CN1674467A - Data transmitting method in short-distance radio network - Google Patents

Data transmitting method in short-distance radio network Download PDF

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CN1674467A
CN1674467A CN 200510069319 CN200510069319A CN1674467A CN 1674467 A CN1674467 A CN 1674467A CN 200510069319 CN200510069319 CN 200510069319 CN 200510069319 A CN200510069319 A CN 200510069319A CN 1674467 A CN1674467 A CN 1674467A
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signal
frequency expansion
frequency
expansion sequence
sequence
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CN100361424C (en
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田亚飞
杨晨阳
刘婷婷
郦亮
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WEIXUNZIJING SCIENCE AND TECHNOLOGY Co Ltd BEIJING
Beihang University
Beijing University of Aeronautics and Astronautics
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WEIXUNZIJING SCIENCE AND TECHNOLOGY Co Ltd BEIJING
Beihang University
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Abstract

The present invention relates to a data transmission module in short-distance wireless network, belonging to the field of wireless communication technology. Said method includes the following steps: firstly, creating a mapping table, forming the data bit to be sent into protocol data unit; searching spread-spectrum sequence correspondent to the bit sequence in protocol data unit; pulse-shaping spread-spectrum sequence, modulating it on in-phase and orthogonal carrier to obtain radio-frequency send signal; receiving said signal and making down conversion to obtain baseband receiving signal; estimating and compensating a partial frequency deviation; time synchronizing the signal in front synchronous head place, detecting frame delimiter signal and time synchronizing it; calculating time synchronizing value and deviation estimation value, demodulating physical layer signal head and signal of service data unit so as to obtain data bit of sending end.

Description

Data transmission method in the short-range wireless networking
Technical field
The present invention relates to the data transmission method in a kind of short-range wireless networking, relate in particular to transmission and the reception and the method for reseptance of data in the short-range wireless networking, belong to technical field of wireless communication.
Background technology
Mostly modern wireless communication is transmitted in packets, promptly only transmits a packet between the transceiver at every turn, all will carry out time and Frequency Synchronization between the transceiver before transfer of data begins each time.In the system based on spread spectrum, time synchronized should find the border of frequency expansion sequence, and in the sequence each element respective pulses optimum sampling constantly.And Frequency Synchronization is that the carrier frequency of receiving terminal and transmitting terminal is consistent, to eliminate the influence of frequency shift (FS) to the data demodulation.Therefore, Time and Frequency Synchronization is two very crucial in modern wireless network communication system problems.
In system based on spread spectrum, frequency expansion sequence generally all has good autocorrelation performance, by using the reference signal of known frequency expansion sequence as receiver this locality, conventional time synchronized can be abutted against collect mail number and the reference signal of receiver this locality between do that sliding is correlated with finishes.When frequency expansion sequence in the received signal and the alignment of the frequency expansion sequence in the reference signal, correlation can show a peak value, and in other cases, correlation approaches zero.But, when having bigger frequency deviation in the received signal, the slip correlation of received signal and receiver local reference signal can be subjected to very big influence, under some frequency deviation, even during the alignment of the frequency expansion sequence in frequency expansion sequence in the received signal and the reference signal, correlation also approaches zero.Occurring so big frequency deviation in the received signal mainly is because all use the crystal oscillator of low cost on the transmitter and receiver of short-range wireless networking, the deviation of this oscillator can reach ± 40ppm, for the system that is operated in the 2.4GHz frequency range, so big deviation can cause the frequency shift (FS) of 192KHz, if the cycle of a frequency expansion sequence is 16 μ s, mean that then the phase deviation that frequency deviation causes in this cycle has reached 6.14 π.
In order to use the relevant method deadline of sliding synchronous, need estimate the size of frequency deviation earlier and proofreaied and correct to received signal according to estimated value.The front and back difference is a kind of method commonly used in the frequency offset estimating, it utilizes the periodicity of preamble head place frequency expansion sequence in the received signal, frequency expansion sequence cycle of being separated by is carried out difference to former and later two sampled points, be the conjugation of a back dot product with previous point, to remove the phase place of frequency expansion sequence in the received signal itself, only stay the phase difference that frequency deviation causes, thereby estimate the value of frequency deviation.But, because the interval of phase estimation is-π～π, so this method can only estimate-1/2T s～1/2T sBetween frequency deviation, T here sIt is the cycle of frequency expansion sequence.For the frequency deviation that exceeds this scope, can use U.S. Pat 5,303, the method that 257 (carrier wave in the DSSS communication system is proofreaied and correct, in April, 1994) propose is estimated.This method is estimated the value of frequency deviation by seeking received signal in the maximum of the energy at different frequency place, but the estimated value that it obtains is not accurate enough and amount of calculation is bigger.
Goal of the invention
The objective of the invention is to propose transmission and the reception and the method for reseptance of data in data transmission method, the especially short-range wireless networking in a kind of short-range wireless networking, to reduce the amount of calculation of Time and Frequency Synchronization under the big frequency deviation.In sending method, use the frequency expansion sequence of GCL sequences as the preamble head, use the frequency expansion sequence of the conjugate sequence of GCL sequences, thereby in method of reseptance, compensation is fallen-1/2T as frame delimiter s～1/2T sBetween frequency deviation after, the residue 1/T sUnder the condition of the frequency deviation of integral multiple, still can obtain correlation peak between received signal and the initial frequency expansion sequence, and can utilize the deviation on preamble head place and the frame delimiter place correlation peak location, unite the value that obtains time synchronized and frequency offset estimating.In the process of Time and Frequency Synchronization, the slip between received signal and the initial frequency expansion sequence is relevant can to utilize fast fourier transform to realize, with the amount of calculation of further reduction Time and Frequency Synchronization.
Data transmission method in the short-range wireless networking that the present invention proposes, the sending, receiving method of data wherein comprises following each step:
(1) sets up mapping table between a bit sequence and the frequency expansion sequence;
(2) protocol Data Unit of the data form composed as follows that intermediary of network matter access control sublayer is sent:
The preamble head Frame delimiter Physical layer letter head Service data unit
(3) the mapping table between above-mentioned bit sequence and frequency expansion sequence, the corresponding frequency expansion sequence of bit sequence in retrieval and the protocol Data Unit;
(4) the above-mentioned frequency expansion sequence that retrieves is carried out pulse shaping, become baseband transmit signals;
(5) above-mentioned baseband transmit signals is modulated on homophase and the quadrature carrier, becomes radio frequency transmit signal;
(6) receive above-mentioned radio frequency transmit signal, carry out down-conversion and obtain baseband receiving signals, in the estimation baseband receiving signals-1/2T s～1/2T sFrequency deviation, and compensation, T wherein sIt is the cycle of frequency expansion sequence;
(7) it is slightly synchronous the signal at preamble head place in the above-mentioned baseband receiving signals to be carried out the time, and the time of carrying out again is synchronously smart;
(8) from above-mentioned baseband receiving signals, detect the frame delimiter signal, and it is carried out time synchronized;
(9) according to time synchronized value and frequency offset estimating value in the time synchronized value calculated data receiving course at above-mentioned preamble head place and frame delimiter place;
(10) signal to the letter of the physical layer in baseband receiving signals head and service data unit carries out demodulation, obtains the data bit of transmitting terminal.
The method of reseptance of data wherein comprises following each step:
(1) radio frequency transmit signal of transmitting terminal in the reception short-range wireless networking carries out down-conversion and obtains baseband receiving signals, in the estimation baseband receiving signals-and 1/2T s～1/2T sFrequency deviation, and compensation, T wherein sIt is the cycle of frequency expansion sequence;
(2) it is slightly synchronous the signal at preamble head place in the above-mentioned baseband receiving signals to be carried out the time, and the time of carrying out again is synchronously smart;
(3) from above-mentioned baseband receiving signals, detect the frame delimiter signal, and it is carried out time synchronized;
(4) according to time synchronized value and frequency offset estimating value in the time synchronized value calculated data receiving course at above-mentioned preamble head place and frame delimiter place;
(5) signal to the letter of the physical layer in baseband receiving signals head and service data unit carries out demodulation, obtains the data bit of transmitting terminal.
Set up the method for the mapping table between bit sequence and the frequency expansion sequence in the above-mentioned data transmission method for uplink, may further comprise the steps:
(1) is initial frequency expansion sequence with GCL sequences, initial frequency expansion sequence is carried out cyclic shift, obtain all frequency expansion sequences;
(2) make frequency expansion sequence corresponding with bit sequence, corresponding method is: the decimal number of expression bit sequence is corresponding with the cyclic shift figure place of frequency expansion sequence.
In the above-mentioned data transmission method for uplink, in the packet after the framing,, retrieve frequency expansion sequence corresponding, again this frequency expansion sequence is carried out conjugater transformation with it according to described mapping table to the bit sequence of component frame delimiter.
In the above-mentioned data receive method, the signal at preamble head place in the baseband receiving signals is carried out thick synchronous method of time, comprises following each step:
(1) sampled signal in a frequency expansion sequence cycle of taking-up from the preamble head signal of baseband receiving signals;
(2) initial frequency expansion sequence is carried out conjugater transformation, the initial frequency expansion sequence after the conjugater transformation and the sampled signal in an above-mentioned frequency expansion sequence cycle are multiplied each other;
(3) the above-mentioned later signal that multiplies each other is carried out fast fourier transform, obtain the slip correlation between baseband receiving signals and the initial frequency expansion sequence;
(4) from the length in frequency expansion sequence cycle, deduct the pairing abscissa length of maximum in the above-mentioned slip correlation, be the thick synchronization value of time of preamble head place signal in the baseband receiving signals.
In the above-mentioned data receive method, detect the method for frame delimiter signal in the baseband receiving signals, may further comprise the steps:
(1) generating a frequency is 1/T sMultiple sinusoidal sequence, T wherein sIt is the cycle of frequency expansion sequence;
(2) be starting point with thick synchronization position of time, take out the sampled signal in a frequency expansion sequence cycle;
(3) above-mentioned sampled signal is carried out the front and back calculus of differences, obtain a new difference sequence, this difference sequence and above-mentioned multiple sinusoidal sequence are carried out relevant, obtain a correlation;
(4) above-mentioned correlation is compared with the threshold value of a setting, less than threshold value, the signal in then current this frequency expansion sequence cycle is the frame delimiter signal in the baseband receiving signals as if correlation; If correlation greater than threshold value, is then got the sampled signal in next frequency expansion sequence cycle, repeating step (3)～(4).
In the above-mentioned data receive method,, may further comprise the steps according to the time synchronized value in the time synchronized value calculated data receiving course at preamble head place and frame delimiter place and the method for frequency offset estimating value:
(1) average of the time synchronized value at preamble head place and frame delimiter place is the time synchronized value in the DRP data reception process;
(2) the frequency offset estimating value in the DRP data reception process is k/T s+ Δ f, wherein k is poor between the time synchronized value at frame delimiter place and the above-mentioned average, Δ f for estimated-1/2T s～1/2T sFrequency deviation value.
The short-distance radio network data transmission method that the present invention proposes has the following advantages:
(1) in the data transmission procedure of the inventive method, the mapping of the each several part in the protocol Data Unit all is based on same GCL sequences, and GCL sequences has constant envelope, and therefore the hardware system structure of realizing is simple;
(2) GCL sequences that relates in the inventive method has desirable autocorrelation, is easy to realize the time synchronized in the transfer of data, and makes receiver have the ability of good diversity anti-multipath;
(3) in the inventive method frequency offset estimating be divided into two the step realize-1/2T s～1/2T sBetween frequency deviation estimate 1/T by the method for front and back difference sThe frequency deviation of integral multiple is estimated by the alternate position spike of preamble head place and frame delimiter place correlation peak, therefore can correct very big frequency shift (FS) with very little amount of calculation.
(4) slip between received signal and the initial frequency expansion sequence is relevant in the inventive method realizes by fast fourier transform, greatly reduces the amount of calculation of DRP data reception process;
Characteristic curve is done essence synchronously when (5) utilizing mirror in the inventive method, and the sample rate that has reduced received signal is conciliate the amount of calculation of timing.
Description of drawings
Fig. 1 is data transmission flow figure in the inventive method.
Fig. 2 is a Data Receiving flow chart in the inventive method.
Fig. 3 is the form of protocol Data Unit.
Fig. 4 is the oscillogram of shaped pulse.
Fig. 5 is the slip correlation schematic diagram between received signal and the initial frequency expansion sequence under the different frequency deviations.
Fig. 6 is that the tapped delay line structure is realized the relevant schematic diagram that slides in the prior art.
Fig. 7 is that fast fourier transform architecture is realized the relevant schematic diagram that slides.
Fig. 8 is that received signal is with initially the main lobe of frequency expansion sequence slip correlation and of being shifted also anti-phase thereof duplicate.
Fig. 9 is a characteristic curve schematic diagram when carrying out the smart mirror that relates to synchronously in this method to received signal.
Figure 10 is a synchronization value and the time-frequency decoupling principle schematic diagram during frequency offset estimating value computing time.
Embodiment
Data transmission method in the short-range wireless networking that the present invention proposes, wherein the sending, receiving method of data is at first set up the mapping table between a bit sequence and the frequency expansion sequence; The protocol Data Unit of the data form composed as follows that intermediary of network matter access control sublayer is sent:
The preamble head Frame delimiter Physical layer letter head Service data unit
The mapping table between bit sequence and frequency expansion sequence, the corresponding frequency expansion sequence of bit sequence in retrieval and the protocol Data Unit; The frequency expansion sequence that retrieves is carried out pulse shaping, become baseband transmit signals; Baseband transmit signals is modulated on homophase and the quadrature carrier, becomes radio frequency transmit signal; Receive above-mentioned radio frequency transmit signal, carry out down-conversion and obtain baseband receiving signals, in the estimation baseband receiving signals-1/2T s～1/2T sFrequency deviation, and compensation, T wherein sIt is the cycle of frequency expansion sequence; It is slightly synchronous that the signal at preamble head place in the above-mentioned baseband receiving signals is carried out the time, and the time of carrying out again is synchronously smart; From above-mentioned baseband receiving signals, detect the frame delimiter signal, and it is carried out time synchronized; According to time synchronized value and the frequency offset estimating value in the time synchronized value calculated data receiving course at above-mentioned preamble head place and frame delimiter place; Signal to the letter of the physical layer in baseband receiving signals head and service data unit carries out demodulation, obtains the data bit of transmitting terminal.
The method of reseptance of data wherein at first receives the radio frequency transmit signal of transmitting terminal in the short-range wireless networking, carries out down-conversion and obtains baseband receiving signals, estimates in the baseband receiving signals-1/2T s～1/2T sFrequency deviation, and compensation, T wherein sIt is the cycle of frequency expansion sequence; It is slightly synchronous that the signal at preamble head place in the baseband receiving signals is carried out the time, and the time of carrying out again is synchronously smart; From above-mentioned baseband receiving signals, detect the frame delimiter signal, and it is carried out time synchronized; According to time synchronized value and the frequency offset estimating value in the time synchronized value calculated data receiving course at above-mentioned preamble head place and frame delimiter place; Signal to the letter of the physical layer in baseband receiving signals head and service data unit carries out demodulation, obtains the data bit of transmitting terminal.
Setting up the method for the mapping table between bit sequence and the frequency expansion sequence in the above-mentioned data transmission method for uplink, is initial frequency expansion sequence with GCL sequences at first, and initial frequency expansion sequence is carried out cyclic shift, obtains all frequency expansion sequences; Make frequency expansion sequence corresponding with bit sequence, corresponding method is: the decimal number of expression bit sequence is corresponding with the cyclic shift figure place of frequency expansion sequence.
In the above-mentioned data transmission method for uplink, in the packet after the framing,, retrieve frequency expansion sequence corresponding, again this frequency expansion sequence is carried out conjugater transformation with it according to described mapping table to the bit sequence of component frame delimiter.
In the above-mentioned data receive method, the signal at preamble head place in the baseband receiving signals is carried out thick synchronous method of time, at first from the preamble head signal of baseband receiving signals, take out the sampled signal in a frequency expansion sequence cycle; Initial frequency expansion sequence is carried out conjugater transformation, the initial frequency expansion sequence after the conjugater transformation and the sampled signal in an above-mentioned frequency expansion sequence cycle are multiplied each other; The above-mentioned later signal that multiplies each other is carried out fast fourier transform, obtain the slip correlation between baseband receiving signals and the initial frequency expansion sequence; From the length in frequency expansion sequence cycle, deduct the pairing abscissa length of maximum in the above-mentioned slip correlation, be the thick synchronization value of time of preamble head place signal in the baseband receiving signals.
In the above-mentioned data receive method, detect the method for frame delimiter signal in the baseband receiving signals, at first generating a frequency is 1/T sMultiple sinusoidal sequence, T wherein sIt is the cycle of frequency expansion sequence; With thick synchronization position of time is starting point, takes out the sampled signal in a frequency expansion sequence cycle; Above-mentioned sampled signal is carried out the front and back calculus of differences, obtain a new difference sequence, this difference sequence and above-mentioned multiple sinusoidal sequence are carried out relevant, obtain a correlation; Above-mentioned correlation is compared with the threshold value of a setting, and less than threshold value, the signal in then current this frequency expansion sequence cycle is the frame delimiter signal in the baseband receiving signals as if correlation; If correlation greater than threshold value, is then got the sampled signal in next frequency expansion sequence cycle, repeat said process.
In the above-mentioned data receive method, according to the time synchronized value in the time synchronized value calculated data receiving course at preamble head place and frame delimiter place and the method for frequency offset estimating value, at first the average of the time synchronized value at preamble head place and frame delimiter place is the time synchronized value in the DRP data reception process; Frequency offset estimating value in the DRP data reception process is k/T s+ Δ f, wherein k is poor between the time synchronized value at frame delimiter place and the above-mentioned average, Δ f for estimated-1/2T s～1/2T sFrequency deviation value.
Illustrated in figures 1 and 2 is the transmission and the receiving course block diagram of short-distance radio network data transmission method of the present invention.In process of transmitting, at first set up a mapping table, then armed data bit is formed a protocol Data Unit, the bit sequence that bit in the protocol Data Unit is divided into one group of group by vertical order, retrieve the frequency expansion sequence of every group of bit sequence correspondence according to mapping table, these frequency expansion sequences are modulated at last on the inphase quadrature two-way carrier wave and launch through pulse shaping.In receiving course, at first radio frequency receiving signal is down-converted to baseband receiving signals, pass through then-1/2T s～1/2T sThe estimation and the compensation of frequency deviation, the time at preamble head place is synchronously thick and synchronously smart, frame delimiter detects, the data bit of demodulation to obtain launching carried out in the time synchronized at frame delimiter place and time-frequency decoupling zero at last.In the following description ,-1/2T s～1/2T sFrequency deviation be called as 1/T sThe frequency deviation of little several times.
Sending method in the short-distance radio network data transmission method of the present invention at first will be set up a mapping table, is used for retrieving and the corresponding frequency expansion sequence of armed bit sequence.In this mapping table, initial frequency expansion sequence is a GCL sequences, and other frequency expansion sequence is the cyclic shift of this initiation sequence.The GCL sequences that constitutes initial frequency expansion sequence is made up of N element, and N is an even number, wherein n element a nExpression formula be,
a n = exp ( j Mπ n 2 N ) ,
Here n=0,1 ..., N-1, M are the integers relatively prime with N, equaling 1 with M in following each several part is that example describes.GCL sequences is the sequence of complex numbers of permanent envelope, and its phase place is nonlinear change with sampled point, and frequency is linear change with sampled point, so can regard it as the sample sequence of linear FM signal.This sequence is proposed in 1972 by David C.Chu, again it is called the Zadoff-Chu sequence in the world.
Other frequency expansion sequence in the mapping table is produced through cyclic shift by initial frequency expansion sequence.Each bit sequence just corresponding a kind of cyclic shift wherein, concrete corresponding relation is the figure place that the decimal representation of bit sequence has determined cyclic shift.
The inventive method adopts the transmission mode based on packet, and the load of each packet is called as service data unit.Service data unit needed to form earlier protocol Data Unit before being launched, to make things convenient for the correct reception of system to these data.The form of protocol Data Unit as shown in Figure 3, it comprises preamble head, frame delimiter, physical layer letter head and four parts of service data unit.
The preamble head is used for detecting the arrival of received signal, and the auxiliary automatic gain that carries out is controlled, and the time of carrying out and work such as Frequency Synchronization, channel estimating.The preamble head is made up of one group of bit 0 that repeats, and in one embodiment of the invention, it is made up of 32 bits 0.
Frame delimiter is used to refer to the end of preamble head and the beginning of data field, also be used for assisting the work of Time and Frequency Synchronization, it also is made up of one group of bit 0 that repeats, but after the bit sequence at frame delimiter place was mapped to frequency expansion sequence, the element of frequency expansion sequence will be got conjugation.In one embodiment of the invention, frame delimiter is made up of 8 bits 0.
Physical layer is believed information such as a length that is used for representing service data unit, modulation system, data transfer rate.In one embodiment of the invention, the modulation system and the data transfer rate of service data unit are all fixed, and physical layer letter head is made up of 8 bits, the byte number in the expression service data unit.Data transfer rate also can be variable, and for example physical layer letter head is made up of 12 bits, and wherein 8 bits are used for representing the byte number in the service data unit, and 2 bits are used for representing 4 kinds of possible data transfer rates, and two other bit is as keeping.
Physical layer service data is used for the data that send transmission medium access control sublayer, its variable-length.
Bit in the physical layer protocol data unit just can be launched through spread spectrum and modulation.The bit sequence that at first bit in the protocol Data Unit is divided into one group of group by vertical order, retrieve the frequency expansion sequence of every group of bit sequence correspondence then according to mapping table, the element of these frequency expansion sequences is modulated to then on the inphase quadrature two-way carrier wave and launches through pulse shaping.In the following description, the element of the frequency expansion sequence chip that is otherwise known as.
The purpose of pulse shaping mainly is that the power spectrum that transmits is adjusted, and reduces its interference to adjacent channel.In a kind of possible embodiment, the impulse response of the raised cosine roll off filter after the employing brachymemma is as shaped pulse, and the impulse response of raised cosine roll off filter is
h ( t ) = sin ( πt / T ) πt / T cos ( απt / T ) 1 - ( 4 α 2 t 2 / T 2 ) ,
In the following formula, α is a roll-off factor, and T is a chip period.When α=0.2, the impulse response of the raised cosine roll off filter after the brachymemma as shown in Figure 4.
GCL sequences has desirable cycle autocorrelation performance, and promptly two identical GCL sequences only just have the correlation of non-zero in alignment, and correlation all is zero under other situation.This characteristic can be formulated as,
R ( k ) = Σ n = 0 N - 1 a ( n + k ) % N a n * = N , k = 0 0 , k = 1 , · · · , N - 1
Autocorrelation value when R in the formula (k) expression displacement is k, N is the length of frequency expansion sequence, and % represents to ask modular arithmetic, and promptly after n+k surpassed N, since 0 calculating, this was equivalent to GCL sequences is done circulative shift operation the subscript of a again.
At 1/T sThe influence of frequency deviation of integral multiple under, GCL sequences produces the effect of cyclic shift, and the figure place of cyclic shift and 1/T sMultiple equate that this characteristic can be formulated as,
exp ( j πn 2 N ) · exp ( j 2 πk N n ) = exp ( - j k 2 π N ) · exp ( j π ( n + k ) 2 N )
Perhaps,
exp ( - j πn 2 N ) · exp ( j 2 πk N n ) = exp ( j k 2 π N ) · exp ( j π ( n - k ) 2 N )
First expression in left side GCL sequences in the following formula, second expression 1/T sK frequency deviation doubly; First expression in the right is relevant still with an irrelevant fixed skew of n with k, and second expression circulation moves the GCL sequences behind the k position.To the GCL sequences of M=1, k/T sFrequency deviation make it produce the effect of cyclic shift left, to the GCL sequences of M=-1, k/T sFrequency deviation make it produce the effect of cyclic shift to the right, and in both cases, the fixed skew that the right is first also is anti-phase.In an embodiment, what preamble head place used is the initial frequency expansion sequence that repeats in the cycle, i.e. the GCL sequences of M=1, and the frame delimiter place uses is the conjugate sequence of the initial frequency expansion sequence that repeats in the cycle, the i.e. GCL sequences of M=-1.
Above-mentioned character has illustrated the problem of three aspects: (1) 1/T sThe frequency deviation of integral multiple do not influence the size of received signal and initial frequency expansion sequence slip correlation peak, only influence the position of correlation peak, and the size of frequency deviation is depended at the interval of moving, position.When not having frequency deviation, because received signal is the GCL sequences behind the pulse shaping, initial frequency expansion sequence also is a GCL sequences, thus the relevant cycle auto-correlation that just is equivalent to GCL sequences of slip of received signal and initial frequency expansion sequence, and at 1/T sThe frequency deviation of integral multiple under, received signal just is equivalent to take place cyclic shift, so the size of the slip correlation peak of received signal and initial frequency expansion sequence can not change, just corresponding mobile has taken place in the position of correlation peak.(2) relevant can the realization of slip of received signal and initial frequency expansion sequence with fast fourier transform.Be right 1/T sThe frequency deviation of integral multiple can allow GCL sequences produce the effect of cyclic shift, and 1/T sThe frequency deviation of integral multiple be equivalent to the column vector of inverse Fourier transform matrix (hereinafter to be referred as the IDFT matrix), therefore can use fast fourier transformation algorithm to realize the cyclic shift of initial frequency expansion sequence and relevant with received signal.(3) time synchronized and 1/T sThe estimation of integer frequency offset can unite in locational difference by preamble head place and frame delimiter place slip correlation peak and solve.Because at 1/T sUnder the effect of integer frequency offset, deviation all can take place in the position of the slip correlation peak of preamble head place and frame delimiter place received signal and initial frequency expansion sequence, and the direction of deviation is opposite, the size of deviation is relevant with the size of frequency deviation, therefore can utilize the position calculation of the correlation peak that this two place obtains to go out the correct time synchronization value, and 1/T sThe value of frequency deviation of integral multiple.
The following describes concrete method of reseptance.Frequency deviation in the received signal not all is 1/T also sIntegral multiple, but arbitrarily the frequency deviation of size can resolve into 1/T sIntegral multiple and decimal times two parts, i.e. any frequency deviation f=k/T s+ Δ f, wherein fractional part of frequency offset Δ f is-1/2T s～1/2T sA value.Though k/T sTo received signal and the not influence of size of the relevant peak value that slides between the initial frequency expansion sequence, but Δ f is influential to it, and Δ f approaching more ± 1/2T s, correlation peak approaches zero more.Fig. 5 influence of frequency deviation of having drawn to correlation peak, wherein abscissa is represented the time migration of received signal and initial frequency expansion sequence, and ordinate is represented the frequency shift (FS) in the received signal, and ordinate is represented the correlation between received signal and the initial frequency expansion sequence.Work as frequency deviation as can be seen at k/T sWhen neighbouring, the size of peak value does not have marked change, and just the position has taken place to move, and departs from k/T and work as frequency deviation sWhen far away, correlation peak diminishes rapidly.Therefore fractional part of frequency offset Δ f is that compensation is fallen earlier, and the slip that just can carry out then between received signal and the initial frequency expansion sequence is relevant.
Because the value of Δ f is positioned at-1/2T s～1/2T sBetween, it a frequency expansion sequence in the cycle caused phase deviation between-π～π, so this part frequency deviation can use before and after the method for difference estimate.Baseband receiving signals after the down-conversion is sampled, take out the point in some frequency expansion sequence cycles of interval in the sampled signal at synchronous head place in the past, allowing the point of front do conjugater transformation multiplies each other with the point of back again, multiplied result is sued for peace, again to ask the angle, just obtained the value that fractional part of frequency offset is estimated divided by 2 π and frequency expansion sequence cycle then.Here a plurality of multiplied result summations are the influences for smooth noise.The method of this front and back difference can be expressed as with formula,
Δf = 1 2 π T s ∠ Σ i = 0 M - 1 ( r i * r i + N )
R in the formula iI sampled point in the expression received signal, N represents the sampling number that a frequency expansion sequence cycle is interior, and M represents to be used for average number of times, and ∠ represents difference value is asked the angle, T sThe expression frequency expansion sequence cycle.
Compensation is fallen after the fractional part of frequency offset, just can begin to carry out the work of time synchronized.Here time synchronized comprises frequency expansion sequence synchronously and chip synchronization two parts, and frequency expansion sequence is in order to find the original position of frequency expansion sequence synchronously, and the time that is otherwise known as is slightly synchronous, just have only the original position of having determined frequency expansion sequence can carry out correct demodulation.Chip synchronization is the peak for shaped pulse on each element that finds frequency expansion sequence, can sample to received signal with the moment of the best like this, thus the amount of calculation that can reduce sample rate and separate timing.In the present invention, time slightly is that the position of the relevant peak value of the slip by seeking received signal and initial frequency expansion sequence obtains synchronously, and the time essence be synchronously utilize slip correlation main lobe upward peak both sides be separated by two points of a chip period and when reflecting characteristic curve obtain.Because the influence of integer frequency offset, value that slightly obtains synchronously in the preamble head place time of doing and the value that slightly obtains synchronously the time of doing at the frame delimiter place are not the original positions of frequency expansion sequence accurately, and the original position of frequency expansion sequence just can obtain after the time-frequency decoupling zero accurately.
The time of at first carrying out preamble head place below is slightly synchronous.To received signal with the initial frequency expansion sequence relevant use usually tapped delay line structure shown in Figure 6 that slides, but the amount of calculation of tapped delay line structure is bigger, so in the present invention, the relevant structure of fast fourier transform (hereinafter to be referred as FFT) of using of slip realizes.Shown in Figure 7 is that FFT realizes the relevant schematic diagram that slides, get the sampled signal in a frequency expansion sequence cycle at preamble head place, allow its conjugate sequence corresponding points multiply each other with initial frequency expansion sequence, multiplied result is carried out the slip correlation that the FFT computing has promptly obtained received signal and initial frequency expansion sequence, and the length that thick synchronous value of time equals the frequency expansion sequence cycle deducts the length of the pairing abscissa of correlation peak.Realize that with FFT the relevant principle of slip can be expressed as with formula,
R ( k ) = Σ n = 0 N - 1 r [ n ] a * [ ( n + k ) % N ] = exp ( - j k 2 π N ) · Σ n = 0 N - 1 ( r [ n ] a * [ n ] ) exp ( - j 2 kπ N n )
Here R (k) expression slip correlation, initial frequency expansion sequence a[n is represented in first equal sign back] the k time cyclic shift and received signal r[n] relevant process, first of second equal sign back is one and only follows the relevant phase place of k, the part of suing for peace is later represented received signal r[n] and initial frequency expansion sequence a[n] conjugate multiplication, do relevant with the k row of inverse Fourier transform matrix again.As can be seen, N slip correlation can be realized with the FFT that a N is ordered.A[n in the following formula] cyclic shift and a[n] relation can be written as with formula,
a [ ( n + k ) % N ] = exp ( j k 2 π N ) a [ n ] exp ( j 2 kπ N n ) .
Adopting the FFT computing to finish the slip correlation ratio adopts the tapped delay line structure to finish the relevant amount of calculation that greatly reduces of slip.In order to obtain N slip correlation, the tapped delay line structure need be N 2Individual complex multiplication, and the FFT structure only needs N+ N/ 2Log 2N complex multiplication, wherein to take advantage of again be the conjugation of received signal and the initial frequency expansion sequence amount of calculation when doing multiplication to N, N/ 2Log 2N is the amount of calculation of FFT computing.With N=16 is example, and the tapped delay line structure needs 256 to be taken advantage of again, and the FFT structure only needs 48 to take advantage of again.
The time of carrying out preamble head place then is synchronously smart.Because GCL sequences has desirable autocorrelation performance, therefore the frequency expansion sequence in the received signal and this locality are Dirac functions with reference to the slip correlation between the frequency expansion sequence, thereby the slip correlation between received signal and the initial frequency expansion sequence is exactly the waveform of shaped pulse.Because the top of shaped pulse main lobe is more smooth, the position of peak value is subjected to The noise easily, do not determine the peak of shaped pulse so do not use the peak of slip correlation among the present invention, but determine the peak of shaped pulse at a distance of two points of a chip period according to slip correlation peaks both sides, thisly utilize correlation main lobe trailing edge to carry out the synchronous method of essence to be called as the delay jitter method.Shown in Figure 8 to be received signal postpone also anti-phase one of a chip period and duplicate with the slide main lobe of the relevant correlation that obtains and it of initial frequency expansion sequence, two one side of something that align among Fig. 8 characteristic curve just can obtain mirror shown in Figure 9 time of adding up.During mirror characteristic ordinate be on the correlation main lobe at a distance of the size differences of two points of a chip period, abscissa has reflected the symmetrical degree of these two points about peak value.When these two points are symmetrical about peak value, its difference is zero, corresponding abscissa also is zero, when these two points asymmetric about peak value, be that the center of these two points is when departing from the position of desirable peak value, their missionary society is mapped to the value on the abscissa, departs from the value of desirable peak and this value is exactly the center of these two points.Concrete grammar is, after slightly finishing synchronously,, they are subtracted each other from two points of correlation peak two side-draws at a distance of a chip period, difference according to them just can retrieve the position that correlation peak departs from the shaped pulse peak value from when mirror characteristic curve, must arrive smart synchronous value of time like this.Compare with the top that the correlation main lobe is smooth, characteristic curve is more precipitous during mirror, so very little timing offset can obtain bigger reflection on the curve when mirror, therefore utilizes this method can obtain very accurate synchronization value.
Preamble head place's deadline thick synchronously and smart synchronously after, also slightly synchronous in the frame delimiter place deadline, at first to carry out frame delimiter for this reason and detect.The principle that frame delimiter detects is the difference on frequency expansion sequence according to preamble head and frame delimiter, and preamble head place adopts is initial frequency expansion sequence in the mapping table, the conjugate sequence of the initial frequency expansion sequence that the frame delimiter place adopts.Though these two sequences are conjugation, all belong to GCL sequences, to ask single order to lead to their phase place and can obtain multiple sinusoidal sequence, difference just is the frequency difference of multiple sinusoidal sequence.The process of asking single order to lead to the phase place of sequence can realize by the front and back difference of sequence being made the chip period in interval.The frequency expansion sequence at preamble head place and ask single order to lead resulting multiple sinusoidal sequence to its phase place can be expressed as with formula,
a n = exp ( j π n 2 N ) , b n = exp ( j 2 πn N ) .
Because between the multiple sinusoidal sequence of different frequency is quadrature,, utilizes this character can carry out frame delimiter and detect so the correlation between the multiple sinusoidal sequence that multiple sinusoidal sequence that preamble head place obtains and frame delimiter place obtain is zero.Concrete grammar is that generating a frequency earlier is 1/T sMultiple sinusoidal sequence, promptly be that the single order of the initial frequency expansion sequence in preamble head place is led sequence, then the sampled signal that receives is carried out the at interval front and back calculus of differences of a chip period, be 1/T with differentiated sequence and the frequency that generates earlier sMultiple sinusoidal sequence do relevantly, the thresholding of a correlation and a setting is compared, still be a preamble signal if correlation, illustrates current demand signal greater than thresholding, need continue to do detection, detected frame delimiter if correlation less than thresholding, is then thought.In one embodiment of the invention, above-mentioned thresholding is made as N/2.
After frame delimiter detects, finish the time synchronized at frame delimiter place with above-mentioned FFT structure, because smart synchronous value of time is at preamble head place and as broad as long at the frame delimiter place, thus only need do here once slide relevant to obtain thick synchronous value of time.Slip to the frame delimiter place is relevant, gets the sampled signal in a frequency expansion sequence cycle at the frame delimiter place, allows its corresponding points with initial frequency expansion sequence multiply each other, and it is just passable that multiplied result is carried out the FFT computing.
The work that will finish at last is the time-frequency decoupling zero, i.e. the value that solves thick synchronization value of correct time and integer frequency offset according to thick synchronous value of preamble head place's time and thick synchronous value of frame delimiter place time.As shown in figure 10, k/T sFrequency deviation can allow the correlation peak at preamble head place to a left avertence k chip, allows the correlation peak at frame delimiter place to a right avertence k chip; And-k/T sFrequency deviation can allow the correlation peak at preamble head place to a right avertence k chip, allows the correlation peak at frame delimiter place to a left avertence k chip.Therefore after slightly the finishing synchronously of frame delimiter place, just can carry out the time-frequency decoupling zero according to the position relation of preamble head and frame delimiter two place's correlation peaks.Specific practice is, the thick synchronization value addition in two places, its average is exactly the thick synchronization value of correct time, and the difference of the thick sync bit at frame delimiter place and the thick synchronization value of correct time is exactly the k value, thereby can obtain the value of integer frequency offset.Total frequency deviation value equal integer frequency offset value and the fractional part of frequency offset value that estimates above and, i.e. f=k/T s+ Δ f.According to the time thick synchronously and the synchronous result of time essence readjust the original position and the sampling instant of frequency expansion sequence, the value according to frequency offset estimating is compensated frequency deviation again, has just finished Time and Frequency Synchronization thus, data demodulates just can successfully have been carried out in the back.
In one embodiment of the invention, the method that data demodulates is used and all possible frequency expansion sequence is crossed line correlation realizes.Get the sampled signal in a frequency expansion sequence cycle, this signal has carried out overdeviation and has proofreaied and correct, it is relevant to obtain N correlation to allow itself and N frequency expansion sequence in the mapping table do respectively, from this N correlation, select maximum one, its pairing frequency expansion sequence just is considered to the transmitting sequence in the received signal in current this frequency expansion sequence cycle, thereby the pairing bit sequence of this frequency expansion sequence is exactly the data bit that demodulates.

Claims (7)

1, the data transmission method in a kind of short-range wireless networking is characterized in that the sending, receiving method of data comprising following each step:
(1) sets up mapping table between a bit sequence and the frequency expansion sequence;
(2) protocol Data Unit of the data form composed as follows that intermediary of network matter access control sublayer is sent: The preamble head Frame delimiter Physical layer letter head Service data unit
(3) the mapping table between above-mentioned bit sequence and frequency expansion sequence, the corresponding frequency expansion sequence of bit sequence in retrieval and the protocol Data Unit;
(4) the above-mentioned frequency expansion sequence that retrieves is carried out pulse shaping, become baseband transmit signals;
(5) above-mentioned baseband transmit signals is modulated on homophase and the quadrature carrier, becomes radio frequency transmit signal;
(6) receive above-mentioned radio frequency transmit signal, carry out down-conversion and obtain baseband receiving signals, in the estimation baseband receiving signals-1/2T s～1/2T sFrequency deviation, and compensation, T wherein sIt is the cycle of frequency expansion sequence;
(7) it is slightly synchronous the signal at preamble head place in the above-mentioned baseband receiving signals to be carried out the time, and the time of carrying out again is synchronously smart;
(8) from above-mentioned baseband receiving signals, detect the frame delimiter signal, and it is carried out time synchronized;
(9) according to time synchronized value and frequency offset estimating value in the time synchronized value calculated data receiving course at above-mentioned preamble head place and frame delimiter place;
(10) signal to the letter of the physical layer in baseband receiving signals head and service data unit carries out demodulation, obtains the data bit of transmitting terminal.
2, the data transmission method in a kind of short-range wireless networking is characterized in that the method for reseptance of data comprising following each step:
(1) radio frequency transmit signal of transmitting terminal in the reception short-range wireless networking carries out down-conversion and obtains baseband receiving signals, in the estimation baseband receiving signals-and 1/2T s～1/2T sFrequency deviation, and compensation, T wherein sIt is the cycle of frequency expansion sequence;
(2) it is slightly synchronous the signal at preamble head place in the above-mentioned baseband receiving signals to be carried out the time, and the time of carrying out again is synchronously smart;
(3) from above-mentioned baseband receiving signals, detect the frame delimiter signal, and it is carried out time synchronized;
(4) according to time synchronized value and frequency offset estimating value in the time synchronized value calculated data receiving course at above-mentioned preamble head place and frame delimiter place;
(5) signal to the letter of the physical layer in baseband receiving signals head and service data unit carries out demodulation, obtains the data bit of transmitting terminal.
3, the method for claim 1 is characterized in that wherein setting up may further comprise the steps the method for the mapping table between bit sequence and the frequency expansion sequence:
(1) is initial frequency expansion sequence with GCL sequences, initial frequency expansion sequence is carried out cyclic shift, obtain all frequency expansion sequences;
(2) make frequency expansion sequence corresponding with bit sequence, corresponding method is: the decimal number of expression bit sequence is corresponding with the cyclic shift figure place of frequency expansion sequence.
4, the method for claim 1 is characterized in that to the bit sequence of component frame delimiter, retrieving frequency expansion sequence corresponding with it according to described mapping table in the packet after the framing, again this frequency expansion sequence is carried out conjugater transformation.
5, method as claimed in claim 1 or 2 is characterized in that the signal at preamble head place in the baseband receiving signals is carried out thick synchronous method of time, comprises following each step:
(1) sampled signal in a frequency expansion sequence cycle of taking-up from the preamble head signal of baseband receiving signals;
(2) initial frequency expansion sequence is carried out conjugater transformation, the initial frequency expansion sequence after the conjugater transformation and the sampled signal in an above-mentioned frequency expansion sequence cycle are multiplied each other;
(3) the above-mentioned later signal that multiplies each other is carried out fast fourier transform, obtain the slip correlation between baseband receiving signals and the initial frequency expansion sequence;
(4) from the length in frequency expansion sequence cycle, deduct the pairing abscissa length of maximum in the above-mentioned slip correlation, be the thick synchronization value of time of preamble head place signal in the baseband receiving signals.
6, method as claimed in claim 1 or 2 is characterized in that detecting the method for frame delimiter signal in the baseband receiving signals, may further comprise the steps:
(1) generating a frequency is 1/T sMultiple sinusoidal sequence, T wherein sIt is the cycle of frequency expansion sequence;
(2) be starting point with thick synchronization position of time, take out the sampled signal in a frequency expansion sequence cycle;
(3) above-mentioned sampled signal is carried out the front and back calculus of differences, obtain a new difference sequence, this difference sequence and above-mentioned multiple sinusoidal sequence are carried out relevant, obtain a correlation;
(4) above-mentioned correlation is compared with the threshold value of a setting, less than threshold value, the signal in then current this frequency expansion sequence cycle is the frame delimiter signal in the baseband receiving signals as if correlation; If correlation greater than threshold value, is then got the sampled signal in next frequency expansion sequence cycle, repeating step (3)～(4).
7, method as claimed in claim 1 or 2 is characterized in that may further comprise the steps according to the time synchronized value in the time synchronized value calculated data receiving course at preamble head place and frame delimiter place and the method for frequency offset estimating value:
(1) average of the time synchronized value at preamble head place and frame delimiter place is the time synchronized value in the DRP data reception process;
(2) the frequency offset estimating value in the DRP data reception process is k/T s+ Δ f, wherein k is poor between the time synchronized value at frame delimiter place and the above-mentioned average, Δ f for estimated-1/2T s～1/2T sFrequency deviation value.
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