A high data-rate, software-defined underwater acoustic modem

Most underwater acoustic modems offer only low data rates. This is largely because they operate at low frequency, which limits the channel bandwidth available, and hence the symbol rate. The low frequency acoustic channel suffers from substantial multipath and doppler effects, which constrain the signal quality at the receiver. As a result only 1 or 2 bits per symbol are achieved, with the effective data rate further reduced by error control coding. High frequency acoustic signals are heavily attenuated in water, severely constraining the range of high frequency links. High frequency signals however offer substantially greater signal bandwidth, and probably improved channel quality which guides our design choice of a high frequency acoustic modem for underwater communication. Contemporary Field Programmable Gate Arrays (FPGAs) can provide good system functionality at low cost and with the flexibility to perform rapid testing and development of communication algorithms. They may also be competitive in production systems. In this paper we describe current progress in development of a high frequency, high data-rate modem which is implemented entirely in FPGA. This differs from most existing modems which are based on DSP processors. Being software defined, the modem is flexible because the parameters can be reconfigured with relative ease, minimising the cost of rework as the design evolves. This modem will not only demonstrate the feasibility of high frequency FPGA based modems, but will also be a valuable tool to provide a better understanding of the high frequency acoustic channel, and demonstrate the utility of absorption to enhance channel re-use rates in underwater acoustic networks. The modulator has been implemented in the FPGA, to produce laboratory and open water tests that conform to modelling. The demodulator has been implemented in Matlab, and recovers the carrier, code synchronisation and data from recordings of both laboratory and open water tests. Coding of the demodulator into the FPGA is currently in progress.

[1]  Hua Lee,et al.  An underwater acoustic telemetry modem for eco-sensing , 2005, Proceedings of OCEANS 2005 MTS/IEEE.

[2]  Milica Stojanovic,et al.  Underwater Acoustic Communication , 2015 .

[3]  Milica Stojanovic,et al.  Underwater acoustic communications , 1995, Proceedings of Electro/International 1995.

[4]  S. Singh,et al.  The WHOI micro-modem: an acoustic communications and navigation system for multiple platforms , 2005, Proceedings of OCEANS 2005 MTS/IEEE.

[5]  M.J. Ryan,et al.  On the Benefits of High Absorption in Practical Multi-hop Networks , 2007, OCEANS 2007 - Europe.

[6]  P. Baldi,et al.  Software Acoustic Modems for Short Range Mote-based Underwater Sensor Networks , 2006, OCEANS 2006 - Asia Pacific.

[7]  Milica Stojanovic,et al.  Underwater Acoustic Digital Signal Processing and Communication Systems , 2002 .

[8]  Jeff Feigin,et al.  Practical Costas loop design , 2002 .

[9]  P. Casari,et al.  Cognitive Spectrum Access for Underwater Acoustic Communications , 2008, ICC Workshops - 2008 IEEE International Conference on Communications Workshops.

[10]  M. Stojanovic,et al.  Design and Capacity Analysis of Cellular-Type Underwater Acoustic Networks , 2008, IEEE Journal of Oceanic Engineering.

[11]  Michael R. Frater,et al.  HIGH-CAPACITY UNDERWATER COMMUNICATIONS , 2007 .

[12]  Charalampos C. Tsimenidis,et al.  T9 - Signal Waveform Design for Underwater Acoustic Communications , 2007, OCEANS 2007.

[13]  C. R. Benson,et al.  The high frequency underwater acoustic channel , 2010, OCEANS'10 IEEE SYDNEY.

[14]  Ying Li,et al.  Design of a Low-Cost Underwater Acoustic Modem , 2010, IEEE Embedded Systems Letters.

[15]  J. G. Proakis,et al.  Direct sequence spread spectrum based modem for under water acoustic communication and channel measurements , 1999, Oceans '99. MTS/IEEE. Riding the Crest into the 21st Century. Conference and Exhibition. Conference Proceedings (IEEE Cat. No.99CH37008).

[16]  John S. Heidemann,et al.  Low-power acoustic modem for dense underwater sensor networks , 2006, WUWNet '06.

[17]  John Aasted Sørensen,et al.  Time-area efficient multiplier-free filter architectures for FPGA implementation , 1995, 1995 International Conference on Acoustics, Speech, and Signal Processing.

[18]  Milica Stojanovic,et al.  On the relationship between capacity and distance in an underwater acoustic communication channel , 2007, MOCO.

[19]  Lee Freitag,et al.  FSK and PSK performance of the utility acoustic modem , 1999, Oceans '99. MTS/IEEE. Riding the Crest into the 21st Century. Conference and Exhibition. Conference Proceedings (IEEE Cat. No.99CH37008).

[20]  Craig Benson,et al.  Design of a high frequency FPGA acoustic modem for underwater communication , 2010, OCEANS'10 IEEE SYDNEY.

[21]  Mónica Arroyuelo,et al.  FPGA-Based Digital filters using Bit-Serial arithmetic , 2007 .

[22]  Pierre-Philippe J. Beaujean,et al.  A performance study of the high-speed, high-frequency acoustic uplink of the HERMES underwater acoustic modem , 2009, OCEANS 2009-EUROPE.