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FPGA Design Students

Posted May 01, 2018

Director, Operations Permalink

Posted April 26, 2018

Random Access Signaling in Underwater Acoustic Channels

Posted October 26, 2017

Iterative Information Processing: Advances towards Optimal Data Communications

Posted July 07, 2016

UMDCC Wikispace

Posted September 22, 2015

OFDM Transmission for Doubly Dispersive Underwater Acoustic Channels - Ali Bassam

Posted September 17, 2015

2014 NSERC Research Report

Posted September 17, 2015

Iterative demodulation and channel estimation for joint random access satellite communications

Posted May 21, 2015

Atmospheric Magnetic Noise Measurements in Urban Areas

Posted May 21, 2015

Trellis and Turbo Coding: Chapters 1-2

Posted January 26, 2015

Software Guidelines

Posted April 17, 2014

2014 International Zurich Seminar on Communications

Posted March 13, 2014

Information Theory and Applications Workshop 2014

Posted March 13, 2014

On the Dynamics of the Error Floor Behavior in (Regular) LDPC Codes

Posted September 25, 2013

Improving the design of relay nodes for cooperative opportunistic beamforming

Posted September 25, 2013

Cooperative opportunistic beamforming using integrated relay node prototype

Posted September 25, 2013

Asymptotic analysis of joint timing acquisition and multiple packet reception

Posted September 25, 2013

A QoE-Oriented Strategy for OFDMA Radio Resource Allocation Based on Min-MOS Maximization

Posted September 25, 2013

Frequency domain iterative equalization for single-carrier FDMA

Posted September 25, 2013

Causes and dynamics of LDPC error floors on AWGN channels

Posted September 25, 2013

Near-Far Resistant MIMO Iterative Receiver for Uplink LTE

Posted September 25, 2013

Hardware implementation challenges of modern error control decoders

Posted September 25, 2013

Multiple access demodulation in the lifted signal graph with spatial coupling

Posted September 25, 2013

Comparison of UWB approaches applied to EHF satellite communications

Posted September 25, 2013

Typicality extraction in a Speaker Binary Keys model

Posted September 25, 2013

I-vectors in the context of phonetically-constrained short utterances for speaker verification

Posted September 25, 2013

A 4-GHz Active Scatterer in 130-nm CMOS for Phase Sweep Amplify-and-Forward

Posted September 25, 2013

Connecting spatially coupled LDPC code chains

Posted September 25, 2013

Achieving gaussian multiple access channel capacity with spatially coupled sparse graph multi-user m

Posted September 25, 2013

Achieving AWGN Multiple Access Channel Capacity with Spatial Graph Coupling

Posted September 25, 2013

New codes on graphs constructed by connecting spatially coupled chains

Posted September 25, 2013

Improving spatially coupled LDPC codes by connecting chains

Posted September 25, 2013

Low power asynchronous packet-based baseband transceiver for wireless sensor networks

Posted September 25, 2013

The Ultra Maritime Digital Communications Centre is seeking MASc level FPGA design students. The students will be responsible for for FPGA design tasks while working towards a Master of Applied Science degree at Dalhousie University. The ideal candidate will possess excellent math skills, an interest in advanced communication systems, and the ability to take an idea successfully from algorithm through to prototype.

Contact Christian Schlegel for more information and to apply.

The Ultra Maritime Digital Communications Centre is seeking an experienced engineer/scientist to lead the operations of the laboratory's new Permalink underwater acoustic testing platform (see elsewhere on this website). Responsibilities include maintaining the operational hardware and software, leading the planning of testing and sea trials, analyzing test results in collaboration with the research team. This position also requires interaction with the engineering team and participating industry as well as suppliers, and presentation and dissemination of data. 

Qualifications: we prefer the successful candidate to have a graduate degree in electrical engineering, familiarity with signal processing, communications, and underwater acoustics, as well as a keen sense of scientific methods and a high degree of self motivation and autonomy. Oral and written communications skills, ability to work in teams, and strong presentation skills are also desired.


Contact Christian Schlegel for more information and to apply.

These are slides from a talk given by Dr. Schlegel and Dr. Truhachev on

Underwater Acoustic Channel Signaling presented in September of 2017.

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Presentation given by Dr. Christian Schlegel at UMass Dartmouth June 29, 2016.

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The main page for UMDCC's OFDM project which provides an overview of the project. Methodologies, theoretical background by means of tutorials, and up-to-date lists of Simulink Models as well as Vivado Projects are kept here.

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In this thesis, an OFDM simulator is designed based on the theory presented, and tested with a real underwater acoustic (UWA) channel. The UWA channel is analyzed and a simplified model is presented that holds under achievable conditions. The SOS model is developed for the UWA channel, and uses the stretched exponential function to model the Doppler power spectrum. The result is an SOS simulator which is then added to the OFDM simulator. The OFDM simulators are shown to have a very good performance under real, quasi-stationary UWA channels. OFDM theory is presented and then applied to the UWA channel to combat frequency-selectivity. OFDM transmission on UWA channels is analyzed in great detail, with special emphasis on how the Doppler effect distorts the signal. A complete model which shows the channel effects on the received signal is developed. This is followed by ICI parametrization and two methods of Doppler compensation. 

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Annual Report prepared by the UMDCC lab staff detailing the research efforts to date.

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Dickson, P., Schlegel., C. 2014

Future high-density multiple-user interactive satellite communications is investigated by proposing advancements in receiver design for random access on the uncoordinated satellite up-link. Joint detection and multiple packet reception (MPR) techniques are applied to show that it is possible to surpass the capacity of the current single-user random access channel. This is accomplished through adaptation of the concept of generalized modulation and the use of iterative estimation coupled with advanced interference cancellation techniques.

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Schlegel, C., Mallay, M., Touesnard, C. 2014

The theory of atmospheric magnetic noise is reviewed and we discuss how it impacts magnetoinductive communications systems. Magnetic noise measurements are then conducted to obtain quantitative values of the noise levels at both indoor and outdoor locations. Themeasurements, using an industrial-grade magnetometer, are compared with results from Comité Consultatif International des Radiocommunications (CCIR) measurements conducted using an electric antenna, and then converted via the E-H relationship in vacuum. Both measurements are in agreement other than in a small frequency range, whereas the CCIR electric measurements show pessimistic minimal values, possibly due to electrical interference.

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The first two chapters of Dr. Christian Schlegel's new book Trellis and Turbo Coding introduces the topics of error control coding, advanced modulation techniques, and provide the reader with a probabilistic viewpoint of modern communications systems. The full text will be available through Wiley Publishers in 2015.

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Document outlining the standards which all software developed by or for Ultra Maritime Digital Communications Centre must adhere to.

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Energy Limits of Message-Passing Error Control Decoders,

Christian Schlegel's 2014 International Zurich Seminar on Communications Presentation

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The Interplay between Error Control Coding and Joint Detection,

Christian Schlegel's presentation for the 2014 Information Theory and Applications Workshop.

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Schlegel, C.; Shuai Zhang    2010   

It is shown that dominant trapping sets of regular low-density parity-check (LDPC) codes, so-called absorption sets, undergo a two-phased dynamic behavior in the iterative message-passing decoding algorithm. Using a linear dynamic model for the iteration behavior of these sets, it is shown that they undergo an initial geometric growth phase which stabilizes in a final bit-flipping behavior where the algorithm reaches a fixed point. This analysis is shown to lead to very accurate numerical calculations of the error floor bit error rates down to error rates that are inaccessible by simulation. The topology of the dominant absorption sets of an example code, the IEEE 802.3an (2048,1723) regular LDPC code, are identified and tabulated using topological relationships in combination with search algorithms.

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Messier, G.G.; Bousquet, J. -F; Magierowski, S.    2011   

Cooperative opportunistic beamforming (CoopOBF) uses a relay node to augment channel fading in order to improve the multi-user diversity achieved using opportunistic scheduling. This paper discusses a very simple, all analog CoopOBF relay prototype capable of reflecting and amplifying the source node signal while, at the same time, imposing an arbitrary phase shift on that signal. Performance measurements collected from the prototype will be used in simulation to evaluate CoopOBF performance. These simulations will also be used to illustrate how best to improve the current relay hardware design in order to maximize the capacity improvement achieved when using CoopOBF.

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Messier, G.G.; Bousquet, J. -F; Magierowski, S.    2011   

Presented is a way to implement cooperative opportunistic beamforming using an all-analogue relay node. Unlike most cooperative transmission schemes, this approach does not require signal delay buffers or synchronisation at the relay. As a result, a very simple, all-analogue relay design is possible. The measured performance of an integrated prototype of the relay is used to predict the throughput improvement cooperative opportunistic beamforming will achieve on a multi-user link.

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Truhachev, D.    2011   

A multiple packet receiver (MPR), which jointly performs timing acquisition of the incoming packets and decoding of the packet payloads, is analyzed. The payload decoding consists of iteratively performed parallel interference cancellation, followed by individual error control decoding. Timing acquisition is repeated at every stage of the interference cancellation in order to acquire packets that are otherwise covered by interference. The case in which packets are received at multiple power levels is considered, and it is proved that the system is capable to operate close to the multiple access channel capacity. An upper bound on the gap between the achievable spectral efficiency and the channel capacity is derived in terms of the preamble length (timing acquisition window).

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Sacchi, C.; Granelli, F.; Schlegel, C.    2011   

A balanced strategy for OFDMA radio resource allocation based on game theory concepts is presented. Its main novelty with respect to state-of-the-art methods is that resource allocation is based on application-oriented Mean Opinion Score (MOS), rather than the aggregate system data rate. Thus, users' data flows cooperate in a proactive way in order to jointly maximize the Quality of Experience (QoE). Experimental results show that the MOS achievable by the proposed resource allocation strategy is higher than the one provided by uncoordinated strategies based on water-filling and cooperative strategies based on pure data rate maximization.

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Jar, M.; Bouton, E.; Schlegel, C.    2011   

In this paper, the performance of a jointly Gaussian approach (JGA) as a detection method for Single Carrier Frequency Division Multiple Access (SC-FDMA) is analyzed. Combined with an iterative detector, the JGA can efficiently remove residual interference by exchanging extrinsic log-likelihood ratios (LLRs) with a successive error control decoder. At the cost of a moderate increase in complexity, this system can significantly enhance overall performance. Monte Carlo simulations are used to illustrate the gains in terms of bit error rates (BER) of the JGA over traditional non-iterative equalization methods, as well as the throughput gains for the uplink-scenario of the long-term evolution (LTE) standard.

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Shuai Zhang; Schlegel, C.    2011   

It is well-known that the performance of low-density parity-check codes is compromised by the emergence of an error floor, which is caused by so-called trapping sets. By identifying the dominant trapping sets, this error floor can be estimated analytically using a linear model. In this paper, this linear approach is improved to make the analysis more accurate. Then, guided by the error probability formula, a simple but effective method to improve the code performance in the error floor region is proposed, by introducing a boosting factor to the log-likelihood ratios returned from unsatisfied check nodes during the early decoding stages. It is shown that the effect of the dominant trapping sets can thus be reduced. The dominance of trapping sets can be further reduced by extending the computational range of the LLRs at the decoder. To illustrate these ideas, a short regular LDPC code constructed by Tanner, as well as the IEEE 802.3 LDPC code, are studied.

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Krzymien, L.; Schlegel, C.    2011   

Equalization for uplink MIMO SC-FDMA LTE multi-stream transmission is considered utilizing linear filtering methods and redundancy in the form of channel coding. The equalizer jointly removes inter-symbol (ISI) as well as spatial (MIMO) interference. It is observed that in an unequal received power situation, gains over traditional MMSE frequency equalization can be obtained via group-based cancellation with turbo equalization. It is shown that signal co-existence is possible with this methodology and therefore QoS for cell-edge users can be maintained at considerably higher noise levels as compared to a baseline receiver.

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Schlegel, C.; Gaudet, V.    2011   

The basic design challenges for large-scale modern error control decoders based on message passing are examined in this review and exploratory paper. Space, complexity, and power consumption figures are of most interest to the design engineer, and the state-of-the art of current implementations are presented. Fundamental limits of performance versus power and complexity are discussed, and innovative state-of-the art approaches to address these challenges are highlighted.

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Schlegel, C.; Truhachev, D.    2011   

Demodulation in a random multiple access channel is considered where the signals are chosen uniformly randomly with unit energy, a model applicable to several modern transmission systems. It is shown that by lifting (replicating) the graph of this system and randomizing the graph connections, a simple iterative cancellation demodulator can be constructed which achieves the same performance as an optimal symbol-by-symbol detector of the original system. The iterative detector has a complexity that is linear in the number of signals (users), while the direct optimal approach is known to be NP-hard. However, the maximal system load of this lifted graph is limited to α<; 2:074, even for signal-to-noise ratios going to infinity - the system is interference limited. We then show that by introducing spatial coupling and anchoring of the lifted graph, this limitation can be avoided and arbitrary system loads are achievable. Our results apply to several well-documented system proposals, such as IDMA, partitioned spreading, and certain forms of MIMO communications.

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Valente, D.; Cianca, E.; Mukherjee, S.; Rossi, T.; Ruggieri, M.; Prasad, R.    2012   

In this paper, the advantages of UWB (Ultra-Wide Band) transmission for satellite communications are investigated together with the ones coming from the use of EHF (Extremely High Frequency) where there is the possibility of exploiting a huge spectrum availability. In particular, a comparison among UWB approaches is shown in terms of BER performance, considering hardware impairments.

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Bousquet, P.; Bonastre, J.-F.    2012

In the field of speaker recognition, the recently proposed notion of ‚Speaker Binary Key‚ provides a representation of each acoustic frame in a discriminant binary space. This approach relies on an unique acoustic model composed by a large set of speaker specific local likelihood peaks (called specificities). The model proposes a spatial coverage where each frame is characterized in terms of neighborhood. The most frequent specificities, picked up to represent the whole utterance, generate a binary key vector. The flexibility of this modeling allows to capture non-parametric behaviors. In this paper, we introduce a concept of ‚typicality‚ between binary keys, with a discriminant goal. We describe an algorithm able to extract such typicalities, which involves a singular value decomposition in a binary space. The theoretical aspects of this decomposition as well as its potential in terms of future developments are presented. All the propositions are also experimentally validated using NIST SRE 2008 framework.   

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Larcher, A.; Bousquet, P.; Kong Aik Lee; Matrouf, D.; Haizhou Li; Bonastre, J.-F.    2012

Short speech duration remains a critical factor of performance degradation when deploying a speaker verification system. To overcome this difficulty, a large number of commercial applications impose the use of fixed pass-phrases. In this context, we show that the performance of the popular i-vector approach can be greatly improved by taking advantage of the phonetic information that they convey. Moreover, as i-vectors require a conditioning process to reach high accuracy, we show that further improvements are possible by taking advantage of this phonetic information within the normalisation process. We compare two methods, Within Class Covariance Normalization (WCCN) and Eigen Factor Radial (EFR), both relying on parameters estimated on the same development data. Our study suggests that WCCN is more robust to data mismatch but less efficient than EFR when the development data has a better match with the test data.

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Bousquet, J. -F; Magierowski, S.; Messier, G.G.    2012

This article demonstrates the cooperative diversity improvement achieved using a 120- active scatterer built in 130-nm CMOS technology. The low-power all-analog device acts as a repeater, or relay, for phase sweep amplify-and-forward cooperative transmission. The device relies on microwave reflection to amplify, dynamically phase modulate, and reradiate the incident signal. This reduces the duration of the fades experienced in the indoor radio channel and improves error correction code performance. Radio channel propagation measurements collected using the relay prototype clearly show the effect of the phase modulation on fading and system level simulations conducted using the propagation data show a fivefold increase in coverage area.

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Truhachev, D.; Mitchell, D.G.M.; Lentmaier, M.; Costello, D.J.    2012

Codes constructed from connected spatially coupled low-density parity-check code (SC-LDPCC) chains are proposed and analyzed. It is demonstrated that connecting coupled chains results in improved iterative decoding performance. The constructed protograph ensembles have better iterative decoding thresholds compared to an individual SC-LDPCC chain and require less computational complexity per bit when operating in the near-threshold region. In addition, it is shown that the proposed constructions are asymptotically good in terms of minimum distance.

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Truhachev, D.    2012

Communication over a Gaussian multiple access channel (GMAC) is considered. Each user modulates his data as a superposition of redundant data streams. The interconnection of the modulated data symbols can be described by means of a sparse graph. The transmitted modulation graphs couple at the receiver, which performs joint detection based on iterative interference cancellation. We prove that the GMAC capacity can be achieved by such a system even for the case when all the users access the channel with equal power and transmit with equal rate.

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Truhachev, D.    2012

Communication over a multiple access channel is considered. Each user modulates his signal as a superposition of redundant data streams where interconnection of data bits can be represented by means of a sparse graph. The receiver observes a signal resulting from the coupling of the sparse modulation graphs. Iterative interference cancellation decoding is analyzed. It is proved that spatial graph coupling allows to achieve the AWGN channel capacity with equal power and rate transmissions.

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Truhachev, D.; Mitchell, D.G.M.; Lentmaier, M.; Costello, D.J.    2012

A novel code construction based on spatially coupled low-density parity-check (SC-LDPC) code chains is presented. The proposed code ensembles are described by graphs in which individual SC-LDPC code chains of various lengths serve as edges. We demonstrate that connecting several appropriately chosen SC-LDPC code chains results in improved iterative decoding thresholds compared to those of a single coupled chain in addition to reducing the decoding complexity required to achieve a specific bit error probability.

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Truhachev, D.; Mitchell, D.G.M.; Lentmaier, M.; Costello, D.J.    2012

In this paper, we study ensembles of connected spatially coupled low-density parity-check codes (SC-LDPCCs), i.e., ensembles described by graphs in which regular SC-LDPCC chains of various lengths serve as edges. We show that, by carefully connecting individual SC-LDPCC chains, we obtain LDPC code ensembles with improved iterative decoding thresholds compared to those of a single coupled chain, in addition to reducing the decoding complexity required to achieve a specific bit error probability. Moreover, we show that, like the component SC-LDPCC chains, the proposed constructions have a typical minimum distance that grows linearly with block length.

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Ahmadi, M.; Cockburn, B.; Schlegel, C. 2012

Random-access packet-based communication schemes are suitable for wireless sensor networks since medium access in their applications is often uncoordinated while sensor nodes communicate bursty flows of data. Preamble detection is an important task in packet-based communication protocols. The implementation of a previously proposed preamble detection scheme for low-power, wide-band, asynchronous packet communications which includes built-in characterization features is presented here. The baseband transmitter design was fabricated on IBM's 130-nm digital CMOS process and the baseband receiver design was prototyped on a Xilinx FPGA. Silicon prototypes of the fabricated design were successfully tested. The performance of the preamble detector measured at hardware speed is reported.