CN114580279B - An adaptive coding method for low-orbit satellite communication based on LSTM - Google Patents
An adaptive coding method for low-orbit satellite communication based on LSTM Download PDFInfo
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Abstract
Description
技术领域Technical Field
本发明涉及计算机网络技术领域,特别涉及一种基于长短时间记忆网络(Lon gShort Term Memory,LSTM)的低轨卫星通信自适应编码(Adaptive Coding Mod ulation,ACM)方法。The present invention relates to the field of computer network technology, and in particular to an adaptive coding (Adaptive Coding Modulation, ACM) method for low-orbit satellite communication based on a long short-term memory network (Lon gShort Term Memory, LSTM).
背景技术Background technique
低轨卫星为距离地球表面几十到几百千米的卫星,由于其距离地表较近,信道容量较中、高轨道卫星提升。低轨卫星可以无死角覆盖,为空中、地面设施提供高质量通信,战略地位十分重要。低轨卫星通信面临着极端天气可用和吞吐量迅速提升的双重挑战:低轨卫星需要在救灾、极地、雨雪等场景下依旧保持高度可用性,且伴随着网络带宽提升,视频内容增加,网络的总吞吐量会进一步提升,在无人驾驶、观看视频等领域应用时,需要更低的时延和更高的带宽。Low-orbit satellites are tens to hundreds of kilometers away from the earth's surface. Due to their proximity to the surface, their channel capacity is higher than that of medium- and high-orbit satellites. Low-orbit satellites can provide coverage without blind spots and provide high-quality communications for air and ground facilities. Their strategic position is very important. Low-orbit satellite communications face the dual challenges of availability in extreme weather and rapid throughput increases: low-orbit satellites need to maintain high availability in scenarios such as disaster relief, polar regions, rain and snow, and with the increase in network bandwidth and video content, the total throughput of the network will be further improved. When used in areas such as unmanned driving and watching videos, lower latency and higher bandwidth are required.
自适应编码(Adaption Coding Modulation,ACM)是重要的提升卫星频带利用率以提高吞吐量的方法。在传统的卫星通信中,通常为雨衰提供了6dB裕值,但是由于云层厚度不同,全球各地雨衰值不同,而且雨天才有雨衰值,晴天的雨衰为0,因此在实践中通常根据天气进行ACM,以提升吞吐量。低轨卫星通信当中的ACM具有技术难点,比如:低轨卫星运动速度快,切换频繁,需要快速实时预测;全球各地雨衰值不同,需要建立全球模型;全球天气动态变化,难以快速捕捉、同步。Adaptive Coding Modulation (ACM) is an important method to improve satellite frequency band utilization and thus throughput. In traditional satellite communications, a 6dB margin is usually provided for rain attenuation. However, due to different cloud thicknesses, rain attenuation values vary across the globe. Moreover, there is only a rain attenuation value on rainy days, and the rain attenuation on sunny days is 0. Therefore, in practice, ACM is usually performed based on the weather to improve throughput. ACM in low-orbit satellite communications has technical difficulties, such as: low-orbit satellites move fast and switch frequently, requiring fast real-time predictions; rain attenuation values vary across the globe, requiring the establishment of a global model; global weather changes dynamically, making it difficult to quickly capture and synchronize.
在低轨卫星通信自适应编码问题中,研究者有使用识别天线噪声温度、线性回归、指数回归、支持向量回归(Support Vector Regression,SVR)等方法对信号噪声比(Signal-to-Noise Ratio,SNR)进行预测,但是它们均未利用卫星具有强运动规律的信息。长短时间网络(Long short-term memory,LSTM)是一种具有记忆性的循环神经网络,它由遗忘门、输入门、输出门控制对历史信息的记忆程度与对新信息的采纳程度,并通过记忆单元可以实现对卫星过往信息的识别。In the problem of adaptive coding for low-orbit satellite communications, researchers have used methods such as identifying antenna noise temperature, linear regression, exponential regression, and support vector regression (SVR) to predict the signal-to-noise ratio (SNR), but none of them use the information that satellites have strong motion patterns. Long short-term memory (LSTM) is a recurrent neural network with memory. It controls the degree of memory of historical information and the degree of adoption of new information by forgetting gates, input gates, and output gates, and can recognize past satellite information through memory units.
发明内容Summary of the invention
本发明针对现有技术的缺陷,提供了一种基于LSTM的低轨卫星通信自适应编码方法。In view of the defects of the prior art, the present invention provides a low-orbit satellite communication adaptive coding method based on LSTM.
为了实现以上发明目的,本发明采取的技术方案如下:In order to achieve the above invention object, the technical solution adopted by the present invention is as follows:
一种基于LSTM的低轨卫星通信自适应编码方法,包括以下:An adaptive coding method for low-orbit satellite communication based on LSTM, comprising the following:
步骤1、地面设备获取当地实时天气与经纬度;Step 1: The ground equipment obtains the local real-time weather and longitude and latitude;
步骤2、根据存储在地面设备中的卫星轨道信息生成卫星的位置信息,以三维坐标表示;Step 2: Generate satellite position information based on satellite orbit information stored in ground equipment, expressed in three-dimensional coordinates;
步骤3、建立利用实时天气、经纬度和位置信息、基于LSTM的预测SNR模型;Step 3: Establish a LSTM-based prediction SNR model using real-time weather, longitude and latitude, and location information;
步骤4、根据查表法选择最优的编码方案。Step 4: Select the optimal coding scheme based on the table lookup method.
进一步地,步骤1的具体步骤如下:Furthermore, the specific steps of step 1 are as follows:
步骤1.1地面设备获取自身经纬度;Step 1.1 The ground device obtains its own latitude and longitude;
步骤1.2地面设备根据经纬度请求网站获取实时天气;Step 1.2 The ground device requests the website to obtain real-time weather according to the latitude and longitude;
需要注意的是,由于低轨卫星与地面设备单次通信时间很短,通常为几分钟,因此认为通信开始时刻的天气即为本次通信的天气,故仅需在通信开始时请求一次天气情况即可;It should be noted that since the single communication time between low-orbit satellites and ground equipment is very short, usually a few minutes, the weather at the start of communication is considered to be the weather for this communication, so it is only necessary to request the weather conditions once at the start of communication;
进一步地,步骤2的具体步骤如下:Furthermore, the specific steps of step 2 are as follows:
步骤2.1地面设备需要存储每个卫星的轨道信息,并具备找出在指定时间内可以通信的卫星的能力;轨道信息是通过计算描述并预测卫星位置的信息,由两行轨道要素形式表示,采用两行80字符的ASCII码来存储数据,存储所占的空间很少;Step 2.1 The ground equipment needs to store the orbital information of each satellite and have the ability to find the satellites that can communicate within a specified time. The orbital information is the information that describes and predicts the satellite position through calculation. It is represented by two lines of orbital elements and uses two lines of 80 characters of ASCII code to store data. The storage space is very small.
步骤2.2将卫星的位置由轨道信息转化为三维坐标;Step 2.2 converts the satellite position from orbital information into three-dimensional coordinates;
进一步地,步骤3的具体步骤如下:Furthermore, the specific steps of step 3 are as follows:
步骤3.1使用实时天气、经纬度和位置信息组成序列Step 3.1 Use real-time weather, latitude and longitude, and location information to form a sequence
(UElat,UElon,Satlat,SatLon,Satalt,Weather);(UE lat ,UE lon ,Sat lat ,Sat Lon ,Sat alt ,Weather);
其中UElat,UElon分别为地面设备的经纬度,Satlat,SatLon,Satalt为卫星的经纬度和高度,Weather为当地的实时天气;Where UE lat and UE lon are the latitude and longitude of the ground equipment, Sat lat , Sat Lon and Sat alt are the latitude and longitude and altitude of the satellite, and Weather is the local real-time weather.
步骤3.2将步骤3.1中的序列输入LSTM网络进行训练,使用MAE作为误差函数;MAE为真实的SNR与预测的SNR之间的差值的绝对值;误差函数是用来进行反向传播的,更新网络中的参数;Step 3.2: Input the sequence in step 3.1 into the LSTM network for training, and use MAE as the error function; MAE is the absolute value of the difference between the actual SNR and the predicted SNR; the error function is used for back propagation to update the parameters in the network;
步骤3.3使用训练的LSTM进行预测、验证;Step 3.3 Use the trained LSTM for prediction and verification;
其中,验证步骤是为了证明在网络没有过拟合,将全部数据集分为训练集、验证集、测试集三个部分,并在训练时观测验证集上的情况,以确定模型的过拟合情况;The verification step is to prove that the network is not overfitting. The entire data set is divided into three parts: training set, validation set, and test set. The situation on the validation set is observed during training to determine the overfitting of the model.
进一步地,步骤4的具体步骤如下:Furthermore, the specific steps of step 4 are as follows:
根据预测的SNR查表选择编码方案,选择误包率(Package Error Rate,PER) 小于0.1的冗余率最低的编码方案;Select a coding scheme based on the predicted SNR by looking up the table, and choose the coding scheme with the lowest redundancy rate with a packet error rate (PER) less than 0.1;
其中,误包率是在通信中一帧数据内存在误码的概率,通常认为小于0.1即可正常通信;Among them, the packet error rate is the probability of a bit error in a frame of data during communication. It is generally believed that normal communication is possible when it is less than 0.1;
其中,冗余率是前向纠错编码中用于纠错的比特数占总比特数的比例,即冗余率=(用于纠错的编码数/总比特数)×100%。The redundancy rate is the ratio of the number of bits used for error correction in the forward error correction coding to the total number of bits, that is, redundancy rate=(number of codes used for error correction/total number of bits)×100%.
与现有技术相比,本发明的优点在于:Compared with the prior art, the advantages of the present invention are:
1.使用LSTM对包含天气信息在内的信道质量SNR进行预测,考虑了前几个时刻的SNR,充分利用了卫星运行规律;1. Use LSTM to predict the channel quality SNR including weather information, taking into account the SNR of the previous moments and making full use of the satellite operation rules;
2.由于LSTM可以学习到经纬度等信息,进而学习到不同地区的雨衰值,得到了全球通用模型;2. Since LSTM can learn information such as longitude and latitude, it can then learn the rain attenuation values of different regions and obtain a global universal model;
附图说明BRIEF DESCRIPTION OF THE DRAWINGS
图1为本发明实施例中LSTM网络结构图;FIG1 is a diagram showing the structure of an LSTM network according to an embodiment of the present invention;
图2为本发明实施例中LSTM神经元结构图;FIG2 is a diagram of the structure of an LSTM neuron in an embodiment of the present invention;
图3为本发明实施例中不同编码方案冗余率的误包率图;FIG3 is a diagram of packet error rates for different coding scheme redundancy rates according to an embodiment of the present invention;
图4为本发明实施例中不同方法在全球不同地区的MAE累积分布图 (CumulativeDistribution Function,CDF);FIG4 is a cumulative distribution diagram (Cumulative Distribution Function, CDF) of MAE in different regions around the world for different methods in an embodiment of the present invention;
图5为本发明实施例中不同方法在全球不同地区最佳编码方案匹配率 (OptimalMatch Ration,OMR)的CDF图。FIG5 is a CDF diagram of the optimal coding scheme matching ratio (Optimal Match Ration, OMR) of different methods in different regions of the world according to an embodiment of the present invention.
具体实施方式Detailed ways
为使本发明的目的、技术方案及优点更加清楚明白,以下根据附图并列举实施例,对本发明做进一步详细说明。In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and examples.
如图1所示,本实施例论述的是一种基于LSTM的低轨卫星通信自适应编码方法在卫星-地面通信方面的应用。As shown in FIG1 , this embodiment discusses the application of an LSTM-based low-orbit satellite communication adaptive coding method in satellite-to-ground communication.
本实施例基于LSTM网络,该网络负责识别地面用户(User Equipment,UE) 的二维位置和卫星的三维位置以及UE所在处的天气情况,并根据过往时刻的通信质量预测得到下一时刻的SNR。应用本发明所述一种基于LSTM的低轨卫星通信自适应编码方法实施例如下:This embodiment is based on an LSTM network, which is responsible for identifying the two-dimensional position of the ground user (User Equipment, UE) and the three-dimensional position of the satellite and the weather conditions where the UE is located, and predicting the SNR at the next moment based on the communication quality at the past moment. The embodiment of the low-orbit satellite communication adaptive coding method based on LSTM described in the present invention is as follows:
步骤1、地面设备获取当地实时天气与其经纬度:Step 1: The ground equipment obtains the local real-time weather and its latitude and longitude:
步骤1.1地面设备获取自身经纬度,如UE的实时经纬度为(UElat,UElon),该经纬度信息可以由GPS卫星定位或者基站定位得到,若缺失以上信息,可以使用 UE最后交互的地面基站位置作为缺省位置;Step 1.1 The ground device obtains its own longitude and latitude. For example, the real-time longitude and latitude of the UE is (UE lat , UE lon ). The longitude and latitude information can be obtained by GPS satellite positioning or base station positioning. If the above information is missing, the last ground base station location interacted by the UE can be used as the default location;
步骤1.2地面设备根据经纬度请求网站获取实时天气,在获取到了经纬度信息后,UE可以请求天气API以获得此地的实时天气;Step 1.2 The ground device requests the website to obtain real-time weather according to the longitude and latitude. After obtaining the longitude and latitude information, the UE can request the weather API to obtain the real-time weather of the location;
其中,API为Application Programming Interface,应用程序界面的缩写,用户向API发送请求,API会给出相应的答复;API is the abbreviation of Application Programming Interface. Users send requests to API, and API will give corresponding responses.
需要注意的是仅有每次链接开始时需要查询当地天气,因为低轨卫星的连接时间都很短,一般为几分钟。以Starlink为例,其通信直径为1100千米,最长的连接时间为170秒,因此仅当连接开始时查询天气不会对服务器造成过大负担,也不会额外占用过多通信资源。It should be noted that the local weather needs to be queried only at the beginning of each connection, because the connection time of low-orbit satellites is very short, generally a few minutes. Taking Starlink as an example, its communication diameter is 1,100 kilometers and the longest connection time is 170 seconds. Therefore, querying the weather only at the beginning of the connection will not cause too much burden on the server, nor will it take up too many additional communication resources.
步骤2、根据存储在地面设备中的卫星轨道信息生成卫星的位置信息,以三维坐标表示:Step 2: Generate satellite position information based on satellite orbit information stored in ground equipment, expressed in three-dimensional coordinates:
步骤2.1地面设备需要存储每个卫星的轨道信息,并具备找出在指定时间内可以通信的卫星的能力:Step 2.1 The ground equipment needs to store the orbital information of each satellite and have the ability to find the satellite that can communicate within the specified time:
卫星轨道的信息多以两行轨道信息存储,这种存储方式为全球通用,且十分节省存储空间,即使存储目前在轨的全部卫星的轨道信息也只需800KB空间。Satellite orbit information is mostly stored in two lines of orbit information. This storage method is universally used and saves a lot of storage space. Even storing the orbit information of all satellites currently in orbit only requires 800KB of space.
表1卫星CALSPHERE 1轨道信息Table 1 Satellite CALSPHERE 1 orbit information
表1为2022年1月4日发射的卫星CALSPHERE 1的轨道参数信息:Table 1 shows the orbital parameter information of the satellite CALSPHERE 1 launched on January 4, 2022:
第一行第一列表示其NASA唯一编号,U表示非机密卫星;The first row and the first column indicate its NASA unique number, and U indicates a non-confidential satellite;
第一行第二列表示该飞行器国际编号;The first row and second column indicate the international number of the aircraft;
第一行第三列为发射时间,比如22意味着2022年,004.58268302为其在2 022年的第4.58268302天发射;The third column of the first row is the launch time. For example, 22 means 2022, and 004.58268302 means it was launched on the 4.58268302nd day of 2022.
第二行的第二列为轨道倾角;The second column of the second row is the orbital inclination;
第二行第三列为升交点经度;The third column of the second row is the longitude of the ascending node;
第二行第四列为轨道偏心率;The second row and fourth column are the orbital eccentricity;
第二行第五列为近地点角距;The second row and the fifth column are the perigee angular distance;
第二行第六列为平近点角;The second row and sixth column is the mean anomaly angle;
第二行第七列为平运动速率;The second row and the seventh column are the horizontal motion rate;
通过以上轨道信息可以计算出在当前时间内在通信距离内的卫星及其具体位置。The above orbital information can be used to calculate the satellites within the communication distance and their specific positions at the current time.
步骤2.2将卫星的位置由轨道信息转化为三维坐标,可以采用拉格朗日多项式插值、牛顿多项式插值、内维尔逐次线性插值等方法将轨道信息转换为三维坐标信息,在仿真场景下可以使用卫星仿真软件STK(System Toolkit,STK)获取卫星不同时刻的位置;Step 2.2: Convert the satellite position from orbital information to three-dimensional coordinates. Lagrange polynomial interpolation, Newton polynomial interpolation, Neville successive linear interpolation and other methods can be used to convert orbital information into three-dimensional coordinate information. In the simulation scenario, satellite simulation software STK (System Toolkit, STK) can be used to obtain the position of the satellite at different times.
步骤3、建立利用步骤1、步骤2中信息、基于LSTM的预测SNR的模型;Step 3: Establish a model for predicting SNR based on LSTM using the information in steps 1 and 2;
步骤3.1使用步骤1、步骤2中信息组成序列Step 3.1 Use the information in steps 1 and 2 to form a sequence
将步骤1和步骤2中得到的信息组合起来,并且用One-Hot编码的方式表示天气信息,在实践中使用(Sunny,Cloudy,Rainy)表示天气,当晴天时编码为(1,0,0),多云时为(0,1,0),认为雨雪天气均为降水天气,统一视为降雨天气,编码为(0,0,1);Combine the information obtained in step 1 and step 2, and use One-Hot coding to represent the weather information. In practice, (Sunny, Cloudy, Rainy) is used to represent the weather. When it is sunny, it is coded as (1, 0, 0), and when it is cloudy, it is coded as (0, 1, 0). Rainy and snowy weather are all considered precipitation weather, and are uniformly regarded as rainfall weather, coded as (0, 0, 1);
至此构建了输入LSTM网络的八元组So far, the eight-tuple input to the LSTM network has been constructed
xt=(UElat,UElon,Satlat,SatLon,Satalt,Sunny,Cloudy,Rainy),其中UElat,UElon分别为地面设备的经纬度,Satlat,SatLon,Satalt为卫星的经纬度和高度, (Sunny,Cloudy,Rainy)表示当地天气;x t =(UE lat ,UE lon ,Sat lat ,Sat Lon ,Sat alt ,Sunny,Cloudy,Rainy), where UE lat ,UE lon are the longitude and latitude of the ground equipment, Sat lat ,Sat Lon ,Sat alt are the longitude and latitude and altitude of the satellite, and (Sunny,Cloudy,Rainy) represents the local weather;
在仿真时每个时刻即每隔1秒均有一条对应的信息。During the simulation, there is a corresponding piece of information at each moment, that is, every 1 second.
步骤3.2将上一步中的序列输入LSTM网络进行训练,使用MAE作为误差函数;Step 3.2 Input the sequence in the previous step into the LSTM network for training, using MAE as the error function;
LSTM网络的结构图如图1所示,引入了嵌入层(Embedding Layer)分别处理天气和位置信息。有3个神经元负责处理One-Hot编码的天气信息,5个神经元负责处理位置信息。嵌入层后面为1层LSTM层,该层含有100个神经元,并负责对过往信息的记忆;LSTM层后面为含有100个神经元的全连接层,负责整合L STM层的信息;最后为含有一个神经元的输出层,输出预测的SNR。The structure of the LSTM network is shown in Figure 1. The embedding layer is introduced to process weather and location information respectively. There are 3 neurons responsible for processing One-Hot encoded weather information, and 5 neurons responsible for processing location information. The embedding layer is followed by an LSTM layer, which contains 100 neurons and is responsible for memorizing past information; the LSTM layer is followed by a fully connected layer containing 100 neurons, which is responsible for integrating the information of the LSTM layer; and finally, there is an output layer containing one neuron, which outputs the predicted SNR.
LSTM网络依靠三个门函数解决了长期依赖的问题,可以依靠门函数记住长时间的信息,这三个门函数分别是遗忘门、输入门和输出门,如图2所示;The LSTM network solves the problem of long-term dependency by relying on three gate functions. It can remember long-term information by relying on gate functions. These three gate functions are forget gate, input gate and output gate, as shown in Figure 2.
(1)遗忘门:当网路得到新的输入时,网络如果需遗忘旧的信息,此时通过遗忘门来完成。遗忘门是LSTM网络的重要组成部分,可以控制哪些信息需要保留、哪些信息要遗忘,并且避免梯度随时间反向传播时引发的梯度爆炸和梯度消失的难题。遗忘门决定LSTM网络从上一时刻的网络状态Ct-1中遗忘什么信息。遗忘门读取上一时刻输出值ht-1和此时输入值xt,然后通过sigmoid激活函数将其映射到0到1之间的数值,最终该数值再与网络状态Ct-1相乘,来决定Ct-1该丢弃什么信息。当遗忘门数值为1时表示完全地保留网络状态Ct-1的信息,当该数值为0时表示完全地丢弃上一时刻网络状态Ct-1的信息。遗忘门的表达式为:(1) Forget gate: When the network receives new input, if the network needs to forget the old information, this is done through the forget gate. The forget gate is an important component of the LSTM network. It can control which information needs to be retained and which information needs to be forgotten, and avoid the problems of gradient explosion and gradient vanishing caused by the gradient back propagation over time. The forget gate determines what information the LSTM network forgets from the network state C t-1 at the previous moment. The forget gate reads the output value h t-1 at the previous moment and the input value x t at this moment, and then maps it to a value between 0 and 1 through the sigmoid activation function. Finally, this value is multiplied by the network state C t-1 to determine what information C t-1 should discard. When the forget gate value is 1, it means that the information of the network state C t-1 is completely retained. When the value is 0, it means that the information of the network state C t-1 at the previous moment is completely discarded. The expression of the forget gate is:
ft=σ(Wf[ht-1,xt]+bf), ft =σ( Wf [ht -1 , xt ]+ bf ),
(2)输入门:确定哪部分新的输入信息被保留在网络状态中。输入门用于控制网络当前输入数据xt流入记忆单元的多少,即有多少输入信息xt可以保存到当前网络状态Ct中。输入门包含两部分,第一部分:由sigmoid激活函数组成、产生的介于0到1之间的控制信号it,用来控制此时的网络状态输入的程度;第二部分为通过tanh层产生的当前时刻的候选网络状态/>这个值将由it决定添加到网络状态中的程度。输入门的状态表达式为:(2) Input gate: determines which part of the new input information is retained in the network state. The input gate is used to control how much of the network's current input data xt flows into the memory unit, that is, how much input information xt can be saved in the current network state Ct . The input gate consists of two parts. The first part: a control signal i t between 0 and 1 generated by a sigmoid activation function, which is used to control the network state at this time. The second part is the candidate network state at the current moment generated by the tanh layer/> This value will be added to the network state to a certain extent by it . The state expression of the input gate is:
it=σ(Wi[ht-1,xt]+bi), it =σ( Wi [ht -1 , xt ]+ bi ),
在获得了遗忘门和输入门的状态后,可以更新网络的状态:After obtaining the status of the forget gate and the input gate, the status of the network can be updated:
其中Ct为最终确定的此刻网络状态。Where Ct is the final network status at this moment.
(3)输出门:输出值基于当前时刻网络状态,但是会有过滤、筛选的过程。输出门也包括两部分操作:第一部分为由sigmoid激活函数组成产生的介于0到 1之间的控制信号ot;第二部分为将经过tanh函数后产生的输出信息tanh(Ct)与控制信号ot相乘,得到最终的此刻的输出值ht。输出门控制记忆单元Ct对当前输出值ht的影响,即记忆单元中的哪些部分会在此刻被输出。(3) Output gate: The output value is based on the current network state, but there will be a filtering and screening process. The output gate also includes two operations: the first part is the control signal o t between 0 and 1 generated by the sigmoid activation function; the second part is to multiply the output information tanh(C t ) generated by the tanh function with the control signal o t to obtain the final output value h t at this moment. The output gate controls the influence of the memory unit C t on the current output value h t , that is, which parts of the memory unit will be output at this moment.
在误差反向传播的过程中,使用MAE(Mean Absolute Error)作为误差度量标准,因为相比于MSE(Mean Squared Error)而言,MAE倾向于在误差很小时继续减小误差,而MSE由于其平方的属性会出现梯度消失。In the process of error back propagation, MAE (Mean Absolute Error) is used as the error metric because compared to MSE (Mean Squared Error), MAE tends to continue to reduce the error when the error is very small, while MSE will have a vanishing gradient due to its square property.
在训练时可以从网上获取全球各地的分时天气信息,During training, you can obtain real-time weather information from all over the world from the Internet.
步骤3.3使用训练完成的LSTM进行预测、验证;Step 3.3 Use the trained LSTM to perform prediction and verification;
由于神经网络具有过拟合的倾向,将整体数据集按照7:2:1的比例分为训练集、验证集、测试集,三个数据集的数据互不重合,并被打乱。在训练时每隔 10个Epoch对验证集进行预测,以观察网络是否过拟合。Since neural networks tend to overfit, the overall data set is divided into a training set, a validation set, and a test set in a ratio of 7:2:1. The data of the three data sets do not overlap and are shuffled. During training, the validation set is predicted every 10 epochs to observe whether the network is overfitting.
在训练结束后对测试集进行采样,获得最终的训练结果。After the training is completed, the test set is sampled to obtain the final training results.
训练时学习率选择0.001,batch size设为128,相关的时刻设置为5。During training, the learning rate is set to 0.001, the batch size is set to 128, and the related time is set to 5.
训练后,对比不同方法的MAE如表2:After training, the MAE of different methods is compared as shown in Table 2:
表2不同方法的MAETable 2 MAE of different methods
可以看出LSTM与真实值的误差是其中最小的。It can be seen that the error between LSTM and the true value is the smallest.
图3的横轴为MAE,纵轴为全球不同地点的累计分布函数(Cumulative Distribution Function,CDF)。由图中可以看出在全球的不同地点LSTM均表现优于其他方法。The horizontal axis of Figure 3 is MAE, and the vertical axis is the Cumulative Distribution Function (CDF) of different locations around the world. It can be seen from the figure that LSTM performs better than other methods in different locations around the world.
步骤4、根据查表法选择最优的编码方案。Step 4: Select the optimal coding scheme based on the table lookup method.
根据太空咨询系统咨询委员会(Consultative Committee for Space DataSystems,CCSDS)规定,近地轨道卫星的通信编码为伪随机低密度校验码(Quas i-cyclicLow Density Parity Check,QC-LDPC)中的AR4JA码(accumulate-r epeat-4-jagged-accumulate,AR4JA)。CCSDS使用了AR4JA码并规定了3种不同的数据率,分别为50%,66%,80%。如图4所示,在较低信噪比时,通信环境较差,应当选择数据率较低的、冗余率较高的编码方案以保证通信质量;而通信质量较好时,应当选择可以传输更多数据的编码方案以提高总体吞吐量。According to the Consultative Committee for Space Data Systems (CCSDS), the communication code for low-Earth orbit satellites is the AR4JA code (accumulate-repeat-4-jagged-accumulate, AR4JA) in the pseudo-random low-density parity check code (QC-LDPC). CCSDS uses the AR4JA code and specifies three different data rates, 50%, 66%, and 80%. As shown in Figure 4, when the signal-to-noise ratio is low, the communication environment is poor, and a coding scheme with a lower data rate and a higher redundancy rate should be selected to ensure the communication quality; when the communication quality is good, a coding scheme that can transmit more data should be selected to improve the overall throughput.
在实践当中,选择了误包率PER小于0.1的冗余率最低的编码方案作为最佳编码方案,这在实际的低轨卫星通信场景中也是经常使用的。并以最佳匹配率(O ptimal MatchRation,OMR)表示自适应编码系统整体的性能表现。OMR为在不同的预测手段下,可以选对最优编码方案数占总测试数的比例。In practice, the coding scheme with the lowest redundancy rate and a packet error rate PER less than 0.1 is selected as the optimal coding scheme, which is also often used in actual low-orbit satellite communication scenarios. The optimal match ratio (OMR) is used to represent the overall performance of the adaptive coding system. OMR is the ratio of the number of optimal coding schemes that can be selected under different prediction methods to the total number of tests.
表3不同方法的OMRTable 3 OMR of different methods
在图5中可以看到相较于其他方法而言,LSTM的OMR是最高的,而且在全球不同地点性能表现方差也比其他方法小。As can be seen in Figure 5, compared with other methods, LSTM has the highest OMR, and the performance variance in different locations around the world is also smaller than other methods.
本领域的普通技术人员将会意识到,这里所述的实施例是为了帮助读者理解本发明的实施方法,应被理解为本发明的保护范围并不局限于这样的特别陈述和实施例。本领域的普通技术人员可以根据本发明公开的这些技术启示做出各种不脱离本发明实质的其它各种具体变形和组合,这些变形和组合仍然在本发明的保护范围内。Those skilled in the art will appreciate that the embodiments described herein are intended to help readers understand the implementation methods of the present invention, and should be understood that the protection scope of the present invention is not limited to such special statements and embodiments. Those skilled in the art can make various other specific variations and combinations that do not deviate from the essence of the present invention based on the technical revelations disclosed by the present invention, and these variations and combinations are still within the protection scope of the present invention.
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