Cognitive Radio in a Frequency-Planned Environment: Can it Work?

Erik Axell

Erik G. Larsson and Mikael Skoglund, IEEE GLOBECOM, 2007

SENDORA – SEnsor Network for Dynamic and cOgnitive Radio Access

Linköping University THALES Communications Institut Eurocom Kungliga Tekniska Högskolan Helsinki University of Technology Norwegian University of Science and Technology Telenor ASA Universitat de València Università degli Studi di Roma

The Scenario

Some Fundamental Questions

Cognitive radios must transmit at very low power. How low must it be?

Cognitive radios must expect very low C/(I+N) from primary system. What orders of magnitude?

At an acceptable loss in primary system coverage, how large is the “area of cognitive operation”?

Basic Assumptions and Some Terminology Path loss and lognormal fading

n-reuse frequency planning for primary system

SINR for primary system, with primary base station power P0

-SINR is the SINR achieved with probability 1-

Primary System Operating Point

Primary system is either noise limited, interference limited, or in-between.

Quantify this in terms of ratio between noise and co-channel interference at the primary cell border:

- [dB]: purely noise limited

[dB]: purely interference limited

With Cognitive Users SINR is now

Suppose we can accept reduction in primary cell radius from r to r’. Then assume M cognitive users, each with power P, uniformly distributed in circular ring.

How large can the circular ring, the ”area of cognitive operation,” be?

Feasible Operating Regions, with 7-reuse

,, CP NI

C

NI

C

Feasible Operating Regions, with 21-reuse

“Forbidden Region,” 12-reuse

Asymptotic Sensitivity Requirements

The additional (compared to primary receivers) sensitivity requirement is

and satisfies

Main Conclusions

If cognitive users are to be introduced, they must Be few in numbers, since the aggregate power scales with the

number of devices Transmit with extremely low power, such as -30 dB below the

primary system Have very sensitive radios, in the order of 20-30 dB more sensitive

than the primary system radios.