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Evaluating the Effectiveness of Repetition in Low Mobility Scenarios for 802.11ah

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selima
8 diapositives · 240 Views · Jul 21, 2014

This study investigates the applicability of repetition schemes for error correction in 802.11ah wireless sensor networks under low mobility conditions. Our simulations demonstrate that channel coherence times are relatively long, leading to high correlation at low speeds. We find that due to the lack of frequency selectivity, repetition schemes primarily provide benefits through energy doubling rather than diversity gains. Our conclusions suggest further exploration of alternative techniques beyond repetition to address potential coverage issues in real-world applications.

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  1. On the Suitability of Repetition for 802.11ah Date:2012-01-17 Authors: , Renesas Mobile Corporation

  2. Abstract We present results on channel coherence times under low mobility. Our results suggest that repetition schemes may not be applicable under low mobility sensor applications. , Renesas Mobile Corporation

  3. Motivation • Repetition is a simple scheme to provide error correction • Repeat a message to be transmitted over the channel multiple times • Hope that the channel will not corrupt in the same way all repeated messages • Increase the energy per symbol repeated • Under i.i.d. Rayleigh fading repetition has time diversity gains • Repetition was suggested in e.g., [1], [2], [3], to increase the range in 802.11ah • In [3] several methods of repetition in the frequency or time domain were proposed for 802.11ah , Renesas Mobile Corporation

  4. Simulation Parameters • Rayleigh fading (NLOS scenario) • Jakes Doppler Spectrum • Exponentially decaying delay profile • Carrier frequency 900 MHz • Scenarios , Renesas Mobile Corporation

  5. Simulation Results • At 1 MHz and 2 MHz the frequency correlation is at least 0.5 • Channel is not frequency selective • Repetition in frequency will not gain from frequency selectivity (gains merely from doubling energy per symbol) , Renesas Mobile Corporation

  6. Simulation Results • The channel correlation up to 10ms for low mobility is high • For mobility of 3 km/h the channel coherence time is 71ms • Repeated symbols will face the same channel • Gains only from doubling energy per symbol , Renesas Mobile Corporation

  7. Conclusions • Our simulations showed that under low mobility the • Channel is not frequency selective • Channel coherence time is much larger than the expected duration of a transmission • Repetition can only benefit from doubling energy/symbol • 3dB requirement is based on very particular measurements • Cannot guarantee that coverage problems would not happen in real life. • Repetition doubles transmission time • Negative hit for energy consumption • Investigate further • The needed supported path loss with expected TX powers • Other techniques beyond repetition; e.g. Multi-hop , Renesas Mobile Corporation

  8. References [1] 11-11-0035-01-00ah-coverage-extension-for-ieee80211ah [2] 11-11-1482-02-00ah-preamble-format-for-1-mhz [3] 11-11-1490-01-00ah-repetition-schemes-for-tgah , Renesas Mobile Corporation