputs the original data bits 0 and 1. The data bits output from the frequency discrimination circuit 38 are converted to parallel data by the S / P conversion circuit 40 and given to the control unit 42, and the control unit 42 determines a command or data from the received data, and if it is a write command, The data is written to the nonvolatile memory 44 using the EEPROM, and if it is a read command, the data is read from the specified address of the nonvolatile memory 44.

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

The read data read from the non-volatile memory 44 by the read access of 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 outputs data bits 0, 1 as will become clear later.
Generates a pseudo-random sequence signal based on the oscillation output of the oscillator 50. For example, a data bit 0 generates an M0 sequence signal having a predetermined word length, and a data bit 1 generates an M1 sequence signal having the same word length. The pseudo random sequence signal generated from the signal generator 48 is supplied to the coil 34 to induce a high-frequency magnetic field, and power is induced in the coil 30 on the reader / writer 10 side. At this time, the transmission / reception changeover switch 26 is off as shown in the figure, and the signal induced in the coil 30 is amplified by the preamplifier 82 and then supplied to the correlator 84. The correlator 84 has one of the two pseudo random sequence signals on the data carrier 12 side, for example, a replica of the M1 sequence signal,
The M1 'sequence signal is used as a reference value, and a correlation value φ is obtained by performing a correlation calculation with the received signal in a correlator 84.
Data bit 0, compared with a predetermined threshold value δ set in advance
Determine 1 and output. The data bits obtained based on the correlation calculation of the correlator 54 are converted to parallel data by the S / P conversion circuit 56 and output to the control unit 16. The control unit 16 is provided with a data buffer 58, and after storing data from the host CPU in the data buffer 58, the data carrier 12
, And the data received from the data carrier 12 is stored in the data buffer 58 and then transmitted to the host CPU. Data writing and data reading from the non-volatile memory 44 of the normal data carrier 12 are, for example, taking communication from the reader / writer 10 to the data carrier 12 as an example.
Each time a bit transfer request is received from the data carrier 12, data is transmitted from the reader / writer 10 one bit at a time.

FIG. 2 is a block diagram showing an embodiment of a data transmission system using the spectrum communication of the present invention used when data is transmitted from the data carrier 12 to the reader / writer 10 in FIG.

First, the data carrier 12 shows a modulation circuit section composed of the signal generator 48 shown in FIG.

That is, in the data carrier 12, the data d (t) taking the value of bits 1 and 0 is given to the discriminator 52,
It is determined whether the value of (t) is 1 or 0. If d
If (t) = 0, an output is generated in the multiplier 54, and the M-sequence generator 56 generates an M0-sequence signal as a first pseudo-random-sequence signal. On the other hand, if d (t) = 1, the multiplier 58
And the M-sequence generator 60 generates an M1-sequence signal.

M1 and M0 series signal generated in the M sequence generator 56 and 60 is, for example, a 63 word length (= 2 ⁶ -1), the shift register and the shift register of six stages consisting in shifting bits b0~b5 specifically And an output of an arbitrary shift stage, an exclusive-OR operation is performed, and the result is input to an input shift stage.

M1 sequence signal obtained through the multiplier 54 or 58 or
The M0 sequence signal is provided to a multiplier 62,
Spread spectrum modulation of 1MHz frequency signal. For example
The code waveform of the M1, M0 sequence signal is +1 at bit 1 and bit 0
-1 is multiplied by the signal generated from the signal generator 64 to perform spread spectrum modulation. 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 reader / writer 10 inputs a signal induced in the coil 30 by the high frequency magnetic field of the coil 34 of the data carrier 12 via the attenuator 66, and converts the signal into digital data by the A / D converter 68. The A / D converter 68 outputs 8-bit data using a sampling clock of, for example, 20 MHz. The output of the A / D converter 68 is given to the shift register 70, which is generated on the data carrier 12 side.
It has the number of shift stages for storing sampling data of 63 words length of the M1 and M0 sequence signals. The sampling data for 63 words in length stored in the shift register 70 is supplied to the multiplier 72, and the M1 'encoded sequence as a correlation replica stored in the reference value memory 74, that is, the M sequence on the data carrier 12 side is generated. An M1 'sequence signal is generated which is a copy of the M1 sequence signal generated by the device 56. Stored in the reference value memory 74.
The number of M1 'series signal data is also stored as data having the same resolution as the number of shift stages of the shift register 70, and the multiplier 72 outputs each shift stage output of parallel sampling data of the shift register 70 and each of the reference value memories. Multiply with memory stage output.

The output of the multiplier 72 is provided to an adder 75 to calculate the sum thereof, and the output of the adder 75 becomes the correlator output φ.
That is, φ = ΣS (n) · R (n) (1) where S (n) is sampled by the A / D converter 68, the shift register 70, the multiplier 72, the reference value memory 74, and the adder 75. Data R (n) is subjected to correlation calculation to become reference value data.

The correlation value φ output from the adder 75 is supplied to a discriminating circuit 76 and compared with a predetermined threshold value δ. If the correlation value φ is larger than the threshold value δ, the output circuit 78 outputs data d.
(T) = 1 is output. On the other hand, if the correlation value φ is smaller than the threshold value δ, the data d (t) = 0 is output from the output circuit 80.

In the present invention, the data transmission system using spread spectrum communication shown in FIG.
The M1 and M0 sequence signals are shifted by the M sequence generators 56 and 60 provided in 12 so that the cross-correlation φ10 between the M1 sequence signal and the M0 sequence signal is largely shifted to the minus side.

That is, the process gain P _G in the data transmission method of the present invention, to define the _{P G = φ11 (τ) -φ10} (τ).

Here, φ11 indicates that the transmission pattern is M1 and the correlation replica is M
An autocorrelation function when the transmission pattern is 1 ', and a cross-correlation function when the transmission pattern is M0 and the correlation replica is M1'.

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 is sufficiently large on the plus side as the correlation value φ calculated by the correlation calculation on the reader / writer 10 side. And the cross-correlation function φ
If 10 is greater on the negative side, it is possible to increase the process gain P _G given by the second equation (2). Thus if a large process gain P _G, + φ11 and -
By setting the threshold value δ such that the threshold value δ is located in the middle of φ10, it is possible to improve communication reliability with respect to an increase in transmission distance.

Further, when the process gain P _G is large, codes 2
It is also effective when assigning with multiple values greater than the value.

Next, in the second embodiment of the present invention, a GOLD code is used instead of the M1 and M0 sequence signals shown in FIG. That is, in order to increase the process gain, the present invention is a method of transmitting two code sequences shifted in such a manner that the correlation function φ10 largely appears on the minus side in accordance with the data bits. Therefore, it is not possible to obtain such a large negative value of φ10. Therefore, in the second embodiment of the present invention, GO having a large degree of freedom is used.
An LD code is introduced to obtain a larger value of the cross-correlation function φ10 on the minus side.

Next, as a third embodiment of the present invention, the code waveforms of the M1 and M0 sequences generated by the M sequence generators 56 and 60 on the data carrier 12 side in FIG. 2 are converted into Manchester codes.

That is, as shown in FIG. 3 (a), for example, a code waveform which is inverted to 0 after three consecutive data bits 1 from the reader / writer 10 in FIG. 1 is applied to the coil 30 of the reader / writer 10 in FIG. If supplied, the coil 34 on the data carrier 12 side will obtain a reception waveform that is considerably distorted with respect to the transmission rectangular wave shown on the right side of FIG. 3 (a). The distortion of the received waveform is not so large when the transmitted waveform is inverted for each bit, but as shown in FIG. 3 (a), for example, when the data bit 1 is continuous, the received waveform becomes considerably distorted. Therefore, the value of the positive side of the autocorrelation function φ11 obtained on the receiving side cannot be made too large.

Therefore, in the third embodiment of the present invention, FIG.
For example, when the data bit 1 is continuous as shown in FIG. 3, Manchester conversion is performed so that a code waveform is inverted in the middle for each data bit. As shown in the received waveform on the right side of FIG. 9B, distortion is minimized, energy loss is improved, and a large value on the positive side of the autocorrelation function is obtained.

The Manchester of code waveform of the pseudo random sequence signal generated in such a transmission side (bit expansion), reduced at the same time as the process gain P _G itself energy loss can be increased, even more communication reliability of the expansion of transmission distance , Can be improved.

Specifically, 6 generated by the M-sequence generators 56 and 60 in FIG.
Instead of 3 word lengths (= 2 ⁶ -1), half 31 word lengths (= 2 ⁵ −
The code sequence of 1) is generated and converted into Manchester with 2 bits per code, and finally generated as a Manchester-converted code sequence having a length of 63 words.

This Manchesterization is realized in the second embodiment of the present invention.
The same applies to the GOLD code.

According to the experiment by the inventor of the present invention, the process gain with respect to the transmission distance has the largest Manchester GOLD code,
Next, Manchester M-sequence code, then GOLD code, then M
It was confirmed that the order of the sequence codes was obtained.

It has been confirmed that the Manchester implementation significantly improves the process gain when the Manchester GOLD code is used in the present invention. In the Manchester GOLD code, the cross-correlation function φ10 is considerably large and goes to the minus side, so the autocorrelation function φ
Therefore, the value of the threshold δ for determining the data bit from the correlation value can be set to a considerably small value, which can greatly contribute to the expansion of the transmission distance.

Next, as a fourth embodiment of the present invention, when the process gain decreases with an increase in the transmission distance, and the threshold value δ for discriminating the data bits 1, 0 from the correlation value φ is fixed, Since the threshold value is determined so as to be an optimum value at the transmission distance of, for example, 6 mm, the characteristics deteriorate considerably when the transmission distance is increased to 8 mm or 10 mm. Therefore, in the fourth embodiment of the present invention, it is determined how much the transmission distance is based on the received energy, for example, the amplitude of the received waveform, and the threshold δ is changed in accordance with the transmission distance to thereby determine the optimum threshold value according to the transmission distance. By setting δ, communication reliability can be ensured even when the transmission distance is increased.

In the embodiment of FIG. 2, one system and a correlation calculation circuit are provided on the reader / writer 10 serving as the receiving side, and the correlation value is determined based on the threshold δ to demodulate the data bits 1, 0. However, for the M0 sequence signal of the data carrier 12 on the reader / writer 10 side, two systems having the same correlation circuit using M0 ′ as a correlation replica are used, and the magnitude relationship between the correlation values of the two correlation circuits is compared. Thus, the data bits 1 and 0 may be determined.

In the above embodiment, the spread spectrum communication is used for the communication from the data carrier 12 to the reader / writer 10. On the other hand, the spectrum for the communication and the bidirectional communication from the reader / writer 10 to the data carrier 12 is reversed. Of course, spread communication may be used.

Further, in the above embodiment, the M sequence and the GOLD code are taken as examples, but the present invention is not limited to this, and an appropriate pseudo random sequence can be used as it is.

[Effects of the Invention] As described above, according to the present invention, the cross-correlation functions are shifted from each other so as to largely appear on the negative side.
Since two pseudo-random code sequences are transmitted according to data bits 1 and 0, it is possible to increase the process gain given as the difference between the autocorrelation function and the cross-correlation function to guarantee communication reliability for an increase in transmission distance. it can.

In addition, since the pseudo random sequence code waveform is converted into Manchester and transmitted, energy loss due to distortion of the received waveform due to electromagnetic induction coupling can be improved and a large process gain can be obtained.

Furthermore, by judging how much the transmission distance is based on the amplitude of the received waveform, etc., and setting an optimal threshold for judging data bits from the correlation calculation output value according to the transmission distance, communication reliability against the expansion of the transmission distance is improved. Performance can be further guaranteed. Further, the amount of correlation calculation processing is reduced by half, and the number of correlation calculators is reduced.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of the present invention; FIG. 2 is a configuration diagram of an embodiment showing one embodiment of the present invention; FIG. 3 is an explanatory diagram of transmission and reception waveforms of the present invention by Manchester. In the figure, 10: reader / writer (transmitting unit) 12: data carrier (receiving unit) 14: interface 16, 42: control unit (CPU) 18, 46: P / S conversion circuit 20: FSK modulation circuit 22, 50 Oscillator 24: Power amplifier 26: Transmission / reception switch 28, 32: Core 30, 34: Coil 36: Power rectifier circuit 38: Frequency discriminator 40, 56: S / P conversion circuit 44: Non-volatile memory (EEPROM) 48: Signal Generators 52, 76: Discriminating circuits 54, 58, 62, 72: Multipliers 56, 60: M-sequence generator 54, 56: Reference value memory 64: Signal generator 66: Attenuator 68: A / D converter 70: Shift register 74: Reference memory 75: Adder 78, 80: Output circuit 82: Preamplifier 84: Correlator 88: Data buffer

Continuation of the front page (72) Inventor Uhiko Takeuchi 2-16-46 Minami Kamata, Ota-ku, Tokyo Tokyo Keiki Co., Ltd. (56) References JP-A-63-296424 (JP, A) JP-A-2 −246539 (JP, A) JP-A-2-89431 (JP, A)

Claims (4)

(57) [Claims] A bit data is transmitted bit by bit from a transmitting unit to a receiving unit in response to a bit transfer request, and a first pseudo random number corresponding to one logical value of a data bit is transmitted to the transmitting unit. A pseudo-random sequence generator for generating a sequence signal and for generating a second pseudo-random sequence signal in accordance with the other logical value of the data bit; A correlation circuit that performs a correlation calculation with either the first or second pseudo-random sequence signal stored as
In a data transmission system using spread-spectrum communication provided with a determination circuit that determines a logical value of a data bit by comparing an output value of the correlation circuit with a predetermined threshold value, as the pseudo-random sequence generator, Data using spread-spectrum communication, wherein two pseudo-random sequence signals in which the value of a cross-correlation function between the first random sequence signal and the second pseudo-random sequence signal increases to the negative side are generated. Transmission method. 2. The pseudo-random sequence generator generates an M-sequence signal or a GOLD-sequence signal shifted from each other so that the cross-correlation function of two pseudo-random sequence signals largely appears on the negative side. Item 2. A data transmission method using spread spectrum communication according to item 1. 3. A data transmission system using spread spectrum communication according to claim 1, wherein said pseudo random sequence generator generates a waveform pattern of a pseudo random sequence signal converted to Manchester. 4. A data transmission system using spread spectrum communication according to claim 1, wherein a threshold value of a discriminator provided in said receiving side unit is changed according to a magnitude of received energy.