Communication Engineering

1. A Talk on
Carrier Frequency Offset
Estimation for Non-Contiguous
OFDM Receiver in
Cognitive Radio Systems
Presented By: Md. Shahidullah Kawsar
EEE, Khulna University of Engineering & Technology
Source: GLOBECOM 2013 IEEE, Georgia, USA

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

3. 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

4. NC-OFDM: Non-Contiguous
Orthogonal Frequency Division Multiplexing
NC-OFDM is normal OFDM with a mask just as string of 1s and 0s
indicates the presence or absence of a carrier.
Applications
 To acquire (SSI) Spectrum
Synchronization Information.
 To suppress the carriers which
interfere with the primary
transmission.

5. 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) and
results in Bit Error Rate (BER)
degradation.
 Integer CFO: It introduces a cyclic
shift of data sub-carriers and a
phase change.

6. 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

7. MSEE vs SNR with SIR = 0dB
MSEE: Mean Square Estimation Error
SNR: Signal to Noise Ratio
SIR: Signal to Interference Ratio

8. MSEE vs SNR with SIR = -6 dB

9. MSEE vs SIR with SNR = 10 dB

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

11. 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.

12. Thank You