POWER CONTROL IN COGNITIVE RADIO SYSTEMS BASED ON SPECTRUM SENSING SIDE INFORMATION. Karama Hamdi, Wei Zhang, and Khaled Ben Letaief The Hong Kong University of Science and Technology Communications, 2007. ICC '07. IEEE International Conference. Outline. Introduction System Model
POWER CONTROL IN COGNITIVE RADIO SYSTEMS BASED ON SPECTRUM SENSING SIDE INFORMATION
Karama Hamdi, Wei Zhang, and Khaled Ben Letaief
The Hong Kong University of Science and Technology
Communications, 2007. ICC '07. IEEE International Conference
 S. Haykin, “Cognitive radio: brain-empowered wireless communications,” IEEE J. Sel. Areas in Commun., vol. 23, pp. 201–220, Feb. 2005.
PTx’s transmit power: Qp
CR’s transmit power: Qc
Δ (dB): the signal attenuation of the distance Rd
μ (dB): the margin of protection
:denotes the average SNR at the cognitive radio
Eγ[.]: the expectation over the random variable γ which is Rayleigh distributed.
Γ: the gamma function
 A. Ghasemi and E. S. Sousa, “Collaborative spectrum sensing for opportunistic access in fading environments,” (DySPAN’05),
1. This figure show that when the average SNR increases the probability of missing becomes smaller
2. For a specified average SNR, a larger Pf will result in the decrease of Pm because of the decrease of the threshold used in energy detection
We can obtain a relationship between Pm and d (or η) for the given Qp/σ2 and α.
It is obvious that the distance d (or η) can decided by Pm
Numerical results demonstrate that when the cognitive radio is far from the primary transmitter, a high probability of missing is obtained.
For a fixed distance d, A higher transmit SNR can get a better sensing performance, i.e. a lower Pm, because the received SNR is enhanced.
Yi denotes the energy collected by the cognitive radio in the time slot i.
Once Pm is determined, d (or η) can be obtained from the previous formula
where Qp‘ and Qc‘ denote the received signal power from the primary transmitter and the cognitive radio, respectively
α and μ are constants
It can be seen from the above formula, that the value of the allowable Qc depends on the SNR loss ψ
This shows the proportional relationship between Pm and the SNR loss due to the distance d.
It demonstrates that the allowable transmit power of the cognitive radio can be increased when a heavy SNR loss occurs between the cognitive radio and the primary receiver