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Incremental Pilots in OFDM. Parichaya Shrivastava. 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?. Why use OFDM?. Higher spectral efficiency Lower multi-path distortion.

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Incremental pilots in ofdm

Incremental Pilots in OFDM

ParichayaShrivastava


What will we discuss
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?


Why use ofdm
Why use OFDM?

  • Higher spectral efficiency

  • Lower multi-path distortion








Ofdm challanges
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



Main equation:

Channel estimation equation





Why incremental pilots
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


P/S

S/P

16-QAM

Transmitter with channel encoder

Data sub-carriers

IFFT

CP

010

010001

Channel encoder

Pilot PN Sequence

BPSK

DAC

Pilot subcarriers


Incremental pilots trade off
Incremental pilots trade-off

Loss in redundancy acceptable

Better CE

Better BER

Less redundancy:

Worse BER



Work to do
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


  • References:

  • Eric Phillip Lawrey, “Adaptive Techniques for multiuser OFDM” Phd Thesis. Online http://www.skydsp.com/resources/OFDM_thesis_lawrey.PDF

  • Marina Mondi, “Orthogonal Frequency Division Multiplexing/Modulation : OFDM”. Online.

  • Keithley Corporation, “An Introduction to Orthogonal Frequency Division Multiplex Technology”. Online http://www.ieee.li/pdf/viewgraphs/introduction_orthogonal_frequency_division_multiplex.pdf

  • 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

  • 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



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