Fixed Point Implementation of the QCELP Speech Coder

The Qualcomm code excited linear prediction (QCELP) speech coder was adopted to increase the capacity of the CDMA Mobile System (CMS). In this paper, we implemented the QCELP speech coding algorithm by using TMS320C50 fixed point DSP chip. Also the fixed point simulation was done with C language. The computation complexity of QCELP on TMS320C50 was about 33 MIPS and program size was 10k words and data memory was 4k words. In the normal call test on the CMS, where mobile to mobile call test was done in the bypass mode without double vocoding, mean opinion score for the speech quality was 3.11.     

Few‐Layered WS2 Nanoplates Confined in Co,N‐Doped Hollow Carbon Nanocages: Abundant WS2 Edges for Highly Sensitive Gas Sensors

Edges of 2D transition metal dichalcogenides (TMDs) are well known as highly reactive sites, thus researchers have attempted to maximize the edge site density of 2D TMDs. In this work, metal‐organic framework (MOF) templates are introduced to synthesize few‐layered WS₂ nanoplates (a lateral dimension of ≈10 nm) confined in Co, N‐doped hollow carbon nanocages (WS₂_Co‐N‐HCNCs), for highly sensitive NO₂ gas sensors. WS₂ precursors are assembled in the surface cavity of Co‐based zeolite imidazole framework (ZIF‐67) and subsequent pyrolysis produced WS₂_Co‐N‐HCNCs. During the pyrolysis, the carbonized ZIF‐67 are doped by Co and N elements, and the growth of WS₂ is effectively suppressed, creating few‐layered WS₂ nanoplates functionalized Co‐N‐HCNCs. The WS₂_Co‐N‐HCNCs exhibit outstanding NO₂ sensing characteristics at room temperature, in terms of response (48.2% to 5 ppm), selectivity, response and recovery speed, and detection limit (100 ppb). These results are attributed to the enhanced adsorption and desorption kinetics of NO₂ on abundant WS₂ edges, confined in the gas permeable HCNCs. This work opens up an efficient way for the facile synthesis of edge abundant few‐layered TMDs combined with porous carbon matrix via MOF templating route, for applications relying on highly active sites.     

ONVisor: Towards a scalable and flexible SDN‐based network virtualization platform on ONOS

Network virtualization (NV) technologies have attracted a lot of attention as an essential solution for future networking infrastructure. The NV enables multiple tenants to share the same physical infrastructure and to create independent virtual networks (VNs) by decoupling the physical network in terms of topology, address, and control functions. One feasible way to realize full NV involves considering solutions based on the software‐defined networking (SDN) paradigm using its programmability. The SDN contributes many benefits to both network operations and management including programmability, agility, elasticity, and flexibility. There are several SDN‐based NV solutions; however, they suffered from a lack of scalability, high availability. Also, they have high latency between control and data plane because of proxy‐based architecture. In this thesis, we introduce a new NV platform, named Open Network Hypervisor (ONVisor). The design objectives include, among the features, (1) multitenancy, (2) scalability, (3) flexibility, (4) isolated VNs, and (5) VN federation. ONVisor was designed and implemented by extending Open Network Operating System, an open‐source SDN controller. The main features of ONVisor are (1) isolated control and data plane per VN, (2) support of distributed operations, (3) extensible translators, (4) on‐platform VN application development and execution, and (5) support of heterogenous SDN data‐plane implementations. Several experiments are conducted on various test scenarios in different test environments in terms of control and data plane performance compared to nonvirtualized SDN network. The results show that ONVisor can provide VNs a little bit lower control plane performance and similar data plane performance.     

All‐Solution‐Processed Indium‐Free Transparent Composite Electrodes based on Ag Nanowire and Metal Oxide for Thin‐Film Solar Cells

Fully solution‐processed Al‐doped ZnO/silver nanowire (AgNW)/Al‐doped ZnO/ZnO multi‐stacked composite electrodes are introduced as a transparent, conductive window layer for thin‐film solar cells. Unlike conventional sol–gel synthetic pathways, a newly developed combustion reaction‐based sol–gel chemical approach allows dense and uniform composite electrodes at temperatures as low as 200 °C. The resulting composite layer exhibits high transmittance (93.4% at 550 nm) and low sheet resistance (11.3 Ω sq^‐1), which are far superior to those of other solution‐processed transparent electrodes and are comparable to their sputtered counterparts. Conductive atomic force microscopy reveals that the multi‐stacked metal‐oxide layers embedded with the AgNWs enhance the photocarrier collection efficiency by broadening the lateral conduction range. This as‐developed composite electrode is successfully applied in Cu(In_1‐x,Ga_x)S₂ (CIGS) thin‐film solar cells and exhibits a power conversion efficiency of 11.03%. The fully solution‐processed indium‐free composite films demonstrate not only good performance as transparent electrodes but also the potential for applications in various optoelectronic and photovoltaic devices as a cost‐effective and sustainable alternative electrode.     

Highly Improved Sb2S3 Sensitized‐Inorganic–Organic Heterojunction Solar Cells and Quantification of Traps by Deep‐Level Transient Spectroscopy

The light‐harvesting Sb₂S₃ surface on mesoporous‐TiO₂ in inorganic–organic heterojunction solar cells is sulfurized with thioacetamide (TA). The photovoltaic performances are compared before and after TA treatment, and the state of the Sb₂S₃ is investigated by X‐ray diffraction, X‐ray photoelectron spectroscopy, and deep‐level transient spectroscopy (DLTS). Although there are no differences in crystallinity and composition, the TA‐treated solar cells exhibit significantly enhanced performance compared to pristine Sb₂S₃‐sensitized solar cells. From DLTS analysis, the performance enhancement is mainly attributed to the extinction of trap sites, which are present at a density of (2–5) × 10¹⁴ cm^?3 in Sb₂S₃, by TA treatment. Through such a simple treatment, the cell records an overall power conversion efficiency (PCE) of 7.5% through a metal mask under simulated illumination (AM 1.5G, 100 mW cm^–2) with a very high open circuit voltage of 711.0 mV. This PCE is, thus far, the highest reported for fully solid‐state chalcogenide‐sensitized solar cells.     

Collectively Exhaustive Electrodes Based on Covalent Organic Framework and Antagonistic Co‐Doping for Electroactive Ionic Artificial Muscles

In this study, high‐performance ionic soft actuators are developed for the first time using collectively exhaustive boron and sulfur co‐doped porous carbon electrodes (BS‐COF‐Cs), derived from thiophene‐based boronate‐linked covalent organic framework (T‐COF) as a template. The one‐electron deficiency of boron compared to carbon leads to the generation of hole charge carriers, while sulfur, owing to its high electron density, creates electron carriers in BS‐COF‐C electrodes. This antagonistic functionality of BS‐COF‐C electrodes assists the charge‐transfer rate, leading to fast charge separation in the developed ionic soft actuator under alternating current input signals. Furthermore, the hierarchical porosity, high surface area, and synergistic effect of co‐doping of the BS‐COF‐Cs play crucial roles in offering effective interaction of BS‐COF‐Cs with poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), leading to the generation of high electro‐chemo‐mechanical performance of the corresponding composite electrodes. Finally, the developed ionic soft actuator based on the BS‐COF‐C electrode exhibits large bending strain (0.62%), excellent durability (90% retention for 6 hours under operation), and 2.7 times higher bending displacement than PEDOT:PSS under extremely low harmonic input of 0.5 V. This study reveals that the antagonistic functionality of heteroatom co‐doped electrodes plays a crucial role in accelerating the actuation performance of ionic artificial muscles.     

Nonvolatile flash memory device using Ge nanocrystals embedded in HfAlO high-/spl kappa/tunneling and control oxides: Device fabrication and electrical performance

We fabricated a nonvolatile Flash memory device using Ge nanocrystals (NCs) floating-gate (FG)-embedded in HfAlO high-/spl kappa/ tunneling/control oxides. Process compatibility and memory operation of the device were investigated. Results show that Ge-NC have good thermal stability in the HfAlO matrix as indicated by the negative Gibbs free energy changes for both reactions of GeO/sub 2/+Hf/spl rarr/HfO/sub 2/+Ge and 3GeO/sub 2/+4Al/spl rarr/2Al/sub 2/O/sub 3/+3Ge. This stability implies that the fabricated structure can be compatible with the standard CMOS process with the ability to sustain source-drain activation anneal temperatures. Compared with Si-NC embedded in HfO/sub 2/, Ge-NC embedded in HfAlO can provide more electron traps, thereby enlarging the memory window. It is also shown that this structure can achieve a low programming voltage of 6-7 V for fast programming, a long charge retention time of ten years maintaining a 0.7-V memory window, and good endurance characteristics of up to 10/sup 6/ rewrite cycles. This paper shows that the Ge-NC embedded in HfAlO is a promising candidate for further scaling of FG Flash memory devices.     

An Analog Front‐End Circuit for ISO/IEC 14443‐Compatible RFID Interrogators

An analog front‐end circuit for ISO/IEC 14443‐compatible radio frequency identification (RFID) interrogators was designed and fabricated by using a 0.25 µm double‐poly CMOS process. The fabricated chip was operated using a 3.3 Volt single‐voltage supply. The results of this work could be provided as reusable IPs in the form of hard or firm IPs for designing single‐chip ISO/IEC 14443‐compatible RFID interrogators.