1 / 20

Kaywan Afkhamie Larry Yonge (Intellon) srinivas.katar@intellon

Joint Optimization of Transmit Pulse Shaping, Guard Interval Length, and Receiver-side Narrow-band Interference in the HomePlug AV OFDM System. Haniph Latchman Richard Newman (Univ. of Florida) nemo@cise.ufl.edu. Kaywan Afkhamie Larry Yonge (Intellon) srinivas.katar@intellon.com.

laughter
Download Presentation

Kaywan Afkhamie Larry Yonge (Intellon) srinivas.katar@intellon

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Joint Optimization of Transmit Pulse Shaping, Guard Interval Length, and Receiver-side Narrow-band Interference in the HomePlug AV OFDM System Haniph Latchman Richard Newman (Univ. of Florida) nemo@cise.ufl.edu Kaywan Afkhamie Larry Yonge (Intellon) srinivas.katar@intellon.com Tim Davidson (McMaster Univ.)

  2. Talk Organization • Why OFDM? • Physical channel characteristics • Pulse Shaping • Conclusions

  3. Why OFDM? • Frequency adaptability • Static: unavailable bands • Dynamic: jammers, freq-selective fading • Reduced ICI • Reduced ISI

  4. Powerline Channel • High attenuation • Frequency selective multipath fading • Transfer fcn varies with outlet pair, time • Subject to FCC (and other) regulations • Subject to interference • RC toys • shortwave communications

  5. FCC Limits 10 amateur bands, totaling 3.8 Mhz 30 dB lower than -50 dBm/Hz otherwise allowed

  6. Powerline Channel Examples Delay Spread Attenuation Good channel Bad channel

  7. Cyclic Prefix • Diminishes ISI • Should be at least as long as delay spread • Represents overhead in PHY

  8. Delay Spread Histogram

  9. Symbol Length Considerations • CP should be at least 4 microseconds • Symbol length should be much longer • Longer symbols cause fragmentation effects in MAC

  10. HomePlug OFDM Parameters • Longer symbols: CP is less overhead • Reduced b/w per carrier -> easier notching • FFT H/W more complex • Increased susceptibility to ICI, clock freq. error

  11. Notching Strategies • Notch filters (FIR or IIR) • Difficult to adapt to different regulations • Cumbersome to build tunable filters • Difficult to accommodate variable number of notches • Turn off offending carriers • In and near bands • Desire quick roll-off to minimize loss

  12. OFDM Pulse Shaping • 3072 point symbol (T = 40.96 usec) • CP added (tprefix) • Roll-off interval (RI) – overlap symbols during RI • Total effective symbol length is Guard Interval (GI) + T

  13. Pulse Shaping Goals • Maximize system bandwidth utilization • Minimize length of pulse shaping waveform • (reduces effect of cyclic prefix) • Minimize adverse effects on receiver • Narrow band jammer mitigation • Difficult to optimize simultaneously

  14. Approach to Pulse Shaping • Measure many channels • Vary noise • Vary channel characteristics • Evaluate three alternatives • Raised cosine • Gaussian window • Piecewise linear taper • Tune each manually • Maximize number of carriers • Minimize overhead

  15. Candidate Pulse Shapes

  16. PSD of Candidates

  17. Cyclic Prefix Selection • Match to pulse shape • Receiver runs 90 sample Hanning window for narrow band interference mitigation • Run on noise-free channels

  18. Simulation Approach • 120 channel responses measured, put into DB • Tx generates QPSK modulated packets • Multipath noise computed per response, added • Rx processes SNR per channel per carrier • Bits per carrier sum per channel, average over channels

  19. Simulation Results • GI length selected for best performance per shape • Best rate results for each pulse shape shown

  20. Conclusions • Raised cosine has least distortion, but can’t overcome fewer carriers • Both RC and Gaussian shapes absorb ISI significantly in shaped portion • PWL method is efficient - allows longer GI and still performs 2% better than RC • PWL’ optimizes starting position at which samples fed into FFT • PWL’ is 3.2% better than RC for this DB (0.5 dB improvement)

More Related