Electrical Engineering
      and Computer Sciences

Electrical Engineering and Computer Sciences


UC Berkeley


2008 Research Summary

A Cooperation-based Approach to Spectrum Reuse

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Omar Mohammed Bakr, Kannan Ramchandran and Ben Wild

In this research, we present a new framework for cognitive radio spectrum reuse based on cooperation. Unlike traditional cognitive radio systems, which rely on spectrum sensing for reuse, in this framework, primary and secondary systems collaborate to improve the spatial reuse aspect of the overall system. We show that more effective spectrum utilization can be achieved with cooperation without significant changes to existing systems.

The basic components of our proposed architecture are summarized in Figure 1. In this figure, a cognitive radio transmitter (employing multiple antennas) receives feedback from the primary receiver. This feedback assists the cognitive radio transmitter in shaping its beam pattern such that the radiation in the direction of the primary receiver is effectively zero (null). Once this is accomplished, the cognitive radios can start transmitting and receiving data on the entire spectrum band without interfering with the primary. In a practical scenario, the primary receiver could be a cellular base station, in which case the desired frequency band would be the cellular uplink. The cognitive radios could be cell phones trying to establish direct peer-to-peer links without having to communicate through the base station.

Our goal is to analyze the different performance metrics associated with this approach (e.g., interference, hardware complexity), as well as the different issues related to integrating it with existing systems. We also develop and analyze several beam-forming and nulling algorithms that can potentially enhance spatial reuse while reducing the hardware complexity requirements.

Figure 1
Figure 1: Basic architecture for spectrum reuse