Minimizing the Age of Information in Wireless Networks with Stochastic Arrivals

We consider a wireless network with a base station serving multiple traffic streams to different destinations. Packets from each stream arrive to the base station according to a stochastic process and are enqueued in a separate (per stream) queue. The queueing discipline controls which packet within each queue is available for transmission. The base station decides, at every time t, which stream to serve to the corresponding destination. The goal of scheduling decisions is to keep the information at the destinations fresh. Information freshness is captured by the Age of Information (AoI) metric. In this paper, we derive a lower bound on the AoI performance achievable by any given network operating under any queueing discipline. Then, we consider three common queueing disciplines and develop both an Optimal Stationary Randomized policy and a Max-Weight policy under each discipline. Our approach allows us to evaluate the combined impact of the stochastic arrivals, queueing discipline and scheduling policy on AoI. We evaluate the AoI performance both analytically and using simulations. Numerical results show that the performance of the Max-Weight policy is close to the analytical lower bound

Walk or wait?: An empirical analysis of street crossing decisions

We examine the behaviour of pedestrians wishing to cross a stream of trasffic at signalized intersections. We model each padestrian as making a desccrete crossing choice by comparing the gaps between vehicles in traffic to an individual-specific "critical gap" that characterizes the individual's minimal acceptable gap. We propose both parametric and nonparametric approaches to estimate the distribution of critical gaps in the population of pedestrians. To estimate the model, we gather field data on crossing decisions and vehicle flows at three intersections in New Delhi. The estimates provide information about heterogeneity in critical gaps across pedestrians and intersections and permits simulation of the effect of changes in traffic light sequence (flows)on pedestran crossing behavior and waiting times.

The Obama Administration’s November 2014 Immigration Initiatives: Questions and Answers

[Excerpt] On November 20, 2014, President Obama delivered a televised address wherein he broadly described the steps that his administration is taking to “fix” what he has repeatedly described as a “broken immigration system.” Following the President’s address, executive agencies made available intra-agency memoranda and fact sheets detailing specific actions that have already been taken, or will be taken in the future. These actions generally involve either border security, the current unlawfully present population, or future legal immigration. The announced executive actions—particularly the granting of deferred action and employment authorization to some unlawfully present aliens, discussed below (see “Unlawfully Present Population”)—have revived debate about the executive’s discretionary authority over immigration like that which followed the Administration’s June 2012 announcement of the Deferred Action for Childhood Arrivals (DACA) initiative. DACA has permitted some unlawfully present aliens who were brought to the United States as children and raised here to obtain temporary relief from removal and, in many cases, employment authorization. Some have argued that DACA constitutes an abdication of the executive’s duty to enforce the laws and runs afoul of specific requirements found in the Immigration and Nationality Act (INA), among other things. Others, however, have maintained that the DACA initiative is a lawful exercise of the discretionary authority conferred on the executive by the Constitution and federal statute. Similar arguments will likely be made as to the November 2014 actions, which affect a significantly larger number of aliens than DACA. This report provides the answers to key legal questions related to the various immigration-related actions announced by the Obama Administration on November 20, 2014. Because the various documents outlining these actions have been available for a limited period of time, and additional information is expected to be released in the future, these answers are necessarily preliminary. It is anticipated that the report will be updated to reflect further developments