Wireless standards continue to evolve: adaptive modulation and coding, space-time coding and beam forming are, for example, designed to help satisfy the need for higher data rates. The events of 9/11 demonstrated the compelling need for communications systems interoperability and compatibility.
It’s no surprise, then, that software defines radio is capturing so much attention. Because traditional radio implementations are hardwired, they lack flexibility and ease of use – in effect, requiring a complete system redesign each time a new radio application challenge has to be met. Software defined radio (SDR) thus represents a complete paradigm shift: it replaces fixed, application-specific hardware with flexible, reconfigurable hardware that can be reprogrammed in order to deliver the required functionality, thus offering a degree of capability and flexibility that were previously not achievable. Software defined radio also represents a paradigm shift in that it moves radio applications from the analog domain to a domain where the majority of functions are implemented digitally.
The availability of very high speed digital to analog converters (DAC) for transmit and analog to digital converters (ADC) for receive have, to a large extent, made the SDR revolution possible – as has the availability of successive generations of DSP technology which move very high speed digital data between these converters and process it in real time.
Digital signal processing has traditionally been at the heart of software defined radio, and the function can be accomplished using a range of hardware solutions: application specific integrated circuits (ASIC); purpose-designed digital signal processors; and general purpose processors.
But now, another shift in technology is taking place which is transforming the market for software defined radio just as it is transforming other markets. The technology in question is FPGA (field programmable gate array). Rapid advances in the gate capacity and operating speed of FPGAs has opened up an opportunity for performing real-time digital signal processing on a single FPGA that was not possible several years ago, making it suitable for applications that demand not only the high speed, compute-intensive performance currently delivered by digital signal processing, but also reconfigurability. Reconfigurable cores are now available from a range of vendors that enable the implementation of modulator, demodulator and CODEC functionality in the FPGA.
Beyond this, new FPGA devices utilize extremely small silicon geometries that allow very high clock speeds at low core voltages, while Ball Grid Array (BGA) packaging enables the provision of thousands of I/O lines from a compact footprint.
FPGA technology is thus becoming an increasingly important player in software defined radio primarily because of the additional flexibility it brings – and flexibility is the defining characteristic of the new approach to radio applications. FPGAs have evolved from being a flexible logic design platform to a signal processing engine: not only are system designers porting an increasing number of signal processing functions in FPGAs, but also the flexibility of having the ability to integrate logic design with signal processing is driving designers to replace traditional DSPs with FPGAs. |