Alex Stephenne

BER improvement in a TDMA/FDMA cellular system using antenna array

Signals, Systems, and …, 1999

We propose a novel strategy based on Capon's method for multiple signal extraction in TDMA/F... more We propose a novel strategy based on Capon's method for multiple signal extraction in TDMA/FDMA cellular mobile communications. In this method, called SF-Capon, each intracell cochannel (IC) user is alternatively asked to decrease its transmitted power for a few bits. This enables the estimation of a so-called signal-free (SF) correlation matrix, which is then used in connection with Capon's method to compute an improved beamforming weight vector with reduced sensitivity to DOA error and angular spread. The ...

A new cepstral prefiltering technique for estimating time delay under reverberant conditions

Signal Processing, 1997

... Processing 59 (1997) 253266 A new cepstral prefiltering technique for estimating time delay u... more

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A Downlink Switched-Beam OFDM Pilot Scheme Based on Subcarrier-Multiplexing

... Emails:{semlani,affes}@emt.inrs.ca, [email protected]. ... To serve as reference, w... more

System and Method for an Agile Wireless Access Network

Estimation of angular parameters of a signal at an antenna array

Cramér-Rao lower bounds for frequency and phase NDA estimation from arbitrary square QAM-modulated signals

Ieee Transactions on Signal Processing, Sep 1, 2010

In this paper, we derive for the first time the analytical expressions of the exact Cramér-Rao lo... more In this paper, we derive for the first time the analytical expressions of the exact Cramér-Rao lower bounds (CRLBs) of the carrier frequency and the carrier phase from square quadrature amplitude modulated (QAM) signals, assuming the noise power and the signal amplitude to be completely unknown. The signal is assumed to be corrupted by additive white Gaussian noise (AWGN). The main contribution of this paper consists in deriving the analytical expressions for the non-data-aided (NDA) Fisher information matrix (FIM) for higher-order square QAM-modulated signals. We prove that the problem of estimating the synchronization parameters is separable from the one of estimating the signal and the noise powers by showing that the FIM is block diagonal. Besides, we show analytically that the phase CRLB is higher than the frequency CRLB, implying that it is much easier to estimate the frequency than the distortion phase. It will be seen that the CRLBs differ widely from one modulation order to another in the medium SNR range. The newly derived expressions corroborate previous attempts to numerically or empirically compute the considered CRLBs as well as their asymptotical expressions derived only in special SNR regions.

format_quoteThe derived expressions quantify the achievable performance in carrier frequency and phase estimation from square QAM signals, enhancing estimation strategies.format_quote

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A Useful Integral for Wireless Communication Theory and Its Application in Amplify-And-Forward Multihop Relaying

2010 Ieee Global Telecommunications Conference Globecom 2010, Dec 1, 2010

In this paper, infinite integrals involving the product of Bessel functions of different argument... more In this paper, infinite integrals involving the product of Bessel functions of different arguments are solved in closedform. These solutions provide novel expressions in the error rate analysis for wireless amplify and forward (AF) systems with an arbitrary number of variable-gain relays. Here we show that the error probability can be described by generalized hypergeometric functions, namely Lauricella functions. This work represents a significant improvement on previous contributions and extends previous formulas pertaining to dual-hop transmissions over identical Nakagami-m fading channels. Numerical examples show an excellent match between simulation and theoretical results.

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Capacity of cognitive AF relay networks with multiple primary receivers

2014 Ieee Wireless Communications and Networking Conference, Apr 1, 2014

A Context-Aware Cognitive SIMO DL Transceiver for LTE HetNet Enhanced Pico-Cell Range Expansion

2015 IEEE International Conference on Ubiquitous Wireless Broadband (ICUWB), 2015

A context-aware cognitive SIMO transceiver for increased LTE-HetNet system-level DL-throughput

2015 International Wireless Communications and Mobile Computing Conference (IWCMC), 2015

MIMO relaying with interference via the CMGF transform

2015 IEEE International Conference on Communications (ICC), 2015

On the Performance of Dual-Hop Fixed Gain Relaying Systems over Composite Multipath/Shadowing Channels

2010 IEEE 72nd Vehicular Technology Conference - Fall, 2010

... Based on the newly derived analytical expressions of the cumulative distribution function (CD... more

A Useful Integral for Wireless Communication Theory and Its Application in Amplify-And-Forward Multihop Relaying

2010 IEEE Global Telecommunications Conference GLOBECOM 2010, 2010

In this paper, infinite integrals involving the product of Bessel functions of different argument... more In this paper, infinite integrals involving the product of Bessel functions of different arguments are solved in closedform. These solutions provide novel expressions in the error rate analysis for wireless amplify and forward (AF) systems with an arbitrary number of variable-gain relays. Here we show that the error probability can be described by generalized hypergeometric functions, namely Lauricella functions. This work represents a significant improvement on previous contributions and extends previous formulas pertaining to dual-hop transmissions over identical Nakagami-m fading channels. Numerical examples show an excellent match between simulation and theoretical results.

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On the Level Crossing Rate and Average Fade Duration of Composite Multipath/Shadowing Channels

IEEE GLOBECOM 2008 - 2008 IEEE Global Telecommunications Conference, 2008

In this paper, we consider composite mulipath/shadowing fading channels characterized by Nakagami... more In this paper, we consider composite mulipath/shadowing fading channels characterized by Nakagamim fading with Inverse Gaussian shadowing, and Rice fading with Inverse Gaussian shadowing. These channel models are very convenient for land mobile satellite systems and communications with low mobility or stationary users. From an analytical standpoint, one major advantage of these models is that they lead to closed-from expressions for the envelope probability density function (pdf) and the cumulative density function (CDF). Moreover, in this paper, we derive mathematically tractable new expressions for fundamental channel statistics such as the level crossing rate (LCR) and the average fade duration (AFD). Also, we validate our analytical results by providing several numerical examples showing the LCR and the AFD as a function of the Nakagami-m factor, Rice factor, and shadowing spread.

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A New Data-Aided Carrier Frequency Offset Estimation Algorithm for OFDM Systems

2006 IEEE 7th Workshop on Signal Processing Advances in Wireless Communications, 2006

ABSTRACT This paper proposes a new data-aided carrier frequency offset (CFO) estimation scheme fo... more ABSTRACT This paper proposes a new data-aided carrier frequency offset (CFO) estimation scheme for OFDM communications suitable for frequency-selective fading channels. The proposed method is based on the transmission of a specially designed synchronization symbol that creates a particular signal structure between the received observation samples at the receiver. This structure is exploited to derive a very accurate maximum likelihood (ML) CFO estimator. To reduce the estimation complexity, a simplified version with lower computational load is derived which exhibits only a moderate loss in accuracy. This simplified version could typically be employed in the acquisition phase while the original version would allow for a very accurate subsequent tracking phase. Simulations over frequency-selective fading channels confirm the superiority of the proposed method compared to most recent algorithms presented in the literature

ML-based joint estimation of frequency and sampling clock offsets for OFDM systems

2008 IEEE 9th Workshop on Signal Processing Advances in Wireless Communications, 2008

In this paper, we present a joint algorithm to estimate the fine symbol timing and carrier freque... more In this paper, we present a joint algorithm to estimate the fine symbol timing and carrier frequency offsets of wireless orthogonal frequency division multiplexing (OFDM) signals. To jointly estimate synchronization parameters using the maximum likelihood (ML) criterion, we propose to transmit a special pilot symbol. By using a periodic training sequence, we convert the problem of obtaining the ML solution from searching exhaustively over the entire uncertainty range to that of solving a polynomial, thereby greatly reducing the computational load. With the proposed orthogonal and periodic training sequence, we obtain a closed-form expression for the synchronization parameters, hence greatly simplifying the algorithm complexity. Simulations demonstrate that the joint estimation method provides better accuracy than existing joint and separate sampling clock and carrier frequency offsets estimation algorithms.

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Capacity and Error Rate Analysis of Cognitive MIMO AF Relaying Systems

IEEE Wireless Communications Letters, 2014

ABSTRACT This letter investigates spectrum-sharing cognitive amplify-and-forward relay networks e... more ABSTRACT This letter investigates spectrum-sharing cognitive amplify-and-forward relay networks employing the maximum ratio transmission/maximum ratio combining scheme at the multiple-antenna source-destination pair. It derives closed-form expressions for the ergodic capacity and for the symbol error rate lower bound and its asymptotic value when considering Nakagami-m fading and interference constraints on N primary receivers.

Performance of a New Low-Complexity Angular Spread Estimator in the Presence of Line-of-Sight

2008 IEEE Wireless Communications and Networking Conference, 2008

This paper focuses on the problem of angular spread (AS) estimation at the base station in a macr... more This paper focuses on the problem of angular spread (AS) estimation at the base station in a macro-cellular system when a line-of-sight (LOS) component is potentially present. We will limit our study to low-complexity methods prone to practical implementation. The paper demonstrates the limitations of the well-known low complexity AS estimation method, spread root-MUSIC. As supported by simulations, it introduces

Maximum Likelihood SNR Estimation of Linearly-Modulated Signals Over Time-Varying Flat-Fading SIMO Channels

IEEE Transactions on Signal Processing, 2015

In this paper, we tackle for the first time the problem of maximum likelihood (ML) estimation of ... more In this paper, we tackle for the first time the problem of maximum likelihood (ML) estimation of the signal-to-noise ratio (SNR) parameter over time-varying single-input multiple-output (SIMO) channels. Both the data-aided (DA) and the non-data-aided (NDA) schemes are investigated. Unlike classical techniques where the channel is assumed to be slowly time-varying and, therefore, considered as constant over the entire observation period, we address the more challenging problem of instantaneous (i.e., short-term or local) SNR estimation over fast time-varying channels. The channel variations are tracked locally using a polynomial-in-time expansion. First, we derive in closed-form expressions the DA ML estimator and its bias. The latter is subsequently subtracted in order to obtain a unbiased DA estimator whose variance and the corresponding Cramér-Rao lower bound (CRLB) are also derived in closed form. Due to the extreme nonlinearity of the log-likelihood function (LLF) in the NDA case, we resort to the expectation-maximization (EM) technique to iteratively obtain the exact NDA ML SNR estimates within very few iterations. Most remarkably, the new EM-based NDA estimator is applicable to any linearly-modulated signal and provides sufficiently accurate soft estimates (i.e., soft detection) for the unknown transmitted symbols. Therefore, hard detection can be easily embedded in the iteration loop in order to improve its performance at low SNR levels. We show by extensive computer simulations that the new estimators are able to accurately estimate the instantaneous per-antenna SNRs as they coincide with the DA CRLB over a wide range of practical SNRs.

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Maximum likelihood SNR estimation over time-varying flat-fading SIMO channels

2014 IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP), 2014

ABSTRACT In this paper, we propose a new signal-to-noise-ratio (SNR) maximum likelihood (ML) esti... more ABSTRACT In this paper, we propose a new signal-to-noise-ratio (SNR) maximum likelihood (ML) estimator over time-varying single-input multiple-output (SIMO) channels, for both data-aided (DA) and non-data-aided (NDA) cases. Unlike the classical techniques which assume the channel to be slowly time-varying and, therefore, considered as constant during the observation period, we address the more challenging problem of instantaneous SNR estimation over fast time-varying channels. The channel variations are locally tracked using a polynomial-in-time expansion. In the DA scenario, the ML estimator is developed in closed-form expression. In the NDA scenario, however, the ML estimates of the per-antenna SNRs are obtained iteratively, with very few iterations, using the expectation-maximization (EM) procedure. Our estimator is able to accurately estimate the instantaneous SNRs over a wide range of average SNR. We show through extensive Monte-Carlo simulations that the new estimator outperforms previously developed solutions.

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