Maurice G. Bellanger

Specification and design of a prototype filter for filter bank based multicarrier transmission

The specifications of filter banks for multicarrier transmission systems with a large number of subchannels are discussed, with application to xDSL and power line communication in mind. The near perfect reconstruction (PR) modulated approach is considered and the importance, for the system, of the prototype filter delay is stressed. An existing design technique known to be particularly relevant to the context is revisited from a frequency sampling perspective. The performance results in terms of subchannel noise floor and delay are given for several filter lengths and an experimental validation is provided. Finally, an improvement to the design technique is proposed, which brings a gain of 3.3 dB in subchannel interference power level.

On the duality between fast QR methods and lattice methods in least squares adaptive filtering

The authors show that fast QR methods and lattice methods in least squares adaptive filtering are duals and follow from identical geometric principles. Whereas the lattice methods compute the residuals of a projection operation via the forward and backward prediction errors, the QR methods compute instead the weights used in the projections. Within this framework, the parameter identification problem is solved using fast QR methods by showing that the reflection coefficients and tap parameters of a least squares lattice filter operating in the joint process mode are immediately available as internal variables in the fast QR algorithms. This parameter set can be readily exploited in system identification, signal analysis, and linear predictive coding, for example. The relations derived also lead to a fast least squares algorithm of minimal complexity that is a hybrid between a QR and a lattice algorithm. The algorithm combines the order recursive properties of the lattice approach with the robust numerical behavior of the QR approach. >

A fast least-squares algorithm for linearly constrained adaptive filtering

An extension of the field of fast least-squares techniques is presented. It is shown that the adaptation gain, which is updated with a number of operations proportional to the number of transversal filter coefficients, can be used to update the coefficients of a linearly constrained adaptive filter. An algorithm that is robust to round-off errors is derived. It is general and flexible. It can handle multiple constraints and multichannel signals. Its performance is illustrated by simulations and compared with the classical LMS-based Frost (1972) algorithm.

Physical layer for future broadband radio systems

Future broadband radio systems have ambitious objectives in terms of performance and quality of service. Moreover, new network topologies are likely to be introduced. Therefore, the physical layer has to evolve to meet the new requirements. With this in mind, the filter bank multicarrier (FBMC) technique is proposed as an enhancement to the present OFDM technique. After a brief presentation of the FBMC principle, the adaptation to the radio context is described. Then, the main features which impact radio networks are reviewed with emphasis on the potential benefits of the evolution. The paper provides an overview of the work carried out in the European research project EC-FP7-Phydyas (physical layer for dynamic access and cognitive radio).

FS-FBMC: An alternative scheme for filter bank based multicarrier transmission

An alternative scheme, named frequency spreading filter bank multicarrier (FS-FBMC), is introduced for multicarrier transmission. It is based on the FFT and closely follows the principle of OFDM, while preserving the key advantages of FBMC, namely the absence of guard time and the spectral separation of the sub-channels. It is optimal in the sense that it can provide perfect equalization of the transmission channel without the need for an additional delay and it maximizes the signal-to-noise ratio in the receiver. It generalizes the classical FFT-PPN approach, which, in fact, is a technique to remove some redundancy in the computations.

Annals of telecommunications

This international journal publishes original peer-reviewed papers in the field of telecommunications. It covers all the essential branches of modern telecommunications, ranging from digital communications to communication networks and the internet, to software, protocols and services, uses and economics. This large spectrum of topics accounts for the rapid convergence through telecommunications of the underlying technologies in computers, communications, content management towards the emergence of the information and knowledge society.

Efficiency of Filter Bank Multicarrier Techniques in Burst Radio Transmission

The filter bank multicarrier (FBMC) technique has been proposed in the FP7 European research program, as an enhancement to the OFDM technique for future broadband radio systems. Besides gains in efficiency, mainly due to the absence of cyclic prefix, an important feature of FBMC is the absence of spectral leakage, which makes it particularly appealing for cognitive radio. However, in burst transmission, the filter impulse response introduces transitions which extend the length of the burst with respect to OFDM and may reduce the gains in efficiency. After a brief overview of the FBMC technique, the exploitation in burst transmission is discussed. The effect of cutting the initial and final transitions of the burst is investigated. The level of temporary spectral leakage introduced by this operation is assessed. It is shown that cuts leading to an increase in burst length of half a symbol with respect to OFDM affect the first and the last symbol only, resulting in a minor reduction in bit loading for these symbols. Application to the time division duplex access mode is considered, as well as the case of the presence of a preamble in the burst. For implementation, it is proposed to resort to a simple memory preloading technique, which has the advantage of compatibility with OFDM in dual mode systems.

Exact DCT-based spatial domain interpolation of blocks in images

In many processing and coding techniques, images are decomposed into blocks of pixels and the DCT is used to transform those blocks. In some situations, blocks are dropped or lost, and, at some point in the processing, they must be restored from their neighborhood in the images. It is shown that an exact interpolation of image blocks can be performed in the spatial domain, using the DCT. The conditions for a solution to exist are derived and the corresponding algorithm requires 8 multiplies per restored pixel. The exact interpolation approach outperforms the alternative methods in the simulations presented, at a significantly smaller computation cost.

Maximum likelihood detection in spatial multiplexing with FBMC

In FBMC transmission systems, the bit rate is maximized when OQAM modulation is employed. One of the characteristics of this modulation is that the received data symbols are accompanied by interference terms, which complicates the application of ML techniques in optimal decoders. Two approaches are proposed to cope with this situation. The first one exploits the MMSE estimation of the interference terms and it introduces no additional delay. In the second one, the interference terms are calculated from past, present and future data symbols, either already decided or estimated. The gains provided by these approaches, with respect to MMSE, are assessed and illustrated by simulation.

Improved design of long FIR filters using the frequency masking technique

Frequency specifications imposing small transitions between pass-bands and stop bands lead to FIR filters having long impulse responses and highly correlated coefficients. Multirate techniques can reduce the resulting redundancy and the combination of a sharp undersampled filter with a couple of interpolating filters can lead to significant gains in arithmetic complexity. The alternative implementation proposed, and the corresponding filter design can bring an additional gain in the total operation count.