Design of a Mobile Adapter to Address Frequency Regulations for Rural Cellular Operators

Despite the widespread use of mobile phones, some rural areas still lack cellular connectivity primarily due to the high operating and deployment cost of traditional base stations. With the use of software-defined radio base stations, costs of traditional base stations have been drastically reduced. However, operation of a base station still requires ownership of the licensed cellular band. In this paper, we present our implementation of a GSM network operating in the public utility frequency band (380MHz-400MHz) of the Philippines. A mobile adapter is implemented and attached to mobile phones allowing phones to communicate with the base station. The mobile adapter utilizes direct frequency translation to convert the licensed GSM signal of mobile phones to the 380MHz-400MHz frequency band. An implementation of a software-defined base station demonstrated that mobile phones can connect to the network by attaching the mobile adapter. The mobile adapter is foreseen to remove the costly license barrier to operation of local cellular operators by advantageously using both unused and underutilized frequencies, allowing more communities to set up their own networks and gain access to cellular connectivity.