Hichem Besbes

A fast adaptive predistorter for nonlinearly amplified M-QAM signals

M-QAM has been considered to achieve high bandwidth efficiency for broadband wireless communications. However, due to its envelope fluctuation, it exhibits large spectral re-growth and performance degradation when the transmit power amplifier operates in a nonlinear region close to saturation. In this paper, an adaptive predistortion technique suitable for DSP implementation at the baseband signals is introduced to counter-balance the AM/AM and AM/PM nonlinear effects of the transmit power amplifier. Based on nonlinear adaptive Volterra filtering, the proposed pre-distortion technique shows that M-QAM can be used with a transmit power amplifier operating near saturation to a highest power efficiency, while its transmitted spectrum and performance are kept close to those in a linear channel. The convergence behavior of the adaptive predistortion technique is analyzed. The spectral re-growth and performance of a 16 QAM system using a predistorter/SSPA are evaluated using simulation. The adaptive predistortion technique has a low complexity and fast convergence.

A fast adaptive polynomial predistorter for power amplifiers

In this paper, an adaptive polynomial predistortion technique is introduced to counterbalance the AM/AM and AM/PM nonlinear effects of the transmit power amplifier. Based on a polar coordinate representation, the proposed adaptation method has low complexity and guarantees a fast rate of convergence. Simulation results on spectra, bit error rates, and intermodulation distortion show that with the polynomial predistorter, M-QAM can be used with a transmit power amplifier operating near saturation to achieve the highest power efficiency, while its transmitted spectrum and performance are kept close to those in a linear channel. The effects of the quantization are also presented.

QoS and Energy Aware Cooperative Routing Protocol for Wildfire Monitoring Wireless Sensor Networks

Wireless sensor networks (WSN) are presented as proper solution for wildfire monitoring. However, this application requires a design of WSN taking into account the network lifetime and the shadowing effect generated by the trees in the forest environment. Cooperative communication is a promising solution for WSN which uses, at each hop, the resources of multiple nodes to transmit its data. Thus, by sharing resources between nodes, the transmission quality is enhanced. In this paper, we use the technique of reinforcement learning by opponent modeling, optimizing a cooperative communication protocol based on RSSI and node energy consumption in a competitive context (RSSI/energy-CC), that is, an energy and quality-of-service aware-based cooperative communication routing protocol. Simulation results show that the proposed algorithm performs well in terms of network lifetime, packet delay, and energy consumption.

Fast communication: Frequency estimation of real-valued single-tone in colored noise using multiple autocorrelation lags

The problem of frequency estimation of a real-valued sinusoid in colored noise is addressed. A new estimator using higher-order lags of the sample autocorrelation is proposed, and a statistical analysis is provided. Computer simulations are included to validate the theoretical development and to demonstrate that the proposed approach outperforms several existing frequency estimators in terms of estimation accuracy.

On exact convergence results of adaptive filters: the finite alphabet case

Abstract This paper introduces a tailored approach for the convergence analysis of adaptive filters governed by the LMS algorithm. The finite alphabet input case is considered, which corresponds to real digital transmission contexts. Complete and rigorous proofs for almost sure and mean-square convergences are provided without any constraining independence assumptions on the observation vector. An exact and useful bound of the critical step size is presented. Exact transient performances such as critical step size, speed of transient decrease, optimal step size and directionality of convergence, are deduced.

A Simple Superposition Coding Scheme for Optimizing Resource Allocation in Downlink OFDMA Systems

In this paper, we propose to apply a simple superposition coding strategy for downlink of OFDMA systems. The novelty of this paper consists on allowing at most two users to share the same subchannel. The main idea is to consider the subchannels allocated to the users with the weakest link, and allow these subchannels to be shared by some potential users who can transmit some number of bits with only a small amount of power. To decrease the overhead of the proposed OFDMA system, we restrict to use a predetermined superposition encoding|decoding scheme. We address the problem of resource allocation, which consists on finding the optimal subchannel assignment in the OFDMA system. A low complexity algorithm, denoted Share Specific Subcarrier Allocation (SSSA) is then proposed. It offers a fairness allocation among users. This can be done by taking into account all user’s buffer states information. Simulation results confirm that the proposed technique outperforms the classical algorithms in terms of total throughput and dropping probability.

Outage Performance of OFDM Ad-Hoc Routing with and without Subcarrier Grouping in Multihop Network

In this contribution, we investigate Decode and Forward (DF) OFDM Ad-hoc Routing strategy with bottleneck maximization. We derive the exact outage probability and diversity order for the different scenarios: with and without subcarrier grouping and with and without joint selection, where joint selection refers to the selection of the last two hops together. When joint selection is performed, numerical results show that a power gain can be obtained when using subcarrier grouping technique.

Radio resource allocation scheme for intra-inter-cell D2D communications in LTE-A

Device-to-Device (D2D) communications provide the means to users of cellular networks for reusing licensed spectrum by creating a direct link between two devices. However, enabling D2D communications in a cellular network presents a challenge in resource allocation because of the potential severe interference it may cause to the cellular network due to the reuse of the spectrum with the cellular users. Such interference can be prevented otherwise diminish if radio resource assigned intelligently with the coordination from the eNodeB (eNB). In this paper, we analyze the resource allocation problem in a multi cell environment and we propose a new scheme for Intra-Inter-Cell D2D communication when both Intra Cell D2D (Intra-cell-D2D) and Inter Cell D2D communication(Inter-cell-D2D) are present in the system.

Application of smoothed estimators in spectrum sensing technique based on model selection

In cognitive radio networks, secondary user (SU) does not have rights to transmit when the primary user (PU) band is occupied, thats why a sensing technique must be done. Recently, a new blind spectrum sensing technique based on distribution analysis was developed for sensing the spectrum holes in the PU band. Specifically, assuming that the noise of the radio spectrum band can still be adequately modeled using Gaussian distribution, this detector decide if the distribution of the received signal fits the noise distribution or not. This technique is computationally simple and fast. In this paper1, we investigate the effect of applying smoothed estimators for this spectrum sensing technique. We will show that the application of smoothed periodograms offers good performances and keeps a reasonable complexity. Simulations results and performances evaluation presented in this paper are based on experimental measurements captured by Eurécom RF Agile Platform.

A New Modulation Scheme for Rapid Blind Timing Acquisition using Dirty Template Approach for UWB Systems

Timing acquisition is one of the major challenges in ultra-wideband (UWB) communications. The timing with dirty template (TDT) approach is an attractive technique for UWB systems, which is characterized by its low complexity and fast acquisition in the data-aided (DA) mode. However, in the non-data-aided (NDA) mode, the performance of this approach degrades due to the random symbol effect. In this paper, we propose to overcome this issue by adopting orthogonal pulse-shape modulation (PSM) proposed in L.B. Michael et al. (2002), (M. Pinchas and B.Z. Bobrovsky, 2003). Our algorithm uses a train of alternating orthogonal Hermite pulses to modulate the transmitted symbols. The application of the TDT approach to the proposed scheme shows an enhancement of synchronization speed in the NDA mode. Simulations confirm performance improvement of TDT with the proposed modulation relative to the original TDT in terms of the mean square error (MSE) and the acquisition probability.