This paper details the Wireless at Virginia Tech Center for Wireless Telecommunications' (CWT) design and
implementation of its Smart Radio (SR) communication platform. The CWT SR can identify available spectrum within
a pre-defined band, rendezvous with an intended receiver, and transmit voice and data using a selected quality of service
(QoS). This system builds upon previous cognitive technologies developed by CWT for the public safety community,
with the goal of providing a prototype mobile communications package for military and public safety First Responders.
A master control (MC) enables spectrum awareness by characterizing the radio environment with a power spectrum
sensor and an innovative signal detection and classification module. The MC also enables spectrum and signal memory
by storing sensor results in a knowledge database. By utilizing a family radio service (FRS) waveform database, the
CWT SR can create a new communication link on any designated FRS channel frequency using FM, BPSK, QPSK, or
8PSK modulations. With FM, it supports analog voice communications with legacy hand-held FRS radios. With digital
modulations, it supports IP data services, including a CWT developed CVSD-based VoIP protocol. The CWT SR
coordinates spectrum sharing between analog primary users and digital secondary users by applying a simple but
effective channel-change protocol. It also demonstrates a novel rendezvous protocol to facilitate the detection and
initialization of communications links with neighboring SR nodes through the transmission of frequency-hopped
rendezvous beacons. By leveraging the GNU Radio toolkit, writing key modules entirely in Python, and utilizing the
USRP hardware front-end, the CWT SR provides a dynamic spectrum test bed for future smart and cognitive radio
research.
This paper explores methods to excise broadband interference signals from a Global Positioning System (GPS) spread spectrum signal using bilinear transformations. The Wigner-Ville Distribution allows for signal and jammer time-frequency characterization. The jammer signals, identified in the Time-Frequency (T-F) domain, are excised by zeroing peak amplitudes above a statistically determined detection threshold. The GPS signal is synthesized using inverse Wigner transform involving least squares amplitude and phase matching. Pre-processing increases Pseudo-Random Noise (PRN) correlator performance due to significant reduction in effective Jammer-to-Signal ratio (JSR). The proposed technique improves receiver robustness for large classes of broadband jammers, not limited to instantaneously narrowband jammers with a constant modulus or well defined instantaneous frequencies, while improving bit-error-performance and GPS Coarse Acquisition (C/A) and tracking in hostile interference environments.
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