Routing and Scheduling Algorithms in Resource-Limited Wireless Multi-Hop Networks

The recent advances in the area of wireless networking present novel opportunities for network operators to expand their services to infrastructure-less wireless systems.Such networks, often referred to as ad-hoc or multi-hop or peer-to-peer networks, require architectures which do not necessarily follow the cellular paradigm. They consist of entirely wireless nodes, fixed and/or mobile, that require multiple hops (and hence relaying by intermediate nodes) to transmit their messages to the desired destinations. The distinguishing features of such all-wireless network architectures give rise to new trade-offs between traditional concerns in wireless communications (such as spectral efficiency, and energy conservation) and the notions of routing, scheduling and resource allocation. The purpose of this work is to identify and study some of these novel issues, propose solutions in the context of network control and evaluate the usual network performance measures as functions of the new trade-offs.To these ends, we address first the problem of routing connection-oriented traffic with energy efficiency in all-wireless multi-hop networks. We take advantage of the flexibility of wireless nodes to transmit at different power levels and define a framework for formulating the problem of session routing from the perspective of energy expenditure. A set of heuristics are developed for determining end-to-end unicast paths with sufficient bandwidth and transceiver resources, in which nodes use local information in order to select their transmission power and bandwidth allocation. We propose a set of metrics that associate each link transmission with a cost and consider both the cases of plentiful and limited bandwidth resources, the latter jointly with a set of channel allocation algorithms. Performance is measured by call blocking probability and average consumed energy and a detailed simulation model that incorporates all the components of our algorithms has been developed and used for performance evaluation of a variety of networks.In the sequel, we propose a "blueprint" for approaching the problem of link bandwidth management in conjunction with routing, for ad-hoc wireless networks carrying packet-switched traffic. We discuss the dependencies between routing, access control and scheduling functions and propose an adaptive mechanism for solving the capacity allocation (at both the node-level and the flow-level) and the route assignment problems, that manages delays due to congestion at nodes and packet loss due to error prone wireless links, to provide improved end-to-end delay/throughput. The capacity allocations to the nodes and flows and the route assignments are iterated periodically and the adaptability of the proposed approach allows the network to respond to random channel error bursts and congestion arising from bursty and new flows

Routing Session Traffic in Fixed All-Wireless Networks under Energy and Bandwidth Limitations

In this paper we study the effects of limited bandwidthresources in the development of energy-efficient routing algorithmsfor connection-oriented traffic in fixed wireless ad-hoc networks. Afrequency division multiple access scheme is considered, in whichnodes must schedule their transmissions by selecting frequencychannels from a limited set in an interference-free fashion. In ourearlier work, we had developed a set of algorithms for determiningend-to-end unicast paths based on link metrics. We argue that inorderto address the effects of limited frequency resources,such algorithms must be coupled with channel allocation mechanismsfor providing conflict free frequency assignments over selectedroutingpaths. To these ends, we propose a set of link metricsfor selecting candidate routing paths and a set of heuristics forfrequency allocation. We evaluate their performance using ourdetailedsimulation model

Energy-Efficient Routing for Connection-Oriented Traffic in Wireless Ad-hoc Networks

We address the problem of routing connection-oriented traffic in wireless ad-hoc networks with energy efficiency. We outlinethe trade-offs that arise by the flexibility of wireless nodes totransmit at different power levels and define a framework forformulating the problem of session routing from the perspective ofenergy expenditure. A set of heuristics are developed for determiningend-to-end unicast paths with sufficient bandwidth and transceiverresources, in which nodes use local information in order to selecttheir transmission power and bandwidth allocation. We propose a setofmetrics that associate each link transmission with a cost andconsiderboth the cases of plentiful and limited bandwidth resources, thelatter jointly with a set of channel allocation algorithms.Performance is captured by call blocking probability and averageconsumed energy. A detailed simulation model has been developed andused to evaluate the algorithms for a variety of networks

Routing Algorithms in All-Mobile Wireless Networks

In networks with mobile radio nodes in which connectivity varies, rapidly with time, it is necessary to develop algorithms for identifying, and maintaining paths between communicating pairs of nodes. Motivated by, earlier work that accomplishes such a task for data gram packet service, we develop a similar algorithm for connection-oriented service. The algorithm establishes circuit routes for initial connection based on a mechanism of short packets exchange and takes advantage of the possibility to convert a connectivity change into a ``soft'' failure to maintain and re-route on-going sessions. In this paper we give a presentation of the algorithm which is currently undergoing extensive simulation-based evaluation. A copy of this report has been published in the proceedings of The 1st Annual Advanced Telecommunications/Information Distribution Research Program Conference, January 21-22, 1997. </ul

Proteome changes during transition from human embryonic to vascular progenitor cells

Summarization: Human embryonic stem cells (hESCs) are promising in regenerative medicine (RM) due to their differentiation plasticity and proliferation potential. However, a major challenge in RM is the generation of a vascular system to support nutrient flow to newly synthesized tissues. Here we refined an existing method to generate tight vessels by differentiating hESCs in CD34+ vascular progenitor cells using chemically defined media and growth conditions. We selectively purified these cells from CD34- outgrowth populations also formed. To analyze these differentiation processes, we compared the proteomes of the hESCs with those of the CD34+ and CD34- populations using high resolution mass spectrometry, label-free quantification, and multivariate analysis. Eighteen protein markers validate the differentiated phenotypes in immunological assays; nine of these were also detected by proteomics and show statistically significant differential abundance. Another 225 proteins show differential abundance between the three cell types. Sixty-three of these have known functions in CD34+ and CD34- cells. CD34+ cells synthesize proteins implicated in endothelial cell differentiation and smooth muscle formation, which support the bipotent phenotype of these progenitor cells. CD34- cells are more heterogeneous synthesizing muscular/osteogenic/chondrogenic/adipogenic lineage markers. The remaining >150 differentially abundant proteins in CD34+ or CD34- cells raise testable hypotheses for future studies to probe vascular morphogenesis.Presented on: Journal of Proteome Researc