CN100433745C - Receiving frequency compensating method for pi/4 four-phase differential phase-shift key-control modulating mode - Google Patents

Receiving frequency compensating method for pi/4 four-phase differential phase-shift key-control modulating mode Download PDF

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CN100433745C
CN100433745C CNB2004100273467A CN200410027346A CN100433745C CN 100433745 C CN100433745 C CN 100433745C CN B2004100273467 A CNB2004100273467 A CN B2004100273467A CN 200410027346 A CN200410027346 A CN 200410027346A CN 100433745 C CN100433745 C CN 100433745C
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frequency
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frequency departure
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蔡永明
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Global Innovation Polymerization LLC
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Abstract

The present invention relates to a receiving frequency compensating method of a pi/4 four-phase differential phase shift key control modulating mode, which is used for a receiver of a base station or a terminal. The method comprises the following procedures that a received radio frequency carrier signal carries out lower frequency conversion and analog-to-digital conversion; data after the analog-to-digital conversion is orthogonally decomposed to obtain a baseband data IQ component; the IQ component is differentially calculated by a baseband to obtain a component calculation result comprising receiving and transmitting frequency deviation, which compensates the frequency deviation of the judged data. The method of the present invention has the advantages of calculation complexity simplification, system cost saving and system efficiency enhancement. The compact frequency deviation compensating method with low complexity is realized at the receiving end.

Description

The receive frequency compensation method of a kind of п/4 four-phase DPSK modulation systems
Technical field
The present invention relates to a kind of modulator approach of radio digital communication system, relate in particular to the base station of PHS (personnel hand system) system that uses PI/4 DQPSK (π/4 four-phase DPSKs) modulation technique in the wireless digital moving communicating field and the receive frequency compensation method in the terminal.
Background technology
Two basic equipments are arranged usually: base station and terminal in the wireless digital mobile communication system.Between base station and the terminal by carrying out wireless telecommunications after the digital modulation.During specific implementation, all be to adopt modulation technique that base band data is carried out up-conversion to become the radio-frequency carrier signal transmission of posting a letter usually in terminal or base station, carry out received signal after when receiving, again radio-frequency carrier signal being carried out down-conversion and handle, send and receive this process in the realization that cooperatively interacts of base station and terminal room.Consider cost factor; usually base station and terminal room realize that in specific design allowing to send carrier wave has certain frequency departure; when if application system is not considered the deviation of this transmitting-receiving frequency can cause the receptivity of real application systems to descend to some extent when carrying out the receiving demodulation signal processing.
In order to improve receptivity, realize receive frequency and transmission frequency with frequently, existing known technology can be taked two class methods usually:
1) insert pilot tone system, promptly insert one or more sine waves that are called pilot tone when sending useful signal on suitable frequency location, receiving terminal just goes out carrier wave by this pilot extraction;
2) direct method does not send pilot tone specially, and receiving terminal directly extracts carrier wave from send signal.
In direct method, normally carry out to received signal just can extracting carrier component after certain nonlinear transformation, its mainly contain a square converter technique, square around-France, inphase quadrature is around-France etc.Needs and concrete modulation system were carried out combination when these methods realized.
At U.S. Patent number 5,588,026, name is called " a kind of compensation method of phase shift keying frequency departure " " Method of compensating phase shift keying frequency offset " and has realized a kind ofly in the direct method realizing that with the M quadratic method receive frequency and transmission frequency are with frequency, its main implementation procedure is as follows: will import received signal and do the biquadratic conversion earlier, to N code element (symbol) summation that adds up, do average more then.With the average that the obtains tan of negating, the arctan function result who obtains is removed M again, obtain frequency departure angle to be compensated this moment.At last this frequency departure offset and judgement data to be demodulated are multiplied each other, promptly obtained the data after frequency departure compensates.
From above simple narration, can see that this method can take more system resources when realizing, require to realize arctan function; Can certainly simplify the realization of arctan function by the method for look-up table, but because limited bits, the precision that arctan function is realized can descend obviously.
Summary of the invention
The object of the present invention is to provide the receive frequency compensation method of a kind of π/4 four-phase DPSK modulation systems, by overcoming the implementation complexity height in the existing known technology, take the more shortcoming of resource, a kind of implementation efficiency height, method that complexity is low are provided.
Technical scheme of the present invention is as follows:
The receive frequency compensation method of a kind of π/4 four-phase DPSK modulation systems, it is used for the receiver of base station or terminal, and this method may further comprise the steps:
A) radio-frequency carrier signal that receives is carried out down-conversion, analog-to-digital conversion;
B) data after A is carried out quadrature and decompose, obtain base band data IQ component;
C) in base band this IQ component is carried out calculus of differences by π/4 four-phase DPSK modulation systems, obtain the judgement data X to be demodulated that influenced by frequency departure kAnd Y k
The data of judgement to be demodulated are carried out frequency departure as follows to be calculated:
X k＝W kW k-1+Z kZ k-1
Y k＝Z kW k-1-W kZ k-1
Wherein, k is a sequence number, W kBe k the base band data I component that obtains after the quadrature decomposition; Z kBe k the base band data Q component that obtains after the quadrature decomposition;
Continuous a plurality of result of calculation summations are averaged, obtain frequency departure mean value;
D) data of judgement to be demodulated are carried out the frequency departure compensating operation.
Described method, wherein, described step c) specifically comprises:
C21) in digital signal processor spare, carry out differential ference spiral according to following formula earlier:
Figure C20041002734600061
Wherein, θ (k) is the phase modulation of k code element;
According to following formula, two paths of signals W kAnd Z kCarry out differential ference spiral by differential decoder, decoder is worked in such a way,
X k＝W kW k-1+Z kZ k-1
Y k＝Z kW k-1-W kZ k-1；
C22) obtain containing the function of frequency departure parameter according to the formula of following table:
Figure C20041002734600063
Wherein, X k, Y kBe the judgement data to be demodulated behind the differential decoding, α is the angle of transmitting-receiving carrier frequency difference on the frequency correspondence;
C23) summation is averaged, and obtains frequency departure mean value.
Described method wherein, carries out frequency departure compensation and is according to the following equation carrying out the frequency departure compensation with the data of frequency departure mean value after to differential ference spiral, and the data after the compensation are adjudicated as the data source of adjudicating:
Xk′＝Xk*cos(α)+Yk*sin(α)
Yk′0＝Yk*cos(α)-Xk*sin(α)。
Adopt the method for the invention, compared with prior art, simplified the complexity of computing, the system that saved realizes cost, has improved system's implementation efficiency, and has realized a kind of more succinct, method of carrying out the frequency departure compensation that implementation complexity is low at receiving terminal.
Description of drawings
Fig. 1 is the received signal treatment system block diagram of the PI/4 DQPSK modulating system of the inventive method;
Fig. 2 is the flow chart of the realization frequency departure compensation of the inventive method;
Fig. 3 is the PHS base station receive path framework schematic diagram of the inventive method;
Fig. 4 carries out frequency compensated base band signal process schematic flow sheet for the PHS base station of the inventive method.
Embodiment
Below in conjunction with accompanying drawing, preferred embodiment of the present invention is described in detail, and the concrete enforcement that is combined in the PHS system base-station is described in further detail.
The method basic process of the frequency departure compensation of a kind of PI/4DQPSK modulation system of the present invention is as follows:
According to the modulation system of PI/4DQPSK, realize in the following manner when receiver is handled: earlier the radio-frequency carrier signal that receives is carried out down-conversion, analog-to-digital conversion is carried out the quadrature decomposition then and is obtained base band data IQ component.In base band the IQ data of this reception are carried out calculus of differences,, comprised the component of transmitting-receiving frequency deviation in the operation result because receive frequency is different with transmission frequency.
Consider the implementation of real system characteristic and PI/4DQPSK, the absolute value of contained frequency departure component will be less than 45 degree in the operation result, and theoretical demodulation phase is positive and negative 45 degree and positive and negative 135 degree simultaneously.According to this characteristic, the result behind the calculus of differences by four anti-operations of quadrant, is found the solution and obtains an instantaneous exemplary frequency deviation values.A N continuous reception data are as above handled, and summation is averaged then, just obtains a frequency departure average.
The frequency departure average that obtains is carried out inverse operation according to the result of calculus of differences, realize frequency departure compensation operation a N continuous data.It is exactly as formula C23 that concrete compensation realizes, detailed compensation process is: the frequency deviation value of only having used single code element in this formula, consider the air traffic channel characteristic, need do same processing to a N continuous symbol data, frequency deviation value function cos α and the corresponding respectively summation of sin α that N symbol data obtained are averaged, and obtain a mean value after N symbol data handled: cos α and sin α.The cos α and the sin α that obtain after the average treatment are being applied to formula C23, just can be in the hope of the judgement data to be demodulated behind N the symbol data compensate of frequency deviation.
From above narration, it is simple to see that this method is carried out the computing of frequency departure compensation, on implementation efficiency also than higher.
Be the received signal treatment system block diagram of the PI/4 4DQPSK modulating system of the inventive method as shown in Figure 1, carry out the differential ference spiral algorithm in base band, this is in DSP, FPGA a kind of processing method commonly used under the background of popularization and application day by day.When considering that reception and transmission frequency there are differences, its some dependency relations are as follows:
The base band differential ference spiral mode of PI/4DQPSK:
Suppose that aerial radio-frequency carrier received signal is:
Figure C20041002734600081
k*T≤t＜(k+1)*T，k＝0..∞(1)
Wherein, T is the duration of a code element.w c=2* π * f c, f cThe carrier frequency of the radiofrequency signal of receiving for the base station.
Figure C20041002734600082
Receive the additive phase that produces for the space Transmission Connection.
The aerial radio-frequency carrier signal that receives is carried out down-conversion and quadrature decomposition, multiplies each other, be through the low frequency signal that leaches behind the low pass filter by two-way homophase, orthogonal signalling and local carrier ω:
Figure C20041002734600084
Wherein, θ (k) is the phase modulation of k code element.
According to formula (2), two paths of signals W kAnd Z kCarry out differential ference spiral by differential decoder.Decoder is worked in such a way,
X k＝W kW k-1+Z kZ k-1
Y k＝Z kW k-1-W kZ k-1 (3)
(3) are expanded into,
Figure C20041002734600091
Figure C20041002734600092
= cos { θ ( k ) - θ ( k - 1 ) + ( ω c - ω ) * [ t ( k ) - t ( k - 1 ) ] }
= cos ( Δθ ( k ) + ( ω c - ω ) * T )
Figure C20041002734600095
= sin { θ ( k ) - θ ( k - 1 ) + ( ω c - ω ) * [ t ( k ) - t ( k - 1 ) ] }
= sin [ Δθ ( k ) + ( ω c - ω ) * T ]
Wherein, Δ θ (k)=θ (k)-θ (k-1)
ω c-ω＝2*π*(f c-f)＝2*π*Δf
... by above derivation, can obtain X k, Y kFor containing the variable of frequency deviation f.
Be the flow chart of frequency departure compensation as shown in Figure 2, in the system of Fig. 1, carry out this frequency compensated flow chart after the influence of consideration frequency departure.
According to the modulation of PI/4 DQPSK, the phase difference θ that has determined two code elements is in following four numerical value: [π/4 ,-π/4, π * 3/4 ,-π * 3/4].
With X in the formula (4) kAnd Y kFinal result launch, establish (ω c-ω) * T=α obtains, as | α | and during＜π/4, formula (4) can be simplified the relation formula that try to achieve in the table 1:
The relation table of variable after table 1 frequency departure function and the differential ference spiral
At last the data of judgement to be demodulated are carried out the frequency departure compensating operation.
Derivation from formula (4) is learnt, establishes when not having frequency deviation f, and the variable of judgement to be demodulated is
Xk’＝cos(Δθ(k))
Yk’＝sin(Δθ(k))(5)
Then have following formula to set up:
Xk′＝cos(Δθ(k)+α-α)
＝cos(Δθ(k)+α)cos(α)+sin(Δθ(k)+α)sin(α)
＝Xk*cos(α)+Yk*sin(α)
Yk′＝sin(Δθ(k)+α-α)
＝sin(Δθ(k)+α)cos(α)-cos(Δθ(k)+α)sin(α)
＝Yk*cos(α)-Xk*sin(α)
(6)
Obviously, the data of the judgement to be demodulated of frequency departure compensation have been obtained carrying out in the formula (6).According to the above derivation of equation, in flow chart, realized the receive frequency difference compensation function.
This method can be used for the reception of radio digital communication field PHS system base-station or terminal and the compensation of transmission frequency deviation is used.
The PHS system adopts PI/4 DQPSK modulation technique, and base station and terminal allow the transmission frequency deviation to be ± 3ppm.The compensation of system docking receipts frequency departure realizes not doing requirement, but in order further to improve the receiving sensitivity of base station or terminal, need carry out the receiving frequency deviation compensation when reception is handled.In addition, the PHS system is the TDD/TDMA system, and frequency departure is calculated the real-time requirement, requires the implementation efficiency height, requires resource overhead the least possible simultaneously.
The receive path that has shown the PHS system base-station as shown in Figure 3 partly constitutes.At first base station equipment will be carried out down-conversion by radio frequency part from the aerial radio-frequency carrier signal (earlier through the PI/4DQPSK modulation) that antenna receives, there are certain frequency departure in the local frequency that this base station receive path is used and the frequency of aerial radio-frequency carrier signal, be input to base band at last through the intermediate-freuqncy signal after the down-conversion and carry out signal processing, the base band signal process hardware components is made of devices such as analog to digital converter, Digital Signal Processing DSP and programmable device FPGAs, and the signal processing of base band mainly realizes in DSP.
The base band signal process flow chart that has shown the receive frequency deviation compensation as shown in Figure 4.At first change by analog to digital converter, the data after will changing are then carried out the quadrature decomposition, and the IQ component data that obtains is input among the DSP.In DSP, carry out differential ference spiral according to formula (3) earlier, obtain containing the function of frequency departure parameter then according to the formula of table 1, summation is averaged then, according to formula (6) data after the differential ference spiral are carried out the frequency departure compensation at last, the data after the compensation are adjudicated as the data source of judgement.After as above handling, just realized the compensation of receive frequency and transmission frequency deviation.
Through the base station after such frequency departure compensation deals, the complexity of algorithm process is low, and it is few to take resource, and real-time is stronger, can guarantee in the certain frequency deviation range that after implementing this method receiving sensitivity does not obviously worsen, and has improved the receiving sensitivity of practical application simultaneously indirectly.
More than be detailed description, can not therefore limit that its protection range should be as the criterion with claims to scope of patent protection of the present invention to the preferred embodiment of the inventive method.

Claims (3)

1. the receive frequency compensation method of π/4 four-phase DPSK modulation systems, it is used for the receiver of base station or terminal, and this method may further comprise the steps:
A) radio-frequency carrier signal that receives is carried out down-conversion, analog-to-digital conversion;
B) data after A is carried out quadrature and decompose, obtain base band data IQ component;
C) in base band to this IQ component by the judgement data X to be demodulated that obtains after π/4 four-phase DPSK modulation systems are carried out calculus of differences influenced by frequency departure kAnd Y k, the data of judgement to be demodulated are carried out frequency departure as follows calculate:
X k＝W kW k-1+Z kZ k-1
Y k＝Z kW k-1-W kZ k-1
Wherein, k is a sequence number, W kBe k the base band data I component that obtains after the quadrature decomposition; Z kBe k the base band data Q component that obtains after the quadrature decomposition;
Continuous a plurality of result of calculation summations are averaged, obtain the mean value of frequency departure;
D) data of judgement to be demodulated are carried out the frequency departure compensating operation.
2. the receive frequency compensation method of π according to claim 1/4 four-phase DPSK modulation systems is characterized in that described step c) specifically comprises:
C21) in digital signal processor spare, carry out differential ference spiral according to following formula earlier:
Figure C2004100273460002C1
Figure C2004100273460002C2
Wherein, θ (k) is the phase modulation of k code element;
According to following formula, two paths of signals W kAnd Z kCarry out differential ference spiral by differential decoder, decoder is worked in such a way,
X k＝W kW k-1+Z kZ k-1
Y k＝Z kW k-1-W kZ k-1；
C22) obtain containing the function of frequency departure parameter according to the formula of following table:
Figure C2004100273460003C1
Wherein, X k, Y kBe the judgement data to be demodulated behind the differential decoding, α is the angle of transmitting-receiving carrier frequency difference on the frequency correspondence;
C23) summation is averaged, and obtains frequency departure mean value.
3. the receive frequency compensation method of π according to claim 2/4 four-phase DPSK modulation systems, it is characterized in that, carry out frequency departure compensation and be according to the following equation carrying out the frequency departure compensation, the data after the compensation are adjudicated as the data source of adjudicating with the data of frequency departure mean value after to differential ference spiral:
Xk′＝Xk*cos(α)+Yk*sin(α)
Yk′＝Yk*cos(α)-Xk*sin(α)
Wherein, X k', Y k' be the judgement data to be demodulated of having carried out the frequency departure compensation behind the differential decoding.
CNB2004100273467A 2004-05-21 2004-05-21 Receiving frequency compensating method for pi/4 four-phase differential phase-shift key-control modulating mode Expired - Fee Related CN100433745C (en)

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US7668256B2 (en) * 2006-07-20 2010-02-23 Alcatel-Lucent Usa Inc. Method and apparatus for the generation and detection of optical differential varied-multilevel phase-shift keying with pulse amplitude modulation (ODVMPSK/PAM) signals

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Publication number Priority date Publication date Assignee Title
CN1270724A (en) * 1997-08-08 2000-10-18 埃瑞康姆公司 Method and system for rapid initial signal detection in a wireless communications system
CN1301447A (en) * 1998-04-14 2001-06-27 弗兰霍菲尔运输应用研究公司 Method and apparatus for fine frequency synchronization in multi-carrier demodulation systems
US6396880B1 (en) * 1998-04-17 2002-05-28 Analog Devices Inc π/4 DQPSK encoder and modulator
CN1423493A (en) * 2001-12-07 2003-06-11 深圳市中兴通讯股份有限公司上海第二研究所 Signal receiving method and apparatus in wireless base station

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