Cellular Digital Packet Data Systems Research Articles

Evaluating the effects of information technology on problem-oriented-policing. If it doesn't fit, must we quit?

Technologies promise to make our organizations more productive, efficient or effective. But our experience does not always fulfill this promise. Public safety agencies are the target of a barrage of new information technologies offering better performance, many of which are attractive because they can be financed through federal grants. But when evaluations are performed of these technologies, improvements do not always result. This article describes the experiences of a state police agency (SPA) during its use of cellular digital packet data (CDPD) systems to support its problem-oriented policing (POP) project. The CDPD system should have improved the SPA's POP operations; in practice, it was not as clear. Although participants believed the CDPD technology worthwhile, there were only a few minor differences between POP officers that did and did not use it. This evaluation suggests the need for better databases to measure performance as well as more informed federal funding of ways to assess the impact of technologies.

Optimal channel assignment strategies for forced channel hopping in CDPD systems

To provide an acceptable call blocking probability in circuit-switched cellular networks, such as the Advanced Mobile Phone System (AMPS) networks, a significant fraction of the channel capacity in each cell is normally unused. This “free” capacity can be effectively used for packet data transmissions that yield to voice traffic when necessary. Cellular Digital Packet Data (CDPD) is a packet-switched data service which may share radio channels with the AMPS service on a secondary basis to tap this “free” capacity. The length of time that a CDPD stream can occupy a channel is greatly influenced by the channel assignment strategies of both the AMPS and the CDPD systems. This paper investigates these channel assignment strategies and their effects on the CDPD channel holding times, in comparison with the optimal channel assignment strategy that interrupts the CDPD service only when a new AMPS call finds no other idle channels in the cell site. One such optimal strategy is the cooperative strategy in which the CDPD and AMPS networks actively communicate with each other. It is shown that other optimal strategies exist without the need of communications between the two systems. The effects of AMPS traffic levels, number of channels, and number of CDPD streams at the cell site on the CDPD channel holding time and channel utilization are also considered.

A performance study of CDPD

Cellular digital packet data (CDPD) is a wireless extension to data networks, which utilizes the idle capacity (radio channels) of cellular systems. This paper studies the performance of the CDPD system to investigate how the CDPD traffic and the voice traffic affect the CDPD blocking probability. The results offer guidelines for the CDPD network planning.

Modeling the sleep mode for cellular digital packet data

Cellular digital packet data (CDPD) utilizes sleep mode mechanism to conserve the power of mobile end systems (M-ESs). A timer called T203 determines how quick an M-ES enters the sleep mode, and another timer called T204 determines how often the M-ES wakes up. A large T204 value and a small T203 value can effectively reduce the power consumption at the cost of degrading the frame transmission performance, i.e., more lost frames, longer frame waiting times, and larger waiting variance. When the power consumption budget is determined in a CDPD system design, our study provides guidelines to determine the timer values as well as the buffer size to optimize the frame transmission performance.

Wireless communication and computing at the construction jobsite

For many years, the walkie-talkie has been synonymous with the construction industry. During jobsite project execution, there are three variables which can either hinder or facilitate successful results, namely, quality, quantity, and timing of information. Wireless data communications technology is capable of delivering just-in-time information within the `last mile' between the trailer and a desired location on the jobsite. This paper reports on a study which surveyed information needs at the jobsite, emerging wireless data communications technology, and assessed the extent to which wireless data technology can fulfill the information needs of the jobsite [J.M. de la Garza, I. Howitt, Wireless communication and computing at the jobsite, Research Report 136-11, Construction Industry Institute, Austin, TX, 1997]. We have organized jobsite information needs into the following ten categories: (a) requests for information, (b) materials management, (c) equipment management, (d) cost management, (e) schedule and means and methods, (f) jobsite record keeping, (g) submittals, (h) safety, (i) QC/QA, and (k) future trends. Each category was analyzed in terms of its appropriateness to take advantage of wireless technology. The four formats considered to transmit information wirelessly were: (a) live voice, (b) live video, (c) batched data, and (d) live data. Current wireless communication technology has been classified into the following five classes: (a) circuit-switched wireless data systems, (b) packet-switched wireless data systems—this class was further subdivided into specialized mobile radio systems and cellular digital packet data systems, (c) wireless local area networks, (d) paging systems, and (e) satellite-based data communications. A primer for wireless communications covering both fundamental and advanced communications concepts has also been included to enable a better understanding of the issues involved in making trade-offs while configuring a wireless jobsite communication system. The example presented in this paper shows how a contractor can define a subset of information needs by choosing from those already articulated herein and determine if a given wireless technology should even be considered as a viable way of meeting the information needs that such company has.

CELLULAR DIGITAL PACKET DATA FOR INTELLIGENT VEHICLE HIGHWAY SYSTEMS

For Intelligent Vehicle Highway Systems (IVHS) to be a reality, a communication system, which can provide reliable communication capability in mobile environment, is needed. A cellular system capable of supporting data traffic, can satisfy many of the IVHS communication requirements; such as traveller information and traffic management, public transit monitoring and control, fleet management, truck monitoring, hazard and collision warning. Cellular Digital Packet Data (CDPD) is a data transmission service which coexists with current cellular systems in the same frequency band and is presently being deployed. In this paper, we briefly summarize the salient features of CDPD system and evaluate its data transmission capacity. We also study suitability of CDPD for IVHS applications. Our study suggests that CDPD is capable of satisfying many of the functional requirements of IVHS. Furthermore, a mature IVHS system (with 50% penetration) will need approximately 36.5% of the capacity of CDPD system, even when the cellular system with which CDPD coexists, operates at its 2% Erland Capacity. With lesser penetration of IVHS, even smaller percentage of CDPD capacity will be needed. In conclusion, CDPD seems to be a promising technology for IVHS and should be further explored.