R. James Duckworth

Content-Addressable and Associative Memory

Publisher Summary This chapter describes the field of content-addressable memory (CAM) and associative memory and the related field of associative processing. Traditional computers rely on a memory architecture that stores and retrieves data by addressing specific memory locations. The basic problems with conventional address-based systems have led researchers to investigate the potential benefits of CAMs, where information is stored, retrieved, or modified based upon the data itself, rather than by its arbitrary storage location. Modern parallel processing architectures, such as data flow machines, exploit application parallelism to increase their execution performance. Systems that rely on data flow properties do not execute efficiently using a traditional memory, where each data word can only be accessed serially by its location in a large sequential array. The chapter highlights the use of CAM in modern parallel processing architectures, focusing on its advantages and disadvantages. In an associative memory, the user must assign state variables to conceptual items and the connections between them. The associative recall takes the form of a response pattern obtained on the output when presented with a key pattern on the input. A further input in the form of a mask pattern includes context information that selects closeness of recall. In this way, a broad search might turn up enough information to allow a narrower search using a new key or mask context. The various elements in the memory can be linked by direct or indirect association. The chapter describes associative storage, retrieval, and processing methods, along with associative memory and processor architectures.

Transactional Array Reconciliation Tomography for Precision Indoor Location

A novel system is described for precision indoor location and tracking of personnel inside a building using RF signals exchanged with reference units deployed outside the building without benefit of infrastructure or site survey. Localization in high multipath without multilateration by fusion of unidirectional signals using singular array reconciliation tomography is reviewed. The bidirectional signal fusion approach is introduced with transactional array reconciliation tomography. Underlying theory is developed, and performance evaluated with simulated and experimental data.

Gyroscope assisted scalable visual simultaneous localization and mapping

This paper describes the development and evaluation of an indoor localization algorithm using Visual Simultaneous Localization and Mapping (VSLAM) aided by gyroscope sensor information. Indoor environments pose several challenges which could cause a vision only system to fail due to tracking errors. Investigation revealed significant feature loss in a vision only system when traversing plain walls, windows and staircases. However, the addition of a gyroscope helps in handling such difficult conditions by providing additional rotational information. A portable system consisting of an Inertial Measurement Unit (IMU) and a stereo camera has been developed for indoor mapping. The images and gyroscope rates acquired by the system are stored and post-processed using a new Gyroscope Assisted Scalable Visual Simultaneous Localization and Mapping Algorithm (GA-ScaViSLAM). The algorithm has been evaluated for data-sets collected in the Atwater Kent building, Worcester Polytechnic Institute. This algorithm was found to be more robust in comparison to the vision only system. The Ga-ScaViSLAM was found to have an error (rms) of 0.6 m in the indoor environment over a total path length of 77m.

Indoor navigation for first responders

On December 3, 1999, a tragedy occurred in Worcester, Massachusetts, at a fire in a large aging bric…

Detecting and locating fallures in communication networks

The connectivity of a strongly connected network may be destroyed after link damage. Since many networks are connected by directed links, the reachability may be restored by altering the direction of one or more of the links and thus reconfiguring the network. The location of the failed link must first be determined. In this paper, we examine new methods to determine the location of failed links and nodes in networks. A routing test approach is proposed and the conditions under which communication networks may be tested are discussed. Finally, an adaptive algorithm and a heuristic algorithm that can locate a single failed link or a single failed node are presented.