In this letter, we investigate the physical layer security in multi-user multi-relay networks, where each relay is not merely a traditional helper, but at the same time, can become a potential eavesdropper. We first propose an efficient low-complexity user and relay selection scheme to significantly reduce the amount of channel estimation as well as the amount of potential links for comparison. For the proposed scheme, we derive the closed-form expression for the lower bound of ergodic secrecy rate (ESR) to evaluate the system secrecy performance. Simulation results are provided to verify the validity of our expressions and demonstrate how the ESR scales with the number of users and relays.

With quick topology changes due to mobile node movement or signal fading in MANET environments, conventional routing restoration processes are costly to implement and may incur high flooding of network traffic overhead and long routing path latency. Adopting the traditional shortest path tree (SPT) recomputation and restoration schemes used in Internet routing protocols will not work effectively for MANET. An object of the next generation SPT restoration system is to provide a cost-effective solution using an adaptive learning control system, wherein the SPT restoration engine is able to skip over the heavy SPT computation. We proposed a novel SPT restoration scheme, called Cognitive Shortest Path Tree Restoration (CSPTR). CSPTR is designed based on the Network Simplex Method (NSM) and Sensitivity Analysis (SA) techniques to provide a comprehensive and low-cost link failure healing process. NSM is used to derive the shortest paths for each node, while the use of SA can greatly reduce the effort of unnecessary recomputation of the SPT when network topology changes. In practice, a SA range table is used to enable the learning capability of CSPTR. The performance of computing and communication overheads are compared with other two well-known schemes, such as Dijstra's algorithm and incremental OSPF. Results show that CSPTR can greatly eliminate unnecessary SPT recomputation and reduce large amounts of the flooding overheads.

This study utilizes a new adaptive sense current controller to get an accurate power supply. The proposed controller effectively reduces output ripple voltage of converters operated over the load current range. This reduction is realized using an adaptive sense current circuit that automatically adjusts the inductor current according to operational conditions. The proposed boost converter is designed and fabricated with a standard TSMC 3.3/5 V 0.35-µm 2P4M CMOS technology. The experimental results show that the power-conversion efficiency of the proposed boost converter is 2-5% higher than that of the conventional converter with a current-limited circuit. The proposed circuit greatly reduces (i.e. by 76%) output ripple voltage compared with the conventional circuit at a 10 mA loading current.

Configurable clock is necessary for many applications such as digital communication systems, however, using the conventional direct digital frequency synthesizer (DDS) as a pulse or clock generator may cause jitter problems. People usually employ phase-interpolation approaches to generate a pulse or clock with correct time intervals. This work proposes a new phase-interpolation DDS scheme, which uses the output of the phase accumulator to provide an initial voltage on an integration capacitor by pre-charging in the first phase, and then performs integration operation on the same integration capacitor in the second phase. By using single capacitor integration, the instability of the delay generator existed in the phase-interpolation DDS can be avoided, and the impact caused by capacitance error in the circuit implementation also can be reduced. Furthermore, without ROM tables, the proposed DDS using pre-charging integration not only reduces the spurious level of the clock output, but also has a low hardware complexity.

Much recent research concentrates on designing an Intrusion Detection System (IDS) to detect the misbehaviors of the malicious node in MANET with ad-hoc and mobility natures. However, without rapid and appropriate IDS response mechanisms performing follow-up management services, even the best IDS cannot achieve the desired primary goal of the incident response. A competent containment strategy is needed to limit the extent of an attack in the Incident Response Life Cycle. Inspired by the T-cell mechanisms in the human immune system, we propose an efficient MANET IDS response protocol (T-SecAODV) that can rapidly and accurately disseminate alerts of the malicious node attacks to other nodes so as to modify their AODV routing tables to isolate the malicious nodes. Simulations are conducted by the network simulator (Qualnet), and the experiment results indicate that T-SecAODV is able to spread alerts steadily while greatly reduce faulty rumors under simultaneous multiple malicious node attacks.

The development of image acquisition technology and display technology provide the base for popularization of high-resolution images. On the other hand, the available bandwidth is not always enough to data stream such high-resolution images. Down- and up-sampling, which decreases the data volume of images and increases back to high-resolution images, is a solution for the transmission of high-resolution images. In this paper, motivated by the observation that the high-frequency DCT components are sparse in the spatial domain, we propose a scheme combined with Discrete Cosine Transform (DCT) and Compressed Sensing (CS) to achieve arbitrary-ratio down-sampling. Our proposed scheme makes use of two properties: First, the energy of a image concentrates on the low-frequency DCT components. Second, the high-frequency DCT components are sparse in the spatial domain. The scheme is able to preserve the most information and avoid absolutely blindly estimating the high-frequency components. Experimental results show that the proposed down- and up-sampling scheme produces better performance compared with some state-of-the-art schemes in terms of peak signal to noise ratio (PSNR), structural similarity index measurement (SSIM) and processing time.

In the design of a set-associative cache, maintaining low average access time and reducing the average energy dissipation are important issues. In this paper, we propose a set-associative cache that can provide the flexibility to configure its associativity according to different program behaviors, which means that the proposed cache scheme can be configured from n-way set-associative cache to direct-mapped cache. Besides, the proposed cache scheme also can disable all tag-subarrays and only enable a desired data-subarray when adjacent memory references are within the same block as the previous access. By this scheme, the power consumption can be saved when an n-way set-associative cache configures the cache with lower associativity (less than n) due to only enabling fewer subarrays of the tag memory and data memory, and when the tag checking is eliminated for the intra-block access due to disabling all subarrays of the tag memory. However, the performance is still maintained to the same as the conventional set-associative cache or the direct-mapped cache.

In this paper, we identify the tradeoff between security and reliability in the amplify-and-forward (AF) distributed beamforming (DBF) cooperative network with K untrusted relays. In particular, we derive the closed-form expressions for the connection outage probability (COP), the secrecy outage probability (SOP), the tradeoff relationship, and the secrecy throughput. Analytical and simulation results demonstrate that increasing K leads to the enhancement of the reliability performance, but the degradation of the security performance. This tradeoff also means that there exists an optimal K maximizing the secrecy throughput.