Читать книгу Dynamic Spectrum Access Decisions - George F. Elmasry - Страница 28
2.3 Energy Detection Sensing
ОглавлениеThis is the most common spectrum sensing approach used today. As explained in Chapter 3, the receiver's operator characteristic (ROC) function makes good use of this simple energy detection approach. Chapter 3 covers how same‐channel in‐band sensing can use energy detection sensing with minimal requirements on the receiver to hypothesize the presence of interference.
RSSI is a common expression of energy detection. RSSI is so common that you can look at your phone while having wireless fidelity (WiFi)3 connectivity and count the WiFi connectivity indicator lines on the top of your screen to see how RSSI is commonly mapped to about four levels (no connectivity, low connectivity, medium connectivity, and good connectivity). Laptop WiFi connectivity indicators typically map the WiFi RSSI to five or six levels. Other devices illustrate RSSI in more or less this number of levels.
A simple receiver can collect the energy received on the antenna in a certain frequency band and quantize it. Low computational complexity and simple implementation are what makes energy detection commonly used. In Figure 2.3, energy detection below a certain power threshold constitutes an opportunity for a spectrum band use (e.g., by a secondary user4). On the other hand, energy detection above that threshold constitutes an occupied band. In Figure 2.3, energy detection is the power axis. Deciding the value of that cutoff threshold can be challenging as the primary user signal may suffer from interference, multipath fading, and jamming among other factors that can affect the signal strength. Energy detection becomes especially more challenging when sensing spread spectrum signals that tend to have low energy. Chapter 3 is dedicated to DSA decision making and will discuss how cutoff thresholds can be used.