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.