Performance analysis of a COFDM/FM in-band digital audiobroadcasting system

In this paper, we present a performance analysis of a coded orthogonal frequency division multiplexing DAB system that is power multiplexed over a commercial FM station. We model the mobile channel with a time-frequency scattering function. Results show that the performance of the FM demodulator is crucial, since the level of the residual FM signal has a strong influence on the BER performance of the COFDM system. As with other mobile communication systems, the use of interleaving greatly enhances the performances     

Audio interfaces and signal processing

This paper deals with problems raised by speech and sound pick-up, processing and reproduction in telecommunication systems. Those problems which occur as soon as sound and speech are involved in a communication are briefly explained in the introduction. Then the noise and acoustic echo cancellation problems are discussed and current techniques are presented. The remaining part of the paper is dedicated to sound reproduction techniques which aim at preserving the spatial characteristics of sound and which take into account the characteristics of spatial hearing. Finally, some data about standardization are recalled and future applications are sketched.     

Synthèse sur la réduction conjointe de bruit et d’écho pour lés systèmes mains-libres

In the context of modern telecommunications, hands-free systems allow to talk in a more natural way, without handling a telephone. This leads to new problems which were negligible in classical telephony: the superposition of energetic noise and echo on the speech signal. To solve these problems and to provide a sufficient speech quality, a joint reduction of these perturbations is needed. This paper presents a synthesis of solutions retained to achieve this reduction in the context of mono-channel and two-channel observations.     

Accuracy evaluation of fixed-point based LMS algorithm

The implementation of adaptive filters with fixed-point arithmetic requires computation quality evaluation. The accuracy may be determined by computing the global quantization noise power at the system output. In this paper, a new model for evaluating analytically the global noise power in LMS-based algorithms is presented. Thus, the model is developed for LMS and NLMS algorithms. The accuracy of our model is analyzed by simulations.     

New metric for <Emphasis Type="Italic">IQ</Emphasis> imbalance compensation in optical QPSK coherent systems

We report on a simple alternative method for the compensation of quadrature imbalance in optical quadrature phase-shift-keying (QPSK) coherent systems. By introducing a new metric, the phase imbalance can be determined and compensated. The proposed method is theoretically and numerically analyzed. In particular, it is shown that the method exhibits a small bias of estimated phase imbalance value. Thanks to its deterministic property, this bias can be simply compensated by incorporating at the receiver a phase rotator (or phase shift) whose value can be determined based on an analytical analysis. Moreover, the algorithm is also experimentally validated through bit-error-rate and error vector magnitude (EVM) measurements. A good agreement on the performance of the proposed method with that of the Gram–Schmidt orthogonalization procedure is shown in a 20-Gbit/s optical QPSK experiment. The robustness of both methods was verified with up to \(30^\circ \) phase imbalance by comparing the signal with and without phase imbalance compensation. A 10% reduction in EVM is achieved with our method for a high phase imbalance of \(30^\circ \), while the implementation complexity can be reduced owing to the suppression of the use of square-root operators.