Julien Pons

Performance and Design of an Impulse Noise Detector for OFDM Systems with Reed-Solomon Erasure-Decoding

We develop an analytical framework to evaluate the probability-of-miss and probability-of-false-alarm performance of an impulse noise (IN) detection algorithm for orthogonal frequency-domain multiplexing (OFDM) symbols based on monitoring the post-frequency-domain-equalizer (FEQ) instantaneous error at the output of the QAM constellation demapper over a range of tones (sub-carriers). Using the VDSL system as a reference, we further analyze the impact of impulse-noise detection error events at the scale of the OFDM symbol (miss and false alarm) on the bit-error-rate (BER) performance of interleaved Reed-Solomon (RS) codes with erasure-decoding. The analysis culminates with a sequence of steps to design the parameters of the frequency-domain IN detector based on the design BER of the communication system and practical transceiver features such as noise-margin and seamless-rate-adaptation (SRA). We conclude that a tone-error based frequency-domain IN detector monitoring 100 tones is capable of providing IN detection performance that does not cause a deterioration of the average BER below the VDSL system design BER of 10-7 when interleaved RS coding with erasure-decoding is employed.

New Tight Upper-Bounds on the Error Probability of Multilevel Coded Modulation Schemes

This paper presents two theoretical upper-bounds on the word and bit error probabilities of individual levels of multilevel coded modulation schemes with equal error protection and multistage decoding. Lattice-type or PSK modulation with Ungerboeck partitioning over an AWGN channel is assumed. Inspired by both Imais [1] and Wachsmanns [2] channel models, a new model is introduced, yielding the expression of two upperbounds tighter than those known so far [3][4]. The tightness of the bounds is illustrated with simulation results and compared to existing bounds. Finally, a method for approximating the simulated performance of individual levels is discussed.

8-ary Unbalanced PSK Turbo Coded Modulation with Low Complexity Soft-Demapping

The 8-ary phase shift keying (8-PSK) constellation remains today widely used in turbo coded modulation schemes transmitting 3 coded bits per signal waveform. The present paper investigates a binary turbo coded modulation scheme using unbalanced 8-PSK (8-UPSK) constellations. A 8-UPSK with a structure similar to that of quadrature amplitude modulation (QAM) is proposed, yielding a low complexity calculation of the soft-decision associated with each bit. We suggest an architecture for computing the exact logarithm of the maximum likelihood ratio with a complexity reduced by more than 50% compared to that required for 8-PSK demapping. In addition, Monte-Carlo simulations show that some UPSK turbo coded modulations outperform the regular PSK modulation, hence achieving improved error performance with a reduced computational complexity.

Multistage MIMO detection using reduced basis optimality tests

Reducing the computational complexity of well-performing Multiple Inputs Multiple Outputs (MIMO) detection schemes is a crucial step toward designing high-throughput, low-cost MIMO receivers. In this paper we present a general multistage approach to MIMO detection, where a low complexity detector processes the received signal, and only few selected symbols are reprocessed using a more efficient, but more complex scheme. The global complexity is hence reduced while achieving near optimal symbol-space performance. Extending the work that was presented in [9], data that need further processing are identified using a reduced basis optimality test. Performing the test in the reduced lattice space diminishes the probability of false alarm of our test at no extra cost in terms of complexity, except during initialization. Usage of the secondary detector is thus more efficient as almost no data are unnecessarily reprocessed.

Self-Protection of Turbo- and LDPC-Coded OFDM Systems against Non-Stationary Disturbances

This paper presents a method to protect turbo- and low density parity check (LDPC)-coded OFDM systems against non-stationary disturbances without using external codes. The technique does not alter the structure of the original code and the constellation mapper/demapper, but requires the insertion of a so-called self-protection unit (SPU) between the coding and constellation mapping units. The SPU enhances the burst-error-correction capabilities of turbo and LDPC codes by combining erasure-decoding, subframing (i.e., reordering the coded data into subframes), and the optional use of subframe interleaving to spread error bursts. Self-protected systems exhibit a reduced latency and storage capacity compared to classical channel interleaving schemes with similar protection level.