Olivier Berder

Optimal minimum distance-based precoder for MIMO spatial multiplexing systems

We describe a new precoder based on optimization of the minimum Euclidean distance d/sub min/ between signal points at the receiver side and for use in multiple-input multiple-output (MIMO) spatial multiplexing systems. Assuming that channel state information (CSI) can be made available at the transmitter, the three steps ( noise whitening, channel diagonalization and dimension reduction), which are currently used in investigations on MIMO systems, are performed. Thanks to this representation, an optimal d/sub min/ precoder is derived in the case of two different transmitted data streams. For quadrature phase-shift keying (QPSK) modulation, a numerical approach shows that the precoder design depends on the channel characteristics. Comparisons with maximum signal-to-noise ratio (SNR) strategy and other precoders based on criteria, such as water-filling (WF), minimum mean square error (MMSE), and maximization of the minimum singular value of the global channel matrix, are performed to illustrate the significant bit-error-rate (BER) improvement of the proposed precoder.

Cooperative MIMO Schemes Optimal Selection for Wireless Sensor Networks

A cooperative MIMO scheme selection is proposed for wireless sensor networks where energy consumption is the most important design criterion. Space-time block codes are designed to achieve maximum diversity for a given number of transmit and receive antennas with very simple decoding algorithm. In radio fading channel, STBC require less transmission energy than SISO technique for the same bit error rate and can be employed practically in wireless sensor networks by using the cooperative MIMO scheme. Considering Alamouti and Tarokh space-time block codes, the number of antennas at both the transmission and the reception sides are selected with respect to the transmission distance. By using cooperative MIMO transmission instead of SISO, it is shown that the distance between nodes can be increased and a large amount of the total energy can be saved for middle and long distance transmission. The energy efficiency of cooperative MIMO over SISO and multihop SISO is proved by simulations, and a multi-hop technique for cooperative MIMO is also proposed for good energy-efficiency and limited number of available cooperative nodes

TAD-MAC: Traffic-Aware Dynamic MAC Protocol for Wireless Body Area Sensor Networks

A wireless body area sensor network (WBASN) demands ultra low power and energy efficient protocols. Medium access control (MAC) layer plays a pivotal role for energy management in WBASN. Moreover, idle listening is the dominant energy waste in most of the MAC protocols. WBASN exhibits wide range of traffic variations based on different physiological data emanating from the monitored patient. For example, electrocardiogram data rate is multiple times more in comparison with body temperature rate. In this context, we propose a novel energy efficient traffic-aware dynamic (TAD) MAC protocol for WBASN. The protocol relies on dynamic adaptation of wake-up interval based on a traffic status register bank. The proposed technique allows the wake-up interval to converge to a steady state for fixed and variable traffic rates, which results in optimized energy consumption. A comparison with other energy efficient protocols for three different widely used radio chips i.e., cc2420, cc1000, and amis52100 is presented. The results show that TAD-MAC outperforms all the other protocols under fixed and variable traffic rates. Finally, life- time of a WBASN was estimated and found to be 3-6 times better than other protocols.

Minimum BER diagonal precoder for MIMO digital transmissions

We propose a minimum bit error rate (MBER) diagonal precoder for multi-input multi-output (MIMO) transmission systems. This work is based on previous results obtained by Sampath et al. (IEEE ISPACS, Honolulu, Hawaii, 2000, p. 823) in which the global transmission system (precoder and equalizer) is optimized with the minimum mean square error (MMSE) criterion. This process leads to an interesting diagonality property which decouples the MIMO channel into parallel and independent data streams and allows to perform an easy maximum likelihood (ML) detection. This system is then optimized using a new diagonal precoder that minimizes the BER. Our work is motivated by the fact that, from a practical point of view, people are likely to prefer a system that minimizes the BER rather than the mean square error. The performance improvement is illustrated via Monte Carlo simulations using a quadratic amplitude modulation (QAM).

Impact of Transmission Synchronization Error and Cooperative Reception Techniques on the Performance of Cooperative MIMO Systems

Wireless sensor networks where neighbor nodes can cooperate both at transmission and reception by using the cooperative multi-input multi-output (MIMO) technique are considered. Space-time diversity gain can be exploited to reduce the transmission energy consumption which is very important for average and long range transmission in wireless sensor network (WSN). However, differing from classical MIMO systems, cooperative systems suffer from the lack of synchronization between distributed nodes and the additive noise in the cooperative reception. At the cooperative transmission side, we investigate the effect of transmission synchronization error which generates inter-symbol interference (ISI), decreases the desired signal amplitude and makes the channel state information (CSI) more difficult to be estimated by the receiver. At the cooperative reception side, two strategies of wireless transmission techniques which are energy efficient and have good performance are also presented. The simulation of a cooperative MIMO system using Alamouti and Tarokh space-time block codes (STBC) over Rayleigh fading channels presents a performance degradation in the presence of transmission synchronization error and additional noise of cooperative reception techniques. For a small synchronization error range at cooperative transmission and a reasonable amplification factor in reception, the degradation is negligible and the cooperative MIMO performance is rather good.

Energy-Efficient Cooperative Techniques for Infrastructure-to-Vehicle Communications

In wireless distributed networks, cooperative relay and cooperative multiple-input-multiple-output (MIMO) techniques can be used to exploit the spatial and temporal diversity gains to increase the performance or reduce the transmission energy consumption. The energy efficiency of cooperative MIMO and relay techniques is then very useful for the infrastructure-to-vehicle (I2V) and infrastructure-to-infrastructure (I2I) communications in intelligent transport system (ITS) networks, where the energy consumption of wireless nodes embedded on road infrastructure is constrained. In this paper, applications of cooperation between nodes to ITS networks are proposed, and the performance and the energy consumption of cooperative relay and cooperative MIMO are investigated and compared with the traditional multihop technique. The comparison between these cooperative techniques helps us choose the optimal cooperative strategy in terms of energy consumption for energy-constrained road infrastructure networks in ITS applications.

Minimum Distance Based Precoder for MIMO-OFDM Systems Using a 16-QAM Modulation

A precoder based on the exact optimization of the minimum Euclidean distance dmin between signal points at the receiver side is proposed for MIMO-OFDM systems using a 16-QAM modulation. Assuming that channel state information (CSI) can be made available at the transmitter, the channel is diagonalized and a precoder can be derived. A numerical approach shows that the precoder design depends on the channel characteristics, leading to 8 different precoder expressions. Comparisons with maximum signal-to-noise ratio (SNR) strategy and other precoders based on criteria, such as water-filling (WF), minimum mean square error (MMSE), and maximization of the minimum singular value of the global channel matrix, are performed to illustrate the significant bit-error-rate (BER) improvement of the proposed precoder. In order to make its implementation easier, it is shown that it can be expressed by only two ways without significant performance degradation.

Minimum Euclidean Distance Based Precoders for MIMO Systems Using Rectangular QAM Modulations

From the feedback of the channel state information (CSI), precoding techniques improve the performance of multiple-input multiple-output (MIMO) systems by optimizing various criteria. In this correspondence, an efficient precoder that maximizes the minimum distance (dmin) of two received vectors is studied. This criterion leads to a nondiagonal precoding scheme and allows achieving a full diversity order. However, the optimized solution for MIMO systems using a high-order QAM modulation is rather complex and changes for different constellations. Therefore, we propose herein a general form of minimum Euclidean distance based precoders for all rectangular QAM modulations. It is shown that the new solution optimizes the distance dmin for small and large dispersive channels.

Ultra low power asynchronous MAC protocol using wake-up radio for energy neutral WSN

To extend the system lifetime of WSN, energy harvesting techniques have been considered as potential solutions for long-term operations. Instead of minimizing the consumed energy as for the case of battery-powered systems, the harvesting node is adapted to Energy Neutral Operation (ENO) to achieve a theoretically infinite lifetime. Therefore, consumed energy due to communications is the critical issue to increase the system performance. In this paper, a nano-watt wake-up radio receiver (WUR) is used cooperatively with the main transceiver in order to reduce the wasted energy of idle listening in asynchronous MAC protocols where the node is waiting for potential messages, while still maintaining the same reactivity. Simulation results show that the throughput can be improve up to 82% with 53% energy saving compared to non-WUR approach of the TICER protocol. Our simulations are performed on OMNET++ with three different widely radio chips CC2420, CC2500 and CC1100 using models with measured data.

Duty-cycle power manager for thermal-powered Wireless Sensor Networks

Exploiting energy from the environment to extend the system lifetime of Wireless Sensor Network (WSN), especially thermal energy, is considered as a promising approach. When considering self-powered systems, the Power Manager (PM) plays an important role in energy harvesting WSNs. Instead of minimizing the consumed energy as in the case of battery-powered systems, it causes the harvesting node to converge to Energy Neutral Operation (ENO) in order to achieve a theoretically infinite lifetime. In this paper, a low complexity PM for a thermal-powered WSN is presented. Our PM adapts the duty cycle of the node according to the estimation of harvested energy and the consumed energy provided by a simple energy monitor for a super capacitor based WSN to achieve the ENO. Experiments are performed on a real WSN platform where harvested energy is extracted from the wasted heat of a PC adapter by two thermoelectric generators.