Wireless Local Loop Research Articles

The wireless local loop

In telephony, the loop is defined as the circuit connecting a subscriber's station (e.g., telephone set) with the line terminating equipment in a central office (a switch in the telephone network). The trunks start from the central office in the loop; they break down into several smaller bundles of circuits after moving away from the central office. These circuits are eventually separated into individual drops for the residential homes. The cost of the loop tends to be dominated by the residential side. (It is typically referred to as the "expensive last km"). This statement is particularly true for rural areas. The International Telecommunications Union's (ITU) projection indicates that 150 million new telephone lines will need to be installed in developing countries by the year 2000. As a result, telecommunication operators are looking to wireless technology to replace part of the hard-wire infrastructure. Wireless local loop (WLL) technology is being considered because the radio systems can be rapidly developed, easily extended and are distance insensitive. The WLL eliminates the wires, poles and ducts essential for a wired network.

The economic viability of wireless local loop and its impact on universal service

This paper presents an overview of the economics of wireless transport focusing on Personal Communications Service (PCS) and Local Multipoint Distribution Service (LMDS) as compared with the existing incumbent local exchange carriers, namely the I-LECs. The paper also addresses the issues of universal service and presents an analysis of how wireless may be aviable player in that environment. The paper combines the approaches from several different fields and demonstrates that wireless has applications as a provider of universal services in certain niche areas but it is not a clear universal application. The paper also develops several policy issues as to how best to deal with the issue of universal services and also addresses the issue of how far that social demand should be extended.

Feasibility of using radio relay in low tier wireless local loop systems

Abstract Low tier wireless local loop systems offer great promise for the delivery of basic telephone service in developing nations. In some cases, though, the lack of cable plant needed to interconnect system elements may be a serious impediment. Four radio relay alternatives to cable-based interconnection are described, and the feasibility of each is examined. Economic feasibility is assessed by estimating the required investments. Radio spectrum requirements are also estimated.

Low-tier wireless local loop radio systems. I. Introduction

The article provides the results of a set of analyses conducted to compare two major radio technologies, DECT/PWT-E and PACS, for their suitability in the local loop in the United States to provide voice and data services. DECT, digital enhanced cordless telecommunications, is a radio interface standard developed in Europe mainly for indoor wireless applications and being promoted lately for wireless local loop applications as well. PWT, personal wireless telecommunications, is a DECT-based standard developed by the TIA in the United States for the unlicensed PCS applications. PWT-E, enhanced, is the version that is suitable for the licensed PCS applications. PACS, personal access communications systems, is a total system standard (i.e. radio interface and associated network infrastructures) developed in the United States for licensed PCS applications. (PACS-UA and PACS-UB are the standards for the unlicensed PCS applications.) For the wireless local loop (WLL), we make an assumption that the radio technologies operating in the licensed PCS spectrum are more suitable to provide a quality of service that is expected traditionally from a local exchange company (LEC). Therefore, this article focuses on the PACS and PWT-E, rather than PACS-UB and PWT. Also note that the article focuses on the North American version, PWT-E, rather than the European version, DECT. It provides an introduction to the PACS and PWT technologies.

Low-tier wireless local loop radio systems .2. Comparison of systems

For pt.1 see ibid., no.3, p.84 (1997). The article provides the results of a set of analyses conducted to compare two major radio technologies, DECT/PWT-E and PACS, for their suitability in the local loop to provide voice and data services for customers. The authors first provide brief discussions on the Japanese Personal Handyphone System (PHS) and Omnipoint's Combined CDMA/TDMA (CCT) system as potential candidates. The authors do not currently consider them viable alternatives for local loop since the PHS is not suitable for the US environment, and the CCT system will not be available in the near future. The PACS and PWT-E systems are then compared based on their architecture, service, coverage, and operations-related capabilities. The authors also compare them in proposed deployments in Jacksonville and Miami, Florida. Finally, the authors draw some conclusions from their study.

The effect of narrowbeam antenna and multiple tiers on system capacity in CDMA wireless local loop

The wireless local loop (WLL) system is a local telephone system without wireline connection. It is believed to be a fast and cost-effective means to provide local phone service in rural areas and third world countries. WLL is a fixed radio communication system; narrowbeam antennas can be employed at both the base station and subscriber's side at high spots so that the propagation between base station and house is very close to free space propagation. This gives the WLL system many inherent advantages over the traditional cellular system, such as bigger coverage area, low power, reduced interference, higher capacity, no fast fading, and no handoff. In this article ideal multiple-tier hexagonal cells are used to derive the capacity of a CDMA WLL system. First, the reverse link interference from each tier to the center cell is calculated separately. Then, the interference ratio of reverse links in a WLL system is analytically derived as a function of total tier number. The result shows that interference from other cells is proportional to the beam width of the house antenna. The authors also found that tier number plays a vital role in system capacity in a free-space propagation (20 dB/dec) environment. At the extreme, the system capacity will drop to zero for an infinite-tier cell structure. A WLL simulator is also built to verify the authors' analytical solution.

A direct signaling system for flexible access and deployment of telecommunication services

In current telecommunication networks, the value-added services available to subscribers are almost exclusively offered by the carrier providing local telephony service. This results from two factors: the processing for services is either based in or triggered from software executing on the access telecommunication switches, and signaling links over which subscribers request services are terminated on these access switches. In a direct signaling system, the signaling link from a subscriber does not necessarily terminate on an access switch, but rather on an intelligent server we call a call server. The call server invokes service functions and coordinates their interactions. This direct signaling system may be overlaid on various types of access networks, including circuit-switched telephony, packet telephony, wireless local loop, cable, etc. We discuss the design, implementation, and performance of a direct signaling system, including procedures that provide varying amounts of integration with current telecommunication systems. Our results show that a direct signaling system using a low-delay direct signaling link and in which no changes are made to existing telecommunicatione switches incurs approximately 100 ms higher postdial delay than a standard ISDN system. A direct signaling system in which telecommunication switches provide open interfaces and coordinate processing with direct signaling servers incurs approximately 100 ms lower postdial delay than a standard ISDN system.

PACS: Personal Access Communications System-a tutorial

The Personal Access Communications System (PACS) is an American National Standards Institute common air interface standard developed for the 1.9 GHz PCS band in the United States. PACS uses frequency division duplexing technology and is optimized to support low-mobility pedestrian outdoor usage and wireless local loop applications in a medium-range environment. PACS-Unlicensed B (PACS-UB) is a version of PACS using time division duplexing. PACS-UB has been optimized for private, indoor wireless PBX applications and cordless telephony. Both modes of operation are supported using the same portable hardware and the same signaling protocol.

Digital wireless local loop system

The digital access technologies for the wireless local loop (WLL) or fixed wireless system are discussed. WLL is an important means of providing telephone services more cheaply and quickly in the developing countries than through a wireline system. Capacities of a WLL system based on the IS-54 (now IS-136) TDMA, IS-95A CDMA, and ETSI GSM technologies are developed and compared.

Design trade-offs in cellular/PCS systems

With the increasing demand for all kinds of wireless access services, including cellular/PCS, wireless local loop, and broadband access, the system architects will have opportunities to design new communication systems, not necessarily based on existing wireless standards. In the design of wireless communication systems, there are usually multiple objectives such as low cost, small size, high reliability, and large capacity. The system architect would need to study the trade-offs among different combinations of modulation, coding, multiple access, and antenna techniques to determine the best design. In this tutorial we focus on the trade-offs between user bandwidth and multi-user interference in order to maximize the system capacity. The design trade-offs are depicted on a B-/spl gamma//sub 0/ plane. Where B is the user bandwidth and /spl gamma//sub 0/ is the carrier-to-interference ratio (C/I). For F/TDMA and CDMA systems, the author first shows that the contours of equal system capacity are straight lines with different slope's depending on the propagation environment, and the capacity decreases for increasing B and /spl gamma//sub 0/. Then as feasible solutions, the author plots the different combinations of modulation and coding with diversity to satisfy a certain quality of service in a multipath environment. The best design is obtained by moving a line with a certain slope from the lower left corner in the B-/spl gamma//sub 0/ plane until it touches the first feasible solution. From these plots we can see that, for example, while 1/2-rate channel coding is the best choice for F/TDMA systems, 1/3-rate is better for CDMA systems.

Integration and evolution of existing mobile telecommunications systems toward UMTS

This article indicates potential evolutionary scenarios from several starting points toward the target UMTS and investigates additional options for potential cooperation between existing systems. The definition of any evolution process should start with the definition of the process's target; therefore, the author provides a brief description of the target UMTS. Five evolution scenarios toward UMTS are introduced, including a fixed network offering intelligent network and cordless terminal mobility services, cellular networks (i.e., GSM), cable networks offering wireless local loop, satellite networks, and a standalone UMTS scenario. Cooperation options for the identified systems and operators are identified.

PACS: personal access communications systems an alternative technology for PCS

The personal access communications system (PACS) is an American National Standards Institute common air interface standard developed for the 1.9 GHz PCS band in the United States. The PACS uses frequency division duplexing technology and is optimized to support low-mobility pedestrian outdoor usage and wireless local loop applications in a medium-range environment. PACS-Unlicensed B (PACS-UB) is a version of PACS using time division duplexing. The PACS-UB has been optimized for private, indoor wireless PBX applications and cordless telephony. Both modes of operation are supported using the same portable hardware and the same signaling protocol.

Wireless in Local Loop: Some Key Issues

Wireless links are emerging as a superior alternative to the copper pair for the local loop in telephony. However, to provide for sufficient subscriber density with a reasonable bandwidth allocation, a micro-cellular architecture is a must. Further, the wireless local loop system is best interfaced as a remote access unit to an exchange. The V5.2 standard provides a convenient protocol for interfacing in this manner to all exchanges.