Rep

LOCAL MULTIPOINT DISTRIBUTION SERVICES CS 708 Seminar

NITHYA RANJIT (Roll No. 05091) B. Tech. Computer Science & Engineering

College of Engineering Kottarakkara Kollam 691 531 Ph: +91.474.2453300 http://www.cek.ihrd.ac.in [email protected]

Certificate

This is to certify that this report titled LOCAL MULTIPOINT DISTRIBUTION SERVICES(LMDS) is a bonafide record of the CS 708 Seminar work done by Ms NITHYA RANJIT, Reg No.10264044, Seventh Semester B. Tech. Computer Science & Engineering student, under our guidance and supervision, in partial fulfillment of the requirements for the award of the degree, B. Tech. Computer Science and Engineering of Cochin University of Science & Technology.

October 16, 2008

Guide

Coordinator & Dept. Head

Miss Rekha Mol Lecturer Dept. of Computer Science & Engg.

Mr Ahammed Siraj K K Asst. Professor Dept. of Computer Science & Engg.

Acknowledgments

I express my whole hearted thanks to our respected Principal Dr Jacob Thomas, Mr.Ahammed Siraj sir , Head of the Department, for providing me with the guidance and facilities for the seminar. I wish to express my sincere thanks to Renjith sir, lecturer in Computer Science Department, for his timely advises during the course period of my seminar. I would also express my deep gratitude to my guide Miss Rekha for providing valuable help support necessary for my seminar. I thank all faculty members of College of Engineering Kottarakara for their cooperation in completing my seminar. My sincere thanks to all those well wishers and friends who have helped me during the course of the seminar work and have made it a great success. Above all I thank the Almighty Lord, the foundation of all wisdom for guiding me step by step throughout my seminar. NITHYA RANJIT

Abstract The Local Multipoint Distribution Services (LMDS) is a newly developed technology in broadband wireless point to point communication system operating above 20 GHz. To determine the range of WMAN different technologies are used, there are FSO, LMDS, MMDS, and 802.16 (WiMAX).LMDS technology and its most recent advances will be described in detail in this seminar. This fixed broadband technology can be used to provide real time multimedia file transfer and high speed internet access. LMDS can be deployed in high density nodes in a network and with use of multifed reflected ray in central station antennas. The antenna height and directivity are used in the classification of statistical channel models for Local Multipoint Distribution Service (LMDS). When directional antennas are used and the antennas are sufficiently high providing a line-ofsight (LOS) propagation path between the transmitter and receiver, the statistics of the radio channel can be described by the log normal. The channel statistics fits the Rican distribution, if omni-directional antennas are used. The detailed descriptions of directivity of antennas the direction of arrival signals and limits the number of propagation paths will be done when omni-directional antennas are used and at least one of the antennas is slower than the surrounding obstacles, and hence an LOS propagation path is absent, the radio channel is described by the statistics of the Raleigh distribution. The abovementioned channel models can be used to evaluate the performance of LMDS systems. The term Local indicates that signals ranges over a limit. Multipoint indicates a broadcast signal from subscribers. Distributed defines a wide range of data that can be transmitted, data ranging from any where from voice, video to internet and voice traffic. Located in 28 GHz and 31 GHz bands Broadband radio service designed to provide two way transmission of voice, high speed data and video Low powered transmitters broadcast voice, data and video signals in metropolitan areas The most recent advances in service that provides a highly efficient local access of service is achieved with the multifed printed reflected ray with three simultaneous shaped beams for LMDS Station Antennae. The LMDS systems, its architecture, principle of operation, its potentials areas of applications and latest advancements in the LMDS systems will be discussed.

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Contents 1 INTRODUCTION

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LMDS OVERVIEW

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FIXED WIRELESS TECHNOLOGY

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METHODS OF FIXED WIRELESS COMMUNICATIONS 5

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LMDS THE TECHNOLOGY FOR FIXED WIRELESS LANs 7

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THE PRINCIPLE OF OPERATION

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7 LMDS NETWORK ARCHITECTURE 7.1 SYSTEM EQUIPMENT SEGMENTS . . . . . . . . . 7.2 ARCHITECTURAL OPTIONS . . . . . . . . . . . . .

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WIRELESS LINKS AND ACCESS OPTIONS 8.1 MODULATION . . . . . . . . . . . . . . . . . . . . .

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MICROWAVE PROPAGATION IN LMDS SYSTEMS 14

10 NETWORK-NODE EQUIPMENT

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11 RADIO FREQUENCY EQUIPMENT

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12 LMDS CENTRAL STATION ANTENNAS

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13 ANTENNA DESIGN

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14 APPLICATIONS OF LMDS

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15 NETWORK INTERFACE EQUIPMENT

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16 NETWORK MANAGEMENT

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17 CONCLUSION

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REFERENCES

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1

INTRODUCTION

Local Multipoint Distribution Services LMDS is a broadband wireless access networking solution. This is a cellular access technique for high speed voice, data, Internet and video services in the 25-Ghz and higher spectrum. Higher bandwidth positions this technology to provide a whole range of services including Internet data, TV, music and multimedia services.LMDS is a viable alternative to wired solutions for various small businesses. It is a cost effective business model, especially if rapid deployment in urban areas is required or low-population density areas should be covered with broadband connectivity. Network operators are facing the broadband requirement challenge by improving the existing technologies. LMDS are now being introduced throughout the world. The LMDS services provide many advantages of ease of operation and deployment, flexibility in on demand capacity allocation, and potential support for a broad spectrum of applications, allowing for future development. A major task remaining is the establishment and verification of methods of coverage over shielded areas. The availability of repeaters and reflectors for increased coverage is introduced, which significantly improve coverage. Major applications are TV, Internet, and business-oriented, thus combining professional and entertainment use. The LMDS systems, its architecture, principle of operation, its potentials areas of applications and latest advancements in the LMDS systems will be discussed.

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LMDS OVERVIEW

LMDS is a broadband wireless point-to-multipoint communication system operating above 20 GHz (depending on the country licensing) that can be used to provide digital two- way voice, data, Internet and video services.

Figure 1: LMDS SYSTEM

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The acronym LMDS is derived from the following: L (local)denotes that propagation characteristics of signals in this frequency range limit the potential coverage area of a single cell site; ongoing field trials conducted in metropolitan centers place the range of an LMDS transmitter at up to 5 miles. M (multipoint)indicates that signals are transmitted in a pointto-multipoint or broadcast method; the wireless return path, from subscriber to the base station, is a point-to-point transmission D (distribution)refers to the distribution of signals, which may consist of simultaneous voice, data, Internet, and video traffic. S (service)implies the subscriber nature of the relationship between the operator and the customer; the services offered through an LMDS Network is entirely dependent on the operator’s choice of business.

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FIXED WIRELESS TECHNOLOGY

Until about 1996, the only economical way to connect LAN’s was through a wired infrastructure. In the last three years several new wireless LAN infrastructures are being proposed and built. Wireless local loop is a new wireless option and comes under the Fixed wireless as opposed to mobile. Fixed here, refers to fixed location. It means though the data transmission is wireless, the stations are fixed. They give a very high speed communication. Dense modulation schemes are required and higher signal to noise ratio is required in a fixed wireless scheme.

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4 METHODS OF FIXED WIRELESS COMMUNICATIONS In order to achieve fixed wireless communication, various physical media equipment can be used ranging from infrared, microwave to radio wave. A major problem with using Infrared signal is that they can be obstructed by physical objects, thus there should be an unobstructed path between the communicating equipment, which is not always possible. Microwave systems operate at less than 500 milli watts power. For the fixed service, Broadband wireless access systems are of particular interest. Few reasons for this are, they are very quick to install, and are economical and cost effective. And also interconnection of the base station to fixed PSTN is possible and easy. For using the broadband signal there are various issues that need discussion, one important issue being the spectrum that can be used. The Different Omni Directional High Speed Access Broadband The Federal Communications Commission (FCC) has started a host of omni directional high speed access networks. They are The 38 GHz band: This band is primarily licensed to Winstar and Advanced RadioTelecommunications [1](ARTT). Winstar uses ATM based equipment and provides POTS and high speed data. From the cost point of view, starting with point to point links and then as the network size increases, switching to omni directional cell site is advisable. But then, If for a particular network the shifting overhead is more, its better to start with omni directional networks. The 28 GHz or the LMDS Band: This 28 GHz band was regulated in 1998 with only a few major companies participating. This is called LMDS band as LMDS operates in this band in the United States (It could be different for different countries for example, in Europe, it is the 40GHz band) This has got different blocks of bandwidth. A high degree of ”cellularization” is required with this band. Cell size is about 2 miles in radius. Various new proposals have been made about this which will be discussed in detail. The DEMS band: This band was originally allocated at 18 GHz with 100MHz bandwidth. The only operator in this band is Telegent Corporation. They convinced FCC to allocate it to 24GHz with a 400 MHz allocation. Telegent is deploying a wireless ATM

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The MMDS band: The FCC allocated about 200 MHz of spectrum at 2.1 and 2.5-2.7 GHz frequency for television transmission. In 1995 and 1998 FCC allowed for digital transmission with CDMA (Code Division Multiple Access), QPSK(Phase Shift Keying), VSB (Vestigial Side Band) and QAM(Quadrature amplitude Modulation) modulation schemes. Companies such as Speed Choice and Wave path.

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5 LMDS THE TECHNOLOGY FOR FIXED WIRELESS LANs A cost effective technology that has no hassles of physical connections and can do two way wireless microwave transmission of mixed video, audio and data. LAN cost effective technology that has no hassles of physical connections and can do two way wireless microwave transmission of mixed video, audio and data. LMDS the 28GHz band in America (Europe uses the 40GHz for LMDS), is the one that is being used for wireless LAN. Basically it is a wireless service that transmits fixed broadband microwave signals in the 28 GHz band of the spectrum within small cells roughly 2 to 3 miles in diameter. Pointto-point fixed wireless networks have been commonly deployed to offer high-speed dedicated links between high-density nodes in a network. More recent advances in a point-to-multipoint technology offer service providers a method of providing high-capacity local access that is less capital-intensive than a wireline solution, faster to deploy than wireline, and able to offer a combination of applications. Moreover, as a large part of a wireless network’s cost is not incurred until the customer premises equipment (CPE) is installed, the network service operator can time capital expenditures to coincide with the signing of new customers. LMDS technology provides an effective last-mile solution for the incumbent service provider and can be used by competitive service providers to deliver services directly to end users. Benefits can be summarized as follows: Lower entry and deployment costs. Ease and speed of deployment (systems can be deployed rapidly with minimal disruption to the community and the environment) Fast realization of revenue (as a result of rapid deployment) Demand-based build out (scalable architecture employing open industry standards ensuring services and coverage areas can be easily expanded as customer demand warrants) Cost shift from fixed to variable components (with traditional wireline systems, most of the capital investment is in the infrastructure, while with LMDS a greater percentage of the investment is shifted to CPE, which means an operator spends money only when a revenue-paying customer signs on)

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THE PRINCIPLE OF OPERATION

BASIC PRINCIPLES LMDS are combined high-capacity radio-based communications and broadcast systems with interactivity operated at millimeter frequencies. Early systems, however, were mainly used for analog TV distribution, and it all started with combined transport of data representing TV programs, data, and communication. The possibility of implementing a full-service broadband access network by rebuilding a broadcast network into an interactive network by functionally adding a communications channel for the return was a reality that coincided almost perfectly with the growth of the Internet and data services. Broadband interactivity arrived with digitalization. Interactive LMDS has a point-to-multi-point downlink and a point-to-point uplink, as shown.

Figure 2: Operation of LMDS Operation of LMDS in an area will normally require a cluster of cells with separate base sta-tions for co-located transmitter/receiver sites. One of the base stations sites serve as coordination center the franchise area and connect the LMDS cells to external networks.Intercell networking may be implemented using fiber or short hop radio relay connections. Co-location with mobile base stations allows for infrastructure sharing. Operation in the millimeter range imposes some restrictions. Precipitation effects lead to severe attenuation and limit the

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reliable rangeof operation to 35 km depending on the climatic zone and the frequency of operation. Line of sight(LOS) is also required. Full coverage will however not be possible, and numbers quoted arenormally in the 4070 percent range. Improved coverage is thus required and may be obtained in different ways. The numbers quoted refer to single cells. By introducing some overlapping between cells it may be possible to obtain coverage in shielded areas in one cell from the neighboring cell transmission site. Use of repeaters and reflectors are other possibilities. Thus different site dependent ways of operation will solve the coverage problem. The most severe restriction may be the attenuation caused by transmission through vegetation.Buildings completely shielded by vegetation need an elevated rooftop antenna or some broadband connection to an unshielded site. Propagation issues are by now well understood and are not considered a serious obstacle for reliable operation of millimeter systems of cellular architecture.

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LMDS NETWORK ARCHITECTURE

Various network architectures are possible within LMDS system design. The majority of system operators will be using point-to-multipoint wireless access designs, although point-to-point systems and TV distribution systems can be provided within the LMDS system. It is expected that the LMDS services will be a combination of voice, video, and data. Therefore, both asynchronous transfers mode (ATM) and Internet protocol (IP) transport methodologies are practical when viewed within the larger telecommunications infrastructure system of a nation. The LMDS network architecture consists of primarily four parts: 1)Network operations center(NOC) 2)Fiber-based infrastructure 3)Base station 4)Customer Premise Equipment(CPE)

7.1

SYSTEM EQUIPMENT SEGMENTS

The Network Operation Center NOC contains the Network Management System (NMS) equipment that manages large regions of the customer network. Multiple NOCs can be interconnected. The fiberbased infrastructure typically consists of synchronous optical network (SONET) optical carrier (OC)12, OC3, and DS3 links; Central-office (CO) equipment; ATM and IP switching systems; and interconnections with the Internet and public switched telephone networks (PSTNs). The base station is where the conversion from fibered infrastructure to wireless infrastructure occurs. Base-station equipment includes the network interface for functionalities which may not be present in different designs include local switching. If local switching is present, customers connected to the base station can communicate with one another without entering the fiber infrastructure. This function implies that billing, channel access management, registration, and authentication occur locally within the base station. The alternative base-station architecture simply provides connection to the fiber infrastructure. This forces all traffic to terminate in ATM switches or CO equipment somewhere in the fiber infrastructure. In this scenario, if two customers connected to the same base station wish to communicate with each other, they do so at a centralized location. Billing, authentication, registration, and traffic-management functions are performed centrally. The customer-premises configurations vary widely from vendor to vendor. Primarily, all configurations will include outdoor-mounted

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microwave equipment and indoor digital equipment providing modulation, demodulation, control, and customer-premises interface functionality. The CPE may attach to the network using time-division multiple access (TDMA), frequency-division multiple access (FDMA), or code-division multiple access (CDMA) methodologies. The customer premises interfaces will run the full range from digital signal, level zero (DS0),plain old telephone service (POTS), 10BaseT, unstructured DS1, structured DS1, frame relay, ATM25, serial ATM over T1, DS3, OC3, and OC1. The customer premises locations will range from large enterprises (e.g., office buildings, hospitals, campuses), in which the microwave equipment is shared between many users, to mall locations and residences will be connected. Obviously, different customer-premises locations require different equipment configurations and different price points.

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ARCHITECTURAL OPTIONS

LMDS system operators offer different services and have different legacy systems, financial partners, and business strategies. As a result, the system architecture used will differ between all system operators. The most common architectural type uses co-sited, base-station equipment. The indoor digital equipment connects to the network infrastructure, and the outdoor microwave equipment mounted on the rooftop is housed at the same location. Typically, the radio frequency (RF) planning for these networks uses multiple sectors microwave systems, in which transmit- and receivesector antennas provide service over a 90-, 45-, 30-, 22.5-, or 15-degree beam width. The idealized circular coverage area around the cell site is divided into 4, 8, 12, 16, or 24 sectors. Alternative architectures include connecting the base-station indoor unit to multiple remote microwave transmission and reception systems with analog fiber interconnection between the indoor data unit (IDU) and outdoor data unit (ODU). This approach consolidates the digital equipment, providing increased redundancy, reduced servicing costs, and increased sharing of digital resources over a larger area. The difficulties are typically the lack of analog fiber resources and remote microwave transmission and reception equipment deployment issues. By using remote microwave equipment, there may be a reduced sectorization requirement at each remote location.

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Figure 3: Co-Sited Base Station

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Figure 4: Analog Fiber Architecture

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8 WIRELESS LINKS AND ACCESS OPTIONS Wireless system designs are built around three primary access methodologies: TDMA, FDMA, and CDMA. These access methods apply to the connection from the customer-premises site to the base station, referred to as the uplink. Currently, most system operators and standards activities address the TDMA and FDMA approaches. In the downlink, from base station to customer premises, most companies supply time division multiplexed (TDM) streams either to a specific user site (point-to-point connectivity) or multiple user sites (a point-to-multipoint system design). FDMA scheme in which multiple customer sites share the downstream connection.

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Figure 5: FDMA Access TDMA scheme in which multiple customer sites share both the downstream and upstream channel. With FDMA and TDMA access links, whether downstream or upstream, there are a number of factors that affect their efficiency and usage. For FDMA links, the customer premises site is allocated bandwidth which is either constant over time or which slowly varies over time. For TDMA links, the customer premises is allocated bandwidth designed to respond to data bursts from the customer site. These two access methods will probably provide the majority of access links for LMDS systems over the next few years. The choice between these access links is directly related to the system operator business case, service strategy, and target market.

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Figure 6: TDMA Access

8.1

MODULATION

Modulation methods for broadband wireless LMDS systems are generally separated into phase shift keying (PSK) and amplitude modulation (AM)approaches. The modulation options for TDMA and FDMA access methods are almost the same. The TDMA link modulation methods typically do not include the 64quadrature amplitude modulation (QAM), although this might become available in the future.

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9 MICROWAVE PROPAGATION IN LMDS SYSTEMS An area of continuing research for LMDS systems relates to microwave propagation behavior. The LMDS systems at 28 GHz are most susceptible to rain effects causing a reduction in the signal level. The Comite Consultatif International des Radiocommunications (CCIR) has rainfall attenuation estimation procedures; however, there is limited data and experience in small cell point-to-multipoint systems. Rainfall causes depolarization of the signals, leading to decreased signal level and decreased interference isolation between adjacent sectors and adjacent cell sites. Additional propagation issues relating to foliage also need further study.

Figure 7: Microwave Propagation in LMDS Systems The primary propagation issue in lower-frequency bands is multipath fading. At the LMDS frequencies, multipath fading should not be an important effect. First, LMDS frequencies are much more lineof-sight (LOS)dependent, which means that shadowing and diffraction do not occur as often at lower frequencies. Second, cellular and personal communications service (PCS) systems typically have customer-

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premises locations within six feet of the ground, whereas LMDS systems have customer antennas located high on rooftops. The height of the customer-premises antenna plays a large role in reducing multipath effects. Third, the LMDS antennas are highly directional (pointing to a single cell site), whereas the cellular and PCS antennas have either omnidirectional or loosely sectorized characteristics. Using directional antennas reduces multipath effects. Fourth, in cellular and PCS systems the customer antenna may be moving, whereas LMDS antennas are fixed on a rooftop. Once an antenna becomes fixed, installers can choose better case locations on the rooftop, leading to improved performance. Considering these factors, the cell coverage distance will vary depending on the rainfall statistics in the particular area. Foliage height in relation to commercial and residential building heights also needs to be examined to determine the percentage of building rooftops that can be illuminated from any particular base- station antenna sector.

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NETWORK-NODE EQUIPMENT

The Network-Node Equipment (NNE) provides the basic network gateway for connecting wireline network traffic to the LMDS bandwidth .The NNE is equivalent to the base-station digital equipment. The network-node products provide processing, multiplexing, demultiplexing, compression, error detection, encoding, decoding, routing, modulation, and demodulation. The NNE may also provide ATM switching.

Figure 8: Network-Node Equipment The following functions may be performed at the network node: Digital Signal Compression The conversion of analog television signals to highly compressed digital signals for distribution by the microwave system. Wire line/Wireless Protocol Interfaces Depending on an operator’s service offerings, NNE may be configured to extend video, IP, and voice services over LMDS bandwidth.

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(ATM is emerging as a likely standard for the delivery of voice, data, Internet, and video services over LMDS.) Modulation and Demodulation Signals from the voice, video, and data multiplexing system are modulated before wireless transmission occurs. Similarly, traffic from the microwave receiver is demodulated before wire line transmission. Modulation A digital modulator accepts a digital stream and provides a 4QAM, 16QAM, or 64QAM intermediate frequency (IF) signal for delivery over the LMDS bandwidth. The modulator performs all the functions required to modulate digital video, voice, and data to a standard IF for input to the wireless transmitters. Demodulation A QAM demodulator contains two separately addressable demodulator channels, each capable of accepting 4QAM, 16QAM, 64QAM signals at symbol rates between 1 Mbps and 10 Mbps. TDMA systems may use differential QPSK modulation.

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11 RADIO FREQUENCY EQUIPMENT Network Node LMDS network node RF equipment includes transmitters and receivers as well as transceivers and the antennas they feed. If there is one carrier per transmitter,the system is said to be channelized. If there are multiple carriers per transmitter,the system is said to be broadband. Transmitters Individually modulated signals are combined and applied to the broadband transmitter. Within the transmitter, the very-high-frequency (VHF) signals are converted up to the desired carrier frequency, amplified, and applied to the antenna for transmission. Separate transmitters, receivers, and antennas can be used in each direction to minimize the near-end crosstalk effects between transmit and receive signals. Receivers A separate broadband receiver receives the entire band at carrier frequency and converts the signals to the VHF band. The VHF signals are then applied to coaxial or fiber cable for distribution to the NNE. Transceivers Combined transmitter and receiver functions can be provided in a single broadband transceiver. Antenna Systems Antennas are chosen based on the desired coverage of potential subscribers, taking into consideration the terrain, interfering objects, antenna azimuth pattern, antenna elevation pattern, and antenna gain. Customer-Premises Site Transceiver For two-way data network applications, a transceiver is used to provide a return path for LMDS services. The antenna may be an integral part of the transceiver.The transceiver may be broadband or channelized. Customer Antenna Systems Typical technology choices available include microstrip design, parabolic and grid-parabolic reflectors, and horn designs. The selection is an engineering decision based on the customer’s location. As well, vendors will have various levels of integration with specific antenna technologies.

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12 LMDS CENTRAL STATION ANTENNAS Multifed Printed Reflectarray With Three Stimultaneous Shaped Beams for LMDS Central Station Antenna.A two-layer reflectarray is proposed as a central station antenna for a local multipoint distribution system (LMDS) in the 24.526.5 GHz band. The antenna produces three independent beams in an alternate linear polarization that are shaped both in azimuth (sectored) and in elevation (squared cosecant). The design process is divided into several stages. First, the positions of the three feeds are established as well as the antenna geometry to produce the three beams in the required directions. Second, the phase distribution on the reflectarray surface, which produces the required beam shaping, is synthesized. Third, the sizes of the printed stacked patches are adjusted so that the phase-shift introduced by them matches the synthesized phase distribution.

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Printed reflectarrays are very attractive solutions since they have a number of advantages such as, low profile, mass and volume, they are easy to manufacture and offer possibilities for beam shaping and electronic beam control. A reflectarray consists of a planar array of printed elements illuminated by a primary feed, typically a horn antenna. Each element of the reflectarray introduces a phase-shift to the impinging wave from the feed to produce a focused or contoured beam. The applications for contoured beam reflectarrays are especially interesting since the manufacturing cost and process is the same as for a focused beam.

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Figure 9: Scheme Of The Proposed Multifed Reflectarray

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ANTENNA DESIGN

A. Antenna Definition A central station antenna for an LMDS application requires a shaped beam, squared cosecant in elevation and sectored in azimuth, see minimum and maximum requirements in figure for 30-degree sectors with 5-degree tilt. The elevation masks are the same for all the beams, whereas the azimuth coverage depends on the sector. The three-dimensional masks are obtained through a combination of the elevation and azimuth requirements for each beam. B. Synthesis of the Radiation Pattern Once the 3D masks of requirements and the antenna geometry are dened, the phase of the reection coefcient of each reectarray element is synthesized in order to fulll the required pattern for the central beam.

Figure 10: Radiation Pattern C. Reflectaray Design and Manufacture Once the phase required for the reection coefcient at each reectarray element has been determined, the dimensions of the printed

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patches have to be adjusted to match that phase. In this case, a two-layer conguration, has been selected because it provides a good bandwidth for moderate sized reectarray.

Figure 11: Multifed Printed Reflectaray A breadboard of the designed antenna has been manufactured. The two layers of printed arrays have been produced by achemical etching process and the dimensions of the patches have been veried with a prole projector. The layers have been glued by means of a bonding lm layer in a curing cycle, according to the manufacturer specications. Then, the reectarray is assembled with a support structure, which ensures the position of the feed-horn and the reectarray panel.

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APPLICATIONS OF LMDS

LMDS is first of all a system of high flexibility, allowing for capacity on demand. Changing the cell size through reduction of either cell diameter or illumination angle increases total capacity.Its flexibility with regard to high on-demand capacity in both directions makes it well suited to home offices and teleteaching in the local domain. The first major applications are TV,Internet, and business-oriented, thus combining professional and entertainment use.In Europe LMDS was considered a supplement alternative to cable TV and was actually refred to as wireless cable.With digital television and the possibility for convergence of TV,data,and communications opened up developed of new broadband applicationsThe availability of broadband technology will stimulate the growth of application s such as teleteaching to telemedicine. From Television to Interactive Television The TV business has had strong growth, but the time spent by individuals watching TV has not changed very much. Digital TV represents new possibilities. The first step is the introduction and development of interactive TV, adding new and interesting functionality. More local TV programs will take advantage of LMDS. Interactive TV will stimulate growth in e-commerce; and the more local part of it, such as property trading, apartment renting, car buying and selling, and many other transactions Teleteaching Education, and updating reeducation, is one of the major challenges in many countries today. Lack of educated and skilled teachers, particularly in technology, is a common concern. The local focus of LMDS makes it excellent for high-capacity connections to schools at different levels, connecting a group of local schools as well as providing connections to remote sites. Locally, it would then also be possible to connect to homes and have lessons stored for the use of both pupils and parents. Broadband access will offer possibilities in education we have barely started to explore. The advantage of LMDS in this connection is the flexibility in capacity allocation and the multicast property of the downlink, allowing very efficient delivery for this type of applications.

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15 NETWORK INTERFACE EQUIPMENT At the customer-premises site, a network interface unit (NIU) provides the gateway between the RF component and in-building appliances. NIUs are manageable by the network management system provided in the network-control center.These NIUs are available in scalable and nonscalable forms depending on customer requirements.

Figure 12: NIU Network Implemention

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NETWORK MANAGEMENT

LMDS network management is designed to meet a network operator’s business objectives by providing highly reliable network management services. Network management requires the following: Fault Management This is necessary to identify, localize, and correct errors or faults in the network. Each device within a wireless network should be monitored for troubleshooting or performance. All LMDS devices collect and report statistics pertaining to traffic throughput, boundary condition violations, and management activities. Configuration Management This is necessary in order to provision, inventory, initialize, and back-up network resources. The LMDS equipment should be autodiscovered when new equipment is added to a node. This minimizes the amount of provisioning needed to install or upgrade equipment. Accounting Management This is necessary to collect and process billing information. Each manageable node in the wireless portion of the network should maintain a collection of statistics that can be accessed by a third-party billing system as input. Users should be identified on a per-network user basis. Performance Management This is necessary to collect, filter, and analyze network resource statistics. There are a number of parameters that should be monitored and configured on each network node, from T1 traffic throughput to output power level. The management station should monitor these parameters and adjust them to increase performance. Security Management All information transmitted through the wireless environment must be encrypted between each node in the network. The security-management function should automatically generate and coordinate the keys used to encrypt and decrypt, as well as to authenticate users.

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CONCLUSION

Local Multipoint Distribution Services is a well suited fixed broadband wireless transmissions.LMDS is a technology for a time of growing demand.It offers ease of operations and deployement,flexibility in in on demand capacity allocation and potential support for a broad spectrum of applications. The LMDS system architecture and the basic principles of operation used in providing the LMDS service is described in this seminar.Latest advancements concerning the LMDS Central Station Antenna is also explained.The several advantages of this LMDS technology has led to it being most widely used broadband access methods.LMDS promises a wireless alternative to fiber and coaxial cables, It has the potential to replace the existing wired networks, it may prove to be the easiest way to deliver high speed data and two way video service. Its capability of handling thousands of voice channels with the existing bandwidth makes it a good contestant in the voice industry. With current industry trends, that are tending to merge the telecommunication and the networking industries, LMDS seems to be a soultion that suits all their needs. For the recent digital TV world, LMDS is a very good choice considering the fact that LMDS was designed with Digital TV broadcast in mind.

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References [1] Telenor RD Agne Nordbotten. Lmds systems and their applications. In IEEE Transactions, pages 150–162, June 2006. [2] J. A.; Barba M.; Arrebola, M.; Encinar. Multifed printed reflectarray with three simultaneous shaped beams for lmds central station antenna. Antennas and Propagation, IEEE Transactions on, 56(6):1518–1527, JUNE 2008.

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