Fatma Abdelkefi

A posteriori control of complex Reed Solomon decoding with application to impulse noise cancellation in HIPERLAN/2

In OFDM systems, pilot tones are emitted for synchronization or channel estimation purposes. These pilot tones are generally scattered among the information ones. Our approach is to use these pilot tones as syndromes, in order to correct impulse noise. We previously proposed (see Abdelkefi, F. et al., ISSPA, 2001) a decoding algorithm in three steps: (1) estimate the amount of impulse noise; (2) seek the location; (3) correct the errors. A protection subsystem was introduced after the decoding operation in order to detect malfunction. Indeed, we added a control step which is able to estimate carefully whether the decoding procedure has worked correctly. We now explain this a posteriori control which is based on the hypothesis test. This approach is new in impulse noise cancellation in multicarrier transmission. The efficiency of this technique is also corroborated with simulations in the practical context of HIPERLAN/2.

A Necessary Condition on the Location of Pilot Tones for Maximizing the Correction Capacity in OFDM Systems

This paper presents a new view of the Bose-Chaudhuri-Hocquengem (BCH) code through the addition of some flexibility to the syndromes distribution in the transmitted sequence. In order to get this flexibility, we derive a necessary condition (NC) on the syndromes distribution for decoding BCH codes, which includes the already known Hartmann-Tzeng proposition. This NC is essentially deduced from the decoding process of BCH code, and is related to the locator polynomial and the requested constraints to guarantee a maximal error-correction capacity. The obtained results have the advantage to be applicable for any considered field (finite or not). Furthermore, we prove that when the correction capacity is equal to 2 or 3, the obtained NC becomes also sufficient. This result is very useful in some practical transmission systems such as orthogonal frequency-division multiplexing systems. Once the pilot tones considered in such systems verify the necessary and sufficient condition, it becomes possible to both reduce the peak-to-average-power rate and correct the impulse noise, present in such multicarrier systems. The usefulness of the presented analysis and the exploitation of the derived condition on the pilot tones distribution is illustrated by simulation results in the case of the Hiperlan2 system

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.

Optimized Selective OFDMA in multihop network

Selective OFDMA is a powerfull relaying technique with subcarrier based selection. This scheeme has a high potential to considerably improve the performance of cooperative OFDM systems. However, in practice, the implementation of this technique may suffer from multiple problems caused by the separation of the subcarriers from each others. In this Contribution, we propose a new selection scheme denoted “Optimized Selective OFDMA” that approaches selective OFDMA performance in terms of outage probability while reducing its synchronization problems that may be caused by the subcarriers separation. The outage probability and diversity order of the proposed scheme are derived. The number of the used paths is also analyzed. We proved that for high SNR, the introduced scheme gives exactly the same performance of selective OFDMA with only one path for all the subcarriers.

Cooperative Spectrum Sensing With Heterogeneous Devices: Hard Combining Versus Soft Combining

Practical cognitive radio networks (CRNs) would have users with different capabilities and access levels to prior information about the primary users (PUs). For instance, some users may have the privilege to access information about the PU network, which can be utilized to increase the detection performance, whereas others may need to use simple detectors due to energy consumptions constraints, etc. This level of heterogeneity must be accommodated to enable coexistence of different secondary users’(SUs) networks. This paper presents performance analysis and comparison of hard and soft combining cooperative spectrum sensing schemes in heterogeneous CRNs. A centralized approach is considered for cooperative spectrum sensing with SUs that may use either energy detector, cyclostationary detector, pilot-based detector, or orthogonal frequency division multiplexing-based detector. For hard combining, each cooperative SU senses the spectrum using one of the available detectors and reports one-bit local decision to the fusion center which then applies

POPS-OFDM: Ping-pong Optimized Pulse Shaping-OFDM for 5G systems

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Capacity Analysis of an OFDM-Based Two-Hops Relaying PLC Systems

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Channel estimation errors impact on the sum rate maximisation in a JP-CoMP transmission systems

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Joint network coding and OFDMA based MAC-layer in PLC networks

rule for the final decision. For soft combining, we derive an optimal soft combining scheme based on the Neyman–Pearson criterion. Then, we drive a suboptimal rule to reduce the complexity of the proposed scheme. For the sake of simplicity, we consider only energy and cyclostationary detectors for soft combining. In addition, we study the impact of the cyclic frequency offset in case of a cyclostationary detector. Finally, the paper is supported with extensive simulation results that demonstrate the performance of proposed schemes in terms of probability of detection and probability of false alarm.

Novel power and time allocation algorithm for a Dynamic TDMA slot assignment multiuser transmission schemes

Recently, Orthogonal Frequency Division Multiplexing (OFDM) has gained more attention as an effective technique for high data rate future wireless communication systems. In order to provide maximal spectral efficiency, the prototype waveform, used in these systems, must guarantee orthogonality even the rapidly time-varying and strongly delay-spread characteristics of the channel propagation. However, its performance gain degrades in the presence of the system Inter-Carrier Interference (ICI) and Inter-Symbol Interference (ISI) which make it essential to develop an efficient technique to overcome these interference over the time-frequency dispersion of the radio mobile channel. In this paper, we propose a Ping-pong Optimized Pulse Shaping-OFDM (POPS-OFDM) algorithm that maximizes the received Signal to Interference plus Noise Ratio (SINR) by systematically optimizing the OFDM waveforms at the Transmitter (TX) and Receiver (RX) sides. We derived the exact closed-form expression of the SINR of the considered multicarrier system and the optimized waveform is searched as a linear combination of several of the most localized Hermite functions. The results confirm the advantage behind the POPS-OFDM algorithm in enhancing the performance compared to multicarrier systems using conventional waveforms. Simulations are given to support our claims.