I have really good experience with GPS tracking i was worked on a GPS company doing the listeners and back end system.
I have another suggest to implement the system, but any way we can develop this on .NET, just see this if you can.
Languages back end: Java, Scala and Kotlin (Kotlin and Scala have 100% compatibility with java and Java Virtual Machine ).
Framework web server to run the project: undertow, a the best on benchmarks.
Database: MongoDB or Cassandra (i like mongodb) both have much, but much better performance on big data with a project like this, to any SQL database. Trust me, a sql database is no the best choose to do this project.
Real time Queue System: apache kafka, really good queue system with high performance and data persistence.
The parser system is ready on java, only need to implement the protocols, additionally the parser system have connection with apache kafka.
I like intercommunicate all platform with apache kafka and keep a real time connection with web page and kafka way to web sockets (this will allow real time notifications like to alarm and more).
Additionally all platform will be make on open source technologies and can run on multiple Operating System. Some people don't like MS technologies or use windows server, by this reason i think you need use opensource technologies.
this technologies have better performance than you was choose, but if you like use .net and MS-SQL then ill do with that,
too small size to write.
Thanks and bye.