CN102594373A - Method for generating low-complexity SSB (Single Side Band) signals of RFID (Radio Frequency Identification Device) system - Google Patents

Abstract

The invention discloses a method for generating low-complexity SSB (Single Side Band) signals of an RFID (Radio Frequency Identification Device) system, which is suitable for the transmitter design based on the SSB modulating technology in the RFID system. In the method, based on the characteristic that the time domain oversampling is equivalent to the frequency domain prolongation in the corresponding relationship of the time domain and the frequency domain of digital signals, the minimum data volume mapping relationship modulated by coding is obtained by acquisition of the such prior information as signal waveform modulation, hardware sampling rate and the like. The length of the data output through mapping can be shortened through the minimum data volume mapping relationship. Subsequently, the SSB modulating process of the data output based on the minimum data volume mapping relationship is realized by the Fourier transformation, the zero forcing algorithm and the Fourier inversion of base points in sequence. Finally, the sampling precision of the data can be improved through one-time linear interpolation, so that the signals are smooth. According to the method, the processing complexity is simplified by the reduction of the points of the Fourier transformation, and the problem that the realization complexity of the SSB algorithm is high in the RFID system is solved.

Description

A kind of rfid system SSB signal creating method of low complex degree

Technical field

The present invention relates to radio frequency identification (RFID) system field, and be particularly related to the generation method of monolateral band (SSB) modulation signal in this system, be applicable to rfid system card reader transmitter design.This method has solved in the rfid system, generates the too high problem of SSB signal complexity.

Background technology

The increasing all trades and professions that are applied to of RFID communication system, this system have rapidly occupied the main flow of RFID industry with its low-power consumption, low cost, the easy characteristic of disposing.In recent years, for the technical characterictic of further outstanding this industry low-power consumption, the SSB modulation system is admitted by increasing standard, becomes the transmission modulation technique that many industry RFID use.In theory, because the SSB modulation system is only passed through in the radiofrequency signal, positive number sideband or negative sideband carry uses signal energy, and therefore, its energy consumption is 1/2nd of traditional double sideband (DSB) modulation system.The reduction of energy consumption can be equivalent to the lifting of unit energy efficiency of transmission, so this technology makes the further compression power consumption cost of rfid system, strengthens antijamming capability, and the elevator system communication distance and is read label success rate index.But the SSB signal has very big difference with traditional DSB modulation system in realization.Although through theoretical derivation, the SSB modulation system can be generated by DSB modulation carrying out secondary, and its implementation complexity still can be in any more, and characteristic is incompatible with cheaply with rfid system, has seriously limited the popularization of SSB modulation technique in the RFID field.

Usually generate the SSB modulation signal two kinds of implementation methods are arranged.A kind of is to realize that through the hardware chip circuit of SSB filter this chip is directly realized the inhibition for positive number or negative sideband through frequency Hilbert filtering mode.Although the chip solution can realize the SSB modulation signal more efficiently, this solution not only will increase new filter circuit, and can cause the circuit board of traditional DSB modulation system to utilize once more.Therefore, it does not possess soft upgrading ability, and upgrade cost is higher.Another kind method is then carried out software upgrading through the base band algorithm to RFID card reader transmitter, can realize the multiplexing of hardware circuit.In this method, there are two types of algorithms comparatively feasible.One is based on and utilizes the Hilbert digital baseband filter to realize, the theoretical formula of this wave filter is an IIR filter, and promptly the tap number of this wave filter be an infinity.In realization, have only the complexity that can bear according to system to carry out its tap number is simplified.Therefore, this algorithm SSB modulation signal performance that can provide is unsatisfactory.Another kind of algorithm is the spectrum signature according to SSB, and original DSB time-domain signal is carried out Fourier transform, then the positive number sideband or the negative sideband of frequency response is compeled zero computing, is getting back to time domain through Fourier's anti-change at last, generates the time-domain signal of SSB.In this algorithm, the Fourier Transform Algorithm that need count more greatly, this disposal ability to rfid system is unpractical.In practical application, have only the carrying constraint for algorithm complex according to system, needs are carried out the SSB processing signals, carry out section and handle.For example, original one 4096 Fourier transform becomes 16 256 Fourier transform, and after each Fourier transform, carries out independently compeling zero computing and Fourier inversion respectively.Although this algorithm has reduced the requirement to the Fourier transform exponent number, the data after it can cause section to handle, discontinuous in section and intersegmental time domain waveform, and the time-domain signal distortion that causes.

In a word, although the SSB technology is accepted by the RFID field, implementation method that at present should technology still has further raising signal performance, reduces the active demand that realizes low complex degree.We's rule is arisen at the historic moment under this background.

Summary of the invention

Conventional method or has reduced SSB signal quality performance in the implementation procedure of carrying out the SSB modulation technique, or has higher implementation complexity, has certain limitation.Therefore; Need a kind of from the whole aspect consideration of RFID card reader transmitter; With sending the method that signal characteristic and traditional SSB algorithm organically combine, this method is improved transmitter base band algorithm under the prerequisite that does not change original traditional DSB modulation system rfid system circuit; And the complexity of the newly-increased algorithm of strict control makes original system possess the SSB modulation capability.

Technical scheme of the present invention is: the characteristic according to the RFID card reader transmits, reduce the demand of counting of Fourier transform, thereby make system can utilize small point Fourier transform and zero forcing algorithm to realize the inhibition to single sideband singal.And through the difference of digital over-sampled device compensation small point Fourier transform, thereby obtain desirable SSB modulation signal with a little bigger transformation of variables sampling precision.

Usually, adopt fixedly mapping relations coding and envelope modulation technology in the rfid system, for example, PIE coding and ASK modulation technique, this technology is to adopt two kinds of (or limited several kinds) different time domain waveforms to distinguish data 0 and data 1.Therefore, if the definition baseband transmit signals is f _BB(t), then this signal is by f ₁(t), f ' ₁(t), f " ₁(t) ... And f ₀(t), f ' ₀(t), f " ₀(t) ... Deng being combined to form at random arbitrarily of limited quantity waveform sets.For simplify derivation relational assumption data 0, data 1 are represented by a kind of fixed waveform respectively, i.e. f ₀(t) and f ₁(t).

Definition f _RFID(m) binary data sequence that sends of expression rfid system, m is the index number of data sequence, and definition M is the length of this sequence, so the span of sequence index number m be (0, M].Based on above-mentioned mapping relations, can be with the baseband signal f of RFID transmission _BB(t) be established as M waveform time and make up continuously, that is:

f _BB(t)＝{f _BB(1，t)......f _BB(m，t)......f _BB(M，t)}

In the formula, f _BB(m t) represents m the waveform expression formula that binary data shone upon, according to the mapping relations of data 0 with data 1, f _BB(m t) can further be expressed as:

$f_{\mathrm{BB}}(m,t)=\left\{\begin{array}{c}{f}_0\left(t\right),(f_{\mathrm{RFID}}\left(m\right)=0);\\ f_1\left(t\right),(f_{\mathrm{RFID}}\left(m\right)=1);\end{array}\right.$

Because rfid system adopts the envelope modulation technology of fixed waveform more, for example, Fig. 1.Therefore, f ₀(t) and f ₁(t) can be further defined as digital signal f ₀(n) and f ₁(n), n is the time Domain Index of digital signal waveform.For data 0 and data 1, the span of definition n be respectively (0, N ₁] and (0, N ₂], N ₁And N ₂Be respectively the maximum number of samples of data 0 and data 1.Based on to f ₀(t) and f ₁(t) digitization modeling can be derived baseband signal f _BB(t) digital model is:

f _BB(n)＝{f _BB(1，n)......f _BB(m，n)......f _BB(M，n)}

Wherein, f _BB(m n) represents m the digital waveform expression formula that binary data shone upon,

$f_{\mathrm{BB}}(m,n)=\left\{\begin{array}{c}{f}_0\left(n\right),(f_{\mathrm{RFID}}\left(m\right)=0);\\ f_1\left(n\right),(f_{\mathrm{RFID}}\left(m\right)=1);\end{array}\right.$

Base band time domain waveform f based on above-mentioned definition _BB(n), in theory, the generating algorithm of its SSB signal comprises following three steps:

1) through Fourier transform, with base band time domain waveform f _BB(n) change time-domain signal into,

In the formula

Represent Fourier transform, F _BB(k) be the base band frequency-domain waveform of RFID signal, the span of k be (0, K], wherein,

Represent the positive number frequency range

Represent the negative frequency scope.

2) through zero forcing algorithm, the positive frequency or the negative frequency of base band frequency waveform are partly carried out the energy inhibition,

$F_{\mathrm{BB}}^{\&prime;}\left(k\right)=\left\{\begin{array}{c}0,(0<k<\frac{K}{2})\\ F_{\mathrm{BB}}\left(k\right),(\frac{\mathrm{<figure-callout\; id="2"\; label="K"\; filenames="HSA00000416569700012.png"\; state="\{\{state\}\}">K</figure-callout>}}{2}<k<K)\end{array}\right.$ Or $F_{\mathrm{BB}}^{\&prime;}\left(k\right)=\left\{\begin{array}{c}{F}_{\mathrm{BB}}\left(k\right),(0<k<\frac{K}{2})\\ 0,(\frac{\mathrm{<figure-callout\; id="2"\; label="K"\; filenames="HSA00000416569700012.png"\; state="\{\{state\}\}">K</figure-callout>}}{2}<k<K)\end{array}\right.$

3), obtain F ' through Fourier inversion _BB(k) time domain waveform,

In the formula,

Represent Fourier inversion, f ' _BB(n) be the SSB time-domain signal.

The above-mentioned theory method in rfid system, is infeasible.This be because, rfid system can't be born the complexity of Fourier transform usually, although can adopt fast fourier transform algorithm, when counting when too high, its complexity also is high.For example, with the EPC standard of RFIB, binary data sequence f to be sent _RFID(m) length M is generally tens to twenties bits, and message transmission rate is about 100Kbps, adopts the digital-to-analog converter of 10MHz to generate analog signal usually in order to guarantee the envelope detection quality of signals.Therefore under this scene, baseband digital signal f ' length (n) is about 2000 in inferior, needs to realize 2048 Fourier transform, this be rfid system can't bear.

But in fact, the RFID signal is that a kind of transmission rate is low, and wave form varies is communication system more slowly, and utilizing this characteristic is can the Fourier transform of counting greatly be decomposed into three parts.The one, because the wave form varies that the transmission data variation takes place, the 2nd, the variation that data 0 are inner with data 1 waveform, the 3rd, in order to send the waveform of accurate sampling, the over-sampling that carries out.According to the digital signal principle, the digital signal time domain oversampling is not change this signal frequency response, and it is equivalent to this digital signal frequency domain and carries out continuation, and the continuation multiple becomes one-to-one relationship with the over-sampling multiple.Therefore, in the Fourier transform of counting greatly, increased system complexity because the Fourier transform that over-sampling partly causes is counted, and additional gain is not provided.

Utilize above-mentioned RFID signal characteristic, can be with data 0 and data 1 and waveform f ₀(n) and f ₁(n) mapping process is divided into the realization of two steps.Earlier according to f ₀(n) and f ₁(n) relation is found out the minmal sequence that can fully represent 0,1 data difference, is defined as f _Pre-0(n) and f _Pre-1(n), and with this sequence to sending binary sequence f _RFID(m) carry out precoding, obtain precoding sequence f _Pre(l),

f _pre(l)＝{f _pre(1，l)......f _pre(m，l)......f _pre(M，l)}

Wherein, f _Pre(m l) represents m the precoding sequence that binary data shone upon.Then, this precoding sequence being carried out SSB complete, no performance loss handles.Be described three steps of preamble:

1) through Fourier transform, with base band time domain waveform f _Pre(n) change time-domain signal into,

2) through zero forcing algorithm, the positive frequency of the frequency waveform of precoding sequence or negative frequency are partly carried out energy suppress,

3), obtain F ' through Fourier inversion _Pre(k) time domain waveform f ' _Pre(n)

The sequence of process precoding does not comprise the computing of over-sampling, therefore, and to f ' _Pre(n) carry out time domain interpolation or curve fit, can obtain to send signal.

Description of drawings

Fig. 1 is the mapping relations figure of typical encryption algorithm PIE coding in the rfid system.

Fig. 2 is implementation structure figure of the present invention.

Fig. 3 is the internal structure block diagram of middle controller of the present invention.

Embodiment

Specify execution mode of the present invention below:

The present invention is applicable in the rfid system card reader arrangement transmitter, the realization of SSB modulation signal.In force, this card reader arrangement can adopt FPGA (FPGA) or digital signal processor DSP or central processing unit (CPU) or microprocessor realizations such as (MCU).Fig. 2 is the implementation structure figure of this modulated process.Comprise 8 logical blocks among the figure altogether, its major function is respectively:

1) binary sequence 1: this unit is related with the RFID protocol processes, need can directly obtain the binary bits data through the radio open transmission, the i.e. said f of preamble _RFID(m), this sequence length is M.

2) precoding 2: this unit is to binary sequence f _RFID(m) carry out pre-encode operation, the purpose of precoding is according to the transmission map waveform, with minimum information bit, distinguishes the wave character of data 0 and data 1.For example, Fig. 1 is the mapping relations of PIE coding, and data 0 are compiled in this precoding module is binary sequence 10, and data 1 are compiled in this precoding module is binary sequence 1110.The result of precoding is the said f of preamble _Pre(l), the length of this sequence is L.In the output precoding sequence, this unit can write down the multiple to the data expansion of precoding, and sends controller 6 to.Still be encoded to example with PIE, above-mentioned method for precoding is 2 times for the expansion multiple of data 0, and the expansion multiple of data 1 is 4 times.Because in the actual waveform, data 1 are the twices of data 0 length, therefore, its expansion multiple is identical, promptly is 2 times.

3) length adaptive 3: this unit is through the data filling mode, at f _Pre(l) it is individual zero that L ' is mended at head or end, that is,

In the formula, the number of L ' expression zero padding, this value defined does,

In the formula, is defined as the number that rounds up.Making length through this length adapting operation is the binary sequence f of L _Pre(l), become the binary sequence f ' that length is L ' _Pre(l), f ' _Pre(l) length is 2 exponent.Through the length adaptation unit, with the binary sequence f ' that generates _Pre(l) and f _Pre(l) length information exports SSB filter 7 and controller 6 respectively to.

4) the waveform prior information 4: this unit sends the time span information T of signal waveform to controller 6 _pThis temporal information can, and be not limited to obtain through modes such as protocol processing unit, user's exterior arrangement.Be encoded to example with PIE, this time span is the length of data 0, is roughly equal to the arbitrary value between 6.25us to 25us.

5) sampling prior information 5: this unit sends the time sampling interval length information T of digital-to-analog converter to controller 6 _sThis information can, and be not limited to obtain through modes such as hardware feedback, user's exterior arrangement.This value is generally the 0.1us magnitude.

6) controller 6: this unit obtains information from precoding unit 2, length adaptation unit 3, waveform prior information 4, sampling prior information 5, and realizes the control to SSB filter 7 and time domain interpolation unit 8 through the control unit of self.Mainly comprise: (1) controller 6 is through the binary sequence length information after the 3 acquisition precodings of length adaptation unit, and what Fourier changed in this information configuration of SSB controller 11 usefulness SSB filter 7 counts; (2) through from waveform prior information 4, sampling prior information 5 obtain time span information and the sampling time interval information of modulation waveform symbol, be divided by obtain the sampling number of each modulation waveform symbol respectively by above-mentioned two information of sampling number module 9 usefulness for controller 6; (3) controller 6 obtains the binary sequence expansion number information that this module has realized from precoding module 2; Be divided by with sampling number information that obtains in (2) and expansion number information; Obtain remaining over-sampling number of times information, promptly the difference number of times 10, are used to dispose time domain interpolation module 8.

7) the SSB filter 7: this module is compeled zero, Fourier inversion computing through Fourier transform, positive frequency or negative frequency successively to the data of adaptive 3 outputs of length, realizes the SSB filtering to these data.Counting of above-mentioned Fourier transform and Fourier inversion computing is configured through controller 6.

8) time domain interpolation 8: this module is carried out linear interpolation to the data of SSB filter 7 outputs, and interpolation is counted and is configured through controller 6.

Through above-mentioned implementation method, can the present invention be deployed in the transmitter of RFID card reader kind equipment, be used for the SSB signal and realize.

Claims (7)

1. the rfid system SSB signal creating method of low complex degree is characterized in that utilizing small point SSB traffic filter, realizes the SSB modulation of the amount small data quantity mapping relations of RFID forward signal, and realizes the method for equalisation of over-sampled signals through linear interpolation.

2. method according to claim 1, wherein said small point are meant that all data are accomplished the data bulk after shining upon during with minimum data amount characterization signal coded modulation mapping relations.This quantity is 2 exponent.

3. method according to claim 1, wherein said SSB traffic filter is meant treats filtering signal, the filter model of process fast Fourier transform successively, urgent zero computing, Fast Fourier Transform Inverse arithmetic operation.In this model, fast Fourier transform and Fast Fourier Transform Inverse are identical 2 exponent mapping algorithm of counting, compel zero computing and be to the first two/one or the computing of back 1/2nd data zero setting.

4. method according to claim 1, wherein said linear interpolation algorithm are meant utilizes not a plurality of data of point-to-point transmission continuously arbitrarily in the interpolated data of linear function fit, has realized the expansion of data, i.e. over-sampling.The number of interpolated data is utilized minimum data amount in waveform prior information, sampling prior information, the claim 2 in this algorithm, and tripartite surface information obtains by fixed arithmetic.

5. method according to claim 4, waveform prior information are meant the time domain time span information of mapping signal.

6. method according to claim 4, the sampling prior information is meant the time sampling time interval of digital-to-analog converter.

7. method according to claim 4, fixed arithmetic are meant waveform prior information in the claim 5, divided by the prior information of sampling in the claim 6, again divided by minimum data amount in the claim 2.

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