Darryn Lowe

Optimal Adaptive Hyperbolic Companding for OFDM

In this paper, we derive and analyze a companding algorithm based on the hyperbolic tangent and inverse hyperbolic tangent functions for use in orthogonal frequency division multiplexing (OFDM) transceivers. Probability density functions (PDFs) that approximate the transmitted and received OFDM signals in the presence of additive white Gaussian noise (AWGN) are derived and used to analyze the degree of companding relative to the signal-to-noise ratio (SNR) and clipping level. A set of optimal companding linearity coefficients for the multi-band OFDM (MB-OFDM) ultra-wideband (UWB) standard are presented.

A Simulation Study of TCP over the IEEE 802.15.3 MAC

This paper presents the impact of IEEE 802.15.3 MACs channel time allocation methods on a TCP flows performance. We show the importance of having super rate and appropriately sized channel time allocations (CTAs)

A Study of Different Angles for the New Spread Matrix for BSOFDM in UWB Channels

This paper presents a study into different angles for the new spread matrix developed for BSOFDM. It varies the angles for the matrix to develop different constellation schemes which are useful in overcoming the frequency selective channels which are encountered in mobile communication systems. Previously it has been discussed that this new matrix (the rotation matrix) has some advantages over Hadamard and the rotated Hadamard matrix in certain channels. This paper presents a study of varies angles with this new matrix over the UWB channels CM1 to CM4.

Adaptive Overlap-Add Equalization for MB-OFDM Ultra-Wideband

A zero-pad can be used with orthogonal frequency division multiplexing (OFDM) for low-complexity robustness against multipath interference. In this paper, we use adaptive overlap-add (OLA) equalization for improvements of up to 1 dB when used with multi-band OFDM (MB-OFDM) ultra-wideband. A theoretical model that relates the size of OLA window to post-equalizer signal-to-noise ratio is derived. An approximating algorithm is then developed that is suitable for low-complexity implementation, with Monte Carlo simulations used to quantify the performance improvements. We conclude that adaptive OLA equalization is computationally simple and can be implemented while remaining fully compliant with the MB-OFDM standard

Ultra-Wideband Technology for Video Surveillance Sensor Networks

Wireless sensor networks have received a lot of attention in recent years both in the research community and in standards organizations. The emphasis of most sensor network research activities has been on the development of low cost and low power technologies for low bit rate applications. In this paper, we describe our work on ultra-wideband (UWB) sensor network technology targeted for video surveillance applications that require high immunity to noise, interference and jamming, high bit rate, and quality of service support. Such sensor networks are expected to find primary applications in the public safety and military fields. Our emphasis in this paper is on the design of the physical layer that can support such requirements and provide high end-to-end throughput when multi-hopping is used.

ROAR: a multi-rate opportunistic AODV routing protocol for wireless ad-hoc networks

In this paper, we outline a simple approach, called ROAR, that enables the Ad-Hoc On-Demand Distance Vector (AODV) routing protocol to strengthen its routes by recruiting neighbors of nodes on the least cost path as support nodes during the route construction process, and working closely with the medium access control (MAC) to employ an opportunistic forwarding scheme that takes advantage of the node diversity at each hop. We have implemented ROAR in the ns-2 simulator over the IEEE 802.11a physical layer. From our simulation studies conducted using various network topologies and realistic radio propagation model, we find that ROAR increases AODVs packet delivery ratio and end-to-end throughput several orders of magnitude, in particular for hop count based routes. Therefore, ROAR provides a simple add-on that allows routing protocols to reap the benefits of diversity without relying on physical layer approaches.

Adaptive Low-Complexity MMSE Channel Estimation for OFDM

In this paper we present extremely low-complexity adaptive infinite impulse response (IIR) filters that approximate minimum mean square error (MMSE) channel estimation in orthogonal frequency-division multiplexing (OFDM) systems. We show how the packet error rate (PER) can be significantly improved over conventional zero-forcing (ZF) estimation without incurring a significant increase in computational complexity. All quantitative results are provided in the context of multi-band OFDM (MB-OFDM) ultra-wideband (UWB) with standard IEEE channel models

Ultra-Wideband MB-OFDM Channel Estimation with Complementary Codes

In this paper, we design complementary codesets that significantly improve the quality of channel estimation in orthogonal frequency division multiplexing (OFDM) communication systems, with a focus on the recent MB-OFDM ultra-wideband (UWB) standard. The proposed time-domain OFDM channel estimation technique incurs only a nominal increase in computational complexity and is able to be readily retrofitted into the existing MB-OFDM standard. The underlying complementary codesets, found via an evolutionary algorithm, combine with the existing preamble synchronization sequences to yield asymptotically ideal auto-correlation functions (ACFs). We show how improvements exceeding 1 dB can be achieved in end-to-end packet error rate relative to conventional zero-forcing OFDM equalization

An Impulse Ultra-wideband System Capable of Concurrent Transmission and Reception, Part I: Requirements and Innovations

This paper presents a novel ultra-wideband (UWB) system for low power, long range, mid to high data rate mesh networking applications. Combined with the complementary code division multiplexing modulation and the multicode interleaved direct sequence spread spectrum techniques, the system aims to achieve interference resistance, coexistence with legacy systems, and robust performance in hostile multipath environments. The unique feature of the system is the support for concurrent transmission and reception, which will enable a medium access control mechanism with cut-through routing to be developed for high-throughput UWB mesh networks. It is concluded that this new UWB system represents a fundamental advance in UWB technology

Routing in MANETs with address conflicts

Mobile ad-hoc networks (MANETs) are dynamic and multi-hop in nature. As nodes continually join and leave the MANET, managing the problem of address conflicts is particularly challenging. In the past, researchers have gone to great lengths to ensure that nodes are assigned unique addresses and various protocols and policies have been designed to resolve address conflicts. In this paper, we argue that current solutions, originally designed for static wired networks, put unnecessary stress on the dynamic operation of a MANET. To solve, this problem, we present a MANET that can continue to operate even when there are conflicting addresses. Unlike previous solutions, our technique does not break applications by requiring nodes to renumber. Further, the overheads introduced by traditional address allocation and maintenance protocols are removed. All these improvements are effected by introducing of a new routing sub-layer that enables a reactive routing protocol to route packets through a MANET that is experiencing address conflicts. This routing sub-layer provides features such as conflict avoidance forwarding, conflict notification, and enhanced address resolution.