Software defined radio technology has been widely adopted for new military and aerospace platforms, government signal intelligence and homeland security systems, and now more extensively in commercial wireless voice and data networks as well. These modern communication systems need to squeeze more channels of traffic into an expensive slice of precious radio spectrum. Military and government requirements for secure communications mandate real-time encryption and decryption schemes that must be increasingly more resistant to interception. In multinational theater of war combat operations, communications systems must selectively ensure certain specific links and reliably deny others.
As a result, communications systems are increasingly shifting towards digital modulation using advanced spread-spectrum code modulation schemes that require transmission channels with wider bandwidths. These new wideband schemes, coupled with the exploding market demand for additional channels for video, voice, and data services, pushes software radio systems toward higher speed A/D and D/A converters, more powerful DSP resources, and faster system interconnects between components and between system boards. FPGAs deliver an excellent solution to all of these difficult demands and, as a result, now play key roles in virtually all new software radio systems.
Software Radio Drives FPGA Technology
As soon as they became available, hardware design engineers began to take advantage of FPGAs (field programmable gate arrays) for connecting highspeed software radio peripherals like wideband A/D and D/A converters, digital receivers, and communication links to programmable processors in embedded real-time systems. Because of their flexibility, FPGAs are especially well suited to handle the clocking, synchronization, and other diverse timing circuitry needed to tame these specialized devices. In addition, FPGAs are excellent for data formatting tasks like serialto- parallel conversion, data packing, time stamping, multiplexing, and packet formation. Shrinking die geometries and other advances in chip technology have made FPGA silicon much faster and denser. But more importantly, the addition of new high-performance DSP resources and interfaces marked a watershed event that dramatically changed the architectural paradigm of software radio systems.
FPGAs are now incorporated in software radio products primarily for their digital signal processing engines and new gigabit serial fabric engines, thus stealing the spotlight from the more mundane traditional roles that they still serve admirably. Without exception, the latest device offerings from major FPGA vendors offer second or third generation DSP blocks. They include extended precision multiplier/accumulators, advanced arithmetic units, logic engines, and flexible memory structures that can be tailored into block memory, dual-port RAM, FIFO memory and shift registers.