WO2022021656A1

WO2022021656A1 - Power distribution method for oam-mimo dynamic channel

Info

Publication number: WO2022021656A1
Application number: PCT/CN2020/127132
Authority: WO
Inventors: 王洋; 修艳磊; 施盼盼; 廖希; 林峰
Original assignee: 重庆邮电大学
Priority date: 2020-07-30
Filing date: 2020-11-06
Publication date: 2022-02-03
Also published as: CN111769856A; CN111769856B

Abstract

The present invention relates to a power distribution method for an OAM-MIMO dynamic channel, and belongs to the technical field of wireless communications. In a dynamic OAM-MIMO scenario, the state of a channel may change along with the movement of a receiver, and due to the presence of feedback delay and estimation error in a system, it is hard to accurately obtain channel state information, resulting in unsatisfactory capacity performance of the system. Comparing the present invention with a traditional previous power continuation algorithm and average power distribution algorithm, the capacity performance of an OAM-MIMO system can be effectively improved where total power resources of the system are limited. A final simulation experiment result also shows that, when a working frequency is 10 GHz, a wavelength is 3 cm, the number of array elements is 8, the transmitting and receiving radius of a UCA is 9 cm, and channel state information is unknown, the power pre-distribution algorithm provided in the present invention is obviously better than the traditional average power distribution algorithm and previous power continuation algorithm.

Description

Power allocation method for OAM-MIMO dynamic channel

technical field

The invention belongs to the technical field of wireless communication, and relates to a power allocation method for OAM-MIMO dynamic channel.

Background technique

As wireless subscribers continue to grow, it becomes more and more challenging to meet the demands of continued capacity growth in wireless networks. In order to meet the growing demand with limited resources, it is necessary to rely on new technologies to improve system capacity and spectrum utilization.

According to Maxwell's theory, electromagnetic radiation carries both energy and momentum, and momentum can be decomposed into Linear Momentum (LM) and Angular Momentum (AM), where angular momentum includes spin angular momentum (Spin Angular Momentum, SAM) and Orbital Angular Momentum (OAM). The spin angular momentum is related to the polarization mode of the electromagnetic wave, and its value is Planck's constant, which corresponds to the left and right circular polarizations respectively. The orbital angular momentum is related to the vortex phase structure of the electromagnetic field, and its value is called topological charge and modal value. The superposition of different eigenstates are mutually orthogonal. The electromagnetic wave carrying orbital angular momentum is different from the plane electromagnetic wave in that there are more phase rotation factors. The specific manifestation is that the phase wavefront has a spatial helical phase structure around the beam axis, so it is often called a vortex wave. Due to the physical orthogonality between vortex waves of different eigenstates, multiple signals can be modulated onto vortex waves of different eigenstates for independent transmission, so that it does not depend on traditional resources such as time and frequency. It greatly increases the channel capacity of the wireless communication system, and provides a new solution for studying the problem of the shortage of wireless communication spectrum resources.

In the OAM-MIMO communication system, the vortex electromagnetic waves of different modes are equivalent to independent channels. By assigning power values to the vortex electromagnetic waves of different modes, the system capacity can be maximized, which is improved in the case of limited power resources. The performance of OAM-MIMO communication system is very necessary.

In the previous OAM-MIMO communication systems, the researched power allocation schemes are all based on static scenarios, and both the receiver and the transmitter are stationary. However, in practical applications, the receiver is often in a moving state, which makes the channel state of the system change with the movement of the receiver. Due to feedback delay and estimation error in dynamic scenarios, it is usually difficult for the system to obtain channel state information accurately. When the channel state information is unknown, using the traditional average power allocation method or continuing the previous power allocation method will cause waste of power resources. Therefore, how to effectively allocate power resources under dynamic channels determines the performance of the OAM-MIMO communication system to a certain extent.

SUMMARY OF THE INVENTION

In view of this, the purpose of the present invention is to provide a power allocation method for OAM-MIMO dynamic channel.

To achieve the above object, the present invention provides the following technical solutions:

In a dynamic scene OAM-MIMO multi-modal multiplexing communication system, the transmitter is placed at the top of the room, the receiver moves on the ground, and both the transmit and receive antennas are uniform circular arrays composed of N antenna elements. where D is the distance from the transmitting antenna array to the ground, d _n,m is the distance from the transmitting antenna m to the receiving antenna n, x is the projection of the distance from the center of the circle projected from the transmitting array to the ground to the center of the receiving array on the x-axis, and y is the distance on the x-axis. Projection of the y-axis. Therefore, the distance d _n,m from the transmitting antenna m to the receiving antenna n can be expressed as:

where R _t and R _r are the radii of the transmitting array and the receiving array, respectively,

and

are the azimuth angles of the transmitting array and receiving array antenna elements, respectively,

and θ ₀ are the initial phases of the two array antenna elements, respectively.

In the LOS scenario, the complex channel gain between the mth transmit antenna and the nth receive antenna of the MIMO system is:

in,

represents the constant term corresponding to antenna attenuation. Therefore, the MIMO channel matrix can be expressed as:

When the transmitter and receiver transmit multiple modes, the receiver will receive the vortex signals of the multiple modes, so that the demodulation vector of the multiple mode vortex signals is used for the received l-mode vortex signal, Its process can be expressed as:

Among them, H is the channel matrix that the receiver moves to (x, y), n is the independent and identically distributed Gaussian white noise, where λ _{q, l} represent

The multiplication result, x _l =w _t ^T x _t is the transmitted signal, W _r =[w ₁ ,w ₂ ,...,w _L ] ^T is the demodulation matrix for demodulating L OAM modes at the receiving end,

is the demodulation vector of a single OAM mode q. Therefore, the Signal-to-Interference-and-Noise-Ratio (SINR) of the l-mode vortex signal can be expressed as:

where σ ² represents the variance of the noise signal, and p _l represents the transmit power of the vortex wave with OAM mode 1. It can be concluded that the channel capacity of 1 modal under the signal-to-interference-noise ratio is:

C _l =log ₂ (1+SINR _l )

From the channel capacity when transmitting a single l mode in the above formula, it is easy to write that the system capacity when the number of modes transmitted by the transmitter and receiver is L is:

In an OAM-MIMO system in a dynamic scene, the OAM modal spectra of the receiver at the trajectory points A and J are the same, as well as at the trajectory points F and U, and the OAM modal spectra at the trajectory points A and F are the same. There is a slight difference, and the OAM modal spectrum at the four trajectory points is the highest in mode 4. Since the radiation field of the vortex wave is symmetrical around the center of the axis, the trajectory points A and J are also symmetrical with the transmitter projection as the midpoint, as are the trajectory points F and U, so the OAM modal spectrum is also consistent, and the trajectory AFJU The projected distances from the four points to the transmitter are the same, so the OAM modal spectrum at A and F is not much different, and the slight difference comes from the interference caused by modal demodulation.

In the dynamic scene OAM-MIMO system, the channel capacity of the receiver at the four trajectory points of AFJU is the same, which shows that the channel state of the receiver at the same distance from the projection of the transmitter is the same. This is because the vortex wave radiation field is axisymmetric, so the channel state of the receiver at any position on the same circle is consistent.

In an OAM-MIMO system in a dynamic scene, when the receiver moves along the trajectory point, the value of the mode with the largest proportion of the OAM mode is constantly changing. This is because the distance between the receiver and the projection of the transmitter changes continuously during the movement process, and the modal channel state also changes continuously, so the modal value with the largest OAM modal proportion also changes continuously. Therefore, at the trajectory point where the channel state information is unknown, continuing the power allocation value of the previous trajectory point will cause the system performance to degrade.

To sum up, the state of the modal channel is constantly changing during the movement of the receiver. If the average power allocation method is adopted or the previous power allocation method is continued, more power may be allocated to the sub-channels with small channel gain. , and a smaller power is allocated to a sub-channel with a larger channel gain, which causes a great waste of power and leads to poor system performance. From the previous analysis, it can be seen that the modal channel states at the symmetrical trajectory points are consistent, so through the prediction of the modal channel state, in the case of unknown channel state information, the power pre-allocation method based on the moving trajectory can be adopted. Realizing the power allocation to the channel of the dynamic scene can well overcome the defects of the traditional method and realize the maximization of the capacity of the OAM-MIMO communication system.

The beneficial effects of the present invention are:

The invention predicts the channel state information of the next receiver locus point by using the channel state information of the known receiver locus point according to the difference and connection of the channel state information of the OAM-MIMO system at different receiver positions in the dynamic scene, and then predicts the channel state information of the next receiver locus point according to the prediction. The obtained channel state information finds a matching power allocation vector to complete the power pre-allocation of the next receiver trajectory point, which maximizes the system capacity under the condition of limited power. And its performance is greatly improved compared to the traditional average power distribution method or the continuation of the previous power distribution method.

Other advantages, objects, and features of the present invention will be set forth in the description that follows, and will be apparent to those skilled in the art based on a study of the following, to the extent that is taught in the practice of the present invention. The objectives and other advantages of the present invention may be realized and attained by the following description.

Description of drawings

In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be preferably described in detail below with reference to the accompanying drawings, wherein:

1 is a schematic diagram of an OAM-MIMO multi-modal multiplexing communication system in a dynamic scene;

Fig. 2 is a schematic diagram of a moving track point of a receiver according to a rectangle;

Fig. 3 is the schematic diagram of the moving track point of the receiver according to the S shape;

Figure 4 shows the OAM modal spectrum of the receiver at four symmetrical positions of the AFJU (modal values are 1, 2, 3, and 4);

Fig. 5 is the channel capacity of the receiver at four symmetrical positions of AFJU;

Fig. 6 is a graph showing the change of OAM modal proportion with the moving trajectory of the receiver, (a) is the graph of the change of OAM modal proportion with the rectangular trajectory, (b) is the graph of the change of OAM modal proportion with the S-shaped trajectory;

Figure 7 is a graph showing the variation of system channel capacity with trajectory points, (a) is a graph of the variation of system channel capacity with a rectangular trajectory, and (b) is a graph of the variation of system channel capacity with an S-shaped trajectory;

FIG. 8 is a flow chart of the power pre-allocation algorithm based on the movement trajectory proposed by the present invention;

Figure 9 shows the performance comparison of the known CSI water injection allocation algorithm and the CSI unknown three power allocation algorithms under the rectangular trajectory;

Figure 10 shows the performance comparison of the water injection allocation algorithms with known CSI and the three power allocation algorithms with unknown CSI under the S-shaped trajectory.

detailed description

The embodiments of the present invention are described below through specific specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the drawings provided in the following embodiments are only used to illustrate the basic idea of the present invention in a schematic manner, and the following embodiments and features in the embodiments can be combined with each other without conflict.

Among them, the accompanying drawings are only used for exemplary description, and represent only schematic diagrams, not physical drawings, and should not be construed as limitations of the present invention; in order to better illustrate the embodiments of the present invention, some parts of the accompanying drawings will be omitted, The enlargement or reduction does not represent the size of the actual product; it is understandable to those skilled in the art that some well-known structures and their descriptions in the accompanying drawings may be omitted.

The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar components; in the description of the present invention, it should be understood that if there are terms “upper”, “lower”, “left” and “right” , "front", "rear" and other indicated orientations or positional relationships are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the indicated device or element must be It has a specific orientation, is constructed and operated in a specific orientation, so the terms describing the positional relationship in the accompanying drawings are only used for exemplary illustration, and should not be construed as a limitation of the present invention. situation to understand the specific meaning of the above terms.

The present invention considers an OAM-MIMO multi-modal multiplexing communication system in a dynamic scene, as shown in FIG. 1 . The transmitter of the system is placed at the top of the room, the receiver moves on the ground, the transmitting and receiving antennas are uniform circular arrays composed of N antenna elements, where D is the distance from the transmitting antenna array to the ground, and d _n,m is The distance from the transmitting antenna m to the receiving antenna n, x is the projection of the distance from the center of the transmitting array to the ground projection to the center of the receiving array on the x-axis, and y is the projection on the y-axis.

It is assumed that the distance between the center of the receiving antenna array and the projected center of the transmitting antenna array is (x ² +y ² ) ^1/2 , where x and y are their projections on the x-axis and the y-axis, respectively. The distance d _n,m from the transmitting antenna m to the receiving antenna n can be expressed as:

where D is the distance from the transmitting antenna array to the ground, R _t and R _r are the radii of the transmitting and receiving arrays, respectively,

and θ _n =2πn/N+θ ₀ are the azimuth angles of the transmitting array and receiving array antenna elements, respectively,

Because the receiver is in a moving state, the receiver and the transmitter are in a state of misalignment in most cases. When the receiver and transmitter transmit multiple modalities, the misalignment of the transmitting array and the receiving array will cause interference between the modal channels. In order to study the influence of interference between modal channels when the transmitter and receiver transmit multiple modalities, we first analyze the situation where the transmitter transmits a single modal and the receiver receives multiple modalities. Assuming that the number of antenna elements in both the transmitting array and the receiving array is N, and the number of modes transmitted by the transmitter and receiver is L, when the transmitter transmits a vortex signal with an OAM mode of l, the transmitted signal can be expressed as:

x _l = w _t ^T x _t

where the feed vector of the l-modal vortex wave

x _t denotes the original signal to be modulated onto the l-mode, and x _l denotes the transmitted l-mode vortex signal. At the receiving end, the output signals of the N receiving antennas are:

Among them, H is the channel matrix H[h _n,m (d _n,m (x,y))] that the receiver moves to (x,y), and n is the independent and identically distributed Gaussian white noise. When the transmitter and receiver transmit multiple modes, the receiver will receive the vortex signals of the multiple modes, so that the demodulation vector of the multiple mode vortex signals is used for the received l-mode vortex signal, Its process can be expressed as:

The demodulation matrix W _r =[w ₁ ,w ₂ ,...,w _L ] ^T for demodulation of L OAM modes at the receiving end, the demodulation vector of a single OAM mode q

W _rn is still IID Gaussian white noise. It can be known that when the demodulation vector w _q is consistent with the OAM modal value of the feeding vector w _t ,

The result is the transmission gain of the l-modal channel, while the OAM modes of the two vectors are inconsistent,

The result is the channel interference caused by the l-mode channel to the q-mode channel. Therefore, the above formula can be expressed as:

y _l =[λ _1,l ,...,λ _q,l ,...,λ _L,l ] ^T x _l +n

where λ _q,l represents

the result of the multiplication. When the transceivers are aligned at line-of-sight, λ _q,l has a value only if the OAM mode is equal to l. While the receiver is in a moving state, the receiver and the transmitter are in a state of misalignment in most cases, resulting in λ _{q, l} also have a value when the OAM mode q and l are not equal, indicating that the l mode channel is for q Channel interference caused by modal channels. Therefore, the Signal-to-Interference-and-Noise-Ratio (SINR) of the l-mode vortex signal can be expressed as:

C _l =log ₂ (1+SINR _l )

In the dynamic scene OAM-MIMO system, due to the symmetry of the vortex wave radiation field, the channel state of the receiver at a special position is the same.

Figures 2 and 3 show two kinds of receiver movement trajectory point diagrams, which are respectively a rectangular movement trajectory (as shown in Figure 2) and an S-shaped movement trajectory (as shown in Figure 3). In the rectangular movement track, a ₁ , a ₂ , b ₁ , and b ₂ represent the length of the transmitter projection center from the AF track line, the length from the MR track line, the length from the RW track line, and the length from the FM track line, respectively. The blue circle represents the receiver, the purple circle represents the projection of the transmitter on the ground, and the receiver moves from the trajectory point A to the trajectory point W around the transmitter on the ground. In the S-shaped moving trajectory, a ₁ , a ₂ , b ₁ , and b ₂ represent the length of the transmitter projection center from the OR trajectory, the length from the GI trajectory, the length from the AG trajectory, and the distance from the RX trajectory, respectively. , the blue circle represents the receiver, the purple circle represents the projection of the transmitter on the ground, and the receiver moves from the trajectory point A to the trajectory point X.

According to the symmetry of the vortex radiation field, four symmetrical trajectory points of the AFJU in the rectangular trajectory are selected to analyze the OAM modal spectrum and channel capacity of the receiver at its position, as shown in Figure 4 and Figure 5, respectively. As can be seen from Figure 4, the OAM modal spectrum of the receiver at the four points of the rectangular moving trajectory AFJU has inter-modal interference. At the same time, it can be found that the OAM modal spectrum of the receiver at the trajectory points A and J are consistent, also at trajectory points F and U, while the OAM modal spectra at trajectory points A and F are slightly different. It can be seen from Figure 5 that with the increase of the signal-to-noise ratio, the channel capacity of the receiver at the four trajectory points of AFJU is the same, indicating that the channel state of the receiver at the same distance from the projection of the transmitter is the same .

Table 1 Simulation parameters of receiver rectangular movement trajectory

Figure 6 shows the change of the OAM modal proportion with the moving trajectory of the receiver, in which (a) is the change of the OAM modal proportion with the rectangular trajectory. The simulation parameters are shown in Table 1, and (b) is the OAM modal proportion. The ratio changes with the S-shaped trajectory, and the simulation parameters are shown in Table 2. The point connected by the red dotted line is the maximum modal value of the OAM modal proportion at the current trajectory point. As can be seen from the figure, when the receiver moves along the trajectory point, the modal value with the largest proportion of OAM mode is constantly changing. This is because the distance between the receiver and the projection of the transmitter changes continuously during the movement process, and the modal channel state also changes continuously, so the modal value with the largest OAM modal proportion also changes continuously. Therefore, at the trajectory point where the channel state information is unknown, continuing the power allocation value of the previous trajectory point will cause the system performance to degrade.

Table 2 Simulation parameters of receiver S-shaped movement trajectory

Figure 7 shows the variation of the channel capacity with the trajectory points, in which (a) is the variation of the system channel capacity with the rectangular trajectory, and the simulation parameters are shown in Table 1; (b) is the variation of the system channel capacity with the S-shaped trajectory, the simulation The parameters are shown in Table 2, the signal-to-noise ratio SNR=30dB, and the power distribution adopts the water injection distribution algorithm. It can be clearly seen that the channel capacity is consistent at symmetrical trajectory points. It can be concluded that during the moving process of the receiver, the modal channel state is constantly changing, but the modal channel state at the symmetrical trajectory points is consistent, so it can be predicted by the modal channel state, in the unknown channel state In the case of information, the power of each modal channel is pre-allocated.

Referring to FIG. 8 , the specific steps of the power pre-allocation algorithm based on the movement trajectory are described below.

1. Assuming that the number of transmittable modes in the system is N, the total power that can be allocated is P _t . Initialize the power allocation set {P _m-1 ,...,P _mj } and the channel state set {h _m-1 ,...,h _mj } at the first j known trajectory points, where the jth trajectory point The power allocation vector and channel state vector at are the power values allocated to each modal channel and the gain of each modal channel, as shown below:

P _mj =[p ₁ ,...,p _N ] ^T

h _mj = [λ ₁₁ ,...,λ _NN ] ^T

2. First, in the channel state set {h _m-2 ,...,h _mj } of the known track points, search for the same channel state vector h _mk as the channel state h _m-1 of the previous track point, k=2, ...,j, if there is a channel state vector h _mk equal to h _m-1 , then judge the channel state vector h _m-2 , h _m-k+1 and h _mk-1 , when the channel state vector h _m When _-2 is equal to h _m-k+1 , h _mk-1 is the prediction vector h _m of the current trajectory point; when the channel state vector h _m-2 is equal to h _mk-1 , h _m-k+1 is The prediction vector h _m of the current trajectory point; if the channel state vector h _m-2 is not equal to both, continue to search for the channel state vector h _mk . If there is no channel state vector h _mk equal to h _m-1 , it means that the channel state of the previous track point is not consistent with the channel state of any other known track point, and it is difficult to predict the channel state of the current track point.

3. According to the current channel state vector h _m obtained by channel prediction, find the corresponding P _m in the power allocation set {P _m-1 ,...,P _mj } at the known trajectory points, and then assign the power allocation vector P _m is applied to the track point where the current channel state information is unknown to complete the pre-allocation of the power value.

Figures 9 and 10 describe the performance comparison between the known CSI water injection allocation algorithm, the CSI unknown equal power allocation algorithm and the continuation of the previous power allocation algorithm and the power pre-allocation algorithm under the rectangular trajectory and the S-shaped trajectory, respectively. Among them, (a)-(d) respectively represent the performance comparison of the three power allocation algorithms under the unknown CSI at the four points of the EJQW in the rectangular trajectory and the water injection allocation algorithm with known CSI. It can be seen from the two figures that in the case of unknown CSI, the performance of the power pre-allocation algorithm is significantly better than that of the equal power allocation algorithm and the continuation of the previous power allocation algorithm, which can improve the capacity performance of the system.

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 preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be Modifications or equivalent replacements, without departing from the spirit and scope of the technical solution, should all be included in the scope of the claims of the present invention.

Claims

A power allocation method for OAM-MIMO dynamic channel, characterized in that: the method comprises the following steps:

The first step: OAM-MIMO multi-modal multiplexing communication system model design based on dynamic channel;

The OAM-MIMO multi-modal multiplexing communication system based on dynamic channel consists of transmitter, receiver and beamformer. The beamformer is used to generate signals with multiple modes, the transmitter is used to transmit vortex electromagnetic wave signals, and the receiver is used to receive The machine is used to receive and demodulate vortex signals with multiple modes;

The second step: deriving the signal-to-interference-noise ratio and system capacity at a single trajectory point of the OAM-MIMO multi-modal multiplexing communication system based on the dynamic channel;

According to the OAM-MIMO multi-modal multiplexing communication system based on the dynamic channel designed in the first step, the signal-to-interference-noise ratio and the total system capacity of each mode in the system at a single trajectory point are deduced;

Step 3: Derive the relationship of the system capacity under each trajectory point;

According to the system capacity at a single trajectory point obtained in the second step, the relationship between the system capacity between each trajectory point under the rectangular trajectory point and the S-shaped trajectory point is deduced;

Step 4: Multi-modal transmission power allocation optimization for dynamic scenarios;

According to the relationship between the system capacity of each trajectory point deduced in the third part, the power pre-distribution algorithm based on the moving trajectory is used to optimally distribute the system power, and the optimal power distribution solution is obtained.
The power allocation method for an OAM-MIMO dynamic channel according to claim 1, wherein the receiver is in a moving state and transmits multiple modes at the same time, and the number of transmitted modes is equal to the number of antennas.
The power allocation method for OAM-MIMO dynamic channels according to claim 1, wherein the transmitter and the receiver are both a uniform circular antenna array, and each antenna array element is evenly distributed on the circumference And all antenna elements have the same antenna polarization direction.
The power allocation method for OAM-MIMO dynamic channels according to claim 1, wherein in the second step, the signal-to-interference-noise ratio of a single track point is:

The channel capacity is thus:
The power allocation method for OAM-MIMO dynamic channels according to claim 1, wherein in the third step, the rectangular track points are a total of 23 points evenly distributed on the four sides of the rectangle, and S The shape trajectory points are a total of 24 points evenly distributed on each side of the S shape.
The power allocation method for OAM-MIMO dynamic channel according to claim 1, characterized in that: the relationship between each track point is: for each track point symmetrical to each other, their channel capacity is the same.