CN101902424A - Differential decoding method in short-range wireless network - Google Patents

Abstract

The invention relates to a differential decoding method in a short-range wireless network, belonging to the technical field of wireless communication. Firstly, the characteristic of cycle repetition of a transmission pilot frequency sequence is utilized to carry out front and back conjugation correlation and accumulation on a received pilot frequency digital signal, thus a reference differential correlation value is obtained; the local spread spectrum modulation sequence is subject to the same operation of front and back conjugation and accumulation so as to obtain a conjugation correlation value; the conjugation correlation value and the reference differential correlation value are related to obtain a complex number correlation value; and according to the characteristics of positive number and negative number of the real part of the complex number correlation value, data decoding is realized. The differential decoding method of the invention lowers decoding calculated amount and improves data decoding performance under the influence of frequency shift, so that a receiver has lower power dissipation and the receiving performance under bigger frequency shift, thus avoiding the error code transmission problem of the traditional differential decoding.

Description

Differential decoding method in a kind of short-range wireless networking

Technical field

The present invention relates to differential decoding method in a kind of short-range wireless networking, relate in particular to Data Receiving and demodulation method in the short-range wireless networking, belong to technical field of wireless communication.

Background technology

Modern wireless communication adopts the bag transmission mechanism, and receiver receives wireless signal by radio frequency after detecting the signal of issuing oneself, obtains baseband receiving signals again behind over-sampling.For baseband receiving signals, at first utilize header data deadline, carrier synchronization and frame to delimit operation, find the position of effective transmission information in the pack arrangement data message.

The recovery that utilizes baseband receiving signals to finish transmission information is exactly a data demodulates, and it has directly determined the consistency of received signal with true transmission information, has determined the quality of whole transmitting-receiving performance.Therefore, data demodulates is a vital problem in the modern wireless network communication system.

Spread spectrum communication is present a kind of communication mode commonly used, frequency expansion sequence generally all has good autocorrelation performance in the spread spectrum system, by using the reference signal of known frequency expansion sequence as receiver this locality, conventional data demodulates can be abutted against collect mail number and the reference signal of receiver this locality between do coupling and be correlated with and finish.When the alignment of the frequency expansion sequence in the received signal and the frequency expansion sequence in the local reference signal and when mating fully, correlation can show a peak value, and in other cases, correlation approaches zero.For the system of phase shift keying modulation system, the phase information of correlation when received signal is relevant fully with local reference signal has been reacted the information of modulating data, so has been utilized the phase information of this correlation can realize data demodulates.But, when having frequency shift (FS) in the received signal, the correlation of received signal and receiver local reference signal can be subjected to very big influence, particularly under big frequency deviation condition, even during the alignment of the frequency expansion sequence in frequency expansion sequence in the received signal and the reference signal, correlation also no longer is a maximum related value, and the phase place of this correlation also can be affected, thereby can't judge the phase difference of received signal and local signal, also just can't decode the reception data of phase shift keying modulation.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 ± more than the 40ppm, for the system that is operated in the 900MHz frequency range, so big deviation can cause the frequency shift (FS) of 72KHz, 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 ± 2.304 π.

Synchronous in order to use the relevant method of coupling to finish data demodulates, need estimate the size of frequency deviation earlier and proofreaied and correct to received signal according to estimated value.In addition, system for the phase shift keying modulation, need recover the phase information of received signal when decoding just can effectively decode, but wireless data is propagated the influence that tends to be subjected to wireless multipath channel, decline and barrier in air, and the phase change that when last down-conversion, produces of radio-frequency devices, all phase place to received signal exerts an influence, thereby causes decode procedure when recovering the phase information of received signal, the phase change that needs first estimation and compensate for channel and radio frequency to bring.But the error that evaluated error and phase compensation operation are introduced can further influence demodulation performance.

Summary of the invention

The coding/decoding method of difference utilizes the good correlation properties of frequency expansion sequence before and after the objective of the invention is to propose in a kind of short-range wireless networking, and front and back are relevant between at first receiving digital signals being carried out, and obtain a new reception sequence of correlation values; Local 16 groups of band spectrum modulation sequences are carried out identical front and back associative operation, also can obtain 16 groups of new local sequence of correlation values; It is relevant with 16 groups of local sequence of correlation values respectively to receive sequence of correlation values, obtains one group of sequence of correlation values, seeks the binary representation of maximum related value position, as the result of data demodulates.

Differential decoding method in the short-range wireless networking that the present invention proposes comprises following each step:

(1) receive the radiofrequency signal that transmitting terminal sends in the short-range wireless networking, carry out down-conversion and obtain baseband receiving signals, this baseband receiving signals is carried out 2 samplings obtain the received signal of sampling, the time in sampling interval is designated as T _C

(2) pilot frequency sequence of the receiving terminal in the short-range wireless networking from above-mentioned received signal begins, and reads the received signal of two code-element period length continuously, and this received signal sequence is designated as L=[l ₁, l ₂..., l _N, l _N+1..., l _2N], wherein N represents the sampled signal number in the code-element period length;

(3) conjugate operation is carried out in the received signal pointwise of the previous code-element period of above-mentioned received signal sequence, obtain conjugation sampled signal sequence

Each signal in the conjugation sampled signal sequence and this signal sampled signal after N sampling interval is multiplied each other, obtain a difference sequence of correlation values, be designated as C=[c ₁, c ₂..., c _N], wherein

() ^*The expression conjugate operation;

(4) above-mentioned all correlations of difference sequence of correlation values are added up, obtain the reference difference correlation

(5) receiving terminal in the short-range wireless networking reads the received signal when previous code-element period length from the time synchronized position, is designated as r=[r ₁, r ₂..., r _N], and the received signal that reads a code-element period length, be designated as r '=[r ' ₁, r ' ₂..., r ' _N];

(6) conjugate operation is carried out in the received signal r ' pointwise of an above-mentioned last code-element period after, multiply each other with current received signal r and add up, obtain the conjugation correlation, be designated as

(7) with above-mentioned reference difference correlation R _RefCarry out multiplying each other with conjugation correlation R after the conjugate operation, obtain plural correlation

(8) get above-mentioned plural correlation

Real part numerical value P, if this real part numerical value P greater than zero, decoded result is 1 so, otherwise decoded result is 0.

Differential decoding method in the short-range wireless networking that the present invention proposes has the following advantages:

(1) the inventive method is used the differential decoding algorithm, has avoided the influence to algorithm performance of carrier frequency shift and multipath channel, effectively improves the accuracy of decoding;

(2) decoding algorithm of the inventive method need not earlier to carry out to received signal carrying out relevant decoding with local sequence again behind the compensate of frequency deviation, has avoided the evaluated error brought in frequency offset estimating and the compensation process, has improved the accuracy of decoding;

(3) the inventive method does not need carrier frequency is estimated and compensated, and has reduced the implementation complexity of receiving system and has simplified receiving algorithm;

(4) the differential decoding algorithm of the inventive method need not to utilize the decoded result of previous code element, and the error propagation problem of having avoided the traditional differential method to introduce has improved decoding performance.

Description of drawings

Fig. 1 is the schematic diagram of differential coding in the inventive method.

Embodiment

Differential decoding method in the short-range wireless networking that the present invention proposes, at first receive the radiofrequency signal that transmitting terminal sends in the short-range wireless networking, carry out down-conversion and obtain baseband receiving signals, this baseband receiving signals is carried out 2 samplings obtain the received signal of sampling, the time in sampling interval is designated as T _CThen, the pilot frequency sequence of the receiving terminal in the short-range wireless networking from above-mentioned received signal begins, and reads the received signal sequence L=[l of two code-element period length continuously ₁, l ₂..., l _N, l _N+1..., l _2N], wherein N represents the sampled signal number in the code-element period length; Conjugate operation is carried out in received signal pointwise to the previous code-element period of above-mentioned received signal sequence, obtains conjugation sampled signal sequence

Each signal in the conjugation sampled signal sequence and this signal sampled signal after N sampling interval is multiplied each other, obtain a difference sequence of correlation values, be designated as C=[c ₁, c ₂..., c _N], wherein () ^*The expression conjugate operation; Above-mentioned all correlations of difference sequence of correlation values are added up, obtain the reference difference correlation

Receiving terminal in the short-range wireless networking reads the received signal when previous code-element period length from the time synchronized position, is designated as r=[r ₁, r ₂..., r _N], and the received signal that reads a code-element period length, be designated as r '=[r ' ₁, r ' ₂..., r ' _N]; After the received signal r ' pointwise of an above-mentioned last code-element period carried out conjugate operation, multiply each other with current received signal r and add up, obtain the conjugation correlation, be designated as With above-mentioned reference difference correlation R _RefCarry out multiplying each other with conjugation correlation R after the conjugate operation, obtain plural correlation

Get above-mentioned plural correlation

Real part numerical value P, if this real part numerical value P greater than zero, decoded result is 1 so, otherwise decoded result is 0.

Introduce method of the present invention in detail below in conjunction with drawings and Examples.

Differential decoding method carries out down-converted and sampling, sampling period T code fetch sheet period T as shown in Figure 1 at first to received signal in the short-range wireless networking that the present invention proposes _cHalf.In the IEEE802.15.4 standard, stipulated the code-element period T of 900MHz frequency range BPSK modulation _sBe chip period T _c15 times, so the symbol signal in each cycle sampling obtains N=T _s/ T=30 sampled point.Stipulated that in the IEEE802.15.4 standard wireless data structure adopts the bag transmission structure, promptly only transmit a certain amount of data at every turn, pilot frequency sequence need at first be transmitted in front at each packet, be used for allowing receiver know whether data reach receiver front end, and be used for finishing receiving gain control, time synchronized and carrier frequency synchronization.In this embodiment, the time synchronized of considering front end is finished.

The mode of differential coding is adopted in regulation 900MHz frequency range BPSK modulation in the IEEE 802.15.4 standard, shown in figure one.If current data bit to be sent is 0, constantly the data behind the differential coding are identical with last one for data behind the differential coding so, if current data bit to be sent is 1, constantly the data behind the differential coding are opposite with last one for data behind the differential coding so, if the data behind the promptly last moment differential coding are 0, data behind the so current differential coding are 1, otherwise the data behind the current differential coding are 0.

In addition, the mode of direct sequence spread spectrum is adopted in regulation 900MHz frequency range BPSK modulation in the IEEE 802.15.4 standard, and it is the frequency expansion sequence of N that a data bit can be become one-period length by spread spectrum, and this frequency expansion sequence is designated as s=[s ₁, s ₂..., s _N], if the data behind the differential coding that band sends are 0, the corresponding data sequence that sends is s behind the spread spectrum so ₀=s=[s ₁, s ₂..., s _N], if the data behind the differential coding that band sends are 1, the corresponding data sequence that sends is s behind the spread spectrum so ₁=-1 * s=[-s ₁,-s ₂... ,-s _N].

Common data decode all is that received signal is relevant with local frequency expansion sequence respectively, if correlation is a positive number, illustrate that the data of decoding are 0, otherwise correlation is a negative, and decoded results is 1 so.But for the wireless communication system that has frequency shift (FS), the correlation of received signal and local sequence can be subjected to having a strong impact on of frequency deviation, the matching degree of no longer corresponding received signal of correlation phase place and local sequence, therefore directly related under offset frequency situation to finish data decode be infeasible.In addition, wireless channel also can exert an influence to received signal, causes the amplitude of received signal and phase place that change has all taken place, and this all can influence the correlation phase place of received signal and local frequency expansion sequence.

Consider that frequency shift (FS) mainly causes the influence of phase deviation to received signal, and for the sampled point in the identical time interval, the superposeed phase place of linear change of the phase place of received signal.Because the frequency shift (FS) influence of phase place to received signal is a linear change, the phase deviation that frequency deviation causes in the both identical time interval is identical, therefore the phase deviation that frequency shift (FS) causes in the identical time interval is identical, be correlated with by code-element period received signal is at interval carried out conjugation, the influence of wireless channel and frequency shift (FS) be converted into the influence of stationary phase.

Physical layer data sends the employing pack arrangement in the IEEE 802.15.4 standard, and the top data of each packet are the pilot frequency sequences that send in the cycle.At first, the pilot frequency sequence of the receiving terminal in the short-range wireless networking from above-mentioned received signal begins, and reads the received signal sequence L=[l of two code-element period length continuously ₁, l ₂..., l _N, l _N+1..., l _2N], because the influence of wireless channel and carrier frequency shift, the pilot signal of reception can be expressed as:

$l_i=s_{\mathrm{mod}(i,N)}\·\left|h\right|e^{{\mathrm{j\θ}}_h}\·e^{j2\mathrm{\π}\·\mathrm{\Δf}\·i\·T_c},$

Wherein, | h| and θ _hAmplitude and the phase place of representing wireless channel respectively, Δ f represents the frequency carrier skew.

Conjugate operation is carried out in received signal pointwise to the previous code-element period of above-mentioned received signal sequence, obtains conjugation sampled signal sequence

Each signal in the conjugation sampled signal sequence and this signal sampled signal after N sampling interval is multiplied each other,

$c_i=l_i^{*}\·l_{i+N}=s_i^{*}\·\left|h\right|e^{-j{\mathrm{\θ}}_h}\·e^{-j2\mathrm{\π}\·\mathrm{\Δf}\·i\·T_c}\·s_i\·\left|h\right|e^{j{\mathrm{\θ}}_h}\·e^{j2\mathrm{\π}\·\mathrm{\Δf}\·(i+N)\·T_c}$

$={\left|s_i\right|}^2\·{\left|h\right|}^2\·e^{j2\mathrm{\π}\·\mathrm{\Δf}\·N\·T_c},$

Obtain a difference sequence of correlation values, be designated as C=[c ₁, c ₂..., c _N], wherein, () ^*The expression conjugate operation; Above-mentioned all correlations of difference sequence of correlation values are added up, obtain the reference difference correlation:

$R_{\mathrm{ref}}=\underset{i=1}{\overset{N}{\mathrm{\Σ}}}{c}_i$

$=e^{j2\mathrm{\π}\·\mathrm{\Δf}\·N\·T_c}\·{\left|h\right|}^2\·\underset{i=1}{\overset{N}{\mathrm{\Σ}}}{\left|s_i\right|}^2.$

Because the identical cycle data of data that pilot frequency sequence sends, so R _RefThe result that conjugation is correlated with before and after representing when adjacent two code elements transmission data are identical.

Before receiving terminal in the short-range wireless networking begins data decode, utilized pilot data to finish time synchronized.From sync bit, read received signal during decoding, be designated as r=[r when previous code-element period length ₁, r ₂..., r _N], the data of supposing current transmission are D ₁=1 or-1, received signal can be expressed as:

$r_i=D_1\·s_i\·\left|h\right|e^{{\mathrm{j\θ}}_h}\·e^{j2\mathrm{\π}\·\mathrm{\Δf}\·i\·T_c}.$

Read the received signal of a code-element period length simultaneously, be designated as r '=[r ' ₁, r ' ₂..., r ' _N], suppose that last one data that send constantly are D ₀=1 or-1, going up the one-period received signal so can be expressed as:

$r_i^{\′}=D_0\·s_i\·\left|h\right|e^{{\mathrm{j\θ}}_h}\·e^{j2\mathrm{\π}\·\mathrm{\Δf}\·(i-N)\·T_c}.$

After the received signal r ' pointwise of previous code-element period carried out conjugate operation, multiply each other with current received signal r and add up, obtain the conjugation correlation:

$R=\underset{i=1}{\overset{N}{\mathrm{\Σ}}}{r}_i\·r_i^{\′*}$

$=\underset{i=1}{\overset{N}{\mathrm{\Σ}}}{D}_0{\·s}_i^{*}\·\left|h\right|e^{-j{\mathrm{\θ}}_h}\·e^{-j2\mathrm{\π}\·\mathrm{\Δf}\·(i-N)\·T_c}\·D_1\·s_i\·\left|h\right|e^{j{\mathrm{\θ}}_h}\·e^{j2\mathrm{\π}\·\mathrm{\Δf}\·i\·T_c}$

$=D_0\·D_1\·e^{j2\mathrm{\π}\·\mathrm{\Δf}\·N\·T_c}\·{\left|h\right|}^2\·\underset{i=1}{\overset{N}{\mathrm{\Σ}}}{\left|s_i\right|}^2.$

With above-mentioned reference difference correlation R _RefCarry out multiplying each other with conjugation correlation R after the conjugate operation, obtain plural correlation:

$P=R\·R_{\mathrm{ref}}^{*}$

$=D_0\·D_1\·e^{j2\mathrm{\π}\·\mathrm{\Δf}\·N\·T_c}\·{\left|h\right|}^2\·\underset{i=1}{\overset{N}{\mathrm{\Σ}}}{\left|s_i\right|}^2\·e^{-j2\mathrm{\π}\·\mathrm{\Δf}\·N\·T_c}\·{\left|h\right|}^2\·\underset{i=1}{\overset{N}{\mathrm{\Σ}}}{\left|s_i\right|}^2$

$=D_0\·D_1\·{\left|h\right|}^4\·{\left(\underset{i=1}{\overset{N}{\mathrm{\Σ}}}{\left|s_i\right|}^2\right)}^2.$

Get above-mentioned plural correlation Real part numerical value P, if this real part numerical value P illustrates D greater than zero ₁With a last data D ₀Identical, decoded result is 1 so, otherwise explanation D ₁With a last data D ₀Difference, decoded result are 0.

Claims (1)

1. the differential decoding method in the short-range wireless networking is characterized in that this method comprises following each step:

(1) receive the radiofrequency signal that transmitting terminal sends in the short-range wireless networking, carry out down-conversion and obtain baseband receiving signals, this baseband receiving signals is carried out 2 samplings obtain the received signal of sampling, the time in sampling interval is designated as T _C

(2) pilot frequency sequence of the receiving terminal in the short-range wireless networking from above-mentioned received signal begins, and reads the received signal of two code-element period length continuously, and this received signal sequence is designated as L=[l ₁, l ₂..., l _N, L _N+1..., l _2N], wherein N represents the sampled signal number in the code-element period length;

(3) conjugate operation is carried out in the received signal pointwise of the previous code-element period of above-mentioned received signal sequence, obtain conjugation sampled signal sequence

Each signal in the conjugation sampled signal sequence and this signal sampled signal after N sampling interval is multiplied each other, obtain a difference sequence of correlation values, be designated as C=[c ₁, c ₂..., c _N], wherein

() ^*The expression conjugate operation;

(4) above-mentioned all correlations of difference sequence of correlation values are added up, obtain the reference difference correlation

(5) receiving terminal in the short-range wireless networking reads the received signal when previous code-element period length from the time synchronized position, is designated as r=[r ₁, r ₂..., r _N], and the received signal that reads a code-element period length, be designated as r '=[r ' ₁, r ' ₂..., r ' _N];

(6) conjugate operation is carried out in the received signal r ' pointwise of an above-mentioned last code-element period after, multiply each other with current received signal r and add up, obtain the conjugation correlation, be designated as

(7) with above-mentioned reference difference correlation R _RefCarry out multiplying each other with conjugation correlation R after the conjugate operation, obtain plural correlation

(8) get above-mentioned plural correlation

Real part numerical value P, if this real part numerical value P greater than zero, decoded result is 1 so, otherwise decoded result is 0.

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