Ronan Farrell

Bounding the integrator outputs of second-order sigma-delta modulators

The development to date of the bounds for the outputs of the integrators of second-order sigma-delta modulators has relied on a mixture of theoretical analysis and extensive use of simulation. This paper presents a new approach that analyzes the behavior of such systems, and identifies the external boundaries of the trapping region for the outputs of the integrators. With this approach, it is possible to develop tight results for the standard second-order modulator with constant input, without the need for simulation. This approach is flexible, and can be adapted for other second-order architectures, and gives strong insight into the behavior of these systems.

Optimal Communication-Computation Tradeoff for Wireless Multimedia Sensor Network Lifetime Maximization

We address the issue of network lifetime maximization for a special class of wireless sensor networks namely, wireless multi-media sensor networks. High data rates, in these networks at the sensor nodes, compared to the conventional sensor networks and the presence of high temporal correlation in the sampled data make them a suitable candidate for the in-network processing, primarily at the sensor node itself. Using these distinguishing features of wireless multi-media sensor networks to our advantage, we have proposed a framework achieving an optimal tradeoff between communication and computation power consumption leading to network lifetime maximization under the delay quality of service constraints. The distributed implementation of the algorithm realizing the proposed framework is achieved using duality theory. A max-min fairness index based measure of network lifetime maximization is studied as a function of end-to-end delay thresholds. Numerical results show how the total network power consumption is distributed between the communication and the computation power consumption components. The results also provide an insight about the maximum and minimum nodal power consumptions. Our results show that the superior performance in terms of max-min fairness index at higher end-to-end delay thresholds is mainly attributed to the relative lower computation cost compared to the communication cost.

Software-Defined Radio Demonstrators: An Example and Future Trends

Software-defined radio requires the combination of software-based signal processing and the enabling hardware components. In this paper, we present an overview of the criteria for such platforms and the current state of development and future trends in this area. This paper will also provide details of a high-performance flexible radio platform called the maynooth adaptable radio system (MARS) that was developed to explore the use of software-defined radio concepts in the provision of infrastructure elements in a telecommunications application, such as mobile phone basestations or multimedia broadcasters.

Energy-Efficient Zero-Forcing Precoding Design for Small-Cell Networks

We consider small-cell networks with multiple-antenna transceivers and base stations (BSs) cooperating to jointly design linear precoders to maximize the network energy efficiency, subject to a sum power and per-antenna power constraints at individual BSs, as well as user-specific quality of service (QoS) requirements. Assuming zero-forcing precoding, we formulate the problem of interest as a concave-convex fractional program to which we proposed a centralized optimal solution based on the prevailing Dinkelbach algorithm. To facilitate distributed implementations, we transform the design problem into an equivalent convex program using Charnes-Coopers transformation. Then, based on the framework of alternative direction method of multipliers (ADMM), we develop a decentralized algorithm, which is numerically shown to achieve fast convergence. Since BSs are generally power-hungry, it may be more energy-efficient if some BSs can be shut down, while still satisfying the QoS constraints. Toward this end, we investigate the problem of joint precoder design and BS selection, which is a mixed Boolean nonlinear program, and then provide an optimal solution by customizing the branch-and-bound method. For real-time applications, we propose a greedy algorithm which achieves near-optimal performance in polynomial time. Numerical results are provided to demonstrate the effectiveness of the proposed algorithms.

Using high pass sigma-delta modulation for Class-S power amplifiers

Switching power amplifiers offer the potential for superior efficiencies if used at radio frequencies. However many existing bandpass architectures require a switching frequency four times that of the signal, making implementation difficult. In this paper we propose to use a high-pass sigma-delta modulator to reduce the switching rate to only twice of the signal. We will present a solution to the problem of the reflected image and demonstrate its viability for use in mobile telephony.

Wideband 0.18μm CMOS VCO using active inductor with negative resistance

This paper presents a wideband voltage controlled oscillator topology based on an active inductor generating negative resistance. The proposed architecture covers a frequency band between 1.325 GHz - 2.15 GHz with average in-band phase noise of -86 dBc/Hz at 1 MHz offset from the carrier frequency. Power consumption of the oscillator core is 28 mW from a 1.8 V supply. The circuit has been simulated in Eldo RF (Design Architect IC, Mentor Graphics) using UMC 0.18 mum 1P6M Salicide RF CMOS model libraries.

A Resource Management Tool for Implementing Strategic Direction in an Academic Department.

This paper reports on a load balancing system for an academic department, which can be used as an implementation mechanism for strategic planning. In essence, it consists of weighting each activity within the department and performing workload allocation based on this transparent scheme. The experience to date has been very positive, in terms of achieving strategic change and staff contentment.

An Efficiency Maximization Design for SWIPT

A joint power splitting and beamforming design for multiuser multiple-input single-output (MISO) systems where receivers have capability of decoding information and harvesting energy simultaneously from received signals is considered. The objective is to maximize the ratio of the achieved utility to the total power consumption subject to harvested power requirements and power budget at a base station (BS). The utility function of interest combines the sum rate and the total harvested power. The design problem is nonconvex, and thus, global optimality is difficult to achieve. To solve this problem locally we first convert the problem into a more tractable form, and then propose an iterative algorithm which is guaranteed to achieve a Karush-Kuhn-Tucker solution. Numerical results are provided to demonstrate the superior performance of the proposed method.

Value-Chain Engineering of a Tower-Top Cellular Base Station System

In this paper we present a value chain analysis of mobile phone basestations, with a focus on possible antenna based tower-top electronics. Through this analysis we are able to present a number of possible architectural solutions and provide guidance on performance and reliability criterion.

A cross-layer framework for optimal delay-margin, network lifetime and utility tradeoff in wireless visual sensor networks

For wireless multimedia sensor networks a distributed cross-layer framework is proposed, which not only achieves an optimal tradeoff between network lifetime and its utility but also provides end-to-end delay-margin. The delay-margin, defined as the gap between maximum end-to-end delay threshold and the actual end-to-end delay incurred by the network, is exploited by the application layer to achieve any desired level of delay quality-of-service. For optimal performance tradeoff an appropriate objective function for delay-margin is required, which is obtained by employing sensitivity analysis. Sensitivity analysis is performed by incorporating delay-margin in the end-to-end delay constraints while penalizing its price in the objective function. For distributed realization of proposed cross-layer framework, the optimal tradeoff problem is decomposed into network lifetime, utility and delay-margin subproblems coupled through dual variables. The numerical results for performance evaluation show that compromising network utility does not guarantee both lifetime and delay-margin improvement, simultaneously, for the set of operating points. Performance evaluation results also reveal that the fairness among different delay-margins, corresponding to different source-destination node pairs, can be improved by relaxing the end-to-end delay threshold.