Answer: Software-defined radio:- A software-defined radio is one that can be configured to any radio or frequency standard through the use of software. For example, if one was a subscriber of idea and moved into an area where idea did not have service, but airtel did, the phone would automatically switch from operating on a $CDMA$ frequency to a $TDMA $frequency. In addition, if a new standard were to be created, the phone would be able to support that new standard with a simple software update. Electronic communications is a typical communication systems have been implemented by certain dedicated hardware and likely dedicated application specific integrated chips based on specific communication system parameters designed for use.
A software-defined radio in the context of 4G would be able to work on different broadband networks and would be able to transfer to another network seamlessly while travelling outside the user's home network. A software-defined radio best advantage is its great flexibility to be programmed for emerging wireless standards. By using new software, user can update the programme effectively without any modifications in the hardware and infrastructure. As with software-defined radio, users can download the interface automatically while entering into the new territory and the data should be formatted to some standard, no issues with roaming. Data formation will be chosen by packet layer, which splits Into small packets. It is quite different from the way that we use computers to run different applications and programs on the same computing facility. Software defined radio allows multiple systems realised by programs to run on a single hardware platform is therefore attractive under such scenarios.
In other words to execute wireless communications. we usually use $DSPs$ for physical layer baseband implementation and embedded processes for networking functions and control. $SDR$ hardware structure can be summarised as shown in below figure :-