ofdm in cr
TRANSCRIPT
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Optimal Power allocation in OFDM based CR system
Vaibhav KumarY13PG052
The LNM IIT, Jaipur
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Outline Introduction Cognitive Radio System Model Spectrum of SU in OFDM based CR system Transceiver diagram of SU Mathematical modeling of Interference constraint Formulation of Power allocation problem Power increment water-filling Power- decrement water-filling Comparison of the proposed algorithm with IPWF Conclusion References
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Introduction In CR systems the transmission of SU is required to satisfy the PU's interference limit to protect the PU's performance
Constraint 1 : Maximum allowable collision probability which is related to spectrum sensing.
Constraint 2 : Interference power limit which introduces power restrictions on the channel output which is different form conventional wireless systems.
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Cognitive Radio System Model
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Spectrum of SU in OFDM based CR system
Assumption : The distance between the SU and the nearest undetectable PU transmitter is known in advance. The PU transmitter is assumed to be just at the margin of the reliable sensing region
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Transceiver diagram of SU in OFDM based CR system
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Mathematical modeling of interference constraintAssume Gj is the power constraint in the jth sub-channel after the sensing, then
Rj = radius of the protection region of PUj
dj = Distance between the SU's transmitter and the nearest undetectable PUj transmitterηj = Interference power limit of PUj
βj = Path attenuation factor
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Formulation of Power Allocation Problem
: Channel-to-Noise Ratio
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Power Increment Water Filling Consider the problem with total power constraint Ptotal + Δ
The channels are divided into three sets
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Lemma 1 : If all channel satisfy or
Then the new water level becomes
The new powers in each channel are for Pi Є Q U R and
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Power Decrement Water Filling
Lemma 2 : Assume that Pi Є C satisfies the following condition
Then the new water level is
and
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A comparison of the proposed algorithm and the IPWF (Iterative partitioned water filling) algorithm
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Conclusion : A new low-complexity optimal power allocation algorithm for OFDM based CRN is proposed
By exploiting some properties of the water-filling algorithm, a new power-increment and power-decrement water filling algorithms are proposed
In future, the algorithm may be extended to be applicable to realistic Cognitive Radio Networks
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References [1] P. Wang et al. , “Power allocation in OFDM based cognitive radio system” in Proc. IEEE Global Telecommunication Conference (Globecom 2007), Washington, DC, Nov. 2007, pp.- 4061-4065
[2] Qi, Quilin and Yang, Yaoqing Lamar, “An efficient Water-filling algorithm for Power-allocation in OFDM based CR system” (2012). CSE conference and workshop papers