Antoine Stephan

Efficient Allocation Algorithms for Multicarrier Spread-Spectrum Schemes in UWB Applications

In this paper, we propose a multicarrier spread spectrum (MC-SS) waveform for high data rate UWB applications, taking into account the American and the European UWB contexts. This new waveform for UWB is presented as an evolution of the well known Multiband OFDM Alliance (MBOA) solution and does not increase the system complexity significantly. First, we optimize the number of spreading codes to maximize the system range for a fixed QPSK constellation. Secondly, we use variable constellation orders and we propose a low-complexity resource allocation algorithm that maximizes the system throughput. We show that our adaptive MC-SS system transmits information at much higher attenuation levels and with higher throughput compared to the MBOA solution, and can be advantageously exploited for UWB applications.

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.

MIMO UWB Systems Based on Linear Precoded OFDM for Home Gigabit Applications

In this paper, we investigate the use of multiple-input multiple-output (MIMO) techniques with linear precoded orthogonal frequency division multiplexing (LP-OFDM) waveform for high data rate ultra-wideband (UWB) systems. This scheme is an evolution of the multiband OFDM (MB-OFDM) solution supported by the WiMedia Alliance. The aim of this paper is to obtain a very high data rate of around one gigabit for home access networks (HAN) and to improve the system range for lower data rates, while not significantly increasing the system complexity compared to the WiMedia solution. Firstly, a single- input single-output (SISO) LP-OFDM system study is led to highlight the benefits of adding a preceding function to an OFDM signal in the UWB context. In an analytical study, different system choices and parameterization strategies are proposed in order to minimize the mean bit-error-rate (BER) and consequently improve the system range. Secondly, a MIMO scheme is added and global system simulations are performed on a proposed new geometric statistic MIMO channel model. We show that the proposed system can considerably improve the system range at low data rates, and can reach very high data rates up to 1 Gbit/s with comparable BER performances to WiMedia.

Resource allocation for multicarrier CDMA systems in ultra-wideband communications

Ultra-wideband (UWB) is a fast emerging technology that has attracted considerable interest in short range, high data rate wireless personal area networks (WPAN) applications. One of the main candidates for WPAN standardization is the multiband orthogonal frequency division multiplexing (MB-OFDM), supported by the Multiband OFDM Alliance (MBOA). In this paper, we propose a new low- complexity resource allocation algorithm applied to a spread spectrum multicarrier multiple-access (SS-MC-MA) waveform, which is new for high data rate UWB applications. The proposed scheme aims at maximizing the systems throughput while taking into consideration the WPAN environment and respecting the OFDM parameters of the MBOA solution. The adaptive allocation algorithm applied to OFDM and SS-MC-MA leads to roughly double the throughput compared to the MBOA solution at low attenuation levels. Furthermore, at high attenuation levels, SS- MC-MA outperforms the adaptive OFDM. Hence, we conclude that the proposed adaptive SS-MC-MA can especially be advantageously exploited for high attenuation UWB applications.

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.

Mean BER minimization loading algorithm for linear precoded OFDM

The problem of minimization of mean bit error rate (BER) of a linear precoded orthogonal frequency division multiplexing (LP-OFDM) system is considered. The discrete bit loading algorithms are proposed, which minimize the mean BER of the system for a target bit rate under a peak power constraint. The results are shown for a power line communication system using a well-known multipath channel model. The other, more common, robustness optimization problem is the margin maximization. The obtained results are compared with those of the margin maximization for both OFDM and LP-OFDM schemes. It is shown that the proposed LP-OFDM allocation performs better than the previously published algorithms for poor SNR. Moreover, it is observed that the LP-OFDM allocations have lower computational complexity than the OFDM allocations.

Bit rate maximization loading algorithm with mean BER-constraint for linear precoded OFDM

The bit loading algorithms are proposed for orthogonal frequency division multiplexing (OFDM) and linear precoded OFDM under power spectral density and mean bit error rate (BER) constraints. These algorithms maximize the bit rate of the system while respecting a mean BER. The advantages of both linear procoded OFDM and classical OFDM are analyzed under different scenarios. It is shown that the proposed allocations perform better than the allocations under peak error rate constraint, while respecting a power spectral density constraint. The performance of the proposed algorithms is also better than the previously proposed algorithm under mean BER constraint. Moreover, it is observed that the algorithms for linear precoded OFDM under mean BER constraint have significantly lower computational complexity.

Multi-user cross-layer allocation design for LP-OFDM high data rate UWB systems

In this paper, we investigate a cross-layer design for the packet scheduling and the resource allocation in UWB systems. This design considers the combination of queuing and channel state information (CSI) which provides QoS support for multimedia applications in UWB. For the physical layer, the use of a linear precoded orthogonal division multiplexing (LP-OFDM) waveform is proposed because of its significant performance increase compared to the WiMedia proposal. For the medium access control layer, scheduling is performed in order to differentiate between the different users and to satisfy their quality of service constraints. This cross-layer approach optimizes the system spectral efficiency and solves the problem in the WiMedia solution of cohabitation of more than three users sharing the three sub-bands of the same channel. Simulation results show that the proposed scheme leads to a considerable improvement in resource allocation and can guarantee the required quality of service.