Wireless receiver

Abstract

To provide a radio receiver capable of removing an arbitrary waveform from a signal waveform in which data are modulated to a signal modulated with the arbitrary waveform when a tag modulates data to various radio waves existing in the air, which makes it possible to eliminate necessity of dedicated transmitter in a system with a dedicated reader for transmitting radio wave to a wireless tag and receiving a response from the tag for reading data from the wireless tag and a dedicated tag which modulates data to an unmodulated signal from the reader when the tag transmits a reply.SOLUTION: An I signal component 30 and a Q signal component 31 which are complex components outputted by orthogonal demodulation of received transmission wave, and an I signal component 37 and a Q signal component 38 which are complex components outputted by orthogonal demodulation of received re-transmission wave are inputted to a complex correlation detection circuit 39, and demodulation data 43 are outputted from a correlation detection output 40.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a receiver for receiving a signal obtained by remodulating a general wireless communication signal with a carrier wave of a specific frequency and specific data, and demodulating the specific data.

Background Art

[0002] Wireless tags for identifying individuals using radio are used in various places. Their identification uses the power generated from the radio wave transmitted from an identification device called a reader, and the identification data is modulated onto the carrier wave transmitted from the reader and then retransmitted, which is received by the reader to read the identification data.

[0003] When the transmission wave of the reader is modulated, when the tag modulates the identification data thereon, the identification data is modulated onto a carrier wave whose amplitude and phase change instantaneously at every moment, and the modulation output becomes very complex, and it is difficult to receive this and demodulate the identification data.

[0004] Therefore, when transmitting data from the reader to the wireless tag, as shown in FIG. 1, following the preamble 1, the signal modulated with the command 2 and the parameter 3 is transmitted. When transmitting data from the wireless tag, only the unmodulated carrier wave 4 is transmitted. The wireless tag modulates and transmits a response 5 consisting of individual identification data on this carrier wave.

[0005] As shown in the timing of the command exchange in the communication between the wireless tag reader / writer and the wireless tag shown in FIG. 2 of Patent Document 1, and also in the modulated data waveform of the Interrogator (i.e., the wireless tag reader / writer) at the handover timing shown in Figure 17 of Non-Patent Document 1, when the wireless tag transmits data, the wireless tag reader / writer transmits an unmodulated radio wave toward the wireless tag. The wireless tag modulates and retransmits the identification data on the carrier wave. Since the identification data is modulated on the carrier wave, the receiving side can easily demodulate the identification data by a general demodulation method. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2008-293538 [Non-patent literature]

[0007] [Non-Patent Document 1] International standard ISO / IEC 18000-6:2004(E) [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] When individual identification data is further modulated onto a modulated radio signal, demodulation is possible by inverse calculation if the carrier waveform at the time of modulating the identification data and the original modulated waveform are known. However, because the amplitude and phase fluctuations are not only due to the modulated waveform but also due to radio wave propagation, there are many unknown fluctuation items, making it extremely difficult to demodulate the identification data.

[0009] If it becomes possible to remove unknown variable items from a signal that has been modulated with an arbitrary waveform and then further modulated with individual identification data, and if the identification data can be demodulated, then it would be possible for a wireless tag to modulate the identification data into radio waves flying around in space, without the need for a reader to transmit radio waves. Therefore, the challenge lies in how to remove the arbitrary waveform modulation component.

[0010] The present invention aims to solve the above problems and realize a receiver that can read identification data without requiring a dedicated reader. [Means for solving the problem]

[0011] To achieve the above objective, in the schematic configuration shown in Figure 2, the present invention receives a transmitted wave 7 modulated with an arbitrary waveform using an antenna 8, and switches the high-frequency current 14 that flows due to the reception using a transistor 9. Modulation data 13 is input to the input of the transistor 9, and it is switched according to this modulation data 13. teeth The individual data 11 is transmitted to the output of the oscillator circuit 10 by the modulation circuit 12 This is the modulated output. The wireless tag consists of these circuits connected to antenna 8. The switched high-frequency current 14 is transmitted via the transmission wave 7 to Modulation data 13 of modulation death It is transmitted as a retransmitted wave 15 and received by the receiver 16. Transistor 9 can be replaced with other nonlinear elements, as long as the high-frequency current 14 can be modulated with the modulation data 13.

[0012] Figure 3 shows the frequency spectrum of a wireless signal, where retransmitted waves 18 and 19 appear at frequencies f1 above and below the transmitted wave 17, respectively. Frequency f1 corresponds to the oscillation frequency of the oscillator circuit 10 in Figure 2. The modulation data 13 in Figure 2 is the frequency of the oscillator circuit 10. f 1 carrier (subcarrier) Since the signal is modulated with identification data 11, it has a frequency bandwidth spread corresponding to the frequency components of identification data 11. The retransmitted waves 18 and 19 are outputs modulated with modulation data 13 relative to the transmitted wave 17, so their bandwidth is even wider than the original frequency bandwidth of the transmitted wave 17 by an amount corresponding to the frequency bandwidth spread of the modulation data 13.

[0013] Since the receiver only needs to receive either retransmitted wave 18 or retransmitted wave 19, it is possible to receive only the desired signal by passing it through a bandpass filter that allows only one of the retransmitted waves to pass through.

[0014] Figure 4 shows the flow of transmitted and received wireless signals and their waveforms using mathematical formulas. The transmitted wave 21 from the transmitter 20 is modulated with an arbitrary waveform x(t) at a carrier frequency fc, where x(t) is a complex number. The retransmission terminal 22, which corresponds to a wireless tag, transmits a signal containing identification data to the transmitted wave 21. (Modulation data 13) The retransmitted wave 23 is transmitted after modulation. The retransmitted wave 23 is a signal modulated with the identification data signal y(t) at a frequency shifted by f1 above or below the carrier frequency fc of the transmitted wave 21. y(t) is a complex number.

[0015] In order for the receiver 24 to receive the retransmitted wave 23 and demodulate the identification data, it is necessary to remove any unknown arbitrary waveform x(t) from the receiver 24. Therefore, the receiver 24 is provided with a means for receiving the transmitted wave 21 and demodulating x(t). By regenerating the carrier wave of the transmitted wave 21 with a carrier regeneration circuit and performing orthogonal demodulation using orthogonal carrier components, x'(t), which consists of real and imaginary components, can be extracted.

[0016] However, this complex component x'(t) extracted by the receiver does not strictly coincide with x(t). Time delays due to the propagation path from the transmitter and phase differences of the orthogonal components are added. These fluctuating factors are unknown and cannot be easily determined. Therefore, simply adding, subtracting, multiplying, or dividing x'(t) from the retransmitted wave 23 received by the receiver 24 will not remove x(t).

[0017] While it is not possible to determine the exact value of x(t), there will always be cases where there is a high correlation between x(t) and x'(t). The correlation value, which also takes into account phase variations in the time interval T, can be expressed by the following formula.

[0018]

number

[0019] When the variation of the discrimination data signal y(t) is gentle compared to the correlation detection time T, the correlation value Q(τ) between the retransmission wave 23 received by the receiver 24 and x’(t) is expressed by the following mathematical formula and has a waveform that varies according to the value of y(t).

[0020]

Equation

[0021] By obtaining the correlation value between the received waveform x’(t) of the transmission wave and the received waveform of the retransmission wave, the waveform of the discrimination data signal y(t) can be extracted, and by reproducing the data timing, it becomes possible to obtain the discrimination data.

Brief Description of the Drawings

[0022] [Figure 1] A drawing showing the timing of the transmission signals of the reader and the tag. [Figure 2] A schematic configuration diagram of the system in which the present invention is used. [Figure 3] A drawing showing the spectra of the transmission wave and the retransmission wave. [Figure 4] A drawing showing the flow of the transmitted and received signals and the signal waveforms by mathematical formulas. [Figure 5] A drawing showing an embodiment of the present invention.

Modes for Carrying Out the Invention

[0023] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

Examples

[0024] FIG. 5 shows an embodiment of the present invention. The transmission wave is received by the receiving antenna 25, amplified by the LNA 26, and then only the signal with the necessary bandwidth centered on the center frequency fc of the transmission wave is passed through the filter 27. The oscillator 28 oscillates a sine wave with the frequency fc and supplies it to the quadrature demodulator 29. The output of the filter 27 is demodulated by the quadrature demodulator 29, and the I signal component 30 and the Q signal component 31 are output.

[0025] The receiving antenna 32 receives the retransmitted wave, amplifies it with the LNA 33, and then filters 34 to allow only the signal with the required bandwidth, centered around the retransmitted wave's center frequency fr, to pass through. The oscillator 35 oscillates a sine wave at frequency fr and supplies it to the quadrature demodulator 36. The output of the filter 34 is demodulated by the quadrature demodulator 36, outputting the I signal component 37 and the Q signal component 38. Since quadrature demodulation is a linear transformation, it is equivalent to inserting filters on the baseband signals, namely the I signal component 30 and the Q signal component 31, and the I signal component 37 and the Q signal component 38, instead of filters 27 and 34.

[0026] The I signal component 30 and Q signal component 31, and the I signal component 37 and Q signal component 38, which are the outputs of the respective quadrature demodulators, are input to the complex correlation detection circuit 39, which outputs a correlation output 40. The correlation output 40 corresponds to the identification data signal of the retransmission terminal. This correlation output 40 is input to the timing extraction circuit 41, which extracts the clock timing of the identification data.

[0027] The output of the timing extraction circuit 41 is input to the determination circuit 42, which determines the data from the correlation output 40 and outputs demodulated data 43. [Industrial applicability]

[0028] This invention allows data from wireless tags to be read even with wireless signals modulated with any waveform. Therefore, it is possible to read data by utilizing various radio waves flying around in space without using a radio wave transmitting reader, and it can be used in systems that easily read data from tags in various locations. [Explanation of Symbols]

[0029] 1: Preamble signal, 2: Command signal, 3: Parameter signal, 4: Unmodulated signal, 5: Response signal, 6: Transmitter, 7: Transmitted wave, 8: Antenna, 9: Transistor, 10: Oscillator circuit, 11: Identification data, 12: Modulation circuit, 13: Modulated data, 14: High-frequency current, 15: Retransmitted wave, 16: Receiver, 17: Transmitted wave, 18: Retransmitted wave, 19: Retransmitted wave, 20: Transmitter, 21: Transmitted wave, 22: Retransmission terminal, 23: Retransmitted wave, 24: Receiver, 25: Receiving antenna, 26: LNA, 27: Filter, 28: Oscillator, 29: Quadrature demodulator, 30: I signal component, 31: Q signal component, 32: Receiving antenna, 33: LNA, 34: Filter, 35: Oscillator, 36: Quadrature demodulator, 37: I signal component, 38: Q signal component, 39: Complex correlation detector, 40: Correlation output, 41: Timing extraction circuit, 42: Decision circuit, 43: Demodulated data

Claims

[Claim 1] A wireless receiver that receives from an antenna a first wireless communication signal transmitted with arbitrary modulation from an unspecified transmitter, and a second wireless communication signal that is retransmitted by modulating specific data obtained by modulating individual data on a subcarrier into the said wireless communication signal, wherein the wireless receiver is provided with a complex correlation detection means that inputs a first complex signal output after quadrature demodulation following the first wireless communication signal has passed through a first bandpass filter that allows the first wireless communication signal to pass through, and a second complex signal output after quadrature demodulation following the second bandpass filter that allows the second wireless communication signal to pass through, and determines the complex correlation between the two, and demodulates and outputs the specific data from the output of the complex correlation detection means.

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