CN111654315A - Co-existing wireless communication system based on interference elimination - Google Patents
Co-existing wireless communication system based on interference elimination Download PDFInfo
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- CN111654315A CN111654315A CN202010483358.XA CN202010483358A CN111654315A CN 111654315 A CN111654315 A CN 111654315A CN 202010483358 A CN202010483358 A CN 202010483358A CN 111654315 A CN111654315 A CN 111654315A
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B7/00—Radio transmission systems, i.e. using radiation field
- H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
- H04B7/022—Site diversity; Macro-diversity
- H04B7/026—Co-operative diversity, e.g. using fixed or mobile stations as relays
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
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- H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
- H04L25/0202—Channel estimation
- H04L25/0224—Channel estimation using sounding signals
- H04L25/0228—Channel estimation using sounding signals with direct estimation from sounding signals
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L25/00—Baseband systems
- H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
- H04L25/03—Shaping networks in transmitter or receiver, e.g. adaptive shaping networks
- H04L25/03006—Arrangements for removing intersymbol interference
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- Y02D—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN INFORMATION AND COMMUNICATION TECHNOLOGIES [ICT], I.E. INFORMATION AND COMMUNICATION TECHNOLOGIES AIMING AT THE REDUCTION OF THEIR OWN ENERGY USE
- Y02D30/00—Reducing energy consumption in communication networks
- Y02D30/70—Reducing energy consumption in communication networks in wireless communication networks
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Abstract
The invention belongs to the technical field of wireless communication, and particularly relates to a symbiotic wireless communication system based on interference elimination. The invention designs the information transmission format of the reflection equipment, the receiver firstly detects the transmitter symbol, then reconstructs the direct link signal, subtracts the reconstructed direct link signal from the received signal by utilizing the interference elimination technology, and then detects the symbol of the reflection equipment by utilizing the Maximum Ratio Combining (MRC) method. The method has the advantages that the serial interference elimination technology is applied to the symbiotic wireless communication system, the recovery method of the reflection equipment symbols in the symbiotic wireless communication system is effectively simplified, and the demodulation reliability is improved.
Description
Technical Field
The invention belongs to the technical field of wireless communication, and particularly relates to a symbiotic wireless communication system based on interference elimination.
Background
The technology of the internet of things is one of important technical means for realizing the future intelligent society, various devices can be connected to carry out unified management, and the daily life and work of human beings are facilitated. Because a large number of devices exist in the internet of things, the power consumption and the manufacturing cost of the devices are factors which must be considered, namely, the devices of the internet of things should meet the requirements of low power consumption and low manufacturing cost, so that a large number of devices of the internet of things can be arranged to realize the interconnection of everything.
The symbiotic wireless communication system is a communication system with low energy consumption and low manufacturing cost. In the system, three devices, namely a transmitter, a reflecting device and a receiver, exist, the transmitter transmits a wireless signal, the reflecting device changes the amplitude and the phase of the wireless signal according to self information after receiving the signal, and the receiver demodulates the signal after receiving the signal and recovers symbols transmitted by the transmitter and the reflecting device. The reflection device realizes different reflection coefficients by selecting different impedances to realize the modulation of signals. The characteristics of symbiotic wireless communication enable the symbiotic wireless communication to become an internet of things technology with wide application prospects, and low-power-consumption communication equipment can be arranged on a large scale in the future internet of things, so that the transmission of equipment information and the coverage of wide areas are realized.
Serial interference cancellation techniques are proposed in third generation mobile communication technology for reducing or eliminating inter-user interference in multi-user detection. The specific method is that firstly, the symbols of the user with large signal power are demodulated, then the symbols are used for reconstructing the signal of the user, the signal of the user is subtracted from the received signal, and then the symbols of other users are detected until the symbol detection of all the users is completed. By using successive interference cancellation techniques, the reliability of user symbol demodulation can be greatly improved.
Disclosure of Invention
The invention provides an interference elimination-based symbiotic wireless communication system, which is based on that two links, namely a direct link and a reflection link, exist in the symbiotic wireless communication system, and the signal intensity of the direct link is stronger than that of the reflection link, so that the thought of a serial interference elimination technology is utilized, the direct link is demodulated and reconstructed firstly, the reconstructed signal is subtracted from a received signal, and when the elimination effect is ideal, the obtained signal can be regarded as a reflection link signal polluted by noise, and then the reflection link is demodulated to obtain a symbol sent by reflection equipment.
The technical scheme adopted by the invention is that an information transmission format of the reflection equipment is designed, a receiver firstly detects a transmitter symbol, then reconstructs a direct link signal, subtracts the reconstructed direct link signal from a received signal by utilizing an interference elimination technology, and then detects the symbol of the reflection equipment by utilizing a Maximum Ratio Combining (MRC) method, wherein the method specifically comprises the following steps:
a symbiotic wireless communication system comprises a transmitter, a receiver and a reflection device, wherein the transmitter, the receiver and the reflection device adopt a single antenna, a transmission signal of the transmitter and a signal of the reflection device are synchronous, namely the starting position and the ending position of a transmitter symbol and a reflection device symbol are the same, and 1 reflection device symbol corresponds to 1 OFDM symbol; defining a time-domain complex baseband signal transmitted by a transmitter as scb[n]The time domain complex baseband signal received by the receiver is rcb[n]The signal generated by the reflecting device is cn]Adopting on-off keying modulation mode, bit 1 corresponding to reflection device being in reflection state, bit 0 corresponding to reflection device being in non-reflection state, using f [ n ] for channel between transmitter and receiver]Representing a total power of 1, called direct link channel, a channel g between the transmitter and the reflecting device, a channel v n between the reflecting device and the receiver]Indicates that the total power is 1, g and v [ n ]]Together forming a reflected link channel;
signal transmission:
the time domain expression of the ith OFDM symbol generated by the transmitter is:
wherein N represents the number of subcarriers, NcpDenotes the cyclic prefix length, si[k]Is a symbol on the k subcarrier in the ith OFDM symbol, NfThe number of OFDM symbols contained in one frame of OFDM signal is also the number of reflecting device symbols contained in one frame of reflecting device signal;
i.e. a frame of OFDM signal is represented as:
the OFDM signal transmitted by the transmitter reaches the receiver through a direct link channel, and the direct link signal is:
wherein P isdFor the average power of the direct link signal received by the receiver:
wherein P istIs the average transmission power of the transmitter, GtIs the antenna gain of the transmitter, GrIs the antenna gain of the receiver, λ is the wavelength of the carrier, DfIs the distance from the transmitter to the receiver, v1Is the path loss factor;
the reflection device firstly sends a pilot symbol 0, the receiver estimates the direct link channel according to the pilot symbol, and then the reflection device sends a pilot symbol 1 and a data symbol, and the reflected link signal is:
where Δ γ is the relative signal-to-noise ratio of the direct link and each reflected link:
wherein α is the reflection coefficient, GtagIs the antenna gain of the receiver, DgIs the distance from the transmitter to the reflecting device, v2、v3Is the path loss factor, F ═ λ2/(4π)2;
Signal receiving:
the receiver receives the direct link signal, the reflected link signal and the noise at the same time, and the signals are as follows:
rcb[n]=rd[n]+rb[n]+u[n]
Receiver first pairDemodulating the direct link signal, recovering the transmitter symbols, and estimating the direct link signalSubtracting the recovered direct link signal from the received signal yields:
remove rrem[n]Cyclic prefix of each symbol in the sequence to obtainPerforming DFT conversion on the signal to obtain the following expression:
wherein, V [ k ]]Is a channel v [ n ]]The DFT of the signal is transformed,resulting from the DFT-transform addition of the residual direct link signal and noise, which, in the ideal cancellation case,is a DFT transform of noise; in the above equation, the first term on the right side of the equation, except ciThe other variables can be regarded as a channel, and then symbols of each path of subcarriers can be combined by using a maximum ratio combining method, and then a reflection device symbol c is solvedi;
Estimating a composite channel consisting of a direct link channel and a reflected link channel:
wherein A iscIs a set of values for the symbols of the reflecting device,is formed byThe column vector of the component is composed of,is formed by Rrem,i[k]A column vector of components.
In the above scheme, the specific method for estimating the direct link signal is as follows:
removing the cyclic prefix of each OFDM symbol, wherein the ith OFDM symbol with the cyclic prefix removed is expressed as:
then, DFT conversion is carried out:
wherein, F [ k ]]Is channel f n]The N-point DFT transform of (1),is the sum of the noise and the DFT transform of the reflected link signal.
Then using the known pilot symbols s0[k]Estimating a direct link channel to obtain the following expression:
here for convenience of illustration, division on the right of the expression isThis need not be done in practice.
As known from the central limit theorem, the OFDM signal can be regarded as an independent and identically distributed complex gaussian random variable sequence. Thus, using maximum likelihood detection to recover the subcarrier symbols of each OFDM data symbol, the following expression can be obtained:
wherein A issIs a set of values for the sub-carrier symbols.
Reconstructing the ith OFDM symbol transmitted by the transmitter using the recovered subcarrier symbol as:
and a transmission signal of the transmitter:
for the estimated channelIFFT is carried out to obtain the time domain estimation of the direct link channel as
The direct link signal arriving at the receiver can then be estimated as
The method has the advantages that the serial interference elimination technology is applied to the symbiotic wireless communication system, the recovery method of the reflection equipment symbols in the symbiotic wireless communication system is effectively simplified, and the demodulation reliability is improved.
Drawings
FIG. 1 shows a system architecture diagram of the present invention;
FIG. 2 shows a design of a reflective link signal transmission format in the present invention;
FIG. 3 is the bit error rate performance of a transmitter symbol for a receiver designed in accordance with the present invention at different relative SNR;
fig. 4 shows the error rate performance of the symbol of the reflecting device under different relative snr conditions for the receiver designed by the present invention.
Detailed Description
The technical scheme of the invention is further described in detail by combining the accompanying drawings:
the invention considers the situation that a single reflection device, a transmitter, a receiver and the reflection device adopt a single antenna, and the signal of the transmitter and the signal of the reflection device are synchronous, namely the starting position and the ending position of the symbol of the transmitter and the symbol of the reflection device are the same. The OFDM signal has a plurality of subcarriers corresponding to a plurality of subcarrier channels, each subcarrier corresponds to a reflection device symbol in a symbiotic wireless communication system, each subcarrier corresponding to the same reflection device symbol is regarded as a path of signal at the moment, and the reflection device symbol can be detected by using a maximum ratio combining algorithm. For the case that the signal of the transmitter is a single carrier signal, multiple antennas can be used at the receiving end to transmit one reflective device symbol on multiple channels, and then the maximum ratio combining (IC-MRC) algorithm based on interference cancellation proposed by the present invention is used to detect the transmitter symbol and the reflective device symbol.
Suppose that the transmitter transmits an OFDM signal scb[n]The time domain signal received by the receiver is rcb[n]The signal generated by the reflecting device is cn]An on-off keying (OOK) modulation scheme is used, where bit 1 corresponds to the reflective state of the reflective device and bit 0 corresponds to the non-reflective state of the reflective device. The reflecting device is located in close proximity to the transmitter to ensure that it can be activated. Channel between transmitter and receiver using f [ n ]]Indicating a total power of 1, called the direct link channel. Transmitter and reflection apparatusG, and a channel v n between the reflecting device and the receiver]Indicates that the total power is 1, g and v [ n ]]Together forming a reflected link channel. The whole system structure is shown in fig. 1.
The above channel is a model for small-scale fading, and the following discusses large-scale fading of the channel and the received power of the signal. The large scale fading and signal received power of the direct link will be described first. Suppose the average transmission power of the transmitter is PtThe average power of the direct link signal received by the receiver is PdFrom the free space path loss model, the following expression can be obtained:
wherein G istIs the antenna gain of the transmitter, GrIs the antenna gain of the receiver, λ is the wavelength of the carrier, DfIs the distance from the transmitter to the receiver, v1Is the path loss factor. To simplify the description of the above equation, let F be λ2/(4π)2Then the above formula becomes
The large scale fading and signal received power of the reflected link are next described. The reflection link consists of two paths, transmitter to reflection device and reflection device to receiver. First, the first path is discussed, assuming that the average power of the signal at the reflecting device is PgThen there is
Wherein G istagIs the antenna gain of the receiver, DgIs the distance from the transmitter to the reflecting device, v2Is the path loss factor.
Next, the second path is discussed, assuming that the reflection coefficient is α, the average power of the signal reflected by the reflecting device is
Ptag=|α|2Pg(4)
The signal then reaches the receiver via a channel v, where the power of the signal is
Wherein D isvIs the distance, v, of the reflecting device from the receiver3Is the path loss factor.
By combining the formulas (3), (4) and (5), the average power of the reflected link signal can be obtained to be
The signal received by the receiver is expressed as
rcb[n]=rd[n]+rb[n]+u[n](7)
Wherein r isd[n]For direct link signals to reach the receiver, rb[n]For the reflected link signal to reach the receiver, u n]Is a circularly symmetric complex Gaussian variable with a mean of 0 and a variance ofThe expression for the direct link signal is
The expression for the reflected link signal is
Where c n is the signal of the reflecting device.
Setting the noise variance to 1, the direct link signal-to-noise ratio can be defined as
Accordingly, define the reflected link signal-to-noise ratio as
Then defining the relative signal-to-noise ratio of the direct link and the reflected link as
Equation (9) can be written as:
because the signal power of the reflection link is weaker than that of the direct link signal, the receiver estimates the direct link channel by using the pilot symbols, then regards the reflection link as interference and detects the transmitter symbols, and then reconstructs the direct link signal to obtainSubtracting this signal from the received signal yields the following expression
Under the condition of ideal interference elimination effect, r obtained in the last steprem[n]The signal is a reflected link signal polluted by noise, and at this time, the detection method of maximum ratio combining can be utilized to combine each subcarrier, and then the symbol of the reflection device is recovered.
In order to ensure that the receiver can estimate the direct link channel and the reflected link channel, the transmission format of the reflected link signal needs to be designed. The reflecting device first transmits a pilot symbol 0, the receiver can estimate the direct link channel, and then the reflecting device transmits a pilot symbol 1 and a data symbol. After the interference is eliminated, the channel estimation of the reflection link can be obtained by estimating the channel by using two pilot symbols in the received signal, and then the receiver detects the reflection device symbol by using a maximum ratio combining method. The transmission format of the reflected link signal is shown in fig. 2.
Fig. 3 shows the error rate performance of the transmitter symbols at different relative snrs for the receiver designed by the present invention. Fig. 4 shows the error rate performance of the symbol of the reflecting device under the condition of different relative signal-to-noise ratios of the receiver designed by the invention. In simulation, the number of OFDM subcarriers N is 64, and the length of cyclic prefix NcpThe subcarrier symbols are 4QAM symbols, 16. The number of symbols in a frame of the reflecting device is 10, and the number of symbols in an OFDM frame is also 10. Channel f [ n ]]And v [ n ]]The channels are independent 8 paths of equal power channels, the total power is 1, and the fading of each path of channel meets the complex Gaussian distribution. Channel g is a rayleigh fading channel, i.e. satisfies a complex gaussian distribution with a mean of 0 and a variance of 1. Channel realization times of 106The noise power is
In fig. 3, the OFDM labeled curve shows the bit error rate curve for the receiver using linear least squares channel estimation and maximum likelihood detection for direct link only. When the reflected link signal power is less than the noise, i.e. gammadLess than- (△ gamma)dBThe bit error rate curve of the transmitter symbols is very close to the bit error rate curve of the OFDM system. When the reflected link signal power is greater than the noise, i.e. gammadGreater than- (△ gamma)dBAnd when the error rate curve of the transmitter symbol is reduced, the reduction speed gradually approaches to an error platform, and the error rate corresponding to the error platform is reduced by one order of magnitude along with the reduction of the relative signal-to-noise ratio by 10 dB. From the analysis, it is known that the error rate performance of the transmitter symbols is acceptable.
In fig. 4, the curve marked ED indicates the ber of the symbol of the reflector when the receiver uses energy detection directly on the received signal, when △ γ is a fixed value, ED performance is poor, curve drop is slow, IC-MRC algorithm performance is better than ED, and in the direct link snr γdGreater than- (△ gamma)dBAt the same time, it can be observed that the performance of the IC-MRC algorithm is reduced by 10dB as △ gamma is reduced by 10 dB.
Claims (1)
1. A symbiotic wireless communication system based on interference elimination is characterized by comprising a transmitter, a receiver and a reflection device, wherein the transmitter, the receiver and the reflection device adopt a single antenna, a transmission signal of the transmitter and a signal of the reflection device are synchronous, namely the starting position and the ending position of a transmitter symbol and the starting position of a reflection device symbol are the same, and 1 reflection device symbol corresponds to 1 OFDM symbol; defining the OFDM signal transmitted by the transmitter as scb[n]The time domain signal received by the receiver is rcb[n]The signal generated by the reflecting device is cn]Adopting on-off keying modulation mode, bit 1 corresponding to reflection device being in reflection state, bit 0 corresponding to reflection device being in non-reflection state, using f [ n ] for channel between transmitter and receiver]Representing a total power of 1, called direct link channel, a channel g between the transmitter and the reflecting device, a channel v n between the reflecting device and the receiver]Indicates that the total power is 1, g and v [ n ]]Together forming a reflected link channel;
signal transmission:
the time domain expression of the ith OFDM symbol generated by the transmitter is:
wherein N represents the number of subcarriers, NcpDenotes the cyclic prefix length, si[k]Is a symbol on the k subcarrier in the ith OFDM symbol, NfThe number of OFDM symbols contained in one frame of OFDM signal is also the number of reflecting device symbols contained in one frame of reflecting device signal;
one frame OFDM signal is represented as:
the OFDM signal transmitted by the transmitter reaches the receiver through a direct link channel, and the direct link signal is:
wherein P isdFor the average power of the direct link signal received by the receiver:
wherein P istIs the average transmission power of the transmitter, GtIs the antenna gain of the transmitter, GrIs the antenna gain of the receiver, λ is the wavelength of the carrier, DfIs the distance from the transmitter to the receiver, v1Is the path loss factor;
the reflection device firstly sends a pilot symbol 0, the receiver estimates the direct link channel according to the pilot symbol, and then the reflection device sends a pilot symbol 1 and a data symbol, and the reflected link signal is:
where Δ γ is the relative signal-to-noise ratio of the direct link and the reflected link:
wherein α is the reflection coefficient, GtagIs the antenna gain of the receiver, DgIs the distance from the transmitter to the reflecting device, DvIs the distance, v, of the reflecting device from the receiver2、v3Is the path loss factor, F ═ λ2/(4π)2;
Signal receiving:
the receiver receives the direct link signal, the reflected link signal and the noise at the same time, and the signals are as follows:
rcb[n]=rd[n]+rb[n]+u[n]
wherein u [ n ]]Is a circularly symmetric complex Gaussian variable with a mean of 0 and a variance of
The receiver first demodulates the direct link signal to recover the transmitter symbols, and then estimates the direct link signalSubtracting the recovered direct link signal from the received signal yields:
remove rrem[n]Cyclic prefix of each symbol in the sequence to obtainPerforming DFT conversion on the signal to obtain the following expression:
wherein, V [ k ]]Is a channel v [ n ]]The DFT of the signal is transformed,is a DFT transform of noise;
estimating a composite channel consisting of a direct link channel and a reflected link channel:
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