CN106878218A - A kind of high reliability demodulation method for IEEE802.15.4 - Google Patents
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/18—Phase-modulated carrier systems, i.e. using phase-shift keying
- H04L27/22—Demodulator circuits; Receiver circuits
- H04L27/233—Demodulator circuits; Receiver circuits using non-coherent demodulation
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/0014—Carrier regulation
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/0014—Carrier regulation
- H04L2027/0024—Carrier regulation at the receiver end
- H04L2027/0026—Correction of carrier offset
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Abstract
A kind of high reliability BPSK demodulation methods for IEEE802.15.4, useful frequency offset information is extracted first with the corresponding channel received data of the lead code of 32 bits, then receiving sampled signal to the corresponding complex base band of PSDU carries out bit-level difference processing, obtains adjudicating observation, afterwards using extract frequency offset information to judgement observation compensate after carry out detection judgement, the PSDU data that will finally receive send MAC layer to and carry out CRC check.The present invention is based on influence negligible theory of the noise to useful signal when the Taylor series expansion and big signal to noise ratio of arcsin function, there is provided a kind of low-power consumption suitable for IEEE 802.15.4, highly reliable and inexpensive incoherent BPSK receivers.
Description
Technical field
The present invention relates to communication signal waveforms detection technique field, specifically a kind of height for IEEE802.15.4
Reliability BPSK demodulation methods.
Background technology
IEEE 802.15.4 are ZigBee, the basis of the specification such as WirelessHART, describe low rate radio individual office
The physical layer and media access control protocol of domain net.It is initially operating in the ISM band of 868/915MHz, 2.4GHz, data
Transmission rate reaches as high as 250kbps.Low-power consumption, the advantage of low cost make it in data sampling and processing and analysis, remote control
Essence is made the various fields such as agricultural automation, environmental protection and monitoring and is applied widely.The newest standards provided in 2011
In, 314-316MHz, 430-434MHz, 779-787MHz and 950-956MHz working frequency range are added again.
As shown in figure 1,802.15.4 agreements are different with message transmission rate using modulation system on different carrier wave frequency ranges.
48 channels are provided altogether in four typical frequency ranges:1 channel of 868MHz frequency ranges, 10 channels of 915MHz frequency ranges, 2450MHz
16 channels of frequency range, 21 channels of 950MHz frequency ranges.As shown in Fig. 2 in 868/915/950-MHz frequency ranges, signal transacting mistake
Cheng Xiangtong, simply data rate is different.Sender is first by the binary data difference of physical layer data protocol element (PPDU)
Coding, then again by differential coding after it is each the piece sequence that length is 15 is converted to position, finally using BPSK modulate to letter
On road.Differential coding is that the bit that each original bit of data and previous differential coding are generated is carried out into XOR:Wherein EnIt is the result of differential coding, RnIt is the original bit to be encoded, En-1It is last differential coding
As a result.To the packet that each sends, R1It is first original bit, calculates E1When assume E0=0.Differential ference spiral process and volume
Code process is similar to:To the packet that each is received, E1It is first bit of needs demodulation, calculates E1When vacation
Determine E0=0.As shown in figure 3, each bit after differential coding is converted into the piece sequence that length is 15.Sequence after spread spectrum makes
Modulated onto carrier wave with BPSK modulation systems.
As shown in figure 4, the first character section of IEEE 802.15.4 protocol physical layers data frame structures is that four bytes amount to
Complete zero lead code of 32, transceiver can complete piece synchronously and symbol during lead code is received according to the feature of preamble sequence
Number synchronization.Frame starting separator (SFD) field length is a byte, and its value is fixed as 0xA7, is expressed as physical frame
Start, transceiver finishes receiving the bit synchronization that can only accomplish data after lead code, could be same by the value 0xA7 for searching for SFD fields
Walk in byte.By low 7 expression of byte, its value is exactly the length of physical frame load to frame length, therefore physical frame is negative
The length of load is not over 127 bytes.The payload length of physical frame is variable, referred to as physical layer service data
(PSDU), it is generally used to carry mac frame.
Being traditionally used for the demodulation method of IEEE802.15.4 has two kinds, and a kind of is 868/915/950- as shown in Figure 5
Tradition typical case's complex base band non-coherent demodulation method of MHz frequency ranges.WithAfter representing channel transmission
The complex base band sampled signal for receiving, wherein s (k) is transmission data to be detected, s (k) ∈ {+1, -1 }, ω0=2 π f0,f0With
θ is respectively frequency shift (FS) and phase offset, keeps constant in whole data frame, TcRepresent spreading code chip cycle, η0K () is
Complex base band additive white Gaussian noise, demodulating process can be summarized as:
Step one, receive sampled signal and calculate using the corresponding complex base band of lead code of 32 bits and contain frequency offset information
Observation Y:
Wherein, J represents the total number of bits amount of lead code, J=32, and N represents spreading length, N=15,1≤m≤J-1,
0≤n≤N-1, p [n+Nm] represent the channel reception value of corresponding n-th chip of m-th bit of lead code, ()*Table
Show and take conjugate operation, η1Represent all of noise item.
Step 2, sampled signal is received to the corresponding complex base band of PSDU carry out bit-level difference processing, obtain judgement observation
Value A [m]:
Wherein, r [n+Nm] represents the channel reception value of corresponding n-th chip of m-th bit of PSDU, η2[m] represents all
Noise item, E [m] represent send m-th bit data.
Step 3, using the Y in step one0Frequency offset information is extracted, the A [m] in step 2 is compensated laggard
Row detection judgement:
Wherein,Represent that, to m-th court verdict of bit data, q () is quantization function, | | modulo operation is represented,
Re () is represented and is taken real part computing, and Im () is represented and taken imaginary-part operation.Bloch, M.R., Hayashi, M. and Thangaraj,
A. exist in September, 2010《IEEE Transcactions on Signal Processing》On the article " IEEE that delivers
802.15.4BPSK receiver architecture based on a new efficient detection scheme”
In provide a kind of computational methods of the quantization function of YBody,It is the phase of Y, is also N ω0TcEstimation
Value,Computational methods be specifically described as:
The detection judging process of formula (3) needs to extract frequency offset information N ω from Y in advance0TcEstimateThen to A
[m] is compensated.As described above, the weak point of tradition typical case's non-coherent demodulation method is:From formula (4), step 3
It is middle to need to obtain frequency offset information N ω by the arctangent cp cp operation of division arithmetic and complexity0TcEstimateThis for
Energy is supplied for the strictly limited 802.15.4 network terminals, and computation complexity is larger, and energy consumption is larger, and cost of implementation is higher.
Another demodulation method is to reduce the extraction frequency deviation compensated information N ω from Y0TcImplementation complexity, by
Lee, S., Kwon, H., Jung, Y. and Kim, J.S. exist in August, 2007《Electronics Letter》On the text delivered
Chapter " Efficient non-coherent demodulation scheme for IEEE 802.15.4LR-WPAN
A kind of demodulation method of the reduced form proposed in systems ", the quantization function to Y is improved, can be described as:
From formula (5), in this reduction procedure, frequency offset information N ω0TcEstimateCan be specifically described as:
It can be seen that, the demodulation method of the reduced form is also required to extract frequency offset information N ω from Y in advance0TcEstimate
Then A [m] is compensated.It is right with formula (5)Approximate processing process larger error, i.e. formula (6) certainly will be produced inclined to frequency
Shifting information N ω0TcEstimation procedure there is more serious " cross and estimate " or " owing to estimate " phenomenon, reliability can be caused significantly
Decline, preferably balance matching is not reached between complicated and performance is realized.As shown in fig. 6, compared to traditional typical case's complex radical
Band non-coherent demodulation method, the performance loss of the demodulation method of reduced form is serious, the carrier frequency used in emulation for
924MHz, frequency shift (FS) be maximum 80ppm specified in IEEE 802.15.4 agreements, phase offset θ (0,2 π] in obey
It is uniformly distributed, the data length of PSDU is 20 bytes (160 bit), and 3000 frame mistakes are at least gathered under each signal to noise ratio.And
802.15.4 network MAC layer judges the correctness of transmission frame, automatic repeat request (ARQ) using CRC (CRC)
Agreement determines therefrom that whether transmission frame needs to retransmit, and without using forward error correction (FEC) mechanism, therefore physical layer modulation is deemed-to-satisfy4
The quality of energy will produce tremendous influence to energy consumption.It is poor in channel condition, communication distance farther out when, received signal power loss
It is larger.Now, if using the demodulation method of the reduced form, same PSDU data frames may could succeed by repeatedly re-transmission
Received by MAC layer.The communication process of multiple re-transmission will also consume huge energy if data volume is huge, and this can reduce energy
Supply the service life of deficient 802.15.4 networks.
The content of the invention
In order to solve deficiency of the prior art, Taylor series expansion and big signal to noise ratio of the present invention based on arcsin function
When influence negligible theory of the noise to useful signal, there is provided it is a kind of low computation complexity suitable for IEEE 802.15.4, low
The incoherent BPSK demodulation methods of power consumption, high reliability and low cost.
To achieve these goals, the concrete scheme that uses of the present invention for:
A kind of high reliability BPSK demodulation methods for IEEE802.15.4, the data frame of transmitting terminal physical layer by spread spectrum and
Channel is transferred to receiving terminal after BPSK modulation, and data frame includes 32 lead codes and physical layer service data of bit
PSDU;The complex base band sampled signal that receiving terminal is received is expressed asWherein s (k) is to be detected
Transmission data, s (k) ∈ {+1, -1 }, ω0=2 π f0,f0Frequency shift (FS) and phase offset are respectively with θ and in whole data frame
Constant, the T of middle holdingcRepresent spreading code chip cycle, η0K () is complex base band additive white Gaussian noise;Specifically demodulation step is:
Step one, lead code frequency deviation sight of the corresponding channel received data extraction comprising frequency offset information using 32 bits
Measured value Y:
Wherein, J represents the total number of bits amount of lead code, and J=32, N represents spreading length, N=15,1≤m≤J-1,0≤n≤N-
1, p [n+Nm] represents the channel reception value of corresponding n-th chip of m-th bit of lead code, ()*Expression takes conjugation fortune
Calculate, η1Represent all of noise item;
Step 2, bit-level difference processing is carried out to the corresponding complex base band sampled signals of PSDU, obtain judgement observation A [m]:
Wherein, r [n+Nm] represents the channel reception value of corresponding n-th chip of m-th bit of PSDU, η2[m] represents all
Noise item, E [m] represent send m-th bit data;
Step 3, using in step one frequency deviation observation Y extract frequency offset information, the A [m] in step 2 is compensated
After carry out detection judgement:
Wherein,M-th bit data that detection judgement is obtained is represented, q () is quantization function, and q (Y) is embodied as:
Wherein, | | modulo operation is represented,Represent A [m] frequency offset N ω0TcEstimate;
The PSDU data that step 4, detection will be received after terminating send MAC layer to carries out CRC check;
In the step 3,Computing formula be:
Wherein, Re () is represented and is taken real part computing, and Im () is represented and taken imaginary-part operation.
As a kind of preferred scheme, in the step 3Computational methods simplified, obtain:
Beneficial effect:
1st, the demodulation method and further reduced form that the present invention is provided all are fully able to meet IEEE 802.15.4 agreements to property
The requirement of energy, specifies in IEEE 802.15.4 agreements, when it is 20 byte (160 bits) that signal to noise ratio is 5~6dB, PSDU,
Packet Error Ratio is less than 1 × 10 less than 1%, i.e. PER-2, particularly it has been fully able to meet requirement when signal to noise ratio is about 1dB;
2 compare with traditional typical case's complex base band non-coherent demodulation method, and the present invention has lower computation complexity, lower energy
Consumption and lower cost of implementation, tradition typical case complex base band non-coherent demodulation method by a division and an arctangent cp cp operation come
To frequency offset information N ω0TcEstimator, from formula (10), frequency offset information N ω of the invention0TcEstimation side
Method at most needs three times to compare, multiplication, a division and add operation twice twice;The frequency shift (FS) letter of further reduced form
Breath N ω0TcMethod of estimation at most need three times to compare, multiplication, a division and an add operation twice, therefore with more
Low computation complexity, lower energy consumption and lower cost of implementation;
3 compare with the demodulation method of traditional reduced form, and the present invention has reliability higher, the demodulation of traditional reduced form
Method formula (6) is to N ω0TcCarry out approximate evaluation, i.e., with 0,- π andFour kinds of phases are to N ω0TcEstimated, caused
Error is larger, and the present invention is using formula (10) to frequency offset information N ω0TcEstimated, " cross and estimate present in estimation procedure
Meter " or " owing to estimate " phenomenon are weaker, and more preferably, reliability is higher for performance.
Brief description of the drawings
Fig. 1 is four frequency range fundamental characteristics figures of IEEE 802.15.4 protocol physical layers;
Fig. 2 is IEEE 802.15.4 agreement 868/915/950-MHz frequency range physical layer data transmission process figures;
Fig. 3 is IEEE 802.15.4 agreement 868/915/950-MHz frequency ranges spread spectrum mapping mode figure;
Fig. 4 is IEEE 802.15.4 protocol physical layers frame assumption diagrams;
Fig. 5 applies to typical case's tradition non-coherent demodulation method structure chart of 868/915/950-MHz frequency ranges;
Fig. 6 applies to the traditional demodulation method and reduced form demodulation method Performance comparision figure of 868/915/950-MHz frequency ranges;
Fig. 7 is that two kinds of demodulation methods that the present invention is provided and existing two kinds of typical cases demodulation deemed-to-satisfy4 can compare figure;
Fig. 8 is frequency deviation side-play amount f0Probability distribution graph.
Specific embodiment
Embodiments of the present invention are illustrated below according to accompanying drawing.
A kind of high reliability BPSK demodulation methods for IEEE802.15.4, the data frame of transmitting terminal physical layer is by expanding
Channel is transferred to receiving terminal after frequency and BPSK modulation, and data frame includes the lead code of 32 bits and Physical Layer Service Data
Unit PSDU;The complex base band sampled signal that receiving terminal is received is expressed asWherein s (k) is to treat
The transmission data of detection, s (k) ∈ {+1, -1 }, ω0=2 π f0,f0Frequency shift (FS) and phase offset are respectively with θ and entirely counting
According to keeping constant, T in framecRepresent spreading code chip cycle, η0K () is complex base band additive white Gaussian noise;Specific demodulation step
For:
Step one, lead code frequency deviation sight of the corresponding channel received data extraction comprising frequency offset information using 32 bits
Measured value Y:
Wherein, J represents the total number of bits amount of lead code, J=32, and N represents spreading length, N=15,1≤m≤J-1,
0≤n≤N-1, p [n+Nm] represent the channel reception value of corresponding n-th chip of m-th bit of lead code, ()*Table
Show and take conjugate operation, η1Represent all of noise item;
Step 2, bit-level difference processing is carried out to the corresponding complex base band sampled signals of PSDU, obtain judgement observation A [m]:
Wherein, r [n+Nm] represents the channel reception value of corresponding n-th chip of m-th bit of PSDU, η2[m] represents all
Noise item, E [m] represent send m-th bit data;
Step 3, using in step one frequency deviation observation Y extract frequency offset information, the A [m] in step 2 is compensated
After carry out detection judgement:
Wherein,M-th bit data that detection judgement is obtained is represented, q () is quantization function, and q (Y) is embodied as:
Wherein, | | modulo operation is represented,Represent A [m] frequency offset N ω0TcEstimate;
The PSDU data that step 4, detection will be received after terminating send MAC layer to carries out CRC check;
In the step 3,Computing formula be:
Used as the further form for simplifying, the quantization function described in step 3 isWherein:
Theoretical foundation of the invention is described below.
First, to tan at x=0-1X carries out Taylor series expansion and can obtain:
When | x | is smaller, there is approximation relation tan-1x≈x。
As frequency offset N ω0TcOn the premise of smaller and signal to noise ratio is larger,Value it is smaller.Can direct tan- 1X ≈ x carry out being obtained after simplifying treatment to formula (4):
But as frequency offset N ω0TcIn the case that larger or signal to noise ratio snr is not high,Value it is larger.tan-1x≈x
Approximate calculation to formula (4) will bring larger error, cause the extreme loss of final performance.I.e. formula (16) is only applicable to frequency
Side-play amount is smaller and two larger constraintss of signal to noise ratio under detection process.
To obtain the low complex degree frequency offset estimation methods under a kind of unconfined condition, we using arcsin function and
The equivalence relation of arctan function can be obtained:
If in first and fourth quadrant of complex plane coordinate system, i.e., Y fallsThen have:
If in second and third quadrant of complex plane coordinate system, i.e., Y fallsThen have:
According to formula (17) and formula (18), formula (4) can equivalence be changed into:
Secondly, to sin at x=0-1X carries out Taylor series expansion and can obtain:
Then when | x | is smaller, there is approximation relation sin-1x≈x。
Due toIt is permanent under the conditions of any frequency offset and signal to noise ratio to set up, therefore can be directly sharp
Use sin-1X ≈ x are in formula (19)Item carries out simplifying available:
3rd, the calculating process of the fraction of formula (20), it is contemplated that further simplify to it.When signal to noise ratio is larger, we
There is following approximation relation:
4th, with formula (21) it is only approximate to the molecule Im (Y) of formula (20) fraction after can obtain:
As shown in fig. 7, the demodulation method that the present invention is provided compares with traditional canonical reduction form demodulation method, performance is more excellent
More, reliability is higher.The carrier frequency used in emulation is 924MHz, frequency shift (FS) f0Angular distribution as shown in Figure 8 is obeyed,
Phase offset θ (0,2 π] in obey and be uniformly distributed, the data length of PSDU is 20 bytes (160 bit), each signal to noise ratio
Under at least gather 3000 frame mistakes.It can be seen that, two kinds of demodulation method performances that the present invention is provided be in two kinds of traditional demodulation methods it
Between.Simplify demodulation method with tradition to compare, when Packet Error Ratio is 1 × 10-3, the gain not less than 1.3dB can be obtained.Therefore this hair
The two schemes of bright offer have reached more preferable balance matching between implementation complexity and performance.
Further the theoretical foundation of reduced form is:With formula (21) to the molecule Re (Y) and denominator Im in formula (20) fraction
(Y) while can be obtained after approximate:
Calculating process can further be simplified, the consumption of energy is reduced.
Claims (2)
1. a kind of high reliability BPSK demodulation methods for IEEE802.15.4, the data frame of transmitting terminal physical layer is by spread spectrum
Receiving terminal is transferred to channel after BPSK modulation, data frame includes the lead code of 32 bits and Physical Layer Service Data list
First PSDU;The complex base band sampled signal that receiving terminal is received is expressed asWherein s (k) is to be checked
The transmission data of survey, s (k) ∈ {+1, -1 }, ω0=2 π f0,f0Frequency shift (FS) and phase offset are respectively with θ and in whole data
Constant, T is kept in framecRepresent spreading code chip cycle, η0K () is complex base band additive white Gaussian noise;Specific demodulation step
For:Step one, lead code frequency deviation sight of the corresponding channel received data extraction comprising frequency offset information using 32 bits
Measured value Y:
Wherein, J represents the total number of bits amount of lead code, and J=32, N represents spreading length, N=15,1≤m≤J-1,0≤n≤N-
1, p [n+Nm] represents the channel reception value of corresponding n-th chip of m-th bit of lead code, and () * is represented and taken conjugation fortune
Calculate, η1Represent all of noise item;
Step 2, bit-level difference processing is carried out to the corresponding complex base band sampled signals of PSDU, obtain judgement observation A [m]:
Wherein, r [n+Nm] represents the channel reception value of corresponding n-th chip of m-th bit of PSDU, η2[m] represents all of
Noise item, E [m] represents m-th bit data for sending;
Step 3, using in step one frequency deviation observation Y extract frequency offset information, the A [m] in step 2 is compensated
After carry out detection judgement:
Wherein,M-th bit data that detection judgement is obtained is represented, q () is quantization function, and q (Y) is embodied as:
Wherein, | | modulo operation is represented,Represent A [m] frequency offset N ω0TcEstimate;
The PSDU data that step 4, detection will be received after terminating send MAC layer to carries out CRC check;
It is characterized in that:
In the step 3,Computing formula be:
Wherein, Re () is represented and is taken real part computing, and Im () is represented and taken imaginary-part operation.
2. a kind of high reliability BPSK demodulation methods for IEEE802.15.4 as claimed in claim 1, it is characterised in that:
To in the step 3Computational methods simplified, obtain:
。
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