Wireless Local Loop System Research Articles

A wireless local loop system based on wideband CDMA technology

This article describes a wireless local loop system based on wideband CDMA technology. The unique features of CDMA technology make it a formidable alternative for fixed wireless telephone applications. The W-CDMA technology used by this WLL system is selected to provide primarily ISDN-like services and data rates to subscribers. This technology also provides a smooth transition into the third generation wireless technology. The air interface used in this WLL system is an interim TTA standard, which specifies a CDMA-based protocol operating in the 2.30-2.40 GHz band. The standard allows two types of bandwidth (5 and 10 MHz). The WLL system described in this article includes the WLL gateway switch, the radio port controller and the radio interface unit. The gateway switch connects the radio system to the PSTN and ISDN. The RPC provides concentration and control functions to a number of base stations called RPs. The RIU is comprised of the fixed units attached to the residential or commercial buildings. Also included are the radio port operation and maintenance (RPOM) unit, which is responsible for maintaining and managing the radio network elements, and the interworking function unit, which is used as a gateway to data services such as the Internet and PSPDN.

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 WLL technologies, WLL service descriptions, and some examples of WLL products.

Frequency reuse scheme with reduced co-channel interference for fixed cellular systems

A new frequency reuse scheme which reduces co-channel interference in comparison with the conventional scheme is presented for use in fixed cellular or wireless local loop systems where the antennas of subscriber units are fixed and directional. The new scheme is evaluated in a three-sector cell plan employing frequency reuse numbers N = 4 and N = 7 as a function of the subscriber unit antenna directivity. It is shown that a substantial improvement is obtained with the new scheme compared to the conventional scheme if the subscriber unit antenna beam width is narrower than ~150 degrees. For the case of a 60 degree antenna beam width, for example, the improvement is > 7 dB in the signal to co-channel interference ratio averaged along the cell boundary for both N = 4 and N = 7 cases.

Spectrum and technology of a wireless local loop system

This article shows that the wireless local loop (WLL) may not necessarily provide more capacity than mobile cellular systems if an FDMA or TDMA system is used. CDMA has proven to have higher capacity than the other multiple access schemes due to the nature of CDMA systems. In industrial countries, the requirements of WLL are quality and service features. In developed countries, the requirement is a low-cost high-capacity system, even if voice quality must be sacrificed. Therefore, the system design aspects are different.

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.

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.

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.

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.