Spectrum Monitoring Algorithms for Wireless and Satellite Communications

Doctoral thesis (2018)

Nowadays, there is an increasing demand for more efficient utilization of the radio frequency spectrum as new terrestrial and space services are deployed resulting in the congestion of the already crowded ... [more ▼]

Nowadays, there is an increasing demand for more efficient utilization of the radio frequency spectrum as new terrestrial and space services are deployed resulting in the congestion of the already crowded frequency bands. In this context, spectrum monitoring is a necessity. Spectrum monitoring techniques can be applied in a cognitive radio network, exploiting the spectrum holes and allowing the secondary users to have access in an unlicensed frequency band for them, when it is not occupied by the primary user. Furthermore, spectrum monitoring techniques can be used for interference detection in wireless and satellite communications. These two topics are addressed in this thesis. In the beginning, a detailed survey of the existing spectrum monitoring techniques according to the way that cognitive radio users 1) can detect the presence or absence of the primary user; and 2) can access the licensed spectrum is provided. Subsequently, an overview of the problem of satellite interference and existing methods for its detection are discussed, while the contributions of this thesis are presented as well. Moreover, this thesis discusses some issues in a cognitive radio system such as the reduction of the secondary user's throughput of the conventional \listen before talk" access method in the spectrum. Then, the idea of simultaneous spectrum sensing and data transmission through the collaboration of the secondary transmitter with receiver is proposed to address these concerns. First, the secondary receiver decodes the signal from the secondary transmitter, then, removes it from the total received signal and finally, applies spectrum sensing in the remaining signal in order to decide if the primary user is active or idle. The effects of the imperfect signal cancellation due to decoding errors, which are ignored in the existing literature, are considered in our analysis. The analytical expressions for the probabilities of false alarm and detection are derived and numerical results through simulations are also presented to validate the proposed study. Furthermore, the threat of interference for the satellite communications services is studied in this thesis. It proposes the detection of interference on-board the satellite by introducing a spectrum monitoring unit within the satellite transponder. This development will bring several benefits such as faster reaction time and simplification of the ground stations in multi-beam satellite systems. Then, two algorithms for the detection of interference are provided. The first detection scheme is based on energy detector with signal cancellation exploiting the pilot symbols. The second detection scheme considers a two-stage detector, where first, the energy detector with signal cancellation in the pilot domain is performed, and if required, an energy detector with signal cancellation in the data domain is carried out in the second stage. Moreover, the analytical expressions for the probabilities of false alarm and detection are derived and numerical results through simulations are provided to verify the accuracy of the proposed analysis. Finally, this thesis goes one step further and the developed algorithms are evaluated experimentally using software defined radios, particularly universal software radio peripherals (USRPs), while it concludes discussing some open research topics. [less ▲]

Weak Interference Detection with Signal Cancellation in Satellite Communications

in The 42nd IEEE International Conference on Acoustics, Speech and Signal Processing, ICASSP 2017 (2017)

Interference is identified as a critical issue for satellite communication (SATCOM) systems and services. There is a growing concern in the satellite industry to manage and mitigate interference ... [more ▼]

Interference is identified as a critical issue for satellite communication (SATCOM) systems and services. There is a growing concern in the satellite industry to manage and mitigate interference efficiently. While there are efficient techniques to monitor strong interference in SATCOM, weak interference is not so easily detected because of its low interference to signal and noise ratio (ISNR). To address this issue, this paper proposes and develops a technique which takes place on-board the satellite by decoding the desired signal, removing it from the total received signal and applying an Energy Detector (ED) in the remaining signal for the detection of interference. Different from the existing literature, this paper considers imperfect signal cancellation, examining how the decoding errors affect the sensing performance, derives the expressions for the probability of false alarm and provides a set of simulations results, verifying the efficiency of the technique. [less ▲]

Harmful Interference Threshold and Energy Detector for On-Board Interference Detection

in 22nd Ka and Broadband Communications Conference 2016 (2016)