Energy adaptive MAC protocol for IEEE 802.15.7 with energy harvesting

The medium access control (MAC) protocol for indoor visible light communication (VLC) with energy harvesting is explored in this paper. The unfairness of throughput exists among devices due to the significant difference of their energy harvesting rates which changes with distance, acceptance angle and the obstruction probability. We propose an energy harvesting model, a new obstruction probability model and an energy adaptive contention algorithm to overcome the unfairness problem. This device can adjust its contention window according to the energy harvesting rate. As a result, the device with lower energy harvesting rate can get shorter contention window to improve its transmission opportunity. Simulation results show that our MAC protocol can achieve a higher degree of fairness.     

An analytical model on network blocking probability

We present a new analytical model on the blocking probability of the three-stage Clos (1953) network. Due to the effect of approximations, a common problem with previously proposed analytical models is that they may not be very accurate in some cases. In particular, the blocking probability in these models contradicts the well-known deterministic nonblocking condition for the Clos network. The most notable feature of the newly proposed model is that it can more accurately describe the blocking behavior of the network and is consistent with the deterministic nonblocking condition     

An integrated function generator with two-dimensional electronic programming capability

Describes a novel, electronically programmable function generator which has been designed, fabricated, and tested. Output is a piecewise linear function of the input and both coordinates of the function breakpoints can be independently programmed.     

一种应用于GNSS/蜂窝网混合定位接收机的多标准频率合成器

A fully integrated hybrid integer/fractional frequency synthesizer is presented.With a single multiband voltage-controlled-oscillator(VCO),the frequency synthesizer can support GPS,Galileo,Compass and TDSCDMA standards.Design is carefully performed to trade off power,die area and phase noise performance.By reconfiguring between the integer mode and fractional mode,different frequency resolution requirements and a constant loop bandwidth for each standard can be achieved simultaneously.Moreover,a long sequence length,reduced hardware complexity multi-stage-noise-shaping(MASH).-.modulator is employed to reduce fractional spur in the fractional mode.Fabricated in a 0.18 m CMOS technology,the frequency synthesizer occupies an active area of 1.48 mm2 and draws a current of 13.4-16.2 mA from a 1.8 V power supply.The measured phase noise is lower than-80 dBc/Hz at 100 kHz offset and-113 to-124 dBc/Hz at 1 MHz offset respectively,while the measured reference spur is-71 dBc in integer mode and the fractional spur is-65 dBc in fractional mode.     

一种VOD系统的分析模型

对全连网络的分布式视频点播系统进行了性能分析，提出了一种VOD系统的分析模型，可以利用这一模型计算视频请球发生拥塞的概率以及网络的带宽要求，同时还可以得到在通信和存储费用两者之间的一个折衷方案。     

An analytical model for performance evaluation of multimedia applications over EDCA in an IEEE 802.11e WLAN

We extend the modeling heuristic of (Harsha et al. 2006. In IEEE IWQoS ’06, pp 178 – 187) to evaluate the performance of an IEEE 802.11e infrastructure network carrying packet telephone calls, streaming video sessions and TCP controlled file downloads, using Enhanced Distributed Channel Access (EDCA). We identify the time boundaries of activities on the channel (called channel slot boundaries) and derive a Markov Renewal Process of the contending nodes on these epochs. This is achieved by the use of attempt probabilities of the contending nodes as those obtained from the saturation fixed point analysis of (Ramaiyan et al. 2005. In Proceedings ACM Sigmetrics, ’05. Journal version accepted for publication in IEEE TON). Regenerative analysis on this MRP yields the desired steady state performance measures. We then use the MRP model to develop an effective bandwidth approach for obtaining a bound on the size of the buffer required at the video queue of the AP, such that the streaming video packet loss probability is kept to less than 1%. The results obtained match well with simulations using the network simulator, ns-2. We find that, with the default IEEE 802.11e EDCA parameters for access categories AC 1, AC 2 and AC 3, the voice call capacity decreases if even one streaming video session and one TCP file download are initiated by some wireless station. Subsequently, reducing the voice calls increases the video downlink stream throughput by 0.38 Mbps and file download capacity by 0.14 Mbps, for every voice call (for the 11 Mbps PHY). We find that a buffer size of 75KB is sufficient to ensure that the video packet loss probability at the QAP is within 1%.     

M2M小数据业务的IEEE 802.11WLAN分析模型

机器对机器(M2M,machine to machine)通信有着巨大的市场潜力,无线局域网(WLAN)作为3G网络的主要补充必将承载大量M2M业务。针对具有时延容忍、耐性重试等特点的典型的M2M小数据业务,提出了一种大时间尺度退避的IEEE 802.11 DCF网络分析模型,推导了MAC层服务时间的概率分布;建立IPP/G/1/K离散时间排队系统模型,研究了非饱和负载下M2M业务在WLAN非理想信道中传输的QoS性能。算法仿真结果表明,大时间尺度退避机制有效提高了系统的吞吐量,降低了系统阻塞率。     

Analysis of service extensible capability for extensible network service model

The capability of providing network service extensibility is the major demand of next generation network,it is also the main challenge of network service model technology.The extensible network service model was proposed in response to the demand of network development.Firstly,an overview of the basic principles of the extensible network service model was expounded.And then,from the point of view of principle analysis,the service extension capability of the service model was qualitatively analyzed.Finally,using the analytic method of network service extensible capability,the service extension capability of the service model was quantitative analyzed from two perspectives of theory and practical application.The qualitative analysis and the quantitative analysis show that the extensible network service model has strong service extensible capability.     

综合网管体系结构研究及信息模型建立

通过分析综合网管建设的必要性及当前各种解决方案存在的问题，采用从上至下的思想，提出了一种实用的开放性管理框架，实现了业务管理层和网络管理层之间的无缝融合，可以完成多专业网管系统的综合管理，同时采用LML语言定义了管理信息模型。     

An analytical two-dimensional model for silicon MESFETs

A model that predicts small-geometry effects in Si MESFETs has been developed. It is based on a two-dimensional (2-D) analytical solution of Poisson's equation in the subthreshold regime that applies to the junction-isolated structure typical of silicon devices. The model is in excellent agreement with numerical simulations from the PISCES 2-D device analysis program. The analytical model provides the physical basis for a subthreshold current model for small-geometry MESFETs. A scaling scheme for MESFETs, derived from the analytical model, that predicts a minimum-acceptable gate length of 0.15 μm for these devices is proposed     

An analytical breakdown model for short-channel MOSFET's

Avalanche-induced breakdown mechanisms for short-channel MOSFET's are discussed. A simple analytical model that combines the effects due to the ohmic drop caused by the substrate current and the positive feedback effect of the substrate lateral bipolar transistor is proposed. It is shown that two conditions must be satisfied before breakdown will occur. One is the emission of minority carriers into the substrate from the source junction, the other is sufficient avalanche multiplication to cause significant positive feedback. Analytical theory has been developed with the use of a published model for short-channel MOSFET's. The calculated breakdown characteristics agree well with experiments for a wide range of processing parameters and geometries.     

An analytical model for adaptive routing networks

Real-time network routing (RTNR) is a new adaptive routing method. With RTNR, switches have a simple way of exchanging link status bit map information, thereby determining the availability and load conditions of the direct and all two-link paths to the destination. Link busy-idle status is exchanged between the network nodes using a bit map data exchange through the common channel signaling (CCS) network, and calls are set up where there is the most available capacity in the network. To date the analysis of RTNR networks has been limited to simulation models. The present authors develop an analytical model for the AT&T network under RTNR, which is shown to provide good agreement with simulation models. The analytical model for RTNR networks uses an Erlang fixed point method to solve the nonlinear equations describing dynamical network behavior. The equations include the link state probability, network flows, link arrival rates, adaptive trunk reservation level, and adaptive path selection depth. The link state model provides the aggregate link state probabilities through solution of the birth-death equations, and models the adaptive nature of trunk reservation. The network flow model provides a method to calculate the traffic flow using the least busy concept employed in RTNR, and also models the adaptive nature of the path selection depth. The analytical model addresses asymmetrical networks, and computational examples show the differences from the simulation model to be small. The authors also use the analytical model to examine key RTNR parameters over a range of values     

An integrated management environment for network resources andservices

Technological and human factors have contributed to increase the complexity of the network management problem. Heterogeneity and globalization of network resources, on one hand, have increased user expectations for flexible and easy-to-use environments; on the other hand, they have suggested entirely novel ways to face the management problem. Several research efforts recognize the need for integrated solutions to manage both network resources and services in open, global, and untrusted environments. In addition, these solutions should permit the coexistence of different management models and should interoperate with legacy systems. In the paper, we define a general architecture based on a distributed processing environment (DFE) that offers a large set of facilities to the application level. We have developed the MESIS management environment shaped after the above architecture and its DPE facilities with mobile agents technology. MESIS handles, in a uniform way, both resources and services, and focuses on two crucial properties: interoperability to overcome heterogeneity, and security to grant users safe and protected operations. The Agent Interoperability Facility supports compliance with CORBA-based management systems and with MASIF agent platforms. The Agent Security Facility provides authentication, integrity, privacy, authorization, and secure interoperation with CORBA systems     

An analytical framework for reliability evaluation of d-dimensional IEEE 802.11 broadcast wireless networks

Wireless Networks - In this paper, we validate that the deterministic distance-based analytical model can be used to estimate the reliability of one-dimensional (1-D) 802.11 broadcast wireless...     

An analytical model for input-buffered optical packet switches with reconfiguration overhead

The overhead associated with reconfiguring a switch fabric in optical packet switches is an important issue in relation to the packet transmission time and can adversely affect switch performance. The reconfiguration overhead increases the mean waiting time of packets and reduces throughput. The scheduling of packets must take into account the reconfiguration frequency. This work proposes an analytical model for input-buffered optical packet switches with the reconfiguration overhead and analytically finds the optimal reconfiguration frequency that minimizes the mean waiting time of packets. The analytical model is suitable for several round-robin (RR) scheduling schemes in which only non-empty virtual output queues (VOQs) are served or all VOQs are served and is used to examine the effects of the RR scheduling schemes and various network parameters on the mean waiting time of packets. Quantitative examples demonstrate that properly balancing the reconfiguration frequency can effectively reduce the mean waiting time of packets.     

An analytical model with flexible accuracy for deep submicron DCVSL cells

Differential cascoded voltage switch logic (DCVSL) cells are among the best candidates of circuit designers for a wide range of applications due to advantages such as low input capacitance, high switching speed, small area and noise-immunity; nevertheless, a proper model has not yet been developed to analyse them. This paper analyses deep submicron DCVSL cells based on a flexible accuracy-simplicity trade-off including the following key features: (1) the model is capable of producing closed-form expressions with an acceptable accuracy; (2) model equations can be solved numerically to offer higher accuracy; (3) the short-circuit currents occurring in high-low/low-high transitions are accounted in analysis and (4) the changes in the operating modes of transistors during transitions together with an efficient submicron I-V model, which incorporates the most important non-ideal short-channel effects, are considered. The accuracy of the proposed model is validated in IBM 0.13 µm CMOS technology through comparisons with the accurate physically based BSIM3 model. The maximum error caused by analytical solutions is below 10%, while this amount is below 7% for numerical solutions.     

An analytical model for high electron mobility transistors

In this paper we present a new model for HEMT's which is based on a single analytical function that describes the electron concentrations in the two dimensional electron gas and in the AlGaAs layer. Besides accounting for the AlGaAs conduction, the model includes the effect of mobility degradation, channel length modulation in the saturation region and the series resistances R_S and R_D. The model results in closed form expressions for the current, transconductance, output conductance and gate capacitance. Finally, the theoretical predictions of the model are compared with the experimental data and shown to be in good agreement over a wide range of bias conditions     

An analytical model for the epitaxial bipolar transistor

In the n⁺pn^?n⁺ transistor, high-current effects in the base and collector regions are linked within the current ranges of practical interest. To describe such effects, we have derived an analytical model that is based primarily on five assumptions: (1) the structure is approximately one-dimensional; (2) recombination is negligible in the base and collector quasi-neutral regions, and in the three space-charge regions; (3) high-current effects are negligible in the emitter and n⁺-substrate regions; (4) the Fletcher boundary conditions (or the Misawa boundary conditions) can be used for the three space-charge regions; and (5) the ambipolar approach can be used for the base and collector quasi-neutral regions. The primary findings predicted by the n⁺pn^?n⁺ transistor model are: In current ranges of practical interest (usable current gain), the electron concentration profile has a significant “vertical step” located at the collector-base metallurgical junction for all values of collector current. In the limit of extremely-high-current operation, this step tends to vanish. In the current range where the current gain begins to decline rapidly with increasing collector current, the electron concentration at the base boundary of the collector-base space-charge region goes approximately as the square of the hole concentration at the collector boundary of the same region. Because of this relationship, a charge-control calculation is more difficult than a straightforward calculation of carrier concentration for a given degree of accuracy. The n⁺pn^?n⁺ transistor model (which consists of twelve algebraic equations) is particularly useful for the practically important case of an epitaxial bipolar transistor having a very thin, heavily-doped base region.     

An analytical model for the low- emitter-impurity-concentration transistor

The epitaxial transistor model developed by Grung and Warner is adapted for predicting the characteristics of the low-emitter-impurity-concentration (LEC) transistor. The model predicts the following results for the low region (the lightly-doped emitter region): through a given cross section, the minority-carrier drift current is typically larger than the minority-carrier diffusion current. In other words, the model predicts that the conventional low-level minority-carrier diffusion equation is invalid for the low region, especially for typical bias levels. As a result, the effect of the electric field on minority carriers cannot be neglected in the low region of the LEC transistor and (by extension) in the corresponding low regions of such devices as the epitaxial diode and the integrated-injection-logic transistor.