Marc De Courville

Orthogonal Frequency Division Multiplexing for Terrestrial Digital Broadcasting

This chapter has explained the current status of OFDM systems as used in digital broadcasting and more specifically in the DAB application. By proposing a discrete modeling of these systems based on the polyphase filter bank formalism, the flexibility brought by the multicarrier concept has been shown to allow many different tunings. This freedom is intrinsically linked to the way multicarrier systems transmit symbols in the time-frequency plane and to the selectivity of the (de-)modulator filters, allowing the use of simple equalization schemes.

Linear precoded OFDM transmissions with MMSE equalization: Facts and results

This contribution aims at analyzing the performance of large linear precoded OFDM transmissions over fading wireless channels with limited diversity and MMSE equalization. Linear Precoding consists in multiplying by a N ◊ K isometric matrix a K dimensional vector obtained by serial to parallel conversion of a symbol sequence to be transmitted. Based on the Free Probability Theory, asymptotical analysis (N tends to infinity, K tends to infinity and K/N >tends to a constant) of the SINR is conducted to understand the different parameters involved in Linear Precoded OFDM schemes. The theoretical results are confirmed by numerical simulations when considering convolutional coding with finite memory.A novel semi-blind estimation scheme is proposed for an uncoded space-time system that uses a multi-element array pilot integration (MEA-PI) algorithm with Hadamard orthogonal structure combined with an auto-tracking algorithm. Central to the new method is a real-time channel estimator that introduces a very low pilot symbol overhead during the training process. The method is also capable of tracking the time variation of the channel using both the training vectors and a decision feedback algorithm during data acquisition process. As a result, a robust method of estimating the channel coefficients is possible, enabling the method to be used in real-time for a time-varying channel with a relatively short coherence time. The bit-error probability performance of this semi-blind method is investigated for different system configurations using non-linear MMSE decoding. It is found that the new method shows very little degradation in performance compared with the case where perfect channel estimates are assumed.

Multi-RAU pilots for ROF enabled distributed antenna systems

Future cellular systems require an aggressive frequency reuse in order to provide the expected data rates. For these systems, interference is a major issue to be addressed by the physical layer. Radio over fiber enabled distributed antenna systems can provide a competitive solution to mitigate interference. In this architecture, multiple non collocated remote antenna units (RAU) are transparently connected to a single central unit which performs coordination and joint processing. In downlink context, multi-RAU channel estimation is a key feature which allows the mobile station to combat interference using joint detection. However, pilot patterns in current cellular standards are designed for single cell scenarios and are not adapted to the DAS context. We propose here a generic capacity analysis framework to assess the impact of multi-RAU channel estimation on the link performance. This framework is then applied to highlight the enhancement provided by a proposed modification of LTE pilot patterns suitable to the DAS topology. We show that pilot coordination between neighbouring RAUs combined with interference cancellation on the terminal side provides a substantial gain to the downlink user throughput.

A multicode approach for high data rate UWB system design

This contribution provides a very high data rate UWB system design based on direct sequence spreading. In order to attain >500 Mbps for short range communication, two classical solutions are feasible: either use very short spreading sequences or very large bandwidth. These classical strategies increase intersymbol interference. In contrast, our approach consists in allocating multiple long codes to each user. Long codes allow to cope with channel impairments while the use of multiple codes maintains very high bit rates. With such high data rates the receiver obviously has to be simple by requiring a low complexity digital processing. This paper shows that the proposed strategy is compatible with simple receivers. In fact, even if the amount of interference increases, joint usage of very long codes and simple linear receiver can result in high data rate, high performance UWB system. This assertion is substantiated through comparisons with existing UWB solutions.

Reconfigurable Low Density Parity Check (LDPC) Code Interleaving for SIO and MIMO OFDM Systems

This contribution derives an algorithm for optimizing the mapping of irregular and systematic low density parity check (LDPC) code word bits onto orthogonal frequency division multiplexing (OFDM) carriers in the context of a frequency selective fading channel in both, a single-transmit single-receive (SISO channel) and multiple-transmit multiple-receive (MIMO channel) antennas scenario. The absolute values of the frequency domain channel coefficients are assumed to be known and the LDPC code to be given (contrary to existing proposals where the LDPC code is optimized with respect to a given propagation channel). The proposed solution can alternatively be interpreted as an adaptive interleaver (which is inherently available in software defined radio type of system implementations) optimized for a given channel impulse response. In a typical WLAN (IEEE802.11n) scenario, the proposed mapping technique improves the system performance by up to approx. 0.7 dB compared to a linear (direct) mapping