CN106936748A - A kind of low-power consumption BPSK receivers for IEEE802.15.4 - Google Patents

Abstract

A kind of low-power consumption BPSK receivers for IEEE 802.15.4, reception process is：First, receiver obtains useful frequency offset information by being processed the corresponding channel received data of lead code；Secondly, difference processing is carried out to the corresponding channel received datas of PSDU so that detection is used；Finally, judgement is detected after being compensated to the reception data of PSDU by the frequency offset information of the past preamble reception extracting data.A kind of present invention noncoherent receiver simultaneously with " low-power consumption, highly reliable and low cost " characteristic according to the Taylor series expansion Theoretical Design of arctan function.Detection performance of the invention is compared with traditional typical case's complex base band noncoherent receiver and almost not lost, and implementation complexity is but substantially reduced, and consumption of the network equipment to energy can be greatly reduced.

Description

A kind of low-power consumption BPSK receivers for IEEE802.15.4

Technical field

It is specifically a kind of for IEEE 802.15.4's the present invention relates to communication signal waveforms detection technique field Low-power consumption BPSK receivers.

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.In the newest standards of work 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 protocol data unit (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 E_nIt is the result of differential coding, R_nIt is the original bit to be encoded, E_n-1It is the knot of last differential coding Really.To the packet that each sends, R₁It is first original bit, calculates E₁When assume E₀=0.Differential decoding process and coding Process is similar to：To the packet that each is received, E₁It is first bit of needs decoding, calculates E₁When assume 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 is used BPSK modulation systems are modulated onto carrier wave.

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.

The BPSK receivers of traditional 802.15.4 networks mainly have two kinds, and a kind of is as shown in Figure 5 868/915/ Tradition typical case's complex base band noncoherent receiver of 950-MHz frequency ranges.WithRepresent channel transmission The complex base band sampled signal for receiving afterwards, wherein s (k) is transmission data to be detected, s (k) ∈ {+1, -1 }, ω₀=2 π f₀,f₀ Frequency shift (FS) and phase offset are respectively with θ, keep constant in whole data frame, T_cRepresent spreading code chip cycle, η₀(k) It is complex base band additive white Gaussian noise.Then the detection process shown in Fig. 5 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 Y₀：

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, sampled signal is received to the corresponding complex base band of PSDU carry out bit-level difference processing, obtain judgement observation Value A₀[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 deviation offset information is extracted, to the A in step 2₀[m] compensates laggard Row detection judgement：

Wherein,Receiving terminal is represented to m-th court verdict of bit data, q () is quantization function,| | represent modulo operation.Bloch, M.R., Hayashi, M. and Thangaraj, A. were in 2010 years September exists《IEEE Transcactions on Signal Processing》On article " the IEEE 802.15.4 BPSK that deliver One kind is provided in receiver architecture based on a new efficient detection scheme " Y₀Quantization function computational methodsWhereinIt is Y₀Phase, be also frequency offset information N ω₀T_c Estimate,Computational methods be specifically described as：

Wherein, Re () is represented and is taken real part computing, and Im () is represented and taken imaginary-part operation.

As described above, the weak point of tradition typical case's complex base band noncoherent receiver is：The detection judging process of formula (3) Need in advance from Y₀Middle extraction frequency offset information N ω₀T_cEstimateThen to A₀[m] is compensated.Can by formula (4) Know, needed in step 3 by division arithmetic and complicated arctangent cp cp operation from Y₀In obtain frequency offset information N ω₀T_cEstimate EvaluationThis is for energy supplies the strictly limited 802.15.4 network terminals, and energy consumption is larger.

To reduce from Y₀Middle extraction frequency deviation compensated information N ω₀T_cImplementation complexity, Lee, S., Kwon, H., Jung, Y., And Kim, J.S. exist in August, 2007《Electronics Letter》On article " the Efficient non-that deliver In coherent demodulation scheme for IEEE 802.15.4 LR-WPAN systems ", in traditional typical case A kind of receiver of reduced form is proposed on the basis of complex base band noncoherent receiver, to frequency deviation observation Y₀Quantization function Change, specifically can be described as：

From formula (5), in this reduction procedure, frequency offset information N ω₀T_cEstimateCan be specifically described as：

It can be seen that, the weak point of traditional reduced form receiver is：The program is also required in advance from Y₀Middle extraction frequency shift (FS) letter Breath N ω₀T_cEstimateThen to A₀[m] is compensated.Its essence is to carry out approximate processing to formula (1) with formula (6), so that Substantially reduce the implementation complexity of traditional scheme.But formula (6) certainly will produce larger error to the approximate processing process of formula (1), i.e., Formula (6) is to frequency offset information N ω₀T_cEstimation procedure there is more serious " cross and estimate " or " owing to estimate " phenomenon, can cause Declining to a great extent for detection reliability, does not reach preferably balance matching between complicated and performance is realized.As shown in fig. 6, phase Than in not simplified receiver, the detection performance loss of traditional reduced form receiver is serious.The carrier frequency used in emulation Rate is 924MHz, and frequency shift (FS) is maximum 80ppm specified in IEEE 802.15.4 agreements, phase offset θ (0,2 π] in Obedience is uniformly distributed, and the data length of PSDU is 20 bytes (160 bits), 3000 frames is at least gathered under each signal to noise ratio wrong By mistake.And 802.15.4 network MAC layers do not use forward error correction (FEC) mechanism, but sentenced using CRC (CRC) The correctness of disconnected transmission frame, automatic repeat request (ARQ) agreement determines therefrom that whether transmission frame needs to retransmit.Therefore physical layer is received The quality of machine performance just directly has an immense impact on to energy consumption.It is poor in channel condition, communication distance relatively far away from when, receive Signal power loss is larger.Now, if using the reduced form receiver, same PSDU data frames may be by repeatedly re-transmission Could succeed and be passed through by MAC layer verification.The communication process of multiple re-transmission will also consume huge energy if data volume is huge, This can reduce the service life of the deficient 802.15.4 networks of energy supply.

The content of the invention

In order to solve two kinds of deficiencies of traditional noncoherent receiver, the Taylor series expansion based on arctan function is theoretical, The present invention provides a kind of low-power consumption BPSK receivers suitable for IEEE 802.15.4, and computation complexity and energy resource consumption are lower, The service life of IEEE802.15.4 network equipments can significantly be extended.

To achieve these goals, the scheme that uses of the present invention for：

A kind of low-power consumption BPSK receivers for IEEE 802.15.4, 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, in whole data frame Constant, the T of middle holding_cRepresent spreading code chip cycle, η₀K () is complex base band additive white Gaussian noise；The specific steps of reception process For：

Step one, lead code frequency deviation sight of the corresponding channel received data extraction comprising frequency offset information using 32 bits Measured value Y₀：

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, sampled signal is received to the corresponding complex base band of PSDU carry out bit-level difference processing, obtain judgement observation A₀ [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 frequency deviation observation Y in step one₀Frequency offset information is extracted, and to the A in step 2₀[m] is carried out Detection judgement is carried out after compensation：

Wherein,M-th bit data that detection judgement is obtained is represented, q () is quantization function, q (Y₀) be embodied as：

Wherein, | | modulo operation is represented,Represent A₀[m] frequency offset information N ω₀T_cEstimate；

The PSDU data that step 4, detection will be received after terminating send MAC layer to carries out CRC check；

In the step 3,Circular be：

Wherein, Re () is represented and is taken real part computing, and Im () is represented and taken imaginary-part operation.

Beneficial effect：

1st, specify in IEEE 802.15.4 agreements, when it is 20 byte (160 bits) that signal to noise ratio is 5~6dB, PSDU, by mistake Bag rate will be less than 1 × 10 less than 1%, i.e. PER^-2, as shown in fig. 7, the present invention has just been entirely capable of when signal to noise ratio is 0.6dB Agreement is enough met to detecting the requirement of performance；

2 compare with traditional typical case's complex base band noncoherent receiver, and the present invention has lower computation complexity and lower energy Consumption, from formula (4), tradition typical case's complex base band noncoherent receiver is by a division and an arctangent cp cp operation come to frequency Rate offset information N ω₀T_cEstimator, from formula (10), the frequency offset information N ω that the present invention is announced₀T_cEstimation side Only need to once to compare in method, a division and an add operation, the implementation complexity of comparison operation and add operation is remote Far below arctangent cp cp operation, therefore method of estimation of the invention has lower computation complexity and lower energy consumption；

3 compare with traditional typical case's low complex degree receiver, and the present invention has detection reliability higher, traditional reduced form Receiver formula (6) is to N ω₀T_cEstimated, i.e., with 0,- π andFour kinds of phases are to N ω₀T_cEstimated, the mistake for causing Difference is larger, and the present invention is using the calculation of formula (10) to frequency offset information N ω₀T_cEstimated, present in estimation procedure " cross and estimate " or " owing to estimate " phenomenon is weaker, and more preferably, reliability is higher for detection 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 receiver structure figure of 868/915/950-MHz frequency ranges；

The traditional receivers and reduced form that Fig. 6 applies to 868/915/950-MHz frequency ranges receive machine testing Performance comparision figure；

Fig. 7 is the receiver and existing two kinds of typical receptions machine testing Performance comparision figure that the present invention is announced；

Fig. 8 is frequency deviation side-play amount f₀Probability distribution graph；

Fig. 9 is Y under complex coordinate plane₀Corresponding angle [alpha] figure during in different zones.

Specific embodiment

Embodiments of the present invention are illustrated below according to accompanying drawing.

A kind of low-power consumption BPSK receivers for IEEE 802.15.4, 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, in whole data Constant, T is kept in frame_cRepresent spreading code chip cycle, η₀K () is complex base band additive white Gaussian noise；The specific step of reception process It is rapid as follows：

Step one, lead code frequency deviation sight of the corresponding channel received data extraction comprising frequency offset information using 32 bits Measured value Y₀：

Step 2, sampled signal is received to the corresponding complex base band of PSDU carry out bit-level difference processing, obtain judgement observation A₀ [m]：

Step 3, using the frequency deviation observation Y in step one₀Frequency offset information is extracted, and to the A in step 2₀[m] is carried out Detection judgement is carried out after compensation：

Wherein,M-th bit data that receiving terminal judgement is obtained is represented,| | represent modulo operation.Using frequency deviation observation Y₀The frequency offset information N ω of extraction₀T_cEstimate, while as judgement observation A₀The frequency of [m] The estimate of rate offset information,Specific calculating process be：

Wherein, Re () is represented and is taken real part computing, and Im () is represented and taken imaginary-part operation.

The PSDU data that step 4, detection will be received after terminating send MAC layer to carries out CRC check.

Simplify as further, due to | Y₀| >=0, therefore for judgement in formula (13) according to " Re { A₀[m]·q(Y₀)}≥0” For have：

Therefore | Y₀| item does not interfere with the final judging result of formula (13), in ignoring the quantization function in formula (13) | Y₀| item and withSubstituteJust can be obtained to mutually differentiation：

The corresponding detection performance of the quantization function shown in quantization function and formula (15) in formula (13) is completely the same, and formula (15) is gathered around There is lower implementation complexity, can further reduce the consumption to the energy, improve the service life of device.

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。

Secondly, as frequency offset N ω₀T_cOn the premise of smaller and signal to noise ratio snr is larger,Set up.It is directly sharp Use tan^-1X ≈ x carry out being obtained after simplifying treatment to formula (4)：

But as frequency offset N ω₀T_cIn the case that larger or signal to noise ratio is not high,tan^-1X ≈ x are to formula (4) Approximate calculation will bring larger error, cause finally to detect the extreme loss of performance.I.e. formula (16) is only applicable to frequency shift (FS) Measure the situation under smaller and two larger constraintss of signal to noise ratio.

To obtain the low complex degree frequency offset estimation methods under a kind of unconfined condition, equivalence transformation is carried out to formula (4) Treatment.As shown in figure 9, working as Y₀Angle meetOrWhen,Set up, now use tan^-1x The approximation of ≈ x will not introduce larger error.Therefore can continue using following computational methods：

As shown in figure 9, working as Y₀Phase meetWhen, Wo Menyou：

Work as Y₀Phase meetWhen, Wo Menyou：

Can be obtained by formula (19) and formula (21)

Similarly, Y is worked as₀Angle meetWhen, Wo Menyou：

Can be obtained by formula (17), formula (22) and formula (23)：

From formula (24),WithIt is permanent in respective regional extent to set up, therefore directly use approximate pass It is tan^-1X ≈ x are in formula (24)Approximate calculation is without introducing larger error, it can thus be concluded that arriving:

Finally, comparison expression (6) and formula (24) understand, uses approximation relation tan^-1X ≈ 0 are in formula (24)Can be obtained after simplification To in formula (6)Therefore have conclusion：To in formula (24)Approximation relation tan is used respectively^-1X ≈ 0 and tan^-1After x ≈ x simplify It is availableWith

Obvious approximation relation tan^-1X ≈ x compare tan^-1X ≈ 0 have smaller approximate error, therefore what the present invention proposed a plan Detection performance is higher than the receiver reliability of traditional reduced form.

As shown in fig. 7, the receiver that the present invention is announced compares with traditional two kinds of receivers, ensureing the situation of performance Under, lower computation complexity and lower energy consumption can be realized, supply strictly limited IEEE802.15.4 nets for energy For network device, can significantly extend its service life.The carrier frequency used in emulation is 924MHz, frequency shift (FS) f₀Obey Triangular symmetrical distribution as shown in Figure 8, phase offset θ (0,2 π] in obey and be uniformly distributed, the data length of PSDU is 20 Byte (160 bits), at least gathers 3000 frame mistakes under each signal to noise ratio.It can be seen that, receiver and tradition that the present invention is announced The detection performance of typical complex base band noncoherent receiver is basically identical, and performance loss is extremely low.With the receiver of traditional reduced form Compare, when Packet Error Ratio is 1 × 10-3, the gain not less than 1.7dB can be obtained.Therefore the scheme that the present invention is announced is realizing complexity More preferable balance matching has been reached between degree and detection performance.

Claims (1)

1. a kind of low-power consumption BPSK receivers for IEEE 802.15.4, 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, in whole data frame Constant, the T of middle holding_cRepresent spreading code chip cycle, η₀K () is complex base band additive white Gaussian noise；The specific steps of reception process For：

Step one, corresponding frequency deviation observation of the reception data extraction comprising frequency offset information of lead code using 32 bits Y₀：

$\begin{array}{c}{Y}_0=\frac{1}{(J-1)N}\underset{m=1}{\overset{J-1}{\Σ}}\underset{n=0}{\overset{N-1}{\Σ}}p\[n+Nm\]\·p^{*}\[n+N(m-1)\]\\ =e^{{\mathrm{jN\ω}}_0{T}_c}+{\mathrm{\η}}_1\end{array},$

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, sampled signal is received to the corresponding complex base band of PSDU carry out bit-level difference processing, obtain judgement observation A₀ [m]：

$\begin{array}{c}{A}_0\[m\]=\underset{n=0}{\overset{N-1}{\Σ}}r\[n+Nm\]\·r^{*}\[n+N(m-1)\]\\ =\left\{\begin{array}{cc}{\mathrm{Ne}}^{{\mathrm{jN\ω}}_0{T}_c}+{\mathrm{\η}}_2\[m\],& E\[m\]=0\\ -{\mathrm{Ne}}^{{\mathrm{jN\ω}}_0{T}_c}+{\mathrm{\η}}_2\[m\].& otherwise\end{array}\right.\end{array},$

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 the frequency deviation observation Y in step one₀Frequency offset information is extracted, and to the A in step 2₀[m] is carried out Detection judgement is carried out after compensation：

$\hat{E}\[m\]=\left\{\begin{array}{cc}0,& \mathrm{Re}\{A_0\[m\]\·q\left(Y_0\right)\}\≥0\\ 1.& otherwise\end{array}\right.,$

Wherein,M-th bit data that detection judgement is obtained is represented, q () is quantization function, q (Y₀) be embodied as：

Wherein, | | modulo operation is represented,Represent A₀[m] frequency offset information N ω₀T_cEstimate；

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,Circular be：

Wherein, Re () is represented and is taken real part computing, and Im () is represented and taken imaginary-part operation.