tly larger than the Transmitting video is nearly 100 times more noise floor due to the front-end amplifier. demanding than voice, and is rarely implemented in One example of unpredicted noise injection is the GPP or DSP. Rather, video encoding is usually imple- ADC conversion process, which can inject noise into mented on special purpose processors due to the ex- the signal through a variety of sources. The ADC tensive cross-correlation required to calculate the motion quantization process injects noise into a signal. This vectors of the video image objects. Motion vectors effect becomes especially noticeable when a strong substantially reduce the number of bits required to signal that is not the signal of interest is present in an faithfully encode the images. In turn, a flexible archi- adjacent channel. Even though it will be removed by tecture for implementing these special purpose engines is digital filtering, the stronger signal sets the dynamic the use of FPGAs to implement the cross-correlation range of the receiver by affecting the AGC, in an effort motion-detection engines. to keep the ADC from being driven into saturation. Some systems specify a recommended maximum latency limit, such as 150 milliseconds for ITU-T G114. CHAPTER 2.4a The software defined radio as a platform for cognitive radio Thus, the effective signal-to-interference and noise a particular type of application. In the context of CR, the ratio (SINR) of the received signal is lower than might application in which we are most interested is signal otherwise be expected from the receiver front-end. To processing. overcome this problem and similar ones, software so- The other key aspect of the GPP is the use of an MMU. lutions will not suffice, and flexible front-ends that are Because GPPs are designed for generic applications, they able to reject signals before sampling become neces- are usually coupled with an OS. This os creates a level of sary. Tunable RF components, such as tunable filters abstraction over the hardware, allowing the dev