Application of cognitive radio principles to wireless channel sounding

Channel sounding is generally conducted under the assumption that the wireless channel is free from interfering signals, i.e., in clear channels. As regulators begin to deploy new services in spectrum that is already occupied by other services, channel sounding must often be conducted in occupied channels with all the obvious attendant difficulties. Here, we propose alternative sense-decide-act strategies based upon cognitive radio principles that can mitigate interference when a conventional vector network analyzer is used to collect swept-frequency measurements of static channels. We show that a three-step process involving: 1) the use of sensing to reduce the probability that the channel sounder will interfere with a transmission that is underway, 2) robust estimation to eliminate outliers due to measurements corrupted by transmissions that began while the measurement was underway, and 3) estimation of the number of samples required to yield estimates of the channel response that fall within an acceptable confidence interval. Implementation of the scheme using an Agilent E8362C PNA vector network analyzer augmented by an external sensing receiver and control software yields pristine channel measurements even in the presence of significant interference.