阅读说明：本技术 一种空间等离子体云团信道特性及通信性能的快速估算方法 (Method for rapidly estimating channel characteristics and communication performance of space plasma cloud cluster ) 是由 谢守志 许正文 薛昆 赵海生 吴健 郑延帅 徐朝辉 高敬帆 于 2021-05-13 设计创作，主要内容包括：本发明公开了一种空间等离子体云团信道特性及通信性能的快速估算方法,包括如下步骤：步骤1,计算空间等离子体云团有效区域：步骤2,估算空间等离子体云团最大多径时延：步骤3,估算空间等离子体云团最大多普勒频移：步骤4,估算空间等离子体云团信道相干带宽：步骤5,估算空间等离子体云团信道相干时间：步骤6,估算空间等离子体云团的最大通信速率：步骤7,估算空间等离子体云团通信误码率。本发明所公开的方法,给出了包括最大多径时延、最大多普勒频移、相干带宽、相干时间、最大通信速率以及通信误码率在内的信道特性及通信系统性能的估算方法,针对空间等离子体云团信道的特殊性,具有一定的快捷性和有效性。(The invention discloses a method for quickly estimating channel characteristics and communication performance of space plasma cloud clusters, which comprises the following steps: step 1, calculating an effective area of a space plasma cloud cluster: step 2, estimating the maximum multipath time delay of the space plasma cloud cluster: step 3, estimating the maximum Doppler frequency shift of the space plasma cloud: step 4, estimating the spatial plasma cloud channel coherence bandwidth: step 5, estimating the spatial plasma cloud channel coherence time: step 6, estimating the maximum communication rate of the space plasma cloud: and 7, estimating the space plasma cloud cluster communication error rate. The method disclosed by the invention provides the estimation method of the channel characteristics and the communication system performance including the maximum multipath time delay, the maximum Doppler frequency shift, the coherent bandwidth, the coherent time, the maximum communication speed and the communication error rate, and has certain rapidity and effectiveness aiming at the particularity of the space plasma cloud channel.)

1. A method for rapidly estimating channel characteristics and communication performance of space plasma cloud is characterized by comprising the following steps:

step 1, calculating an effective area of a space plasma cloud cluster:

assuming that the frequency of the electric wave is f, the electron density of a certain point of the space plasma cloud is N_eThen its plasma frequency f_pCan be calculated from the following formula:

when the radio wave with frequency f passes through the point neglecting the influence of the earth magnetic field, the refractive index n is calculated as follows:

setting a threshold value n₀When n > n₀Only then will this point affect the propagation of the radio wave at that frequency, n₀The electron density N can be calculated by substituting the electron density into the formula (1) and the formula (2)₀：

The effective area of the spatial plasma cloud is calculated using equation (3): electron density of cloud cluster is greater than N₀The region of (d) and an effective region corresponding to a radio wave of frequency f;

step 2, estimating the maximum multipath time delay of the space plasma cloud cluster:

let the height of the cloud cluster center point from the ground be h and the horizontal distance from the emitting point be l_ctThe distance between the transmitting point and the receiving point is l_trCalculating according to the step 1 to obtain the width w of the cloud cluster in the horizontal direction_cWidth in the vertical direction of h_cCalculating to obtain the transmitting point to the receiving pointTwo path lengths l with the largest path difference₁And l₂：

The maximum multipath time delay tau calculation method of the space plasma cloud cluster is as follows:

c is the speed of light;

step 3, estimating the maximum Doppler frequency shift of the space plasma cloud:

suppose that the maximum wind speed in the latitudinal direction at the cloud cluster height is v, as obtained by the wind field model HWM07₁The maximum wind speed in the warp direction is v₂A height direction velocity v_vThe resultant velocity v in the horizontal direction_hComprises the following steps:

suppose v_hAnd if the included angle between the high-altitude wind field and the connecting line between the transmitting point and the receiving point is theta, the speed of the high-altitude wind field along the connecting line between the transmitting point and the receiving point is as follows:

v_tr＝v_hcosθ (8)

let the distance between the transmitting point and the receiving point be l_tr，t₁The height between the cloud cluster center and the ground is h₁The horizontal distance between the cloud cluster center and the emission point is l_ct1Calculating by using the method in the step 1 to obtain the width h of the cloud cluster in the vertical direction_c1Then t is₁Propagation path length l of time radio wave_t1Comprises the following steps:

t₂the height h between the cloud cluster center and the ground at any moment₂＝h₁+v_v(t₂-t₁) Horizontal distance l between cloud cluster center and emission point_ct2＝l_ct1+v_tr(t₂-t₁) Calculating by using the method in the step 1 to obtain the width h of the cloud cluster in the vertical direction_c2Then t is₂Propagation path length l of time radio wave_t2Comprises the following steps:

relative moving speed v between transmitting point and receiving point_dThe calculation method is as follows:

space plasma cloud maximum doppler shift f_dThe calculation method is as follows:

c is the speed of light, f is the frequency of the electric wave;

step 4, estimating the spatial plasma cloud channel coherence bandwidth:

calculating according to the step 2 to obtain the maximum multipath time delay tau of the space plasma cloud cluster, and then the coherent bandwidth B of the space plasma cloud cluster is_cThe calculation method is as follows:

step 5, estimating the spatial plasma cloud channel coherence time:

calculating according to the step 3 to obtain the maximum Doppler frequency shift f of the space plasma cloud cluster_dThen its channel coherence time T_cThe calculation method is as follows:

step 6, estimating the maximum communication rate of the space plasma cloud:

calculating the coherent bandwidth B of the spatial plasma cloud channel according to the step 4_cThe channel bandwidth can be obtainedAccording to shannon's theorem, the channel capacity C can be expressed as:

wherein S is the average power of the received signal, N is the noise power,

the average power S of the received signal may be determined by the transmitted power P_tThe path loss is calculated and obtained, and the path loss is divided into two parts, wherein one part is free space loss L_fThe other part is the absorption loss L of ionized layer and cloud cluster_iThe calculation method respectively comprises the following steps:

L_f＝20lgf+20lgd+32.44 (16)

L_i＝8.68∫_SβdS (17)

f is the radio frequency, d is the free space propagation distance,in order to be an absorption index,c is the speed of light, ω is the angular frequency,f_pis the plasma frequency and v is the collision frequency;

the average power S of the received signal can be expressed as:

noise figure F of antenna_aThe calculation method is as follows:

F_a＝c_a-d_algf (19)

c_aand d_aIs a set constant;

thermal noise power n_tCan be expressed as:

n_t＝KT₀B_n (20)

k is Boltzmann constant, and has a value of 1.38 × 10^-23J/K，T₀Is ambient temperature, B_nA noise bandwidth for the receiver;

the noise power N is:

carrying the average power S and the noise power N of the received signals into a formula (15), wherein the calculated channel capacity C is the maximum communication rate of the space plasma cloud;

step 7, estimating the space plasma cloud cluster communication error rate:

when the signal-to-noise ratio is larger than 1, the error rates of 2ASK, 2FSK and 2PSK can be calculated by the following formulas respectively:

2ASK：

2FSK：

2PSK：

r is the signal-to-noise ratio and is obtained by dividing the average power S of the received signal in step 6 by the noise power N.

Technical Field

The invention belongs to the technical field of new concept communication, and particularly relates to a method for quickly estimating channel characteristics and communication performance of a space plasma cloud in the field.

Background

Emergency communication has become a focus of global attention as a supplement to everyday communication means. In recent years, a lot of natural disasters such as tsunami in the indian ocean in 2004, attack of extremely large storm snow and freezing rain in most areas in south China in 2008, and 8-level earthquake in Wenchuan in Sichuan, etc. occur, because the conventional communication network in the affected area is physically damaged, the disaster area is out of contact with the outside for a long time, rescue delay is caused, and serious casualties and property loss are caused. Therefore, strategic emergency communication systems for developing the countries of the world are actively constructed, and refer to the minimum communication systems for ensuring that the strategic weapons are commanded under the emergency condition of communication interruption, wherein the conventional communication means of all levels of command posts are attacked and destroyed in the most dangerous war environment, particularly after the critical attack is suffered. Strategic emergency communication systems must have a variety of communication means to cope with "double" threats, must have the capabilities of persistent storage, mobility, interference resistance, area coverage, effective transmission under nuclear explosion conditions, and the like, and can ensure the survival and emergency communication guarantee capabilities in various war environments.

Short-wave and ultra-short-wave remote communication and emergency communication can be realized by using high-density plasma layer junctions or special areas such as an E layer (Es layer) and meteor trails, but the short-wave and ultra-short-wave remote communication and emergency communication cannot be controlled independently depending on natural environment and are limited in use, so that research and development of an independent and reliable new concept communication technology becomes urgent. The method utilizes an aircraft platform such as a sounding rocket and the like to inject specific chemical substances into an ionized layer, can artificially change plasma components and structures of the ionized layer, generate high-density ionized clouds in the ionized layer, form a strong reflection/scattering area of radio waves, and construct an air bridge, thereby realizing autonomous and reliable remote wireless communication. At present, domestic and foreign documents carry out detailed research on the generation and evolution mechanism of the space plasma cloud, but the channel characteristics of the space plasma cloud and the performance of a communication system forming a link are rarely reported. Although the channel characteristics and the communication performance of the space plasma cloud can be calculated by the ray tracing method, the ray tracing method has the defects of long calculation time, poor real-time performance and the like. Therefore, it is very necessary to develop a method for rapidly estimating the channel characteristics and communication performance of the spatial plasma cloud.

Disclosure of Invention

The invention aims to provide a method for quickly estimating the channel characteristics and the communication performance of a space plasma cloud.

The invention adopts the following technical scheme:

the improvement of a method for quickly estimating the channel characteristics and the communication performance of space plasma cloud clusters is that the method comprises the following steps:

step 1, calculating an effective area of a space plasma cloud cluster:

assuming that the frequency of the electric wave is f, the electron density of a certain point of the space plasma cloud is N_eThen its plasma frequency f_pCan be calculated from the following formula:

when the radio wave with frequency f passes through the point neglecting the influence of the earth magnetic field, the refractive index n is calculated as follows:

setting a threshold value n₀When n > n₀Only then will this point affect the propagation of the radio wave at that frequency, n₀The electron density N can be calculated by substituting the electron density into the formula (1) and the formula (2)₀：

The effective area of the spatial plasma cloud is calculated using equation (3): electron density of cloud cluster is greater than N₀The region of (d) and an effective region corresponding to a radio wave of frequency f;

step 2, estimating the maximum multipath time delay of the space plasma cloud cluster:

let the height of the cloud cluster center point from the ground be h and the horizontal distance from the emitting point be l_ctThe distance between the transmitting point and the receiving point is l_trCalculating according to the step 1 to obtain the width w of the cloud cluster in the horizontal direction_cWidth in the vertical direction of h_cCalculating to obtain the length l of the two paths with the maximum path difference between the transmitting point and the receiving point₁And l₂：

The maximum multipath time delay tau calculation method of the space plasma cloud cluster is as follows:

c is the speed of light;

step 3, estimating the maximum Doppler frequency shift of the space plasma cloud:

assumed to pass through the wind field model HWM07Maximum wind speed v in the latitudinal direction at cloud cluster height₁The maximum wind speed in the warp direction is v₂A height direction velocity v_vThe resultant velocity v in the horizontal direction_hComprises the following steps:

suppose v_hAnd if the included angle between the high-altitude wind field and the connecting line between the transmitting point and the receiving point is theta, the speed of the high-altitude wind field along the connecting line between the transmitting point and the receiving point is as follows:

v_tr＝v_h cosθ (8)

let the distance between the transmitting point and the receiving point be l_tr，t₁The height between the cloud cluster center and the ground is h₁The horizontal distance between the cloud cluster center and the emission point is l_ct1Calculating by using the method in the step 1 to obtain the width h of the cloud cluster in the vertical direction_c1Then t is₁Propagation path length l of time radio wave_t1Comprises the following steps:

t₂the height h between the cloud cluster center and the ground at any moment₂＝h₁+v_v(t₂-t₁) Horizontal distance l between cloud cluster center and emission point_ct2＝l_ct1+v_tr(t₂-t₁) Calculating by using the method in the step 1 to obtain the width h of the cloud cluster in the vertical direction_c2Then t is₂Propagation path length l of time radio wave_t2Comprises the following steps:

relative moving speed v between transmitting point and receiving point_dThe calculation method is as follows:

space plasma cloud maximum doppler shift f_dThe calculation method is as follows:

c is the speed of light, f is the frequency of the electric wave;

step 4, estimating the spatial plasma cloud channel coherence bandwidth:

calculating according to the step 2 to obtain the maximum multipath time delay tau of the space plasma cloud cluster, and then the coherent bandwidth B of the space plasma cloud cluster is_cThe calculation method is as follows:

step 5, estimating the spatial plasma cloud channel coherence time:

calculating according to the step 3 to obtain the maximum Doppler frequency shift f of the space plasma cloud cluster_dThen its channel coherence time T_cThe calculation method is as follows:

step 6, estimating the maximum communication rate of the space plasma cloud:

calculating the coherent bandwidth B of the spatial plasma cloud channel according to the step 4_cThe channel bandwidth can be obtainedAccording to shannon's theorem, the channel capacity C can be expressed as:

wherein S is the average power of the received signal, N is the noise power,

the average power S of the received signal may be determined by the transmitted power P_tAnd calculating the path loss L to obtain the path loss which is divided into two parts, wherein one part is free space loss Lf, and the other part is ionized layer and absorption loss Li of the cloud cluster, and the calculating methods respectively comprise the following steps:

L_f＝20lg f+20lg d+32.44 (16)

L_i＝8.68∫_SβdS (17)

f is the radio frequency, d is the free space propagation distance,in order to be an absorption index,c is the speed of light, omega is the angular frequency, f_pIs the plasma frequency and v is the collision frequency;

the average power S of the received signal can be expressed as:

noise figure F of antenna_aThe calculation method is as follows:

F_a＝c_a-d_a lgf (19)

ca and d_aIs a set constant;

thermal noise power n_tCan be expressed as:

n_t＝KT₀B_n (20)

k is Boltzmann constant, and has a value of 1.38 × 10^-23J/K，T₀Is ambient temperature, B_nA noise bandwidth for the receiver; the noise power N is:

carrying the average power S and the noise power N of the received signals into a formula (15), wherein the calculated channel capacity C is the maximum communication rate of the space plasma cloud;

step 7, estimating the space plasma cloud cluster communication error rate:

when the signal-to-noise ratio is larger than 1, the error rates of 2ASK, 2FSK and 2PSK can be calculated by the following formulas respectively:

r is the signal-to-noise ratio and is obtained by dividing the average power S of the received signal in step 6 by the noise power N.

The invention has the beneficial effects that:

the method disclosed by the invention provides the estimation method of the channel characteristics and the communication system performance including the maximum multipath time delay, the maximum Doppler frequency shift, the coherent bandwidth, the coherent time, the maximum communication speed and the communication error rate, and has certain rapidity and effectiveness aiming at the particularity of the space plasma cloud channel.

The method disclosed by the invention can quickly evaluate the channel characteristics and the communication system performance of the space plasma cloud cluster, can quickly and effectively optimize and provide a proper communication frequency band based on the method, and lays a foundation for the application of the space plasma cloud cluster in the communication direction.

Drawings

FIG. 1 is a schematic flow diagram of the process of the present invention;

FIG. 2 is a spatial plasma cloud model;

FIG. 3 is a schematic diagram of the multipath effect of wave propagation;

fig. 4 is a diagram illustrating the doppler effect of radio wave propagation.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in further detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

The embodiment 1 discloses a method for quickly estimating channel characteristics and communication performance of a spatial plasma cloud, which comprises estimating an effective region of the spatial plasma cloud, estimating channel characteristics and estimating communication performance, wherein the estimation of the effective region of the spatial plasma cloud is the basis of all work, the channel characteristics and the communication performance of the spatial plasma cloud are estimated according to the calculated effective region of the spatial plasma cloud, the channel characteristics of the spatial plasma cloud comprise multipath time delay, Doppler frequency shift, coherence bandwidth and coherence time, and the performance of a spatial plasma cloud communication system comprises communication rate and communication error rate. As shown in fig. 1, the method specifically comprises the following steps:

step 1, calculating an effective area of a space plasma cloud cluster:

combining the radio wave frequency and the space-time distribution of the electron density of the space plasma cloud cluster, calculating to obtain an effective area of the space plasma cloud cluster according to a set refractive index threshold, wherein different radio wave frequency bands correspond to different effective areas;

the space plasma cloud generation and the time-space evolution model can give the time-space distribution of the electron density of the space plasma cloud at a certain moment, as shown in fig. 2. The propagation characteristics of the electric waves with different frequencies after passing through the space plasma cloud are different, so that the effective areas of the cloud are different for the electric waves with different frequencies. Assuming that the frequency of the electric wave is f, the electron density of a certain point of the space plasma cloud is N_eThen its plasma frequency f_pCan be calculated from the following formula:

when the radio wave with frequency f passes through the point neglecting the influence of the earth magnetic field, the refractive index n is calculated as follows:

a threshold value n can be set₀When n > n₀Only then will this point affect the propagation of the radio wave at that frequency, n₀The electron density N can be calculated by substituting the electron density into the formula (1) and the formula (2)₀：

The effective area of the spatial plasma cloud can be calculated by using the formula (3): electron density of cloud cluster is greater than N₀The region of (d) and an effective region corresponding to a radio wave of frequency f;

step 2, estimating the maximum multipath time delay of the space plasma cloud cluster:

and calculating the path difference between the shortest path and the longest path of the electric wave under the most extreme condition based on the space scale of the effective area of the space plasma cloud cluster, thereby estimating the maximum multipath time delay of the space plasma cloud cluster.

According to the method in the step 1, calculating the effective area of the space plasma cloud, wherein the height is h, and the width is w. Fig. 3 shows two propagation paths under the most extreme condition between the transmitting point and the receiving point, that is, the path difference between the two paths is the largest, and the maximum multipath delay of the spatial plasma cloud can be estimated by calculating the path difference between the two paths. Assuming that the height of the cloud cluster center point from the ground is h and the horizontal distance from the emitting point is l_ctThe distance between the transmitting point and the receiving point is l_trCalculating according to the step 1 to obtain the width w of the cloud cluster in the horizontal direction_cWidth in the vertical direction of h_cAccording to the geometrical relationship in FIG. 3Respectively calculating the length l of the path 1₁Length l of path 2₂：

The maximum multipath time delay tau calculation method of the space plasma cloud cluster is as follows:

c is the speed of light;

step 3, estimating the maximum Doppler frequency shift of the space plasma cloud:

based on the high-altitude atmospheric wind field model and the space plasma cloud space-time evolution model, the path difference of the electric wave paths at different moments under the condition of the maximum wind speed is calculated, and the moving speed of the receiving point relative to the transmitting point is obtained on the basis, so that the maximum Doppler frequency shift of the space plasma cloud is estimated.

The space plasma cloud electric wave Doppler effect can be considered to be mainly caused by a high-altitude wind field, and the change characteristic of the high-altitude wind field can be obtained according to an international reference wind field model HWM 07. Assuming that the maximum latitudinal wind speed at the cloud cluster height obtained through a wind field model is v₁The maximum wind speed in the warp direction is v₂A height direction velocity v_vThe resultant velocity v in the horizontal direction_hComprises the following steps:

suppose v_hAnd if the included angle between the high-altitude wind field and the connecting line between the transmitting point and the receiving point is theta, the speed of the high-altitude wind field along the connecting line between the transmitting point and the receiving point is as follows:

v_tr＝v_h cosθ (8)

fig. 4 shows the paths of the electric waves propagating through the cloud cluster at two different times, and it is assumed that the distance between the transmitting point and the receiving point is l_tr，t₁The height between the cloud cluster center and the ground is h₁The horizontal distance between the cloud cluster center and the emission point is l_ct1Calculating by using the method in the step 1 to obtain the width h of the cloud cluster in the vertical direction_c1Then t is₁Propagation path length l of time radio wave_t1Comprises the following steps:

t₂the height h between the cloud cluster center and the ground at any moment₂＝h₁+v_v(t₂-t₁) Horizontal distance l between cloud cluster center and emission point_ct2＝l_ct1+v_tr(t₂-t₁) Calculating by using the method in the step 1 to obtain the width h of the cloud cluster in the vertical direction_c2Then t is₂Propagation path length l of time radio wave_t2Comprises the following steps:

relative moving speed v between transmitting point and receiving point_dThe calculation method is as follows:

space plasma cloud maximum doppler shift f_dThe calculation method is as follows:

c is the speed of light, f is the frequency of the electric wave;

step 4, estimating the spatial plasma cloud channel coherence bandwidth:

under the generalized stationary uncorrelated scattering (WSSUS) assumption, the coherence bandwidth is defined as the 3dB bandwidth of the correlation function, and more generally, the channel coherence bandwidth can be derived from its maximum delay. Calculating according to the step 2 to obtain the maximum multipath time delay tau of the space plasma cloud cluster, and then the coherent bandwidth B of the space plasma cloud cluster is_cThe calculation method is as follows:

step 5, estimating the spatial plasma cloud channel coherence time:

calculating according to the step 3 to obtain the maximum Doppler frequency shift f of the space plasma cloud cluster_dThen its channel coherence time T_cThe calculation method is as follows:

step 6, estimating the maximum communication rate of the space plasma cloud:

and comprehensively considering the noise level of the receiving point based on the spatial plasma cloud cluster channel coherent bandwidth and the signal power of the receiving point obtained by calculation, and finally estimating the spatial plasma cloud cluster communication rate.

Calculating the coherent bandwidth B of the spatial plasma cloud channel according to the step 4_cIn general engineering, 1/5 to 1/3 of coherent bandwidth are signal bandwidths, and this embodiment adopts 1/3 to calculate, that is, channel bandwidthAccording to shannon's theorem, the channel capacity C can be expressed as:

wherein, S is the average power of the received signal, N is the noise power, and the unit is W.

The average power S of the received signal may be determined by the transmitted power P_t(unit dB) and path loss L (unit dB), the path loss is divided into two parts, one part is free space loss L_fThe other part is the absorption loss L of ionized layer and cloud cluster_iThe calculation method respectively comprises the following steps:

L_f＝20lg f+20lg d+32.44 (16)

L_i＝8.68∫_SβdS (17)

L_fand L_iIn dB, f is the radio frequency, in MHz, and d is the free space propagation distance, in km.

In order to be an absorption index,c is the speed of light, omega is the angular frequency, f_pIs the plasma frequency and v is the collision frequency;

the average power S of the received signal can be expressed as:

noise mainly takes thermal noise and artificial noise received from environment into consideration, and first, the noise coefficient F of the antenna is calculated_aThe calculation method is as follows:

F_a＝c_a-d_a lgf (19)

c_aand d_aThe values for setting the constants are shown in the following table.

Thermal noise power n_tCan be expressed as:

n_t＝KT₀B_n (20)

k is Boltzmann constant, and has a value of 1.38 × 10^-23J/K，T₀Is ambient temperature, in units of K, B_nIs the receiver noise bandwidth in Hz;

the noise power N is:

carrying the average power S and the noise power N of the received signals into a formula (15), wherein the calculated channel capacity C is the maximum communication rate of the space plasma cloud;

step 7, estimating the space plasma cloud cluster communication error rate:

considering several common modulation modes, namely 2ASK, 2FSK and 2PSK, respectively, and adopting a coherent demodulation method, when the signal-to-noise ratio is far greater than 1, the bit error rate can be calculated by the following formula:

r is the signal-to-noise ratio and is obtained by dividing the average power S of the received signal in step 6 by the noise power N.

In conclusion, the method disclosed by the invention can realize the rapid estimation of the space plasma cloud channel characteristics and the communication performance, is effective and has relatively high accuracy, is particularly suitable for the real-time rapid estimation of the space plasma cloud channel characteristics and the communication performance, and has important value and significance for the development and application of the space plasma cloud communication technology.