A study on timedomain approach for channel estimation

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A study on time-domain approach for channel
estimation

• Student???
• Advisor Prof. ???

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Outline

• Introduction
• General LS-based estimation
• Frequency pilot time average method
• FPTA-1
• FPTA-2
• Most significant taps method
• Simulation

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Introduction

• In OFDM systems, if complexity is affordable,
  time interpolation can be used to improve the
  performance.
• Most of the channel estimation approaches can be
  viewed as DFT-based approaches, where LS channel
  estimates are fed to IFFT block to get time
  domain channel estimates and transformed back to
  frequency domain by FFT.

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General time domain and frequency domain channel
estimation

• In usual time domain and frequency domain channel
  estimation, the pilot signal is Pk with pilot
  ratio 1/Kwhere K, m and i are integersA is
  pilot amplitude and MN/K is an integer

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General time domain and frequency domain channel
estimation

• Suppose the channel has a discrete-time impulse
  response
• Hence, the received frequency domain pilot signal
  will be

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General time domain and frequency domain channel
estimation

• As for the received noise
• In this method, Pk is PN-sequence, pn and
  Pk are both noise-like. Hence the
  pilot-to-noise ratio in the time-domain and in
  the frequency are about the same.

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Frequency pilot time average (FPTA) method

• The pilot signal is shown as
• Hence

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FPTA

• If the FPTA method is used for channel estimation
  with the pilot signal in the time domain, the
  pilot-to-noise ratio is
• Since there are K identical parts of time-domain
  pilot samples, the corresponding parts of
  received samples are averaged over K parts.

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FPTA-1

• Consider only the pilot affected by multipath
  channel and Gaussian noise

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FPTA-1

• Averaging the received signal over K parts
• Repeat the ravg K times to reconstruct the
  received samples y

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FPTA-1

• Hence, the channel frequency response at pilot
  tones can be estimated

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FPTA-2

• Use FFTravg together with FFTpo, where po is
  one of the identical parts of time-domain pilot
  samples.

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Proposed time-domain method

• In practical situation, there are not so many
  channel paths with significant energy. Hence,
  many samples will have little or no energy at all
  except noise perturbation.
• Neglect those nonsignificant channel taps may
  introduce some performance degradation, but at
  the same time it will eliminate the noise
  perturbation.

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Proposed time-domain method

• The time-domain received samples
• After averaging
• The raw LS channel estimation

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Proposed time-domain method

• Just choose the most significant J taps
• Thus the frequency response estimate is

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Proposed time-domain method

• Where
• Ignore the residual term and mse is

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Simulation results
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Reference

• H. Minn and V.K. Bhargava, An investigation into
  time-domain approach for OFDM channel
  estimation, IEEE Trans. on Broadcasting, vol.46
  no.4, pp.240-248, Dec 2000.
• C.S. Yeh and Y. Lin, Channel estimation using
  pilot tones in OFDM systems, IEEE Trans. on
  Broadcasting, vol.45, no.4, pp.400-409, Dec 1999.