Telex Magloire Nkouatchah Ngatched

Visible Light Communications (VLC) Technology

This article reviews the visible light communications (VLC), a technology in which the visible spectrum is modulated to transmit data. It presents the VLC communication system: the transmitter, the channel, and the receiver. The single and multichannel transceivers are presented. The channel for a system that uses a single light-emitting diodes (LED) and the matrix representing the multicolor channel are discussed. Various modulation schemes, basic techniques used to implement a VLC system, and different causes of dimming are discussed. In addition, standardization of the VLC technology, applications, as well as challenges for VLC practical implementation and commercialization are reviewed. Keywords: dimming control; MIMO; modulation methods; optical wireless communications; VLC; VLC technology

Performance analysis of cognitive radio networks with channel assembling and imperfect sensing

This paper investigates the performance of a wideband cognitive radio network where each cognitive user can assemble multiple primary channels. Two channel assembling schemes are considered: a constant channel assembling (CCA) and a variable channel assembling (VCA). In the variable channel assembling scheme, cognitive users assemble their channels on the basis of the number of detected residual channels that are unoccupied by primary users or cognitive users. The effects of imperfect spectrum sensing (with false alarms and misdetections) are taken into account and it is assumed that spectrum handover is implemented in the secondary network. These channel assembling schemes are analyzed by using Continuous-time Markov chains (CTMC), and the system performance is evaluated in terms of throughput, blocking probability, and forced termination probability. Numerical results show that channel assembling achieves lower forced termination probability, but does not increase achieved system throughput and leads to higher blocking probability. They also show that VCA outperforms CCA in terms of throughput and forced termination probability.

Spatial Modulation in MIMO Limited-Feedback Spectrum-Sharing Systems With Mutual Interference and Channel Estimation Errors

This letter investigates spatial modulation (SM) in multiple-input multiple-output (MIMO) spectrum-sharing systems in an effort to improve the overall spectral efficiency. Specifically, we study the secondary system performance adopting the SM technique under mutual primary-secondary interferences and channel estimation errors (CEEs). With limited feedback from the primary receiver, a closed-form expression for the average pairwise error probability, a tight upper bounded average bit error rate expression, and an approximate simple, yet accurate expression are derived over Rayleigh fading channels. Simulation results, which corroborate the numerical ones, show the importance of SM in improving the overall secondary performance and its robustness to CEEs.

Joint timing and frequency synchronization based on weighted CAZAC sequences for reduced-guard-interval CO-OFDM systems.

A novel joint symbol timing and carrier frequency offset (CFO) estimation algorithm is proposed for reduced-guard-interval coherent optical orthogonal frequency-division multiplexing (RGI-CO-OFDM) systems. The proposed algorithm is based on a constant amplitude zero autocorrelation (CAZAC) sequence weighted by a pseudo-random noise (PN) sequence. The symbol timing is accomplished by using only one training symbol of two identical halves, with the weighting applied to the second half. The special structure of the training symbol is also utilized in estimating the CFO. The performance of the proposed algorithm is demonstrated by means of numerical simulations in a 115.8-Gb/s 16-QAM RGI-CO-OFDM system.

Cooperative AF Relaying With Beamforming and Limited Feedback in Cognitive Radio Networks

This letter studies cooperative beamforming for dual-hop amplify and forward cognitive relay networks comprising a pair of secondary source-destination and multiple antenna relay in the presence of a pair of primary transmitter-receiver. The aim of this work is to improve the secondary system performance with limited feedback from the primary receiver while using a mean value-based power allocation strategy. We derive closed-form expressions for the outage probability and average error probability over Rayleigh fading channels. Numerical and simulation results demonstrate the impact of the limited feedback on the secondary system performance and show that an acceptable performance is achieved when compared with the case of perfect channel state information.

Efficient decoding of generalized low-density parity-check codes based on long component codes

A class of pseudo-random compound error-correcting codes, called generalized low density (GLD) parity-check codes, has been proposed recently. As a generalization of Gallagers low-density parity check (LPDC) codes, GLD codes are also asymptotically good in the sense of minimum distance criterion and can be effectively decoded based on iterative soft-input soft-output (SISO) decoding of individual constituent codes. The code performance and decoding complexity of GLD codes are heavily dependent on the employed SISO decoding algorithm. In this paper, we present an efficient SISO decoding algorithm for GLD codes. The proposed algorithm utilizes Kanekos decoding algorithm for soft-input hard-output decoding. These hard outputs are converted to soft-decision using reliability calculations. The algorithm proposed here presents a major advantage over existing decoding algorithms for GLD codes by being applicable even when long and powerful component codes are used. The complexity of the proposed algorithm is less than that of trellis-based decoding algorithms with a performance degradation of only 0.3 dB.

Analysis of Cognitive Radio Networks with Channel Aggregation and Imperfect Sensing

This paper considers a cognitive radio network where the cognitive user has a constant bandwidth which is K times that of a primary user. The primary system consists of constant

Multiple-Votes Parallel Symbol-Flipping Decoding Algorithm for Non-Binary LDPC Codes

M

Outage capacity and throughput analysis of multiuser FSO systems

primary channels and the cognitive system consists of

Analysis of cognitive radio networks with channel assembling, buffering, and imperfect sensing

N=\left\lfloor M/K\right\rfloor