Jean-Yves Baudais

Multi-carrier CDMA over copper lines - comparison of performances with the ADSL system

This paper deals with the comparison of two multi carrier modulation techniques over existing copper twisted pairs: the Discrete Multi Tone (DMT) modulation and the Multi Carrier Code Division Multiple Access (MC-CDMA) modulation. The first form has been proposed for Asymmetrical Digital Subscriber Line (ADSL). However in ADSL, the wire pairs suffer from disturbances such as transients, radio-frequency noise. Among them, impulse noise is considered to be one of the most damaging impairments. Then, our proposal intends to limit the effects of such a noise thanks to the use of the latter form of modulation which combines multi carrier technique with spread spectrum. In order to improve the performances of the system proposed still further various detection techniques are studied. In this context, we show that the MC-CDMA technique presents better performances than the normalised ADSL technique under identical simulation parameters (data rate, bandwidth, transmitted power, coding, interleaver).

Multi-carrier CDMA using interference cancelation

In this paper, various detection techniques in the synchronous case of a multiuser MC-CDMA system operating in frequency selective Rayleigh channel are compared with respect to the achievable spectral efficiency. It is shown that a parallel interference cancellation MMSE scheme with two stages could be a good compromise between performance and complexity.

Optimization of linear precoded OFDM for high-data-rate UWB systems

We investigate the use of a linear precoded orthogonal frequency division multiplexing (LP-OFDM) waveform for high-data-rate ultra-wideband (UWB) systems. This waveform applied for the first time to UWB applications is an evolution of the multiband OFDM (MB-OFDM) solution supported by WiMedia-MBOA (MultiBand OFDM Alliance). The aim of this paper is twofold. Firstly, an analytical study of the LP-OFDM waveform allows to find how to efficiently precode an OFDM signal in order to improve the robustness of the system. Secondly, a global system study is led to highlight the benefits of adding a precoding function to an OFDM signal in the UWB context. Different system choices and parameterization strategies are thus proposed. In both analytical and global system studies, the LP component is optimized without channel state information (CSI) at the transmitter side, as in the MBOA solution. To go further, the MBOA constraints are relaxed, and an additional optimization is performed, with a CSI at the transmitter. The analytical and simulation results show that the joint use of linear precoding and OFDM leads to a significant performance increase compared to the MBOA solution. This improvement is due to the precoding scheme that provides better exploitation of the channel diversity.

STBC MC‐CDMA systems: comparison of MMSE single‐user and multiple‐user detection schemes over Rayleigh and MIMO METRA channels

The performance of MMSE single-user detection (SD) and multi-user detection (MD) STBC multi-carrier code division multiple access (MC-CDMA) systems are analysed and compared in the case of two transmit antennas and one or two receive antennas over Rayleigh fading channels and then over the stochastic multiple input multiple output (MIMO) METRA channel model. With two transmit and one receive antennas, MD achieves a gain of roughly 1u2009dB for non-full load systems while the same performance is obtained with MD and SD for full load systems. Besides, with two receive antennas, we present a sub-optimal and an optimal MMSE SD MIMO MC-CDMA schemes, this last one offering a very good performance. Finally, the very good behaviour of MMSE space-time block coding (STBC) MC-CDMA systems is confirmed over the realistic multi element transmit receive antennas (METRA) MIMO channel. Copyright

Electro magnetic compatibility for Power Line Communications

Within the ICT OMEGA project, a thorough study of the Electro Magnetic Compatibility (EMC) issues linked to Power Line Communications (PLC) has been conducted. In this paper, we present our investigations carried out in the context of a frequency bandwidth extension of PLC systems up to 100 MHz. The current status of EMC regulations for PLC is first recalled. An experimental study is then presented for the assessment of the effect of electromagnetic field radiation from an electrical network, in the 30 – 100 MHz band. Recommendations are given for the injected PSD levels to be used for future studies within the OMEGA project. From these results, the capacity of the PLC channel is evaluated in terms of outage probability. This analysis shows that an extended bandwidth up to 100 MHz provides capacities in excess of 1 Gbps, while satisfying the current emission limits. Finally, the possible countermeasures for the mitigation of EMC issues are discussed.

Range improvement of UWB systems using adaptive multicarrier spread‐spectrum and MIMO techniques

In this paper, we investigate the use of multiple-input multiple-output (MIMO) techniques with a linear precoded orthogonal frequency division multiplexing (LP-OFDM) waveform, known as spread-spectrum multicarrier multiple access (SS-MC-MA), for high data rate ultra-wideband (UWB) systems. This scheme is an evolution of the well-known multiband OFDM (MB-OFDM) solution supported by the WiMedia Alliance. The aim of this paper is to improve the UWB system range while not significantly increasing the system complexity compared to the WiMedia solution. Firstly, an analytical study of the single-input single-output (SISO) LP-OFDM waveform allows to find how to efficiently precode an OFDM signal in order to improve the system range. To go further and exploit the available spatial diversity, a MIMO component is added and a new geometric statistic MIMO channel model is considered. Secondly, a global MIMO LP-OFDM system study is led to highlight the benefits of combining MIMO and LP techniques for UWB applications. The analytical and simulation results show that the joint use of MIMO and LP-OFDM leads to a significant range improvement compared to the WiMedia solution. Copyright

Adaptive Spread Spectrum Multicarrier Multiple-Access for UWB Systems

Ultra-wideband (UWB) has emerged as an exciting technology for short range, high data rate wireless personal area networks (WPAN) applications. The multiband orthogonal frequency division multiplexing (MB-OFDM) scheme is one of the main candidates for WPAN standardization. In this paper, we propose a new UWB waveform based on a spread spectrum multicarrier multiple-access (SS-MC-MA) scheme that respects the OFDM parameters of the MB-OFDM solution. Then, we suggest an efficient low-complexity resource allocation algorithm that maximizes the total system throughput. Furthermore, we dynamically distribute the time-frequency codes that provide frequency hopping between users, in order to improve our system performance. We show that our proposed system transmits data at much higher attenuation levels and higher throughputs compared to the MB-OFDM system. Consequently, we conclude that our proposed system can be advantageously exploited for high data rate UWB applications.

Improved Throughput over Wirelines with Adaptive MC-DS-CDMA

In this paper, we present a finite-granularity loading algorithm for multicarrier direct sequence code division multiple access (MC-DS-CDMA). The resulting adaptive scheme represents an extension of classical digital multitone (DMT) with spreading in the time domain. The presented algorithm assigns subcarriers, spreading codes, bits and energy per code in order to maximize the data rate in a single user network, or to maximize the minimum data rate in a multiuser network. The optimization is realized at a target symbol error rate and for a given power spectral density (PSD). Optimal allocation is performed through analytical study, and simulation results of the new scheme are presented in single user digital subscriber line (DSL) and multiuser power line communication (PLC) contexts. Compared to DMT, it is shown that the time spreading component of MC-DS-CDMA system yields throughput improvement against a weak increase of complexity

STBC MC-CDMA systems for indoor and outdoor scenarios

We compare the performance of Alamoutis space-time block coded MC-CDMA systems for indoor and outdoor realistic scenarios with zero forcing or minimum mean square error detection schemes. Two different configurations of the system are considered for the two scenarios. The different results obtained as well for indoor as for outdoor scenarios demonstrate that spatial diversity improves significantly the performance of MC-CDMA systems. Then, Alamoutis STBC MC-CDMA schemes derive full benefit from the frequency and spatial diversities and can be considered as a very realistic and promising candidate for the air interface downlink of the 4th generation mobile radio systems.

Performance of MMSE STBC MC-CDMA over Rayleigh and MIMO Metra Channels

The performance of MMSE Single-user Detection (SD) and Multi-user Detection (MD) STBC MC-CDMA systems are analysed and compared in the case of two transmit antennas and one or two receive antennas over Rayleigh fading channels and then over the stochastic MIMO METRA channel model. With two transmit and one receive antennas, MD achieves a gain of roughly 1 dB for non-full load systems while the same performance are obtained with MD and SD for full load systems. Besides, with two receive antennas, we present a sub-optimal and an optimal MMSE SD MIMO MC-CDMA schemes, this last one offering a very good performance/complexity trade-off. Finally, the very good behaviour of MMSE STBC MC-CDMA systems is confirmed over the realistic METRA MIMO channel.