Dian Zhou

Analytical Evaluation of Retransmission Schemes in Wireless Sensor Networks

Retransmission has been adopted as one of the most popular schemes for improving transmission reliability in wireless sensor networks. Many previous works have been done on reliable transmission is ...

Modeling and analysis of Rayleigh fading channels using stochastic network calculus

Deterministic network calculus (DNC) is not suitable for deriving performance guarantees for wireless networks due to their inherently random behaviors. In this paper, we develop a method for Quality of Service (QoS) analysis of wireless channels subject to Rayleigh fading based on stochastic network calculus. We provide closed-form stochastic service curve for the Rayleigh fading channel. With this service curve, we derive stochastic delay and backlog bounds. Simulation results verify that the bounds are reasonably tight. Moreover, through numerical experiments, we show the method is not only capable of deriving stochastic performance bounds, but also can provide guidelines for designing transmission strategies in wireless networks.

Traffic Splitting with Network Calculus for Mesh Sensor Networks

In many applications of sensor networks, it is essential to ensure that messages are transmitted to their destinations as early as possible and the buffer size of each sensor node is as small as possible. In this paper, we firstly propose a mesh sensor network system model. Based on this system model, the expressions for deriving the delay bound and buffer requirement bound are presented using network calculus. In order to balance traffic load and improve resource utilization, three traffic splitting mechanisms are proposed. The numerical results show that the delay bound and buffer requirement bound are lowered while applying those traffic splitting mechanisms. And thus the performance of the whole sensor network is improved.

Deterministic Worst-Case Performance Analysis for Wireless Sensor Networks

Dimensioning wireless sensor networks requires formal methods to guarantee network performance and cost in any conditions. Based on network calculus, this paper presents a deterministic analysis method for evaluating the worst-case performance and buffer cost of sensor networks. To this end, we introduce three general traffic flow operators and derive their delay and buffer bounds. These operators are general because they can be used in combination to model any complex traffic flowing scenarios in sensor networks. Furthermore, our method integrates variable duty cycle to allow the sensor nodes to operate at lower rates thus saving power. Moreover, it incorporates traffic splitting mechanisms in order to balance network workload and nodes buffers. To show how our method applies to real applications, we conduct a case study on a fresh food tracking application, which monitors the food freshness in realtime. The experimental results demonstrate that our method can be either used to perform network planning before deployment, or to conduct network reconfiguration after deployment.

Performance Analysis of Flow-Based Traffic Splitting Strategy on Cluster-Mesh Sensor Networks

Performance analysis is crucial for designing predictable and cost-efficient sensor networks. Based on the network calculus theory, we propose a flow-based traffic splitting strategy and its analytical method for worst-case performance analysis on cluster-mesh sensor networks. The traffic splitting strategy can be used to alleviate the problem of uneven network traffic load. The analytical method is able to derive close-form formulas for the worst-case performance in terms of the end-to-end least upper delay bounds for individual flows, the least upper backlog bounds, and power consumptions for individual nodes. Numerical results and simulations are conducted to show benefits of the splitting strategy as well as validate the analytical method. The numerical results show that the splitting strategy enables much better balance on network traffic load and power consumption. Moreover, the simulation results verify that the theoretic bounds are fairly tight.

A current shaping technique to lower phase noise in LC oscillators

A novel LC-tank oscillator, where bias noise is decoupled and drain current is shaped in order to reduce phase noise, is presented. Active devices work in a class-C manner, the drain current is pulse shaped and peaks when the oscillator is insensitive to perturbations. Based on the ISF theory, this current shape can improve phase noise performance. Closed-form 1/f2 phase noise equations are derived and compared with those of the classic LC-tank oscillator with the same bias and LC-tank. Simulations agree with conclusions from the theory and show 5.5 dB improvement in 1/f2 phase noise at 1-MHz offset.

Stochastic coverage in event-driven sensor networks

One of the primary tasks of sensor networks is to detect events in a field of interest (FoI). To quantify how well events are detected in such networks, coverage of events is a fundamental problem to be studied. However, traditional studies mostly focus on analyzing the coverage of the FoI, which is usually called area coverage. In this paper, we propose an analytic method to evaluate the performance of event coverage in sensor networks with randomly deployed sensor nodes and stochastic event occurrences. We provide formulas to calculate the probabilities of event coverage and event missing. The numerical results show how these two probabilities change with the sensor and event densities. Moreover, simulations are conducted to validate the analytic method. This method can provide guidelines for determining the amount of sensor nodes to achieve a certain level of coverage in event-driven sensor networks.

Sizing of MOS device in LC-tank oscillators

Since previous publications show conflicting results about sizing device, relationship between device size and 1/f2 phase noise is studied and closed-form equations are derived in order to help designers to size devices in LC-tank oscillators for good phase noise performance. The analysis is divided into two steps. Firstly, periodic noise transfer functions of each VCO noise source to the output of switch FETs are derived, and the impact of sizing on these functions is discussed. Secondly, phase noise equations are derived with these functions. Experiments show that phase noise predicted by the equations agrees with that from simulations.

Low noise amplifier architecture analysis for UWB system

This paper analyzes the architecture of wideband low noise amplifier (LNA) for multi-band orthogonal frequency division multiplexing modulation (MB-OFDM) ultra-wideband (UWB) system. Noise matching and input impedance matching are compared among different LNA architectures. Power consumption and area for different kinds of LNA architectures are also compared through the figure of merit (FOM).

Low Noise Amplifier Architecture Analysis for OFDM-UWB System in 0.18μm CMOS

This paper analyzes architectures of the low noise amplifier (LNA) for orthogonal-frequency-division-multiplexing ultra-wideband (OFDM-UWB) application. Until now, most UWB LNA implementations are focusing how to realize a single LNA covering the whole frequency band. In this work three popular wide-band LNA architectures are compared to a proposed parallel LNA architecture in which different amplifiers cover different frequency bands. Our study reveals that by reusing the source degenerated inductor between the different frequency bands, the parallel LNA architecture can achieve better performance than the single wide-band LNA (S11≪-10 dB, voltage gain≫15 dB, NF≪4.5 dB, power consumption≪10 mW) at the expense of a slightly increased circuit area.