An emergency rescue communication system and method based on parallel reconfigurable metasurface

Abstract

The application belongs to the technical field of wireless communication network, and provides an emergency disaster relief communication system and method based on parallel reconfigurable metasurfaces. The system comprises a plurality of backpack RIS enhancement stations, a single-antenna disaster-stricken user terminal and a vehicle-mounted base station. Each backpack RIS enhancement station comprises a single reconfigurable metasurface, and each reconfigurable metasurface comprises a plurality of reflection units. The single-antenna disaster-stricken user terminal is used for transmitting communication signals to the reconfigurable metasurfaces of the plurality of parallel backpack RIS enhancement stations. Each reconfigurable metasurface is used for receiving the incident signals, adding phase shifts to the phase shift vectors added to the incident signals, and reflecting the signals to the vehicle-mounted base station. The vehicle-mounted base station is used for receiving the reflected signals. The application combines the advantages of reconfigurable metasurfaces, studies the application of the reconfigurable metasurfaces in the emergency disaster relief communication scenario, further improves the cost-effectiveness and energy efficiency of the emergency disaster relief communication, and improves the reliability and effectiveness of the communication.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of wireless communication networks, and particularly relates to an emergency disaster relief communication system and method based on parallel reconfigurable metasurfaces. BACKGROUND

[0002] The statements in this section merely provide background information related to the application and do not necessarily constitute prior art.

[0003] When major disasters such as heavy rain, earthquake, volcano, tsunami, etc. occur, communication facilities may be damaged, base stations may be collapsed, and optical cables may be broken, etc. There are problems such as failure of wired communication such as fixed telephone, Internet, and public mobile communication network of 4 / 5G mobile phones. As a new technology, reconfigurable metasurface (RIS) has received extensive attention in recent years and can be considered as a key enabling technology for future 6G wireless communication networks. The reconfigurable metasurface can convert the uncontrollable wireless channel into a controllable entity, especially when the direct link is blocked, additional transmission gain is generated. Unlike existing relay technology, RIS works in duplex mode, the working frequency range is from microwave to visible light, and it is approximately passive. Therefore, RIS has extremely high cost-effectiveness and energy efficiency, and in the reconfigurable metasurface-based wireless communication that has been realized, it is widely used in nodes such as transceivers and shows excellent performance. It is of great prospect and significance to explore the reconfigurable metasurface communication technology in emergency disaster relief communication.

[0004] The reconfigurable metasurface is composed of a large number of small reflecting units, each of which can independently adjust the changes of the incident electromagnetic wave, and such changes can be about phase, amplitude, frequency or even polarization. So far, in most studies on reconfigurable metasurfaces, such changes are only considered as phase shifts of incident electromagnetic waves. Essentially, when the direct link communication quality is not good, the reconfigurable metasurface can intelligently configure the wireless environment to improve the reliability and effectiveness of signal transmission between the sender and the receiver. Due to the easy-to-deploy nature of the reconfigurable metasurface, it is envisaged in the future that it can be placed in indoor walls, building facades, etc., or even clothes worn by people.

[0005] Currently, the research focus of reconfigurable metasurface technology is that the reconfigurable metasurface acts as a reflecting surface, which is similar to a relay, but compared with traditional relay technology, it can effectively control the phase, amplitude, frequency, etc. of the incident electromagnetic wave, but it discards the complex encoding and decoding, mixing, filtering, etc. operations in the relay. At the same time, the reconfigurable metasurface is generally controlled by a field programmable gate array (FPGA) in a software programming manner, which has much less energy consumption and is approximately passive.

[0006] However, in the current emergency rescue communication scene, there is a problem of communication interruption caused by line failure, which leads to the inability to quickly lock the trapped personnel. SUMMARY

[0007] To solve the technical problems in the background art, the present application provides a parallel reconfigurable metasurface-based emergency rescue communication system and method, which combines the advantages of reconfigurable metasurfaces, studies its application in emergency rescue communication scenarios, and further improves the cost-effectiveness and energy efficiency of emergency rescue communication, and improves the reliability and effectiveness of communication.

[0008] To achieve the above purpose, the present application adopts the following technical solutions:

[0009] The first aspect of the present application provides a parallel reconfigurable metasurface-based emergency rescue communication system.

[0010] A parallel reconfigurable metasurface-based emergency rescue communication system, comprising: a plurality of backpack RIS enhancement stations, a single-antenna disaster user terminal and a vehicle-mounted base station, each backpack RIS enhancement station comprising a single reconfigurable metasurface, and each reconfigurable metasurface comprising a plurality of reflection units.

[0011] The single-antenna disaster user terminal is used to transmit communication signals to the reconfigurable metasurfaces of the plurality of parallel backpack RIS enhancement stations; each reconfigurable metasurface is used to receive the incident signal, and after adding a phase shift to the incident signal and the phase shift vector, it is reflected to the vehicle-mounted base station; the vehicle-mounted base station is used to receive the reflected signal.

[0012] The second aspect of the present application provides a parallel reconfigurable metasurface-based emergency rescue communication method.

[0013] A parallel reconfigurable metasurface-based emergency rescue communication method, running on the parallel reconfigurable metasurface-based emergency rescue communication system of the first aspect, comprising:

[0014] The single-antenna disaster user terminal transmits the modulated communication signal;

[0015] According to the positional relationship between the single-antenna disaster user terminal and the plurality of backpack RIS enhancement stations, a channel vector is established respectively; the communication signal is transmitted in free space and incident to the plurality of parallel backpack RIS enhancement stations after passing through the channel vector;

[0016] The phase shift vector added by the metasurface in each backpack RIS enhancement station to the incident signal is established; the incident signal is reflected after adding a phase shift to the incident signal by the phase shift vector added by the reconfigurable metasurface to the incident signal, forming a reflected signal;

[0017] According to the positional relationship between the several back-mounted RIS enhanced stations and the vehicle-mounted base station, channel vectors are respectively established; the reflected signal is transmitted in free space and is received at the vehicle-mounted base station after the channel vector.

[0018] Compared with the prior art, the present application has the beneficial effects that:

[0019] 1. The present application replaces the relay technology used in traditional emergency disaster communication with the currently popular reconfigurable metasurface technology, wherein the affected single-antenna users communicate with the vehicle-mounted base station using L parallel back-mounted RIS enhancement stations in the environment, and the vehicle-mounted base station can send the processed signal to the front command department and the rear command center, respectively.

[0020] 2. The L reconfigurable metasurfaces used in the present application can redefine the random wireless communication environment through software programming, and compared with the traditional relay technology, they do not require any filter, frequency mixer or power amplifier, greatly reducing power consumption and hardware cost.

[0021] 3. Compared with the existing single reconfigurable metasurface used in the communication system, the present application constructs a communication system based on multiple parallel reconfigurable metasurfaces, fully utilizes the advantages of reconfigurable metasurfaces, avoids communication interruption, further reduces the cost-effectiveness and energy efficiency of communication, and improves the reliability and effectiveness of communication.

[0022] 4. The parallel communication system proposed in the present application is expected to become a common model in future 6G communication as the reconfigurable metasurface technology matures and becomes practical.

[0023] 5. The present application uses the central limit theorem to approximate the random channel characteristics and further derives the closed-form solution of the system ergodic capacity upper bound and outage probability. DETAILED DESCRIPTION

[0024] The drawings accompanying the specification of the present application form a part thereof and serve to provide further understanding of the present application, the illustrative embodiments of the present application and its description serve to explain the present application without unduly limiting it.

[0025] Figure 1 is a schematic diagram of a multiple parallel reconfigurable metasurface assisted communication scenario shown in the present application;

[0026] Figure 2 is a schematic diagram of the system ergodic capacity upper bound result when the number of reconfigurable metasurfaces is 1 and 2 (L=1, 2) shown in the present application;

[0027] Figure 3 is a schematic diagram of the system outage probability result when the number of reconfigurable metasurfaces is 1 and 2 (L=1, 2) shown in the present application. DETAILED DESCRIPTION

[0028] The application will be further described below with reference to the drawings and examples.

[0029] It should be noted that the following detailed description is exemplary in nature and is intended to provide further description of the application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0030] It is to be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments according to the present application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and / or "comprising," when used in this specification, specify the presence of stated features, steps, operations, elements, components, and / or groups thereof, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and / or groups thereof.

[0031] It should be noted that the flow diagrams and block diagrams in the drawings are representative of the architecture, functionality, and operation of possible implementations of the methods and systems according to various embodiments of the present disclosure. It should also be noted that each block in the flow diagrams and block diagrams can represent a module, a segment, or a portion of code, which includes one or more executable instructions for implementing the specified logical functions ("instructions"). It should also be noted that in some alternative implementations, the functions noted in the blocks can occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently or the blocks can sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that each of the blocks of the flow diagrams and / or block diagrams, and combinations thereof, can be implemented by special purpose hardware-based systems that perform the specified functions or operations, or combinations of special purpose hardware and

[0032] Terminology:

[0033] RIS refers to reconfigurable metasurface;

[0034] FPGA refers to field programmable gate array;

[0035] LOS refers to line of sight;

[0036] NLOS refers to non-line of sight;

[0037] CLT refers to central limit theorem.

[0038] Example 1

[0039] This example considers Figure 1The emergency rescue communication scenario shown in the figure. An emergency rescue communication system based on a parallel reconfigurable metasurface includes L backpack-type RIS enhancement stations (in parallel form), a disaster-stricken single-antenna user, and a vehicle-mounted base station receiving end.

[0040] Single-antenna disaster-stricken users refer to disaster-stricken users carrying emergency communication terminals, which are only equipped with a single omnidirectional antenna.

[0041] The piggyback RIS enhancement platform is equipped with a single reconfigurable metasurface, each of which includes N reflective units. These N basic units are numbered 1, 2, ..., N.

[0042] The vehicle-mounted base station receiving end is equipped with a single omnidirectional antenna to process the signals received from L backpack-mounted RIS enhancement stations and transmit the processed signals to the forward command post and the rear command center respectively.

[0043] Example 2

[0044] This embodiment provides a parallel reconfigurable metasurface-based emergency rescue communication method, which operates on the parallel reconfigurable metasurface-based emergency rescue communication system described in Example 1, including the following steps:

[0045] (1) First, a single-antenna user transmits a modulated communication signal;

[0046] (2) establishing channel vectors based on the positional relationship between the single-antenna user and the L piggyback RIS enhancement stations; the communication signal in step (1) is transmitted in free space and incident on the L parallel piggyback RIS enhancement stations after passing through the channel matrix;

[0047] (3) establishing a phase shift vector added by the metasurface in each piggyback RIS enhancement station to the incident signal; the incident signal in step (2) is reflected after the phase shift vector added by the reconfigurable metasurface to the incident signal is added to form a reflected signal;

[0048] (4) Based on the positional relationship between the L backpack-mounted RIS enhancement stations and the vehicle-mounted base station, channel vectors are established respectively; the reflected signal formed in step (3) is transmitted in free space and is received at the vehicle-mounted base station after passing through the channel vector.

[0049] (5) The vehicle-mounted base station determines to send the received signal to the front command post or the rear command center. The method is consistent with traditional emergency rescue. This embodiment only studies the communication before this node.

[0050] First, a single-antenna user transmits a modulated communication signal x, as shown in equation (1):

[0051]

[0052] In formula (1), A c The expression of the amplitude of the transmitted signal, f c The expression of the frequency of the transmitted signal, t represents time, and j represents a complex number.

[0053] Since the L back-mounted RIS enhancement stations construct a virtual line-of-sight transmission path between nodes, the channel model of the scene is modeled using the Ricean channel model, and the channel vector of the user related to the lth back-mounted RIS enhancement station is shown in formula (2):

[0054]

[0055] In formula (2), d represents the distance between two nodes, and it is assumed that the distance from all back-mounted RIS enhancement stations R l to the user in the scene is the same, that is, l∈{1,2…L}, where h represents the channel from the user to the back-mounted RIS enhancement station. In addition, a represents the path loss index, and it is assumed that all path loss indexes are the same, that is, a l = a h ; K represents the Rician factor, and it is assumed that all Rician factor values are the same, that is, K l = K, l∈{1,2…L}; and represent the normalized LOS component and NLOS component, respectively.

[0056] According to the characteristics of the reconfigurable metasurface, the phase shift vector Θ l added by the lth reconfigurable metasurface to the incident signal is established, as shown in formula (3):

[0057]

[0058] In formula (3), φ i represents the phase shift added by the i th reflection unit of the reconfigurable metasurface to the incident signal, i∈{1,2…N}, and N represents that each reconfigurable metasurface is composed of N reflection units;

[0059] Next, the channel vector of the lth back-mounted RIS enhancement station related to the vehicle-mounted base station is shown in formula (4):

[0060]

[0061] In formula (4), d represents the distance between two nodes, and it is assumed that the distance from all back-mounted RIS enhancement stations R l to the vehicle-mounted base station in the environment is the same, that is, l∈{1,2…L}, where g represents the channel from the back-mounted RIS enhancement station to the vehicle-mounted base station. In addition, a represents the path loss index, and it is assumed that all path loss indexes are the same, that is, al = a g ; K represents the Rician factor, and it is assumed that all Rician factor values are the same, i.e. K l = K, l e {1, 2…L}; and represent the normalized LOS component and NLOS component, respectively.

[0062] The vehicle-mounted base station receives the signal forwarded by the L back-mounted RIS enhancement stations, and the received signal y is shown in equation (5):

[0063]

[0064] In equation (5), P represents the transmission power, n represents the Gaussian white noise in the channel independent of the input signal, and n ~ N(0, σ 2 ), σ 2 is the variance of the Gaussian white noise.

[0065] The maximum signal-to-noise ratio γ of the received signal y at the vehicle-mounted base station is shown in equation (6):

[0066]

[0067] The L back-mounted RIS enhancement stations in this system are each composed of N basic units, so the maximum signal-to-noise ratio can be further expressed as equation (7):

[0068]

[0069] In order to maximize the received signal-to-noise ratio, the phase shift of the RIS basic unit should be adjusted to satisfy equation (8):

[0070]

[0071] In equation (8), ∠ represents the complex phase extraction operation. When equation (8) is satisfied, the vehicle-mounted base station obtains the maximum signal-to-noise ratio, which can be shown as equation (9):

[0072]

[0073] In equation (9), the symbol the symbol

[0074] In a wireless communication system, channel capacity and outage probability are two important indicators for evaluating the effectiveness and reliability of communication, so we will analyze the system capacity and outage probability in this scenario in detail. First, the channel capacity theoretical expression definition is shown in equation (10):

[0075]

[0076] As can be seen from the above analysis of the signal-to-noise ratio, γ in Equation (10) max has an exact distribution that is difficult to solve. Therefore, it is very difficult to calculate the exact ergodic channel capacity. However, with the help of Jensen's inequality, an easy-to-process upper bound of the ergodic capacity can be obtained as shown in Equation (11):

[0077]

[0078] The elements of the channel vector |g li | and |h li | respectively follow the Rice distribution. The expectation and variance of the product of the two can be respectively expressed as shown in Equations (12) and (13):

[0079]

[0080]

[0081] In Equations (12) and (13), represents the Laguerre polynomial. With the help of the Central Limit Theorem (CLT), the expectation and variance of A in the expression of γ max are respectively and VAR[A] = LN × VAR[|g li ||h li |].

[0082] Thus, an upper bound of the system ergodic capacity is obtained as shown in Equation (14):

[0083]

[0084] The outage probability theory in a wireless communication system is defined as the probability that the instantaneous signal-to-noise ratio drops below a predetermined threshold ρ th The following probability, and its expression is as shown in Equation (15):

[0085]

[0086] According to the above analysis of the present invention, A is a random variable that follows a Gaussian distribution, that is Using the cumulative distribution function (CDF) of the Gaussian distribution, the outage probability can be obtained as shown in Equation (16):

[0087]

[0088] In Equation (16), erf(·) represents the error function.

[0089] The present invention uses the central limit theorem to provide an easily analyzable closed-form solution for the upper bound of the ergodic channel capacity and the outage probability, thereby clearly expressing the impact of the number L of piggyback RIS enhancers and the number N of reflector units in the RIS on the above two indicators.

[0090] In this embodiment, the path loss index α is set h =α g =2, signal-to-noise ratio threshold ρ th =10dB, the Rician factor value K of all channels involved in the system l = 1, the number of reconfigurable metasurface basic units N = 16, and the system operates in a bandwidth of 180KHz and a noise power spectrum density of -173dBm / Hz. After 10,000 Monte Carlo simulation experiments, when the number of piggyback RIS enhancement stations in the system is 1 or 2 (i.e., L = 1 and 2), the system traversal capacity upper bound change curve is as follows: Figure 2 As shown in the figure, the system interruption probability change curve is as follows: Figure 3 The results show that by increasing the number of backpack RIS enhancement stations, the cost-effectiveness and energy efficiency of the communication system can be further improved, and the reliability and effectiveness of communication can be effectively improved.

[0091] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. An emergency rescue communication system based on parallel reconfigurable metasurface, characterized in that, The application relates to an emergency rescue communication system based on parallel reconfigurable metasurfaces. The system comprises a plurality of RIS enhancement stations, a single-antenna disaster user terminal and a vehicle-mounted base station, each RIS enhancement station comprises a single reconfigurable metasurface, and each reconfigurable metasurface comprises a plurality of reflection units. The single-antenna disaster user terminal is used for transmitting a communication signal to the reconfigurable metasurfaces of the plurality of parallel RIS enhancement stations; each reconfigurable metasurface is used for receiving the incident signal, adding a phase shift to the phase shift vector added to the incident signal, and reflecting the signal to the vehicle-mounted base station; and the vehicle-mounted base station is used for receiving the reflected signal. The vehicle-mounted base station receives the signals forwarded by the L RIS enhancement stations, and the received signal y is: where P represents the transmit power, n represents the Gaussian white noise independent of the input signal in the channel, n ~ N(0, σ 2 ), σ 2 is the variance of the Gaussian white noise; gl l represents the channel vector related to the vehicle-mounted base station of the lth back-mounted RIS enhanced station; Θl l represents the phase shift vector added to the incident signal by the lth reconfigurable metasurface; hl l represents the channel vector related to the lth back-mounted RIS enhanced station of the user; x represents the modulated communication signal transmitted by the single-antenna user; The maximum signal-to-noise ratio gamma of the received signal y at the vehicle-mounted base station is: The maximum signal-to-noise ratio is: To maximize the received signal-to-noise ratio, the phase shift of the reflecting unit should be adjusted to: In the formula, ∠ represents an extraction complex phase operation; when the phase shift of the reflection unit is satisfied The vehicle-mounted base station obtains the maximum signal-to-noise ratio: Symbols Symbols 2. The parallel reconfigurable metasurface-based emergency rescue communication system according to claim 1, wherein, The vehicle-mounted base station is equipped with a single omnidirectional antenna, and the reflected signal is processed and transmitted to the front command department and the rear command center.

3. The parallel reconfigurable metasurface-based emergency rescue communication system according to claim 1, wherein, The single-antenna disaster user terminal refers to an emergency communication terminal carried by a disaster user, and the terminal is only equipped with a single omnidirectional antenna.

4. An emergency rescue communication method based on parallel reconfigurable metasurface, characterized in that, The application is applied to the emergency rescue communication system based on parallel reconfigurable metasurfaces, and the system comprises the following steps: The single-antenna disaster user terminal transmits a modulated communication signal. According to the positional relationship between the single-antenna disaster user terminal and the plurality of RIS enhancement stations, channel vectors are respectively established; the communication signal is transmitted in free space, and the signal is incident to the plurality of parallel RIS enhancement stations after passing through the channel vectors. The phase shift vectors added to the incident signal by the metasurfaces in the RIS enhancement stations are established; the incident signal is reflected after the phase shift vectors added to the incident signal by the reconfigurable metasurfaces add phase shifts, and the reflected signal is formed. According to the positional relationship between the plurality of RIS enhancement stations and the vehicle-mounted base station, channel vectors are respectively established; the reflected signal is transmitted in free space, and the signal is received at the vehicle-mounted base station after passing through the channel vectors.

5. The parallel reconfigurable metasurface-based emergency rescue communication method according to claim 4, characterized in that, The channel vector related to the single-antenna disaster user terminal and the lth RIS enhancement station is: where d denotes the distance between two nodes, and here we assume that all the back-carrying RIS-enhanced stations R l have the same distance to the user, i.e. where h denotes the channel from the user to the back-carrying RIS-enhanced station; a denotes the path loss exponent, and here we assume that all the path loss exponents are the same, i.e. l a h = a l ; K denotes the Rician factor, and here we assume that all the Rician factor values are the same, i.e. l K h = K, l e {1, 2,..., L}; and denote the normalized LOS component and NLOS component, respectively.

6. The parallel reconfigurable metasurface-based emergency rescue communication method according to claim 4, characterized in that, The first reconfigurable metasurface adds a phase shift vector Θ to the incident signal l : In the formula, φ i represents the phase shift added by the i-th reflective unit of the reconfigurable metasurface to the incident signal, i∈{1,2…N}, N represents that each reconfigurable metasurface is composed of N reflective units.

7. The parallel reconfigurable metasurface-based emergency rescue communication method according to claim 4, characterized in that, The channel vector related to the lth RIS enhancement station and the vehicle-mounted base station is: where d denotes the distance between two nodes, and it is assumed that all the backpack RIS enhanced stations R l have the same distance to the vehicle-mounted base station, i.e. where g denotes the channel from the backpack RIS enhanced station to the vehicle-mounted base station, and a denotes the path loss exponent, which is assumed to be the same for all the backpack RIS enhanced stations, i.e. l a = a g ; K denotes the Rician factor, which is assumed to be the same for all the backpack RIS enhanced stations, i.e. l K = K, l e {1, 2,..., L}; and denote the normalized LOS component and NLOS component, respectively.

8. The parallel reconfigurable metasurface-based emergency rescue communication method according to claim 4, characterized in that, The theoretical expression of the ergodic channel capacity in the wireless communication system is defined as: wherein γ max indicates that the vehicle-mounted base station obtains the maximum signal-to-noise ratio; By means of the Jensen inequality, the upper limit of the ergodic capacity is obtained: Channel vector element |g li | and h li | are subject to a Rice distribution, respectively, and the expectation and variance of their product are given by Where d represents the distance between two nodes. Here, it is assumed that all the backpack RIS enhancement platforms R l The distance to the user is the same, that is Where h represents the channel from the user to the backpack RIS enhancement station; α represents the path loss index, and it is assumed that all path loss indices are the same, that is, α l =α h ; K represents the Rician factor. Here we assume that all Rician factor values ​​are the same, that is, K l =K, l∈{1,2...L}; represents the Laguerre polynomial, and with the help of the Central Limit Theorem (CLT), we get γ max The expectation and variance of A in the expression are and VAR[A]=LN×VAR[|g li ||h li |]; Thus, we obtain the upper bound of the system ergodic capacity: wherein the symbol the symbol channel vector element |g li | and |h li |; L represents the L RIS enhancement stations, and N represents that each reconfigurable metasurface is composed of N reflection units.

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