Software Defined Radios

A software defined radio (SDR) is a radio that is flexible (reprogrammable) to accommodate various physical layer formats and protocols. It can be viewed as a system that processes digital baseband, controls RF and power subsystems, through software to support multi-mode, multi-function, multi-band wireless operations. Such a system also requires reconfigurable hardware that can be reprogrammed to support current and future physical layer formats. Therefore SDRs can be considered as a collection of hardware and software technologies that enable reconfigurable system architectures for wireless networks and user terminals. It is an enabling technology that will allow seamless communication over multiple standards and services.

Existing technologies for voice, video, and data use different packet structures, data types, and signal processing techniques. The supporting technologies and networks that the radio might have to use can vary with the physical location of the user. To successfully communicate with different systems, the radio must communicate and decode the signals of devices using different air interfaces. This lack of compatibility is clearly evident today with the plethora of cellular and wireless networking standards: AMPS, IS-95, IS-136, GSM, W-CDMA, CDMA2000, 802.11, and Bluetooth. Land mobile radio systems, particularly among public safety agencies such as local police, the FBI, and the U.S. Customs Service, are incompatible. Even the military faces these incompatibility issues among its wireless systems. The importance of seamless wireless communications was emphasized during September 11 attacks where coordination among military, public safety, and commercial and private disaster relief services were essential to minimize loss of life. SDR is particularly well suited for emergency situations because it can be configured quickly via software.

Inertia must be overcome in moving away from conventional radio design and toward software radio design techniques. Software radio designers need to be trained in the interaction of their subsystem with other modules in the system. In the past, the design started with the hardware and then the software was designed around the hardware. This order is flipped for a software radio design, and the design of hardware and software is more tightly coupled. A new design methodology is needed that requires superior system design skills and an understanding of all the subsystems involved. Hence, a generic design procedure for SDRs will include but will not be limited to systems engineering, RF chain planning, analog to digital and digital to analog conversion selection, selection of digital signal processing hardware architecture, and software architecture design. To educate engineers for the future, MPRG has initiated a graduate level course in software radios that emphasizes these new design principles.

MPRG’s research program studies how software radio technology and cross layer optimization techniques can improve the performance of wireless communications systems. Through service and interface negotiations between devices, our research has the dual goals of allowing the application layer to operate independently of the physical layer and dynamically optimizing the communication systems for each application. It is anticipated that these goals can be simultaneously accomplished by using both vertical and horizontal cross-layer negotiations in a completely reconfigurable system, i.e., a software radio, which uses a radio knowledge representation language to describe device capabilities. Other ongoing software radio efforts in the group involve research incorporating smart antenna techniques, multiple input multiple output (MIMO) space-time processing, linearization and characterization of power amplifiers for multi-carrier application, single channel direction finding and design of reconfigurable modem System on Chip (SoC) architecture for use in handsets. The links on this site will guide you through the details of work done on software radios at MPRG.