Enabled by Multi-access Edge Computing (MEC) in a WiFi-cellular heterogeneous network, the tasks of mobile terminals (MTs) can be offloaded via the cellular network to the MEC servers or cloud ...server, or via the WiFi network to alleviate transmission congestion of the cellular network. The MEC also enables service caching to cache the programs/libraries/databases of the tasks to avoid repeated input data uploading. Existing research works lack joint optimization on the task offloading and service caching for MEC in the WiFi-cellular heterogeneous network. In this paper, a novel resource management scheme for joint task offloading and service caching is proposed to maximize the energy consumption benefits of all the MTs covered by a WiFi-cellular heterogeneous network while guaranteeing the task processing delay tolerance of each MT. We consider the constraints on limited computing and storage resources of the MEC servers equipped on the cellular base station and the WiFi access point, and we also consider cellular channel allocation for the task offloading. We design an iterative algorithm based on the alternating optimization technique to solve the proposed mixed integer nonlinear programming problem efficiently. Extensive simulations are conducted in multiple scenarios by varying different crucial parameters. The numerical results demonstrate that our scheme can largely improve the system performance in all the scenarios, and energy consumption reduction optimized by our scheme is 16.24%-43.09% higher than those by the comparative works.
A growing number of Internet-connected sensors have already promoted the advance of sensor search service. Accessing all available objects to find the sought sensor results in huge communication ...overhead, thus a low-overhead and high-precision prediction model (LHPM) is proposed to improve the sensor search efficiency. We design the approximation method to lower the reporting energy cost. Then a multistep prediction method is proposed to accurately estimate the sensor state. Furthermore, a sensor ranking method is presented to assess the matching probabilities of sensors, so as to effectively reduce the communication overhead of the search process. Simulation results demonstrate the validity of the proposed prediction model in the area of content-based sensor search.
Mobile edge computing (MEC) can augment the computation capabilities of mobile terminals (MTs) through offloading the computational tasks from the MTs to the MEC-enabled base station (MEC-BS) ...covering them. However, the load of MEC-BS will rise as the increase of the scale of tasks. Existing schemes try to alleviate the load of MEC-BS through refusing, postponing, or queuing the offloading requests of the MTs; thus, the users' QoS will largely deteriorate due to service interruption and prolonged waiting and execution time. In this paper, we investigate the cooperations of multiple MEC-BSs and propose a novel scheme to enhance the computation offloading service of an MEC-BS through further offloading the extra tasks to other MEC-BSs connected to it. An optimization algorithm is proposed to efficiently solve the optimization problem which maximizes the total benefits of time and energy consumptions gained by all the MTs covered by the MEC-BS. A balance factor is used to flexibly adjust the bias of optimization between minimizations of time and energy consumption. Extensive simulations are carried out in eight different scenarios, and the results demonstrate that our scheme can largely enhance the system performance, and it outperforms the reference scheme in all scenarios.
Android operating system occupies a high share in the mobile terminal market. It promotes the rapid development of Android applications (apps). However, the emergence of Android malware greatly ...endangers the security of Android smartphone users. Existing research works have proposed a lot of methods for Android malware detection, but they did not make the utilization of apps' functional category information so that the strong similarity between benign apps in the same functional category is ignored. In this paper, we propose an Android malware detection scheme based on the functional classification. The benign apps in the same functional category are more similar to each other, so we can use less features to detect malware and improve the detection accuracy in the same functional category. The aim of our scheme is to provide an automatic application functional classification method with high accuracy. We design an Android application functional classification method inspired by the hyperlink induced topic search (HITS) algorithm. Using the results of automatic classification, we further design a malware detection method based on app similarity in the same functional category. We use benign apps from the Google Play Store and use malware apps from the Drebin malware set to evaluate our scheme. The experimental results show that our method can effectively improve the accuracy of malware detection.
As a unique geological hazard in a high-geo-stress environment, rockburst happens with strong suddenness, randomness, and destructiveness, but the mechanism of its occurrence in a deep-buried tunnel ...in a high-geo-stress environment needs further study. Based on the analyses of the stress field of the rockburst section of Ping’an Tunnel, which is over-long and deep-buried, the occurrence mechanism of rockburst is figured out. Furtherly, the intensity and location of rockburst are predicted by using the rockburst criterion. Results show that there exists large compressive stress at the side wall of the tunnel, which is the main cause of rockburst. Under a high-geo-stress condition, due to the existence of unfavorable factors like structural planes, high intensity rockburst is likely to happen in the middle of the tunnel face after the sudden release of original rock stress. Arranging stress-releasing holes in the rockburst section can effectively reduce the possibility of rockburst by releasing the original rock stress in advance. The research results can deepen the understanding of the mechanism of rockburst in a high-geo-stress environment and provide scientific basis for the prevention and control of rockburst in similar engineering projects.
In this paper, a novel efficient continuous piecewise nonlinear companding scheme is proposed for reducing the peak-to-average power ratio (PAPR) of orthogonal frequency division multiplexing (OFDM) ...systems. In the proposed companding transform, signal samples with large amplitudes is clipped for peak power reduction, and the signal samples with medium amplitudes is nonlinear transformed with power compensation. While the signal samples with small amplitudes remain unchanged. The whole companding function is continuous and smooth in the range of positive numbers, which is beneficial for guaranteeing the bit error rate (BER) and power spectral density (PSD) performance. This scheme can achieve a significant reduction in PAPR. And at the same time, it cause little increment in BER and PSD performance. Simulation results indicate the superiority of the proposed scheme over existing companding schemes.
Water–air interaction (mixing of gas and water and gas dissolution into water) is one of the main reasons for gas loss in air cushion surge chambers. With the increase of water head in hydraulic ...power generation systems, the heat and mass transfer process at the water–air interface under high-pressure conditions intensifies, and the water–air interaction is further strengthened. If some gas is mixed/dissolved in water and enters downstream pipelines, it will affect the safety of the unit. At present, there has been no theoretical or systematic research on gas loss and related water gas two-phase flow in air cushion surge chambers under high-pressure conditions. Therefore, this article established an air loss model for an air cushion surge chamber based on the VOF model and gas–liquid mass transfer theory. We analyzed the mechanism of gas loss in the gas chamber through simulation and quantitatively expressed the gas loss. The results indicate that during a typical large fluctuation process, the gas–liquid mass transfer process at the water–air interface, air mass, and vortex is very strong, with a pressure chamber of approximately 923.89 m3. The gas dissolved in water enters the water diversion system, with a length of 28.75 m3. High pressure gas enters the water diversion system in the form of air masses. When considering the water inlet on the right side of the air chamber, the total gas loss in the air chamber is slightly lower (854.18 m3) and no mixed air mass was detected entering the connecting pipe.
An adaptive power loading algorithm with uniform (nonadaptive) bit allocation is proposed for constant data rate OFDM systems in this letter. This algorithm aims to minimize the transmit power while ...guaranteeing the target mean bit error rate (BER). The power loading is based on the unequal-BER (UBER) strategy which permits unequal mean BERs on different subcarriers. The closed-form expressions for optimal BER and power distributions are derived. Simulation results indicate the superiority of the proposed algorithm.
Sink mobility can improve the energy efficiency and data gathering performance in wireless sensor networks. However, mobility of the sink station may be constrained in some applications and it ...becomes a challenge to optimize the network performance for random distribution and hierarchical topology. We focus on prolonging the network lifetime and keep the data gathering performance at an acceptable level. To address this issue, we propose a comprehensive data gathering scheme based on graphing technique, called double optimization of energy efficiency (DOEE) to optimize the energy consumption of all sensor nodes hierarchically. The objective problem of DOEE is solved with a heuristic algorithm. Along with the scheme, we also specialize a route discovery protocol and its corresponding dynamic gateway protocol to balance the energy consumption among sensor nodes. The proposed algorithm and protocols are evaluated in the simulation platform Network Simulation-3 and the experiment results show our technique has superior performance.
Android occupies a very large market share in the field of mobile devices, and quantities of applications are created everyday allowing users to easily use them. However, privacy leaks on Android ...terminals may result in serious losses to businesses and individuals. Current permission model cannot effectively prevent privacy data leakage. In this paper, we find a way to protect privacy data on Android terminals from the perspective of privacy information propagation by porting the concept of contextual integrity to the realm of privacy protection. We propose a computational model of contextual integrity suiting for Android platform and design a privacy protection system based on the model. The system consists of an online phase and offline phase; the main function of online phase is to computing the value of distribution norm and making privacy decisions, while the main function of offline phase is to create a classification model that can calculate the value of the appropriateness norm. Based on the 6 million permission requests records along with 2.3 million runtime contextual records collected by dynamic analysis, we build the system and verify its feasibility. Experiment shows that the accuracy of offline classifier reaches up to 0.94. The experiment of the overall system feasibility illustrates that 70% location data requests, 84% phone data requests and 46% storage requests etc., violate the contextual integrity.
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