Demonstration of PC-based and DSP-based Implementations of an OFDM Acoustic Modem

The success of multicarrier modulation in the form of OFDM in radio channels illuminates a path one could take towards high-rate underwater acoustic communications, and recently there are intensive investigations on underwater OFDM. In this workshop, we would like to demonstrate two projects that have been undertaken at University of Connecticut on the implementations of an OFDM acoustic modem, whose receiver algorithms are developed in [1], [2]. • PC-based implementation as described in [3]. This implementation is based on Matlab programming on two laptops, as shown in Fig. 1. Two laptops can communicate with each other via two-way acoustic links. • DSP-based implementation as described in [4]. This implementation is based on a TMS320C6713 DSP board, as shown in Fig. 2. For an OFDM block duration of 230 ms, the demodulation-plus-decoding time at the receiver is about 200 ms, and hence a real-time one-way communication is accomplished. The bandwidth is 5.5 kHz, and the overall data rate is 3.1 kbps after rate 1/2 convolutional coding. These prototypes work well for in-air acoustic channels and are expected to work well for underwater acoustic channels with stationary transceivers [3]. The resampling operation in [2] for fast-varying channels due to mobile transceivers has not been implemented.