Space-time coding spatial modulation method and system based on intelligent reflecting surface

Abstract

The invention belongs to the field of wireless communication, and provides a space-time coding spatial modulation method and system based on an intelligent reflecting surface, and the method comprises the steps: carrying out the different phase modulation of a signal transmitted by a single transmitting antenna at different time slots through employing the characteristics of RIS, enabling the transmitted signal to have a format similar to Alamouti space-time coding, and enabling the transmitted signal to have a space-time coding format; therefore, a second-order transmit diversity can be obtained; and meanwhile, the known channel state information is utilized to reconstruct the propagation channel, so that the signal-to-noise ratio at the selected receiving antenna is maximized, and the system performance is improved. In addition, the method provided by the invention supports a linear decoding method of a receiving end, so that the decoding complexity is relatively low. A simulation experiment shows that under different parameter configurations and different spectrum efficiencies, the scheme (RIS-AlaSM) has better bit error rate performance compared with the existing RIS-RQRM (RIS-RQRM) based on the RIS.

Description

Technical Field

[0001] The present invention belongs to the technical field of wireless communications, and in particular relates to a space-time coding spatial modulation method and system based on an intelligent reflection surface. Background Art

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

[0003] Smart Reflective Surface (RIS) is a plane composed of a large number of low-power reflective units. It can control the amplitude, phase, polarization and other parameters of the incident signal, reconstruct the wireless propagation environment, and significantly improve the performance of the communication system. It has become one of the most promising candidate technologies for the sixth-generation wireless communication system (6G). On the other hand, spatial modulation (SM) technology is a new type of digital modulation technology in 6G. SM has attracted widespread attention from academia and industry because it can use the index number of the antenna to transmit additional information bits. RIS-SM technology can simultaneously utilize the advantages of both RIS and SM technologies to achieve the green and energy-efficient design goals of the 6G communication system.

[0004] Recently, scholars have proposed a variety of different RIS-SM schemes: "Reconfigurable intelligent surface assisted space shift keying" proposed a RIS-based space shift keying (SSK) scheme, in which the transmitter uses SSK modulation, and RIS uses the known channel state information (CSI) to set the reflection phase to the channel phase of the activated antenna, thereby maximizing the signal-to-noise ratio (SNR); "Reconfigurable intelligent surface-based index modulation: A new beyond MIMO paradigm for 6G" proposed RIS-SM and RIS-SSK schemes with activated receiving antennas, in which the reflection unit on the RIS aligns its phase with the activated antenna at the receiving end, so that the signals on it can be coherently superimposed. In order to improve the spectrum efficiency of RIS-SM and RIS-SSK in the previous two schemes, "Receive quadrature reflecting modulation for RIS-empowered wireless communications" proposed a RIS-based orthogonal reflection modulation (RIS-RQRM) scheme, in which all reflection units are divided into two groups, which are respectively aligned with the receiving antennas of the same direction and orthogonal directions at the receiving end to maximize the receiving SNR. However, none of the above solutions can obtain transmit diversity, and thus cannot effectively resist the influence of channel fading. Summary of the invention

[0005] In order to solve the above problems, the present invention proposes a space-time coded spatial modulation method and system based on an intelligent reflective surface. Since the present invention adopts a space-time transmission method, second-order transmit diversity can be obtained. Therefore, it has better bit error performance than the existing RIS-RQRM scheme under the same spectrum efficiency. This scheme has an effect on improving the bit error performance.

[0006] According to some embodiments, a first solution of the present invention provides a space-time coded spatial modulation method based on a smart reflective surface, which adopts the following technical solution:

[0007] The space-time coded spatial modulation method based on the intelligent reflective surface adopts a single-input multiple-output system assisted by the intelligent reflective surface. The intelligent reflective surface RIS has N reflective units, and each reflective unit on the intelligent reflective surface is controlled by the RIS controller, including:

[0008] The channel matrix between the smart reflection surface and the receiving end is determined by using the number of receiving antennas at the receiving end, the number of reflection units in the RIS, and the channel coefficient;

[0009] Determine the phase deflection of the transmitted unit pulse signal by the reflection units of different groups according to the information bits to be transmitted and the modulation order of different groups in different time slots; determine the reflection phase of the reflection units of different groups according to the information bits to be transmitted and the receiving antenna in different time slots; determine the reflection signal of the reflection unit by the reflection phase and the phase deflection;

[0010] The receiving end receives the reflected signal and uses the maximum likelihood method to perform decoding detection.

[0011] Furthermore, the channel matrix between the smart reflection surface and the receiving end is determined by utilizing the number of receiving antennas at the receiving end, the number of reflection units in the RIS, and the channel coefficient, specifically:

[0012] The number of reflection units is used as the number of columns of the channel matrix, and the number of receiving antennas at the receiving end is used as the number of rows of the channel matrix;

[0013] The channel coefficients from each reflection unit to each receiving antenna are used as elements of the channel matrix;

[0014] Construct a channel matrix from the smart reflection surface to the receiving end.

[0015] Furthermore, the method occupies two symbol periods to transmit a frame of signal, and a single transmitting antenna at the transmitting end sends unit pulse signals to the intelligent reflecting surface in both the first time slot and the second time slot.

[0016] Furthermore, the reflection units on the smart reflection surface are evenly divided into two groups.

[0017] Further, the phase deflection of the unit pulse signal transmitted by the reflection units of different groups is determined by using different groups of information bits to be transmitted and modulation orders in different time slots, specifically:

[0018] In the first time slot, based on the modulation order and the first group of information bits to be transmitted, the RIS controller controls the first group of reflection units to perform phase deflection on the unit pulse signal;

[0019] In the first time slot, based on the modulation order and the third group of information bits to be transmitted, the RIS controller controls the second group of reflection units to perform phase deflection on the unit pulse signal;

[0020] In the second time slot, based on the modulation order and the first group of information bits to be transmitted, the RIS controller controls the first group of reflection units to perform phase deflection on the unit pulse signal;

[0021] In the second time slot, the second group of reflection units are controlled by the RIS controller to perform phase shift on the unit pulse signal based on the modulation order and the third group of information bits to be transmitted.

[0022] Further, the determination of reflection phases of different groups of reflection units according to different groups of information bits to be transmitted and receiving antennas in different time slots is specifically as follows:

[0023] In the first time slot, aligning the phases of the first group of reflection units with the receiving antenna determined by the second group of information bits to be transmitted, thereby determining the reflection phase of each reflection unit in the group;

[0024] In the first time slot, aligning the phases of the second group of reflection units with the receiving antenna determined by the fourth group of information bits to be transmitted, thereby determining the reflection phase of each reflection unit in the group;

[0025] In the second time slot, the phases of the first group of reflection units are aligned with the receiving antenna determined by the second group of information bits to be transmitted, so as to determine the reflection phase of each reflection unit in the group;

[0026] In the second time slot, the phases of the second group of reflection units are aligned with the receiving antenna determined by the fourth group of information bits to be transmitted, so as to determine the reflection phase of each reflection unit in the group.

[0027] Further, the use of the reflection phase and the phase deflection to determine the reflection signal of the reflection unit is specifically:

[0028] In the first time slot, a first reflection signal of the first time slot is determined according to the product of the phase deflection of the first group of reflection units to the unit pulse signal and the reflection coefficient determined by the reflection phase of the first group of reflection units;

[0029] In the first time slot, a second reflection signal of the first time slot is determined according to the product of the phase deflection of the second group of reflection units on the unit pulse signal and the reflection coefficient determined by the reflection phase of the second group of reflection units;

[0030] In the second time slot, a first reflection signal of the second time slot is determined according to the product of the phase deflection of the first group of reflection units to the unit pulse signal and the reflection coefficient determined by the reflection phase of the first group of reflection units;

[0031] In the second time slot, a second reflection signal of the second time slot is determined according to the product of the phase deflection of the second group of reflection units to the unit pulse signal and the reflection coefficient determined by the reflection phase of the second group of reflection units.

[0032] Further, the receiving end receives the reflected signal and performs decoding detection using a maximum likelihood method, specifically:

[0033] The phase of each element in the channel matrix is ​​taken to obtain a phase matrix and a phase vector corresponding to the activated receiving antenna, and then a signal matrix model received by the receiving end is determined;

[0034] calculating an equivalent form of the signal matrix model, and determining an equivalent channel matrix based on the equivalent form of the signal matrix model;

[0035] The orthogonality of the equivalent channel matrix is ​​used to reduce the ML decoding into two low-dimensional ML decoders;

[0036] Two low-dimensional ML decoders are used to jointly decode the reflected signals of the two time slots, and then the information bits of the reflected signals are inversely mapped according to the decoding results.

[0037] Furthermore, the reflected signal constitutes an N×2-dimensional space-time code X, thereby obtaining second-order transmit diversity, wherein N is the number of reflection units.

[0038] According to some embodiments, a second solution of the present invention provides a space-time coded spatial modulation system based on a smart reflective surface, which adopts the following technical solution:

[0039] The space-time coded spatial modulation system based on the intelligent reflective surface includes:

[0040] A transmitting end, including a single transmitting antenna, for transmitting a transmitting signal to the smart reflecting surface;

[0041] The intelligent reflection surface includes a plurality of reflection units, which are used to determine the phase deflection of the transmitted unit pulse signal by the reflection units of different groups using different groups of information bits to be transmitted and modulation orders in different time slots; determine the reflection phases of the reflection units of different groups according to the different groups of information bits to be transmitted and the receiving antennas in different time slots; determine the reflection signal of the reflection unit using the reflection phase and the phase deflection, and reflect the reflection signal to the receiving end;

[0042] The receiving end includes multiple receiving antennas for receiving reflected signals and performing decoding detection using the maximum likelihood method.

[0043] Compared with the prior art, the present invention has the following beneficial effects:

[0044] The present invention focuses on the defect that existing RIS-SM and other schemes cannot obtain transmit diversity, and proposes a space-time coding spatial modulation transmission and fast decoding method based on RIS, referred to as the RIS-AlaSM scheme. In this scheme, the characteristics of RIS are used to first perform different phase modulations on the signal emitted by a single transmitting antenna in different time slots, so that the transmitted signal has a format similar to Alamouti space-time coding, thereby obtaining second-order transmit diversity; at the same time, the propagation channel is reconstructed using known channel state information to maximize the signal-to-noise ratio (SNR) at the selected receiving antenna, thereby improving system performance. In addition, the proposed RIS-AlaSM method supports the linear maximum likelihood decoding method at the receiving end, and thus has a lower decoding complexity. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0046] Figure 1 It is a flow chart of a space-time coding spatial modulation method based on a smart reflective surface in an embodiment of the present invention;

[0047] Figure 2 is a performance comparison of the RIS-AlaSM scheme and the RIS-RQRM scheme in an embodiment of the present invention when the spectrum efficiency is 4 bpcu;

[0048] Figure 3 It is a performance comparison between the RIS-AlaSM scheme and the RIS-RQRM scheme in the embodiment of the present invention when the spectrum efficiency is 6bpcu. DETAILED DESCRIPTION

[0049] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0050] It should be noted that the following detailed descriptions are all illustrative and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0051] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0052] In the absence of conflict, the embodiments of the present invention and the features of the embodiments may be combined with each other.

[0053] Embodiment 1

[0054] like Figure 1 As shown, this embodiment provides a space-time coded spatial modulation method based on an intelligent reflective surface. The space-time coded spatial modulation method based on an intelligent reflective surface adopts a single-input multiple-output system assisted by an intelligent reflective surface. The intelligent reflective surface RIS has N reflective units. The RIS controller is used to control each reflective unit on the intelligent reflective surface. The method includes the following steps:

[0055] The channel matrix between the smart reflection surface and the receiving end is determined by using the number of receiving antennas at the receiving end, the number of reflection units in the RIS, and the channel coefficient;

[0056] Determine the phase deflection of the transmitted unit pulse signal by the reflection units of different groups according to the information bits to be transmitted and the modulation order of different groups in different time slots; determine the reflection phase of the reflection units of different groups according to the information bits to be transmitted and the receiving antenna in different time slots; determine the reflection signal of the reflection unit by the reflection phase and the phase deflection;

[0057] The receiving end receives the reflected signal and uses the maximum likelihood method to perform decoding detection.

[0058] The specific sending and detection algorithms of this embodiment are as follows:

[0059] In view of the defect that the existing spatial modulation (SM) technology assisted by smart reflective surface (RIS) cannot obtain transmit diversity to resist channel fading, this embodiment proposes an Alamouti coded spatial modulation transmission method based on RIS, referred to as RIS-AlaSM method. The system model and assumptions adopted by this method are as follows: In a single-input multiple-output (SIMO) system deploying smart reflective surface RIS, the transmitter has a single antenna and the receiver has n R The RIS has N reflection units (RUs), which are located in the near field of the transmitter and can be considered as part of the transmitter. In addition, there are obstacles between the transmitter and the receiver, so there is no direct propagation from the transmitter to the receiver. The signal from the transmitter must be reflected by the RIS before it can reach the receiver. The RF link can control the status of each RU on the RIS through a RIS controller, and all channel state information (CSI) is known on the RIS, which can be used to reconstruct the phase of the channel.

[0060] The RIS-AlaSM scheme takes two symbol periods to transmit a frame of signal. The single transmitting antenna at the transmitting end sends a unit pulse signal 1=e in each time slot. j2π The N reflection units (RUs) on the RIS are equally divided into two groups, each with N / 2 RUs.

[0061] The channel matrix between the smart reflection surface and the receiving end is determined by using the number of receiving antennas at the receiving end, the number of reflection units in the RIS, and the channel coefficient. Specifically, it is:

[0062] The number of reflection units is used as the number of columns of the channel matrix, and the number of receiving antennas at the receiving end is used as the number of rows of the channel matrix;

[0063] The channel coefficients from each reflection unit to each receiving antenna are used as elements of the channel matrix;

[0064] Construct a channel matrix from the smart reflection surface to the receiving end.

[0065] Specifically, let n R ×N-dimensional matrix Indicates from N RU to n R The channel matrix between the root receiving antennas, where the (l,i)th element h l,i =|h l,i |exp(jθ l,i ) represents the channel coefficient from the i-th RU to the l-th receiving antenna, θ l,i Represents the phase of the channel coefficient, exponential function exp(jθ) = e jθ Assuming that the number of information bits to be transmitted in two symbol periods is B bits, the B information bits to be transmitted are divided into four parts, namely, B=B1+B2+B3+B4.

[0066] The implementation process of the transmitter of this scheme is divided into the following four steps:

[0067] Step 1: In the first time slot, based on the modulation order and the first group of information bits to be transmitted, the RIS controller controls the first group of reflection units to perform phase deflection on the unit pulse signal; in the first time slot, the phases of the first group of reflection units are all aligned with the receiving antenna determined by the second group of information bits to be transmitted, thereby determining the reflection phase of each reflection unit in the group;

[0068] In the time slot t1, B1=log2M bits can be mapped to any integer k1 between {0,1,…,M-1}, which is used to control the first group of RUs to shift the phase of the transmitted pulse signal 1 of the first time slot t1 via the controller. (radians), where parameter M is the modulation order; at the same time, B2 = log2n R bits in n R Select one of the receiving antennas, that is, m1∈{1,…,n R} represents the index number of the receiving antenna selected by the first group of RUs, so that the phases of the N / 2 RUs in the first group are aligned with the m1th receiving antenna, that is, the reflection phase on the i-th RU in this group is set to Therefore, the signal reflected from the i-th RU in the first group of RUs in the t1 time slot is It can be expressed as

[0069]

[0070] Step 2: In the first time slot, based on the modulation order and the third group of information bits to be transmitted, the RIS controller controls the second group of reflection units to perform phase deflection on the unit pulse signal; in the first time slot, the phases of the second group of reflection units are aligned with the receiving antenna determined by the fourth group of information bits to be transmitted, thereby determining the reflection phase of each reflection unit in the group;

[0071] In the time slot t1, B3=log2M bits can be mapped to any integer k2 between {0,1,…,M-1}, which is used by the controller to control the second group of RUs to shift the phase of the pulse signal 1 transmitted in the first time slot t1. (radians); at the same time, B4 = log2n R bits in n R Select one of the receiving antennas, that is, m2∈{1,…,n R} represents the index number of the receiving antenna selected by the second group of RUs, so that the phases of the N / 2 RUs in the second group are aligned with the m2th receiving antenna, that is, the reflection phase on the i-th RU in this group is set to Therefore, the signal reflected from the i-th RU in the second group of RUs in the t1 time slot is It can be expressed as

[0072]

[0073] For the reflection phase setting of the reflection unit, the phase of the corresponding channel coefficient can be compensated to make the complex channel coefficient a real value, thereby maximizing the signal-to-noise ratio on the selected receiving antenna.

[0074] Step 3: In the second time slot, based on the modulation order and the first group of information bits to be transmitted, the RIS controller controls the first group of reflection units to perform phase deflection on the unit pulse signal; in the second time slot, the phases of the first group of reflection units are aligned with the receiving antenna determined by the second group of information bits to be transmitted, thereby determining the reflection phase of each reflection unit in the group;

[0075] Accordingly, at time slot t2, the phase of the pulse signal transmitted by the first group of RUs is shifted (radians); at the same time, the phases of the N / 2 RUs in the first group are aligned with the m1th receiving antenna, that is, the reflection phase on the i-th RU in this group is set to Therefore, the signal reflected from the i-th RU in the first group of RUs in the t2 time slot is It can be expressed as

[0076]

[0077] Step 4: In the second time slot, based on the modulation order and the third group of information bits to be transmitted, the RIS controller controls the second group of reflection units to perform phase deflection on the unit pulse signal. In the second time slot, the phases of the second group of reflection units are aligned with the receiving antenna determined by the fourth group of information bits to be transmitted, thereby determining the reflection phase of each reflection unit in the group;

[0078] Accordingly, in the time slot t2, the second group of RUs shifts the phase of the pulse signal transmitted in the second time slot t2 to (radians); at the same time, the phases of the N / 2 RUs in the second group are aligned with the m2th receiving antenna, that is, the reflection phase on the i-th RU in this group is set to Therefore, the signal reflected from the i-th RU in the second group of RUs at time slot t2 is It can be expressed as

[0079]

[0080] In summary, B bits of information can be transmitted in the first time slot only. The second time slot uses the B information bits generated in the first time slot to perform redundant operations again. The purpose is to form a 2x2 dimensional space-time code matrix, so that the second-order transmission diversity can be obtained, which significantly reduces the bit error rate curve. Therefore, this scheme requires two time slots to transmit B information bits.

[0081] After the above four steps of reflection method, at time slots t1 and t2, the lth receiving antenna (l=1,…,n R ) can be expressed as

[0082]

[0083]

[0084] Where: w l,t represents the additive Gaussian white noise at the lth receiving antenna in the tth time slot, which has a mean of 0 and a variance of σ 2 The complex Gaussian distribution of .

[0085] Equations (5) and (6) represent the signals received by the lth receiving antenna in two time slots, respectively. Then, at the receiving end, the equations must be solved simultaneously based on the two received signals to solve the unknowns k1, k2, m1, and m2. After solving them, the bits are inversely mapped and compared with the initial B bits to calculate the bit error rate.

[0086] The receiving end receives the reflected signal and performs decoding detection using the maximum likelihood method, specifically:

[0087] The reflected signals of different time slots are used to solve equations simultaneously to determine the signal matrix model received by the receiving end;

[0088] calculating an equivalent form of the signal matrix model, and determining an equivalent channel matrix based on the equivalent form of the signal matrix model;

[0089] The orthogonality of the equivalent channel matrix is ​​used to reduce the ML decoding into two low-dimensional ML decoders;

[0090] Two low-dimensional ML decoders are used to jointly decode the reflected signals of the two time slots, and then the information bits of the reflected signals are inversely mapped according to the decoding results.

[0091] Specifically, the phase of each element in the channel matrix is ​​obtained to obtain a phase matrix and a phase vector corresponding to the activated receiving antenna, and then a signal matrix model received by the receiving end is determined, including:

[0092] First, use the channel matrix to define the phase matrix:

[0093] Defining the Phase Matrix The function angle(H) represents the phase of each channel coefficient in the matrix H, and Φ1 and Φ2 represent the front and back of the phase matrix Φ. Column and rear List.

[0094] The N×1-dimensional phase vector between the two groups of RUs and the m1th and m2th receiving antennas is defined as:

[0095]

[0096] Where: Φ1(m1) represents the m1th row of the matrix Φ1, and the superscript () T Represents vector transpose. Further, the exponential vector of vector p is defined as

[0097] Arranging the above received signals (5) and (6) into matrix form yields:

[0098]

[0099] That is, Y = HX + W, where: Representation vector 1st to List, Representation vector No. To N columns, symbol It can be seen from equation (8) that the signal reflected by the RIS forms an N×2-dimensional space-time code X. It is easy to verify that any two different codes X and

[0100] The rank of the difference is 2. According to the rank criterion for designing space-time coding, the transmission scheme can obtain second-order transmit diversity.

[0101] 2. Low-complexity detection method of RIS-AlaSM scheme

[0102] Assuming that the receiver has accurate channel state information CSI, the maximum likelihood (ML) decoding of the RIS-AlaSM scheme can be expressed as

[0103]

[0104] Among them, the ML decoding in formula (9) needs to jointly decode the four parameters (k1, k2, m1, m2), so it is necessary to calculate the ML metric The decoding complexity is high. Since it is observed that the encoding matrix in equation (8) satisfies orthogonality, the above ML decoding can be decoupled into two low-dimensional ML decodings by using orthogonality, thereby reducing the decoding complexity.

[0105] Calculate the equivalent form of the signal matrix model, and determine the equivalent channel matrix based on the equivalent form of the signal matrix model, specifically:

[0106] Since the receiver has accurate channel state information CSI, the system model (8) can be expressed as

[0107]

[0108] Where: n R ×2-dimensional matrix Depending on the activated receive antenna index m1 and m2, it has the following form

[0109]

[0110] H1 and H2 are the front and back faces of the channel matrix H. Column and rear Let n R ×1-dimensional vectors y1 and y2 represent two columns of the received signal Y, and let n R ×1-dimensional vectors h1 and h2 represent matrices Take the conjugate of y2 and reorganize the received signal Y into 2n R ×1-dimensional column vector, the equivalent model of formula (10) is obtained as

[0111]

[0112] Where: H eq is 2n R ×2-dimensional equivalent channel matrix. It can be verified that the equivalent channel matrix Heq The two columns g1 and g2 are mutually orthogonal, that is, (superscript () H denotes taking the conjugate transpose).

[0113] The orthogonality of the equivalent channel matrix is ​​used to reduce the ML decoding dimension into two low-dimensional ML decoders. Therefore, the ML detector in equation (9) can be decoupled into two independent low-dimensional ML detectors:

[0114]

[0115]

[0116] The estimated values ​​of the activated receive antenna indices m1 and m2 are

[0117]

[0118] Therefore, the two low-dimensional ML decoders based on (12) and (13) complete the joint decoding of the four parameters (k1, k2, m1, m2), and the final estimated values ​​of k1 and k2 are and Then by and The value of can be inversely mapped to the information bit, which can then be compared with the B information bits input by the transmitter to calculate the bit error rate (BER). As can be seen from formula (12), the reduced-dimensional ML detector only needs to calculate The sub-ML metric reduces the decoding complexity.

[0119] At the receiving end, we need to estimate the B bits input by the transmitting end, and all the B bits are contained in two parts: the first part of the bits is contained in k1 and k2 in the phase deviation values ​​of the unit pulse signal transmitted by each group of RUs, and the second part is contained in the index numbers m1 and m2 of the receiving antennas selected by each group of RUs. Therefore, equations (12) and (13) are used to estimate (k1, k2) and (m1, m2) respectively. After these two parts are estimated, B information bits can be inversely mapped.

[0120] 3. Spectral efficiency

[0121] The spectrum efficiency of RIS-AlaSM is

[0122]

[0123] The unit of spectrum efficiency of spatial modulation (SM) transmission is bpcu, bits / per channel use, which indicates the number of bits that can be transmitted using the channel per unit time.

[0124] 4. Diversity order

[0125] By calculating the minimum codeword distance of the RIS-AlaSM scheme, we can calculate the minimum codeword distance for two different RIS-AlaSM signals X and have Therefore, the RIS-AlaSM scheme can obtain second-order transmit diversity.

[0126] The focus of this embodiment is to propose a transmission scheme for RIS-assisted communication, that is, what kind of coding scheme should be adopted at the transmitting end to obtain better system performance. Of course, the receiving end must have corresponding decoding measures, so the detection algorithm of the receiving end is also provided. After the scheme detects the estimated values ​​of the four parameters, the information bits can be inversely mapped, thereby realizing the transmission of information. By comparing the information bits obtained by the receiving end with the B information bits sent by the transmitting end, the bit error rate of the scheme during transmission can be calculated to measure the performance of the scheme.

[0127] 5. Simulation Experiment

[0128] This section presents the simulation results of the bit error performance of the RIS-AlaSM scheme and compares it with the bit error performance of the RIS-RQRM algorithm.

[0129] For the sake of fairness, the error performance of the RIS-AlaSM scheme and the RIS-RQRM scheme are compared below at the same spectral efficiency. Figure 2 and Figure 3 The error performance comparison of the two transmission schemes when the spectrum efficiency is 4bpcu and 6bpcu is given in Figure 2 and Figure 3 In the example, the number of reflection units N on the RIS is set to 128 and 64 respectively. Figure 2 and Figure 3 It can be seen that at the spectrum efficiency of 4bpcu and 6bpcu, the RIS-AlaSM scheme has a significant performance gain over the RIS-RQRM scheme. This is because the former can obtain second-order transmit diversity while the latter only obtains first-order diversity. Therefore, the RIS-AlaSM scheme is more resistant to wireless channel fading than the RIS-RQRM scheme. In addition, it is observed that when the number of reflection units N on the RIS is large, both schemes have different degrees of performance improvement. This is because the reflection of the RU on the RIS forms a coherent superposition of signals at the activated receiving antenna. When the number of RUs is larger, the SNR at the activated receiving antenna is larger, so the performance improvement is more obvious.

[0130] Embodiment 2

[0131] This embodiment provides a space-time coded spatial modulation system based on a smart reflective surface, including:

[0132] A transmitting end, including a single transmitting antenna, for transmitting a transmitting signal to the smart reflecting surface;

[0133] The intelligent reflection surface includes a plurality of reflection units, which are used to determine the phase deflection of the transmitted unit pulse signal by the reflection units of different groups using different groups of information bits to be transmitted and modulation orders in different time slots; determine the reflection phases of the reflection units of different groups according to the different groups of information bits to be transmitted and the receiving antennas in different time slots; determine the reflection signal of the reflection unit using the reflection phase and the phase deflection, and reflect the reflection signal to the receiving end;

[0134] The receiving end includes multiple receiving antennas for receiving reflected signals and performing decoding detection using the maximum likelihood method.

[0135] The examples and application scenarios implemented by the above modules and corresponding steps are the same, but are not limited to the contents disclosed in the above embodiment 1. It should be noted that the above modules as part of the system can be executed in a computer system such as a set of computer executable instructions.

[0136] The description of each embodiment in the above embodiments has different emphases. For parts not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0137] The proposed system can be implemented in other ways. For example, the system embodiment described above is only illustrative, and the division of the modules is only a logical function division. In actual implementation, there may be other division methods, such as multiple modules can be combined or integrated into another system, or some features can be ignored or not executed.

[0138] Although the above describes the specific implementation mode of the present invention in conjunction with the accompanying drawings, it is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art on the basis of the technical solution of the present invention without creative work are still within the scope of protection of the present invention.

Claims

1. A space-time coded spatial modulation method based on an intelligent reflective surface, using a single-input multiple-output system assisted by an intelligent reflective surface, wherein the intelligent reflective surface RIS has N reflective units, and each reflective unit on the intelligent reflective surface is controlled by a RIS controller, characterized in that: include: The channel matrix between the smart reflection surface and the receiving end is determined by using the number of receiving antennas at the receiving end, the number of reflection units in the RIS, and the channel coefficient; Determine the phase deflection of the transmitted unit pulse signal by the reflection units of different groups according to the information bits to be transmitted and the modulation order of different groups in different time slots; determine the reflection phase of the reflection units of different groups according to the information bits to be transmitted and the receiving antenna in different time slots; determine the reflection signal of the reflection unit by the reflection phase and the phase deflection; The receiving end receives the reflected signal and uses the maximum likelihood method to perform decoding detection.

2. The space-time coded spatial modulation method based on the smart reflective surface according to claim 1, characterized in that: The channel matrix between the smart reflection surface and the receiving end is determined by using the number of receiving antennas at the receiving end, the number of reflection units in the RIS, and the channel coefficient, specifically: The number of reflection units is used as the number of columns of the channel matrix, and the number of receiving antennas at the receiving end is used as the number of rows of the channel matrix; The channel coefficients from each reflection unit to each receiving antenna are used as elements of the channel matrix; Construct a channel matrix from the smart reflection surface to the receiving end.

3. The space-time coded spatial modulation method based on the smart reflective surface according to claim 1, characterized in that: The method occupies two symbol periods to transmit a frame of signal, and a single transmitting antenna at the transmitting end sends a unit pulse signal to the intelligent reflecting surface in both the first time slot and the second time slot.

4. The space-time coded spatial modulation method based on the smart reflective surface according to claim 1, characterized in that: The reflection units on the smart reflection surface are evenly divided into two groups.

5. The space-time coded spatial modulation method based on smart reflective surface according to claim 1, characterized in that: The method of using different groups of information bits to be transmitted and modulation orders in different time slots to determine the phase deflection of the unit pulse signal transmitted by different groups of reflection units is specifically as follows: In the first time slot, based on the modulation order and the first group of information bits to be transmitted, the RIS controller controls the first group of reflection units to perform phase deflection on the unit pulse signal; In the first time slot, based on the modulation order and the third group of information bits to be transmitted, the RIS controller controls the second group of reflection units to perform phase deflection on the unit pulse signal; In the second time slot, based on the modulation order and the first group of information bits to be transmitted, the RIS controller controls the first group of reflection units to perform phase deflection on the unit pulse signal; In the second time slot, the second group of reflection units are controlled by the RIS controller to perform phase shift on the unit pulse signal based on the modulation order and the third group of information bits to be transmitted.

6. The space-time coded spatial modulation method based on smart reflective surface according to claim 1, characterized in that: The determination of reflection phases of different groups of reflection units according to different groups of information bits to be transmitted and receiving antennas in different time slots is specifically as follows: In the first time slot, aligning the phases of the first group of reflection units with the receiving antenna determined by the second group of information bits to be transmitted, thereby determining the reflection phase of each reflection unit in the group; In the first time slot, aligning the phases of the second group of reflection units with the receiving antenna determined by the fourth group of information bits to be transmitted, thereby determining the reflection phase of each reflection unit in the group; In the second time slot, the phases of the first group of reflection units are aligned with the receiving antenna determined by the second group of information bits to be transmitted, so as to determine the reflection phase of each reflection unit in the group; In the second time slot, the phases of the second group of reflection units are aligned with the receiving antenna determined by the fourth group of information bits to be transmitted, so as to determine the reflection phase of each reflection unit in the group.

7. The space-time coded spatial modulation method based on smart reflective surface according to claim 1, characterized in that: The use of the reflection phase and the phase deflection to determine the reflection signal of the reflection unit is specifically as follows: In the first time slot, a first reflection signal of the first time slot is determined according to the product of the phase deflection of the first group of reflection units to the unit pulse signal and the reflection coefficient determined by the reflection phase of the first group of reflection units; In the first time slot, a second reflection signal of the first time slot is determined according to the product of the phase deflection of the second group of reflection units on the unit pulse signal and the reflection coefficient determined by the reflection phase of the second group of reflection units; In the second time slot, a first reflection signal of the second time slot is determined according to the product of the phase deflection of the first group of reflection units to the unit pulse signal and the reflection coefficient determined by the reflection phase of the first group of reflection units; In the second time slot, a second reflection signal of the second time slot is determined according to the product of the phase deflection of the second group of reflection units to the unit pulse signal and the reflection coefficient determined by the reflection phase of the second group of reflection units.

8. The space-time coded spatial modulation method based on smart reflective surface according to claim 1, characterized in that: The receiving end receives the reflected signal and performs decoding detection using the maximum likelihood method, specifically: The phase of each element in the channel matrix is ​​taken to obtain a phase matrix and a phase vector corresponding to the activated receiving antenna, and then a signal matrix model received by the receiving end is determined; calculating an equivalent form of the signal matrix model, and determining an equivalent channel matrix based on the equivalent form of the signal matrix model; The orthogonality of the equivalent channel matrix is ​​used to reduce the ML decoding into two low-dimensional ML decoders; Two low-dimensional ML decoders are used to jointly decode the reflected signals of the two time slots, and then the information bits of the reflected signals are inversely mapped according to the decoding results.

9. The space-time coded spatial modulation method based on smart reflective surface according to claim 1, characterized in that: The reflected signals constitute an N×2-dimensional space-time code X, and a second-order transmit diversity is obtained, wherein N is the number of reflection units.

10. A space-time coded spatial modulation system based on a smart reflective surface, characterized in that: include: A transmitting end, including a single transmitting antenna, for transmitting a transmitting signal to the smart reflecting surface; The intelligent reflection surface includes a plurality of reflection units, which are used to determine the phase deflection of the transmitted unit pulse signal by the reflection units of different groups using different groups of information bits to be transmitted and modulation orders in different time slots; determine the reflection phases of the reflection units of different groups according to the different groups of information bits to be transmitted and the receiving antennas in different time slots; determine the reflection signal of the reflection unit using the reflection phase and the phase deflection, and reflect the reflection signal to the receiving end; The receiving end includes multiple receiving antennas for receiving reflected signals and performing decoding detection using the maximum likelihood method.

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