Hermes: data transmission over unknown voice channels

  • Authors:

  • Aditya Dhananjay;Ashlesh Sharma;Michael Paik;Jay Chen;Trishank Karthik Kuppusamy;Jinyang Li;Lakshminarayanan Subramanian

  • Affiliations:

  • New York University, New York, NY, USA;New York University, New York, NY, USA;New York University, New York, NY, USA;New York University, New York, NY, USA;New York University, New York, NY, USA;New York University, New York, NY, USA;New York University, New York, NY, USA

  • Venue:
  • Proceedings of the sixteenth annual international conference on Mobile computing and networking
  • Year:
  • 2010

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Abstract

While the cellular revolution has made voice connectivity ubiquitous in the developing world, data services are largely absent or are prohibitively expensive. In this paper, we present Hermes1, a point-to-point data connectivity solution that works by modulating data onto acoustic signals that are sent over a cellular voice call. The main challenge is that most voice codecs greatly distort signals that are not voice-like; furthermore, the backhaul can be highly heterogeneous and of low quality, thereby introducing unpredictable distortions. Hermes modulates data over the extremely narrow-band approximately 3kHz bandwidth) acoustic carrier, while being severely constrained by the requirement that the resulting sound signals are voice-like, as far as the voice codecs are concerned. Hermes uses a robust data transcoding and modulation scheme to detect and correct errors in the face of bit flips, insertions and deletions; it also adapts the modulation parameters to the observed bit error rate on the actual voice channel. Through real-world experiments, we show that Hermes achieves approximately 1.2 kbps goodput which when compared to SMS, improves throughput by a factor of 5× and reduces the cost-per-byte by over a factor of 50x