Tue Huynh Huu

In this paper, a new coding scheme, for MIMO-OFDM systems that tends to exploit both space, time, and frequency diversity is introduced. The code, partially based on the well-known Alamouti scheme, works with a configuration of two transmit and nr receive antennas and requires a channel with coherent impulse response during two OFDM signaling intervals. Monte Carlo simulations have been run to compare the new scheme with other designs. Simulations have shown that this scheme performs better than direct MIMO-OFDM transposition of space-time codes (e.g. transpositions of Alamouti scheme). Despite the reduced code rate 1/2 of this scheme, its performances show a superior diversity order characterized by a steeper slope of the bit error rate curves. Simulations were also run to gauge the effects of errors on channel parameters estimation. These errors were simulated through, a model derived from a MIMO-OFDM channel estimation technique

This work deals with the transmission of turbo coded symbols in a frequency selective time varying channel. To reduce the channel effect, we use the turbo equalizer proposed in Laot et al. (2001). The equalizer consists of an intersymbol interference canceller and a MAP-BCJR decoder. Unlike Laot, where data information is convolutionally coded, in this paper, we use a turbo encoder. Thus, we have to redefine the channel reliability factor used by the MAP-BCJR decoding algorithm. We propose a new metric that takes into account the statistics of the signal at the equalizer output. Simulations show that the redefined channel reliability improves BER performance and the proposed equalizer is better than the classical DFE equalizer.

Les auteurs présentent des méthodes d’études de systèmes asservis non linéaires à entrée aléatoire: de Fokker-Planck-Kolmogorov, de linéarisation statistique, de Wiener. En utilisant un exemple précis, celui d’un asservissement de 2eordre comportant dans la boucle de retour une non-linéarité polynomiale impaire quelconque, les auteurs comparent ces méthodes et montrent la rapidité et la précision de la méthode de linéarisation statistique.

Over the past few years, digital technologies have been growing in such a way that a new generation of fully digital audio broadcasting systems can now become cost effective. For this purpose coded orthogonal frequency division multiplexing (COFDM), a new transmission technique designed in Europe, seems promising. To avoid the allocation of a new bandwidth in the United-States, some groups are proposing the use of power multiplexing to transmit two different signals over the same bandwidth. The objective of this work is to analyze the feasibility of this system taking into account the CD-like quality level of digital audio broadcasting systems (DAB)

... for lmcs channel and system design implications, Diploma Thesis, Carleton University, Ottawa, Canada (1999). WC Jakes, Microwave mobile communications, Wiley, New York (1974). J. Proakis, Digital communications, McGraw-Hill, New York (1995). A. Abdi and M. Kaveh, A ...

The performances of a multicarrier modulation (COFDM) system in an urban mobile radio channel is analyzed using a computer-aided analysis tool called SPW. This multicarrier modulation system, with convolutional coding and interleaving, provides an extremely bandwidth efficient and multipath resistant transmission method. COFDM gives a remarkable performance in selective Rayleigh channels at a much higher bit rate than conventional systems

The utilization of multiple antennas and space–time codes in multiple-input and multiple-output (MIMO) communication systems significantly improves the transmission channel capacity without using additional bandwidth and power. The improvement is achieved by decomposing the spatial structure of transmission channels and performing appropriate temporal and spatial multiplexing. In this paper, we propose a novel theoretical framework for MIMO channel modeling and characterization in order to facilitate the MIMO system design and performance evaluation. The channels are represented in space, time, wave vector, and frequency domains while the space–time and wave vector–frequency interdependences are considered. A realization of the theoretical framework, in a form of a practical framework, is also proposed to address the channel modeling and characterization at both transmitter and receiver sides. The utilization of the practical framework in MIMO communication system design is discussed to illustrate its applications in realistic scenarios. The angle of arrival estimation based on the proposed practical framework using field test measurement data is also presented as illustrative examples.

Systematic design of pipelined recursive filters is presented. The procedure is based on a multiplication algorithm which generates the result with most significant digit first. Since the latency of such a multiplier is low, a reduced number of pipelining delays may be introduced in the reduction loop, resulting in a high sampling rate. The implementation obtained exhibits minimum hardware and ensures minimum latency. It is shown that its flexibility allows, on one hand, the ability to choose freely the number system radix and, on the other hand, the interleaving of two multiplier arrays into one. This is illustrated by the realization of a second-order all-pole filter, operating in a radix-4 representation and using only one array to perform two multiplications. In this way, long interconnections are avoided and denser and more regular layout is achieved. It turns out that the design procedure can also be applied successfully to various types of realization where multiplications are required

Compressed sensing, viewed as a type of random undersampling, considers the acquisition and reconstruction of sparse or compressible signals at a rate significantly lower than that of Nyquist. Exact reconstruction from incompletely acquired random measurements is, under certain constraints, achievable with high probability. However, randomness may not always be desirable in certain applications. Taking a nonrandom approach using deterministic chaos and following closely a recently proposed novel efficient structure of chaos filters, we propose a chaos filter structure by exploring the use of chaotic deterministic processes in designing the filter taps. By numerical performance, we show that, chaos filters generated by the logistic map, while being possible to exactly reconstruct original time-sparse signals from their incompletely acquired measurements, outperforms random filters.

ABSTRACT Many equalizers based on neural networks have been proposed across the literature. Unfortunately, the complexity and the slow convergence still have to be overcome for neural equalizers to be implemented in real time. This paper presents neural equalizers suitable for multi-level QAM constellations, and trained using complex extended Kalman and RLS algorithms, which makes them more robust against severely dispersive channels, like broadband outdoor or indoor mobile communication channels. The activation function is optimized to obtain good performance for large size signal constellations (i.e. up to 256-QAM). Extensive simulations show the benefits and limitations of these neural equalizers over traditional decision-feedback equalizers.

... INFLUENCE OF A CLASS OF MAN-MADE NOISE ON QAM MULTICARRIER SYSTEMS Huu Tuê Huynh, Paul Fortier, and Gilles-Y. Delisle Department of Electrical and Computer Engineering Laval University, Ste-Foy, Quebec, G1K 7P4 Canada Tel: (418) 656-2984, Fax: (418 ...

It is known that in the personal communication systems environment, additive noise is not Gaussian. Experimental studies show that this type of noise obeys the class A Middleton man-made noise statistics. The influence of such noise is very severe on the probability error rate for a matched filter detector. To improve the detection performance, a non-linear detector should be used. This structure is based on the maximum likelihood approach which exploits multiple samples of the incoming signal. The improvement has been established by Spaulding and Middleton (1977) for the binary case. This paper generalizes this approach to M-ary signal detection, namely M-QAM, which is the most popular scheme in practice

A generalized version of Graph-based Ant System and its applicability and convergence Hoang Trung Dinh1, Abdullah Al Mamun1, Huu Tuê Huynh2 Depar men of Elee rical and Computer Engineering ... (4), at any time an agent makes a move, if q < qo then Pr{Pi(m, Ui)} is the ...

ABSTRACT A number of authors have sought to combine equalization and decoding in an iterative system in order to reduce the effects of frequency and temporal dispersiveness of time-varying frequency-selective channels. In the recent literature, several architectures based on these iterative systems have been proposed. One can note architectures which combine a maximum a posteriori (MAP) equalizer and decoder, architectures formed by an interference canceller and MAP decoder, architectures implementing a decision feedback equalizer and a MAP decoder, etc. Most of these architectures require accurate channel estimation to adapt the equalizer filters or to execute the MAP equalizers. This article presents a turbo equalizer architecture for time-varying frequency-selective channels without channel estimators. The proposed turbo equalizer consists of an interference canceller in direct-adaptation mode and a turbo decoder. In order to reduce noise correlation, the addition of a transverse filter to the interference-canceller architecture is proposed. The reliability factor for variable time-varying frequency-selective channels is also redefined in order to improve the performance of the turbo decoder. The architecture of the proposed turbo equalizer reduces considerably the effects of frequency and temporal dispersiveness of time-varying frequency-selective channels depending on the normalized Doppler frequency range.

With the emergence of the multi-antenna systems, the spatial information becomes particularly significant to the modern communications systems. In this paper we present a new technique to describe and to characterize the channels and systems in space and in wave vector domains. First, we review briefly the wave vector concept, the wave vector spectrum and the 3-dimensional (3D) Fourier transform. Then a set of new impulses and new kernel functions is defined in order to establish a tool to characterize the communications channels and systems. The applications of each kernel function are also discussed. This new technique is a promising and a powerful tool to design and optimize the Multiple-Input Multiple-Output (MIMO) communications systems. The results in this paper are limited to the plane wave scenario.

... [6] HT Huynh, P. Fortier, B. Vo, “Influence of Impulse Rate on the QAM Error Probability in a Non-Gaussian Noise Envi-ronment”, Sixth Communications Theory Mini-Conference in Conjunction with Globecom'97, Phoenix, Arizona, November 5-7, 1997. [7] HT Huynh, P. Fortier ...

This paper considers the influence of a deterministic phase error for coherent M-QAM demodulators in a non-Gaussian environment; the latter is modeled as a combination of a white Gaussian process and a filtered Poisson process whose enveloped amplitude obeys the Rayleigh distribution. General results show that when approaching the critical limit, the symbol error rate quickly reaches a plateau having a relatively large width

It is well known that a pipelined architecture helps the efficient implementation of the LMS algorithm. However, this type of architecture requires delays in the processing. In the open literature, the LMS algorithm with a single delay has been extensively studied. In this work, different types of delays are introduced into the architecture of the LMS algorithm. The influence of these delays on the algorithm behavior is analyzed theoretically and by simulations. Results lead to a number of constraints on the delays. The convergence conditions and the stationary residual error have also been obtained

In this paper, we discuss and present simulation results for the performances of COFDM systems using turbo codes and operating in a mobile radio environment. Results show that the echo power has a much stronger influence than the guard time interval or echo delay. This scheme is shown to be an excellent solution for transmission over bandlimited mobile channels.

Symbol timing and carrier frequency synchronization are crucial to OFDM systems. One of the blind synchronization methods is the cyclic prefix (CP) based maximum likelihood (ML) symbol timing and carrier frequency synchronization which correlates the cyclic prefix and the last part of the OFDM symbol. However, the performance of this method is seriously reduced in the time-variant multipath channel. In this paper, we propose a new CP which has two parts. One part is a copy of the head of the last symbol and the other part is a copy of the tail of that symbol. Both parts have the length of half of the CP. As a result of this new CP, the starting time of one OFDM symbol is allowed to fall into its effective period (the absolute value of the symbol timing error should be smaller than CP/2). The performance of OFDM systems is improved significantly with this new CP