Search results for: I. Fijalkow
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Linear precoders have been shown to perform reasonably well at low SNR when the basestation of a MIMO downlink employs one-bit digital-to-analog converters to quantize the precoder outputs. However, at medium-to-high SNRs, an error floor is encountered due to the coarse quantization. This paper examines methods for slightly perturbing the transmitted signal prior to quantization in an effort to improve...
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To increase the throughput of transmission systems, MIMO transmission have become a natural path. Two different MIMO schemes can be envisioned: point to point communications and multi-point to point communications. We propose in this paper to study the performances of multi-point to point communication (also referred to as multi-user transmissions) for different receivers and with or without channel...
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In this contribution, we address a new second order approach for multichannel zero forcing equalization with controlled delay. The method basically exploits the second order whiteness input signal properties and condition of left invertibility of the multichannel. Channel identification is investigated in a second step. In comparison of existing methods, the proposed method has the interesting properties...
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In GPS applications, positioning techniques are based on the characteristics of the pseudo-random code autocorrelation function. They don't take into account the eventuality of multipath propagation. One reflected signal may greatly disturb the measures of the usual Early-Late method. A maximum a posteriori (MAP) estimator is proposed in this study, introducing a multi-path model and prior laws on...
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The good convergence tracking properties of spatio-temporal equalizers are pointed out and analyzed when there is effective diversity. The analysis is illustrated in the case of a frequency offset between the baud and sampling clocks that induces important time-variations.
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This paper addresses the convergence rate study of the Fractionally-Spaced Equalizer updated by Constant Modulus Algorithm (FSE-CMA). By analyzing the average algorithm behavior we compare the FSE-CMA to the FSE-LMS. Although the FSE-CMA is based on a fourth order statistics criterion, we will show for constant modulus input that the algorithm has the amazing property to converge locally twice as...
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To mitigate in-band and out-of-band linearity problems due to an Orthogonal Frequency Division Multiplexing (OFDM) signal used on a high power amplifier (PA), we propose to improve a linearization technique called baseband digital predistortion. The new algorithm differently processes the samples depending on their power. Predistortion improvement is studied in simulation on a class A PA and then...
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Nonlinearity problems for power amplifiers are well known and many linearization techniques have been proposed in the literature, especially digital baseband predistortion. Orthogonal Frequency Division Multiplexing (OFDM) has a very high Peak-to-Average Power Ratio (PAPR), making it very sensitive to non linearities. We have chosen the Active Constellation Extension (ACE) to reduce the crest factor,...
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IEEE Transactions on Signal Processing > 2011 > 59 > 5 > 2244 - 2256
This paper addresses the spectrum-sharing for wireless communication where a cognitive or secondary user shares a spectrum with an existing primary user (and interferes with it). We propose two lower bounds, for the primary user mean rate, depending on the channel state information available for the secondary-user power control and the type of constraint for spectrum access. Several power control...
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This paper addresses the spectrum-sharing for wireless communication with a licensee-primary and a secondary users interfering with each other. We propose a new practical power control policy for the secondary user, under outage performance requirements for both users, with partial knowledge of channel state information.
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This paper presents a link adaptation strategy for non-binary LDPC code over a time-variant frequency-selective channel. The algorithm is based first on the adoption of waterfilling technique to wisely adapt the transmitted power. It is shown that as long as best subchannels are identified with the waterfilling algorithm, an equal power distribution can be applied with performance comparable to the...
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In this paper, we deal with the time slot allocation in time-hopping ultra-wide band (TH-UWB) ad-hoc networks in order to maximize the total sum rate. This problem is known to be a discrete NP-hard optimization problem and hence cannot be solved with a computationally efficient algorithm. Moreover, the sum rate maximization often leads to starvation of links experiencing bad channel conditions. Our...
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We consider two different users sharing the same spectrum resource, interfering with each other, under outage performance requirements for both the users. We derive a practical condition to enable the spectrum-sharing under simultaneous outage performance. Furthermore, when the condition is fulfilled, we provide equations to define the two-dimensional region of allocated powers (P1, P2), for the two...
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In this paper we propose a Successive Interference Cancelation (SIC) method in the case of UWB-OFDM transmission system in order to compensate for the effects of an imperfect frequency synthesizer. Our aim is to mitigate the interferences due to the spurs, allowing a less constrained implementation of the circuits.
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IEEE Transactions on Communications > 2010 > 58 > 3 > 975 - 985
In this paper, we present a simple and effective precoding technique to mitigate inter-symbol interference from multiple transmissions of the same packet in automatic repeat request (ARQ) protocols over slowly time-varying frequency-selective channels. We minimize the power of inter-symbol interference by introducing phase-precoding transmission diversity among subsequent ARQ transmissions. For each...
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In this paper, we address the problem of optimization of the training sequence interval for MIMO (multiple-input multiple-output) flat fading channels when an iterative receiver composed of a likelihood generator and a maximum a posteriori (MAP) decoder is used. At each iteration of the receiver, the channel is estimated using the hard decisions on the transmitted symbols at the output of the decoder...
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In this paper, we jointly optimize the training interval length and the power allocation for MIMO (multiple-input multiple-output) flat fading channels when a maximum a posteriori (MAP) detector is used at the receiver and the training and data powers are allowed to vary. We calculate the equivalent signal-to-noise ratio (SNR) at the output of the MAP detector. Based on this expression, we define...
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In this paper, we investigate the performance of a bit-interleaving diversity (BID) scheme for multiple packet transmissions over multiple-input multiple-output (MIMO) frequency-selective channel in the context of hybrid automatic repeat request protocols. We show under the maximum likelihood decoding rule that a BID scheme outperforms an identically interleaved transmit scheme. Moreover, we identify...
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We propose a new algorithm for the IQ imbalance estimation and equalization of an Orthogonal Frequency Division Multiplexing (OFDM) system in the presence of a Carrier Frequency Offset (CFO) and of a dense multipath environment. Our algorithm has a low complexity and needs a single pilot symbol. Through numerical simulation and in the context of quick estimations of front-end non-idealities, our algorithm...
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In a frequency selective channel for wireless applications, we provide a new resources allocation procedure that enables the transmission of scalable images in accordance with end-to-end Quality of Service (QoS) constraints. This scheme is based on an Unequal Error Protection (UEP) policy with the possible truncation of the source data layers (after the source coding stage) and an optimal use of the...
