Omar H.A.,University of Waterloo |
Zhuang W.,University of Waterloo |
Li L.,Communications Research Center Canada
IEEE Transactions on Mobile Computing | Year: 2013
The need of a medium access control (MAC) protocol for an efficient broadcast service is of great importance to support the high-priority safety applications in vehicular ad hoc networks (VANETs). This paper introduces VeMAC, a novel multichannel TDMA MAC protocol proposed specifically for a VANET scenario. The VeMAC supports efficient one-hop and multihop broadcast services on the control channel by using implicit acknowledgments and eliminating the hidden terminal problem. The protocol reduces transmission collisions due to node mobility on the control channel by assigning disjoint sets of time slots to vehicles moving in opposite directions and to road side units. Analysis and simulation results in highway and city scenarios are presented to evaluate the performance of VeMAC and compare it with ADHOC MAC, an existing TDMA MAC protocol for VANETs. It is shown that, due to its ability to decrease the rate of transmission collisions, the VeMAC protocol can provide significantly higher throughput on the control channel than ADHOC MAC. © 2002-2012 IEEE.
Dumais P.,Communications Research Center Canada
IEEE Journal of Quantum Electronics | Year: 2011
Thermal stress birefringence in buried-core waveguides is studied analytically and numerically to determine the role of cladding and core composition, core aspect ratio and over-etch depth. An analytical expression is derived for the over-etch depth required for stress birefringence compensation. Analytical expressions for the core stress are given for over-etched rectangular buried-core waveguides. The range of upper cladding thermal expansion coefficient over which stress birefringence compensation can be obtained through over-etching is established. © 2011 IEEE.
Wu J.,Communications Research Center Canada
Computer Networks | Year: 2011
We survey the state-of-the-art technologies in Wavelength Division Multiplexing (WDM) network reconfiguration. Our focus is the strategies and triggering methods. We compare the proposed technologies in the literature from different perspectives: traffic-changes triggered vs. other events triggered, centrally-managed strategies vs. distributed strategies, new lightpath demands known vs. future user traffic unknown, adaptive/reactive approaches vs. proactive approaches, traffic prediction based vs. traffic uncertainty proof approaches. We outline the entire landscape of the strategies and triggering methods of WDM network reconfiguration from WDM network operators' point of view. There are gaps in research and in field trials, which must be addressed, so that the great potentials of WDM network reconfiguration may be realized to add significant flexibility in network operations. © 2011 Elsevier B.V. All rights reserved.
Petosa A.,Communications Research Center Canada
IEEE Antennas and Propagation Magazine | Year: 2012
Frequency-agile antennas can be designed to switch between a set of discrete frequencies, or to be tuned over a continuous range of frequencies. Methods for achieving discrete or continuous frequency tuning can be grouped into three categories: mechanical actuation, tunable materials, and integrated electronic devices. Example tuning techniques in each class are presented, highlighting strengths and weaknesses of each method. © 1990-2011 IEEE.
Mihailov S.J.,Communications Research Center Canada
Sensors | Year: 2012
Because of their small size, passive nature, immunity to electromagnetic interference, and capability to directly measure physical parameters such as temperature and strain, fiber Bragg grating sensors have developed beyond a laboratory curiosity and are becoming a mainstream sensing technology. Recently, high temperature stable gratings based on regeneration techniques and femtosecond infrared laser processing have shown promise for use in extreme environments such as high temperature, pressure or ionizing radiation. Such gratings are ideally suited for energy production applications where there is a requirement for advanced energy system instrumentation and controls that are operable in harsh environments. This paper will present a review of some of the more recent developments. © 2012 by the authors; licensee MDPI, Basel, Switzerland.
Dumais P.,Communications Research Center Canada
Journal of Lightwave Technology | Year: 2012
A semianalytical study of modal birefringence in weakly strained and weakly guiding buried-core waveguides is presented. In this paper, modal birefringence is expressed as a sum of form birefringence and stress birefringence. Stress birefringence is expressed as an overlap between the modal field and the stress birefringence distribution. This distribution is expressed analytically as two constant-value areas to which a spatially variant stress distribution emanating from the waveguide core is overlaid. The analysis can be expanded to include the effect of overetching and other variations that can be defined as mechanical inclusions in the cladding layer. Expressions for modal birefringence control as a function of material parameters are given, for the case of square, rectangular, and overetched waveguides. The conditions for width-independent birefringence control are identified. Modal birefringence values obtained from the analysis are compared to those obtained by finite-element analysis for the case of square, rectangular, and overetched waveguides. The modal birefringence values are shown to be within 5% of each other for a typical silica-on-silicon waveguide. © 2012 British Crown.
Communications Research Center Canada | Date: 2012-08-23
A method of producing a thermally stable grating allows the grating to be placed in environments where temperatures reach 1000 C. These gratings may be concatenated so as to form a sensor array. The method requires a step of lowering the characteristic intensity threshold of a waveguide by at least 25%, followed by irradiating the waveguide with femtosecond pulses of light having a sufficient intensity and for a sufficient duration to write the grating so that at least 60% of the grating remains after exposures of at least 10 hours at a temperature of at least 1000 C. Pre-writing a Type I grating before writing a minimal damage Type II grating lowers the characteristic threshold of the waveguide so that a stable low damage type II grating can be written; alternatively providing a hydrogen or deuterium loaded waveguide before writing the grating lowers the characteristic threshold of the waveguide.
Communications Research Center Canada | Date: 2012-04-05
A system has a first transmitter for transmitting a first wireless signal within a first frequency. A second transmitter is for transmitting a second wireless signal with overlapping frequency. The first transmitter and the second transmitter are disposed sufficiently proximate to another such that the wireless signals substantially interfere resulting in a combined wireless signal with negative SNR for each of the first wireless signal and the second wireless signal, the negative SNR being a result of at least the other of the first wireless signal and the second wireless signal. A receiver is located for receiving a received wireless signal comprising substantially interfering encoded data signals having negative SNR. The receiver is for selecting from the substantially interfering encoded data signals a signal of interest and for decoding said signal of interest relative to at least the other substantially interfering data signal within the received wireless signal.
Communications Research Center Canada | Date: 2011-03-16
The invention relates to a method and circuit for linearizing amplifiers and other nonlinear circuits for multi-carrier signals. An output signal from the amplifier is sampled, and a correlation matrix of size NxN is computed from the sampled signal, wherein N execeeds the number of multiplexed carriers in the signal. A signal-to-distortion ratio (SDR) is then estimated based on a ratio of one or more largest to one or more smallest eigenvalues of the correlation matrix, and the signal into the amplifier is pre-distorted so as to maximize the SDR.
Communications Research Center Canada | Date: 2012-02-29
The invention relates to compressing of sparse data sets contains sequences of data values and position information therefor. The position information may be in the form of position indices defining active positions of the data values in a sparse vector of length N. The position information is encoded into the data values by adjusting one or more of the data values within a pre-defined tolerance range, so that a pre-defined mapping function of the data values and their positions is close to a target value. In one embodiment, the mapping function is defined using a sub-set of N filler values which elements are used to fill empty positions in the input sparse data vector. At the decoder, the correct data positions are identified by searching though possible sub-sets of filler values.