CN102163988A

CN102163988A - Synchronization of air interface downlink channel for radio frequency identification (RFID) adopting shift m-sequence family for spectrum spreading

Info

Publication number: CN102163988A
Application number: CN2010101161604A
Authority: CN
Inventors: 刘礼白
Original assignee: Individual
Current assignee: Individual
Priority date: 2010-02-22
Filing date: 2010-02-22
Publication date: 2011-08-24
Anticipated expiration: 2030-02-22
Also published as: CN102163988B

Abstract

The invention discloses the synchronization of an air interface downlink channel for radio frequency identification (RFID) adopting a shift m-sequence family for spectrum spreading, belongs to the field of short-range communication and is related to the application of a radio frequency identification system spread spectrum technology. In the synchronization, in a reader-writer query time bucket, a label extracts a clock from a shift m-sequence family spread spectrum signal transmitted by a reader-writer; and in a label response time bucket, the label extracts the clock from a carrier signal which is transmitted by the reader-writer and key-modulated by clock light modulation amplitude. A label clock extraction circuit comprises two code edge clock extraction circuits and an injection synchronization oscillating ring. The injection synchronization oscillating ring consists of an injection OR gate and a delay unit, and aims to purify the clock and keep continuous the clock. A data clock is extracted by a given state extraction circuit in a shift m-sequence, M-ary coding is performed on the shift m-sequence, and a given multi-state extraction circuit is set in the shift m-sequence according to an exponent of an M-ary number to extract the data clock.

Description

The displacement m sequence spread-spectrum RFID of family air interface down channel is synchronous

Technical field

The invention belongs to the short haul connection field, relevant with wireless sensor network (WSN), radio-frequency (RF) identification air interface systems such as (RFID) with device design.

Background technology

Short haul connection is one of new technical field of Showed Very Brisk in recent years.Wireless sensor network in this (WSN) and radio-frequency (RF) identification (RFID) technology are especially outstanding, have great industrial prospect.WSN and RFID belong to short haul connection together, so technical some general character that exists.

The evolution of radio-frequency (RF) identification (RFID) air interface technologies is from the low frequency to the high frequency, arrives the carrier frequency lifting process of hyperfrequency and microwave again, also be operating distance from contact to contactless, be applied to radiation field application and development process from induction field.The most representative technical specification that is suitable for the radiation field application in the world is the air interface communication parameter series standard of ISO/IEC 18000-4/-6/-7 radio-frequency (RF) identification (RFID) system.Spell out in the regulation about transmission system of these standards, Direct swquence spread spectrum (DSSS) is not adopted technology.Therefore,, do not see the research and development achievement report of relevant Direct swquence spread spectrum (DSSS) technology both at home and abroad in radio-frequency (RF) identification (RFID) air interface applies.

Direct swquence spread spectrum (DSSS) technology is widely used in other communication system, for example among the cdma cellular mobile communication system IS-95, with overlength (2 ⁵²-1) Wei m sequence is as time reference, two length (2 ¹⁵-1) Wei m sequence is as spread-spectrum code, with 64 Walsh sign indicating numbers as user's access code. in the WCDMA system, used the m sequence preference to producing the Gold sequence. in blue tooth design, used frequency hopping spread spectrum (HFSS) technology etc.

Closely there is article to claim to replace counter in the RFID electronic tag, the report of choosing with control command with linear feedback shift register.In fact there is not really to bring into play the technical advantage of m sequence.

The invention reside in provides a kind of new implementation method to using displacement m sequence family spread-spectrum air interface Synchronization Design.Be suitable for providing the clock source by main website (read write line), slave station (label) extracts clock by what main website (read write line) sent in the carrier wave of clock modulation, and requires synchronizing speed fast, the application scenario that frequency accuracy is high.For example, when passive label RFID displacement m sequence family spread-spectrum air interface synchronous network.Compare with existing design, existing ISO/IEC18000-6 standard for passive label, receiving the signal that is subjected to the director data waveform modulated that the period reception is sent by read write line, is extracted clock information from received signal, in order to calibration local clock source; Only send carrier wave at tag responses period read write line, the transmission of the self-dependent clock of label source driving data, because passive label lacks the frequency stabilization measure, there is frequency drift in the label clock, can not satisfy displacement m sequence extension frequency spectrum synchronous network demands of applications.

Summary of the invention

The present invention is based on the synchronous design requirement of displacement m sequence extension frequency spectrum short haul connection air interface down channel.Be applicable to the design of passive label rfid system clock source; Also can be used for other short range communication systems.

Source of synchronising signal spontaneous emission (read write line) end that the used method for synchronous of the present invention is based on reception (label) end sends signal.

In displacement m sequence rfid system, for passive label, when read write line sends instruction, label extracts clock from receive command signal, when tag responses, read write line sends the carrier wave through the clock signal modulation, rather than the read write line of existing design is only launched carrier wave.Label extracts clock from modulated carrier.For direct use displacement m sequence extension frequency spectrum design system, the clock that extracts is the chip clock, and for the displacement m sequence extension frequency spectrum design system of using the Manchester code transmission, the clock that extracts is 2 times of chip clocks.The frequency division effect of the spread-spectrum sequence generator by label realizes that the base band bit clock extracts.

Send the instruction period at read write line, read write line sends displacement m sequence extension spectrum signal to label, label extracts clock from the spread spectrum signal that receives, send the reply data period at label, read write line continues to send the carrier wave of modulating through clock to label, its modulating clock frequency equals half that chip leads, and modulation system is shallow amplitude modulation amplitude keying.The modulation degree size will be enough to guarantee that label can extract clock signal from received signal, and does not significantly reduce carrier energy.

Send the reply data period at label, label need not the modulated carrier that receives is implemented to go modulation, directly implements modulation again on the modulated carrier that is received.Modulation system is 2PSK.Modulation signal is the base band data with displacement m sequence extension.

Label uses monostable flipflop and not gate and two extraction branch roads of monostable trigger from the rising edge that receives code stream and the extraction synchronised clock that descends.Be called user code along the Clock Extraction branch road.

By or two sign indicating numbers of goalkeeper close the road along the Clock Extraction branch road, its output feeds back to after 1 code element (τ) time delays unit time-delay again closes road or door, with close the road clock mutually or, constitute and inject oscillation rings synchronously, realize that clock purifies and realize the clock maintenance.

Sign indicating number equals symbol width partly along the monostable trigger time width of Clock Extraction branch road.The use Manchester code equals half of chip width as time-delay (τ) width of the displacement m sequence extension spectrum signal delay unit of transmission pattern, when directly modulating with the signal of displacement m sequence extension frequency spectrum, the time-delay of delay unit (τ) width symbol width equals the chip width.

Description of drawings

Fig. 1. the displacement m sequence extension spectrum signal synchronised clock of Manchester code transmission extracts each symbol connotation among the figure:

M: receive Manchester coded signal

M _CP1: Manchester code rising edge Clock Extraction

M _CP2: Manchester code trailing edge Clock Extraction

∑ _CP: the Manchester code that injects the output of synchronous ring delay circuit closes the road clock

Chip clock (equal manchester clock half) output

Fig. 2. the chip synchronised clock of displacement m sequence extension spectrum signal extracts

Each symbol implication among the figure:

Y: receive displacement m sequence signal

y _Cp1: receiving sequence sign indicating number rising edge Clock Extraction

y _Cp2: receiving sequence sign indicating number trailing edge Clock Extraction

y _Cp: the receiving sequence sign indicating number closes the road along Clock Extraction, y _Cp=y _Cp1+ y _Cp2

∑ _CpClose the road clock through time-delay feedback output.

Embodiment

1. the displacement m sequence extension spectrum signal synchronised clock of Manchester code transmission extracts

The displacement m sequence extension spectrum signal synchronised clock of Manchester code transmission extracts as Fig. 1.

The Manchester code synchronised clock is made up of along Clock Extraction branch road and injection synchronized oscillation ring two sign indicating numbers.

Sign indicating number is that middle part at " 1 " sign indicating number and " 0 " sign indicating number waveform produces saltus step along Clock Extraction, and connects " 1 " sign indicating number and connect " 0 " sign indicating number when transmitting, and the situation of intersymbol waveform generation saltus step is utilized the circuit of waveform saltus step extraction clock information.For rising edge, use the saltus step rising edge of received signal to trigger pulse of monostable trigger generation; For trailing edge, use not gate, produce a pulse by monostable trigger again.

By or goalkeeper's sign indicating number close the road along the Clock Extraction branch road, after a unit time (suitable half chip width) time-delay, feed back to again and close road or door and form and inject the synchronized oscillation ring, involutory road clock is purified.Keep with clock.

2. the spread-spectrum sequence signal stream chip of displacement m sequence family synchronised clock extracts

The chip synchronised clock of m sequence family spread spectrum signal stream extracts as Fig. 2.

Similar to Manchester code synchronised clock extraction circuit, spread-spectrum sequence signal stream synchronised clock extracts by two sign indicating numbers to be formed along Clock Extraction branch road and injection synchronized oscillation ring.

Sign indicating number is to occur waveform saltus step to " 0 " sign indicating number or " 0 " sign indicating number to " 1 " when sign indicating number at each " 1 " sign indicating number in the receiving data stream along Clock Extraction, from sign indicating number along extracting clock.For from " 0 " sign indicating number to " 1 " sign indicating number, use the rising edge of received signal to trigger pulse of monostable trigger generation; To " 0 " sign indicating number, use non-goalkeeper's received signal anti-phase for " 1 " sign indicating number, produce a pulse by monostable trigger again.

Carry branch road by one or two sign indicating numbers of goalkeeper along clock and close the road,, feed back to and close road or door, form and inject the synchronized oscillation ring, realize that clock purifies and keep synchronously again through a unit time (being the 1chip width) time-delay.

3. tag responses period synchronised clock extracts

The same Fig. 1 of principle, just importing received signal is the carrier wave of being sent by read write line through the clock signal modulation, modulating clock speed equals half that chip leads.With extracting clock in the binary code stream of clock extracting circuit shown in Figure 1 by modulated carrier demodulation generation.Its formed clock rate equals to reply displacement m sequence extension Spectrum Code chip and leads.

4. extracting data clock in the displacement m sequence extension spectrum signal code stream extracts

Usually differ (2 between the data bit clock of displacement m sequence extension spectrum signal code stream representative and the chip clock ⁿ-1) doubly.Equal the cycle period of m sequence.Therefore, extract door and can obtain data clock as long as on the m sequence generates shift register, establish an initial condition or other state.For multilevel code displacement m sequence family spread spectrum signal, because of multi-system is counted difference, the base band data clock be 2 systems of the multi-system number index of expressing doubly.For example, 4 scale codings, a sequence period is represented 2 data bits.Should establish two states that equal (or approaching) half sequence length of being separated by and extract door, from sequence, extract 2 times to the clock of sequence period rate.Analogize, 8 scale codings, each sequence signal is represented 3 data bits.Should establish three states that equal (or approaching) 1/3rd sequence lengths of being separated by and extract door, from sequence, extract 3 times to the clock of sequence period rate.

Claims

1. the present invention " the displacement m sequence spread-spectrum RFID of family air interface down channel is synchronous " is coordinated mutually to realize that the label clock extracting circuit is made up of along Clock Extraction and injection synchronized oscillation ring sign indicating number by read write line and label.

2. based on claim 1, feature of the present invention is to use displacement m sequence extension spectrum signal when read write line sends request signal.Send through the clock modulated carrier signal at tag responses period read write line, the modulating clock frequency is to reply half that spread-spectrum sequence chip leads.

3. based on claim 1, feature of the present invention is when label is used read write line and sent the carrier wave that is subjected to the clock modulation and send answer signal, need not the read write line signal that receives is gone modulation.

4. based on claim 1, feature of the present invention is to use monostable flipflop and not gate to add monostable trigger and extracts synchronised clock from rising edge and the trailing edge that receives code stream.Claim sign indicating number along the Clock Extraction branch road.

5. based on claim 1, feature of the present invention be with or door merge the clock of two branch roads, after the time-delay of 1 code element duration (τ), feed back to or door, constitute and inject the synchronized oscillation ring.

6. based on claim 1, feature of the present invention is that the involutory road of synchronized oscillation ring clock frequency is purified and the continuity of maintenance clock with injecting.

7. based on claim 1, feature of the present invention is to approximate symbol width all monostable trigger time partly.

8. based on claim 1, feature of the present invention is that delay unit time-delay (τ) width is the receiving symbol width.For the signal of the displacement m sequence family spread-spectrum of Manchester code transmission, receiving symbol is a spread-spectrum sequence chip width half; With the signal of displacement m sequence family spread-spectrum, the receiving symbol width is a spread-spectrum sequence chip width for directly.

9. based on claim 1, feature of the present invention is to extract door by the state road of displacement m sequence to extract data clock, for multilevel code displacement m sequence extension frequency spectrum, the exponential quantity of then pressing the binary expression of multi-system, the state of establishing a plurality of displacement m sequences extracts door and extracts data clock.