, and is now being converted to a JTRS-compliant radio. When this conversion is completed it will be an SDR. It is currently in various stages of development and production as an interoperable waveform for Europe and the United States [12]. 2.4b.2.4 Examples of SDR 2.4b.3 Aware, adaptive, and CRs Only a few fully SDR systems are available, as shown in Radios that sense all or part of their environment are Figure 2.4b-2 and detailed in Table 2.4b-3. The common considered aware systems. Awareness may drive only characteristic of SDR systems is complete adjustability a simple protocol decision or may provide network in- through software of all radio operating parameters. formation to maintain a radio's status as aware. A radio Other products related to SDR include GNURadio must additionally autonomously modify its operating and the Vanu AnywaveTM Base Station. GNURadio is a parameters to be considered adaptive. This may be ac- free software toolkit that is available on the Internet. complished via a protocol or programmed response. It allows anyone to build a narrowband SDR. Using a When a radio is aware, adaptive, and learns, it is a CR [27]. Linux-based computer, a radio frequency (RF) front-end Only cutting-edge research and demonstration examples and an analog-to-digital converter (ADC), one can build of aware, adaptive, or CRs are available currently. a software-defined receiver. By adding a digital-to-analog converter (DAC) and possibly a power amplifier, one can 2.4b.3.1 Aware radios build a software-defined transmitter [25]. The Vanu AnywaveTM Base Station is a software-defined A voice radio inherently has sensing capabilities in both system that uses commercial off-the-shelf (COTS) hard- audio (microphone) and RF (receiver) frequencies. ware and proprietary software to build a wireless cellular When these sensors are used to gather environmental infrastructure. The goal is simultaneous support for mul- information, it becomes an aware radio. The local RF tiple standards, reduced operating expenses, scalabil