Homomorphic Filtering for Improving Time Synchronization in Wireless Networks

Wireless sensor networks are used to sample the environment in a distributed way. Therefore, it is mandatory for all of the measurements to be tightly synchronized in order to guarantee that every sensor is sampling the environment at the exact same instant of time. The synchronization drift gets bigger in environments suffering from temperature variations. Thus, this work is focused on improving time synchronization under deployments with temperature variations. The working hypothesis demonstrated in this work is that the clock skew of two nodes (the ratio of the real frequencies of the oscillators) is composed of a multiplicative combination of two main components: the clock skew due to the variations between the cut of the crystal of each oscillator and the clock skew due to the different temperatures affecting the nodes. By applying a nonlinear filtering, the homomorphic filtering, both components are separated in an effective way. A correction factor based on temperature, which can be applied to any synchronization protocol, is proposed. For testing it, an improvement of the FTSP synchronization protocol has been developed and physically tested under temperature variation scenarios using TelosB motes flashed with the IEEE 802.15.4 implementation supplied by TinyOS

Full field image ranger hardware

We describe the hardware designed to implement a full field heterodyning imaging system. Comprising three key components - a light source, high speed shutter and a signal generator - the system is expected to be capable of simultaneous range measurements to millimetre precision over the entire field of view. Current modulated laser diodes provide the required illumination, with a bandwidth of 100 MHz and peak output power exceeding 600 mW. The high speed shutter action is performed by gating the cathode of an image intensifier, driven by a 50 Vpp waveform with 3.5 ns rise and fall times. A direct digital synthesiser, with multiple synchronised channels, provides high stability between its outputs, 160 MHz bandwidth and tuning of 0.1 Hz

A Method for Skew-free Distribution of Digital Signals Using Matched Variable Delay Lines

The ability to distribute signals everywhere in a circuit with controlled and known delays is essential in large, high-speed digital systems. We present a technique by which a signal driver can adjust the arrival time of the signal at the end of the wire using a pair of matched variable delay lines. We show an implemention of this idea requiring no extra wiring, and how it can be extended to distribute signals skew-free to receivers along the signal run. We demonstrate how this scheme fits into the boundary scan logic of a VLSI chip

An arbitrarily precise time synchronization algorithm based on Ethernet Switch serialization

It turns out that trying to play a worst-case traversal time (WCTT) scenario on a real experimentation platform is a Real-Time problem with extremely tight constraints. When two packets (with the same destination) arrive to two different input ports of a network switch within a time frame of only a few nanoseconds, the order of these packets in the output port queue will reflect this small nanoseconds arrival difference. Moreover, failing to emit packets within this tiny time frame will exhibit a different scenario than expected, potentially so radically different in farther places of the network that the behavior of the whole system seems affected by a butterfly effect. As we were trying to achieve the most precise clock synchronization we could with standard hardware, we have had the idea to turn this butterfly effect to our benefit and develop an arbitrarily precise time synchronization algorithm that only requires a standard Ethernet switch connecting the two hosts to synchronize and a third host on the network that will serve as a synchronization helper

Accurate and automatic NOAA-AVHRR image navigation using a global contour matching approach

The problem of precise and automatic AVHRR image navigation is tractable in theory, but has proved to be somewhat difficult in practice. The authors' work has been motivated by the need for a fully automatic and operational navigation system capable of geo-referencing NOAA-AVHRR images with high accuracy and without operator supervision. The proposed method is based on the simultaneous use of an orbital model and a contour matching approach. This last process, relying on an affine transformation model, is used to correct the errors caused by inaccuracies in orbit modeling, nonzero value for the spacecraft's roll, pitch and yaw, errors due to inaccuracies in the satellite positioning and failures in the satellite internal clock. The automatic global contour matching process is summarized as follows: i) Estimation of the gradient energy map (edges) in the sensed image and detection of the cloudless (reliable) areas in this map. ii) Initialization of the affine model parameters by minimizing the Euclidean distance between the reference and sensed images objects. iii) Simultaneous optimization of all reference image contours on the sensed image by energy minimization in the domain of the global transformation parameters. The process is iterated in a hierarchical way, reducing the parameter searching space at each iteration. The proposed image navigation algorithm has proved to be capable of geo-referencing a satellite image within 1 pixel.Peer ReviewedPostprint (published version

A point-to-point link for data, trigger, clock and control over copper or fibre

Upgrades of the LHC detectors target significantly higher event rates and higher bandwidth over point-to-point links. The Data, Trigger, Clock and Control (DTCC) is a new custom link protocol for data and control streams over different physical media, as copper or optical fibre. The DTCC link is implemented over 8b10b encoding. A version of the DTCC link over standard Category 6 cables is planned to be used with ALICE EMCal Calorimeters after its LS1 upgrade with a significant increase of the readout rate.Tarazona Martínez, A.; Gnanvo, K.; Martoiu, S.; Muller, H.; Toledo Alarcón, JF. (2014). A point-to-point link for data, trigger, clock and control over copper or fibre. Journal of Instrumentation. 9:1-12. doi:10.1088/1748-0221/9/06/T06004S1129Zhang, F., Muller, H., Awes, T. C., Martoiu, S., Kral, J., Silvermyr, D., … Zhou, D. (2014). Point-to-point readout for the ALICE EMCal detector. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 735, 157-162. doi:10.1016/j.nima.2013.09.023Martoiu, S., Muller, H., Tarazona, A., & Toledo, J. (2013). Development of the scalable readout system for micro-pattern gas detectors and other applications. Journal of Instrumentation, 8(03), C03015-C03015. doi:10.1088/1748-0221/8/03/c03015Toledo, J., Muller, H., Esteve, R., Monzó, J. M., Tarazona, A., & Martoiu, S. (2011). The Front-End Concentrator card for the RD51 Scalable Readout System. Journal of Instrumentation, 6(11), C11028-C11028. doi:10.1088/1748-0221/6/11/c11028Widmer, A. X., & Franaszek, P. A. (1983). A DC-Balanced, Partitioned-Block, 8B/10B Transmission Code. IBM Journal of Research and Development, 27(5), 440-451. doi:10.1147/rd.275.0440Aliaga, R. J., Monzo, J. M., Spaggiari, M., Ferrando, N., Gadea, R., & Colom, R. J. (2011). PET System Synchronization and Timing Resolution Using High-Speed Data Links. IEEE Transactions on Nuclear Science, 58(4), 1596-1605. doi:10.1109/tns.2011.2140130Giordano, R., & Aloisio, A. (2011). Fixed-Latency, Multi-Gigabit Serial Links With Xilinx FPGAs. IEEE Transactions on Nuclear Science, 58(1), 194-201. doi:10.1109/tns.2010.2101083Papakonstantinou, I., Soos, C., Papadopoulos, S., Detraz, S., Sigaud, C., Stejskal, P., … Darwazeh, I. (2011). A Fully Bidirectional Optical Network With Latency Monitoring Capability for the Distribution of Timing-Trigger and Control Signals in High-Energy Physics Experiments. IEEE Transactions on Nuclear Science, 58(4), 1628-1640. doi:10.1109/tns.2011.215436