1. Incremental Pilots in OFDM Parichaya Shrivastava

2. What will we discuss? Brief overview of OFDM – Why use OFDM? – How does it work? Pilots – Why do we need them? Incremental Pilots -Concept -What am I trying to do?

3. Higher spectral efficiency Lower multi-path distortion Why use OFDM?

4. Higher spectral efficiency

5. Example of an OFDM modem

11. Multipath problem

12. A Multipath solution

13. The Multipath solution

14. Example of an OFDM modem

15. OFDM challanges Synchronization requirements are much more strict : – Requires more complex algorithms for time / frequency synch Peak-to-average power ratio – Large signal peaks require higher power amplifiers – Amplifier cost grows nonlinearly with required power

16. Pilot based OFDM system model

17. Main equation: Channel estimation equation

18. Frequency domain channel estimation

19. Pilot allocation 1

20. Pilot allocation 2

21. Why Incremental Pilots? Some channels (e.g. where there is more frequency selective fading), increased number of pilots will help. More pilots -Interpolation error small -> Better channel estimation -> Better BER

22. Channel encoder 010010001 Data sub- carriers Pilot subcarrie rs IFFT CP S/ P 16- QA M Pilot PN Sequence BPSK P/ S DAC Transmitter with channel encoder

23. Incremental pilots trade-off Better CE Better BER Less redundancy: Worse BER Less redundancy: Worse BER Loss in redundancy acceptable

24. Loss in redundancy. Crude figure

25. Work to do See the performance under different channel conditions Different coding schemes (Convolutional, Turbo, LDPC) Complexity of implementing higher coding rates for different coding schemes

26. References: 1.Eric Phillip Lawrey, Adaptive Techniques for multiuser OFDM Phd Thesis. Online http://www.skydsp.com/resources/OFDM_thesis_lawrey.PDF http://www.skydsp.com/resources/OFDM_thesis_lawrey.PDF 2.Marina Mondi, Orthogonal Frequency Division Multiplexing/Modulation : OFDM. Online. 3.Keithley Corporation, An Introduction to Orthogonal Frequency Division Multiplex Technology. Online http://www.ieee.li/pdf/viewgraphs/introduction_orthogonal_frequency_division_multiplex.p df http://www.ieee.li/pdf/viewgraphs/introduction_orthogonal_frequency_division_multiplex.p df 4.Muhammad Saad Akram, Pilot-based Channel Estimation in OFDM Systems. Online http://www2.imm.dtu.dk/pubdb/views/edoc_download.php/5405/pdf/imm5405.pdf http://www2.imm.dtu.dk/pubdb/views/edoc_download.php/5405/pdf/imm5405.pdf 5.Sung-Yoon Jung and Sunghwan Kim, Channel Estimation and LDPC Code Puncturing Schemes Based on Incremental Pilots for OFDM. ETRI Journal, Volume 32, Number 4, August 2010

27. Thank you!