A non-orthogonal multiple access backscatter communication method

Abstract

The invention discloses a non-orthogonal multiple access backscatter communication method, which belongs to the field of communication technology. The non-orthogonal multiple access backscatter communication method comprises: transmitting an electromagnetic wave signal generated by a transmitter to a backscatter tag; the backscatter tag adjusts and spreads the electromagnetic wave signal to obtain a NOMA backscatter signal; the NOMA backscatter signal amplifies the signal through a tunnel diode circuit; the amplified signal is reflected by the backscatter tag and reaches a receiver; the non-orthogonal multiple access backscatter communication method, based on a demodulation scheme of a tunnel diode, increases the power difference between multiple users, thereby improving the demodulation performance, and secondly, through an improved minimum mean square error continuous interference cancellation (MMSE-SIC) algorithm, a special frame design is used to solve the carrier frequency offset (CFO) problem caused by the use of a low-precision oscillator.

Description

Technical Field

[0001] The invention relates to the technical field of communication, in particular to a non-orthogonal multiple access backscatter communication method. Background Art

[0002] Current backscatter communication technology has attracted increasing attention due to its remarkable low power consumption and low cost, and has become a promising technology for connecting everyday IoT devices. These inherent characteristics have driven the deployment of large-scale backscatter tags, making various potential applications such as smart homes, smart cities, and smart industries possible. However, traditional backscatter designs prioritize energy efficiency while using multiple access schemes that sacrifice spectral efficiency, hindering their large-scale application. Therefore, it is necessary to develop a non-orthogonal multiple access backscatter communication system to improve the system's spectral efficiency and achieve large-scale deployment. Summary of the invention

[0003] In view of the above problems existing in the prior art, the present invention is proposed.

[0004] Therefore, the technical problem to be solved by the present invention is a problem.

[0005] To achieve the above object, the present invention provides the following technical solution: a non-orthogonal multiple access backscatter communication method, comprising:

[0006] Transmitting the electromagnetic wave signal generated by the transmitter to the backscattering tag;

[0007] The backscatter tag adjusts and spreads the electromagnetic wave signal to obtain the NOMA backscatter signal;

[0008] The NOMA backscattered signal is amplified by a tunnel diode circuit;

[0009] The amplified signal is reflected by the backscattered tag and reaches the receiver.

[0010] As a further solution of the present invention: the electromagnetic wave signal is modulated and spread-spectrumed through the NOMA scheme of the backscatter tag and the spread spectrum sequence pair in turn.

[0011] As a further solution of the present invention: the spread spectrum sequence is composed of symbols with different amplitudes and phases.

[0012] As a further solution of the present invention: the backscatter signal S out The formula is:

[0013]

[0014] Among them, Γ n is the nth reflection coefficient of the node, Z Lnis the nth load impedance of the node, Z0 is the characteristic impedance of the node, S in is the incident signal.

[0015] As a further solution of the present invention: when all symbols of the spread spectrum sequence have the same amplitude and different phases, the node only needs one Z L = load impedance of Z0;

[0016] When the RF switch of the node is turned on, the backscattered signal S out for:

[0017]

[0018] It means there is no reflection;

[0019] On the contrary, when the RF switch is turned off, the load impedance can be regarded as ∞ and the backscattered signal S out for:

[0020]

[0021] Indicates total reflection.

[0022] As a further solution of the present invention: the NOMA solution adopts modulation of the RF switch control signal.

[0023] As a further solution of the present invention: the amplified signal received by the receiver is demodulated by using an MMSE-SIC algorithm, and CFO is added to the signal.

[0024] As a further solution of the present invention: the receiver estimates the CFO through the frame structure;

[0025] The frame structure preamble is used for frame synchronization, and the prefix and suffix sequences are used for CFO and channel estimation.

[0026] As a further solution of the present invention: the received signal y(t) of the receiver is:

[0027]

[0028] in, is the channel coefficient of the jth node, represents the forward channel from the transmitter to the node, represents the backward channel from the node to the receiver, β j is the attenuation coefficient, is the node signal that includes CFO, It means that the jth node and node signal are included, and the actual frequency shift of the jth node is f s -f j , its f jis the CFO of the jth node, and w(t) is the noise.

[0029] As a further solution of the present invention: the signal received by the receiver including N nodes is expressed as:

[0030]

[0031] where H=(h1,h2,...,h N ) T is the channel vector, is the node signal vector containing CFO, w represents noise, T is the symbol of matrix transpose, The signal indicating label ejection; the time interval T between the prefix sequence and the suffix sequence p =L p +M) / R, where R represents the symbol rate in the tag, L p Represents the effective data length, and M represents the length of Preamble 1 and Preamble 2.

[0032] Compared with the prior art, the beneficial effects of the present invention are: the non-orthogonal multiple access backscatter communication method, based on the demodulation scheme of the tunnel diode, increases the power difference between multiple users, thereby improving the demodulation performance, and secondly, through the improved minimum mean square error successive interference cancellation (MMSE-SIC) algorithm, a special frame design is used to solve the carrier frequency offset (CFO) problem caused by the use of a low-precision oscillator. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work. Among them:

[0034] Figure 1 It is an overall flow chart of the non-orthogonal multiple access backscatter communication method of the present invention.

[0035] Figure 2 The system model block diagram of the non-orthogonal multiple access backscatter communication method of the present invention.

[0036] Figure 3 The frame structure design diagram of the non-orthogonal multiple access backscatter communication method of the present invention.

[0037] Figure 4 The present invention is a flowchart of MMSE-SIC demodulation of the non-orthogonal multiple access backscatter communication method. DETAILED DESCRIPTION

[0038] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below in conjunction with the accompanying drawings.

[0039] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0040] Secondly, the present invention is described in detail with reference to the schematic diagram. When describing the embodiments of the present invention in detail, for the sake of convenience, the cross-sectional diagrams showing the device structure will not be partially enlarged according to the general scale, and the schematic diagrams are only examples, which should not limit the scope of protection of the present invention. In addition, in actual production, the three-dimensional dimensions of length, width and depth should be included.

[0041] Furthermore, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The term "in one embodiment" that appears in different places in this specification does not necessarily refer to the same embodiment, nor is it a separate or selective embodiment that is mutually exclusive with other embodiments.

[0042] Example 1

[0043] like Figures 1 to 4 As shown, the present invention provides a technical solution: a non-orthogonal multiple access backscatter communication method, comprising:

[0044] S1: Transmit the electromagnetic wave signal generated by the transmitter to the backscattering tag;

[0045] Furthermore, backscattering uses electromagnetic waves that already exist in the environment for communication, such as signals emitted by base stations, mobile phones, etc., and a transmitter is used to transmit a single-carrier electromagnetic wave signal existing in the simulated environment, and the electromagnetic wave signal is transmitted to the backscatter tag, wherein the transmitter completes the modulation of the high-frequency carrier by the useful low-frequency signal, and converts it into an electromagnetic wave signal with a certain bandwidth at a certain center frequency and suitable for transmission through an antenna; specifically, the transmitter sends a single-carrier signal, which is emitted into the backscatter node, and is modulated on the backscatter node to emit a backscatter signal.

[0046] S2: The backscatter tag adjusts and spreads the electromagnetic wave signal to obtain the NOMA backscatter signal;

[0047] Specifically, the electromagnetic wave signal is modulated and spread through the NOMA scheme of the backscatter tag and the spread spectrum sequence in turn; wherein the spread spectrum sequence is composed of symbols of different amplitudes and phases, such as the symbol 1+i; the NOMA scheme uses the modulation of the RF switch control signal, which is specifically demodulated through MMSE-SIC.

[0048] The NOMA backscatter signal design simplifies the hardware design of the backscatter tag by switching multiple load impedances to generate multiple frequency-shifted signals with different phases, and allows the generation of signals suitable for the NOMA scheme, wherein multiple load impedance switches are switched through a single-pole multi-throw RF switch according to the impedance matching principle, and the load impedance is set on the tag hardware.

[0049] Furthermore, the backscattered signal S out The formula is:

[0050]

[0051] Among them, Γ n is the nth reflection coefficient of the node, Z Ln is the nth load impedance of the node, Z0 is the characteristic impedance of the node, S in is the incident signal.

[0052] It should be noted that nodes and tags collectively refer to backscatter nodes, which are hardware similar to RFID.

[0053] Specifically, the backscatter node modulates the signal using the NOMA scheme and spreads the signal emitted to the backscatter node using a spreading sequence. The spreading sequence consists of symbols with different amplitudes and phases. When all symbols of the spreading sequence have the same amplitude and different phases, the node only needs one Z L = load impedance of Z0;

[0054] When the RF switch of the node is turned on, the backscattered signal S out for:

[0055]

[0056] It means there is no reflection;

[0057] On the contrary, when the RF switch is turned off, the load impedance can be regarded as ∞ and the backscattered signal S out for:

[0058]

[0059] Indicates total reflection.

[0060] Furthermore, the present invention designs a spreading sequence, and the tag selects the symbols of all spreading sequences from the QPSK symbols; specifically, each element of the spreading sequence comes from the set before normalization: {1+i, -1+i, -1-i, 1-i}; when the code length is L, the total number of available spreading sequences is 4 L ; The elements in a QPSK symbol have the same amplitude, so a load impedance equal to Z0 needs to be assigned to a tag; To improve signal reliability, the tag modulates the incident signal by changing the state of the radio frequency (RF) switch, causing the frequency of the backscattered signal to shift relative to the original excitation signal; The frequency shift helps reduce interference on the direct path, allowing the receiver to distinguish the backscattered signal; The tag achieves information modulation by controlling the state of the RF switch.

[0061] S3: NOMA backscattered signal is amplified by the tunnel diode circuit;

[0062] The amplified signal received by the receiver is demodulated by the MMSE-SIC algorithm, and the CFO is added to the signal. It should be noted that the receiver estimates the CFO through the frame structure; the frame structure preamble is used for frame synchronization, and the prefix and suffix sequences are used for CFO and channel estimation.

[0063] Specifically, since the MMSE-SIC algorithm is affected by the tag power, the negative resistance characteristic of the tunnel diode is used to artificially control the tag power, so that the power difference between the tags is increased, so that the tag data can be better demodulated; a tunnel diode programmable circuit is installed on each tag to control the power; then at the receiving end, the signal is demodulated by the MMSE-SIC algorithm (Minimum Mean Square Error-Successive Interference Cancellation, MMSE-SIC minimum mean square error continuous interference cancellation) and CFO is compensated in the signal; Figure 4 As shown in the figure, the SINR of the tags are sorted during the demodulation process. During this process, the signals of other tags will affect the signal of the tag being demodulated. If the power difference between the tags is artificially increased, the impact of other tag signals will be smaller; and the negative resistance characteristic of the tunnel diode enables it to increase the signal power. This characteristic is used to design a programmable circuit so that the tag power can be controlled, thereby improving the demodulation performance.

[0064] S4: The amplified signal is reflected by the backscatter tag and reaches the receiver.

[0065] The present invention develops a demodulation scheme based on tunnel diodes to increase the power difference between multiple users, thereby improving the demodulation performance. Secondly, the present invention solves the carrier frequency offset (CFO) problem caused by the use of a low-precision oscillator by using an improved minimum mean square error-successive interference cancellation (MMSE-SIC) algorithm and a special frame design.

[0066] Example 2

[0067] Reference Figures 1 to 4 , this embodiment is different from the previous embodiment in that an improved MMSE-SIC demodulation scheme is provided; specifically, due to the existence of carrier frequency offset in the NOMA-Backscatter system; a frame structure is designed to assist the receiver in estimating CFO; for this purpose, a frame structure of the NOMA-Backscatter system is designed to facilitate compensation of CFO in the tag; as Figure 3 The preamble in the frame structure is used for frame synchronization, and the prefix and suffix sequences are used for CFO and channel estimation; the encoded data is used as the payload and spread using the complex spreading sequence; the CFO is calculated at the beginning and end of the frame; in addition, the receiver must eliminate interference from other tags when estimating a certain tag.

[0068] Specifically, assuming that the actual frequency shift of the jth node is f s -f j , where f j is the CFO of the jth node; when the system contains only the jth node and the node signal is expressed as When , the receiver's received signal y(t) is:

[0069]

[0070] in, is the channel coefficient of the jth node, represents the forward channel from the transmitter to the node, represents the backward channel from the node to the receiver, β j is the attenuation coefficient, is the node signal that includes CFO, It means that the jth node and node signal are included, and the actual frequency shift of the jth node is f s -f j , its f j is the CFO of the jth node, w(t) is the noise; f is the frequency, and t is the time.

[0071] Among them, the signal received by the receiver containing N nodes is expressed as:

[0072]

[0073] where H=(h1,h2,...,h N ) T is the channel vector, is the node signal vector containing CFO, w represents noise, T is the symbol of matrix transpose, The signal indicating label ejection; the time interval T between the prefix sequence and the suffix sequence p =L p +M) / R, where R represents the symbol rate in the tag, L p Represents the effective data length, M represents the length of Preamble 1 and Preamble 2, T is the symbol of matrix transposition, Signal that a tab has been ejected.

[0074] Therefore, the phase rotation between the prefix sequence and the suffix sequence caused by CFO is:

[0075]

[0076] Because the phase rotation must satisfy To avoid phase ambiguity during measurement; We get an estimated CFO

[0077] When estimating the CFO of the mth label, we regard the signals of other sections as interference signals to reconstruct the received signal, so we have:

[0078]

[0079] Assume that A is a Hadamard matrix of size M*M, and set P = {y1, y2, ..., y M}, Then the phase of Preamble 1 can be obtained:

[0080]

[0081] Among them, A m,k Yes A m The kth element of . When k ranges from 1 to M, is approximately equal to a constant λ. Then Φ m Rebuild as:

[0082]

[0083] Similarly, the phase of Preamble 1 ism It is expressed as:

[0084]

[0085] Therefore, the phase rotation between Preamble 1 and Preamble 2 of the mth node is Estimate CFO using the following formula:

[0086]

[0087] That is, finally we get all the estimated CFO values After that, frequency offset compensation is performed. When decoding the mth node, the received data y k and Multiply to compensate for the frequency deviation. The mth signal after compensation is expressed as:

[0088]

[0089] when Close to f m hour, Approximately h m x m,k ,h m It is obtained by channel estimation. In this way, in the process of decoding the data of the m-th node or estimating its channel parameters, the CFO of the m-th node can be effectively compensated.

[0090] like Figure 4 The y signal is the signal of the label popping up, and the receiver receives y; the signal of the set is a set A, which contains 1, 2, 3, 4... signals; the untranslated user is the user who demodulates incorrectly during the demodulation process; the SINR is obtained by estimating the channel of the user through the receiver and sorting; CRC is a cyclic redundancy check. Specifically, CRC first appends a check code of R bits to the K bits of data to be sent, and then generates a new frame and sends it to the receiving end; after the receiving end receives the new frame, it verifies whether the received data is correct based on the received data and the check code; the additional check code must make the generated new frame divisible by a specific number jointly selected by the sending end and the receiving end ("modulo 2 division"); the receiving end divides the received new frame by the selected divisor; because a number has been appended before the data frame is sent, the "remainder removal" process has been performed (that is, it can be divided evenly), so the result is no remainder; if there is a remainder, it indicates that an error has occurred in the transmission process of the frame.

[0091] The present invention proposes and implements a non-orthogonal multiple access backscatter communication system, which generates a backscatter signal suitable for the NOMA scheme in resource-constrained hardware, proposes a demodulation scheme based on a tunnel diode, and improves the demodulation performance; designs a special sequence in the frame structure, and uses it to eliminate the frequency deviation effect in MMSE-SIC demodulation; the non-orthogonal multiple access backscatter system of the present invention effectively improves the spectrum efficiency without increasing additional bandwidth, ensures the low energy consumption characteristics of the system through optimized design, and reduces the overall cost of the system.

[0092] Example 3

[0093] This embodiment is different from the previous embodiment in that a specific comparison description is provided. Specifically, the existing solution one adds MUSA through the 5G Internet of Things. The added MUSA can support true scheduling-free high overload access through low-correlation complex domain multivariate codes and advanced multi-user detection based on serial interference cancellation (SIC). After experimental comparison between the existing solution one and this solution, it was found that the load rate is defined as the ratio of the number of tags to the sequence length, the code length is 4, and the number of accessed tags is 8, so the load rate is 200%.

[0094] Existing solution 2 enables OFDMA in Wi-Fi backscatter, and the excitation signal is reflected, modulated and shifted by the tag into the frequency band of the OFDM subcarrier; OFDMA is achieved by coordinating the tags to simultaneously transmit information to the receiver with orthogonal subcarriers through backscattering; the above existing solutions are compared with this solution through simulation experiments, and it is found that the existing effect of this solution shows that the spectrum efficiency is 1.73 times that of the existing advanced solution 2.

[0095] Importantly, it should be noted that the construction and arrangement of the present application shown in a number of different exemplary embodiments are only exemplary. Although only a few embodiments are described in detail in this disclosure, it should be readily understood by those who refer to this disclosure that many modifications are possible, for example, the size, scale, structure, shape and proportion of various elements, and parameter values ​​such as temperature, pressure, etc., mounting arrangements, use of materials, color, directional changes, etc., without substantially departing from the novel teachings and advantages of the subject matter described in the application. For example, the element shown as integrally formed can be composed of multiple parts or elements, the position of the element can be inverted or otherwise changed, and the nature or number or position of the discrete element can be changed or changed. Therefore, all such modifications are intended to be included in the scope of the present invention. The order or sequence of any process or method steps can be changed or reordered according to alternative embodiments. In the claims, any "device plus function" clause is intended to cover the structure of the execution function described herein, and is not only structurally equivalent but also equivalent structure. Without departing from the scope of the present invention, other substitutions, modifications, changes and omissions can be made in the design, operating conditions and arrangement of the exemplary embodiments. Therefore, the invention is not limited to a specific embodiment, but extends to numerous modifications still falling within the scope of the appended claims.

[0096] Furthermore, in order to provide a concise description of exemplary embodiments, all features of an actual embodiment may not be described, i.e., those features that are not relevant to the best mode presently contemplated for carrying out the invention or those features that are not relevant to implementing the invention.

[0097] It should be understood that in the development of any actual implementation, as in any engineering or design project, numerous implementation-specific decisions may be made. Such a development effort may be complex and time-consuming, but for those of ordinary skill having the benefit of this disclosure, the development effort will be a routine task of design, fabrication, and production without undue experimentation.

[0098] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A non-orthogonal multiple access backscatter communication method, characterized in that: include, Transmitting the electromagnetic wave signal generated by the transmitter to the backscattering tag; The backscatter tag adjusts and spreads the electromagnetic wave signal to obtain the NOMA backscatter signal; The NOMA backscattered signal is amplified by a tunnel diode circuit; The amplified signal is reflected by the backscattered tag and reaches the receiver.

2. The non-orthogonal multiple access backscatter communication method according to claim 1, characterized in that: The electromagnetic wave signal is modulated and spread through the NOMA scheme of the backscatter tag and the spreading sequence pair in turn.

3. The non-orthogonal multiple access backscatter communication method according to claim 1 or 2, characterized in that: The spreading sequence consists of symbols of different amplitudes and phases.

4. The non-orthogonal multiple access backscatter communication method according to claim 3, characterized in that: Backscatter signal S out The formula is: Among them, Γ n is the nth reflection coefficient of the node, Z Ln is the nth load impedance of the node, Z0 is the characteristic impedance of the node, S in is the incident signal.

5. The non-orthogonal multiple access backscatter communication method according to claim 4, characterized in that: When all symbols of the spreading sequence have the same amplitude and different phases, the node only needs one Z L = load impedance of Z0; When the RF switch of the node is turned on, the backscattered signal S out for: It means there is no reflection; On the contrary, when the RF switch is turned off, the load impedance can be regarded as ∞ and the backscattered signal S out for: Indicates total reflection.

6. The non-orthogonal multiple access backscatter communication method according to claim 5, characterized in that: The NOMA solution uses RF switches to control the modulation of the signal.

7. The non-orthogonal multiple access backscatter communication method according to claim 6, characterized in that: The amplified signal received by the receiver is demodulated by the MMSE-SIC algorithm, and the CFO is added to the signal.

8. The non-orthogonal multiple access backscatter communication method according to claim 7, characterized in that: The receiver estimates CFO through the frame structure; The frame structure preamble is used for frame synchronization, and the prefix and suffix sequences are used for CFO and channel estimation.

9. The non-orthogonal multiple access backscatter communication method according to claim 8, characterized in that: The received signal y(t) of the receiver is: in, is the channel coefficient of the jth node, represents the forward channel from the transmitter to the node, represents the backward channel from the node to the receiver, β j is the attenuation coefficient, is the node signal that includes CFO, It means that the jth node and node signal are included, and the actual frequency shift of the jth node is f s -f j , its f j is the CFO of the jth node, and w(t) is the noise.

10. The non-orthogonal multiple access backscatter communication method according to claim 9, characterized in that: The signal received by the receiver containing N nodes is expressed as: where H=(h1,h2,...,h N ) T is the channel vector, is the node signal vector containing CFO, w represents noise, T is the symbol of matrix transpose, The signal indicating label ejection; the time interval T between the prefix sequence and the suffix sequence p =L p +M) / R, where R represents the symbol rate in the tag, L p Represents the effective data length, and M represents the length of Preamble 1 and Preamble 2.

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