CN109117685B - Information symbol judgment method of environment backscattering system based on multiple antennas - Google Patents

Information symbol judgment method of environment backscattering system based on multiple antennas Download PDF

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CN109117685B
CN109117685B CN201810890593.1A CN201810890593A CN109117685B CN 109117685 B CN109117685 B CN 109117685B CN 201810890593 A CN201810890593 A CN 201810890593A CN 109117685 B CN109117685 B CN 109117685B
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钟财军
陶琴
陈晓明
张朝阳
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Zhejiang University ZJU
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    • G—PHYSICS
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    • G06K7/00—Methods or arrangements for sensing record carriers, e.g. for reading patterns
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    • G06K7/10316—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation sensing by radiation using wavelengths larger than 0.1 mm, e.g. radio-waves or microwaves using at least one antenna particularly designed for interrogating the wireless record carriers
    • G06K7/10356—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation sensing by radiation using wavelengths larger than 0.1 mm, e.g. radio-waves or microwaves using at least one antenna particularly designed for interrogating the wireless record carriers using a plurality of antennas, e.g. configurations including means to resolve interference between the plurality of antennas
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    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
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    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
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    • G06K7/10198—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation sensing by radiation using wavelengths larger than 0.1 mm, e.g. radio-waves or microwaves setting parameters for the interrogator, e.g. programming parameters and operating modes

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Abstract

The invention relates to an information symbol judgment method of an environment backscattering system based on multiple antennas, wherein the environment backscattering system comprises an environment radio frequency signal source, an electronic tag and a reader, the reader is provided with M receiving antennas, and M is more than or equal to 2; the information symbol judging method comprises the following steps: 1) the environment radio frequency signal source transmits an environment radio frequency signal; 2) the electronic tag is mapped into a reflected or non-reflected environment radio frequency signal according to the transmitted binary symbol; the binary symbols in the electronic tag comprise: a known preamble symbol and an information symbol to be judged; 3) m receiving antennas of the reader receive signals, parameters in the optimal detector are estimated by using the leading symbols, and the optimal detector is used for judging information symbols transmitted by the electronic tags. The invention can achieve any low bit error rate by increasing the signal-to-noise ratio or the number of receiving antennas at the reader end by using the proposed optimal detector, thereby realizing reliable information transmission.

Description

Information symbol judgment method of environment backscattering system based on multiple antennas
Technical Field
The invention relates to the field of wireless communication, in particular to an information symbol judgment method of an environment backscattering system based on multiple antennas.
Background
Ambient backscatter communications has recently been seen as a promising technology for building environmentally friendly and renewable internet of things. By using a backscattering mechanism, a high-power-consumption transmitting circuit at an information transmission end is avoided. Meanwhile, thanks to the current wireless energy transmission technology, the information transmission end does not even need internal battery supply, thereby greatly reducing the battery and maintenance cost.
Based on the above advantages, environmental backscatter communications are receiving high attention from industry and academia, and a large number of prototypes are being implemented. It is important to note that in a practical deployment application, reliable detection techniques are critical, as this is the basis for any application. However, environmental backscatter systems, due to their system characteristics, face some challenges in detection: (1) the ambient radio frequency signal is unknown; (2) the environment radio frequency signal already contains modulation information; (3) the ambient radio frequency signal is to some extent interference.
For this reason, a large number of detection methods have been proposed. The detection performance of the detection method for the single antenna system is unsatisfactory, and meanwhile, an error code platform appears in a high signal-to-noise ratio area, so that the performance of the detector is greatly limited.
As it is known that the multi-antenna technology can improve the performance of the communication system, some detection methods for the multi-antenna system are proposed later. These multi-antenna based detection methods use either power allocation, or the characteristics of WiFi signals, or traversal by assuming known environmental signals and the symbol set of the tag. For example, chinese patent application (CN 105303137a) discloses a method for determining a threshold of a reader/writer of an environmental backscatter system, which uses the reader/writer to calculate the average power of radio frequency signals demodulated by N consecutive reader/writers; probability distribution functions of average power of radio frequency signals demodulated by N continuous readers are obtained when the electronic tag is in a non-reflection state and a reflection state respectively, bit error rates of the electronic tag in the reflection state or the non-reflection state are obtained through calculation respectively, and a first threshold value and a second threshold value of the reader are obtained.
The detection performance of the existing detection judgment method is improved compared with that of a single-antenna system, but the calculation amount is overlarge or certain use limitation exists.
Disclosure of Invention
The invention aims to provide an information symbol judging method based on a multi-antenna environment backscattering system, aiming at the defects of the prior art, and the method is used for designing a corresponding optimal detector, reducing the calculation amount and enabling the detection performance to be optimal. Meanwhile, parameters in the optimal detector for estimating the pilot symbols are designed, so that the information symbol judgment method has practicability in practice.
The technical scheme provided by the invention is as follows:
the method for judging the information symbol of the multi-antenna-based environment backscattering system comprises an environment radio frequency signal source, an electronic tag and a reader, wherein the reader is provided with M receiving antennas, and M is more than or equal to 2; the information symbol judging method comprises the following steps:
1) the environment radio frequency signal source transmits an environment radio frequency signal;
2) the electronic tag is mapped into a reflected or non-reflected environment radio frequency signal according to the transmitted binary symbol; the binary symbols in the electronic tag comprise: a known preamble symbol and an information symbol to be judged;
3) m receiving antennas of the reader receive signals, parameters in the optimal detector are estimated by using the leading symbols, and the optimal detector is used for judging information symbols transmitted by the electronic tags.
Preferably, the mapping manner in step 2) is as follows: the transmission symbol "0" is mapped to the working state of not reflecting the ambient radio frequency signal, and the transmission symbol "1" is mapped to the working state of reflecting the ambient radio frequency signal.
The preamble symbol in the invention means that K consecutive symbols "0" and K consecutive symbols "1" are arranged at the head of the symbol string in each channel coherence time, or K consecutive symbols "1" and K consecutive symbols "0" are arranged at the head of the symbol string in each channel coherence time.
The optimal detector of the invention is as follows:
Figure BDA0001756848930000031
wherein the content of the first and second substances,
Figure BDA0001756848930000032
for receiving the signal matrix, M is the number of receiving antennas of the reader, N is the number of sampling points of the reader in a symbol time interval in the information symbol transmission phase ηoptIs the optimal threshold of the optimal detector; h0And H1Respectively representing that event electronic tag transmission binary symbols are '0' and '1'; tr [. C]Representing trace operations;
Figure BDA0001756848930000033
hsr,htr,hstrespectively obtaining channel parameters from an environment radio frequency signal source to a reader, an electronic tag to the reader and an environment radio frequency signal source to an electronic tag; phi is the reflection coefficient of the electronic tag;
Figure BDA0001756848930000034
and
Figure BDA0001756848930000035
respectively the variance of the environment radio frequency signal and the noise of the reader end; upper labelHRepresenting a conjugate transpose operation.
The optimal threshold of the invention is as follows:
Figure BDA0001756848930000036
wherein, N is the number of sampling points of the reader in a symbol time interval in the information symbol transmission stage; q is the probability of the binary symbol "0" in the electronic tag, and 1-q is the probability of the binary symbol "1" in the electronic tag.
The parameters in the optimum detector of the present invention are
Figure BDA0001756848930000037
And
Figure BDA0001756848930000038
the above parameters can be estimated using the preamble symbols.
Parameters of the invention
Figure BDA0001756848930000039
And
Figure BDA00017568489300000310
the estimation method comprises the following steps:
during transmission of preamble symbol i, using
Figure BDA0001756848930000041
And
Figure BDA0001756848930000042
wherein λ ismax(. represents taking the maximum eigenvalue of the matrix, NtAcquisition of a symbol time interval by a reader for transmitting a preamble symbol phaseThe number of the sample points is,
Figure BDA0001756848930000043
a signal vector representing an nth sample in a kth preamble symbol time interval; i isMRepresenting an M-dimensional identity matrix.
Compared with the prior art, the invention has the beneficial effects that:
(1) the invention adopts the multi-antenna technology in the reader and designs the corresponding optimal detector, thereby reducing the calculation amount and improving the detection performance of the system compared with the single-antenna optimal detector.
(2) The optimal detector of the environment backscattering system based on the multiple antennas overcomes the error code platform phenomenon of the optimal detector with a single antenna, which means that the error code rate can be arbitrarily lowered by increasing the signal-to-noise ratio or the number of receiving antennas at the reader end, thereby realizing reliable information transmission.
Drawings
FIG. 1 is a communication structure diagram of an embodiment of a multi-antenna based environmental backscatter system;
FIG. 2 is a flow chart of a multi-antenna based information symbol determination method in an embodiment;
fig. 3 is a comparison diagram of an optimal detector based on multiple antennas and an optimal detector based on a single antenna in the embodiment.
Detailed Description
The embodiments of the present invention will be described in detail below, but the present invention is not limited to the embodiments below.
As shown in FIG. 1, the multi-antenna based environmental backscatter system is composed of an environmental radio frequency signal source, an electronic tag and a reader, wherein the reader is provided with M receiving antennas, and M is more than or equal to 2. The channel parameters from the environment radio frequency signal source to the reader, from the electronic tag to the reader and from the environment radio frequency signal source to the electronic tag are respectively expressed as hsr,htr,hstAnd assumes that the channel parameters are constant over the coherence time.
As shown in fig. 2, the method for determining an information symbol of a multi-antenna based environmental backscatter system includes:
1) the environment radio frequency signal source transmits an environment radio frequency signal;
2) the electronic tag is mapped into a reflected or non-reflected environment radio frequency signal according to the transmitted binary symbol; the binary symbols in the electronic tag comprise: a known preamble symbol and an information symbol to be judged;
3) m receiving antennas of the reader receive signals, parameters in the optimal detector are estimated by using the leading symbols, and the optimal detector is used for judging information symbols transmitted by the electronic tags.
The electronic tag contains binary symbols and is mapped into a working mode of reflecting or not reflecting the ambient radio frequency signals according to the transmitted binary symbols. The mapping mode is as follows: the transmission symbol "0" is mapped to an operation mode that does not reflect the ambient radio frequency signal, and the transmission symbol "1" is mapped to an operation mode that reflects the ambient radio frequency signal.
The binary symbol in the electronic tag mainly comprises two parts: a. leading symbols, namely K continuous symbols '0' and K continuous symbols '1' are arranged at the head of a symbol string in each channel coherence time and are used for estimating parameters in an optimal detector; b. information symbols, i.e. symbols containing information.
Due to the characteristic of free propagation of radio signals, signals reflected by the electronic tags and signals of an environmental radio frequency signal source can be received at the reader end at the same time, so that after N-point sampling is carried out on each electronic tag symbol time interval, a received signal matrix can be represented as
Figure BDA0001756848930000051
Wherein the content of the first and second substances,
Figure BDA0001756848930000061
wherein the content of the first and second substances,
Figure BDA0001756848930000062
s[n]and w [ n ]]Respectively representing the ambient radio frequency signal and the reception at the nth sampling instant in the symbol time intervalNoise, and all obey variance respectively
Figure BDA0001756848930000063
And
Figure BDA0001756848930000064
complex gaussian distribution of (a); h0And H1Respectively, the event electronic tag transmits binary symbols '0' and '1', and the probabilities are q and 1-q, respectively.
Assuming that the ambient radio frequency signal and the received noise are independent in time, the probability density function of Y can be expressed as:
Figure BDA0001756848930000065
where tr (-) represents trace operation, det (-) represents determinant, superscriptionHRepresenting a conjugate transpose operation; riIs y [ n ]]At event HiCovariance matrix of
Figure BDA0001756848930000066
IMRepresenting an M-dimensional identity matrix.
Suppose h is known(i)And
Figure BDA0001756848930000067
using the maximum a posteriori criterion, the best decision can be written as:
Figure BDA0001756848930000068
where l (y) represents the maximum likelihood function.
Bringing formula (1) into formula (2) to obtain:
Figure BDA0001756848930000069
the following matrix inverses and matrix determinant relationships are given:
Figure BDA00017568489300000610
Figure BDA00017568489300000611
in the belt-in formula (3), the best detector is obtained after finishing as follows:
Figure BDA0001756848930000071
wherein
Figure BDA0001756848930000072
Proposed optimal detector, needs
Figure BDA0001756848930000073
And
Figure BDA0001756848930000074
and (4) information.
The following describes estimating parameters
Figure BDA0001756848930000075
And
Figure BDA0001756848930000076
the electronic tag estimates the parameters by using K continuous leading symbols '0' and K continuous leading symbols '1', respectively.
Thus, during the transmission of K consecutive preamble symbols i, use is made of:
Figure BDA0001756848930000077
and
Figure BDA0001756848930000078
wherein λ ismax(. represents taking the maximum eigenvalue of the matrix, NtThe number of samples taken by the reader within a symbol time interval for the transmission of the leading symbol phase,
Figure BDA0001756848930000079
representing the signal vector sampled the nth time in the kth preamble symbol time interval. I isMRepresenting an M-dimensional identity matrix.
Fig. 3 is a diagram comparing an optimal detector based on multiple antennas and an optimal detector based on a single antenna. The simulation conditions are as follows: 20, Nt＝100，K＝2，φ＝0.5，q＝0.5,
Figure BDA00017568489300000710
Figure BDA00017568489300000711
It can be seen from the curve trend in the figure that the bit error rate of the optimal detector proposed by the present invention decreases with the increase of the signal-to-noise ratio when multiple antennas are used. Meanwhile, the detection performance of the estimated parameters and the accurate parameters under the same conditions is observed, and the performance close to the accurate parameters can be achieved by using the estimated parameters for detection, which shows that the proposed optimal detector has practicability in practice.
Then, the curves corresponding to different antenna numbers are observed: when M is equal to 1, the error rate is high and tends to be constant in a high signal-to-noise ratio region; when an antenna is added, namely M is 2, the error rate obtained by the optimal detector provided by the invention is greatly reduced, and an error code platform under a high signal-to-noise ratio disappears; when M is 5, the error rate is further reduced. The above results indicate that the optimal detector of the multi-antenna based environmental backscatter system proposed by the present invention can achieve an arbitrarily low bit error rate by increasing the signal-to-noise ratio or the number of receiving antennas of the reader, thereby achieving reliable information transmission.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be covered by the present invention.

Claims (5)

1. The method for judging the information symbol of the multi-antenna-based environment backscattering system is characterized by comprising the following steps of:
1) the environment radio frequency signal source transmits an environment radio frequency signal;
2) the electronic tag is mapped into a reflected or non-reflected environment radio frequency signal according to the transmitted binary symbol; the binary symbols in the electronic tag comprise: a known preamble symbol and an information symbol to be judged;
3) m receiving antennas of the reader receive signals, parameters in the optimal detector are estimated by using the leading symbols, and information symbols transmitted by the electronic tags are judged by using the optimal detector;
the optimal detector is as follows:
Figure FDA0002296424800000011
wherein the content of the first and second substances,
Figure FDA0002296424800000012
for receiving the signal matrix, M is the number of receiving antennas of the reader, N is the number of sampling points of the reader in a symbol time interval in the information symbol transmission phase ηoptIs the optimal threshold of the optimal detector; h0And H1Respectively representing that event electronic tag transmission binary symbols are '0' and '1'; tr [. C]Representing trace operations;
Figure FDA0002296424800000013
hsr,htr,hstrespectively obtaining channel parameters from an environment radio frequency signal source to a reader, an electronic tag to the reader and an environment radio frequency signal source to an electronic tag; phi is the reflection coefficient of the electronic tag;
Figure FDA0002296424800000014
and
Figure FDA0002296424800000015
respectively the variance of the environment radio frequency signal and the noise of the reader end; the superscript H denotes the conjugate transpose operation.
2. The method as claimed in claim 1, wherein the preamble symbol is K consecutive symbols "0" and K consecutive symbols "1" at the head of the symbol string within each channel coherence time, or K consecutive symbols "1" and K consecutive symbols "0".
3. The method of claim 1, wherein the optimal threshold is:
Figure FDA0002296424800000021
wherein, N is the number of sampling points of the reader in a symbol time interval in the information symbol transmission stage; q is the probability of the binary symbol "0" in the electronic tag, and 1-q is the probability of the binary symbol "1" in the electronic tag.
4. The method of claim 1, wherein the parameter in the optimal detector is
Figure FDA0002296424800000022
And
Figure FDA0002296424800000023
Figure FDA0002296424800000024
5. the method of claim 1, wherein the parameter is a parameter of the multi-antenna based ambient backscatter system
Figure FDA0002296424800000025
And
Figure FDA0002296424800000026
the estimation method comprises the following steps:
during transmission of preamble symbol i, using
Figure FDA0002296424800000027
And
Figure FDA0002296424800000028
wherein λ ismax(. represents taking the maximum eigenvalue of the matrix, NtThe number of samples taken by the reader within a symbol time interval for the transmission of the leading symbol phase,
Figure FDA0002296424800000029
a signal vector representing an nth sample in a kth preamble symbol time interval; i isMRepresenting an M-dimensional identity matrix.
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