Design of A Software-defined Underwater Acoustic Modem with Real-time Physical Layer Adaptation Capabilities

ABSTRACT

This article describes the design of a custom software-defined modem with adaptive physical layer for underwater acoustic (UWA) communications. The modem consists of a commercial software-defined radio (SDR) interfaced with a wideband acoustic transducer through amplifying circuitry. With this custom-built platform, we focus on the unique physical layer challenges of the underwater acoustic channel to demonstrate the benefits of real-time adaptation in such rapidly varying environments. We first focus on an Orthogonal-Frequency-Division-Multiplexing (OFDM) transmission scheme. In particular, for the forward link, we consider and implement a high-data rate Zero-Padded OFDM (ZP--OFDM) physical layer with a superimposed convolutional error-correction coding scheme. ZP--OFDM offers high re-configurability in terms of number of OFDM subcarriers, modulation type (e.g., BPSK, QPSK), and error-correction coding rate. Real-time adaptation at the transmitter is achieved through a robust feedback link based on a binary chirp spread-spectrum modulation (B-CSS). We demonstrate that joint real-time adaptation of system parameters such as modulation constellation and channel coding rate leads to significant data rate increase under preset bit-error-rate (BER) constraints. Moreover, in the same context, we present for the first time a seamless switch of our SDR transmitter between different signaling technologies such as OFDM and direct-sequence spread-spectrum (DS-SS).

References

1. T. Melodia, H. Kulhandjian, L. Kuo, and E. Demirors. Advances in Underwater Acoustic Networking. In S. Basagni, M. Conti, S. Giordano, and I. Stojmenovic, editors, Mobile Ad Hoc Networking: Cutting Edge Directions, pages 804--852. John Wiley and Sons, Inc., Hoboken, NJ, second edition edition, 2013.
2. G. Sklivanitis, E. Demirors, S. N. Batalama, D. A. Pados, T. Melodia, and J. D. Matyjas. Demonstration of all-spectrum cognitive channelization on GNU Radio and USRPN-210. In Proc. of the NATO Symp. on "Cognitive Radio and Future Networks" (IST-123), The Netherlands, May 2014.
3. L. Ding, K. Gao, T. Melodia, S. N. Batalama, D. A. Pados, and J. D. Matyjas. All-spectrum cognitive networking through joint distributed channelization and routing. IEEE Transactions on Wireless Communications, 12(11):5394--5405, November 2013.
4. G. Kanke, S. N. Batalama, D. A. Pados, and J. D. Matyjas. Cognitive code-division channelization. IEEE Transactions on Wireless Communications, 10(4):1090--1097, April 2011.
5. E. Jones. The application of software radio techniques to underwater acoustic communications. In Proc. of IEEE OCEANS, June 2007.
6. E. M. Sözer and M. Stojanovic. Reconfigurable acoustic modem for underwater sensor networks. In Proc. of ACM Intl. Workshop on Underwater Networks (WUWNet), Los Angeles, 2006.
7. X. Huang and V. Lawrence. Bandwidth-efficient bit and power loading for underwater acoustic OFDM communication system with limited feedback. In Proc. of Vehicular Technology Conf., Hungary, 2011.
8. P. Qarabaqi and M. Stojanovic. Adaptive power control for underwater acoustic communications. In Proc. of IEEE OCEANS, Spain, June 2011.
9. A. Radosevic, T. Duman, J. Proakis, and M. Stojanovic. Adaptive OFDM for underwater acoustic channels with limited feedback. In Proc. of Signals, Systems and Computers (ASILOMAR), 2011.
10. A. Radosevic, R. Ahmed, T. Duman, J. Proakis, and M. Stojanovic. Adaptive OFDM modulation for underwater acoustic communications: Design considerations and experimental results. IEEE Journal of Oceanic Engineering, 39(2):357--370, April 2014.
11. L. Wan, H. Zhou, X. Xu, Y. Huang, S. Zhou, Z. Shi, and J.-H. Cui. Field tests of adaptive modulation and coding for underwater acoustic ofdm. In Proc. of ACM Intl. Conf. on Underwater Networks and Systems (WUWNet), Taiwan, 2013.
12. G. E. Santagati and T. Melodia. Sonar Inside Your Body: Prototyping Ultrasonic Intra-body Sensor Networks. In Proc. of IEEE Conf. on Computer Communications (INFOCOM), Toronto, Canada, April 2014.
13. D. Torres, J. Friedman, T. Schmid, and M. B. Srivastava. Software-defined underwater acoustic networking platform. In Proc. of the ACM Intl. Workshop on UnderWater Networks (WUWNET), Berkeley, 2009.
14. S. Zhou and Z.-H. Wang. OFDM for Underwater Acoustic Communications. John Wiley and Sons, Inc., 2014.
15. L. LeBlanc, M. Singer, P.-P. Beaujean, C. Boubli, and J. Alleyne. Improved chirp FSK modem for high reliability communications in shallow water. In Proc. of MTS/IEEE OCEANS, 2000.