7.2 Conceptualizing Cognitive Radios
Please refer to Section 6.2.1 to review cross layer signaling (CLS) with the WNW radio. You can see how the channel parameters play a major role in ensuring that the higher layer protocols adapt to the changes in the physical layer parameters. We will refer to this approach as the CLS and compare it to the simplest concept of cognitive radio settings (CRS).
In the WNW waveform, CLS communicates physical layer information to the mobile data link (MDL) layer and the MDL layer makes the decision to change the radio parameters (power level, modulation mode, error control coding level, etc.). CRs have similar CLS as shown in Figure 7.2. In addition to CLS from the physical layer to the cognitive engine, the radio metrics are also sent to the cognitive engine (e.g., spectrum sensing metrics). The cognitive engine generates optimum parameters for the radio, which include changing the actual software modules (e.g., change the modulation type) and possibly creating new software components based on knowledge of the surrounding environments. Please be aware that some CR references use the term “radio” loosely. The physical layer is sometimes referred to as the radio. References that focus on cognitive algorithms conceptualize a CR as having three main components: a radio or physical layer, a MAC layer with a cognitive engine as its focus and operating environments (OEs)4 as indicated on the right-hand side of Figure 7.2.