High Bit Rate Ultrasonic Communication through Metal Channels

As low cost, low power wireless networking technologies continue to gain popularity in industrial control and remote sensing applications, greater demand is being placed on network reliability and robustness. The numerous metallic objects found in many industrial environments can make reliable RF coverage difficult to obtain. In cases where system components are physically isolated from one another by metallic barriers (e.g. bulkheads or storage tank walls), direct RF communication between components is not possible. Prior research into the use of ultrasonic signaling as a means of passing data across metallic barriers has proven successful, but it has been observed that acoustic echoing in the channel leads to significant intersymbol interference (ISI) when symbol rate approaches the hundred kilosymbol/second range. An echo cancelation technique was developed to partially suppress these echoes, but its performance was limited due to simplicity of the channel model used. In this paper, we develop a more accurate channel model and use it as the basis for constructing an improved echo cancelation pulse. The new pulse suppresses echoes to a level comparable to the RMS noise amplitude of the channel, greatly reducing ISI. The resulting transceiver is capable of transmitting data at over 5 Mbps using simple pulse amplitude modulation (PAM). This technique thus represents a data rate increase by a factor of five over prior work.