Wireless local loop: architecture, technologies and services

Wireless local loop (WLL) provides two-way calling services to the stationary or “fixed” users, which is intended to replace its wireline counterpart. Today, there are almost 100 WLL systems (either trials or commercial systems). This article describes the WLL, architecture, the WTJ, technologies, WTL service descriptions, and some examples of WLL products. Wireless Local Loop: Architecture, Echnologies and Serr/ices ANTHONY R. NOERPEL, HUGHES NETWORK SYSTEMS YI-BING LIN, CSIE/NCTU his article describes mobile svstems that have been adapted for fixed wireless access or wireless local loop (WLL). Compared with mobile systems, WLL provides two-way communication services to near-stationary users within a small service area. WLL is intended to replace its wireline counterpart (wireline local loop). In telephony, 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, and are broken down into several smaller bundles of circuits after some distance from the central office. These circuits are eventually separated into individual drops for the residence houses. The cost of the loop tends to be dominated by the residence side (and is typically referred to as the “expensive last Km”). This statement is particularly true for rural areas. The central office switch is typically the first point of traffic concentration in the public switched telephone network (PSTN). Especially for older installations where, on the line side of a switch, from the line interface card to the end user equipment, all facilities are dedicated to a single telephone number. Newcr installations use fiber optics to connect residential neighborhoods or business campuses to the central office and statistical multiplexers to concentrate traffic. However, the last few hundred meters of wiring from a residence to the statistical multiplexer, the local loop, is always dedicated. WLL offers a t least three advantages over wireline local loop: Ease of installation and deployment Concentration of resources Ether cannot be pilfered The International Telecommunications Union (ITU) projects that 150 million new telephone lines need to be installed in developing countries by the end of the decade, and the telecommunications operators are looking for wireless technology to replace part of the hard-wire infrastructure. WLL technology [7] has been considered because the radio systems can be rapidly developed, easily extended, and are d i s k “ insensitive. WLL eliminates the wires, poles and ducts essential for a wired network. In other words, the WLL approach significantly speeds the installation process. WLL systems find application in competitive telecommunications markets, in developing telecommunications markets, and in rural and remote markets that cannot be economically scrvcd by conventional wireline access technologies. WLL systems currently deployed are based on a wide range of radio technologies, including satellite technology, cellular technology, and microcellular technology [2]. Wireless Local LOOP Arch itecfure A simplified version of the TR-45.1 architectural reference model for WLL is shown in Fig. 1. In this figure, the wireless access network unit (WANU) consists of the base btatiori transceivers (BTS) or radio ports (RP), the radio controller (RPCU), an access manager (AM), and home location register (HLR), as required. The interface between the WANU and the switch is calledAWLL that can be IS-634,I IS-6S3,2 GR-303,3 VS.l,4 ISDN-BKI, and so on. The air interface between the WANIJ and the user side is called UWLL. The WANU should provide for the authentication and privacy of the air interface, radio resource management, limited mobility management, and over-the-air registration of subscriber units (Sus). I t may also be required to provide Operation and Maintenance (OAMP), routing, billing and switching functions as appropriate or necessary. The WANU also provides protocol conversion and transcoding of voice and data. To support voice-band data and Group 3 Facsimile, I IS-634 is an extension to the GSMA-interface specification to include support for other air interfaces such as PACS, IS-95, and IS-136, including support for mobile-controlled handover, .soft handover, and IS-41C authentication and privacy protocols. IS-453 is an ISDN-based A-inte&ce (radio system PSCS) for 1800 MHz personal communiculions $witching cenler (PCSC) lo support PACS, J-LTTD-014, TL4 IS-661, a composite CDMAJTLIM nir interface compatibility standard for personal communications in 1.8-2.2 GHz for licensed and unlicensed applications or omnipoint. J-STD-009, I 0, -I1 IS-134, J-STD-007 GSM, J-STD-008 IS-95, and J-STD-015 make up Q W-CDMA air interface compatibility stundard,for 1.85-1.99 GHz PCS