In Cognitive Radio, the key to overcome the spectrum scarcity is reliable spectrum sensing, which will allow efficient opportunistic spectral reuse with minimum interference to licensed users. We consider energy detection based sensing that requires efficient noise power estimation technique in order to reliably detect the primary transmissions. We consider three algorithms, viz. Akaike Information Criterion (AIC), Minimum Description Length (MDL), and Rank Order Filtering (ROF), which estimate the noise power in the presence of the signal. The ROF key property is that it attempts to track the non-flat noise floor. Algorithm probability of missed detection is evaluated using data obtained from USRP2 devices. We illustrate that ROF may gain up to 6dB when signal to be detected is in the sub-band where the noise oor is not at (e.g., at the edges of the observed band).

We consider spectrum sensing and Non-Contiguous OFDM) with interference avoidance to facilitate opportunistic secondary transmission. In this application protecting an incumbent primary user of the spectrum from secondary emissions is a key design requirement. We present an adaptive sense-and-car

In primary-secondary coexistence scenarios, protecting an incumbent primary user of the spectrum from secondary spectral emission is a key design requirement. We consider t he GNU Radio based implementation and experimental evaluatio n of a co-existence system employing an opportunistic senseandcarefully-transmit strategy. The interference mitigation is based on the interference avoidance partitioned frequency and ti me windowing (IA-PFT) strategy. The non-contiguous OFDM (NCOFDM) based IA-PFT technique provides enhanced interferen ce suppression using a unique combination of time domain and fr equency domain processing. The energy-based sensing algori thm is enhanced with a noise level estimation technique operati ng in the presence of signal which is based on a rank order filtering algorithm. Such technique does not require “open” out-of-band frequencies or/and silent times for estimating varying noi se floor. Experiments were carried out to evaluate the primary receiver’s performance under the presence of secondary interference a s well as the sensing module’s performance in the presence of the primary transmission. The interference suppression ha s been verified by over-the-air experiments. In particular, experimental primary link performance results demonstrate around 10 dB BER gain relative to an NC-OFDM based suppression and confirm the interference suppression gain predicted by boththe simulation power spectral density and measured spectrum.