ofdm & cognitive radio

A Talk on

Carrier Frequency Offset Estimation for Non-Contiguous

OFDM Receiver in Cognitive Radio Systems

Presented By: Md. Shahidullah KawsarEEE, Khulna University of Engineering & Technology

Source: GLOBECOM 2013 IEEE, Georgia, USA

System model: Cognitive Radio & NC-OFDM Importance of CFO estimation Proposed scheme for CFO estimation Simulation Results Future work opportunity

Outlines

Cognitive Radio (CR)

Possible Applications

Mobile multimedia downloads.Emergency communications services.Broadband wireless networking.Multimedia wireless networking services.

A Software Defined Radio (SDR) with a Cognitive Engine Brain

NC-OFDM: Non-Contiguous Orthogonal Frequency Division Multiplexing

NC-OFDM is normal OFDM with a mask just as string of 1s and 0sindicates the presence or absence of a carrier.

Applications

To acquire (SSI) SpectrumSynchronization Information.

To suppress the carriers whichinterfere with the primarytransmission.

Why do we estimate Carrier Frequency Offset (CFO)?

CFO means frequency error in OFDM systems.

Causes of CFO

Frequency differences between the transmitter and receiver oscillators.

Doppler shift of mobile channels.

Oscillator instabilities.

Categories of CFO

Fractional CFO: It introduces Inter-Carrier Interference (ICI) andresults in Bit Error Rate (BER)degradation.

Integer CFO: It introduces a cyclicshift of data sub-carriers and aphase change.

Proposed scheme for CFO estimation

To verify the accuracy

[A] Hard-Decision-Based Active Subchannel Detection

To distinguish active subchannels from inactive ones

[B] HDD Based MLE Algorithm

To recover the CFO

[C] Cramer-Rao lower Bound with Ideal SSI

MSEE vs SNR with SIR = 0dBMSEE: Mean Square Estimation ErrorSNR: Signal to Noise RatioSIR: Signal to Interference Ratio

MSEE vs SNR with SIR = -6 dB

MSEE vs SIR with SNR = 10 dB

MSEE vs Active Subchannel Ratio with SNR = 10 dB & SIR = 0dB

Conclusion

In order to estimate CFO: HDD is used to distinguish active subchannels from inactive ones. HDD based MLE algorithm is used to recover the CFO. Corresponding CRB with Ideal SSI to verify the accuracy.

Simulation results: Similar MSEE as the relevant CRB when a broad range of SIR is

considered. to set up the SSI and decode the received code bits successfully at

the CR receiver.

Thank You