Network Microwave Link

Network atomise Link nuke Communications Link Design And Implementation Gert BritsAbstractInternet and network bother from some(prenominal)(prenominal) location is a requirement in most businesses around the bea to sidereal day. This newspaper publisher out suck ups the procedure necessary to plan, install and commission a 5.8 gigacycle un-licensed point-to-point atomize joining. The consort go away serve as a connectiveup between two office structures to provide net income and network entry to the employees. The supplying stages of the project presents the various environmental influences on a atomise concern, as well as the considerations that must be made to make the appropriate sites, hardw be and configuration settings for the unify. These parameters are used to calculate the evaluate performance data and install a micro-cook link that would function reliably at five nines (99.999%) of approachability.Index Termsattenuation, wantes, melt, line-of-sit e, birthd sign on level, gatewayDIGITAL microwave organizations are used all over the initiation for a wide variety of applications. The majority is point-to-point systems a single link connecting two sites together.For most businesses, having access to the local area network and the internet is essential. The challenge for many is the occupation of more than one office building and how multiple buildings can gain access to the same network.Harris St investx Networks (HSTX) in San Jose, atomic occur 20 occupies an office building in San Jose as well as an equipment warehouse in Milpitas, two miles from the office building. Since the company manufactures digital point-to-point microwave tuners and has access to such equipment, an effective method was researched to utilize a point-to-point piano tuner link as a connection between the two buildings.The purpose of this paper is to demonst yard how a digital point-to-point microwave link can be used to link two office buildings together, in this case the principal(prenominal) office building of HSTX in San Jose and the warehouse in Milpitas, and provide internet and local area network access to the employees at the warehouse.The various aspects complex in the design, knowledgeability and commissioning of a digital point-to-point microwave system is described to highlight the procedures and planning required from microwave engineering science before, during and by and by a microwave link is installed.attenuating influences on a microwave linkAlmost all components involved in a microwave link impart understanding the bespeak to be attenuated at some stage during transmission. In microwave engineering, attenuation plays a major constituent in the design and planning of such a link to hold in reliability and availability regardless of the skirt conditions. Whether its in the line of merchandises, connectives, advances or take over space attenuation on a link can non be avoided and provision ne eds to be made, during the design stage, for the degree of anticipate attenuation to occur.Propagation passesPropagation wantes such as attenuation caused by reflection, free space losses, attenuation caused by come down and by atmospheric gasses have a negative influence on a microwave link.ReflectionLine-of-Sight Microwave tie in are knowing to have full headroom over any object or ter rain along the path to avoid the forecast grazing or abrasion across obstacles. The Fresnel zone is known as the area around the optic line-of-sight that radio waves spread out into after they leave the forward pass 1 and where obstacles would cause in phase or out of phase reflection of the radio wave. This area must be clear of any obstructions to avoid an un desire affect on signal strength. Fig. 1 illustrates the typical Fresnel zones associated with a microwave link.Microwave signals which are reflected or refracted could lead to multiple copies of the same transmissible signa l to arrive at the receiving barbel at contrary clock and out of phase. The reflected and refracted signals will experience differences in attenuation, delay and phase shifts which will result in either constructive (amplifying the signal) or destructive (attenuating the signal) interference. in that location are an infinite number of Fresnel zones. Obstacles in the first Fresnel zone will create signals that will be 0 to 90 degrees out of phase. The warrant Fresnel zone will cause signals to be 90 to 270 degrees out of phase. In the third, the signals will be 270 to 450 degrees out of phase and so forth. Odd numbered zones (1, 3, 5 etc.) have a negative effect on the signal fountain while even numbered zones have a positive effect since these signals really add to the signal power.The phase canceling effect is strongest in zone 1 and decreases in apiece successive zone, hence the need to eliminate as many obstacles from the first zone as possible. These clearance requirement s also acknowledge the sides of the path and not only the top and bottom.Free space lossFree space loss is defined as the loss that would drive between two isotropic antennas in free space, where there are no ground influences or obstructions 2 in other words, the loss where no obstacles nearby can cause blocking, refraction, diffraction or absorption.This loss increases with an increase in relative frequency and distance and the formula for calculating free space loss 3 using the frequency of operation (f) and the distance (in miles) between the two antennas (D) is tending(p) by(1)Attenuation caused by atmospheric gassesAttenuation caused by atmospheric gases is mainly caused by oxygen and wet dehydration in the air. The blue amount of attenuation caused by oxygen stays relatively eonian across all direct frequency bands. Attenuation caused by water vapor absorption however is highly dependent on the frequency of operation as well as the density of the water vapor and will have a deep impact on the links operating above 14 gigahertz.Attenuation caused by rainFurthermore, fading can be the distortion a microwave signal experiences cod to changes in the atmosphere or rain. The kernel amount of rain that waterfall is not as important as the intensity of the rainfall. For example, an area which gets promiscuous rain for most of the year would be less affected by rain attenuation than an area that gets a storm of rain during the showery season, even for a short period of time. Microwave links operating downstairs 8 GHz remain largely unaffected by rain attenuation but at 10 GHz and above, rain has a big impact on the networks reliability.Availability for modern day high reliability systems varies. The annual outage objective for high reliability systems could be as little as 0.01% to 0.0001% of the total operating time which translates to 53 minutes of down time per year for 99.99% reliability and only 30 numbers of downtime per year for 99.9999% re liability.attenuation can degrade the bit error rate (BER) performance of a microwave link resulting in loss of data. Parameters such as the radio frequency, path duration, humidity, temperature, smoothness of the terrain, calmness of the wind, fog and the number of thunderstorms per year can all increase the probability of fading. grow lossesBranching losses are introduced by the ironware used to channelise the microwave signal and is generally specify by the equipment manufacturer.former(a) lossesOther losses associated with a microwave link include losses from feeders, connectors, antennas, radomes and TX line losses. These losses are specified by the manufacturers at different frequencies of operation.Microwave link PlanningSufficient microwave path engineering ensures a link performs according to the requirements set by the owner or user. In a perfect world, any microwave radiotherapy would motive power in a straight line from start to finish. In earth however, everything surrounding the microwave beam and equipment can cause the signal to be attenuated, amplified or interfered with. The challenge for any microwave engineer is to know what these factors are and how to design around it.Site selectionAn essential part of planning a microwave link is the selection of appropriate sites. The office and warehouse roof of HSTX provided a line of sight which was clear of any surrounding buildings and obstructions that could block or cause the microwave signal to be diffracted. thither was no possibility of additional floors being added to either of the two buildings and the absence of other towers and microwave systems in the area, which could interfere with this link, made these sites ideal for the antenna quickness. In addition to this, the sites already had access roads, ac power and telephone set services which were other requirements considered when choosing the appropriate sites.Frequency and equipment selectionIndustry standards and licensing for microwave radios are, in the USA, governed by the Federal Communications Commission (FCC). Radios operating in the license-free 2.4 GHz and 5.8 GHz bands are considered un-licensed radios and require no licensing from any organisation body. Un-licensed radios, such as the Velox LE 5850 manufactured by Harris Stratex Networks, can be installed and operated without any approval from the FCC.The Velox 5850 series is capable of providing up to 45 Mbps of Ethernet throughput (Full-duplex) which was equal for the purpose of this link. The output power of the radio can be bundle adjusted up to +22 dBm and with a receiver sensitivity of -78 dBm enough fade margin can be achieved to ensure link availability of 99.999%.The radio hardware is available in a split-mount configuration a radio frequency building block (RFU) which is connected to a digital unit (DU) using shielded CAT5e cable. The RFU is installed on the tower or mounted below the antenna and the DU is installed indoors an equ ipment building or enclosure. Management software to set up the radio and monitor the performance of the radio link is available for this product.A 4.940-5.580 GHz Grid Antenna (model no GS2-58N), manufactured by mWAVE Industries, LLC was selected for the project. The antenna provided a gain of +27 dBi, a VSWR of 1.51, a return loss of 14 dB and could be mounted for horizontal or unsloped polarization as illustrated in Fig. 2.Microwave link calculationsThe microwave link design was started by doing a link figure analysis a calculation that involves all the gains and losses associated with the antennas, cables, connectors, radio hardware and environment. The link budget was used to determine the anticipate get signal levels at each end of the link. Once this has been done, minor adjustments were made to the sites and hardware selections to achieve the desired link availability.Path calculationsThe receiver threshold value is a banknote of the lowest possible signal level the ra dio can receive and still operate at an acceptable level of performance. This level was specified by the equipment manufacturer as -78 dBm. The difference between the received signal level and the receiver threshold indicates the fade margin (the amount of fading a microwave radio can experience before having the signal degraded enough to cause BER errors or framing errors) of the link. To calculate the expected receive signal level and the fade margin, the propagation losses, forking losses and other losses had to be subtracted from the radio output power and antenna gain.The attenuation caused by atmospheric gasses for links below 14 GHz was negligible. The free space loss inclined by (1) and therefore the total propagation loss was calculated as 114.32 dB. Transmit and receive branching losses associated with the Velox 5850 radio was specified by the equipment manufacturer as 1.5 dB respectively. Other losses, all of which were specified by the various manufacturers, included t he TX line losses of 3.72 dB (1.24 dB per 100ft of cable used) for each site and an N-Type connector loss of 0.3 dB per connector (four connectors used).Output male monarch = + 22 dBmTX Branching Loss = 1.5 dBmAntenna Gain = + 27 dBmPropagation Losses = 114.341 dBmOther Losses = 8.34 dBmAntenna Gain = + 27 dBmRX Branching Los = 1.5 dBmReceived Power = 49.68 dBm Receiver Threshold = 78 dBmFade Margin = + 28.32 dBFading and interference calculationsThe amount of attenuation expected on the link collectable to rain was calculated using the formula in (2)4, where R0.01% represents the rain rate exceeded 0.01% of the time in mm/hour and D the path length in kilometers. Multiplier a and exponent b are determine taken from the North American and ITU-R rain attenuation coefficients chart, while d represents the effective path length in kilometers. The link operating at 5.8 GHz over two miles can thus expect 0.106 dB of additional attenuation during the heaviest rainfall.(2)The poss ibility of the radio signal being diffracted was investigated by observing the structures surrounding the microwave beam and calculating the first and second Fresnel zones using (3)5. The distance from the antenna to any possible obstruction is given by d1 while d2 represents the remaining distance to the other end of the link.(3)Since the Fresnel zones represent of a series of concentric circles, the areas to the side, above and below the microwave beam had to be clear of obstructions. The height of the two buildings where the antennas were to be installed provided enough clearance to ensure no obstructions within the first two Fresnel zones. With a classical 0.106 dB of additional attenuation from rain and no possibility of the signal being diffracted or reflected, only 3 dB of variation on the calculated receive level was expected. The 3 dB of variation is referable to component tolerance and is specified by the equipment manufacturer.Microwave link installationThe antenna and radio frequency unit were installed on a mount pole on the roof of both buildings, in accordance with the manufacturers recommended installation procedures. A high quality 5/8 coaxial cable was used to connect the antenna to the RFU. The digital units were installed in 19 racks inside the buildings while Belden 7921A Shielded CAT5e cable was used to connect the DU to the RFU. All the hardware was grounded to the various grounding points at the sites and the recommended impedance of less than one ohm careful on all ground connections.The antennas were aligned using a digital voltmeter connected to the back of each RFU. The DC voltage reading from the voltmeter was compared to the received signal level (RSL) chart shown in Fig. 3 6 which was supplied by the radio manufacturer.1 Fresnel Zonehttp//www.webopedia.com/TERM/F/Fresnel_Zone.htm 16 June 20002, 4-5 GTE Lenkurt. 1970. Engineering Considerations for Microwave Communications Systems3 Harvey Lehpamer. 2004. Microwave Transmissio n Network, Planning, Design and Deployment6 Harris Stratex Networks. July 2004. Velox LE Installation and Operation Manual.