Opportunistic

Internet connectivity is nowadays an ubiquitous service. However, on the road we obtain access using costly and limited data cellular network subscriptions. This, along with significant network congestion, severely limits network use. Opportunistic access to indoor APs is limited by three factors. First, establishing a link to an AP requires a significant amount of time, and, second, links on the street usually have poor quality. Third, the lifetime of this link is very short in a moving car, due to indoor APs generally covering small areas of the street. Combined, these factors thwart opportunistic use of APs for Internet access. In this paper, we propose a novel approach that leverages the large number of parked cars to separate these three factors and tackle them independently: a parked car can connect to an AP with a link that, despite its poor quality, has a long lifetime. A moving vehicle can instead benefit from the better link with a parked car and use it as a relay. As our experiments show, our approach enables the use of this free, high throughput channel for a number of non time-sensitive applications, thus reducing cost and the load on the cellular network.

Cellular networks face significant capacity, efficiency and quality challenges because of the exponential growth of cellular data traffic. Multi-hop cellular networks (MCNs) have been proposed to address these challenges through the integration of cellular and device-to-device communications. This work investigates how the adoption and design of opportunistic store, carry and forward mechanisms in MCNs can help importantly decrease the energy consumption for delay tolerant traffic. To this aim, the study first derives an analytical framework to identify in two-hop scenarios the optimum mobile relay location and the location from which the mobile relay should start forwarding the information to the cellular base station in order to minimise the overall energy consumption. The derived optimum configuration is then used as a benchmark for the proposal and design of a novel context-based opportunistic MCN forwarding scheme that exploits context information provided at low cost by the cellular network. Numerical and simulation results demonstrate that the proposed context-based opportunistic forwarding can achieve a performance close to that obtain with the optimum configuration and reduce the energy consumption by more than 90% compared with traditional single-hop cellular communications.

Multiuser diversity refers to a kind of diversity present across different users in a fading environment. This diversity can be exploited by scheduling transmissions so that users transmit when their channel conditions are favorable. Exploiting multiuser diversity access, called also opportunistic access, conducts to a system efficiency that rises with the number of users. Different opportunistic IEEE 802.11 Medium Access Control (MAC) approaches have been proposed. The efficiency study of these approaches by NS-2 simulation is necessary for a performance comparison. The implementation of any opportunistic IEEE 802.11 MAC approach in NS-2 is based on using different cross-layer interactions between the physical layer and the link layer components which are the interface queue and the MAC sub layer. In this paper, we introduce the work that has been done to create a model for implementing these interactions. We also give the different functions we have implemented in NS-2 on the basis of this model. Any opportunistic approach can thus be implemented using these functions. Our contribution is providing an NS-2 extension that can be used to implement protocols exploiting multiuser diversity. We explain how to use our NS-2 extension by giving two examples showing the implementation of new opportunistic MAC protocols.

It has been shown that organized screening decreases prostate cancer (PC) mortality, but the effect of opportunistic screening is largely unknown. To compare the ability to reduce PC mortality and the risk of overdiagnosis between organized and opportunistic screening. The Göteborg screening study invited 10 000 randomly selected men for prostate-specific antigen (PSA) testing every 2 yr since 1995, with a prostate biopsy recommended for men with PSA ≥2.5 ng/ml. The control group of 10 000 men not invited has been exposed to a previously reported increased rate of opportunistic PSA testing. Both groups were followed until December 31, 2012. Observed cumulative PC incidence and mortality rates in both groups were calculated using the actuarial method. Using historical data from 1990-1994 (pre-PSA era), we calculated expected PC incidence and mortality rates in the absence of any PSA testing. The number needed to invite (NNI) and the number needed to diagnose (NND) were calculated by ...

Mobility is attracting more and more interests due to its importance for data forwarding mechanisms in many networks such as mobile opportunistic network. In everyday life mobile nodes are often carried by human. Thus, mobile nodes’ mobility pattern is inevitable affected by human social character. This paper presents a novel mobility model (HNGM) which combines social character and Gauss-Markov process together. The performance analysis on this mobility model is given and one famous and widely used mobility model (RWP) is chosen to make comparison..

It is understood that for a multi-unit series system, whenever one of the units stops to perform a preventive maintenance (PM) action, the whole series system must be stopped. At that time PM opportunities arise for the other units in the system. This paper proposes an opportunistic PM scheduling algorithm for the multi-unit series system based on dynamic programming with the integration of the imperfect effect into maintenance actions. An optimal maintenance practice is determined by maximizing the short-term cumulative opportunistic maintenance cost savings for the whole system. Matlab is considered for the optimization which is based on numerical simulation. Numerical examples are given throughout to show how this approach works. Finally, a comparison between the proposed PM model and other models is given.

In this paper, we model the adversary (eavesdropper) present in the wireless communication medium using probabilistic models. We precisely formulate the security-throughput optimization and derive analytical solutions. The effect of different adversary models, and single and multi-rate modulation schemes (BPSK and MQAM) are studied. Simulation results are given to show that significant throughput gain can be achieved by using link (channel) adaptive and adversary adaptive encryption techniques compared to fixed block length encryption.

The relationship between the distributions of predators and their prey is particularly strong for predators with specialised diets. Predicting the diet of omnivores is, however, more complex. We investigated the diet of the omnivorous nereidid polychaete, Pseudonereis variegata with respect to spatial scale, upwelling and small-scale behaviour. To investigate the diet of P. variegata across a range of spatial scales, shores in the Eastern and Western Regions, within the Warm Temperate South Coast (Agulhas) biogeographic province of South Africa were sampled. Two shores, kilometres apart within an area of upwelling and two within a non-upwelling area were sampled within each region. Gut-contents were composed of plants and animals. Neither region nor upwelling was found to affect the overall diet of P. variegata, with significant differences occurring only between shores in the Eastern Region. When the species were separated into plants and animals, in the Eastern Region, significantly more animals were consumed by P. variegata in the upwelling area compared to the non-upwelling area. Carefully designed laboratory experiments for preference showed that P. variegata consumed amphipods (various species of Gammaridae) and macroalgae (Hypnea spicifera), but rarely ate gastropods (Afrolittorina knysnaensis). It was clear that P. variegata rarely chose to eat gastropods, but there was no experimental evidence to support that they preferred amphipods and macroalgae over gastropods. Findings from the experiment based on gut-contents required knowledge of whether P. variegata were making active choices among the range prey that were available in the field. Similarly, the laboratory experiments in which individuals were offered different types of food required background knowledge of the entire suite of prey consumed and also an understanding of the broader-scale environmental factors influencing the diet of P. variegata. This study, therefore, highlights the usefulness of combining large-scale studies with carefully planned laboratory experiments that consider preferences for specific types of food.

Earnings management is a still attractive issue. It is often associated with negative behavior conducted by management for its own interest. In fact, it also has different side to be examined. There is another motivation to do so, such as to improve the company's operation. This literature study aims to review management motivation of doing earnings management, whether opportunistic or realistic. What conflict that earnings management brings, what pro and cons about it, what would happen if earnings is not managed, whether the company would be better off or worse off.

the HiV pandemic has given rise to a growing population of children at risk for infectious disease, particularly in the developing world where the majority of the estimated 2.5 million children living with human immunodeficiency virus (HiV) worldwide reside. this review will explore the opportunistic infections encountered in the HiV-infected child. Due to space constraints, only the commonest acquired immunodeficiency syndrome (AiDS)-defining infections, including mycobacterial, fungal, viral and parasitic diseases, will be discussed. the epidemiological, clinical and morphological features unique to the HiV-infected child will be highlighted, with special emphasis on the altered or unusual histopathological patterns that may be encountered and ancillary tests that may be valuable in confirming the diagnosis. Where applicable, the changing trends in the era of HAArt, including immune reconstitution inflammatory syndrome (iriS), will be addressed. ultimately, we hope to arm the practising histopathologist with information that will facilitate the accurate and timely diagnosis of imminently treatable opportunistic infections in the HiV-positive child.

Multiuser diversity can be employed in wireless communications to significantly improve system performance by scheduling the channel to the user with the best instantaneous channel-state information (CSI). Conventionally, all users' CSI must be available at the base station (BS) to achieve the benefit of multiuser diversity, thereby inducing enormous system overhead. To solve the overhead issue, we propose a user identification approach (UIDA) in a generic wireless network and demonstrate its application in the orthogonal frequency-division multiplexing (OFDM) system and the multiple-input multiple-output OFDM (MIMO-OFDM) system. In the UIDA, to find the user with the best CSI, all active users simultaneously send response messages to the BS following a broadcast probing message from the BS, and only the selected user's CSI needs to be available at the BS, thus reducing the system overhead. We present a theoretical upper bound of the throughput of the system with the UIDA over general channels, and its tightness over Rayleigh fading channels is verified by simulations. In addition, a modified UIDA is proposed to effectively trade off throughput and fairness performances, where only the active users whose signal-to-noise ratios (SNRs) are above their predetermined thresholds will send response messages. Compared with medium access diversity and multiuser diversity with capture (two alternative approaches in the literature for exploiting multiuser diversity) and with a similar system setup, simulation results show that the UIDA achieves better throughput performance when there are a reasonably large number of users.