Haley M. Jones

Intrinsic Limits of Dimensionality and Richness in Random Multipath Fields

We study the dimensions or degrees of freedom of farfield multipath that is observed in a limited, source-free region of space. The multipath fields are studied as solutions to the wave equation in an infinite-dimensional vector space. We prove two universal upper bounds on the truncation error of fixed and random multipath fields. A direct consequence of the derived bounds is that both fixed and random multipath fields have an effective finite dimension. For circular and spherical spatial regions, we show that this finite dimension is proportional to the radius and area of the region, respectively. We use the Karhunen-Loegraveve (KL) expansion of random multipath fields to quantify the notion of multipath richness. The multipath richness is defined as the number of significant eigenvalues in the KL expansion that achieve 99% of the total multipath energy. We establish a lower bound on the largest eigenvalue. This lower bound quantifies, to some extent, the well-known reduction of multipath richness with reducing the angular power spread of multipath angular power spectrum

On dimensionality of multipath fields: Spatial extent and richness

We establish that an arbitrary narrowband multi path field in any circular region in two dimensional space has an intrinsic functional dimensionality of (πe) R/λ ≈ 8.54 R/λ. that scales only linearly with radius R/λ. in wavelengths. This result implies there is no such thing as an arbitrarily complicated multi path field. That is, a field generated by any number of nearfield and farfield, specular and diffuse multipath reflections is no more complicated than a field generated by a limited number plane waves. As such, there are limits on how rich multipath can be. This result has significant implications including means: i) to determine a parsimonious parameterization for arbitrary multipath fields, ii) of synthesizing arbitrary multi path fields with arbitrarily located nearfield or farfield, spatially discrete or continuous sources. We give examples of multipath field analysis and synthesis.

Congestion-Aware Routing Protocol for Mobile Ad Hoc Networks

Congestion in mobile ad hoc networks leads to transmission delays and packet loss, and causes wastage of time and energy on recovery. Routing protocols which are adaptive to the congestion status of a mobile ad hoc network can greatly improve the network performance. In this paper, we propose a congestion-aware routing protocol for mobile ad hoc networks which uses a metric incorporating data-rate, MAC overhead, and buffer delay to combat congestion. This metric is used, together with the avoidance of mismatched link data-rate routes, to make mobile ad hoc networks robust and adaptive to congestion.

Channel-Aware Routing in MANETs with Route Handoff

In wireless mobile ad hoc networks (MANETs), packet transmission is impaired by radio link fluctuations. This paper proposes a novel channel adaptive routing protocol which extends the Ad hoc On-Demand Multipath Distance Vector (AOMDV) routing protocol to accommodate channel fading. Specifically, the proposed Channel-Aware AOMDV (CA-AOMDV) uses the channel average nonfading duration as a routing metric to select stable links for path discovery, and applies a preemptive handoff strategy to maintain reliable connections by exploiting channel state information. Using the same information, paths can be reused when they become available again, rather than being discarded. We provide new theoretical results for the downtime and lifetime of a live-die-live multiple path system, as well as detailed theoretical expressions for common network performance measures, providing useful insights into the differences in performance between CA-AOMDV and AOMDV. Simulation and theoretical results show that CA-AOMDV has greatly improved network performance over AOMDV.

A system dynamics approach in LCA to account for temporal effects-a consequential energy LCI of car body-in-whites

PurposeThe purpose of this paper is to take steps towards a life cycle assessment that is able to account for changes over time in resource flows and environmental impacts. The majority of life cycle inventory (LCI) studies assume that computation parameters are constants or fixed functions of time. This assumption limits the opportunities to account for temporal effects because it precludes consideration of the dynamics of the product system.MethodsSystem dynamics methods are used in a consequential, fleet-based LCI that accounts for some aspects of the dynamics of the wider system. The LCI model compares the life-cycle energy consumption of car body-in-whites (BIWs) in Australia made from steel and aluminium. It incorporates two dynamic processes: the flow of BIWs into and out of the fleet, and the recycling of aluminium from end-of-life BIWs back into new BIW production. The dynamical model computes both product-based and fleet-based estimates.Results and discussionThe product-based computations suggest that an aluminium BIW consumes less energy than a steel BIW over a single life cycle. The fleet-based computations suggest that the energy benefits of aluminium BIWs do not begin to emerge for some time. The substitution of aluminium for steel is a low-leverage intervention that changes the values of a few parameters of the system. The system has a delayed, damped response to this intervention because the large stock of BIWs is a source of high inertia, and the long useful life leads to a slow decay of steel BIWs out of the fleet. The recycling of aluminium back into BIW production is a moderate-leverage intervention that initially strengthens a reinforcing feedback loop, driving a rapid accumulation of energy benefits. Dominance then shifts to a balancing loop, slowing the accumulation of energy benefits. Both interventions result in a measureable reduction in life-cycle energy consumption, but only temporarily divert the underlying growth trend.ConclusionsThe results suggest that product-based LCIs overestimate the short-term energy benefits of aluminium by not accounting for the time required for the stock of preexisting steel components to decay out of the fleet, and underestimate the long-term energy benefits of aluminium components by not accounting for changes in the availability of recycled aluminium. The results also suggest that interventions such as lightweighting and other efficiency measures alone can slow the growth of energy consumption, but are probably inadequate to achieve sustainable energy consumption levels if the fleet is large.

An analysis framework for mobility metrics in mobile ad hoc networks

Mobile ad hoc networks (MANETs) have inherently dynamic topologies. Under these difficult circumstances, it is essential to have some dependable way of determining the reliability of communication paths. Mobility metrics are well suited to this purpose. Several mobility metrics have been proposed in the literature, including link persistence, link duration, link availability, link residual time, and their path equivalents. However, no method has been provided for their exact calculation. Instead, only statistical approximations have been given. In this paper, exact expressions are derived for each of the aforementioned metrics, applicable to both links and paths. We further show relationships between the different metrics, where they exist. Such exact expressions constitute precise mathematical relationships between network connectivity and node mobility. These expressions can, therefore, be employed in a number of ways to improve performance of MANETs such as in the development of efficient algorithms for routing, in route caching, proactive routing, and clustering schemes.

Connectivity Analysis of Wireless Ad Hoc Networks With Beamforming

In this paper, we present an analytical model for evaluating the impact of shadowing and beamforming on the connectivity of wireless ad hoc networks accommodating nodes equipped with multiple antennas. We consider two simple beamforming schemes: random beamforming, where each node selects a main beam direction randomly with no coordination with other nodes, and center-directed beamforming, where each node points its main beam toward the geographical center of the network. Taking path loss, shadowing, and beamforming into account, we derive an expression for the effective coverage area of a node, which is used to analyze both the local network connectivity (probability of node isolation) and the overall network connectivity (1-connectivity and path probability). We verify the correctness of our analytical approach by comparing with simulations. Our results show that the presence of shadowing increases the probability of node isolation and reduces the 1-connectivity of the network, although moderate shadowing can improve the path probability between two nodes. Furthermore, we show that the impact of beamforming strongly depends on the level of the channel path loss. In particular, compared with omnidirectional antennas, beamforming improves both the local and the overall connectivity for a path loss exponent of alpha < 3. The analysis in this paper provides an efficient way for system designers to characterize and optimize the connectivity of wireless ad hoc networks with beamforming.

Connectivity of ad hoc networks: Is fading good or bad?

In this paper, we investigate the effect of Rayleigh fading on the connectivity of wireless ad hoc networks. We consider static nodes that are equipped with omnidirectional antennas and are randomly distributed in the network according to a uniform distribution. We derive an analytical model for evaluating the impact of Rayleigh fading on the network local connectivity and present an accurate upper bound for 1-connectivity. Furthermore, our numerical results show that the presence of fading can result in an improvement in the overall connectivity, although it reduces the local connectivity of the network.

Connectivity of wireless ad hoc networks with random beamforming: An analytical approach

Random beamforming, where each node selects a main beam direction without any coordination with other nodes, has been proposed as a simple technique to improve connectivity in wireless ad hoc networks. This paper presents an analytical model for evaluating the impact of random beamforming on the connectivity of wireless ad hoc networks in the presence of path loss and shadowing effects. We investigate the connectivity with random beamforming from the view points of a single node and the entire network. The correctness of our analytical approach is validated by comparing the analytical results with simulations. We show that for a path loss exponent of alpha<3, irrespective of shadowing effects, random beamforming improves both the local and overall connectivity compared to omnidirectional antennas.

A system dynamics approach to understanding the influence of lightweight materials on the development of fuel efficient cars

This paper presents a dynamical model that assists in understanding the influence of lightweight materials on the development trajectory of fuel efficient cars. Preliminary results suggest that car mass and powertrain energy consumption may become significantly non-linear and may generally decrease in the coming decades due to the emergence of new technologies.