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

International audienceIn 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 high-light the benefits of adding a precoding function to an OFDM signal in the UWB context. In an analytical study, different sys-tem choices and parameterization strategies are proposed in or-der 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 pro-posed 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

Polaritonic modes in a dense cloud of atoms

We analyze resonant light scattering by an atomic cloud in a regime where near-field interactions between scatterers cannot be neglected. We first use a microscopic approach and calculate numerically the eigenmodes of the cloud for many different realizations. It is found that there always exists a small number of polaritonic modes that are spatially coherent and superradiant. We show that scattering is always dominated by these modes. We then use a macroscopic approach by introducing an effective permittivity so that the atomic cloud is equivalent to a dielectric particle. We show that there is a one-to-one correspondence between the microscopic polaritonic modes and the modes of a homogeneous particle with an effective permittivity

High Zn content of Randall's plaque: A μ-X-ray fluorescence investigation

Kidney stone disease, or nephrolithiasis, is a common ailment. Among the different risk factors usually associated with nephrolithiasis are dehydration, metabolic defects (especially with regard to calcium and oxalate). The presence of a mineral deposit at the surface of the renal papilla (termed Randall's plaque) has all been recently underlined. Of note, Randall's plaque is made of the calcium phosphate, carbapatite, and serves as a nucleus for kidney stone formation. The process by which apatite nanocrystals nucleate and form Randall's plaque remains unclear. This paper deals with the possible relationship between trace elements and the formation of this mineral. The investigation has been performed on a set of Randall's plaques, extracted from human kidney stones, through μ-X-ray diffraction and μ-X-ray fluorescence analyses in order to determine the chemical composition of the plaque as well as the nature and the amount of trace elements. Our data provide evidence that Zn levels are dramatically increased in carbapatite of RP by comparison to carbapatite in kidney stones, suggesting that calcified deposits within the medullar interstitium are a pathological process involving a tissue reaction. Further studies, perhaps including the investigation of biomarkers for inflammation, are necessary for clarifying the role of Zn in Randall's plaque formation

Adaptive multi-carrier spread-spectrum with dynamic time-frequency codes for UWB applications

International audienceIn this paper, we propose a spread spectrum multi-carrier multiple-access (SS-MC-MA) waveform for high data rate UWB applications, taking into consideration the European UWB context. This new UWB scheme respects the parameters of the multiband orthogonal frequency division multiplexing (MB-OFDM) technique which is one of the candidates for wireless personal area networks (WPAN) standardization. We optimize the spreading code length and the number of codes in our proposed scheme in order to maximize the system range for a given target throughput. Furthermore, we dynamically distribute the time-frequency codes that provide frequency hopping between users in order to improve our system range. We show that our adaptive system transmits information at much higher attenuation levels and with larger throughput than the ones of the MB-OFDM proposal. Hence, we conclude that our proposed system can be advantageously exploited for UWB applications

Resource allocation for multicarrier CDMA systems in ultra-wideband communications

International audienceUltra-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 system's 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

Efficient allocation algorithms for multicarrier spread-spectrum schemes in UWB applications

International audienceIn 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

Adaptive multi-carrier spread-spectrum with dynamic time-frequency codes for UWB applications

International audienceIn this paper, we propose a spread spectrum multi-carrier multiple-access (SS-MC-MA) waveform for high data rate UWB applications, taking into consideration the European UWB context. This new UWB scheme respects the parameters of the multiband orthogonal frequency division multiplexing (MB-OFDM) technique which is one of the candidates for wireless personal area networks (WPAN) standardization. We optimize the spreading code length and the number of codes in our proposed scheme in order to maximize the system range for a given target throughput. Furthermore, we dynamically distribute the time-frequency codes that provide frequency hopping between users in order to improve our system range. We show that our adaptive system transmits information at much higher attenuation levels and with larger throughput than the ones of the MB-OFDM proposal. Hence, we conclude that our proposed system can be advantageously exploited for UWB applications

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

International audienceIn 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 (LPOFDM) 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

Mean BER minimization loading algorithm for linear precoded OFDM

ISBN: 978-1-4244-3381-0International audienceThe 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