Cognitive Networks: Towards Self-Aware Networks

11.4. Inherent Reliability Issues

In this section we point out some of the inherent reliability issues in cognitive radio networks.

11.4.1. High Sensitivity to Primary User Signals

To prevent interference to licensed primary users, secondary users should detect the primary transmissions in the first place. To ensure high probability (e.g. 99%) of non-interference to the primary users, stringent sensitivity requirements are placed on the detectors at the unlicensed secondary devices. There are two prominent ways to detect the primary user's transmissions: (a) energy-based and (b) waveform-based sensing. Energy-based sensing does not require any knowledge of the primary user's transmission signal, it is based on the simple fact that any information-baring signal has finite signal strength (power). However, energy-based sensing techniques are prone to false detections and usually take a longer time when the signal is low power. Waveform-based sensing is applied when information about the waveform and signal patterns of the primary users transmission signal is known. This makes the waveform-based sensing techniques perform better than energy-based sensing in terms of speed and reliability. However, in many instances, primary user transmission signal patterns may not be known to the secondary users. Moreover, the FCC mandates ^[], as one of the requirements for cognitive networks, to predict the temperature interference (measured by energy) on nearby primary user's receivers and keep ...