Richard Primerano

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.

High-data-rate ultrasonic through-metal communication

A link-adaptive frequency division multiplexing (OFDM) ultrasonic physical layer is proposed for high-datarate communications through metal walls. The ultrasonic link allows for communication without physical penetration of the metal barrier. Link-adaptive OFDM mitigates the severe frequency- selective fading of the ultrasonic channel and greatly improves throughput over impulse or narrowband communication systems. Throughput improvements of 300% are demonstrated over current narrowband low-frequency techniques, and show improved spectral efficiency over high-frequency techniques found in the literature.

Application of Adaptive OFDM Bit Loading for High Data Rate Through-Metal Communication

The acoustic through-metal channel is characterized by strong multipath components caused by the echoing of acoustic energy within the channel. Transmission at high data rates is therefore difficult to achieve with traditional single-carrier systems. This paper applies an adaptive bit-loading technique to the transmission of digital signals through metal barriers using ultrasonic signaling. The multi-carrier approach discussed here allows us to mitigate severe frequency selectivity of the through-metal communication link and improve spectral efficiency by exploiting the stationary nature of the channel. Experimental performance of bit loading is examined in an ultrasonic through-metal channel. Our results indicate that non-power-scaled rate adaptive bit loading significantly outperforms non-adaptive modulation. Adaptive bit loading was shown to adhere to a strict BER constraint while increasing data rates by roughly 240% from values of 5 Mbps to approximately 12 Mbps when compared to narrowband modulation techniques.

Echo-Cancellation for Ultrasonic Data Transmission through a Metal Channel

The process control industry has shown great interest in implementation of low cost, low power wireless sensor networks. Such networks are much easier to deploy and reconfigure compared to wired alternatives. In this paper, we describe the use of radio-frequency (RF) based sensor networks in sensing and control applications on naval vessels. In this environment, metal bulkheads (which divide the ship into watertight compartments) and other metallic obstacles can lead to unreliable network connectivity. We propose to address the challenge by augmenting the RF network with ultrasonic data repeaters. The repeaters are designed to pass data from one side of a watertight bulkhead to the other without requiring the bulkhead to be physically penetrated. Through experimentation, we observed that echoes of pulses transmitted through the ultrasonic channel (i.e. the bulkhead) lead to considerable intersymbol interference and hinder high data rate transmission. In this paper, we investigate the nature of this interference and propose a method of mitigating its effect. The method applies a pre-distortion filter to the data which leads to destructive interference that reduces the echo amplitude.

On Frictional Forces between the Finger and a Textured Surface during Active Touch

We investigated forces felt by a bare finger in sliding contact with a textured surface, and how they depend on properties of the surface and contact interaction. Prior research has shed light on haptic texture perception. Nevertheless, how texture-produced forces depend on the properties of a touched object or the way that it is touched is less clear. To address this, we designed an apparatus to accurately measure contact forces between a sliding finger and a textured surface. We fabricated textured surfaces, and measured spatial variations in forces produced as subjects explored the surfaces with a bare finger. We analyzed variations in these force signals, and their dependence on object geometry and contact parameters. We observed a number of phenomena, including transient stick-slip behavior, nonlinearities, phase variations, and large force fluctuations, in the form of aperiodic signal components that proved difficult to model for fine surfaces. Moreover, metrics such as total harmonic distortion and normalized variance decreased as the spatial scale of the stimuli increased. The results of this study suggest that surface geometry and contact parameters are insufficient to account for force production during such interactions. Moreover, the results shed light on perceptual challenges solved by the haptic system during active touch sensing of surface texture.

Performance Evaluation of MIMO OFDM Systems in On-Ship Below-Deck Environments

Below-deck compartments on naval vessels provide a challenging environment for wireless networks. The metallic walls of the compartments produce multiple reflections that can degrade signal integrity. Between compartments, the metal bulkheads impede the propagation of electromagnetic waves, limiting network connectivity. Orthogonal frequency-division multiplexing (OFDM) is proposed to mitigate the effects of intersymbol interference (ISI) caused by multiple reflections. Additionally, the use of multiple antennas for channel diversity has shown to improve communications reliability and capacity. Single and multiantenna OFDM physical layers were tested within several below-deck spaces aboard Thomas S. Gates (CG 51), a decommissioned Ticonderoga-class US Navy cruiser. Measurements were taken with four OFDM-based schemes typical of current-generation Wireless Local Area Network (WLAN) technologies. The performance of multiantenna signaling techniques, including 2 × 2 Alamouti space-time coding and 2 × 2 multiple-input-multiple-output spatial multiplexing (MIMO-SM), were compared to the performances of 1 × 2 maximal ratio combining (MRC) and a conventional single-input-single-output (SISO) system. Results indicate that the tested MIMO techniques can approximately double the channel capacity. Throughput as high as 36 Mb/s was achieved in conventional situations where SISO links only admitted rates of 18 Mb/s.

Bit-Loaded PAPR Reduction for High-Data-Rate Through-Metal Control Network Applications

Data transmission through metallic structures is commonly required in industrial control applications. In a number of these applications, mechanically penetrating the structure to pass cables and establish a wired communication link is either impossible or undesirable. Examples of such structures include metal bulkheads, pressure vessels, or pipelines. Ultrasonic signaling has been proposed as a solution for through-metal data transfer without penetrating the structure. The reverberant nature of the through-metal channel, however, can lead to significant intersymbol interference, limiting the data rate achievable by conventional single-carrier communication techniques. In this paper, we describe a through-metal communication technique that exploits the slow-varying nature of the ultrasonic channel to implement an orthogonal-frequency-division-multiplexing-based rate-adaptive peak-to-average power ratio (PAPR) reduction algorithm. Measurements of the proposed adaptive algorithm have demonstrated transmitted throughput rates of up to 14 Mbps while reducing PAPR by up to 3 dB and maintaining a bit error rate of 10- 5 at average transmit powers of roughly 6 dBm. This enhancement provides the required throughput and error rate to support high-rate network applications in otherwise data-limited environments.

A Case Study in System-Level Physics-Based Simulation of a Biomimetic Robot

Biomimetic robots are a new and challenging frontier for robotic systems. Designs inspired by nature are creating new approaches to problems such as to planetary surface exploration, minimally invasive surgery, or inspection of piping and cabling. However, these new biomimetic robotic systems are a challenge to design, simulate, and control. This paper presents a case-study in the design and physics-based simulation of a unique snake-inspired robot. The Drexel Snake Robot is a novel hybrid capable of both undulatory and rectilinear motion. In order to design gaits, test control algorithms and perform path planning for this robot, we develop a system-level physics-based simulation that captures engineering phenomena across many disciplines: mechanical, electrical, software, electronics, and the robots external environment. As the snake robot moves, there is considerable slippage between its feet and the ground. Consequently, contact and friction forces play a significant role in dictating the path followed by the robot for a given set of joint motions. A closed-form equation (or set of equations) describing the robots motion in this environment cannot be derived in a simple manner. Consequently, the material presented here are based the comparison of experimental and simulation results. While developing the simulation model, we detail the process of extracting necessary physical, kinematic and dynamics properties directly from the robots computer-aided design. This process is not straightforward and the paper documents the issues and lessons learned that will be of use to others wishing to create full virtual models for their systems. Finally, we show how to calibrate the simulation model for fidelity and accuracy with several examples showing that it can be used to test gait and mobility patterns and identify nonobvious secondary phenomena to emerge from the design.

Detection performance of spread spectrum signatures for passive, chipless RFID

Time-Domain Reflectometry (TDR) RFID tags are passive, chipless tags that use discontinuities along a transmission line to create reflections. The discontinuities may be designed to produce a bipodal signal encoded with the unique identifier of the tag. When multiple tags are co-located and interrogated simultaneously, multiple access interference degrades the ability of the reader to detect the tags accurately. Reader detection can be improved by using spread spectrum signatures as the unique identifiers to limit interference. This work evaluates the ability of Gold codes and Kasami-Large codes to improve detection performance of a passive, chipless TDR RFID system. Simulations were conducted for varying numbers of simultaneously interrogated tags using synthetic tag responses constructed from the measured waveform of a prototype TDR tag. Results indicate that the Gold Code signature set outperforms the Kasami-Large Code signature set and a random, naïve set for simultaneous interrogation of less than 15 tags. For larger numbers of simultaneous tags, a random set performs nearly as well as the Kasami-Large Code set and provides more useful signatures.

A MATLAB platform for characterizing MIMO-OFDM communications with software-defined radios

A new MATLAB-based, wireless measurement platform using an existing software-defined radio architecture is presented. It augments IEEE 802.11g MIMO-OFDM physical layer schemes with new designs such as Maximal Ratio Combining, Alamouti coding, and Spatial Multiplexing. The platform provides a series of metrics, including channel capacity, Error Vector Magnitude (EVM), and Post-Processing Signal-to-Noise Ratio (PP-SNR) to characterize link and network performance. The software implementation and test protocol of the platform are presented with a validation study demonstrating its application.