Since past few decades, telecommunication systems are continuously evolving from 2G to 3G to 4G etc. This has resulted in multiple technologies and many types of receivers which don't interoperate. As a result seamless roaming is very difficult. Due to constant evolution of link-layer protocol standards (2.5G, 3G and 4G), incompatible radios having specific standards, problem of global roaming and also new standards coming into existence, wireless communication industry is undergoing many hurdles.

Software Defined Radio (SDR) technology tries to address these problems by implementing the functions of a radio in software having a common hardware platform. The software modules required to implement new services/features can be downloaded over-the-air onto the handsets. Thus SDR offers this flexibility without any problem of different standards used.

The implementation of software into the radio systems introduced the concept of software radio. Software radios have brought a revolution in the radio engineering. We can implement different radio functions using suitable software running on common hardware platform. Such radios have been referred to as Software Defined Radio (SDR). Software radios are expected to emerge as platforms for multiband multimode personal communications systems.

Software defined radio (SDR) is a rapidly evolving technology implementing radio functions in software on a common hardware platform. Thus, it provides flexibility in reconfiguring the radio and allowing the wireless devices to quickly adapt to the environment. Software defined radio (SDR) offers flexibility in implementing radio functionality such as signal generation, coding, and modulation, in software.  Thus, the radio can quickly adapt to the environment and it supports multiple standards without requiring different hardware for every standard. Our primary focus is on modulation recognition techniques which is explained in detail in section 3.