CN109495412B - Backscatter communication system receiver design method based on MPSK carrier wave - Google Patents
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Abstract
The invention belongs to wireless communication technology fields, are related to a kind of backscatter communication system receiver design method based on MPSK carrier wave.The present invention establishes the receiver design cycle of environment backscatter communication system from the angle of channel estimation, it is utilized under two kinds of hypothesis of label signal, corresponding channel is different, will test signal and is changed into detection channel, it is directly made decisions using estimation gained signal, reduces Receiver Complexity.
Description
Technical field
The invention belongs to wireless communication technology fields, and it is logical to be related to a kind of backscattering based on MPSK (phase-shift keying (PSK)) carrier wave
Believe system receiver design method.
Background technique
The it is proposed of environment backscatter communication technology solves traditional backscatter communication system, such as radio frequency identification
(RFID) the high consumption of system, low-energy-efficiency problem.The technology is sent to mark using the radiofrequency signal in ambient enviroment as carrier wave
Label, signal a part that label receives meet the normal work of tag circuit for collection of energy, and another part is for anti-
To scattering, the information of label is loaded on carrier wave and is transferred to reader.This mode not only solves energy consumption problem, but also does not influence
Existing communication system.Existing signal detection algorithm can be divided into two major classes: based on energy measuring and be based on Likelihood ration test.The former
Algorithm complexity is low, but the amplitude information of signal is received due to being only utilized, and bit error rate performance is accordingly poor；The latter's bit error rate
Function admirable has sought the joint probability of the environmental signal in a label period when seeking only the likelihood ratio for receiving signal probability distribution
Distribution, algorithm complexity are higher.
Summary of the invention
In order to find equalization point between Receiver Complexity and bit error rate performance, surrounding is utilized the invention proposes a kind of
The channel estimation method of MPSK radiofrequency signal in environment, which can eliminate the phase ambiguity of estimation channel, and be based on
Estimation gained channel, proposes the receiver design method of low complex degree.Due in existing wireless communications system, such as WLAN
(WLAN) and satellite communication (SC) etc., MPSK modulation system is widely used, present invention utilizes such signal, Lai Shixian environment is anti-
To scatter communication.
The present invention establishes the receiver design cycle of environment backscatter communication system from the angle of channel estimation, utilizes
Under two kinds of label signal are assumed, corresponding channel is different, as shown in figure 4, will test signal is changed into detection channel, directly
It is made decisions using estimation gained signal, reduces Receiver Complexity.According to the agreement of wireless communication system, Fig. 1 is shown
The pack arrangement of environmental signal, the period of label signal are L times of environmental signal period, in each environmental signal packet, preceding LpA letter
Number be pilot tone, rear LdA signal is data-signal.The present invention does channel using L environmental signal in a label signal period
Estimation, to accurately estimate channel corresponding to outgoing label signal.Fig. 3 shows environment backscatter communication system of the present invention
System model, transmitting terminal and label are equipped with an antenna, and reader is equipped with K root antenna, and n-th of label signal period is corresponding
In L reception signal slot, the reception signal on first of time slot kth root antenna can be expressed as:
For k=1 ..., K l=1 ..., L.
Wherein, label signal c (n) is used as baseband modulation signal, and α indicates the reflection coefficient of signal c (n), PsRepresent environment
The power of signal, s (n, l) indicate first of environmental signal corresponding with label signal c (n), hkIndicate transmitting terminal to reader the
The low pass channel impulse response of k root antenna, fkIndicate low pass channel impulse response of the label to reader kth root antenna, g expression
Low pass channel impulse response of the transmitting terminal to label, uk(n, l) refers to the noise at reader end.
Signal will be received and be expressed as vector form, as follows:
h0=h h1=h+ α gf
It can be obtained by above-mentioned formula, the difference that label signal sends 0 or 1 is the difference of channel, and observation Fig. 1 can be obtained, be marked
Label have sent two pilot tone c (0)=0 and c (1)=1 before sending the information, with two kinds of channels of marking: h0And h1.The present invention
This feature is utilized, the corresponding estimation channel of label signal is compared with two kinds of marked channels, selects more like letter
Label symbol is as court verdict corresponding to road.Decision rule is as follows:
Design advantage proposed by the present invention apart from receiver is, while reducing Receiver Complexity, design letter
Channel estimation algorithm promotes receiver performance.
The invention also provides the exclusive channel phase estimation algorithms for MPSK environmental signal, can eliminate channel phase
It is fuzzy, improve estimation accuracy.Moreover, the pilot portion of environmental signal is utilized simultaneously for the algorithm and data portion carries out channel
Estimation, obtained estimation channel are more acurrate.The channel phase algorithm for estimating is suitable for single antenna and the received system of multiple antennas simultaneously
System, greatly reduces operation complexity.
The present invention is based on a kind of reaction type apart from receiver, is proposed apart from receiver, ginseng is updated after adjudicating each time
Channel is examined, to promote the accuracy of reference channel, to promote detection performance.
The present invention is also based on proposing apart from receiver a kind of iterative apart from receiver, is adjudicating N number of label signal
Afterwards, corresponding reception signal is divided into two signal collection according to 0 or 1, estimates reference based on all elements in two signal collection
Channel recycles and carries out label signal judgement apart from receiver.Repeat to adjudicate --- estimation --- process to reconvict, directly
To estimation channel convergence.
Beneficial effects of the present invention are, under the premise of not influencing receiver bit error rate performance, reduce and are carried based on MPSK
The Receiver Complexity of the environment backscatter communication system of wave；Relax the item of receiver perfection known channel and noise variance
Part；So that the receiver has more practicability, the development of power-assisted Internet of things system.
Detailed description of the invention
Fig. 1 shows the pack arrangement block diagram of environmental signal and label signal；
Fig. 2 shows the system block diagrams of environment backscatter communication system of the present invention；
Fig. 3 shows the system model of environment backscatter communication system of the present invention；
Fig. 4 shows channel and signal transition diagram of the invention；
Fig. 5 shows the receiver operation block diagram of environment backscatter communication system of the present invention；
Fig. 6 shows receiver design scheme proposed by the present invention and conventional energy detection and Likelihood ration test scheme
Bit error rate comparison.
Specific embodiment
The present invention will be described in detail with simulated example with reference to the accompanying drawing, so that those skilled in the art can be more
Understand the present invention well.
Fig. 2 illustrates system block diagram of the invention, and there are two the communication systems coexisted in such a system: traditional MPSK system
System, is made of radio frequency source (such as satellite communication signals, bluetooth, purple honeybee etc.), special receiver (such as mobile phone terminal)；Environment is reversed
Scatter communication system is formed by radio frequency source, the label of power supply and equipped with the reader of K (K >=1) root antenna.Present invention concern
Environment backscatter communication system, within the system, label load self information on the mpsk signal from radio frequency source,
It is transmitted to reader.The backscatter antenna of label is connected to the switch and RF energy collection module of load impedance, and label is logical
It crosses the switch of switching antenna impedance and then changes the amplitude for reflecting signal and/or phase to modulate the MPSK carrier wave received, penetrate
Frequency energy collection module collects the energy of the mpsk signal in environment.
Fig. 3 illustrates system model of the invention, wherein hkLow pass channel of the expression transmitting terminal to reader kth root antenna
Impulse response, fkIndicate low pass channel impulse response of the label to reader kth root antenna, g expression transmitting terminal to the low of label
Communicate channel shock response.
The low-pass signal that tab end receives are as follows:
Wherein s (n, l) refers to the low pass mpsk signal of unit power, PsIt is average transmission power.
Reader kth root antenna, the signal that k=1,2 ..., K are received are as follows:
yk(n, l)=yd,k(n,l)+yb,k(n,l)+uk(n,l) (5)
Wherein,It is the direct link signal from radio frequency source, yb,k(n, l)=α gfkx(n)c
It (n) is the back-scattered signal that reader is reflected into from tab end, uk(n, l) is that power is σ2Base band additive white Gaussian noise,
I.e.It is assumed that noise is independently of direct link signal and back-scattered signal.Due to label in practice
It is very short with the distance of reader, current invention assumes that each channel fkThere is an individual path and is a constant.
The signal that all antennas of receiver receive is indicated with vector:
If the modulating mode of label signal is OOK, based on two kinds it is assumed that received vector may be expressed as:
Observation is it is found that the difference of two kinds of hypothesis is the difference of the channel before environmental signal: The difference of the two is whether to added the influence of reflection link, but due to reflection coefficient compared with
Small, in low signal-to-noise ratio, the difference of the two is simultaneously little.So either the receiver based on likelihood ratio is still based on energy measuring
Performance of the receiver in low signal-to-noise ratio it is all poor.The present invention is from the angle for reducing Receiver Complexity, with estimation institute
Channel is obtained to distinguish two kinds of hypothesis of label signal.As shown in figure 4, the present invention regards environmental signal as channel, by two kinds of differences
Channel h0And h1Regard the signal of transmitter transmission as, signal is influenced by channel by noise, and receiver has received signal not
It is accurate h0Or h1, label signal judgement is made by comparing the distance between channel.
Accurate channel information can not be obtained in practical application, so can find according to Fig. 1, present invention setting, In
Before label signal sends data, two pilot signals: c (0)=0, c (1)=1 are first sent, corresponding to the two label signals
Estimation channel as reference channel, i.e.,WithIn n-th of label symbol period, estimation gained channel isBy its
It is considered as the signal that receiving end receives, makes judgement by comparing receiving signal and sending the similitude between signal.Decision rule
It is detected for distance shown in formula three:
For this rule, the present invention devises the channel estimation method to environment mpsk signal.Channel estimation is divided into two
Point: channel phase estimation and channel magnitude estimation.
The pack arrangement of environmental signal and the phase characteristic of mpsk signal is utilized in channel phase estimation.With c (0)=0 work
For example, channel estimation method proposed by the present invention is the weighted sum of two parts estimation channel:
It is based on preceding LpObtained by a pilot tone,Interior remaining L is wrapped by onedA data symbol obtains.
By the environmental signal pack arrangement of Fig. 1 it is found that receiver knows preceding LpThe definite information of a frequency pilot sign,
Y (0, l)=h0S (0, l)+u (0, l), l=1,2 ..., Lp (9)
Known environment signal can eliminate the influence of environmental signal also with regard to the phase of known environment signal:
This can approximation regard first of environment symbol period corresponding channel as, the present invention is by it in LpIt is a
The average influence to eliminate noise is done on symbol period.
In information symbol portions, receiving signal is indicated are as follows:
Y (0, l)=h0S (0, l)+u (0, l), l=Lp+1,...,Lp+Ld (13)
When estimating channel, the present invention uses Viterbi-viterbi algorithm or M times of carrier phase estimator.Consider first
In a label symbol period, signal that kth root receiving antenna receives:
yk(0, l)=h0,kexp(j2πm/M)+uk(0,l) (14)
h0=[h0,k], ambient enviroment mpsk signal takes exp (j2 π m/M), a value in m=1,2 ..., M, according to multiple
Number is made of amplitude and phase, and (14) are expressed as follows by the present invention:
yk(0, l)=| yk(0,l)|exp[j(∠h0,k+2πm/M+εk(0,l))] (15)
εk(0, l) is noise ukThe phase of (0, l).The present invention seeks M power to (15) using Viterbi-viterbi algorithm, obtains
It arrives:
[yk(0,l)]M=| yk(0,l)|Mexp[j(M∠h0,k+Mεk(0,l))] (16)
Because the M power of environmental signal phase is 2 π m, exp (2 π m)=1, m=1 ..., M, so environmental signal is to phase
The influence of position can be eliminated.Then, the present invention takes the phase of (16) and divided by M, i.e.,
For the phase estimation value of channel, i ∈ { 0,1 ..., M-1 }.M times of carrier phase estimator can introduce phase ambiguity,
Its accuracy that will affect channel estimation, the present invention are eliminated phase ambiguity using the pack arrangement of environmental signal.Firstly, in order to disappear
Except the influence of noise, phase estimating device is averaged in data symbol part, obtains channel phase estimated value:
The phase value has phase ambiguity, needs to utilize LpA frequency pilot sign estimates gained channel to correct ambiguity, rectifys
Correction method is as follows: choosingM probable value in distanceNearest value estimates gained channel phase as data portion
Position.
Finally, estimate that gained channel is based on data portion
It is that resulting channel magnitude is estimated based on environmental data signal.The present invention devises three kinds of channel magnitude estimations
Algorithm:
(1) signal amplitude averaging method is received
(2) the second moment estimation technique
(3) the amplitude Estimation algorithm based on environmental signal
For each environmental signal l and receiving antenna k, the present invention constructs the rotary variable for receiving signal:
For all possibility value m' ∈ { 1,2 ..., M }, defining index i is
The estimated value of channel magnitude are as follows:
It is above-mentioned to be partially completed the corresponding channel estimation process of label signal c (0)=0, it is obtained according to (8)
For c (1)=1, corresponding estimation channel is obtained with same estimation procedureIn next all labels
Signal slot c (n), the present invention are obtained with same estimation procedure
Obtaining estimation channelLater, label signal is ruled out with distance detection receiver (7):
Many wireless receivers only estimate channel with pilot signal, to obtain accurate estimated result, pilot signal
Number need to increase, this will affect the data transmission efficiency of environmental signal.In order to guarantee that accuracy of estimation and data pass simultaneously
Defeated efficiency, the invention proposes the methods for estimating channel using pilot signal and data-signal simultaneously.
The invention also provides a kind of based on decision-feedback apart from receiver, is updated and is referred to according to decision signal dynamic
Channel.Reference channel is when such as startingWithIf ruling out c (2) is 0, updateIf c (2)=1, more
NewlyAnd the reference channel as c (3) judgement.All reference channels of update are adjudicated each time, are sentenced in this way
Certainly result can be more accurate.
Meanwhile present invention also proposes a kind of based on iterative estimate apart from receiver, is detecting N number of label signal
Afterwards, estimation signal is obtained:Definition
Reception signal corresponding with A0 and A1 can be divided into two reception signal sets, be estimated using all elements in signal collection
Reference channel outWithA label signal judgement is carried out again.Repeating the judgement --- estimation ---, reconvict process, directly
To estimation channel convergence.
The performance for the transceiver that the present invention designs is verified below by simulation result.It is assumed that environmental signal is QPSK letter
Number, label signal OOK, and assume that carrier generator is independent Rayleigh fading letter to the channel of receiver and label
Road, receiver antenna number are 4, poor signal to noise 20dB of the reflection link than direct link.
Fig. 6 shows the property of distance detector proposed by the present invention and conventional energy detector and likelihood ratio detector
It can compare, be averaged the relationship of SNR and the bit error rate for direct link.Wherein, one packet length of environmental signal is 50, pilot signal
Length is 10, and receiver configures 4 antennas, reflects link and direct link signal-to-noise ratio difference is 30dB.The bit error rate is 10-3When,
The optimal detector difference 4dB of distance detector proposed by the present invention and perfect known channel, energy measuring and detector of the present invention
Poor 3.5dB.Distance detector performance based on feedback judgement improves 0.8dB compared with distance detector.Distance inspection based on iteration
It surveys device performance and improves 2dB compared with distance detector.
Claims (2)
1. the backscatter communication system receiver design method based on MPSK carrier wave, the backscatter communication system includes penetrating
Frequency source, label and the reader equipped with K root antenna, wherein label loads self information in the MPSK from radio frequency source
On signal, it is transmitted to reader；The period for defining label signal is L times of the environmental signal period, preceding in each environmental signal packet
LpA signal is pilot tone, rear LdA signal is data-signal；Enable n-th of label signal period corresponding L reception signal slot
In, the reception signal on first of time slot kth root antenna are as follows:
K=1 ..., K, l=1 ..., L
Wherein, label signal c (n) is used as baseband modulation signal, and α indicates the reflection coefficient of signal c (n), PsRepresent environmental signal
Power, s (n, l) indicate first of environmental signal corresponding with label signal c (n), hkIndicate transmitting terminal to reader kth root day
The low pass channel impulse response of line, fkIndicate low pass channel impulse response of the label to reader kth root antenna, g expression transmission
Hold the low pass channel impulse response of label, uk(n, l) refers to the noise at reader end；
Label has sent two pilot tone c (0)=0 and c (1)=1 before sending the information, with two kinds of channels of marking: h0And h1,
Signal will be received and be expressed as vector form:
h0=h, h1=h+ α gf
It is characterized in that, the receiver design method are as follows:
Regard environmental signal as channel, by two different channel h0And h1The signal for regarding transmitter transmission as, in receiving end to letter
Road is estimated, and distinguishes label signal with estimation gained channel, specifically:
It enables label before transmitting data, first sends two pilot signals: c (0)=0, c (1)=1, the two pilot signal institutes
Corresponding estimation channel is as reference channel, i.e.,WithIn n-th of label symbol period, estimation gained channel isIt will
The corresponding estimation channel of label signal and two kinds of marked channels do distance detection, select mark corresponding to more like channel
Symbol is signed as court verdict:
ChannelEstimation method are as follows:
It is based on preceding LpObtained by a pilot tone,Interior remaining L is wrapped by onedA data symbol obtains；
It is rightSetting receiver knows preceding LpThe definite information of a frequency pilot sign, then
Y (n, l)=hns(n,l)+u(n,l)
U (n, l) is that power is σ2Base band additive white Gaussian noise, the phase of environmental signal s (n, l) be it is known, M is environment
The order of phase shift keyed signal；It is rightUsing M times of carrier phase estimator, obtain:
It is that resulting channel magnitude is estimated based on environmental data signal,It is channel phase estimated value:
yk(n, l)=hn,kexp(j2πm/M)+uk(n,l)
hn=[hn,k], ambient enviroment mpsk signal takes exp (j2 π m/M), a value in m=1,2 ..., M.
2. the backscatter communication system receiver design method according to claim 1 based on MPSK carrier wave, feature
It is, the channel magnitudeEstimation method be one of following three kinds of methods:
1) signal amplitude averaging method is received:
2) the second moment estimation technique:
3) based on the amplitude Estimation of environmental signal:
For each environmental signal l and receiving antenna k, the rotary variable for receiving signal is constructed:
To all possibility value m' ∈ { 1,2 ..., M }, defining index i is
The estimated value of channel magnitude are as follows:
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| CN110224965B (en) * | 2019-06-17 | 2021-02-12 | 电子科技大学 | Semi-blind receiver design method based on OFDM backscattering communication system |
| CN110177064B (en) * | 2019-06-17 | 2021-02-12 | 电子科技大学 | Low-complexity receiver design method based on environment backscattering communication system |
| CN116599802A (en) * | 2020-05-25 | 2023-08-15 | Oppo广东移动通信有限公司 | Signal processing method, device and wireless communication system |
| CN117178577A (en) * | 2021-07-20 | 2023-12-05 | Oppo广东移动通信有限公司 | Wireless communication method, first device and second device |
| CN116232443B (en) * | 2023-05-09 | 2023-08-29 | 中国科学技术大学 | Environment WiFi backscattering system and method based on single commercial AP receiver |
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| US7215826B1 (en) * | 2003-04-28 | 2007-05-08 | The United States Of America As Represented By The Secretary Of The Navy | Rendering three-dimensional streak tube imaging lidar (STIL) data to two-dimensional contrast and range mappings thereof |
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