Paul E. Gorday

Link Maintenance Protocol for Cognitive Radio System with OFDM PHY

For secondary usage of spectrum in a cognitive radio system, in order to maintain reliable continuous communication among secondary users, secondary radios need to make contact, communicate and switch to an open RF channel simultaneously when the current channel is reclaimed by a primary user. In this paper, we describe a link maintenance protocol aimed at solving this issue. The communication channel is monitored and dynamically updated based on spectrum availability. Spectral sensing is employed at the receivers to monitor the spectrum and assist in RF channel synchronization between transmitter and receiver. Simulation results characterizing the performance of this protocol are provided. A prototype system with a pair of cognitive radios featuring this protocol is also introduced.

Implementing an Experimental Cognitive Radio System for DySPAN

Motorola Labs implemented an experimental cognitive radio system for use at the Dynamic Spectrum Access Networks (DySPAN) Symposium 2007. To exercise a practical communication link in a shared spectrum, the system provided a live video feed via a dynamically-allocatable OFDM physical layer. Each demonstration unit included an RF signal conditioning module for DySPAN channel allocations, a custom RF transceiver IC, digital signal processing, and an embedded Linux operating system. Connected to the units via Ethernet, a PC presented a graphical user interface, including the video feed and visualization of the spectral sensing, signal detection, and frequency allocation that was taking place in the units.

Performance of chip-level differential detection with phase noise

Chip-level differential encoding/detection of direct-sequence spread-spectrum signals has been shown to improve receiver robustness in the presence of oscillator frequency offsets and fast fading channels. These gains are achieved at the expense of SNR performance in an AWGN channel, with spreading factor governing the tradeoff. This paper explores the performance of chip-level differential detection in the presence of oscillator phase noise. It is shown that phase noise mitigation is an additional benefit of chip-level differential detection, with higher spreading factors permitting the use of lower-cost, noisier oscillators. Simulations of a DS/SS BPSK system illustrate the relationship between phase noise tolerance and spreading factor, and a simple analytical model is derived for efficient evaluation of systems with high spreading factor.

Early Opportunities for Commercialization of TV Whitespace in the U.S

We propose the use of IP-based broadband wireless protocols to address many of the applications needs in the Television White Space (TVWS) frequencies that will be available for secondary usage in the U.S. beginning in 2009. The work includes a discussion of TVWS physical and regulatory characteristic and a view of the TVWS usage models that may be applied in various market spaces, including the home, the enterprise, public safety and wireless mobile service providers. We show that a protocol based on IEEE 802.16e or a similar broadband wireless protocol could be adapted to meet many of the needs in this space.

Toward wireless receivers without crystals

In new low cost, low bit rate wireless protocols such as Zigbee/spl trade/ and Bluetooth/spl trade/, there is significant economic motivation to implement transceivers with a completely integrated alternative to quartz crystals. In this paper, we explore a differential detection based method of recovering a direct sequence spread spectrum signal with a receiver that does not have a crystal reference. Despite the additional frequency offset and phase introduced by using an integrated crystalless reference oscillator, we find that such a receiver is feasible and can perform sufficiently for many applications.