Laurent Pierrugues

DMT performance improvement based on clustering modulation, applications to ADSL

Dynamic bit-loading for ADSL-DMT is driven by the signal-to-noise ratio (SNR) achieved per tone. 14.3 dB of minimum SNR is required to load a tone with the smallest square 4QAM constellation, for a fixed 10/sup -7/ bit error rate (BER). In the presence of physical layer impairments such as loop attenuation, bridge taps or crosstalks, many tones cannot be used because their individual SNR values are too small. On the other hand the associated total unloaded bandwidth exhibits a significant capacity. To benefit from parts of this unloaded bandwidth capacity, trellis coding with one bit or fractional bit loading has been proposed, unfortunately requiring some trellis decoding modifications. This paper introduces a new method called clustering modulation (CM) that does not require any trellis change and which clusters unloaded tones together to increase the SNR after maximum likelihood cluster payload demodulation in the frequency domain. Clustering modulation achieves up to 424 kbits/s of rate improvement on a 2.8 km (9 kfeet) 26AWG loop and up to 200 m of reach increase against SDSL noise B crosstalks.

Enhanced TCM based on a multilevel hierarchical trellis coded modulation (HTCM)

This paper introduces a new multilevel coding scheme, identified as hierarchical trellis coded modulation (HTCM), that significantly improves a given TCM, while maintaining a 100% compatible fallback mode into the original trellis structure. HTCM exhibits a reasonable complexity increase when compared to higher order trellises or full turbo schemes that could reach similar gains. HTCM combines a given TCM code and a very high protection code (HPC), such as turbo code or low-density parity-check (LDPC) code. The HPC encodes the least significant bits of a large constellation, thus increasing the minimum Euclidean distance between TCM coded signals. The paper derives the theoretical HTCM asymptotic gain. HTCM is then applied to enhance the 16-state 4D Wei scheme by 1.76 dB of net coding gain., making use of a rate 1/2 parallel concatenated turbo code for the HPC and a new DSQ (diagonally shifted QAMs) constellation mapping. HTCM modularity, efficiency and relative simplicity open new ways to TCM enhancement that would help many broadband communication fields including wireless, satellite and wired systems.

SIMO-NAR NEXT Canceller for DMT DSL-CPE: a Stochastic Shannon Capacity Perspective

This paper presents and analyzes a frequency domain near end crosstalk (NEXT) canceller tuned to the DMT-DSL CPE. This per tone NEXT canceller is based on a SIMO (Single Input Multiple Output) structure with a Noise Alone Reference (NAR), strongly correlated to the NEXT disturbance of the main stream and orthogonal to the useful signal. Unlike a time domain algorithm, this two sensors frequency solution meaningfully optimizes the SNR per tone, and thus the aggregate capacity of the DMT-system. Since the NEXT coupling highly depends on the relative position of the victim line and the disturbing sources, we provide an analysis technique that fully takes into account the stochastic nature of the NEXT coupling, similar to outage probability used for wireless communication systems. Based on a new stochastic NEXT coupling model of amplitude and phase, that fits real data measurements, and a Monte-Carlo sampling approach, we observe that the SIMO-NAR solution achieves a minimum of 3dB and 9dB SNR improvement in 50% and 10% of the cases, respectively.

Space-frequency modulation for MIMO coordinate copper units

The present paper provides Shannon performance bounds of MIMO cooperative copper units (CCU) in the presence of crosstalk originating in neighboring pairs. Limited here to just two pairs, MIMO CCU operates either in multiplexing or diversity modes transmitting independent or identical data streams. Contrary to the rank instability of frequency dispersive wireless channel, CCU always experience full rank MIMO channels. Nevertheless, the major gain inherent in CCU optimal joint processing does not stem from the channel full rank property but from the possibility to partially cancel the crosstalk. Capacity may indeed be largely increased if the crosstalk correlation experienced by the CCU paths of each impaired tone of the copper bandwidth is leveraged through maximum likelihood estimation. The paper gives the theoretical foundation of this result by deriving an original (according to our knowledge) form of the MIMO Shannon bound in terms of the Fisher information matrix. We finally address a space-frequency modulation (SFM) that combines the selection of the best precoder with the multicarrier modulation.