A Survey on Air-Ground Networks of Unmanned Aerial Vehicles
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摘要:
无人机具有快速部署、成本低廉等优势. 无人机空地网络通过将基站设备部署至升空无人机平台,能从空中快速构建对地覆盖网络,因而在应急救灾、偏远覆盖、智能交通、智慧城市等方面具有广阔的应用前景,近年来受到广泛关注. 面向无人机空地网络应用场景,结合无人机的机动、组网、载荷等特点,围绕无人机空地网络覆盖性能提升、无人机空地网络通感算一体化设计、智能反射面技术辅助的无人机空地网络、鲁棒无人机空地网络四个维度,从网络场景、关键技术挑战、性能优化控制方法等几方面梳理无人机空地网络的研究现状,并探索优化提升无人机空地网络性能的未来研究方向.
Abstract:Unmanned aerial vehicles (UAVs) can be rapidly and cost-effectively deployed. By deploying the base station equipment to the launching UAV platform, the air-ground networks of UAVs can quickly build ground coverage network from the air, so it has broad application prospects in emergency relief, remote area coverage, intelligent transportation, smart city, and other aspects and has received wide attention in recent years. Based on the application scenario of air-ground networks of UAVs, the characteristics of UAVs’maneuver, network, and load were considered. From the four dimensions of coverage performance improvement of air-ground networks, integrated communication-sensing-calculation design of air-ground networks, reconfigurable intelligent surfaces (RIS)-assisted air-ground networks, and robust air-ground networks of UAVs, the research status of air-ground networks of UAVs was reviewed in terms of network scenarios, key technical challenges, and performance optimization control methods. In addition, the future research direction of optimizing the performance of air-ground networks of UAVs was explored.
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轨底坡是铁路轨道的重要几何参数. 合理的轨底坡可以改善轮轨匹配关系,有效降低轮轨接触压力,减少轮轨磨耗,降低轮轨接触疲劳损伤,提高轮轨使用寿命,同时也可提高车辆运行的平稳性[1],但在线路设计、验收和维护过程中几乎很少关注轨底坡. 《高速铁路轨道工程质量验收标准》(TB 10745—2010)[2]中无轨底坡的验收标准,并且在日常的轨道养护维修规则中也未提及关于轨底坡的相关规定. 在线路精调过程中只保证钢轨垂向平顺度和轨距不平顺符合要求,不对轨底坡进行测量和精调.
关于轨底坡的研究从未间断过. 陶功权等[3]建立了B型地铁车辆动力学模型,从动力学角度提出了LM、S1002和 DIN5573 三种不同车轮型面最优的轨底坡匹配;同时从静力学分析的角度提出了地铁车轮型面的最优轨底坡匹配[4]. 陈超[5]分析了LM型面不同轨底坡与磨耗之间的关系,给出了直线段和曲线段的轨底坡推荐值. 周宇等[6]建立基于临界平面法的裂纹萌生寿命预测模型,研究了不同轨底坡对曲线段钢轨疲劳裂纹寿命的影响. 都敏等[7]通过建立弹塑性有限元模型,从轮轨接触应力角度分析了不同轨底坡对磨耗的影响. 刘鹏飞等[8]针对30 t轴重重载线路研究了LM车轮踏面在不同轨底坡下对轮轨接触几何关系,分析了车辆动态曲线通过时轮轨横向力、磨耗指数等因素的影响. 邓建辉等[9]采用不同钢轨材料与LM踏面相匹配,分析了在不同轨底坡条件下轮轨接触斑状态,观测了现场损伤情况. 司道林等[10]通过不同轨底坡条件下,CHN75钢轨与LM车轮踏面的静态轮轨接触,分析了轨道的曲线动态通过性能,给出了1∶20轨底坡适合重载铁路的结论. 李霞等[11]改进了三维接触几何参数算法和三维弹性体非赫兹接触理论,并对比分析了不同轨底坡对轮轨接触参数、摩擦功和接触应力等影响. 关庆华等[12]对比了标准轨底坡条件下,利用基于赫兹接触理论的法向接触刚度计算公式与经验方法的差异. 李霞等[13]对比分析了在两种轨底坡条件下LM和LMA车轮踏面与CHN60钢轨踏面匹配应力结果,得出LM-CHN60 和轨底坡1∶20、LMA-CHN60和轨底坡1∶40匹配较好的结论. 曾向荣等[1]通过国内外对铁路系统的轨底坡取值情况和现场光带的调查,提出了轨底坡建议值. 沈钢等[14]从减轻钢轨侧磨角度,分析了在曲线轨道上设置内外轨合理的轨底坡配比后车辆曲线通过时的滚动圆半径差和轮轮导向性能对侧磨的影响. Sadefhi等[15]基于理论分析和试验评价了轨底坡对铁路轨道几何条件的影响,提出了综合考虑轨底坡影响的轨道几何评价指数.
综上所述,过去对于轨底坡的研究均基于同一轨道上具有相同轨底坡的前提,研究轨底坡对轮轨接触关系和车辆动力学行为的影响. 针对线路中轨底坡存在一定离散性的情况,特别是同一轨道上出现轨底坡变化对车辆动力学行为的影响,值得深入研究. 本文在同一侧钢轨具有不同轨底坡的情况下,分析轨底坡变化对车辆动力学性能的影响,提出轨道线路轨底坡调整与维修的合理化建议,对现有轨道设计与工务维修提供参考.
1. 轮轨静态接触几何分析
轮轨静态接触几何计算是进行轮轨系统关系分析的基础. 迹线法是常用的轮轨接触几何关系计算方法,该方法的算法和数值实现过程参考文献[16-17]. 轮轨接触点分布分析是对现场轮轨接触光带预测的重要指标,同时轮轨接触点分布对车轮踏面磨耗分布具有非常重要的影响. 接触点过于集中会使得车轮磨耗过于集中,容易形成车轮凹磨,以及钢轨局部应力集中,影响车辆运行稳定性[18]. 图1计算了轨底坡从倾斜角度从1∶10到1∶100中的最大、中间和最小3种情况的轮轨接触点分布. 图中车轮廓形与钢轨廓形连接红线为轮轨接触点位置连线,车轮横移量标识在虚线上方数字(左移为正,单位:mm). 可以看出:随轨底坡角度变小轮轨接触点在钢轨表面位置从由外向轨距角内侧偏移,且接触区域逐渐变大. 由此可知:当轨底坡从1∶10突变到1∶100,接触光带将由窄变宽. 通过观测某客运专线一直线轨底坡波动区段同侧钢轨上接触光带,发现接触光带由钢轨中心外侧较窄变成较宽且覆盖轨顶,随后由较宽且覆盖轨顶变较窄的现象.
等效锥度是轮轨匹配除接触点以外的另一重要因素,也是轮对恢复对中能力的体现,图2给出了在不同轨底坡下等效锥度随轮对横移量的变化. 针对LMD型面与CHN60型面在不同的轨底坡匹配中,轨底坡在1∶10~1∶100变化,在横移量小于6 mm时等效锥度呈现从最小到最大(轨底坡1∶30的情况),随后趋于平稳的过程. 在横移量较小的情况下,轨底坡从1∶10到1∶30过程,等效锥度波动比较明显.
2. 轨底坡对车辆动力学性能的影响
2.1 车辆动力学模型
使用多体动力学软件SIMPACK建立某高速车辆动力学模型. 由于前后转向架采用相同的参数,采用SIMPACK子结构模型方式搭建整车模型. 该模型包括1个车体、2个构架、4条轮对、8个轴箱共15个刚体. 轮对通过一系悬挂、轴箱转臂与构架相连,轮对采用轴箱转臂定位方式,一系悬挂由钢弹簧、减振器组成,采用弹簧阻尼单元模拟. 构架通过二系悬挂与车体相连,二系悬挂包括2个空气弹簧、2个横向减振器和横向止挡、2个牵引拉杆、2个抗蛇行减振器和1个抗侧滚扭杆. 模型中考虑一系垂向减振器、二系横向减振器、抗蛇行减振器和横向止挡的非线性特性,其非线性特性见图3.
采用标准60 kg/m CHN60钢轨型面,轨距为1435 mm,采用实测轨底坡,车轮半径为420 mm,车轮型面为LMD,轮背内侧距为1353 mm. 采用沈氏理论计算轮轨蠕滑力,轮轨摩擦系数为0.35.
2.2 动力学仿真分析
轨道作为车辆运行的承载体,轨道参数的变化最为直观的表现则体现在车辆运行品质. 本文针对轨道养护中只关注高低、方向和水平不平顺,忽略轨底坡突变的情况,以车辆运行平稳性和舒适性作为评价指标,分析标准轨底坡和实测线路轨底坡的变化对车辆的影响. 线路轨底坡输入为国内某条运营速度200 km/h的客运专线直线段实测数据,此线路运行车辆为城际动车组. 本文测试区段为填充式垫板区段,测量间隔为25 m,测量结果如表1所示. 通过使用轨道几何尺寸检测小车与轨底坡测量仪检测发现,此段线路未发现轨面高低、方向、水平、扭曲等不平顺超标,但测量发现轨底坡发生较大变化. 通过对现场的观察发现造成轨底坡变化的原因有:线路中使用充填式垫板和橡胶垫板两种类型,充填式垫板充填不密实,设置角度发生变化;长时间运行后,充填式垫板发生压溃等;橡胶垫板,由于钢轨内外侧扣件扣压力不一致,即两侧基于扣件螺栓的扭矩不一致;在轨道精调过程中出现安装偏置的情况;橡胶垫板在使用过程中出现断裂等情况,以上情况均会出现轨底坡变化,其中充填式垫板中表现的轨底坡变化最为明显. 仿真中轨底坡布置分为标准轨底坡(1∶40)、对称布置轨底坡(即右轨轨底坡与实测左轨相同),非对称布置轨底坡(左、右轨均用实测轨底坡)3种情况. 曲线几何参数为客运专线实际曲线参数,曲线半径3500 m、超高125 mm、缓和曲线长 250 m. 轨底坡则采用直线工况对应轨底坡,采用京津线实测轨道不平顺作为轨道激励. 在计算过程中,为排除轮轨磨耗对计算结果的影响,轮轨型面均采用标准型面,同时根据实测轨道的位置,将钢轨的型面按照实测轨底坡情况进行旋转,保证不同截面钢轨最高点和横向轨距点位置均在同一平面上,按照测试纵向里程位置进行设置,即轨底坡参数体现在轨面数据旋转上,钢轨截面之间通过B样条曲线形成映射,保证截面之间的平顺.
表 1 实测线路轨底坡Table 1. Measured cants on tracks距离 /m 曲/直线段 距离 /m 曲/直线段 左轨 左轨 左轨 左轨 0 1∶40 1∶40 625 1∶35 1∶30 150 1∶40 1∶40 650 1∶50 1∶10 175 1∶10 1∶25 675 1∶20 1∶50 200 1∶15 1∶20 700 1∶40 1∶25 225 1∶25 1∶40 725 1∶25 1∶10 250 1∶45 1∶50 750 1∶45 1∶50 275 1∶65 1∶65 775 1∶40 1∶30 300 1∶100 1∶15 800 1∶40 1∶40 325 1∶40 1∶30 825 1∶20 1∶10 350 1∶35 1∶50 850 1∶50 1∶35 375 1∶10 1∶20 875 1∶30 1∶40 400 1∶40 1∶40 900 1∶15 1∶100 425 1∶30 1∶40 925 1∶65 1∶65 450 1∶50 1∶45 950 1∶50 1∶45 475 1∶10 1∶25 975 1∶40 1∶25 500 1∶25 1∶40 1000 1∶20 1∶15 525 1∶50 1∶20 1025 1∶25 1∶10 550 1∶10 1∶50 1050 1∶40 1∶40 575 1∶30 1∶35 1100 1∶40 1∶40 600 1∶20 1∶20 1200 1∶40 1∶40 针对不同的轨底坡设置,通过使用Hopf分岔的方法计算了车辆的临界速度,如图4所示,临界速度随轨底坡变化(从1∶10到1∶100)呈现先提高,到1∶40时达到最大,随后下降最后趋于平缓的趋势. 由此可见,轨底坡的波动变化势必引起车辆临界速度的改变,进而影响车辆的运行平稳性.
故针对同一轨道的轨底坡变化,计算得出车辆在直线和曲线线路条件下垂向和横向sperling平稳性指标分别如图5、6所示. 垂向、横向平稳性指标均小于2.5,达到GB 5599—2019[19]标准规定的“优”级. 车辆在直线和曲线线路上的垂向和横向平稳性均随速度线性增大,其中横向平稳性随速度影响较大;图5可知:直线段和曲线段垂向平稳性指标随速度增加较为缓和,直线段标准轨底坡情况下维持在0.8. 垂向平稳性指标在对称和非对称布置轨底坡情况较标准轨底坡情况,分别增加了32.96%和34.52%. 直线段轨底坡变化对车辆垂向平稳性影响较大,而曲线段影响比较小.
由图6可知:直线线路条件下横向平稳性大于垂向平稳性,对称不规则轨底坡布置和非对称不规则轨底坡布置的平稳性均大于标准轨底坡布置条件,与标准条件相比平稳性指标最大值增加40.65%,曲线条件下增加18.23%. 曲线段的平稳性在3种轨底坡条件下基本一致. 因为车辆以不同速度通过曲线时,由于欠/过超高的存在造成车辆自身的振动大于轨底坡的影响,而直线段的影响主要由轨底坡决定.
本文也根据UIC 513:1994[20]车辆乘坐舒适度标准对车辆的舒适性进行了分析,其直线段和曲线段运行的车辆舒适性和平稳性两者表征基本一致.
从图5、6可以看出:轨底坡的变化在直线段对车辆运行的影响较大,从车体的横向晃动水平也可以看出(图7):轨底坡角度差变化较大的区段,车体横向晃动也比较明显,且与轨底坡角度变化具有伴随状态. 针对车体横向晃动进行频率分析(图8),发现非对称变化轨底坡布置情况下车体晃动频率表现为1.33 Hz,对称变化轨底坡布置情况下为1.62 Hz;若车辆运行速度不变,轨底坡变化间隔缩短一倍,则车辆横向晃动频率则可能随之增加,引起车辆构架加速度报警,进而增加车辆横向晃动的风险. 在曲线段同样存在车辆从过超高进入欠超高状态,发生车轮向曲线外侧横移加之高低股轨底坡差异,造成滚动圆半径差的突变,会加剧车辆的横向晃动.
3. 轨底坡变化对车轮磨耗和滚动接触疲劳分析
本节主要研究同一线路(直线、曲线)轨底坡变化对车辆运行中车轮磨耗和滚动接触疲劳的影响. 采取与上一节一致的工况条件,均针对导向车轮,利用磨耗指数和疲劳损伤指数作为评价指标.
3.1 车轮磨耗分析
采用磨耗指数作为车轮磨耗评价指标,以此分析同一轨道不同轨底坡对车轮磨耗的影响. 其中,第
$i\;\;{\text{(}}i = 1,2, \cdots ,8{\text{)}}$ 个车轮每一个计算时间步t下的磨耗指数为Wi,t=|Tx,iγx,i|+|Ty,iγy,i|, (1) 式中:
$ T_{x,i}^{} $ 、$ T_{y,i}^{} $ 分别为第i个车轮纵向和横向蠕滑力;$ \gamma _{x,i}^{} $ 、$ \gamma _{y,i}^{} $ 分别为第i个车轮接触斑处纵向和横向蠕滑率.然后再利用式(2)计算车辆通过直线或曲线时第 i 个车轮经过 N 个时间步后磨耗指数移动均方根(root mean square, RMS)值为
WRMS,i=√N∑n=1W2i,ntN, (2) 式中:
${W_{i,nt}}$ 为第 i 个车轮的 n 个时间步下的磨耗指数.利用式(1)、(2)计算不同轨底坡布置条件下轮轨磨耗指数均方根值,
$ N $ 取值为500. 由于导向轮对轮轨间相互作用更为剧烈,所以本文采用导向轮的计算结果来讨论不同轨底坡布置对车轮磨耗的影响,利用导向轮磨耗指数最大RMS值统计分析变化规律.图9为车辆以250 km/h 的速度在直线段不同轨底坡布置的车轮磨耗指数对比结果. 同一轮对左右轮的磨耗指数基本一致,但受到轨道坡非对称布置的影响比较大,磨耗指数随着相连钢轨轨底坡的变化而发生变化,且随着非对称布置的轨底坡偏差大而发生在后一段钢轨上,这由于经历轨底坡的大变化,车轮与钢轨接触点发生较大跳跃,造成左右轮径差发生变化,使得车辆发生横向较大蠕滑和横移,增大轮轨间的磨耗指数.
直线段不同轨底坡布置车轮的最大磨耗指数均随速度增加而增加(如图10所示),左右轮的磨耗指数相差较小. 其中在速度大于180 km/h条件下,非对称布置轨底坡对车轮磨耗指数的影响均大于对称布置,同时也大于标准布置轨底坡,两种轨底坡变化情况相对于标准轨底坡情况最大磨耗指数分别增加136.71%和27.65%;轨底坡对称布置和标准轨底坡布置对车轮磨耗指数的影响随速度缓慢增加后加速发展. 非对称布置情况则随速度成指数形式增长. 由图9、10可知:轨底坡非对称布置在直线条件下受速度影响较大.
与直线段的表征不同,由于车辆通过曲线段的欠/过超高情况下,轨底坡的不规则的影响小于曲线参数设置对车辆的影响,故出现了不同轨底坡设置的磨耗指数在速度250 km/h时相一致的情况. 从图11可以看出:导向轮最大磨耗指数也表现为随速度成线性增加的趋势.
3.2 车轮滚动接触疲劳分析
本文采用基于安定图基础上EKBERG提出的表面疲劳指数来评价轮轨接触状态的疲劳程度,从而考量轨道不同轨底坡对车轮表面疲劳的影响. 车轮表面疲劳指数如式(3)所示.
δsurf=μ−2πabk3Fz, (3) μ=√T2x+T2yFz, (4) 式中:μ为轮轨接触位置的牵引系数; a和b分别为轮轨椭圆接触斑的短半轴和长半轴;k为材料纯剪切屈服强度;Fz为轮轨接触斑处法向力;
${T_{x}}$ 和${T_{y}}$ 分别为轮轨接触斑处纵向蠕滑力和横向蠕滑力.由式(3)、(4)可知:轮轨较差的牵引和导向性能(使得纵向/横向蠕滑力数增大)或较糟糕的轮轨几何接触关系(接触斑面积小或轮轨法向力大)均可导致表面疲劳指数增大,加速轮轨材料的疲劳破坏. 表面疲劳指数是基于安定图提出的,因此不能预测轮轨材料的疲劳寿命,而是评价轮轨材料表面发生疲劳损坏的可能性;
$ {\delta _{{\text{surf}}}} $ > 0, 此时轮轨材料变形将发生棘轮效应,塑性变形会持续累积,即能预测表面疲劳出现的可能性.不同速度等级下的车轮疲劳指数如图12所示. 由图12(a)可知:直线段非对称轨底坡布置的表面疲劳指数在不同速度条件下均大于对称轨底坡布置,对称轨底坡布置大于标准轨底坡布置条件,其中非对称布置条件下的车轮表面疲劳指数在0.175左右波动,对称布置条件下车轮表面疲劳指数在1.600左右波动,而标准轨底坡布置则在1.400左右波动.
直线段对称变化和非对称轨底坡布置的左轮表面疲劳指数的最大值比标准条件分别增大25.14%和15.86%;右侧车轮的表面疲劳指数分别增大24.96%和18.29%.
由图12(b)可知:对于曲线段内轨侧车轮,表面疲劳指数在3种轨底坡布置条件下,均随速度增加发生较大的线性增加,且增加幅度一致. 而高股车轮表面疲劳指数基本维持不变,非对称布置条件车轮表面疲劳指数略大于其他两种轨底坡布置情况.
4. 结 论
本文从轮轨关系和车辆动力学两个方面分析了轨底坡变化对车辆动力学行为和轮轨损伤的影响. 从车辆运行的角度分析轨道养护维修的策略. 研究结果表明:
1) 直线段和曲线段在同一轨道上采用对称和非对称轨底坡布置,其车辆垂向、横向平稳性和舒适性指标均大于采用标准轨底坡布置情况. 其中直线段同一轨道对称和非对称轨底坡布置对车辆的平稳性影响较大. 在曲线段同一轨道对称和非对称轨底坡布置对车辆的横向平稳性影响较大.
2) 直线段不同轨底坡布置车轮的最大磨耗指数均随速度呈指数函数增加,左右轮的磨耗指数相差较小. 曲线段不同轨底坡布置车轮的最大磨耗指数均随速度呈线性增加且均大于直线段. 故车辆通过欠/过超高情况下,轨底坡的不规则的影响小于曲线参数设置对车辆的影响.
3) 在直线段相对于标准布置轨底坡的车轮疲劳指数最小,对称轨底坡布置小于非对称布置,三种情况车轮疲劳指数受速度影响较小. 曲线段低股侧车轮表面疲劳指数则与速度成线性增加的趋势,高股侧车轮则受速度影响较小.
综上所述,直线段的轨底坡变化对车辆动力学行为的影响最为直接. 在线路设计、施工、动静态验收和日常养护维修中,从车辆运行的平稳性和舒适性,以及车轮的磨耗以损伤角度,需要对同一轨道内的轨底坡变化予以关注. 在线路维修中针对同一轨道内轨底坡变化情况,如果不方便进行轨底坡调整时可以采用钢轨打磨的方式进行轨面调整,以满足轨底坡的要求.
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表 1 无人机空地网络国内外研究现状汇总
Table 1. Research summary of air-ground UAV networks
场景
描述优化算法 控制手段 性能指标 来源 待进一步解决问题 无人机空地网络覆盖 启发式算法 无人机部署位置、
无人机轨迹用户覆盖百分比 文献[1,13] 现有研究通常针对用户静止场景下,采用传统优化算法实现轨迹与资源控制,以提高网络性能. 当地面用户数量增加且用户出现高移动特性时,如何进一步优化空地双移动约束下的对地网络覆盖性能还需进一步分析 覆盖率 文献[22,24] 凸优化 无人机部署位置、
无人机轨迹、功率覆盖用户数量 文献[14-15] 中断概率 文献[27-30] 聚类算法 无人机基站的三维位置、用户对路径损失的补偿因子 覆盖用户数量 文献[16-17,31] 回声状态网络、深度强化学习 无人机初始部署位置、轨迹、功率控制、带宽 吞吐量(移动用户覆盖问题) 文献[20] 覆盖时间与覆盖率 文献[21] 覆盖效率(覆盖率与覆盖时间比值) 文献[23-26] 基于网络的异构粒子群优化算法 无人机轨迹、带宽 覆盖面积 文献[33] 无人机空地网络通感算一体化 凸优化、聚类 射波束成型、无人机位置、轨迹、飞行速度、用户关联、发射波束成型、感知频率/时间、无人机飞行轨迹 平均用户速率 文献[4,13-15] 现有研究主要围绕通感一体化或通算一体化场景,未充分研究通感算一体化网络设计与优化控制. 此外,在网络控制时所采取的传统优化算法复杂度较高导致其很难适应高度变化的信道场景. 后续研究可针对无人机通感算场景,基于机器学习技术设计低复杂度的无人机通感算一体化网络管控方案 用户关联、功率分配、无人机位置 效用函数 文献[18] 任务卸载比、网络资源、无人机轨迹 能耗 文献[48-49] 深度强化学习 无人机飞行方向、飞行距离、功率分配、信道分配 感知有效性和公
平性文献[19] 任务卸载比、网络资源、无人机轨迹 时延 文献[51] 用户关联、无人机轨迹规划、功率分配 加权频谱效率 文献[52] 无人机轨迹、时隙总数、感知调度 感知目标的平均信息年龄 文献[8] RIS 辅助的无人机空地网络 深度强化学习
算法无人机飞行轨迹、频谱资源、计算资源、智能反射面系数、设备发射功率等 数据新鲜度 文献[61] 当前面向 RIS 辅助的无人机空地网络控制研究通常具有极高的控制复杂度和极大的信息反馈量,如何进一步降低网络控制复杂度并降低网络控制时的信息反馈量,使得其能够更好地适配无线环境变化 能耗 文献[62] 凸优化算法、块坐标下降法 无人机飞行轨迹、频谱资源、计算资源、智能反射面系数、设备发射功率等 能耗 文献[63] 能效 文献[12,65] 鲁棒无人机空地网络 联邦学习 设备选择、无人机部署、子信道分配、传输功率控制 最小化联邦学习模型的收敛时间和学习精度损失 文献[69-71] 当前研究考虑的外部电磁环境相对简单,当面对外部复杂电磁环境与有意干扰情况,如何提升无人机空地网络鲁棒性还需要进一步研究 深度优先搜索算法、连续凸近似、拉格朗日对偶、块坐标下降算法、遗传算法和粒子群算法 用户调度,带宽分配、功率控制、轨迹控制、半径和圆心 能耗效率、最大化每个用户的平均最小传输速率、最大化系统容量、最大化服务用户数 文献[19,72,75-77] 多智能体深度强化学习 飞行轨迹、子载波分配、通信/干扰功率 能耗效率、最大化每个用户的平均最小安全传输速率、最大化每个用户的安全容量 文献[78-81] -
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