David B. Taubenheim

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.

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.