Wireless Local Loop System Research Articles

Analysis of the Wireless Local Loop Systems and their Perspective in Lithuania

The goal of the article is to define the criteria for comparing Wireless Local Loop systems. Criteria are based on modern telecommunication network demands, Standardization organizations requirements and Lithuanian geographic and demographic factors. The criteria are divided into two groups: service criteria and system technology criteria. They are general character criteria, suitable for all wireless systems and all technologies. The comparison of the systems of different vendors and different technologies is done using these criteria. There is no unilateral definition of the best system in this article. Every technician could choose the most suitable system referring to the most important criteria’s. Deployment of such systems is influenced by some factors. These factors are organizational, Lithuanian geographic / demographic and current telecommunication network infrastructure factor. There is analysis of these factors in article too.

Performance Analysis of CDMA WLL Systems with Imperfect Power Control and Imperfect Sectorization

Wireless local loop (WLL) provides reliable, flexible, and economical access to the local telephone service using radio technology in the place of traditional wireline. In this paper, an analytical model is derived to evaluate the effect of both imperfect power control and imperfect sectorization on the performance of code division multiple access (CDMA) WLL systems. The results show that the capacity degradation, due to imperfect power control, is about 25.8% and 11.5% for single cell and multiple cell systems, respectively. Increasing the overlapping angle from to causes the capacity gain to decrease from 6 to 5.53, while the corresponding sectorization efficiency drops from 100% to 92.3%.

INVESTIGATING THE REVERSE LINK ERLANG TRAFFIC CAPACITY OF A POWER CONTROLLED WIRELESS LOCAL LOOP CDMA SYSTEM

In this paper, the reverse link Erlang traffic capacity of a power controlled CDMA based Wireless Local Loop (WLL) voice system equipped with high gain directional antennas at either the base station or users’ houses is investigated. It is shown that the Erlang traffic capacity of CDMA based WLL system is several times that of mobile cellular CDMA system and conventional multiple access systems, such as FDMA and TDMA based systems. Finally the study of Telecom Egypt WLL CDMA2000-1xRTT network is examined as a case study

Analyses of numerical and experimental results for optical signal generation using heterodyne scheme

In this paper, we have proposed a heterodyne technique to generate an optical millimeter-wave signal for ultra-wideband communication. First, we have investigated the characteristics of semiconductor lasers locked to another semiconductor under the RF modulation having many sidebands. The RF-modulated master laser is represented by a series of Bessel functions. This model is then inserted into Lang's rate equations. By numerically solving the resulting rate equations, we have determined the locked laser output characteristics as well as the RF spectrum of the beat signals. The result is that the unselected sidebands can produce undesired beat signals whose power may be comparable to that of the desired beat signal. Furthermore, their strength is affected by the injected ML light power. With reduced ML light, undesired beat signals and the injection-locking bandwidth can be suppressed. Second, we have experimented a new technique for generating millimeter-wave signals from a semiconductor laser. A 32 GHz signal is generated using a multisection semiconductor laser operated under a continuous wave by injecting optical pulses at a repetition rate equal to the fourth subharmonic (8 GHz). The generated millimeter-wave signal exhibits a large subharmonic suppression ratio, a large frequency detuning range, low levels of phase-noise and a large locking range. These simulation results are confirmed by experimental results. The high-frequency signal can be used in the field of ultra-wideband communication employing local multipoint distribution system (LMDS), wireless local loop (WLL) and mobile broadband system (MBS).

Capacity of High Density Macro Cellular Wireless Local Loop System based on Dynamic Channel Selection

Wireless Local Loop (WLL) is emerging as a cost effective alternative to the copper local loop to cater to the increasing demand for telecom services in densely populated urban areas in developing countries. While the wired local loop system provides a line dedicated to each subscriber, the wireless local loop has an additional limitation associated with the sharing of limited radio channels. Further, due to the limited bandwidth provided, the available frequency channels have to be reused, causing radio interference which limits the capacity of the system. In this paper, the traffic that can be handled by a fixed Wireless Local Loop system employing Dynamic Channel Selection has been evaluated, taking into account the radio interference. The effect of three kinds of radio interference—cochannel, adjacent channel and intermodulation—on the capacity of the system has been studied. Two kinds of antenna deployment strategies, omni-directional and sectoral, have been considered in the study. With omni-directional antennas, the capacity of the system was found to be interference limited.We show that the use of directional (sectoring) antennas at the base station overcomes the interference limitation and serves a higher subscriber density. The DECT standard has been assumed for the air interface in this study.

Throughput enhanced wireless in local loop (TWiLL)

Traditionally, voice communication over the local loop has been provided by wired systems. In particular, twisted pair has been the standard means of connection for homes and offices for several years. However in the recent past there has been an increased interest in the use of radio access technologies in local loops. Such systems which are now popular for their ease and low cost of installation and maintenance are called Wireless in Local Loop (WLL) systems. Subscribers' demands for greater capacity has grown over the years especially with the advent of the Internet. Wired local loops have responded to these increasing demands through the use of digital technologies such as ISDN and xDSL. Demands for enhanced data rates are being faced by WLL system operators too, thus entailing efforts towards more efficient bandwidth use. Multi-hop communication has already been studied extensively in Ad hoc network environments and has begun making forays into cellular systems as well. Multi-hop communication has been proven as one of the best ways to enhance throughput in a wireless network. Through this effort we study the issues involved in multi-hop communication in a wireless local loop system and propose a novel WLL architecture called Throughput enhanced Wireless in Local Loop (TWiLL). Through a realistic simulation model we show the tremendous performance improvement achieved by TWiLL over WLL. Traditional pricing schemes employed in single hop wireless networks cannot be applied in TWiLL -- a multi-hop environment. We also propose three novel cost reimbursement based pricing schemes which could be applied in such a multi-hop environment.

Capacity of Multirate Multicell CDMA Wireless Local Loop System with Narrowbeam Antenna and SINR Based Power Control

In this paper, we evaluate the capacity performance of multirate multicell DS-CDMA wireless local loop system with narrowbeam antenna and SINR based power control. Multiple access interference from the surrounding cells in the multicell environment is firstly studied for both uplink and downlink. It can be seen from the results that the capacity can be improved effectively by directional antenna equipped at the subscriber side. More significant improvement can be achieved if multielement antenna array is employed at the base station. In addition, the analysis is also extended to the situation of multimedia multirate transmission. The results show that, regardless of the voice to data user population ratio, the bit rate traffic supported by the system is roughly constant for a set of predetermined parameter values.

The Performance of the corDECT Voice/Data Wireless Local Loop

The traditional wired local loop used to connect each telephone subscriber to the nearest exchange is expensive and unreliable. Wireless Local Loop (WLL) systems largely eliminate these copper wires using wireless technologies and could provide a cost effective solution. corDECT is one such WLL system, based on the DECT (Digital Enhanced Cordless Telecommunications) standard, that provides toll-quality voice and data capability at a cost well below that of a wired local loop.A closed Queueing Network Model (QNM) is proposed for the corDECT system. The model is validated against actual measurements. Our model predicts that the 1,000-line corDECT system would meet a Busy Hour Call Attempt (BHCA) of 36,000 calls/hr, which is far greater than its requirement of 20,000 calls/hr. The bottlenecks that limit the BHCA to 36,000 calls/hr were identified by the model. We show how the system could be expanded to a 10,000-line exchange with a BHCA of over 2,10,000 calls/hr. We also investigate the feasibility of implementing 64 kbps data service along with voice. It is shown that this requires modest hardware improvements.

General aspects of digital technologies for wireless local loops

Wireless local loop (WLL) denotes an access system that uses a wireless link to connect a subscriber's terminal station to the line terminating equipment (local exchange or distribution node) in place of conventional copper cable. Many technical advances in transceiver component design have managed to cut down the overall cost and increase the efficiency of wireless systems making them competitive for the local loop. The technical requirements of a WLL system vary according to the market segment, geographical area and services available or scheduled by the wireline counterpart. Hence, WLL is not described exclusively by a single technology but many technologies have been utilized as wireless local loop systems. These are cellular, cordless, satellite broadcasting or terrestrial microwave distribution technologies that were conceptualized for different market needs. The competition is going to be in service quality, data rate per channel and supplementary services such as videoconference, teleshopping, teleworking, Internet access, etc. However, given the availability of radio frequency spectrum, the declining cost, the speed of installation and the flexibility of technology, wireless local loop tends to become the prevalent solution in telephone network access provision. In this paper, we review the requirements of WLL systems and the technological innovations applicable to wireless transceivers. We also cover various multiple-access systems already implemented in other applications as candidates to offer WLL services. Copyright © 2000 John Wiley & Sons, Ltd.

Current and future services using wireless local loop (WLL) systems

Current and future services using wireless local loop (WLL) systems

Low sequency W‐CDMA codes lead to more economic WLL and infostation terminals

Wireless local loop systems offer many advantages in providing voice and data services to an end user, unfortunately at high cost. Multi-rate wide-band code division modulation (W-CDMA) technology is proposed to serve both high and low data rate users. By an unusual assignment of codes, it is possible to reduce the cost of terminals for the strictly voice and low data rate user. An algorithm is presented to generate multi-rate long and short codes that are orthogonal over all symbol periods and ordered by sequency. Assigning the low sequency codes to the voice and low data rate users leads to a lower radio bandwidth and a lower chip rate. This allows the design of W-CDMA receivers requiring less processing. Therefore these receivers consume less power and cost less. Examples are presented where the effective chip rates are reduced as much as 8:1. Copyright © 2000 John Wiley & Sons, Ltd.

Reverse link performance of wireless local loop CDMA networks

We study the effect of directional subscriber antennas on the reverse link performance of a power-controlled code-division multiple access (CDMA) network in wireless local loop deployments. We investigate the capacity gain that is attained in wireless local loop (WLL) CDMA over mobile cellular systems and its variation as a function of the channel statistics. We also determine the overhead that soft handoff and directional subscriber antennas impose on the WLL system capacity.

Propagation modelling for wireless local loop channel

Wireless local loop (WLL) systems based on cellular, PCS and cordless phone technologies have been deployed widely in developing countries which lack basic telephony infrastructure as a bypass of wire-line local loop. In most of the developed countries, the WLL application was only limited to the remote area as an extension of existing telephone network. However, recent growth of the Internet applications has stimulated demand for a cost-effective high-speed delivery system so that WLL systems are considered as a new contender for broadband services against ISDN, Asymmetrical Digital Subscriber Line (ADSL) and cable TV. In such WLL systems, subscriber antenna might be mounted on rooftops, if not wall or ground, thereby limiting the applicability of most of the propagation models that assume a street-level receiver. Hence it is necessary to fit current propagation models to WLL-specific situations in order to predict path loss for various receiving antenna locations. In this paper WLL propagation models are presented through appropriate modification of several models in the literature. Copyright © 2000 John Wiley & Sons, Ltd.

Wireless local loop as a fixed/mobile convergence solution

At first sight, wireless local loop (WLL) might seem an ideal springboard for fixed mobile convergence (FMC) since it utilizes mobile-like platforms to provide a fixed service. However, a more detailed examination reveals a more complicated picture. For the user, FMC is the provision of a single phone which provides them with service wherever they are. For the network operator, FMC is the use of a single infrastructure to provide fixed and mobile communications. Hence, a combination of a WLL and cellular system provides FMC as far as the operator is concerned but not as far as the user is concerned. More complexity is added when considering whether voice will migrate to mobile networks whilst data will remain on fixed networks. In such a world, WLL systems would predominantly provide data. However, advanced WLL systems using packet switched infrastructure would allow the integration of mobile and fixed networks more readily than could occur with today's architectures.. Because WLL operators do not have legacy circuit switched networks to consider, they can reach the brave new world of packet switching more quickly and hence might well be the leaders in providing FMC in a packet environment. This paper looks at all these issues, and discusses the future role of WLL in the global telecommunications environment. Copyright © 2000 John Wiley & Sons, Ltd.

Current and future services using wireless local loop (WLL) systems

In the telephone networks, the circuit between the subscriber's equipment and the local exchange is called the local loop. Recently, wireless local loop (WLL) has become one of the most promising technologies for local loop systems to provide voice and data services. This paper gives an overview of WLL services. We first introduce a typical architecture of WLL systems. Then, we investigate WLL service requirements on capacity, quality of channel, ease of implementation, and service fee. It is shown that there are remarkable differences in these requirements between developing and developed countries/regions. We outline WLL services, which can be offered with several representative systems (or standards) available today or soon to be available, and compare them with each other. Under the criterion of service requirements, it is shown what systems are suitable for a specific service area. In addition, some further considerations for future multimedia WLL services are discussed with the relevant technologies. Copyright © 2000 John Wiley & Sons, Ltd.

Remote management and upgrade in a wireless local-loop system

Remote management and upgrade in a wireless local-loop system

PBX based mobility manager for wireless local loop

SUMMARY In a typical wireless local loop (WLL) system, a user can only access the wireless services at xed locations. This paper proposes a private branch exchange (PBX) based mobility manager for WLL, which allows users to receive wireless service at any locations within the WLL service area. We show how the mobility manager can be implemented in a PBX environment where the base stations are connected to the PBX using standard line or trunk interfaces. The proposed mobility manager can be tailored to connect wireless system such as DECT or PACS. Copyright ( 2000 John Wiley & Sons, Ltd.

Use of an antenna array at customer stations to improve the capacity in a WLL network

Recent research on adaptive antenna arrays for telecommunications has opened the possibility of a new access technique: space division multiple access (SDMA). This multiple access scheme achieves an increase in the capacity of wireless networks making efficient use of spectrum. Usually, the implementation of antenna arrays is considered at base stations only (for practical reasons) in cellular mobile systems. However, the fixed nature of wireless local loop (WLL) systems allows the operators to take into account more specialized antennas for customer premises. In this paper the implementation of an antenna array at the user station is proposed as a mechanism to improve the system capacity. Different WLL configurations are analysed, whose performances are compared in terms of blocking probability. Obtained results are validated with theoretical models. After this, an evaluation is done from performance plots for analysed configurations. A significant improvement in the proposed configuration is observed from these plots. Copyright © 2000 John Wiley & Sons, Ltd.

Interference analysis in fixed service microwave links due to overlay of broadband SSDS-CDMA wireless local loop system

In this paper the results of the interference analysis in FSdML due to new WLL systems with broadband SSDSdCDMA techniques, sharing the same frequency band, is evaluated. Effects of WLL systems are expressed through the interference noise power at the FDM/FM receiver and BER at the DML receiver output, respectively. The results obtained show that in the typical working conditions with careful cell planning, interference can be neglected, and in most situations WLL overlay would not cause excessive interference in the FSdML. This conclusion is of great importance for the development of telecommunication systems, specially in rural areas, because it is possible to develop telecommunication systems fast and economically, without any additional frequency demands and under favourable economical conditions.

Wireless local loop radio systems

Wireless local loop radio is expected to become a widely accepted technology for rapid access to network infrastructure by remote locations. Characteristics of a wireless local loop system are partially different from those in the mobile cellular system and therefore their design and planning require different considerations. This paper provides first an overview of the wireless local loop systems and then discusses the important design aspects such as the necessary fade margin to achieve a given availability, level crossing rate and average fade duration.