Minimizing latency in data acquisition distributed processing storage and retrieval

Abstract

Achieving low latency is of utmost importance in applications demanding real-time sensing and control as in cyber-physical systems. In this thesis, we explore three different facets of ensuring low latency in such systems. First part of this manuscript considers the design of an encoder-decoder system to facilitate real-time tracking of a physical process modelled as a first order auto-regressive process. Samples from a high-dimensional first-order auto-regressive process generated by an independently and identically distributed random innovation sequence are observed by a sender which can communicate only finitely many bits per unit time to a receiver. The receiver seeks to form an estimate of the process value at every time instant in real-time. We consider a time-slotted communication model in a slow-sampling regime where multiple communication slots occur between two sampling instants. We propose a successive update scheme which uses communication between sampling instants to refine estimates of the latest sample and study the following question: Is it better to collect communication of multiple slots to send better refined estimates, making the receiver wait more for every refinement, or to be fast but loose and send new information in every communication opportunity? We show that the fast but loose successive update scheme with ideal spherical codes is universally optimal asymptotically for a large dimension. However, most practical quantization codes for fixed dimensions do not meet the ideal performance required for this optimality, and they typically will have a bias in the form of a fixed additive error. Interestingly, our analysis shows that the fast but loose scheme is not an optimal choice in the presence of such errors, and a judiciously chosen frequency of updates outperforms it. Next part considers designing load balancing policies that ensures low latency without needing extra overhead in terms of server-side feedback or coordination among the servers. Dispatching policies such as the join sho...