Photocurrent effect on the zero-Bias dynamic resistance of HgCdTe photodiode

A new physical model is presented for the illumination-dependence of the zero-bias resistance-area product (R₀A) of HgCdTe photodiode. The model is based on three independent mechanisms. They are the depletion region volume change with the applied bias, the diffusion distance change with the moving depletion region edge, and the minority carrier accumulation in the depletion region which affects the minority carrier diffusion. Analytic equations are derived for the photodiode current-voltage characteristics and R₀A products. The results of the model have been compared with experimental data obtained from several Hg_0.7Cd_0.3Te diodes with an identical diode structure having different absorbing amount of light. The model showed good agreement with the experimental data.     

Destination-driven routing for low-cost multicast

We present a destination-driven algorithm that optimizes for applications, such as group video or teleconferencing, that require multicast trees with low total cost. The destination-driven algorithm uses a greedy strategy based on shortest-path trees and minimal spanning trees but biases routes through destinations. The performance of the algorithm is analyzed through extensive simulation and compared with several Steiner tree heuristics and the popular shortest-path tree (SPT) method. The algorithm is found to produce trees with significantly lower overall cost than the SPT while maintaining reasonable per-destination performance. Its performance also compares well with other known Steiner heuristics. Moreover, the algorithm does not suffer from high complexity common to most Steiner tree heuristics and builds a route by querying only incident links for cost information     

Development of the Base Station Controller and Manager in the CDMA Mobile System

The base station (BS) in the CDMA Mobile System (CMS) connects calls through the radio interface and is designed to provide mobile subscribers with high quality service in spite of mobile subscribers’ motions. The BS consists of multiple base station transceiver subsystems (BTSs), a base station controller (BSC) and a base station manager (BSM). This paper is concerned with the BSC and the BSM. The BSC is located between the BTSs and the mobile switching center (MSC) connected with the public network, and is responsible for controlling mobile calls from and to mobile subscribers via the BTSs. The BSM provides operator-interfaces per the BS and takes responsibility of operation and maintenance (OAM) of the BS. Design of the BSC is based on two module types: functional module and unit module. The functional module is used to support new services easily and the unit module to increase the system capacity economically. Both modular types are easily achieved by inserting the corresponding modules to the system. Particularly, in order to efficiently support the soft handover which is one of CDMA superior advantages, the BSC adopts a large high-speed packet switch connecting up to 512 BTSs, and thus mobile subscribers can be provided with soft handover in high probability. The BSM is based on a commercial workstation to support OAM functions efficiently and guarantee high reliability of the functions. The BSM uses graphical user interface (GUI) for efficient OAM functions of the BS.     

A Time‐Constrained Information Processing Model in Ubiquitous Environments

As pervasive computing is widely adopted and reliable networks are becoming more easily accessible, there is a rapidly growing need to develop a mechanism to analyze and evaluate the performance of ubiquitous environments. This paper presents an information processing model which characterizes a ubiquitous environment where a variety of pieces of information need to be exchanged among devices within a system. The proposed model not only provides analytical tools to evaluate the performance of devices, but also makes it possible to identify key factors in designing a ubiquitous environment. For illustrative purposes, a test bed is constructed and the performance of the system is assessed based on the proposed model.     

Complex Hydrides for Electrochemical Energy Storage

Complex hydrides have energy storage‐related functions such as i) solid‐state hydrogen storage, ii) electrochemical Li storage, and iii) fast Li‐ and Na‐ionic conductions. Here, recent progress on the development of fast Li‐ionic conductors based on the complex hydrides is reported. The validity of using them as electrolytes in all‐solid‐state lithium rechargeable batteries is also examined. Not only coated oxides but also bare sulfides are found to be applicable as positive electrode active materials. Results related to fast Na‐ionic conductivity in the complex hydrides are presented. In the last section, the future prospects for battery assemblies with high‐energy densities, and Mg ion batteries with the liquid and the solid‐state electrolytes are discussed.     

Improving Radio Frequency Transmission Properties of Graphene via Carrier Concentration Control toward High Frequency Transmission Line Applications

Graphene has been gradually studied as a high‐frequency transmission line material owing to high carrier mobility with frequency independence up to a few THz. However, the graphene‐based transmission lines have poor conductivity due to their low carrier concentration. Here, it is observed that the radio frequency (RF) transmission performance could be severely hampered by the defect‐induced scattering, even though the carrier concentration is increased. As a possible solution, the deposition of the amorphous carbon on the graphene is studied in the high‐frequency region up to 110 GHz. The DC resistance is reduced by as much as 60%, and the RF transmission property is also enhanced by 3 dB. Also, the amorphous carbon covered graphene shows stable performance under a harsh environment. These results prove that the carrier concentration control is an effective and a facile method to improve the transmission performance of graphene. It opens up the possibilities of using graphene as interconnects in the ultrahigh‐frequency region.     

Coexistence of OFDM‐Based IMT‐Advanced and FM Broadcasting Systems

Coexistence analysis is extremely important in examining the possibility for spectrum sharing between orthogonal frequency‐division multiplexing (OFDM)‐based international mobile telecommunications (IMT)‐Advanced and other wireless services. In this letter, a new closed form method is derived based on power spectral density analysis in order to analyze the coexistence of OFDM‐based IMT‐Advanced systems and broadcasting frequency modulation (FM) systems. The proposed method evaluates more exact interference power of IMT‐Advanced systems in FM broadcasting systems than the advanced minimum coupling loss (A‐MCL) method. Numerical results show that the interference power is 1.3 dB and 3 dB less than that obtained using the A‐MCL method at cochannel and adjacent channel, respectively. This reduces the minimum separation distance between the two systems, which eventually saves spectrum resources.     

Adaptive mode decision for H.264 encoder

An adaptive mode decision algorithm is presented, with rate-distortion optimisation that reduces the complexity of the H.264 encoder without loss of image quality and compression ratio. The proposed algorithm uses the property of an all-zero coefficients block that is produced by quantisation and coefficient thresholding to effectively skip unnecessary modes. Experimental results show that the speed of the adaptive mode decision algorithm is two times faster than the full-mode decision algorithm of the JM72 reference encoder, without any coding loss.     

Calculation and measurement of resonant-mode blueshifts inoxide-apertured VCSELs

As the aperture size of oxide-apertured vertical-cavity surface-emitting lasers (VCSELs) shrinks, the lasing wavelength blueshifts. We have calculated this effect using both a scalar effective index model and a full-vector weighted index model. Results were compared against experimental data for two different VCSEL designs emitting near 780 and 850 nm. We find that the full-vector weighted index calculation matches the data remarkably well, while the scalar effective index calculation underestimates the blueshift