Ryan E. Irwin

Resource-Minimized Channel Assignment for Multi-Transceiver Cognitive Radio Networks

The advancement of cognitive radio (CR) has uncovered new dynamics in multi-hop, wireless networking. Given the increased agility of a transceivers frequency assignment, the network topology can be optimized to address end-to-end networking goals. We propose a channel assignment scheme for cognitive radio networks (CRNs) that balances the need for topology adaptation focusing on flow rate maximization and the need for a stable baseline topology that supports network connectivity. We focus on CRNs in which nodes are equipped with multiple radios or transceivers, each of which can be assigned to a channel. First, our approach assigns channels independently of traffic, to achieve basic network connectivity and support light loads such as control traffic, and second, it dynamically assigns channels to the remaining transceivers in response to traffic demand. In this paper, we focus on the traffic-independent (TI) channel assignment with the goal of dedicating as few transceivers as possible to achieving baseline connectivity. By conserving transceivers in the TI assignment, the network is more able to adapt to any traffic demands in a subsequent traffic-driven (TD) assignment. We formulate the problem as a two-stage mixed integer linear program (MILP), with a TI stage and a TD stage. We propose a centralized greedy approach to TI assignment which performs nearly identically to the optimum obtained from the two-stage MILP in terms of the number of transceivers assigned and flow rate in the evaluated scenarios. Subsequently, we propose a distributed greedy TI approach that performs within 9% of the optimum in terms of the number of transceivers assigned and within 1.5% of the optimum in terms of flow rate.

Supporting Dynamic Spectrum Access in Heterogeneous LTE+ networks

With Long Term Evolution Advanced (LTE+) networks likely as the future one world 4G standard, network operators may need to deploy a Dynamic Spectrum Access (DSA) overlay in Heterogeneous Networks (HetNets) to extend coverage, increase spectrum efficiency, and increase the capacity of these networks. In this paper, we propose three new management frameworks for DSA in an LTE+ HetNet: Spectrum Accountability Client, Cell Spectrum Management, and Domain Spectrum Management. For these spectrum management frameworks, we define protocol interfaces and operational signaling scenarios to support cooperative sensing, spectrum lease management, and alarm scenarios for rule adjustment. We also quantify, through integer programs, the benefits of using DSA in an LTE+ HetNet that can opportunistically reuse vacant TV and GSM spectrum. Using integer programs, we consider a topology using Geographic Information System data from the Blacksburg, VA metro area to assess the realistic benefits of DSA in an LTE+ HetNet.

Evaluation of Dynamic Channel and Power Assignment for Cognitive Networks

In this paper, we develop a unifying optimization formulation to describe the Dynamic Channel and Power Assignment (DCPA) problem and an evaluation method for comparing DCPA algorithms. DCPA refers to the allocation of transmit power and frequency channels to links in a cognitive network so as to maximize the total number of feasible links while minimizing the aggregate transmit power. We apply our evaluation method to five representative DPCA algorithms proposed in the literature. This comparison illustrates the tradeoffs between control modes (centralized versus distributed) and channel/power assignment techniques. We estimate the complexity of each algorithm. Through simulations, we evaluate the effectiveness of the algorithms in achieving feasible link allocations in the network, and their power efficiency. Our results indicate that, when few channels are available, the effectiveness of all algorithms is comparable and thus the one with smallest complexity should be selected. The Least Interfering Channel and Iterative Power Assignment algorithm does not require cross-link gain information, has the overall lowest run time, and achieves the highest feasibility ratio of all the distributed algorithms; however, this comes at a cost of higher average power per link.

Traffic-Aware channel assignment for multi-radio wireless networks

This paper studies channel assignment in multi-hop wireless networks in which nodes are equipped with multiple radios, each of which can be assigned to a channel. We argue for an approach that first assigns channels independently of traffic, to achieve basic connectivity and support light loads such as control traffic, and then dynamically assigns channels to the remaining radios in response to traffic demand. The objective is to balance the need for a stable baseline topology and the desire to maximize throughput by dynamically adapting the topology to current network conditions. We call this a traffic-aware (TA) approach, in contrast to both traffic-independent (TI) and traffic-driven (TD) channel assignment and topology control schemes found in the literature. We formulate the problem as a two-stage mixed integer linear program (MILP), and find that our approach supports good connectivity and data rates comparable to those achieved with a TD channel assignment, while achieving lower resource utilization than TI approaches. We also quantify the tradeoffs involved in the decision of what proportion of radios to enable during the traffic-independent stage and what proportion to enable dynamically in response to changing traffic demands.

Channel Assignment Based on Routing Decisions (CARD): Traffic-Dependent Topology Control for Multi-Channel Networks

Dynamic spectrum access (DSA) holds the promise for more efficient utilization of the spectrum, while requiring greater cooperation between PHY, MAC, and NET layers to allocate resources and dynamically react to changing network conditions. In this paper, we propose Channel Assignment based on Routing Decisions (CARD), a mechanism that combines channel assignment and topology control so that at any given time the cognitive network self-organizes into the topology that is best suited to support the current offered traffic. CARD is a distributed mechanism, and each network node relies on local information only. We show that CARD results in an improvement in route length (and, thus, end-to-end delay), aggregate network capacity, and, in some situations, energy efficiency. In the process of designing a DSA medium access con- trol (MAC) scheme, new abstractions that span the physical, data-link, and network layers must be developed. This design encompasses the traditional PHY/MAC/NET functions along with new issues such as neighbor discovery in a multi-channel environment, rendezvous, and intelligent channel assignment. In this paper, we propose an approach that combines channel assignment and topology control, so that at any given time the network self-organizes into the topology that is best suited to support the current offered traffic. This approach, Channel Assignment based on Routing Decisions (CARD), is a distributed mechanism where each node makes decisions given its local information. Each node inspects the current route and attempts to shorten the route through dynamic selection of channels. It produces, whenever feasible, both an interference-free channel assignment for nodes actively involved in routing and shorter routes from source to destination. Preliminary results indicate that this method of jointly assigning channels and routes has benefits such as reduced delay and increased network capacity. In some cases energy-efficiency improvements are also obtained, and if enough channels are available intra- and inter-flow inter- ference avoidance techniques can be applied to improve network throughput.

Resource-Minimized Channel Assignment for Multi-Transceiver Wireless Networks

In this paper, we examine the problem of channel assignment in multi-hop wireless networks in which each node is equipped with multiple transceivers. We summarize various approaches to transceiver channel assignment. Most approaches in the literature seek to assign a channel to each available transceiver. In contrast, we seek to achieve a baseline connected topology that conserves resources, keeping some fraction of the transceivers inactive so as to dynamically react to changing traffic stimuli. We call our scheme resource-minimized channel assignment (RMCA). We show that RMCA achieves basic network connectivity and low interference, while using fewer resources compared to other protocols, and performs well under varied node density and number of transceivers per node. Finally, we evaluate several channel assignment schemes through simulation using a set of widely-accepted networking and graph- theoretic metrics.

A Comparison of Channel Assignment Techniques with Power Control in Ad Hoc Networks

Multi-channel operation in an ad hoc network can improve robustness and reliability by efficiently managing interference and reducing contention. In this paper, we model four dynamic channel assignment techniques under the same set of assumptions, comparing the efficiency of their power and channel allocations. As the number of channels increases, the differences in the performance of the four techniques become more pronounced. Among the techniques studied, the conflict graph-based technique achieves the highest number of feasible links and the lowest average power consumption. I. INTRODUCTION The advent of spectrum-agile radios that can self-organize into a cognitive network opens the possibility of topology con- trol that relies on both channel and transmit power allocation. Links in the network can be established simultaneously on different channels, and network nodes are sometimes equipped with multiple transceivers. The recent impetus towards exploit- ing underused bands or channels through dynamic spectrum access (DSA) has made it difficult to have an infrastructure- based management of channel assignment. Hence there is a growing need for efficient spectrum usage in the context of ad hoc networks. Improving the performance of such multi-channel wireless

Distributed resource control using shadowed subgraphs

As software defined networks (SDN) grow in size and in number, the problem of coordinating the actions of multiple SDN controllers will grow in importance. In this paper, we propose a way of organizing SDN control based on coordinated subgraph shadowing. Graphs are a natural way to think about and describe SDN activity. Subgraphs provide a means to share a subset of a networks resources. Shadowing provides a means to dynamically update shared subgraphs. Leveraging advances in graph databases and our shadowing messaging technique, we discuss our implementation of a multi-domain virtual private network (VPN) using multi-protocol label switching (MPLS).