A Prototype for Making Calls Between Mobile Phones in Areas Without Cellular Network Coverage

Abstract

Mobile phone voice communications using the traditional Global System for Mobile Communications (GSM) signal methods depends on the cellular network operator signal coverage. There is a communication problem when mobile phones users want to communicate to each other when they are located in an area where there is no GSM signal coverage. This study objective was to develop and evaluate a prototype that can enable mobile phone calls between users who are located within an area where there is no mobile operator signal coverage. The prototype focuses on using Asterisk server which is an open source framework that can be used for building voice-protocol real-time communications applications, Session Initiation protocol which is a call setup and signaling protocol and a wireless local area network (WLAN). This study results and analysis demonstrated that the prototype can be successfully used to make phone calls between mobile phones without using cellular network GSM or 3G signals with satisfactory voice quality. According to voice quality standards, the prototype provides acceptable sound quality as evidenced by the measured R-Factor of 93.2. The call establishment time was below a second, which is ideal for real time mobile phone calls communication. The prototype also provided the capability of multiple simultaneous calls between mobile phones. However, mobile phone calls conversations were getting poor and eventually being disconnected when either the calling or called wireless network signal becomes weak. For the wireless network to cover a wide area, an extended distributed wireless local area network using multiple high performance access points, signal repeaters, as well as using a hybrid of wireless and cabled infrastructure is recommended for future studies. Also recommended is a server class hardware to host the IP PBX server as well as integrating the prototype with existing PBXs that are connected to PSTN lines to bridge mobile phones VoIP calls with external PSTN or GSM mobile phone users.