Adaptive Packetization for Conversational Video Service over IEEE 802.11 WLANs with Hidden Terminals

For IEEE 802.11-based wireless local area networks (WLANs), due to inherent random access mechanisms, it is very challenging to provision video services, which are subject to very stringent quality-of-service (QoS) constraints. Collision and fading are two main sources of packet loss in WLANs and as such, both are affected by the packetization at the medium access control (MAC) layer. While a larger packet is preferred to balance protocol header overhead, a shorter packet is less vulnerable to packet loss due to channel fading errors or staggered collisions in the presence of hidden terminals. In this paper, we exploit estimate of collision probabilities to adapt packetization for video frames. We first show analytically that the effective throughput is a unimodal function of packet size when considering both channel fading and staggered collisions. We then design an additive increase and multiplicative decrease (AIMD) packetization strategy which adjusts the MAC-layer packet size based on local estimate of staggered collision probability. It is demonstrated that the proposed approach can greatly improve the effective throughput of WLAN and reduce video frame transfer delay.     

A High Throughput Configurable SDR Detector for Multi-user MIMO Wireless Systems

Spatial division multiplexing (SDM) in MIMO technology significantly increases the spectral efficiency, and hence capacity, of a wireless communication system: it is a core component of the next generation wireless systems, e.g. WiMAX, 3GPP LTE and other OFDM-based communication schemes. Moreover, spatial division multiple access (SDMA) is one of the widely used techniques for sharing the wireless medium between different mobile devices. Sphere detection is a prominent method of simplifying the detection complexity in both SDM and SDMA systems while maintaining BER performance comparable with the optimum maximum-likelihood (ML) detection. On the other hand, with different standards supporting different system parameters, it is crucial for both base station and handset devices to be configurable and seamlessly switch between different modes without the need for separate dedicated hardware units. This challenge emphasizes the need for SDR designs that target the handset devices. In this paper, we propose the architecture and FPGA realization of a configurable sort-free sphere detector, Flex-Sphere, that supports 4, 16, 64-QAM modulations as well as a combination of 2, 3 and 4 antenna/user configuration for handsets. The detector provides a data rate of up to 857.1 Mbps that fits well within the requirements of any of the next generation wireless standards. The algorithmic optimizations employed to produce an FPGA friendly realization are discussed.     

Scene categorization based on local–global feature fusion and multi-scale multi-spatial resolution encoding

With the bag-of-contextual-visual-word (BOCVW) models, we propose a scene categorization method based on local–global feature fusion and multi-scale multi-spatial resolution encoding. First, the performances of the BOCVW models belonging to different features are mutually reinforced by fusing other types of features within local regions. Then, the spatial configuration information is explored using a multi-scale multi-spatial resolution encoding approach. Furthermore, these encoded BOCVW models are globally fused using an improved maximum-margin optimization strategy, which considers the margin between input vectors of different categories and the diameter of the smallest ball containing feature vectors simultaneously. The proposed method has been evaluated on three scene categorization datasets consisting of scene categories 8, 15, and 67, respectively. And its effectiveness has been verified by these experimental results.     

Photoactive Electrodes Incorporating Electrosprayed Bacterial Reaction Centers

Highly efficient light absorption and charge separation within the photosystem and reaction center (RC) complexes of photosynthetic plants and bacteria are of great interest for solar cell and photo detector applications, since they offer almost unity quantum yield and expected ultimate power conversion efficiencies of more than 18% and 12%, respectively. In addition, the charge separated states created by these protein complexes are very long lived compared to conventional semiconductor solar cells. In this work, a novel technique is presented for the deposition of photosynthetic protein complexes, by electrospraying RCs of Rhodobacter sphaeroides onto highly ordered pyrolytic graphite (HOPG) electrodes. Remarkably, it is shown that the RCs not only survive exposure to the high electric fields but also yield peak photocurrent densities of up to 7 μA cm^?2, which is equal to the highest value reported to date.     

A Novel Flexible Hybrid Battery–Supercapacitor Based on a Self‐Assembled Vanadium‐Graphene Hydrogel

A novel flexible hybrid battery–supercapacitor device is proposed consisting of high specific surface area electrodes paired with an electrolyte, which contains a redox species that can exist in more than two oxidation states. The two initially equal half‐cells of the device consist of a reduced graphene oxide hydrogel which encapsulates vanadium ions, synthesized with a single‐step method. During charge, the oxidation state of the vanadium ions changes, resulting in two half‐cells with different potentials which considerably increases the energy density. The achieved maximum capacity of more than 225 mAh g^?1 is roughly eight times higher than that of comparable graphene hydrogel supercapacitors without vanadium content, but the potentiostatic charging time is only double. Operated as a supercapacitor, it retains 95% of the initial capacitance over 1000 cycles. As battery, the losses are more significant, retaining around 50% of the initial capacity. However, these losses during battery operation can be almost entirely restored by electric measures. The vanadium ion addition also improves the self‐discharge characteristics of the device. Moreover, the self‐discharge does not permanently damage the hybrid device since both half‐cells initially consist of the same vanadium graphene hydrogel and discharging resets it to initial conditions.     

AN ENHANCEMENT SCHEME OF TCP PROTOCOL IN MOBILE AD HOC NETWORKS： MME-TCP

Transmission Control Protocol （TCP） optimization in Mobile Ad hoc NETworks （MANETs） is a challenging issue because of some unique characteristics of MANETs. In this paper, a new end-to-end mechanism based on multiple metrics measurement is proposed to improve TCP performance in MANETs. Multi-metric Measurement based Enhancement of TCP （MME-TCP） designs the metrics and the identification algorithm according to the characteristics of MANETs and the experiment results. Furthermore, these metrics are measured at the sender node to reduce the overhead of control information over networks. Simulation results show that MME-TCP mechanism achieves a significant performance improvement over standard TCP in MANETs.     

DESIGN OF TWO-PHASE SINUSOIDAL POWER CLOCK AND CLOCKED TRANSMISSION GATE ADIABATIC LOGIC CIRCUIT

First the research is conducted on the design of the two-phase sinusoidal power clock generator in this paper. Then the design of the new adiabatic logic circuit adopting the two-phase sinusoidal power clocks--Clocked Transmission Gate Adiabatic Logic （CTGAL） circuit is presented. This circuit makes use of the clocked transmission gates to sample the input signals, then the output loads are charged and discharged in a fully adiabatic manner by using bootstrapped N-Channel Metal Oxide Semiconductor （NMOS） and Complementary Metal Oxide Semiconductor （CMOS） latch structure. Finally, with the parameters of Taiwan Semiconductor Manufacturing Company （TSMC） 0.25um CMOS device, the transient energy consumption of CTGAL, Bootstrap Charge-Recovery Logic （BCRL） and Pass-transistor Adiabatic Logic （PAL） including their clock generators is simulated. The simulation result indicates that CTGAL circuit has the characteristic of remarkably low energy consumption.     

Electrical Conductivity of Graphene Composites with In and In-Ga Alloy

Samples of composites of graphene with indium or indium-gallium alloy as the matrix were prepared by a process of spreading exfoliated graphene oxide on the foils, repeatedly folding and rolling. The foils were intermittently annealed and the process repeated by addition of more graphene oxide. Indium flux was used to remove any indium or gallium oxide. The samples were characterized by x-ray diffraction, and optical and scanning electron microscopy (SEM). Electrical resistivity and temperature coefficient of resistance (TCR) were measured using a four-probe method in the temperature range of 260 K to 340 K, and the results were used to determine the volume fraction of graphene from effective mean-field analysis. The volume fraction of graphene remained between 0.11 and 0.14 in samples of In with graphene and between 0.12 and 0.13 in samples of In-Ga with graphene. The results indicate that the electrical resistivity and the TCR of the composite were reduced by the addition of graphene. The resistivity of graphene remained between 1.19 × 10⁻⁶ ohm cm and 1.87 × 10⁻⁶ ohm cm in all samples and was thus almost independent of the matrix composition. The electrical resistivity of graphene was found to be an order of magnitude smaller than that of indium or the indium-gallium alloy.