Binary Continuous Phase Modulations Robust to a Modulation Index Mismatch

International audienceWe consider binary continuous phase modulation (CPM) signals used in some recent low-cost and low-power consumption telecommunications standard. When these signals are generated through a low-cost transmitter, the real modulation index can end up being quite different from the nominal value employed at the receiver and a significant performance degradation is observed, unless proper techniques for the estimation and compensation are employed. For this reason, we design new binary schemes with a much higher robustness. They are based on the concatenation of a suitable precoder with binary input and a ternary CPM format. The result is a family of CPM formats whose phase state is constrained to follow a specific evolution. Two of these precoders are considered. We will discuss many aspects related to these schemes, such as the power spectral density, the spectral efficiency, simplified detection, the minimum distance, and the uncoded performance. The adopted precoders do not change the recursive nature of CPM schemes. So these schemes are still suited for serial concatenation, through a pseudo-random interleaver, with an outer channel encoder

Robust Detection of Binary CPMs With Unknown Modulation Index

International audienceWe consider soft-output detection of a binary continuous phase modulation (CPM) generated through a low-cost transmitter, thus characterized by a significant modulation index uncertainty, and sent over a channel affected by phase noise. The proposed detector is designed by adopting a simplified representation of a binary CPM signal with the principal component of its Laurent decomposition and is obtained by using the framework based on factor graphs and the sum-product algorithm. It does not require an explicit estimation of the modulation index nor of the channel phase and is very robust to large uncertainties of the nominal value of the modulation index. Being soft-output in nature, this detector can be employed for iterative detection/decoding of practical coded schemes based on a serial concatenation, possibly through a pseudo-random interleaver, of an outer encoder and a CPM modulation forma

Blind equalization based on pdf distance criteria and performance analysis

In this report, we address M-QAM blind equalization by fitting the probability density functions (pdf) of the equalizer output with the constellation symbols. We propose two new cost functions, based on kernel pdf approximation, which force the pdf at the equalizer output to match the known constellation pdf. The kernel bandwidth of a Parzen estimator is updated during iterations to improve the convergence speed and to decrease the residual error of the algorithms. Unlike related existing techniques, the new algorithms measure the distance error between observed and assumed pdfs for the real and imaginary parts of the equalizer output separately. The advantage of proceeding this way is that the distributions show less modes, which facilitates equalizer convergence, while as for multi-modulus methods phase recovery keeps being preserved. The proposed approaches outperform CMA and classical pdf fitting methods in terms of convergence speed and residual error. We also analyse the convergence properties of the most efficient proposed equalizer via the ordinary differential equation (ODE) method

An adaptive radius blind equalization algorithm based on pdf fitting

International audienceIn this paper, we investigate blind equalization techniques based on information theoretic criteria. They involve estimating the probability density function (pdf) of transmitted data. Our work is based on previous studies where the Parzen window method has been used to estimate the pdf at the equalizer output. The equalizer is obtained by minimizing the distance between this equalized pdf and some target distribution. With a view to reduce algorithm complexity, we propose a reduced constellation implementation of the adaptive equalizer. We show complexity and performance gain against similar approaches in the literature

CPM Signal for Machine to Machine Communications

The analysis of communication evolution predicts an increase in the number of connected machines. This thesis aims to determine a multi-user communication system adapted to the material limitation of the machines and to the applications constraints. Power and cost efficient digital modulation is required for both economic and environmental reasons; the power consumption on the link should be as low as possible. Constant envelope modulation offers the possibility to use non-linear cost-effective and power efficient amplifiers. Continuous phase modulation (CPM) exhibits constant envelope and the continuous phase makes the power frequency spectrum well confined with the possibility to achieve small spectral side lobes. The advantages of CPM are balanced with the primary disadvantages, which are the complexity at the receiver side, a lack of robustness to the parameters mismatch around their nominal values, and its lower spectral efficiency compared to linear modulation. In this thesis we first considered an AWGN transmission of a CPM with a perfectly estimated modulation index. A reduced complexity per survivor processing (PSP) based CPM demodulation was derived for both single and multiple modulation indices. Second, the robustness issue is addressed on the receiver side and on the transmitter side. On the receiver side, a robust detector was designed based on the factor graph and the sum product algorithm to deal with unknown modulation index errors. Simulations were performed assuming a multiuser binary CPM transmission in the presence of phase noise. At the transmitter side, the robustness to the modulation index mismatch is also solved by the design of an appropriate precoder which limits the accumulation of phase errors. Third, a high spectral efficiency CPM scheme was derived based on an appropriate design of the precoder. In a multiusers scheme, the overall spectral efficiency is increased by using a new AMI-based precoder, where a robust multi-user detection for synchronous binary CPMs signals is performed, based on phase separation.L'analyse de l'évolution des télécommunications prévoit une augmentation du nombre de machines connectées. Cette thèse vise à déterminer un système de communication multi-utilisateur adapté à la limitation matérielle des machines et aux spécificités des applications de collecte d¿informations à grande échelle. Pour des raisons économiques et environnementales, il est nécessaire de réduire la puissance et le coût des systèmes de communications numériques. Il est également nécessaire de réduire la consommation d'énergie afin d¿augmenter la durée de vie des batteries utilisées. La modulation à enveloppe constante permet d'utiliser des amplificateurs non linéaires qui ont un rendement énergétique plus importants que leurs homologues linéaires. Les modulations à phase continue (CPM) mettent en ¿uvre des signaux à enveloppe constante. De plus, la continuité de phase confine la densité spectrale de puissance tout en diminuant le niveau des lobes secondaires. Les principaux inconvénients de la CPM sont la complexité mise en ¿uvre pour une réception optimale, la sensibilité aux dispersions des paramètres d¿émission, et la diminution de son efficacité spectrale par rapport à la modulation linéaire. Dans cette thèse, nous proposons des solutions pour ces trois aspects. Tout d'abord, un démodulateur CPM d¿une complexité réduite basé sur la technique per survivor processing (PSP) a été développé pour une transmission sur un canal Gaussien d'un signal CPM dont l¿indice de modulation est parfaitement estimé. Deuxièmement, nous abordons le problème de la robustesse du côté récepteur puis du côté de l'émetteur vis-à-vis de l¿indice de modulation ; il s¿agit ici de compenser un écart entre l¿indice de modulation nominal et l¿indice de modulation réel et inconnu. Du côté récepteur, un détecteur robuste a été conçu en appliquant un algorithme de type somme-produit sur un graphe biparti afin de compenser l¿erreur présente sur la connaissance de l¿indice de modulation. Les simulations ont été réalisées en considérant un système multi-utilisateur des signaux CPM binaire en présence de bruit de phase. Du côté émetteur, la robustesse est obtenue par la conception d'un pré-codeur approprié conçu pour limiter l'accumulation de l¿erreur de phase. Troisièmement, une amélioration de l'efficacité spectrale d¿un signal CPM binaire est obtenue grâce à la conception d¿un pré-codeur. Dans un système multi-utilisateur synchrone, l¿efficacité spectrale est augmentée en associant chaque émetteur CPM binaire à un pré-codeur de type Alternate Mark Inversion suivie d¿une séparation de phase ; une détection multi-utilisateur est effectuée au récepteur

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New Criteria for Blind Equalization Based on PDF Fitting

International audienceIn this paper, we address M-QAM blind equalization by fitting the probability density functions (pdf) of the equalizer output with the constellation symbols. We propose two new cost functions, based on kernel pdf approximation, which force the pdf at the equalizer output to match the known constellation pdf. The kernel bandwidth of a Parzen estimator is updated during iterations to improve the convergence speed and to decrease the residual error of the algorithms. Unlike related existing techniques, the new algorithms measure the distance error between observed and assumed pdfs for the real and imaginary parts of the equalizer output separately. The proposed approaches outperform CMA and classical pdf fitting methods in terms of convergence speed and residual error