Analysis of the anisotropy in an m-plane GaN film via HVPE on a γ,-LiAIO2 substrate

t. The results show that the electronic transition was influenced by the electric field along the c-axis, which results in an obvious anisotropy, but the influence was weakened by the hexagonal symmetry along the c-axis.     

多速率分层结构CDMA系统联合控制算法

本文对多速率分层结构CDMA系统的联合控制算法进行了研究,提出了一种新的功率、速率和接入联合控制算法。在此基础上,考虑到基站发射功率资源受限以及信道的路径损耗、多径衰落和阴影衰落的影响,得到了系统容量与系统各业务负载的数量以及速率间的关系。另外,该联合控制算法使系统能够自适应地调节VBR业务的速率以及获得最大总有效数据速率;同时通过预测新用户接入系统所需的功率资源,来判断系统是否接受接入请求。最后,利用MonteCarlo方法对该系统算法进行了仿真,给出了相应的仿真结果和分析。     

A traffic control system for IEEE 802.11 networks based on available bandwidth estimation

To support Quality of service (QoS)‐sensitive applications like real‐time video streaming in IEEE 802.11 networks, a MAC layer extension for QoS, IEEE 802.11e, has been recently ratified as a standard. This MAC layer solution, however, addresses only the issue of prioritized access to the wireless medium and leaves such issues as QoS guarantee and admission control to the traffic control systems at the higher layers. This paper presents an IP‐layer traffic control system for IEEE 802.11 networks based on available bandwidth estimation. We build an analytical model for estimating the available bandwidth by extending an existing throughput computation model, and implement a traffic control system that provides QoS guarantees and admission control by utilizing the estimated available bandwidth information. We have conducted extensive performance evaluation of the proposed scheme via both simulations and measurements in the real test‐bed. The experiment results show that our estimation model and traffic control system work accurately and effectively in various network load conditions without IEEE 802.11e. The presence of IEEE 802.11e will allow even more efficient QoS provision, as the proposed scheme and the MAC layer QoS support will complement each other. Copyright © 2006 John Wiley & Sons, Ltd.     

A traffic grooming problem of SONET-WDM rings

In this paper, we present a traffic grooming problem of the SONET-WDM ring. The objective is to minimize the total cost of optical add-drop multiplexers (OADMs) and inter-ring hub equipment, while satisfying intra-ring and inter-ring capacities. We develop integer programming (IP) formulations for the problem and devise some reformulations for enhancing the mathematical representation of the proposed IP model. By investigating the polyhedral structure of the problem, we develop some valid inequalities that provide a tight lower bound for the problem. Dealing with the inherent computational complexity of the problem, we also devise an effective tabu search procedure for finding a feasible solution of good quality within reasonable computation time. Computational results are provided to demonstrate the relative strength of the proposed formulations, and to reveal the efficacy of the lower and upper bound procedures for solving the problem.

Polarity Analysis of Self-Seeded Aluminum Nitride Crystals Grown by Sublimation

Self-seeded aluminum nitride (AlN) crystals were successfully grown in a tungsten crucible by the sublimation method. The polarities along the growth direction of these AlN samples were characterized by chemical etching, combined with high-resolution transmission electronic microscopy (HRTEM) and Raman spectroscopy. It has been proven by our experimental results that etching in KOH solution and in molten KOH-NaOH can be a reliable method to determine the surfaces with different polarities. Chemically active N-polar (0001) AlN surfaces were removed appreciably, while only etch pits related to threading dislocations were observed on Al-polar surfaces after chemical etching. HRTEM images revealed that there are noticeable inversion domain boundaries in the samples. Raman spectrum measurements showed the vibration mode change before and after etching in the same geometrical arrangement.     

Call admission control strategy for system throughput maximization considering both call- and packet-level QoSs

This letter presents a call admission control (CAC) strategy for system throughput maximization in wireless uplink systems. This strategy considers not only the call-level quality of service (QoS) (i.e., blocking probability) but also the packet-level QoS (i.e., outage probability). Using the statistical co-channel interference (CCI) model and state diagram, the outage probability and the blocking probability are investigated as a function of the relative traffic load. We formulate the CAC strategy problem based on relative traffic load, and suggest a solution. The numerical results show that maximum system throughput can be achieved by controlling the relative traffic load. In addition, we illustrate the region where system throughput is constrained by call- and packet-level QoSs. This examination shows that the call and packet-level QoSs must be considered together to achieve maximum system throughput.     

An efficient scheduling algorithm for input-queued switches

This letter presents an efficient scheduling algorithm DTRR （Dual-Threshold Round Robin） for input-queued switches. In DTRR, a new matched input and output by round robin in a cell time will be locked by two self-adaptive thresholds whenever the queue length or the wait-time of the head cell in the corresponding Virtual Output Queue （VOQ） exceeds the thresholds. The locked input and output will be matched directly in the succeeding cell time until they are unlocked. By employing queue length and wait-time thresholds which are updated every cell time simultaneously, DTRR achieves a good tradeoff between the performance and hardware complexity. Simulation results indicate that the delay performance of DTRR is competitive compared to other typical scheduling algorithms under various traffic patterns especially under diagonal traffic.     

Bidirectional SCM Transmission Using a Noise-Suppressed Fabry–Pérot Laser Diode and a Reflective Semiconductor Optical Amplifier in a WDM/SCM-PON Link

We have proposed and experimentally demonstrated a bidirectional hybrid wavelength-division-multiplexed/subcarrier-multiplexed (SCM)-passive optical network based on a noise-suppressed Fabry-Peacuterot laser diode (FP-LD) and a reflective semiconductor optical amplifier (RSOA). For downlink data transmission, an FP-LD with multiple wavelength characteristics was used, and the mode partition noise of the FP-LD was reduced using a gain-saturated SOA with high-pass filter characteristics. For uplink data transmission, the downlink optical source was reused and remodulated by an SCM method, using an RSOA. A bidirectional SCM link with radio frequencies (RFs) of 2.4 GHz in the downlink and 1.0 GHz in the uplink was implemented. To confirm the validity of the proposed configuration, a 16-quadrature amplitude modulation transmission experiment was performed on a 10-km bidirectional optical access link. The transmission performance was investigated by means of the error vector magnitude and RF spectrum     

A 0.25-μm CMOS 1.9-GHz PHS RF Transceiver With a 150-kHz Low-IF Architecture

We present a 1.9-GHz Personal Handy-phone System (PHS) transceiver, fully integrated and fabricated in 0.25-mum CMOS technology. The receiver is based on a 150-kHz low-IF architecture and meets the fast channel switching and DC-offset cancellation requirements of PHS. It includes a low-noise amplifier (LNA), a downconversion mixer, a complex filter, and a programmable gain amplifier. A fractional-N frequency synthesizer achieves seamless handover with a 25 mus channel switching time and a phase noise of -121 dBc/Hz at a 600-kHz offset frequency, with compliant ACS performance. The receiver provides -105 dBm sensitivity and 55 dBc ACS at a 600-kHz frequency offset. The transmitter is based on the direct modulation architecture and consists of an upconversion mixer and a pre-driver stage. The gain of the pre-driver is digitally controllable to suit any type of commercial power amplifier. The transmitter shows a 3% EVM and a 65 dBc ACPR at a 600-kHz offset frequency. The whole transceiver occupies 15.2 mm² and dissipates 70 mA in RX and 44 mA in TX, with a 2.8-V supply     

0.18μm数字CMOS工艺下的高增益运算放大器设计

基于SMIC 0.18μm数字CMOS工艺,设计了一种基于增益增强技术的折叠式共源共栅运算放大器,并采用衬底校准技术增大了运放的输入摆幅,可用于13位30MHz采样频率的流水线模数转换器,分析了受流水线性能限制的运放性能.仿真结果表明运放在1V的输入摆幅下开环增益大于100dB,8.5pF负载电容下单位增益带宽为322MHz,功耗仅为1.9mW.