TRACK 模块的配置与使用 | GNSS Helper
TRACK 是 GAMIT/GLOBK 程序的重要组成部分，该模块使用卡尔曼滤波算法，提供基于差分相位观测量的动态后处理定位功能。随着针对如飞行器、车辆、船舶或浮标等运动设备的 GPS 动态定位技术需求的不断增加，TRACK 模块凭借较高的数据处理精度，已成为该领域最受重视的程序工具之一。
本文将介绍 TRACK 模块的使用和配置过程。
使用方法TRACK 模块目前还只能处理针对 GPS 卫星的观测数据。该模块进行数据处理时，其所有的配置参数都是通过控制文件来输入的，因此控制文件的编辑是该模块的使用过程中最重要的部分。编写好配置文件之后，你可以用以下方式启动 TRACK 程序：
1$ track -f &cmd-file& -a &amb-file& -d &day& -w &week& -s &strings&
参数释义：
-f &cmd-file&：输入的控制文件
-a &amb-file&：输入的模糊度文件；
-d &day&：数据观测的年积日；
-w &week&：数据观测的 GPS 周；
-s &strings&：字符串组。
在这些参数中，只有控制文件是必要的。这里的 -d &day&、-w &week&、-s &strings& 实际上是为了编写控制文件模板而设置的变量。在编辑控制文件时，你可以使用 &day& 来代替年积日，使用 &week& 来代替 GPS 周，然后在运行 TRACK 时通过命令行参数来设置它们的值。
控制文件TRACK 模块的控制文件通常是一个 .cmd 文件，MIT 在其网站上给出了一个。在控制文件中，每一行作为一个控制命令，有效的控制命令必须以至少一个空白字符开始，否则将被当作注释。此外，有些控制命令可能需要多个输入项（例如观测数据），对于这样的命令，其后紧跟的非注释行都将被作为其子项，直到遇到一个空行。
在控制文件中，第一个控制命令必须是输入的观测数据，其后控制命令的顺序可以是任意的。接下来将对最主要的几个控制命令做详细介绍。
观测数据观测数据的输入使用 obs_file 命令，其后的每一行输入一个观测文件。因此其格式为：
123obs_file
&RINEX_file&
其中的 &site& 表示站名，&RINEX_file& 站点对应的观测文件，最后的 &type& 代表站点的活动状态（即静止或运动）。静止的站点使用 “F” 来标记，运动的站点使用 “K” 标记。
示例，输入两个站于 2018 年第 045 日的观测文件，其中 STAT 站为静态站，FLOT 为动态站。因此你可以这样设置：
123obs_file
stat0450.18o
flot0450.18o
星历数据导航卫星的星历数据使用 nav_file 输入。TRACK 程序既可以接收 RINEX 格式的广播星历数据，也可以接收 SP3 格式的精密星历数据。其输入格式为：
&NAVI_file&
这里的 &NAVI_file& 表示星历文件名，&type& 星历的数据类型标记。广播星历使用 NAV 标记，精密星历使用 &SP3& 标记。需注意的是，对于一个时段的解算，目前 TRACK 只能接受一个星历文件。因此如果要处理跨天的数据，你需要手动将星历数据拼接成一个文件。
示例，对应于上文的观测文件，以下命令输入精密星历数据：
igr19883.sp3
解算模式实际的数据处理中，根据观测环境和状态的不同，通常需要采取不同的解算策略。TRACK 提供了许多参数，给予你对解算过程最自由的控制权。为了简化配置过程，TRACK 同样提供了针对不同情况的快速设置。根据动态站载体或动态站和静态站之间的距离，你可以通过 mode 参数来对解算过程进行快速设置。解算模式的控制命令格式为：
1mode &type&
可用的解算模式有：
AIR：动态站位于飞行器上；
SHORT：站点之间的基线长度在 300km 内；
LONG：站点之间的基线长度大于 300km。
示例，要使用 SHORT 模式，只需进行如下配置：
1mode SHORT
概略坐标在默认情况下，TRACK 使用 RINEX 观测数据文件头中的概略坐标。但某些时候，观测文件中的概略坐标可能不正确，这将导致解算出错。此时你可以将正确的站点概略坐标写入到控制文件中。输入概略坐标的控制命令格式为：
12site_pos
这里，&site& 为站名，&X&、&Y&、&Z& 分别为站点在空间直角坐标系下的坐标分量。
示例，对应于上文的观测站，输入其概略坐标：
123site_pos
参考点坐标在默认情况下，TRACK 的解算结果将以所输入的第一个参考站的站心坐标系（即 NEU）的形式输出。当然，你也可以手动配置输出成果的参考点。参考点坐标的输入方式为：
这里的 &X&、&Y&、&Z& 分别为站点在空间直角坐标系下的坐标分量。
示例，配置参考点坐标：
成果输出形式TRACK 程序的数据处理成果默认以 NEU 坐标输出，但你也可以添加其他的成果输出形式。配置成果输出的控制命令为：
1out_type &type&
这里的 &type& 即成果的输出形式，它可以是以下一种或几种：
GEOD：大地坐标系；
NEU：站心坐标系；
DHU：解算结果与初始坐标的差异；
XYZ：空间直角（笛卡尔）坐标系；
DUMP：输出 L1/L2 伪距和相位组合的残差，如果输入了 IONEX 文件，还可以同时输出 TEC（总电子含量）。
以上选项可以自由组合，例如，配置同时输出 NEU 和大地坐标系（BLH）的坐标：
1out_type GEOD+NEU
解算间隔数据处理时选择合适的解算间隔也是很重要的，间隔太稠密将大大延长数据处理所需的时间。默认的数据处理间隔同观测文件一致，但你也可以用以下形式来配置：
1interval &num&
这里的 &num& 以秒作为单位。因此要将数据解算的间隔设置为 30 秒，你可以如下配置：
1interval 30
成果文件TRACK 程序的解算结果主要保存在 SUM 文件中，你可以使用 sum_file 命令来配置结果输出文件：
1sum_file &filename&
这里的 &filename& 即 SUM 文件的文件名。例如，对于上文的解算任务，可以如下配置：
1sum_file TRACK18_045.sum
任务示例MIT 在其网站上给出了一个使用 TRACK 进行，你可以在页面上查看其数据处理成果，也可以下载其在自己的计算机上重新运行。
下载并解压输入文件包之后，使用 cd 命令进入输入文件目录，然后使用如下命令启动 TRACK:
1$ track -f track.cmd -d 356_19 -w 12501 | tee TRAK_356_19.out
TRACK 程序的帮助信息非常详尽，可说是巨细无遗，不加任何参数运行 track 即可看到。MIT 还准备了一份供你随时随地查看。
使用支付宝打赏
使用微信打赏
若你觉得我的文章对你有帮助，欢迎点击上方按钮对我打赏中海达GPS测量仪-中海达RTK
> 中海达V30 Plus GNSS RTK测量系统
中海达V30 Plus GNSS RTK测量系统
V30 Plus是新一代小型化RTK系统，作为经典产品的延续，无论外部材质，操作的优化，内部的存储，还是连接方式都有了巨大的提升。产品特点◇ &新一代小型化RTK系统，镁合金外壳，体积更小，重量更轻；◇ &全频段空气天线，卫星信号接收能力强；◇ &高性能测量引擎，多星系统内核，性能强大精度稳定，支持单北斗解算，完美兼容各种CORS系统。◇ &8GB超大存储空间, 可存储连续200天静态数据；◇ &机身NFC识别,功能超连接更快更高效;◇ &Mini USB通用接口让交互变得更快捷；◇ & 配备iHand30全强固智能手薄，内置4G全网通，支持快充，支持OTG；◇ &专为Android系统开发定制的新一代智能测量软件Hi-Survey；◇ &内置收发一体，电台,功率高低可选，频道116个可调；◇ & 可拆卸5000mAh超大电池，标配2块，进口电芯，更耐用，；◇ &30W高性能外挂电台，功率四档可设，116个频道可调；◇ &小型化仪器箱，重量更轻，体积更小，携带方便；◇ &全新UI界面Hi-Survey软件，全面的道路算法，支持离线地图和dxf/shp数据导入；行业应用施工放样丰富的点、线放样功能，辅以图形化的操作指导，给您的工程施工节约更多成本◆电力交通方便的电力测向、测距、角度计算功能；全面实用的公路测设、中桩、边桩测量，纵、横断面测量功能◆CORS应用面向CORS系统的应用，只需一台RTK移动台即可接收CORS差分信号进行数据采集、施工放样等所有的作业◆CORS建站HD-CORS融合了中海达多年的成熟建站技术，具有运行稳定，传输距离长等优点，是城市连续参考站系统的首选解决方案◆控制测量一次投资，多重功能，iRTK的双频静态测量精度满足任何控制测量要求，配套成熟的专业数据解算软件，可助您完成各种高精度的控制测量工作◆数据采集面向GIS系统设计的手簿操作软件，灵活的编码功能，满足您快速高效的野外数据采集需要◆水上测量配套中海达测绘权威的海洋测量、海洋成图软件及测深仪，轻松实现水下地形测量工作，彻底改变传统的水上测量作业模式◆施工定位（水上）配合中海达海洋施工定位软件，iRTK系统助您精准完成抛石、铺排、打桩等海洋工程，满足海上工程的特殊要求
　　V30 GNSS RTK系统2009年面世，热销近十年，成为中海达最为经典的RTK产品之一，靠是稳定和可靠。稳定，让它不易被替代；可靠，让它赢得信任V30Plus新一代小型化RTK系统作为经典的延续，将这份不易被替代的信任发挥到极致——专注、专业，专家，这就是研发工程师们对它的期望。
V30 Plus技术参数
系统内核：采用多星系统内核
通道数：220
BDS：B1、B2、B3
GPS：L1、L2C/L2P、L5
GLONASS：L1、L2
输出格式：ASCII：NMEA-0183，二进制码
定位输出频率：1Hz~20Hz
差分支持：CMR、RTCM2.X、RTCM3.0、RTCM3.2
静态格式支持：GNS静态数据
数据存储：内置8G存储器
精度和可靠性[1]
RTK定位精度：平面：±（8+1×10?6D）mm&&&
&&&&&&&&&&&&&&&&&&&&&&&&& 高程：±（15+1×10?6D）mm&&
静态定位精度：平面：±（2.5+0.5×10?6D）mm&&
&&&&&&&&&&&&&&&&&&&&&&&&& 高程：±（5+0.5×10?6D）mm&&&
初始化时间：＜10秒
初始化可靠性：＞99.99%
内置3G网络通信模块：
WCDMA/HSDPA/EDGE/GPRS
双模蓝牙通信,NFC闪联
内置收发一体电台：
功率：0.5W/1W/2W可调，&& 频段：450MHz-470MHz
传输速率：19.2kbps/9.6kbps可调，& 频道数：116个频道可调
功率：5W/10W/20W/30W可调，电台频段：450MHz-470MHz
传输速率：19.2kbps/9.6kbps可调，&& 频道数：116个频道可调
面板：单按键
LED指示灯：卫星灯、信号灯、电源灯
5芯接口，USB接口，TNC接口，SIM卡槽
语音播报：可报告接收机工作状态
功能自检：语音播报接收机自检结果
电气物理特性
电池：高容量锂电池5000mAh/块（2块），可拆卸
单块电池网络移动站连续工作时间10小时以上[2]
输入电压：直流6~28V DC
尺寸：Φ164mm×83.5mm
重量： ≤1.4kg（含电池）
功耗：4.2W
材料：外壳采用镁合金材料
防尘防水：IP67，可抗1米水下临时浸泡，完全防止粉尘进入
防摔：抗2米高测杆自然跌落
相对湿度：100%抗冷凝
工作温度：-40℃~＋75℃
存储温度：-55℃~＋85℃
注： [1]测量精度、可靠性受多种因素干扰，包括卫星几何分布、卫星数、观测时间、卫星星历、电离层状况及多路径等。&&&&&&& [2]电池工作时间与工作环境、工作温度及电池寿命有关。
全新一代安卓全键盘手簿&iHand30
　　iHand30安卓手簿——Android专业数据采集器！一改以往中海达的设计思路，大胆创新，顺应客户需求，紧跟当今测绘潮流！采用全新的材料外壳，采用人工力学设计理念，全键盘+触屏的设计让您随意选择输入模式！
采用Android6.0版本操作系统,1.5GHz，4核处理器，3.7英寸高亮专业级户外彩色触摸屏，内置2GB RAM+16GB ROM存储，支持高达128GBSD扩展存储；800万像素高清晰摄像标注功能；多点电容式触摸屏，带触摸笔，满足冬天带各式手套可用；5200毫安的电池容量，可方便拆卸，支持快充，最大工作时间&15小时；支持双卡双待功能！可进行无线视频传输和视频通话功能！高稳定性操作，随心放心！
?& 人体工程学设计，更舒适
?& 强悍硬件配置，运行更流畅
?& 阳光下屏幕清晰可见
?& 全新物理键盘输入法，输入更高效
?& WiFi与蜂窝移动双联智能选择上网
?& USB Type C接口,支持OTG功能
?& 支持快充，充电1小时工作一下午！
iHand30手簿参数
Android 6.0操作系统
1.5G，4核处理器
2GB RAM+16GB ROM；支持T-Flash存储卡，支持高达128GB&
3.7 英寸高亮户外彩色电容触摸屏
物理全键盘，专业定制物理键盘智能输入法
内置 GNSS 天线，支持GPS，GLONASS，AGPS；20通道
内置4G全网通，双卡双待
IEEE 802.11b/g/n,Wapi,AP
内置蓝牙(2.1+4.0)
支持NFC闪联
USB Type C接口，支持OTG功能
可拆卸锂电池3.7V/5200mAh，支持快充
单块电池可连续工作15小时[1]
内置800万像素摄像头(带闪光灯)
高亮Flash LED闪光灯
内置麦克风，具备语音标注功能
支持3.5mm音频插孔
重力感应器，电子罗盘，气压计，光感应器，陀螺仪
长208mm×宽83mm×厚24mm
0.44kg&(含电池)
工作温度：-20℃～+55℃；存储温度：-30℃～+65℃
防尘防水防震
IP67；抗1.2米自由跌落
注:[1]电池工作时间与工作环境、工作温度及电池寿命有关。大学之道，在明明德，在亲民，在止于至善。
GNSS定位协议
GNSS的全称是全球导航卫星系统（Global
Navigation Satellite System），它是泛指所有的卫星导航系统，包括全球的、区域的和增强的，如美国的GPS、俄罗斯的Glonass、欧洲的Galileo、中国的北斗卫星导航系统，以及相关的增强系统，如美国的WAAS（广域增强系统）、欧洲的EGNOS（欧洲静地导航重叠系统）和日本的MSAS（多功能运输卫星增强系统）等，还涵盖在建和以后要建设的其他卫星导航系统。国际GNSS系统是个多系统、多层面、多模式的复杂组合系统。
NMEA 0183是美国国家海洋电子协会（National Marine Electronics Association）为海用电子设备制定的标准格式。目前业已成了GPS导航设备统一的RTCM（Radio
TechnicalCommission for Maritime services）标准协议。
（全球定位数据）
GPS固定语句，这是一帧GPS定位的主要数据，也是使用最广的数据。
$GPGGA,&1&,&2&,&3&,&4&,&5&,&6&,&7&,&8&,&9&,&10&,&11&,&12&,&13&,&14&*&15&&CR&&LF&
&1& UTC时间，格式为hhmmss.sss。
纬度，格式为ddmm.mmmm（前导位数不足则补0）。
纬度半球，N或S（北纬或南纬）。
经度，格式为dddmm.mmmm（前导位数不足则补0）。
经度半球，E或W（东经或西经）。
定位质量指示，0=定位无效，1=定位有效。
使用卫星数量，从00到12（前导位数不足则补0）。
水平精确度，0.5到99.9。
天线离海平面的高度，-9999.9到9999.9米
高度单位，M表示单位米。
大地椭球面相对海平面的高度（-9999.9到9999.9）。
高度单位，M表示单位米。
差分GPS数据期限（RTCM SC-104），最后设立RTCM传送的秒数量。
差分参考基站标号，从0000到1023（前导位数不足则补0）。
GPGSA（卫星PRN数据）
GPS精度指针及使用卫星格式
$GPGSA,&1&,&2&,&3&,&4&,&5&,&6&,&7&,&8&,&9&,&10&,&11&,&12&,&13&,&14&,&15&,&16&,&17&*&18&&CR&&LF&
模式2：M =手动， A =
模式1：定位型式1 =未定位，2 =
二维定位，3 =
三维定位。
第1信道正在使用的卫星PRN码编号（Pseudo Random Noise，伪随机噪声码），01至32（前导位数不足则补0，最多可接收12颗卫星信息）。
第2信道正在使用的卫星PRN码编号
第3信道正在使用的卫星PRN码编号
第4信道正在使用的卫星PRN码编号
第5信道正在使用的卫星PRN码编号
第6信道正在使用的卫星PRN码编号
第7信道正在使用的卫星PRN码编号
第8信道正在使用的卫星PRN码编号
第9信道正在使用的卫星PRN码编号
第10信道正在使用的卫星PRN码编号
第11信道正在使用的卫星PRN码编号
第12信道正在使用的卫星PRN码编号
&15& PDOP综合位置精度因子（0.5 - 99.9）
&16& HDOP水平精度因子（0.5 - 99.9）
&17& VDOP垂直精度因子（0.5 - 99.9）
GPGSV（卫星状态信息）
可视卫星状态输出语句
$GPGSV,&1&,&2&,&3&,&4&,&5&,&6&,&7&,...,&4&,&5&,&6&,&7&*&8&&CR&&LF&
总的GSV语句电文数。
当前GSV语句号。
可视卫星总数，00至12。
卫星编号，01至32。
卫星仰角，00至90度。
卫星方位角，000至359度。实际值。
信噪比（C/No），00至99dB；无表未接收到讯号。
注：每条语句最多包括四颗卫星的信息，每颗卫星的信息有四个，即：卫星编号、卫星仰角、卫星方位角、信噪比。
GPRMC（运输定位数据）
推荐最小数据量的GPS信息（RecommendedMinimum Specific GPS/TRANSIT Data）
$GPRMC,&1&,&2&,&3&,&4&,&5&,&6&,&7&,&8&,&9&,&10&,&11&,&12&*&13&&CR&&LF&
&1& UTC（Coordinated Universal Time）时间，hhmmss（时分秒）格式
定位状态，A=有效定位，V=无效定位
&3&Latitude，纬度ddmm.mmmm（度分）格式（前导位数不足则补0）
纬度半球N（北半球）或S（南半球）
&5&Longitude，经度dddmm.mmmm（度分）格式（前导位数不足则补0）
经度半球E（东经）或W（西经）
地面速率（000.0~999.9节，Knot，前导位数不足则补0）
地面航向（000.0~359.9度，以真北为参考基准，前导位数不足则补0）
&9& UTC日期，ddmmyy（日月年）格式
&10&Magnetic Variation，磁偏角（000.0~180.0度，前导位数不足则补0）
&11&Declination，磁偏角方向，E（东）或W（西）
&12& ModeIndicator，模式指示（仅NMEA版本输出，A=自主定位，D=差分，E=估算，N=数据无效）
（地面速度信息）
地面速度信息(GPVTG)
$GPVTG,&1&,T,&2&,M,&3&,N,&4&,K,&5&*hh
以真北为参考基准的地面航向(000~359度，前面的0也将被传输)
以磁北为参考基准的地面航向(000~359度，前面的0也将被传输)
地面速率(000.0~999.9节，前面的0也将被传输)
地面速率(1.8公里/小时，前面的0也将被传输)
模式指示(仅NMEA版本输出，A=自主定位，D=差分，E=估算，N=数据无效
nmea数据如下：
$,,,N,,E,1,05,2.0,45.9,M,-5.7,M,,0000*77
$GPRMC,,A,,N,,E,15.15,359.95,070306,,,A*54
$,359.95,T,,M,15.15,N,28.0,K,A*04
$GPGGA,,,N,,E,1,06,1.2,44.6,M,-5.7,M,,0000*72
$GPGSA,A,3,14,15,05,22,18,26,,,,,,,2.1,1.2,1.7*3D
$GPGSV,3,1,10,18,84,067,23,09,67,067,27,22,49,312,28,15,47,231,30*70
$GPGSV,3,2,10,21,32,199,23,14,25,272,24,05,21,140,32,26,14,070,20*7E
$GPGSV,3,3,10,29,07,074,,30,07,163,28*7D
对于通常的情况，大家所关心的定位数据如经纬度、速度、时间、航向等均以“$GPRMC”中获取得到。
对于GPS北斗双模模块的输出信息：
如果只将BD、GPS卫星用于位置解算，传送标识符为BD、GP等；如果使用了两个系统的卫星取得位置解算，传送标识符为GN。
没有更多推荐了，
加入CSDN，享受更精准的内容推荐，与500万程序员共同成长！Real-Time Location Systems Using GNSS Modules | DigiKey
ArticleLibrary
> Design Location Tracking Systems Quickly Using GNSS Modules
Design Location Tracking Systems Quickly Using GNSS Modules
投稿人：Digi-Key's North American Editors
Asset tracking is big business. Knowing where valuable items are at any time with a high degree of accuracy increases productivity, enhances security, and lowers cost. However, asset tracking has been limited to high value items because high-quality Global Navigation Satellite System (GNSS) receivers can be difficult to design and implement, expensive, and power hungry.
The introduction of modular GNSS solutions that are specifically designed to extend asset tracking to a much wider range of applications by offering compact, relatively inexpensive, and low power consumption alternatives are much easier to implement. Still, there are many module options to pick from, and they are all sensitive to power supply quality. In addition, battery-operated end products require particular attention to a module&s low-power modes.
This article introduces some GNSS modules and explains how to use them as the basis for real time location systems (RTLS). The article shows how the modules are set up for maximum sensitivity, communication with the host microcontroller, rapid satellite acquisition, and optimal power efficiency.
The basics of GNSS
GNSS RF receivers take advantage of satellite constellations such as the United States& GPS, Russia&s GLONASS, or Europe&s Galileo, to allow outdoor, mobile assets to be located with an accuracy of a few meters or better.
GNSS works by picking up the unique navigation signal from at least three satellites in the orbiting constellation. Synchronization between satellites and receivers enables the respective signal propagation delays (and hence distances) from the satellites to be determined. The intersection of the satellites& signal spheres (with radii equal to the calculated distance) and the Earth&s globe determines the receiver&s precise location.
Each satellite transmits low-power RF signals comprising the satellite&s identification, ephemeris data (detailing the satellite&s current and future orbital position), and its status.
The receiver accuracy is determined by the accuracy of its synchronization with
an error of 1 nanosecond (ns) can cause a positional error of 30 centimeters (cm).
A key operational parameter of the receiver is time-to-first-fix (TTFF). A cold start TTFF, whereby the receiver starts up with no signal or previous positional information, can take up to a minute. If the receiver has not been moved since it was shut down, and still has the previous positional information in the onboard memory, it can perform a warm start which results in a TTFF of around 25 to 30 seconds (s). A hot start occurs when the receiver has very recent positional information in its memory and can therefore accurately predict satellite positions and results in a TTFF of just 1 s.
Because GNSS satellite transmissions are weak, high receiver sensitivity is important. Signal acquisition time improves once the receiver has located the satellites because if the signal is obstructed, the receiver can anticipate the satellite&s next position to regain the signal without having to scan wide swathes of the sky.
New modules ease design
Designing a GNSS system from scratch is a complex business. If the developer has the expertise, then such a strategy could possibly lead to a more differentiated end product in terms of cost, size, and performance, but for the less experienced a module is often a wiser alternative. Modules are assembled, packaged, tested, and (typically) verified units that can be dropped into the end product. Design complexity is eased because the modules eliminate the need for the engineer to develop complex RF circuitry from scratch.
Better yet, a new generation of GNSS modules has been designed to target the kind of applications previously impractical because of the drawbacks of traditional GNSS solutions. Examples include wearable devices, smart watches, and asset tracking of relatively low value items.
Key factors the designer should consider when selecting a module are:
Price: This varies according to volume and other factors.
Positional accuracy: Better positional accuracy relies on a superior clock. The designer should match the accuracy to the requirement of the application.
TTFF: The time taken to acquire satellite signals and calculate position when the module is first activated. Some modules boast algorithms that predict the orbital position of satellites for up to a month in the future, greatly shortening TTFF from a cold start.
Size: Compact dimensions allow the module to be incorporated into small form factors.
Power consumption: Solutions for applications such as asset tracking will typically run from small batteries. Low power consumption will extend battery life.
RF sensitivity: High initial sensitivity is demanded to pick up relatively weak GNSS signals during a cold start. Sensitivity increases once a satellite has been acquired and is being tracked by the receiver.
RF interference immunity: Depending on the host system, GNSS operates in the 1176.45 to 1602.0 MHz range which sits adjacent to GSM frequency allocations. Good GSM band rejection is required to ensure good reception of the GNSS signals.
module is a good example of this new generation of GNSS modules (Figure 1). The module is a drop-in GNSS receiver, operates at 1.575 GHz, measures 13.8 x 9.5 x 1.8 mm, and can run on three different GNSS systems simultaneously to enhance TTFF and location accuracy. The module operates off a 2.8 to 4.2 volt power supply and features several low-power modes to extend battery life. The TTFF is less than 35 seconds from a cold start, and cold start sensitivity is -148 dBm (Figure 1).
Figure 1: Antenova&s Radionova M20050 GNSS module features an internal antenna and operates at 1.575 GHz. (Image source: Antenova)
The device uses the NMEA 0183 data output protocol, a proprietary protocol controlled by the U.S.-based National Marine Electronics Association. The protocol uses simple ASCII serial communications, is widely used in the industry for serial connectivity with GPS receivers, and has been adopted by navigation software such as Google Maps and Microsoft MapPoint. The M20050 exports position data via a UART interface at a default 9600 baud rate.
offers its
of GNSS receiver modules. The devices operate at 1.575 and 1.602 GHz from a 3.0 volt to 4.3 volt power supply. TTFF is less than 33 seconds from a cold start, with cold start sensitivity of -147 dBm. The device uses the NMEA 0183 protocol through a UART interface that also has a default rate of 9600 baud.
The device&s core handles all the necessary initialization, tracking, and calculations autonomously, so no programming is required. The RF section of the TM Series is optimized for low level RF signals and requires no production tuning.
also offers a GNSS module solution in the form of its . While the company lists the device as a GNSS product, it only supports the U.S.-based GPS system, although a GLONASS unit is also available. The Telit module is based on the SiRFstarIV& core, is powered from a 1.8 volt supply, and comes in an 11 x 11 x 2.6 mm package. The TTFF is less than 35 seconds from a cold start, and has a cold start sensitivity of -147 dBm. A key advantage of the Telit product is that it is interoperable with the company&s cellular modules making it easier to design a combined GPS/cellular solution (Figure 2).
Figure 2: Telit&s Jupiter JF2 module is one of the smallest integrated GNSS receivers even though it also combines cellular capability. (Image Source: Telit)
While the modules from Antenova, Linx Technologies, and Telit simplify the design of location tracking systems, it is not a case of soldering the module onto a printed circuit board, adding power and waiting for the first fix. The main design steps required for a working system are antenna selection (or antenna tuning if the module has an internal antenna), a power supply, pairing with an appropriate microprocessor, and programming.
Maximizing sensitivity
Some modules are supplied with a built-in antenna, but others leave the choice to the developer. A built-in antenna removes another design step but will inevitably be a &one-size-fits-all& solution. Leaving the choice of antenna to the designer allows better matching of antennas to the applications.
For example, if the module is fitted to a handheld device, the antenna will be presented to the sky in various orientations, so an antenna with a wide and uniform pattern may yield better overall performance than one with higher gain but a narrower beam. Employing a module without a built-in antenna, such as Linx Technologies& TM Series, allows for experimentation to match the application.
For GNSS applications, the antenna requires good right hand circular polarization characteristics to match the polarization of the satellite signals. Ceramic patches are the most commonly used style of antenna, but many other shapes, sizes and styles are available.
GNSS applications can employ passive or active antenna. The active type operates with a low-noise amplifier (LNA) to improve sensitivity. When using an active antenna, it&s good practice to add a 300 ohm (&O) ferrite bead to connect the VOUT line to the RFIN line. This bead blocks RF interference from the power supply, while allowing a DC voltage onto the RF trace to feed the antenna. A series capacitor inside the module prevents the DC voltage from affecting the bias on the module&s internal LNA.
The key parameter that determines a good RF circuit from a poor one is its impedance (Z). Care must be taken such that the pc board layout of the end product maintains a 50 &O impedance path between the module and antenna. Manufacturers typically provide layout guidelines in their module datasheets to assist in matching impedance and antenna board clearance to maximize sensitivity (Figure 3).
Figure 3: Antenna clearance, facilitated by a pc board area free of traces, is important to maximize sensitivity and improve TTFF. (Image source: Antenova)
Modules with an internal antenna, such as Antenova&s Radionova M20050 device, may require some external tuning to maximize sensitivity and accelerate TTFF. This is not overly complex, typically requiring the addition of a few passive components to compensate for slight antenna detuning caused by board components adjacent to the module. In the case of the Radionova M20050 module, Antenova has simplified the process by adding &AT1& and &AT2& inputs to the module to which the appropriate resistors and inductors can be connected to tune the internal antenna (Figure 3, again).
Module control
Each of the Antenova, Linx Technologies and Telit modules must be connected to a suitable microprocessor for control and configuration. The microprocessor requirements are typically modest and a mid-range, 16-bit device is up to the job. Most GNSS modules communicate via a serial GPIO or UART, so ensure the selected microprocessor has one, or both.
The microprocessor typically uses the NMEA protocol mentioned earlier to communicate with the GNSS module. The protocol defines three types of inputs/outputs: Commands, Write, and Read messages. The modules output a response for each input/output. Commands are used to change the operating state of the module. Write messages change the module&s configuration, and Read messages detail the current configuration.
Inputs are sent to the receiver on the RX line and outputs are sent from the receiver on the TX line. By default, output messages are sent once every second. The protocol allows for both standard and proprietary inputs/outputs (Figure 4).
Figure 4: The microprocessor communicates with the GNSS module via a GPIO or UART, TX and RX connections. Note the use of a 300 &O ferrite bead to limit RF interference from the power supply to the active antenna.) (Image Source: Linx Technologies)
The message structure of the NMEA protocol is straightforward, for example:
&command-ID[,parameter1,parameter2,...,parameterN]&cr&&lf&&
&message-ID,&data1,data2,...,dataN&*&checksum&&cr&&lf&& for messages.
The message ID for standard messages begins with an NMEA &talker& ID: &$GP& indicates GPS, &$GL& indicates GLONASS, and &$GN& indicates global navigation. The GNSS module typically echoes the command back out to the host processor after the command has been executed.
&$GPZDA,,22,08,2017*56&cr&&lf&&, for example, is a GPS message detailing the universal time and date (18:37:46.0 on 22 August 2017).
Many module makers, such as Telit, opt for proprietary schemes for commands (Figure 5). (&$P&& indicates this is a proprietary scheme, and &&STM&& is a manufacturer&s ID, in this case the
chip used in Telit&s Jupiter JF2 GNSS module.)
Command ID
Description
$PSTMINITGPS
Initialize GPS position and time
$PSTMINITTIME1
Intialize GPS time
$PSTMCLREPHS
Clear all ephemeris data
$PSTMDUMPEPHEMS
Dump emphemeris data
Load ephemeris data
$PSTMNMEAONOFF
Toggle the NMBA output ON and OFF
Perform a COLD start
Perform a WARM start
Perform a HOT start
Perform a system reset
$PSTMGPSRESET
Reset the GPS engine
$PSTMGETSWVER
Get the GNSS Library version
$PSTMSBASONOFF
Toggle the SBAS feature ON and OFF
$PSTMSBASSAT
Select the SBAS satellite PRN code
$PSTMSETCONSTMASK
Set the GNSS constellation mask
Figure 5: NMEA protocol proprietary commands for Telit&s Jupiter JF2 GNSS module. (Image source: Telit)
For example:
&$PSTMCOLD,0x02&cr&&lf&& performs a cold start and (optionally) c
&$PSTMINITTIME,23,02,,12&cr&&lf&& initializes the current GPS universal time to 9:44:12 on 23 February 2018.
The module manufacturers have eased the development process by offering evaluation kits that incorporate the GNSS module and include an antenna, or antenna tuning if the module features an internal antenna. Antenova, for example, offers the
RF module evaluation board, and Linx Technologies offers the
development kit for the TM Series. In neither instance is a microprocessor required for evaluating the module as the evaluation kit connects directly to the USB port of a PC, with the PC then supplying the input messages and supervising operation (Figure 6).
Figure 6: Antenova&s M20048 evaluation kit includes a micro USB interface to allow control and configuration from a PC. (Image source: Antenova)
Powering GNSS modules properly is critical
Because they are required to detect weak RF signals, GNSS modules demand a clean, stable power supply to ensure a high signal-to-noise ratio (SNR). The specification varies depending on the selected GNSS module, but generally speaking, peak noise should be kept to less than 20 millivolts (mV) to avoid problems.
While some GNSS modules include an onboard voltage regulator, it is advisable to employ an external primary regulator to supply the module. If a switch-mode voltage regulator is selected to increase efficiency and extend battery life, the designer should consider teaming the device with a low dropout (LDO) linear regulator to limit noise at the GNSS module&s voltage input.
If efficiency is less of a challenge, an LDO regulator alone is a good choice as the bill of materials is lowered and the regulated output is cleaner than that of a switching regulator. It is also good design practice to employ filter circuits to clean up the input voltage regardless of voltage regulator choice.
GNSS modules (for example, the M20050) often include two voltage inputs, one to power the main digital and processing circuitry and a second to provide backup to the RAM and clock.
In addition to controlling and configuring the GNSS module, the host microprocessor manages power supply modes to help extend battery life. For example, the M20050 module supports three such modes: standby, backup, and periodic. Standby shuts down the RF section of the module and puts the processor on standby. The clock and RAM remain powered to maintain module configuration.
Backup mode is entered when the main voltage input is switched off. This mode is designed to aid rapid TTFF when the module awakens from a power saving (sleep) mode because historical ephemeris data is retained in the module&s RAM.
Periodic mode reduces current consumption by waking the module for short durations to reestablish a satellite fix and then return to a sleep mode. This mode is useful for accelerating TTFF because ephemeris data is periodically refreshed rather than just retained (Figure 7).
Figure 7: Periodic mode enables frequent refresh of ephemeris data to ensure rapid TTFF when the GNSS module is activated. (Image source: Antenova)
Conclusion
The proliferation of international satellite-based navigation systems has increased the accessibility and accuracy of GNSS for precise location tracking. While the design of GNSS enabled systems is not easy, GNSS modules greatly simplify matters by providing an assembled, tested and verified solution for asset tracking.
免责声明：各个作者和/或论坛参与者在本网站发表的观点、看法和意见不代表 Digi-Key Electronics 的观点、看法和意见，也不代表 Digi-Key Electronics 官方政策。
Share This Article}