阅读说明：本技术 一种基于反射面的主被动互惠共生传输通信系统 (Active and passive reciprocal symbiotic transmission communication system based on reflecting surface ) 是由 类先富 伍明江 于 2019-11-05 设计创作，主要内容包括：本发明公开了一种基于反射面的主被动互惠共生传输通信系统，包括单天线发射基站、含多个独立可控的反射单元的智能反射面以及单天线主被动协同接收机，智能反射面与传感器连接；单天线发射基站和智能反射面构成互惠共生通信系统发射部分，分别发射主动信号与被动信号；单天线协同接收机同时接收主动信号和被动信号，并分别解调出来自基站的主动信息和来自与智能反射面相连的传感器的被动信息，其中被动信息通过无线信道的时延长度进行指示。本发明能够极大地提高频谱效率和能量效率，并且没有发射额外的射频信号，降低了无线通信系统的电磁干扰，具有极大的应用前景。(The invention discloses an active and passive reciprocity symbiotic transmission communication system based on a reflecting surface, which comprises a single-antenna transmitting base station, an intelligent reflecting surface and a single-antenna active and passive cooperative receiver, wherein the intelligent reflecting surface comprises a plurality of independently controllable reflecting units; the single antenna emission base station and the intelligent reflection surface form a reciprocal symbiotic communication system emission part which respectively emits active signals and passive signals; the single antenna cooperative receiver simultaneously receives the active signal and the passive signal and respectively demodulates the active information from the base station and the passive information from the sensor connected with the intelligent reflecting surface, wherein the passive information is indicated through the time delay length of a wireless channel. The invention can greatly improve the spectral efficiency and the energy efficiency, does not transmit additional radio frequency signals, reduces the electromagnetic interference of a wireless communication system and has great application prospect.)

1. An active and passive reciprocity symbiotic transmission communication system based on a reflecting surface is characterized by comprising a single-antenna transmitting base station, an intelligent reflecting surface and a single-antenna active and passive cooperative receiver, wherein the intelligent reflecting surface comprises a plurality of independently controllable reflecting units, and the intelligent reflecting surface is connected with a sensor; the single-antenna transmitting base station and the intelligent reflecting surface form a transmitting part of a reciprocal symbiotic communication system, and respectively transmit an active signal and a passive signal; each reflection unit of the intelligent reflection surface is independently controllable through the microcontroller, each reflection unit adjusts the phase offset of an incident signal, and the incident signal is stored and then emitted at the same time, so that a controllable time delay effect is formed; the single antenna cooperative receiver receives the active signal and the passive signal at the same time, and demodulates the active information from the base station and the passive information from the sensor connected with the intelligent reflecting surface respectively, wherein the passive information is indicated through the time delay length of a wireless channel.

2. The active-passive reciprocity symbiotic transmission communication system based on reflecting surface according to claim 1, wherein the active signal sent by the single antenna transmitting base station is represented as:

wherein, P is the transmitting power of the base station, and x' is the data actively transmitted by the base station; the active Data adopts single carrier modulation, and the basic unit of the frame structure is an active transmitting symbol consisting of a protection field 'GI seq' and a Data field 'Data'; one frame is composed of one or more active transmit symbols; in addition, a guard field "GI seq" needs to be additionally added to the last actively transmitted symbol in the frame;

the number of the reflection units of the intelligent reflection surface is set to be M, each reflection unit independently adjusts the phase offset according to channel information, in addition, the time delay of a reflection signal is adjusted according to passive information '1' or '0' to be sent, if the '1' bit needs to be sent, the time delay is carried out, but the time delay length does not exceed the length of the 'GI seq' signal, and if the '0' bit needs to be sent, the time delay is not carried out;

the method for realizing the time delay comprises the following steps: the reflection unit stores an incident signal firstly, then sends out the stored signal after a set time delay, and the signal received by the cooperative receiver is a superimposed signal of a signal directly from a base station and a passive signal subjected to time delay modulation:

y(n)＝h_r ^TΘGx(n-k)+h_dx(n)+ω

wherein the content of the first and second substances,

3. The active-passive reciprocity symbiotic transmission communication system based on the reflecting surface according to claim 2, wherein after the cooperative receiver receives the superimposed signal, the cooperative receiver performs the cross-correlation operation with the received signal by using a locally pre-stored protection sequence, and the operation result is:

wherein XC (N) represents the result of the correlation operation, GIseq represents the protection sequence "GI seq", the "GI seq" signal is selected from the ZC sequence, N_dIndicates the sequence length of GIseq;

by setting a threshold value, detecting multipath components in a received signal and time delay of the multipath components relative to a first path, wherein the maximum multipath time delay is controlled by an intelligent reflecting surface, so that passive information '0' is demodulated if the detected maximum multipath time delay is smaller than the set value, and passive information '1' is demodulated if the detected maximum multipath time delay is not smaller than the set value; after the passive information is demodulated, the frequency domain equalization is carried out on the received signal, and then the received signal is converted into a time domain signal through IFFT, namely the demodulation of the active signal is completed.

Technical Field

The invention belongs to the technical field of wireless communication, and particularly relates to an active and passive reciprocal symbiotic transmission communication system based on a reflecting surface. Background

The interconnection of everything is regarded as one of the vision of 5G, which shows that the Internet of things is an important component of 5G and the next generation wireless communication technology, and the ultra-large Internet of things equipment provides great challenges for energy consumption and the wireless communication technology, the battery life of the Internet of things equipment in some scenes is expected to be as long as 10 years, otherwise, frequent replacement of power supply equipment will bring huge cost and maintenance expenses; in addition, due to the lack of spectrum resources, the existing communication spectrum resources are far from meeting the requirement of access of ultra-large-scale internet of things equipment, and the high cost of a wireless communication radio frequency device also causes the cost of deployment of the internet of things to rise.

Recently, the intelligent reflective surface has received great attention from both academic and industrial fields because it can dynamically change the propagation environment of the wireless electromagnetic wave to enhance wireless communication. The intelligent reflecting surface comprises a large number of passive, low-cost, independently controllable reflecting units without radio frequency transmission chains, and the reflecting units are made of artificial metamaterials and can perform phase shift and time delay operation on incident electromagnetic waves, so that a random and uncontrollable wireless propagation environment can be artificially programmed and controlled, and wireless intelligent transmission is realized. The intelligent reflecting surface can dynamically and intelligently adjust the phase shift coefficient according to the channel environment and does not introduce new noise, so that a reflected signal can form a passive beam aiming at a receiver, the wireless communication performance is greatly improved, the intelligent reflecting surface can also carry passive information by carrying out information modulation on an incident signal from a plurality of resource dimensions, and the passive information modulation mode takes the existing electromagnetic wave in the environment as a carrier wave and does not send new electromagnetic signals, thereby reducing the radio interference in the environment. Therefore, the wireless communication system based on the intelligent reflecting surface has high spectral efficiency and high energy efficiency and is very in line with the concept of green communication.

Disclosure of Invention

In order to achieve the purpose, the invention provides an active and passive reciprocal symbiotic transmission communication system based on a reflecting surface. The invention relates to an active and passive reciprocity symbiotic transmission communication system based on a reflecting surface, which comprises a single-antenna transmitting base station, an intelligent reflecting surface and a single-antenna active and passive cooperative receiver, wherein the intelligent reflecting surface comprises a plurality of independently controllable reflecting units, and the intelligent reflecting surface is connected with a sensor. The single-antenna transmitting base station and the intelligent reflecting surface form a transmitting part of a reciprocal symbiotic communication system and respectively transmit an active signal and a passive signal; each reflection unit of the intelligent reflection surface is independently controllable through the microcontroller, each reflection unit adjusts the phase deviation of an incident signal, and the incident signal is stored and then emitted at the same time, so that a controllable time delay effect is formed. The single antenna cooperative receiver simultaneously receives the active signal and the passive signal and respectively demodulates the active information from the base station and the passive information from the sensor connected with the intelligent reflecting surface, wherein the passive information is indicated through the time delay length of a wireless channel.

The active signal sent by the single-antenna transmitting base station is represented as:

where P is the base station transmit power and x' is the data actively transmitted by the base station. The active Data adopts single carrier modulation, and the basic unit of the frame structure is an active transmitting symbol consisting of a protection field 'GI seq' and a Data field 'Data'; one frame is composed of one or more active transmit symbols; in addition, a guard field "GI seq" is additionally added to the last actively transmitted symbol in the frame.

The number of the reflection units of the intelligent reflection surface is set to be M, each reflection unit independently adjusts the phase shift according to channel information, in addition, the time delay of a reflection signal is adjusted according to passive information to be sent, namely '1' or '0', if the '1' bit needs to be sent, the time delay is carried out, but the time delay length does not exceed the length of the 'GI seq' signal, and if the '0' bit needs to be sent, the time delay is not carried out.

The method for realizing the time delay comprises the following steps: the reflection unit stores an incident signal firstly, then sends out the stored signal after a set time delay, and the signal received by the cooperative receiver is a superimposed signal of a signal directly from a base station and a passive signal subjected to time delay modulation:

y(n)＝h_r ^TΘGx(n-k)+h_dx(n)+ω

wherein the content of the first and second substances,representing the channel from the base station to the cooperating receiver, k represents the delay introduced by the intelligent reflecting surface,

representing the channel from the base station to the intelligent reflecting surface,

diagonal phase shift matrix, θ, representing intelligent reflective surfaces_mE 0,2 pi) represents the phase shift angle of the mth reflecting element,

representing the channel of the intelligent reflecting surface to the cooperative receiver, h_r ^TRepresents h_rThe transpose of (a) is performed,

a complex matrix representing rows and columns, omega-CN (0, sigma)²) Representing power as σ²White additive Gaussian noise, CN (mu, sigma)²) Denotes mean μ and variance σ²A circularly symmetric complex gaussian distribution.

In order to obtain the maximum signal-to-noise ratio gain of the receiver, the phase shift of each reflecting unit of the intelligent reflecting surface needs to be optimally adjusted according to the channel information. In fact, as long as it is ensured that the signals passing through each reflection unit of the intelligent reflection surface can be superposed in phase at the receiving end, the received signal-to-noise ratio can be maximized, and therefore, the principle of optimizing and selecting the phase shift coefficient of each reflection unit is to enable all the signals passing through the reflection unit to have the same phase at the receiving end.

The invention considers that the receiving end respectively adopts a correlation method and frequency domain equalization to demodulate passive information and active information. After the cooperative receiver receives the superposed signal, the cooperative receiver performs cross-correlation operation with the received signal by using a locally pre-stored protection sequence, and the operation result is as follows:

wherein XC (n) isIndicating the result of the correlation operation, GIseq indicates the protection sequence "GI seq", the "GI seq" signal selects ZC sequence, N_dIndicates the sequence length of GIseq.

An appropriate threshold value needs to be set according to the channel condition, if XC (n) exceeds a specified threshold value, an effective multipath signal is considered to be detected, the maximum multipath delay of the channel can be detected by the method, the delay difference between the maximum multipath delay and the first path is calculated, if the delay difference exceeds the set threshold value, passive information '1' is demodulated, and if the delay difference does not exceed the set threshold value, passive information '0' is demodulated. The time delay operation of the system is based on frame signals, so the frame rate represents the passive information rate, if the passive information transmission rate needs to be improved, the base station needs to send a short frame signal, otherwise, if the passive information transmission rate is lower, a long frame signal can be sent to improve the transmission rate of the active signal. Therefore, in this system, there is a trade-off relationship between the active and passive transmission rates.

After the passive information is demodulated, the active information is demodulated. The receiving signal of the system is composed of multipath signals, so that a simple one-tap frequency domain equalization algorithm is used at a receiving end to equalize the active signal, and the specific operation mode is that a Data field ' Data ' and a protection field ' GI seq ' behind the Data field ' Data ' are subjected to fast Fourier transform (FFT transform), then frequency domain channel coefficients are used for equalization, a frequency domain value after equalization is obtained, finally the equalized frequency domain value is subjected to inverse fast Fourier transform (IFFT transform) to restore Data ' and GI seq ' of a time domain, the GI seq ' is discarded, active information ' Data ' is finally obtained, and therefore the active and passive demodulation process is completed.

The beneficial technical effects of the invention are as follows:

the invention provides an active and passive reciprocity symbiotic transmission communication system based on a reflecting surface, a base station provides radio frequency carrier waves for an intelligent reflecting surface to modulate passive information in a time delay mode, and meanwhile, the intelligent reflecting surface enables a passive signal reflected to a receiving end to greatly enhance the intensity of an active signal and improve the gain of a signal-to-noise ratio by optimizing a reflection phase shift coefficient, so that active and passive reciprocity symbiotic communication is realized. The scheme is simple to implement, the receiver can demodulate active and passive signals through frequency domain equalization and correlation operation, and compared with a traditional wireless communication system without the assistance of an intelligent reflecting surface, the invention can greatly improve the spectral efficiency and the energy efficiency and has strong application value.

Drawings

FIG. 1 is a schematic diagram of the system of the present invention;

fig. 2 is a frame structure of an active signal transmitted by a base station;

fig. 3 is the bit error rate performance of the present invention.

Detailed Description

The present invention will be described in further detail with reference to the accompanying drawings and examples.

An active and passive reciprocal co-generation transmission communication system based on a reflecting surface is shown in fig. 1 and comprises a single-antenna transmitting base station, an intelligent reflecting surface with M independently controllable reflecting units and a single-antenna active and passive cooperative receiver. The single-antenna transmitting base station and the intelligent reflecting surface form a transmitting part of a reciprocal symbiotic communication system and respectively transmit an active signal and a passive signal; each reflection unit of the intelligent reflection surface is independently controllable through the microcontroller, each reflection unit adjusts the phase deviation of an incident signal, and the incident signal is stored and then emitted at the same time, so that a controllable time delay effect is formed. The single antenna cooperative receiver receives the active signal and the passive signal at the same time, and demodulates the active information from the base station and the passive information from the sensor connected with the intelligent reflecting surface respectively, wherein the passive information is indicated through the time delay length of a wireless channel.

Channel modeling from base station to cooperative receiver directly as Rayleigh fading channel h_d，h_dCN (0, 1). Since the channel G from the base station to the intelligent reflector often has a line-of-sight (LOS) path, it will be

Is modeled as a rice channel. Namely:

wherein, K₁Is the factor of the rice for the rice,and

respectively a line-of-sight path component and a non-line-of-sight (NLoS) path component,the energy of each element of (a) is 1,are independent of each other and are each CN (0,1) compliant. Channel between intelligent reflector and cooperative receiver

Modeling as Rayleigh channel, h_rObey CN (0, 1).

The base station transmission power is normalized to 1, x ' is data sent by the base station, each element of x ' obeys CN (0,1), so the signal transmitted by the base station is represented as x (n) ═ x ' (n)

The signal received by the receiving end is

y(n)＝h_r ^TΘGx(n-k)+h_dx(n)+ω

Wherein k represents the time delay introduced by the intelligent reflecting surface,

diagonal phase shift matrix, θ, representing intelligent reflective surfaces_mE [0,2 π) represents the phase shift angle of the mth reflection unit, ω -CN (0, σ)²) Representing power as σ²White additive gaussian noise.

The base station transmits active signals by a single carrier, the frame format is as shown in fig. 2, a ZC sequence with excellent correlation characteristics is selected as a protection sequence "GI seq", the sequence length is set to 32, the length of a "Data" field is set to 224, therefore, the number of FFT/IFFT transformed points at the receiving end is 256, that is, the length of one transmission symbol is 256, and one frame includes one or more transmission symbols. Each reflection unit of the intelligent reflection surface carries out specific phase shift on an incident signal according to channel information, and the selection principle of a phase shift coefficient is that all reflection signals processed by the reflection units can be superposed in phase at a cooperative receiver so as to maximize receiving gain. According to the passive information to be transmitted, each reflection unit of the intelligent reflection surface introduces the same specific time delay to the incident frame signal, namely if the passive information is '1', the frame signal is delayed by 22 sampling intervals, and if the passive information is '0', the time delay is not introduced.

The cooperative receiver firstly adopts the locally stored 32-bit ZC sequence to carry out correlation operation with the received signal, and the operation result is

Wherein N is_dThe length of the ZC sequence is 32, and the GIseq is the ZC sequence. When XC (n) exceeds a set threshold, then a valid multipath signal is deemed detected. The maximum delay introduced by the wireless channel itself is assumed to be less than 22 sample intervals. Because the maximum multipath time delay is controlled by the intelligent reflecting surface, the maximum multipath time delay of the received aliasing signal is detected firstly, if the value is not less than 22 sampling intervals, passive information '1' is demodulated, and if the value is less than 22 sampling intervals, the intelligent reflecting surface does not introduce time delay to the incident signal, and passive information '0' is demodulated.

And then demodulating the active signal, wherein the frequency domain equalization is adopted to demodulate the active signal due to the existence of multipath signals so as to reduce the complexity of a receiving algorithm. The first 32 samples of the received signal are discarded and the remaining signal is then sliced into 256 symbols. FFT conversion is carried out on each signal with the length of 256, and equalization is carried out by utilizing frequency domain channel information to obtain equalized signals

X_re(k)＝Y(k)/H(k)

Where y (k) denotes FFT of y (n), k is 0,1, … 255, and h (k) denotes a k-th subchannel in the frequency domain. Assuming that the system knows all channel coefficients, the frequency domain channel H can be obtained by FFT transforming the time domain channel.

Then to X_reAnd performing IFFT (inverse fast Fourier transform) conversion to recover the transmitted signal x, and discarding the protection sequence GI seq in x to obtain the Data which is actively transmitted. So as to respectively complete the demodulation of the active and passive signals.

Fig. 3 compares the bit error rate performance of the active and passive reciprocity symbiotic wireless communication system based on the intelligent reflecting surface. The simulation parameters are set as follows, a channel from a base station to a cooperative receiver directly and a channel from an intelligent reflecting surface to the cooperative receiver are modeled into Rayleigh channels, path loss indexes are set to be 3.6 and 2.2 respectively, and reference distances of path loss are set to be 1 m. The channel from the base station to the intelligent reflecting surface is modeled as a Leise channel, the path loss index is set to be 2.2, and the reference distance of the path loss is set to be 3 m. The distances from the base station to the intelligent reflecting surface and the cooperative receiver are both set to be 50m, and the distance from the intelligent reflecting surface to the cooperative receiver is set to be 2 m. Setting the Rice factor K₁＝15dB，σ²-80 dBm. The number of reflecting units is set to be M40 and 80, respectively.

Compared with the traditional wireless communication system without the intelligent reflecting surface, the wireless communication system has the practical significance that the intelligent reflecting surface not only transmits passive information in a passive mode, but also brings remarkable signal-to-noise ratio gain for active transmission, and the gain is increased along with the increase of reflecting units. According to the symbiotic wireless communication system, no new radio frequency signal is introduced, electromagnetic waves in the environment are used as carriers, the spectrum efficiency and the energy efficiency are obviously improved, the hardware cost of the Internet of things equipment is reduced, and a new solution is provided for the Internet of things communication.

Fig. 3 compares the error rate performance when the transmitted active signal is QPSK modulated under different transmission powers, and compares with the conventional active communication without the intelligent reflective surface, and it can be seen that, in the region far from the base station, the intelligent reflective surface greatly improves the performance of the active communication while transmitting the passive signal. Simulation results also show that the passive signal has good anti-noise performance by adopting time delay modulation and related detection, and compared with active transmission, the demodulation signal-to-noise ratio required by passive communication is lower under the condition of the same bit error rate.