ity, spectrum may be sensed in pursuit of channel estimates, and future proofing (cost-effective migration) [26]. interference, or signals of interest. Audio inputs may be Cognitive radio: The technologies required CHAPTER 2.4b Table 2.4b-2 Selected examples of software programmable radios. AN/ARC-210 Provides fully digital secure communications in tactical and air traffic control (ATC) environments (30-400 MHz). Additionally, the radio provides 8.33 kHz channel spacing capability to increase the number of available ATC frequencies, and provides for growth to new very-high-frequency (VHF) data link modes. Currently provided functions are realized through software and provide integrated communications systems with adaptability for future requirements with little or no hardware changes. In other words, the ARC-210 is software programmable. The ARC-210 is integrated into aircraft and operated via MIL-STD-1553B data bus interfaces. Remote control is also available for manual operation. This radio is interoperable with SINCGARS (Single-Channel Ground and Airborne Radio System) and HaveQuick radios [13]. Racal 25 A compliant Project 25 public safety radio operating in the 136-174 MHz band. Its 5 W peak transmit power, rugged and submersible housing, and digital voice with Digital Encryption Standard (DES) make it an advanced radio. The radio uses DSP and flash memory architectures, and supports 12 and 16 kbps digital voice and data modes. Racal posts software upgrades on a protected Internet site. Software programmability enables field upgrades and is possible due to its DSP and flash memory-based architecture [14]. SINCGARS ASIP (Advanced System Improvement Program) Interoperates with SINCGARS radios and enhances operational capability in the Tactical Internet (TI) environment. The ASIP models reduce size and weight, and provide further enhancements to operational capability in the TI environment. SINCGARS ASIP radios are software programmable and provide improved data capability, improved FEC for low-speed data modes