Method for separating multi-stream same-frequency signals in frequency domain based on single-channel metasurface receiver

Abstract

The application provides a multi-stream co-frequency signal frequency domain separation method based on a single-channel metasurface receiver. The method comprises the following steps: step 1: a multi-path parameter estimation method is used to obtain the number of signals, the angle of arrival and the channel coefficient in the current environment, and the switching period of the electromagnetic unit state on the metasurface is determined according to the maximum received signal bandwidth; step 2: a multi-stream co-frequency signal frequency domain separation receiving model based on a single-channel metasurface receiver is established according to the obtained number of signals, the angle of arrival, the signal coefficient and the switching period; step 3: the periodic code word of the metasurface is searched to move the multi-stream co-frequency signals with different angles of arrival to different frequencies, with the maximum signal-to-noise ratio of the received signal of the multi-stream co-frequency signal frequency domain separation receiving model as the target; and step 4: the signals moved to different frequencies are sampled, filtered and demodulated.

Description

Technical Field

[0001] This invention relates to the field of wireless communication technology, and in particular to a method for frequency domain separation of multi-stream co-frequency signals based on a single-channel metasurface receiver. Background Technology

[0002] With the deployment of large-scale MIMO arrays in 5G communication systems, it has become increasingly apparent that the increased number of array elements and radio frequency links has significantly increased the power consumption and cost of the communication system. In practical applications, this has even led to the need for system switching on / off during busy / idle periods to avoid power consumption when only a few users are using the system, resulting in problems such as unstable signal strength and low signal-to-noise ratio. Therefore, ensuring high array gain while reducing array cost and power consumption remains a challenging problem.

[0003] In recent years, reconfigurable intelligent surfaces (RIS) based on metamaterial design have attracted widespread attention as a potential technology for 6G wireless communication systems. RIS are typically two-dimensional planar metamaterial arrays composed of a large number of uniformly arranged passive reflective or transmissive electromagnetic units. They do not require complex radio frequency links and can directly influence electromagnetic waves in free space by manipulating the amplitude, phase, and polarization of each electromagnetic unit. Therefore, compared to traditional massive MIMO array receivers, single-channel receivers based on RIS (referred to as "single-channel RIS receivers") have advantages such as low cost, low power consumption, and ease of deployment.

[0004] Large-scale MIMO arrays employ multiple radio frequency channels, effectively solving the aliasing problem of receiving signals of the same frequency but different directions simultaneously. However, single-channel metasurface receivers only have one radio frequency channel, making it difficult to simultaneously receive signals of the same frequency but different directions. Therefore, a method is needed to enable single-channel metasurface receivers to simultaneously receive signals of the same frequency from different directions in space, thereby achieving multi-stream signal separation and greatly improving spectral efficiency. Summary of the Invention

[0005] To address the high cost of existing multi-stream signal separation methods that require multiple array elements and multiple radio frequency channels, this invention provides a frequency domain separation method for multi-stream co-frequency signals based on a single-channel metasurface receiver.

[0006] This invention provides a method for frequency domain separation of multi-stream co-frequency signals based on a single-channel metasurface receiver, comprising:

[0007] Step 1: Use the multipath parameter estimation method to obtain the number of signals, angle of arrival, and channel coefficient in the current environment, and determine the switching period of the electromagnetic unit state on the metasurface based on the maximum received signal bandwidth;

[0008] Step 2: Establish a frequency domain separation and reception model for multi-stream co-frequency signals based on a single-channel metasurface receiver, according to the number of acquired signals, angle of arrival, signal coefficients, and switching period;

[0009] Step 3: With the goal of maximizing the signal-to-noise ratio of the received signal in the frequency domain separation receiving model of multi-stream co-frequency signals, find the periodic codeword of the metasurface to shift the multi-stream co-frequency signals with different angles of arrival to different frequencies respectively.

[0010] Step 4: Sample, filter, and demodulate the signals moved to different frequencies.

[0011] Furthermore, in step 1, the switching period T of the electromagnetic unit state r With the maximum received signal bandwidth B max The relationship between them is T r ≥1 / B max .

[0012] Further, in step 2, the frequency domain separation and reception model of the multi-stream co-frequency signal is: Y(f)=R(f)*S(f0)+N(f); where R(f) represents the frequency domain influence generated by the state of the electromagnetic unit on the periodically switched metasurface, S(f0) represents the aliasing spectrum of the multi-stream signal with center frequency f0, * represents the convolution operation, and N(f) represents noise.

[0013] Furthermore, in step 3, when the electromagnetic units on the metasurface have discretely adjustable amplitude and / or phase states, the discrete binary particle swarm optimization algorithm is used to find the periodic codewords of the metasurface.

[0014] Furthermore, in step 3, when using the discrete binary particle swarm optimization algorithm to find the periodic codewords of the metasurface, the fitness function is:

[0015]

[0016] Where, θ j Let θ represent the angle of arrival of the j-th stream signal, M represent the number of signals, and θ p ' represents the peak angle of the p-th harmonic radiation pattern, t1 and t2 are weighting coefficients, and F p (θ j ) represents the pattern coefficient of the p-th harmonic in the direction of the j-th flow signal arrival angle.

[0017] Furthermore, in step 4, the sampling rate f s ≥MB max B max The beneficial effects of this invention, representing the maximum received signal bandwidth, are as follows:

[0018] By replacing the front end of a traditional single-antenna, single-channel receiver with a metasurface, and leveraging the metasurface's ability to rapidly change (nanosecond-level) the states of electromagnetic units to control electromagnetic wave frequencies, different periodic adjustments to the states of each electromagnetic unit on the metasurface can be made so that the harmonics generated by different units have varying effects on electromagnetic waves from different directions in space. This allows different harmonics to affect only specific frequency signals in a particular direction, achieving frequency domain separation and reception of multi-stream co-frequency signals. This solves the high cost problem of existing multi-stream signal separation methods requiring multiple array elements and multiple RF channels. This invention can be used to separate and demodulate multi-stream co-frequency aliased signals in a single-channel receiver. Attached Figure Description

[0019] Figure 1 A flowchart illustrating a method for frequency domain separation and reception of multi-stream co-frequency signals based on a single-channel metasurface receiver, provided in an embodiment of the present invention;

[0020] Figure 2 A schematic diagram illustrating the reception of multi-stream signals using a single-channel metasurface receiver, provided as an embodiment of the present invention;

[0021] Figure 3 The harmonic radiation patterns generated by the periodic codewords found in the embodiments of the present invention are as follows: (a)

[0022] (a) Center frequency radiation pattern; (b) +1st harmonic radiation pattern; (c) -1st harmonic radiation pattern; (d) +2nd harmonic radiation pattern; (e) -2nd harmonic radiation pattern;

[0023] Figure 4 The spectrum conditions at the receiver's digital baseband processing module before and after the metasurface is enabled, as provided in the embodiments of the present invention: (a) metasurface not enabled; (b) metasurface enabled. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of the embodiments of this invention will be clearly described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0025] Example 1

[0026] like Figure 1 As shown, this embodiment of the invention provides a method for frequency domain separation and reception of multi-stream co-frequency signals based on a single-channel metasurface receiver, comprising the following steps:

[0027] S101: The multipath parameter estimation method of time oversampling / frequency domain oversampling is used to obtain the number of signals, angle of arrival and channel coefficients in the current environment; and the switching period of the electromagnetic unit state on the metasurface is determined based on the maximum received signal bandwidth;

[0028] Specifically, multipath parameter estimation methods can be sparse reconstruction algorithms or multiple signal classification algorithms. The signals used for parameter estimation can be known or unknown signals.

[0029] Assuming there are M streams of the same frequency in the current environment, the bandwidth of the M streams of the same frequency signal can be expressed as B = [B1, ..., B M ], where M represents the number of signals; let B max The maximum received signal bandwidth is represented by the switching period T of the electromagnetic unit state. r With B max The relationship between them is T r ≥1 / B max .

[0030] S102: Establish a frequency domain separation reception model for multi-stream co-frequency signals based on a single-channel metasurface receiver, according to the number of acquired signals, angle of arrival, signal coefficients, and switching period.

[0031] Specifically, the metasurface can be of any form, including radial, transmissive, and reflective metasurfaces. The electromagnetic units on the metasurface possess continuously / discretely adjustable amplitude / phase states.

[0032] S103: With the goal of maximizing the signal-to-noise ratio of the received signal in the frequency domain separation receiving model of multi-stream co-frequency signals, the periodic codeword of the metasurface is found by means of search, optimization algorithm or model calculation, so as to shift the multi-stream co-frequency signals with different angles of arrival to different frequencies respectively.

[0033] Specifically, the multi-stream co-frequency signal can be a signal with any modulation method and any bandwidth, and the bandwidth of each stream signal can be different.

[0034] When the electromagnetic units on the metasurface have discretely adjustable amplitude / phase states, the periodic codewords of the metasurface can be found through search algorithms or optimization algorithms. The search algorithm can be a discrete space search optimization algorithm such as discrete binary particle swarm optimization.

[0035] When the electromagnetic units on the metasurface have continuously adjustable amplitude / phase states, the periodic codewords of the metasurface can be found through optimization algorithms, model calculations, etc. The optimization algorithms can be block coordinate descent method, alternating optimization, etc.

[0036] S104: Samples, filters, and demodulates signals shifted to different frequencies.

[0037] Specifically, the receiver's sampling frequency fs With the number of multi-stream signals M and the maximum bandwidth B max Related, specifically the relationship is f s ≥MB max

[0038] The multi-stream co-frequency signal separation method provided in this invention applies the multi-dimensional modulation capability of metasurfaces to electromagnetic waves to signal reception, avoiding the problem in existing technologies that require multiple radio frequency channels to receive multi-stream co-frequency signals. This allows the invention to achieve multi-stream signal separation and reception with a single radio frequency channel, significantly reducing the hardware cost of the system.

[0039] Example 2

[0040] refer to Figure 2 , Figure 2 This invention relates to a single-channel metasurface receiver based on a reflective metasurface. Multi-stream signals in space are modulated by the reflective metasurface before entering the single-channel receiver. Specifically, the receiver comprises a horn antenna, a radio frequency channel, a digital baseband processor, and a metasurface controller. The metasurface consists of X rows and Y columns of electromagnetic units. In this embodiment, a column-controlled, N-bit finite-adjustment metasurface is used for illustration. Each column of electromagnetic units on the metasurface can be independently adjusted by 2... N In each phase state, the amplitude response of the electromagnetic unit is always 1. The correspondence between the phase state and the codeword n ​​is as follows: n = [0,...,2] N -1]. The frequency domain separation method for multi-stream co-frequency signals provided in this embodiment of the invention includes the following steps:

[0041] S201: The multipath parameter estimation method of time oversampling / frequency domain oversampling is used to obtain the number of signals, angle of arrival and complex coefficients of the wireless channel in the current environment; and the switching period of the electromagnetic unit state on the metasurface is calculated based on the maximum received signal bandwidth.

[0042] In this embodiment, the transmission signal frequency is f0 and the maximum signal bandwidth is B. max Taking a signal quantity of M as an example, the multipath parameter estimation algorithm can be used to obtain a signal quantity of M and an angle of arrival θ = [θ1,...,θ2]. M ] and channel coefficients H = [H1,...,H M ].

[0043] S202: Based on the number of signals, angle of arrival, channel coefficient and switching period obtained in step S201, establish a frequency domain separation reception model for multi-stream co-frequency signals based on a single-channel metasurface receiver.

[0044] In this embodiment, the frequency domain separation principle of the present invention is described in detail in conjunction with the time-frequency domain reception process of the signal.

[0045] (1) From the time domain perspective, the received signal Ω(t) after being modulated by the electromagnetic unit on the metasurface is as follows:

[0046] Ω(t)=R(t)S(t)+n(t)

[0047] Where R(t) represents the change of Y-column electromagnetic units over time; S(t) represents the signal of M-current reaching each electromagnetic unit on the metasurface from different directions; and n(t) represents noise.

[0048] Considering that the metasurface in this embodiment is a train-controlled metasurface, R(t) can be expressed as: R(t) = [R1(t),...,R y (t),...,R Y [(t)], where R y (t) represents the time control function of the y-th electromagnetic unit, with a switching period of T. r To prevent signal aliasing, the period T needs to be guaranteed. r It is not greater than the reciprocal of the maximum signal bandwidth.

[0049] In this embodiment, R y (t) is composed of a linear combination of L (L≥M) pulse control signals, specifically expressed as:

[0050]

[0051] in, Let be the response coefficient of the metasurface electromagnetic unit in the y-th column electromagnetic unit during the i-th time modulation pulse. The amplitude response coefficient, U is the phase response coefficient; i (t) is the pulse function of the i-th period, expressed as: Where τ=T r / L is the pulse length;

[0052] Periodic signal R y The Fourier series of the p-th harmonic of (t) is

[0053]

[0054] Based on the angle of arrival and channel coefficients of the M-stream signal estimated in step S201, S(t) can be expressed as:

[0055]

[0056] in, Let y = 1, 2, ..., Y, and θ = θ1, θ2, ..., θ M H mLet x represent the wireless channel coefficients of the m-th stream signal. m (t) represents the m-th transmitted signal; considering that the steering vector and wireless channel generally do not change with time, C(θ) is used. m )=[A1(θ m )H m ,...,A Y (θ m )H m ] T This indicates the influence of the wireless channel and steering vector on each stream of signal.

[0057] (2) From the frequency domain perspective, the frequency domain received signal Ω(f) after being modulated by the electromagnetic unit on the metasurface can be expressed as:

[0058] Ω(f)=R(f)*S(f)+N(f)

[0059] =R(f)*(C(θ1)X1(f)+...+C(θ) M )X M (f))

[0060] Where R(f) represents the frequency domain influence produced by each electromagnetic unit on the periodically switched metasurface, and S(f), N(f), X m (f) represents the frequency domain form of the signal reaching the metasurface, the frequency domain form of the noise, and the frequency domain form of the signal transmitted by the m-th stream, respectively.

[0061] Furthermore, the received signal at the p-th harmonic is:

[0062] Ω p =a p [C(θ1)X1(ff p )+...+C(θ M )X M (ff p )]

[0063] in, f represents the Fourier series of the p-th harmonic at each electromagnetic unit. p Indicates the harmonic frequency.

[0064] S203: With the goal of maximizing the signal-to-noise ratio of the received signal in the frequency domain separation receiving model of multi-stream co-frequency signals, a search algorithm is used to find the periodic switching codeword of the metasurface, so as to achieve the effect of shifting multi-stream co-frequency signals with different angles of arrival to different frequencies.

[0065] In this embodiment, it is desirable to transform the signal X = [X1,...,X] into [X1,...,X]. MMoving the signal to different harmonics requires maximizing the received signal-to-noise ratio while adhering to finite phase modulation states. This necessitates searching for a periodically switching codebook across Y columns of metasurface electromagnetic units and L time series. The search objective and conditions can be mathematically expressed as follows:

[0066]

[0067]

[0068] Considering the large search space required, the Discrete Binary Particle Swarm Optimization (BPSO) algorithm can be used, and its fitness function can be set as follows:

[0069]

[0070] Where, θ p ' represents the peak angle of the p-th harmonic radiation pattern, t1 and t2 are weighting coefficients, and F p (θ j Let represent the pattern coefficient of the p-th harmonic in the direction of the j-th current signal arrival angle. In the above formula, the first term aims to align the main lobe with the target signal direction, and the second term aims to maximize the peak value of the main lobe. A smaller fitness function value indicates a better alignment between the main lobe direction and the target signal direction at different harmonic frequencies, and a larger peak value of the main lobe, which better meets the requirements.

[0071] At this point, the design of the periodic codeword R(t) for each electromagnetic unit on the metasurface is complete.

[0072] To illustrate the metasurface codeword design more specifically, consider receiving two signals with a bandwidth of 1000Hz from -30° and 30° directions at the +1st and -1st harmonics, respectively. To prevent interference from non-ideal factors, the reciprocal of twice the bandwidth is chosen as the metasurface codeword switching period. Subsequently, the following periodic codeword is obtained using the BPSO search algorithm:

[0073]

[0074] Here, the i-th row and j-th column represent the state of the j-th RIS electromagnetic unit at the i-th time. Figure 3 The harmonic radiation patterns generated by this set of periodic codewords are given. It can be seen that the +1st harmonic affects the -30° direction.

[0075] The signal response is the largest, and the -1st harmonic has the largest signal response in the +30° direction, which means that the two signals can be shifted to ±1st order frequencies respectively.

[0076] further, Figure 4 (a) Figure 4(b) The spectrum at the receiver's digital baseband is presented before and after the metasurface is turned on. Figure 4 (a) It can be seen that when the metasurface is not activated, the two-stream signals alias at the center frequency, making demodulation of the two-stream signals impossible. From Figure 4 (b) It can be seen that after the metasurface is turned on, the two signals are shifted to the ±2000Hz frequency, and the signal demodulation can be completed by step S204.

[0077] Step S204: Sample, filter and demodulate the signal after metasurface modulation.

[0078] In this embodiment, the sampling rate f s ≥MB max The purpose of sampling the signal is to capture all useful harmonic frequencies. This is based on the switching period T of the electromagnetic unit. r Calculate the frequencies at each harmonic level. For simplicity, the p-th stream data is assumed to be located at the p-th harmonic. In practical applications, different stream signals can be distributed on both sides of the center frequency.

[0079] Subsequently, the harmonics of different stream signals are subjected to spectrum shifting to locate them at the center frequency. The signal Ω of the p-th stream signal after spectrum shifting is... p (t) can be expressed as

[0080]

[0081] Next, the signal y after relocation was analyzed. m (t) is low-pass filtered to obtain y' m (t) can complete the separation of multi-stream signals.

[0082] Finally, for signal y' m By demodulating (t), the content of the m-th stream signal can be obtained.

[0083] It should be noted that this approach considers frequency shifting first, followed by filtering. In practical applications, different bandpass filters can also be designed to directly obtain each stream of signal.

[0084] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for frequency domain separation of multi-stream co-frequency signals based on a single-channel metasurface receiver, characterized in that, include: Step 1: Use the multipath parameter estimation method to obtain the number of signals, angle of arrival, and channel coefficient in the current environment, and determine the switching period of the electromagnetic unit state on the metasurface based on the maximum received signal bandwidth; Step 2: Establish a frequency domain separation and reception model for multi-stream co-frequency signals based on a single-channel metasurface receiver, according to the number of acquired signals, angle of arrival, signal coefficients, and switching period; Step 3: With the goal of maximizing the received signal-to-noise ratio of the multi-stream co-frequency signal frequency domain separation receiving model, search for the periodic codeword of the metasurface to shift multi-stream co-frequency signals with different angles of arrival to different frequencies. When the electromagnetic units on the metasurface have discretely adjustable amplitude and / or phase states, a discrete binary particle swarm optimization algorithm is used to find the periodic codeword of the metasurface. When using the discrete binary particle swarm optimization algorithm to find the periodic codeword of the metasurface, the fitness function is: in, Let M represent the angle of arrival of the j-th stream signal, and M represent the number of signals. This represents the peak angle of the radiation pattern of the p-th harmonic. These are the weighting coefficients. This represents the pattern coefficient of the p-th harmonic in the direction of the j-th current signal arrival angle; Step 4: Sample, filter, and demodulate the signals shifted to different frequencies; sampling rate , This indicates the maximum bandwidth of the received signal.

2. The method for frequency domain separation of multi-stream co-frequency signals based on a single-channel metasurface receiver according to claim 1, characterized in that, In step 1, the switching cycle of the electromagnetic unit state With the maximum received signal bandwidth The relationship between them is .

3. The method for frequency domain separation of multi-stream co-frequency signals based on a single-channel metasurface receiver according to claim 1, characterized in that, In step 2, the frequency domain separation and reception model for the multi-stream co-frequency signal is as follows: ;in, This represents the frequency domain effect caused by the electromagnetic unit states on the periodically switching metasurface. The center frequency is The aliasing spectrum of a multi-stream signal, where * denotes convolution operation. Indicates noise.

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