Topics • Introduction • Link Planning • Reliability (Quality) standards • Radio Equipment • Microwave Propagation • Antenna consideration • Frequency Planning • Procedures • Link Planner • Transmission Planner
Introduction
Introduction
Microwave Radio • Microwave Radio are the point to point fixed links that operate in duplex mode. • Duplex operation operation means means each Radio Radio frequency frequency channel consist of a pair of frequencies one for transmission and other for reception. • The user information that is the base band signal is modulated to an RF carrier and transmitted over the air as electromagnetic waves. • The equipment involve in the Microwave communication includes modem, antennae. • The microwave radio links cover the frequency spectrum from 300MHz to 60GHz.
Electromagnetic Spectrum
Microwave Frequency Bands
Merits and Demerits • Microwave radio communication is cheaper than satellite or leased line services. • Cost effective at low capacities. • Quick and easy installation. • Fast Rollout rate. • Resistant to natural disasters. • Provide better overall availability. • Quicker recovery from disasters. • Line of sight required. • Limited spectrum availability. • Limited BW for high capacity applications.
Planning Process • Transform the customer demands in a transmission plan with a set of quality objectives. • Clearly explain the merits and demerits for all links. • Design topology discussed and approved by customer. • Quality objectives clearly defined. • Equipment discussion. • Fading mechanism. • Frequency Band to be used. • Detail link design such as fade margin, antenna size, equipment protection carried out.
Link Planning
Establish Planning Brief Define Transmission Traffic Define Quality Level Required Identify Customer End site locations MSC,BSC,POWER STATIONS YES
Any Changes ?
Produce Network Diagram Define Capacity Required Determine Radio Routes Identify Repeater Required Path Profiles Detailed Map Work Adjust for Earth Bulge and K factor Determine Link Feasibility NO
Hop OK ?
Radio Surveys Do Path Survey and add obstructions Do Site Survey Determine Link Feasibility Hop OK ?
Procedure and Build Sites
Initial Planning • Site Location: Verify the actual position of the site ,Coordinates checked by GPS. Should be accurate. Beam clearance. • Network Diagram: The sites are plotted on the tool/map to produce an initial network. Determine the link capacity from the sites traffic. Check the LOS on the tool. • Path profile: Produce path profile, taking into account the TRS heights, earth bulge, average vegetation, average building height, fresnell zone clearance. • Radio Surveys: Perform practically the LOS check by flash test , balloon test or path study. • Site survey: Detail site survey conducted. • Frequency consideration: Check according to the area, which frequency band will be suitable. Plan according to the hop length and link availability.
Reliability/Quality Standards
• Network operators want the network be error free at every time. • This is the ideal situation for any network which is not possible. • There are certain quality standards set by ITU-R for the MW planning. • Unavailability: When the system is unusable for more than 10 sec, also when BER is worse than 10exp-3,the system is said to be unavailable. • Unavailability Standards: According to ITU-R, the period of unavailable time begins when in at least on direction of transmission, either one or both of the conditions occur for 10 consecutive seconds. Either the signal is interrupted or the BER in each second is worse than 10 exp-3.These 10sec are the part of unavailable time. • Available time: When the system is restored and the BER becomes better than 10 exp-3 for the 10 consecutive seconds, this time called available time.
Unavailability Causes The unavailability might be due to the following •
Propagation.
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Equipment Failure.
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Other factors.
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Outage due to Propagation:
1. Diffraction Loss. 2. Antenna heights are not sufficient. 3. Ducting. •
The beam refracted in such a way that it does not receive at the other end. use space diversity with large antenna spacing.
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Rain.
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The water molecules absorb the MW energy, greater the size of water droplet more energy absorbed. Snow and mist also causes unavailability. Improved by increasing the system gain, also polarization diversity may be employed. Low frequency band be used. Fade margin be kept large.
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Outages due to Equipment: Duration of outage is determined by the length of time maintenance team take to repair or change the equipment or MTTR.Can be minimized by using HSB systems or twin path.
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Other Factors:
1. Failure in the power supply 2. Fire in equipment room 3. Falling down of tower. •
Minimized if route diversity is employed.
Performance Standards •
The performance of a radio link can be determined by the BER. The total no of errors divided by the total no of bits in a specific period of time.
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Causes of Outages:
1. Multipath fading: Refraction causes multiple radio path to be established in the radio path resulting in the flat fading or Raleigh fading. 2. Background errors: It is due to the thermal noise in the radio receivers. 3. Wind: If the tower is not strong enough the radio beam will not properly received at the other end.
Radio Equipment Characteristics
Equipment Configuration • The MW Radio equipment is divided into three categories: • All Indoor • Split unit • All outdoor
Basic Radio System
PCM MUX
MULTIPLEX INPUT
MODULATE USING FSK OR QAM
UP CONVERSION
PATH
DOWN CONVERSION
DE MODULATE TO BASEBAND
DE MODULATES TO TRIBUTRIES
Branching •
Branching is a general term to describe the circuitry that interface the antenna to the transceiver.
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It is of many types:
1. Hot standby Branching. 2. Space Diversity Branching. 3. Twin Path Branching. 4. Frequency Diversity Branching.
Equipment Characteristics • RF Details • Frequency Range • Tx/Rx Separation • Channel Spacing • Transmitter Characteristics • Transmit output power • Transmit power control • Receiver Characteristics • Receiver Threshold • Maximum Receive Level • Fade Margin • Power Details
Microwave Propagation
Atmospheric effects on propagation • The Radio beam is an electromagnetic wave front wide enough . • The path the electromagnetic waveform depends on the troposphere. (lower portion of the atmosphere). • In the atmosphere the density of the atmosphere decreases with altitude. • The upper portion of the wave front travels faster than the lower. • The beam bends downwards , called refraction. • The bending effect is handled by adding the factor k. k<1,ray beam bends away from the earth, k>1,ray beam bends towards the earth. For normal system planning k=4/3.
• Receiver Threshold: The minimum level through which the MW link works is the threshold value. • Receive signal level: The amount of signal that the antenna is receiving. • Fade Margin: The difference between the nominal receive level and the threshold is available as the safety margin against fading, this is known as fade margin.
Fading on MW links Atmospheric absorption: • The main elements that absorb the MW energy are water vapors and oxygen. • Water vapor absorption and rain attenuation are usually considered above 10GHz. • As the rain rate increases the amount of water in the path increases that causes fading of signal. • The higher the frequency the higher will be the water absorption. • Higher frequency bands are useful for shorter hops. • The attenuation due to mist ,fog, snow are negligible as compared to rain. • Rainfall rates are defined by ITU for different regions.
Fresnell zone • The area around the visual line of sight that the radio waves spread out into after they leave the antenna. • This phenomena results from the electromagnetic wave theory that the wave front has expanding properties as it travels through space. The amount of additional clearance that must be allowed to avoid reflections and attenuations are expressed in fresnell zone. • The 60% of the fresnell zone must be clear from all type of obstacles in order to achieve the required RSL. • The fresnell zone increases with length of hop. • The fresnell zone decreases with increase of frequency.
Multipath Fading or Reflections • Multipath reflection occurs at low frequencies, when the hop lengths are greater. • Multipath signal reception causes the fading in the receive signal level.
Solutions to Multipath reflections • Space diversity can be used to overcome the fading caused by the multipath.
• Install the antenna so that the path to reflecting surface is obstructed.
Frequency Planning
Network structure • In order to simplify and get a common naming convention a four-layer transmission structure shall be used Core Network MSC/BSC EXCHANGE
Access Network
LARGE HUB SITE/SDH HUB SITE
SMALL HUB/PDH HUB
SMALL HUB/PDH HUB
• Topologies: • Stars (Hubs): These are defined as the nodes that connects to the several sites via chains or spurs. • Chains: The no of sites connected in sequence. • Spurs: These are defined as the single link connected to the hub site. • In this network we can connect maximum 8 sites in star and 3 sites in a chain. • BSC sites and Hub sites: BSC site usually requires a large no of microwave terminals. In this network traffic from the Nokia outdoor units collocated with Siemens HUB through DDF and a high capacity multiplexer HiTi7070 to Nokia BSC3i.Traffic from the HUB sites is going through Siemens MW link to BSC.
Frequency Band and channels • TP has three band chunks allocated from FAB in the 18,23,38 GHZ frequencies. • There are 8 spot frequencies (28MHz BW) in 18 GHz , 5 spot frequencies in 23GHz band and 38 GHz band. • The sub bands in 18GHz are B and C and in 23GHz and 38 GHz are sub band A. • All frequencies allocated in 28MHz spacing are used for 16*2 or 34Mbit/s capacity, in order to satisfy the 8*2,4*2 and 2*2 capacity, the channels are split into 14,7,3.5 MHz. • Propagation factors require that 38GHz should be used for smaller hops, while 18 GHz and 23GHz for longer ones. • High and Low end sites should be taken properly. • Normally main hub site is taken as high. • PTCL exchanges are taken as Low.
• The equipment used for transmission is called FXCRRI card. • One FXCRRI card can support up to 32E1s. • Two Radio links with 1+0 configuration and one with 1+1 configuration be connected to one FXCRRI card. • The two ports of FXCRRI card are known as flex bus. • One ultra site can support up to 4 FXCRRI cards. • If FXCRRI cards are not available we can use FIU19. • FIU19 is employed on those sites where ultra site cabinet is not present i.e. PTCL exchanges. • The links with main hub site must be protected 1+1. • The links with PTCL exchanges must be protected. • Use the frequency band according to the region and the length of Hop. • Use frequency channel by giving specific frequency spacing in order to minimize interference.
• First the capacity plan made on paper taking into account the site configuration given by the RF team. • Calculate the E1 usage for each site. • Select the frequency band. • Select the Equipment to be use. • Select the Capacity for each link. • Make frequency plan taking into account the frequency reuse and channel separation. • Plot all the sites in NETACT. • Perform Link Budgeting. • Perform the interference analysis. • Generate report.
• For Road side sites transmit maximum power 18dbm irrespective of the fade margin. • The rain file for k zone,42mm/hr. • For city sites FM be from 35 to 45 db depending on the region. • The link availability be 99.995 %. • The Link unavailability be 0.005%. • The interference level be less than -110 dbm.
BSC3i • BSC can support maximum 660 TRX. • Support 4000 Erlang traffic. • Support 124 ET ports. • Support 248 BTS IDs. • Support 248 BCF IDs. • Maximum 41 dual band sites can be accommodated in one full capacity BSC.
TCSM • 8 Aters are handled by one TCSM. • One TCSM support 116 TCH. • One TCSM has 8 modules.
Radio Link Planning • Define Site (Properties). • Link according to the Transmission plan. • Define the link ID. • Define the Radio Equipment at both link ends. • Select the Transmit power for the Radios. • Select the Operating mode of the link. (Single, HSB, Diversity) • Define the Threshold and BER. • Select the link capacity and the channel number. • Select the antenna size and frequency. • Polarization for both ends. • Define feeders. • Run the propagation predictions. • Select the %age rainfall according to the zone.
• Check the performance of the link. • Fade margin. • Received Signal level. • Outage. • Availability. • Perform the high low wizard. • Perform the interference analysis. • Generate Report. (Link Budget ).
Detail TRS Planning •
NetAct Transmission planner is a graphical tool that provide support for all transmission network area required by planner.
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Transmission planner has five modules:
1. Cellular module. 2. Conduit module. 3. Transmission module. 4. Primary Rate path module. 5. Detail module. •
Cellular Module: This module models the logical connection layer (including BTS,BSC,MSC and their logical connections) and uses nodes which are visible in the transmission view. Basically in this module we define which BTS goes to which BSC and the configuration of the BTS (TRX configuration ,BCF ID,BTS ID).
• Conduit Module: The conduit module models the physical cable infrastructure. Basically in this module we define which BTS goes to which BTS and the type of the link (Fiber optic, Radio link). • Transmission Module: In this module we define the route of the sites and how to go to the BSC. Also we define the type of site in this module (BTS,FIU,Metrohub..) • Primary Rate Path Module: In this module we gave ET to the sites and define its termination. • Detail Module: The detail module defines the detail level information about the actual physical devices in the network. This information includes the block diagram showing the units and the interfaces of the devices, interconnection between the interfaces and cross connections within the devices. • After this we can get the BSC report (site ID, site configuration, BCF, BTS,TRX IDs.), Cross connections, Detail connectivity, Abis allocation plan etc.
DDF Plan • Digital Distribution Frame. • Central connection point for different equipments at the site. • The traffic from BTS terminate at the DDF. • The BSC ET ports terminate at the DDF. • The Back bone transmission nodes terminate at the DDF. • DDF is divided into different blocks. • Normally 63 ports in one block. • When SDH link is involved DDF is replaced by HIT7070. • Siemens HIT7070 is used also to multiplex the E1s. • Normally four cards 202,205,208,211 of 63 E1 capacity in one HIT7070.Extension cabinets can be used. • At each SDH hub site HIT7070 is used for cross connections and multiplexing.
Procedures
• Nominal coordinates from RF team. (SARF) • Nominal Transmission connectivity plan. Decision for the BSC sites. • Check for the PTCL exchanges. Feasibility request to PTCL coordinator. • Link feasibility check on the tool. • Nominal connectivity with the link budgets and TRS priorities send to TP for approval. • Decision from Customer. • Finalize the equipment, frequency bands and quality standards. • Release of SARF. • The nominal plan send to the Zone teams. • SAR visits started.
SAR (Draft Survey) • RF,TXN, Civil, Acquisition jointly visit the candidate. • If the candidate is feasible for each member than the candidate is accepted. TXN Responsibilities
• Check the LOS with each connected site. Should have the Txn plan and site coordinates and all the required equipment. • Propose the minimum Transmission height . • Take 45 deg panoramic pictures. • Mark the obstacles in 360 degree with in 600m. • Mention the Obstacle heights and the distance from the candidate. • Mention the average building height and vegetation. • Take the RF azimuth snapshots.
LOS Survey • LOS team go on both ends of the hop. • The candidate may be roof top or green field. • If roof top, than go at the highest point and perform the Mirror test. • Take the pictures of flash with minimum and maximum zoom. • Give the camera heights. • Propose the TRS height. • Balloon test is performed if Flash test is not feasible. • Capture the balloon ,measure the length of string, that gives the TRS height. • Go for the path study if balloon test is not feasible. • Moving through the LOS, take the obstacles coordinates coming in the path. Take the average vegetation and building height. • Create the path profile. Give comments. • Carry out the reflection analysis if the hop length is large.
