Combination of Space-Time Block Coding with MC-CDMA Technique for MIMO systems with two, three and four transmit antennas

For future wideband wireless networks, space diversity schemes relying on multiple antennas at the receiver and/or at the transmitter are very attractive to combat fadings and improve the transmission performance. In this paper, Multi-Carrier Code Division Multiple Access (MC-CDMA) technique combined with several Space-Time Block Codes (STBC) is analyzed in the case of Nt transmit antennas and Nr receive antennas to provide a diversity order of NtNr for a 2 bps/Hz spectral efficiency. A general method to decode STBC from orthogonal designs associated with MC-CDMAis proposed. Two Single-user Detection techniques, Zero Forcing (ZF) and Minimum Mean Square Error (MMSE), are studied and compared in the downlink synchronous case over frequency selective Rayleigh channels

Estimating and Tracking Wireless Channels Under Carrier and Sampling Frequency Offsets

This article addresses the challenge of estimating and tracking wireless channels under carrier and sampling frequency offsets, which also incorporate phase noise and sampling time jitter. We propose a novel adaptive filter that explicitly estimates the channel impulse response, carrier frequency offset, and sampling frequency offset by minimizing the mean-square error (MSE) and, when the estimated parameters are time-varying, inherently performs tracking. The proposed filter does not have any requirements for the structure of the waveform, but the digital transmitted waveform must be known to the receiver in advance. To aid practical implementation, we derive upper bounds for the filter's step sizes. We also derive expressions for the filter's steady-state MSE performance, by extending the well-known energy conservation relation method to account for the self-induced nonstationarity and coupling of update equations that are inherent in the proposed filter. Theoretical findings are verified by comparison to simulated results. Proof-of-concept measurement results are also provided, which demonstrate that the proposed filter is able to estimate and track a practical wireless channel under carrier and sampling frequency offsets.publishedVersionPeer reviewe

Physical-Layer Reliability of Drones and Their Counter-Measures: Full vs. Half Duplex

In this article, we study the advantages and disadvantages that full-duplex (FD) radio technology brings to remote-controlled drone and counter-drone systems in comparison to classical half-duplex (HD) radio technology. We consider especially the physical-layer reliability perspective that has not yet been comprehensively studied. For establishing a solid analytical background, we first derive original closed-form expressions to evaluate demodulation and detection performance of frequency-hopped and frequency-shift keyed drone remote control signals under external or self-inflicted interference. The developed analytical tools are verified by comparison to simulated results and then used to study the impact that the operation mode has on the operable area of drones and effectiveness of counter-drone systems in different scenarios, linking the physical layer performance to practical safety. Analysis of the scenarios shows that FD operation compared to HD can improve the effectiveness of a counter-drone system and that in FD mode a drone can detect the attacks from the counter-drone system from a greater distance than in HD mode. However, two-way communication between the remote controller and drone in FD mode compared to HD significantly reduces the drone’s operable area when targeted by a smart counter-drone system.Peer reviewe

Known-Interference Cancellation in Cooperative Jamming : Experimental Evaluation and Benchmark Algorithm Performance

Physical layer security is a sought-after concept to complement the established upper layer security techniques in wireless communications. An appealing approach to achieve physical layer security is to use cooperative jamming with interference that is known to and suppressible by the legitimate receiver but unknown to, and hence not suppressible by, the eavesdropper. Suppressing known interference (KI), however, is challenging due to the numerous unknowns, including carrier and sampling frequency offsets, that impact its reception. This letter presents a measurement campaign that captures this challenge and then demonstrates the feasibility of solving that challenge by cancelling the KI using the frequency offsets least mean squares (FO-LMS) algorithm. Results show that KI suppression directly improves processing the signal-of-interest and that cooperative jamming effectively provides security at the physical layer.Peer reviewe

Codage temps-espace en blocs combiné avec un système multiporteuse à étalement de spectre de type MC-CDMA

Ce papier présente les performances de systèmes MIMO MC-CDMA à Nt antennes d'émission et Nr antennes de réception offrant une efficacité spectrale de 1 ou 2 bit/s/Hz. Les résultats sont obtenus pour différents schémas de codage temps-espace en blocs (STBC) dans le cas de la liaison descendante synchrone sur des canaux de Rayleigh sélectifs en fréquence pour les deux techniques de détection Zéro-Forcing (ZF) et Minimum Mean Square Error (MMSE). En outre, une méthode générale pour décoder les codes STBC orthogonaux associés aux signaux MC-CDMA est décrite. Par ailleurs, ces résultats démontrent l'intérêt d'un système STBC MC-CDMA reposant sur l'utilisation de codes temps-espace de rendement 1, et qu'il est en conséquence préférable d'utiliser la redondance au niveau du codage de canal et non au niveau du codage temps-espace

Large-Scale Cortical Dynamics of Sleep Slow Waves

Slow waves constitute the main signature of sleep in the electroencephalogram (EEG). They reflect alternating periods of neuronal hyperpolarization and depolarization in cortical networks. While recent findings have demonstrated their functional role in shaping and strengthening neuronal networks, a large-scale characterization of these two processes remains elusive in the human brain. In this study, by using simultaneous scalp EEG and intracranial recordings in 10 epileptic subjects, we examined the dynamics of hyperpolarization and depolarization waves over a large extent of the human cortex. We report that both hyperpolarization and depolarization processes can occur with two different characteristic time durations which are consistent across all subjects. For both hyperpolarization and depolarization waves, their average speed over the cortex was estimated to be approximately 1 m/s. Finally, we characterized their propagation pathways by studying the preferential trajectories between most involved intracranial contacts. For both waves, although single events could begin in almost all investigated sites across the entire cortex, we found that the majority of the preferential starting locations were located in frontal regions of the brain while they had a tendency to end in posterior and temporal regions

Large expert-curated database for benchmarking document similarity detection in biomedical literature search

Document recommendation systems for locating relevant literature have mostly relied on methods developed a decade ago. This is largely due to the lack of a large offline gold-standard benchmark of relevant documents that cover a variety of research fields such that newly developed literature search techniques can be compared, improved and translated into practice. To overcome this bottleneck, we have established the RElevant LIterature SearcH consortium consisting of more than 1500 scientists from 84 countries, who have collectively annotated the relevance of over 180 000 PubMed-listed articles with regard to their respective seed (input) article/s. The majority of annotations were contributed by highly experienced, original authors of the seed articles. The collected data cover 76% of all unique PubMed Medical Subject Headings descriptors. No systematic biases were observed across different experience levels, research fields or time spent on annotations. More importantly, annotations of the same document pairs contributed by different scientists were highly concordant. We further show that the three representative baseline methods used to generate recommended articles for evaluation (Okapi Best Matching 25, Term Frequency-Inverse Document Frequency and PubMed Related Articles) had similar overall performances. Additionally, we found that these methods each tend to produce distinct collections of recommended articles, suggesting that a hybrid method may be required to completely capture all relevant articles. The established database server located at https://relishdb.ict.griffith.edu.au is freely available for the downloading of annotation data and the blind testing of new methods. We expect that this benchmark will be useful for stimulating the development of new powerful techniques for title and title/abstract-based search engines for relevant articles in biomedical research.Peer reviewe