Spatial Modulation in the Underwater Acoustic Channel
Abstract
Multiple-input multiple-output (MIMO) communication channels are an active area of research for terrestrial wireless applications. The natural bandwidth limitations of the underwater acoustic channel (UAC) combined with the potential for a rich spatial propagation structure suggest the ocean may be another useful application area for MIMO techniques. An underwater acoustic communications experiment was conducted in the waters surrounding Elba, Italy, using spatially modulated signals. Two frequency regimes (9.5-14.5 kHz and 25-35 kHz) were explored over ranges up to 5 km using vertical line arrays suspended from drifting ships. The UAC had an average depth of 100 m. One-way communication links were established at two sites with one site having a rocky (reverberant) bottom and the other having a muddy (absorbent) bottom. The waveform comprised a single data stream with concatenated codes providing error control. The inner code was a high rate BCH code Trellis-coded modulation was used as the basis for the outer code. Successive coded symbols were multiplexed across the available transducer elements. This coding approach effectively maintains the inherent bandwidth efficiency of MIMO signaling. The receiver was an adaptive recursively updated multichannel decision feedback equalizer operating in conjunction with a digital phase-locked loop A packet-based, transport architecture was used and included a training sequence. A Viterbi algorithm was integrated with the equalizer that supported simultaneous tap-weight update and trellis transversal, thereby affording the decision-directed update partial error control. Using appropriate assumptions, channel capacity using a single transducer was estimated to be 5.4 bits/channel use at the soft bottom site. Capacity was maximized at 15.9 bits/channel use using four transducers. More detailed results will be presented along with performance predictions based on both propagation models and measured channel transfer functions7
Document Details
- Document Type
- Technical Report
- Publication Date
- Dec 20, 2004
- Accession Number
- ADA432620
Entities
People
- Daniel Kilfoyle
- Lee Freitag