Nowadays, software radio as a new technology has a great role in advanced communication systems. Using software in designing communication systems has many advantages such as decreasing the cost of implementation, ease of reconfiguration and ability to use multiple standards at the same time in one platform. Recent advances in increasing the process power of the processors makes development of these systems even more feasible than before. In this research, we developed a communication system by employing proper software and hardware tools. GSM standard was used as the basic platform of the implementation, due to its popularity. In the proposed system, first the hardware employs frequency conversion and converts the received signal into digital symbols and then, appropriate software in the Linux operating system performs the necessary actions like demodulation and coding on the received signal. Software can be used to perform the same procedure to the transfer signals. In other words, all of the baseband processing in this system is done by software. Furthermore, for managing the voice calls in this system, a VoIP server is employed in the host computer. The designed system is an access point for GSM which makes audio conversation feasible between internal subscribers. Also, external calls are available by using a gateway; additionally a server is designed for exchanging short messages. Moreover, the system uses cognitive radio concept that means it can sense the energy of sub bands and choose the band with the least energy from primary users for transferring the information. In addition, the range of communication has been increased by deploying the proper devices. The designed system can be used as a portable communication network. This system can be used as a rescue system in case of emergency and it has many applications in security and emergency systems. Keywords: Software Radio, GSM, Cognitive Radio
