1. https://www.engineersgarage.com/contribution/accident-detection-and-messaging-system-using-gsm-and-gps.
2. Understanding GPS: Principles and Applications (Artech House Telecommunications Library), Elliott D. Kaplan (Editor) Hardcover / (1996), (USD 99).
3. GSM Networks: Protocols, Terminology and Implementation by Gunnar Heine.
4. GSM Switching, Services, and Protocols by Joerg Eberspaecher.
5. GSM System Engineering, Asha K. Mehrotra.