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

Precoded FIR and Redundant V-BLAST Systems for Frequency-Selective MIMO Channels

The vertical Bell labs layered space-time (V-BLAST) system is a multi-input multioutput (MIMO) system designed to achieve good multiplexing gain. In recent literature, a precoder, which exploits channel information, has been added in the V-BLAST transmitter. This precoder forces each symbol stream to have an identical mean square error (MSE). It can be viewed as an alternative to the bit-loading method. In this paper, this precoded V-BLAST system is extended to the case of frequency-selective MIMO channels. Both the FIR and redundant types of transceivers, which use cyclic-prefixing and zero-padding, are considered. A fast algorithm for computing a cyclic-prefixing-based precoded V-BLAST transceiver is developed. Experiments show that the proposed methods with redundancy have better performance than the SVD-based system with optimal powerloading and bit loading for frequency-selective MIMO channels. The gain comes from the fact that the MSE-equalizing precoder has better bit-error rate performance than the optimal bitloading method

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

New Iterative Frequency-Domain Detectors for IA-Precoded MC-CDMA Systems

The aim of this paper is to design new multi-user receivers based on the iterative block decision feedback equalization concept for MC-CDMA systems with closed-form interference alignment (IA) at the transmitted side. IA is a promising technique that allows high capacity gains in interfering channels. On the other hand, iterative frequency-domain detection receivers based on the IB-DFE concept can efficiently exploit the inherent space-frequency diversity of the MIMO MC-CDMA systems. In IA-precoded based systems the spatial streams are usually separated by using a standard linear MMSE equalizer. However, for MC-CDMA based systems, linear equalization is not the most efficient way of separating spatial streams due to the residual inter-carrier interference (ICI). Therefore, we design new non-linear iterative receiver structures to efficiently remove the aligned interference and separate the spatial streams in presence of residual ICI. Two strategies are considered: in the first one the equalizer matrices are obtained by minimizing the mean square error (MSE) of each individual data stream at each subcarrier, while in the second approach the matrices are computed by minimizing the overall MSE of all data streams at each subcarrier. We also propose an accurate analytical approach for obtaining the performance of the proposed receivers. Our schemes achieve the maximum degrees of freedom provided by the IA precoding, while allowing close-to-optimum space-diversity gain, with performance approaching the matched filter bound

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

An efficient channel condition aware proportional fairness resource allocation for powerline communications

ISBN: 978-1-4244-2936-3International audiencePowerline communications (PLC) become a viable local area network (LAN) solution for in-home networks. We are witnessing a growing number of in-home devices and services using PLC systems. In this paper, the resource allocation problem with peak BER constraint is investigated in multiuser context. A new proportional fairness resource allocation algorithm which takes into account the channel conditions is proposed for the downlink. This algorithm is based on linear precoded OFDM (LP-OFDM) which enables reliable high bit rate transmission under peak BER constraint. The algorithm tries to maximize the overall throughput of the system under different users required bit rate constraints. Simulations are run over PLC channels and it is shown that proposed algorithms under peak BER constraint give better performance than classical proportional fairness algorithms. In addition, the linear precoding technique brings significant data rate gain and reduces the number of unsatisfied users

An efficient channel condition aware proportional fairness resource allocation for powerline communications

ISBN: 978-1-4244-2936-3International audiencePowerline communications (PLC) become a viable local area network (LAN) solution for in-home networks. We are witnessing a growing number of in-home devices and services using PLC systems. In this paper, the resource allocation problem with peak BER constraint is investigated in multiuser context. A new proportional fairness resource allocation algorithm which takes into account the channel conditions is proposed for the downlink. This algorithm is based on linear precoded OFDM (LP-OFDM) which enables reliable high bit rate transmission under peak BER constraint. The algorithm tries to maximize the overall throughput of the system under different users required bit rate constraints. Simulations are run over PLC channels and it is shown that proposed algorithms under peak BER constraint give better performance than classical proportional fairness algorithms. In addition, the linear precoding technique brings significant data rate gain and reduces the number of unsatisfied users

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