This text presents a modern theory of analysis, control, and optimization for dynamic networks. Mathematical techniques of Lyapunov drift and Lyapunov optimization are developed and shown to enable constrained optimization of time averages in general stochastic systems. The focus is on communication and queueing systems, including wireless networks with time-varying channels, mobility, and randomly arriving traffic. A simple drift-plus-penalty framework is used to optimize time averages such as throughput, throughput-utility, power, and distortion. Explicit performance-delay tradeoffs are provided to illustrate the cost of approaching optimality. This theory is also applicable to problems in operations research and economics, where energy-efficient and profit-maximizing decisions must be made without knowing the future. Topics in the text include the following: - Queue stability theory - Backpressure, max-weight, and virtual queue methods - Primal-dual methods for non-convex stochastic utility maximization - Universal scheduling theory for arbitrary sample paths - Approximate and randomized scheduling theory - Optimization of renewal systems and Markov decision systems Detailed examples and numerous problem set questions are provided to reinforce the main concepts. Table of Contents: Introduction / Introduction to Queues / Dynamic Scheduling Example / Optimizing Time Averages / Optimizing Functions of Time Averages / Approximate Scheduling / Optimization of Renewal Systems / Conclusions

Stochastic Network Optimization with Application to Communication and Queueing Systems

Probability and Measure

(1987). Applied Probability and Queues. Journal of the Operational Research Society: Vol. 38, No. 11, pp. 1095-1096.

https://link.springer.com/content/pdf/10.1057%2Fjors.1987.184.pdf

Applied Probability and Queues

We consider the age-of-information in a multi-class M/G/1 queueing system, where each class generates packets containing status information. Age of information is a relatively new metric that measures the amount of time that elapsed between status updates, thus accounting for both the queueing delay and the delay between packet generation. This gives rise to a tradeoff between frequency of status updates, and queueing delay. In this paper, we study this tradeoff in a system with heterogenous users modeled as a multi-class M/G/1 queue. To this end, we derive the exact peak age-of-Information (PAoI) profile of the system, which measures the “freshness” of the status information. We then seek to optimize the age of information, by formulating the problem using quasiconvex optimization, and obtain structural properties of the optimal solution.

/pdf/optimizing-age-of-information-in-a-multi-class-queueing-3snufoga6j.pdf

Optimizing age-of-information in a multi-class queueing system

Current data collection protocols for wireless sensor networks are mostly based on quasi-static minimum-cost routing trees. We consider an alternative, highly-agile approach called backpressure routing, in which routing and forwarding decisions are made on a per-packet basis. Although there is a considerable theoretical literature on backpressure routing, it has not been implemented on practical systems to date due to concerns about packet looping, the effect of link losses, large packet delays, and scalability. Addressing these concerns, we present the Backpressure Collection Protocol (BCP) for sensor networks, the first ever implementation of dynamic backpressure routing in wireless networks. In particular, we demonstrate for the first time that replacing the traditional FIFO queue service in backpressure routing with LIFO queues reduces the average end-to-end packet delays for delivered packets drastically (75% under high load, 98% under low load). Further, we improve backpressure scalability by introducing a new concept of floating queues into the backpressure framework. Under static network settings, BCP shows a more than 60% improvement in max-min rate over the state of the art Collection Tree Protocol (CTP). We also empirically demonstrate the superior delivery performance of BCP in highly dynamic network settings, including conditions of extreme external interference and highly mobile sinks.

/pdf/routing-without-routes-the-backpressure-collection-protocol-1ak0dr1fnf.pdf

Routing without routes: the backpressure collection protocol

Back-pressure based algorithms based on the algorithm by Tassiulas and Ephremides have recently received much attention for jointly routing and scheduling over multi-hop wireless networks. However a significant weakness of this approach has been in routing, because the traditional back-pressure algorithm explores and exploits all feasible paths between each source and destination. While this extensive exploration is essential in order to maintain stability when the network is heavily loaded, under light or moderate loads, packets may be sent over unnecessarily long routes and the algorithm could be very inefficient in terms of end-to-end delay and routing convergence times. This paper proposes new routing/scheduling back-pressure algorithms that not only guarantees network stability (through-put optimality), but also adaptively selects a set of optimal routes based on shortest-path information in order to minimize average path-lengths between each source and destination pair. Our results indicate that under the traditional back-pressure algorithm, the end-to-end packet delay first decreases and then increases as a function of the network load (arrival rate). This surprising low-load behavior is explained due to the fact that the traditional back-pressure algorithm exploits all paths (including very long ones) even when the traffic load is light. On the otherhand, the proposed algorithm adaptively selects a set of routes according to the traffic load so that long paths are used only when necessary, thus resulting in much smaller end-to-end packet delays as compared to the traditional back-pressure algorithm.

/pdf/on-combining-shortest-path-and-back-pressure-routing-over-1a3js6an98.pdf

On Combining Shortest-Path and Back-Pressure Routing Over Multihop Wireless Networks

Systems and methods for managing communication in an unlicensed band of frequencies to supplement communication in a licensed band of frequencies in unlicensed spectrum are disclosed. The management may comprise, for example, monitoring utilization of resources currently available to a first Radio Access Technology (RAT) via at least one of a Primary Cell (PCell) operating in the licensed band, a set of one or more Secondary Cells (SCells) operating in the unlicensed band, or a combination thereof. Based on the utilization, a first SCell among the set of SCells may be configured or de-configured with respect to operation in the unlicensed band.

Opportunistic supplemental downlink in unlicensed spectrum

We study the problem of distributed scheduling in wireless networks, where each node makes individual scheduling decisions based on heterogeneously delayed network state information (NSI). This leads to inconsistency in the views of the network across nodes, which, coupled with interference, makes it challenging to schedule for high throughputs.

We characterize the network throughput region for this setup, and develop optimal scheduling policies to achieve the same. Our scheduling policies have a threshold-based structure and, moreover, require the nodes to use only the "smallest critical subset" of the available delayed NSI to make decisions. In addition, using Markov chain mixing techniques, we quantify the impact of delayed NSI on the throughput region. This not only highlights the value of extra NSI for scheduling, but also characterizes the loss in throughput incurred by lower complexity scheduling policies which use homogeneously delayed NSI.

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On distributed scheduling with heterogeneously delayed network-state information

Different hand-derived biometric traits have been used for user authentication in many commercial systems. In this paper we have investigated the possibility of using a new biometric trait, the knuckle, for user authentication. Knuckle regions are extracted from the hand images and correlation methods are used for the purpose of verification. Experimental results on a data set of 125 people show that the knuckle is a viable biometric trait, which can be used as an alternative to finger and palm prints or in conjunction with them.

Knuckle based hand correlation for user authentication

The present disclosure presents a method and an apparatus for improving performance of a user equipment (UE) operating in unlicensed spectrum. For example, the disclosure presents a method for receiving, at the UE, a secondary component carrier (SCC) update from a small cell. The example method further includes tuning the UE to a second SCC in response to receiving the update. The update is received at the UE when the small cell operating on a first radio access technology (RAT) determines that a channel associated with a first SCC of the small cell is also in use by another entity operating on a second RAT. As such, improved performance of a user equipment (UE) operating in an unlicensed spectrum may be achieved.

Reddy Akula

Papers

On Combining Shortest-Path and Back-Pressure Routing Over Multihop Wireless Networks

Opportunistic supplemental downlink in unlicensed spectrum

On distributed scheduling with heterogeneously delayed network-state information

Knuckle based hand correlation for user authentication

Performance of a user equipment (UE) in unlicensed spectrum