Mw Transmission (nec) 3l2qb

Prepared by Engr. Jawad Khan BSS/TXN Engineer EPTSC-Cll

What is MW transmission?  Microwave transmission refers to the technology of

transmitting information or power by the use of radio waves whose wavelengths are conveniently measured in small numbers of centimeters; these are called microwaves. This part of the radio spectrum ranges across frequencies of roughly 1.0 gigahertz (GHz) to 30 GHz. These correspond to wavelengths from 30 centimeters down to 1.0 cm.

Advantages of MW.  High frequency small size of antenna  High frequency  narrow beam width  Narrow beam width  no interference and high

bandwidth  Easy in relocation  No bad effects on humans.

Link planning The design and construction of a microwave radio link network is based on a number of factors. These include:  Distance between microwave radio terminals  Terrain properties, eg bodies of water, cliffs, forests, snow  Frequency of operation, often governed by licensing costs, frequency availability, planned distances and even suspectibility to rain fading.  Fading, dispersion and multipath distortion.  Size of antennas, feedline properties, need for towers etc.  Council and community development permissions governing visual intrusions.  Cost of equipment and cost benefit analysis including equipment maintenance.

WHY NEC???  High efficiency/Quality and reliability.  low power consumption  Temperature resistable.

 friendly  Easy software/HW installation.  Software is simple and easily understandable.  Different modulation schemes avaialable.  High system gain/high spectrum effieciency.  Can use freq from 6 GHz upto 52 GHz.

Common MW link Setup. The b/m basic Equipment is required for a MW link.  An indoor unit (IDU)  A Parabolic MW dish Antenna  An outdoor unit (ODU) connected to Antenna.  An IF (intermediate frequency) cable to connect IDU with ODU using standard straight and L connectors.  A negative 48V DC voltage from standard rectifiers.

IF cable.  IF cable is an intermediate frequency cable i.e. its just

a simple coaxial cable but its called IF because it carry information signals in intermediate frequency range i.e. 140MHz (Rx) and 340MHz (Tx).  Coaxial cable has the common property that the it shows more attenuation/losses to high frequency signals.  Short Test is made for IF cable to check cable and connectors.

ODU connection with Dish Ant. ODU can be connected to Dish Ant. In different ways.  Direct mount connection  Using waveguide  Using Hybrid  Using transducer

Protected and unprotected links.  Protected links have main and standby paths available

and one is used at a time. They are represented by (1+1)  Unprotected links have only one path and if that path

gets down, all transmission breaks. They are donated by (1+0).

Different types of common links configuration  Unprotected 1+0  Hotstandby 1+1  Unprotected Twinpath

 Space diversity  Frequency diversity  XPIC (cross polarization interference cancellor).

Details of link configurations.  Unprotected 1+0 link has one 1+0 IDU, one IF cable,

One ODU and one Dish.  HotStandby 1+1 link has one 1+1 IDU, two IF cables, two ODUs and one Dish.  Twin path is the same as Hot standby but it has different traffic on both of its paths at the same time so both paths are unprotected.

Space Diversity link.  SD link has two Dishes (one called main and other

called standby) at each side, 1+1 IDU, two IF cables, two ODUs.  Two IDUs and 4 ODUs can be used to make it more protected.  Both frequency and Polarization are the same for both dishes.  There are three paths made in this configuration i.e. one from Main to Main and two from Main to standby dishes.

Frequency diversity links.  Frequency diversity is the same as space diversity but

the main difference is that frequency of both dishes is different and polarity is the same .

XPIC  PASOLINK NEO can improve its transmission capacity

up to dual STM-1 in 28 MHz bandwidth by using XPIC technology. In case of this capacity upgrading from one STM-1 system, the additional parts are dual polarize antenna, one more ODU/ IDU set, some XPIC cable kit and additional firmware. The upgrading can be realized with existing STM-1 equipment.

Dish size and frequency consideration.  The higher the frequency is, the narrow will be its

beam width and vice versa.  The longer the link distance is, the lower frequency signals are used to get wide beamwidth and better RSL can be achieved.  High freq signals travel less distance then low freq and high freq signals are more attenuated then low freq.  High freq needs small size dish antenna’s then low freq so the longer the link distance is, the smaller freq will be used and dish antenna’s of large size will be used.

Line of Sight. LOS should be clear because MW transmission is point to point transmission and if the dishes are not aligned to each other then better RSL will not be achieved and more closer RSL near threshold RSL, the higher will be the risk of link fluctuation.

Commonly used NEC MW links. The b/m NEC MW links are commonly used in Mobilink Pakistan.  Pasolink V3  Pasolink V4  Pasolink Mx  Pasolink NEO  Pasolink NEO V

E1 capacity. the b/m E1 capacity Equipment is commonly used here.  4 E1  16 E1  48 E1  63 E1 (STM-1)  2 x STM-1 capacity can be obtained using XPIC technology.  C-Node is used to add/drop media in SDH like 63 E1 Pasolink NEO as the media is totally synchronous.

Softwares The b/m softwares are used.  PNMT (for pasolink)  PNMTj (for pasolink NEO) java version.  Software installation will be taught directly during

training.

New link installation/commissioning.  When a new link is installed first check whether

installation has been done according to standard or not. And check safty measures have been taken or not like grounding of IDU/ODU/Surge arrestors/MW rack etc.  Check power using multimeter.  Power on link IDU.  Make sure that you have all required data to configure the new equipment according to link budget. (All NEC IDU’s commissioning will be taught at site visits.)

Before and after LVD connections.  Make sure that all your links are connected before LVD

to avoid link outages during low voltages.  LVD stands for low voltage disconnection. It disconnects BTS power supply when voltages are lowered till -42VDC.  If your link power connections are after LVD then with the disconnection of BTS, all your links will be powered off too.

Common troubleshooting steps.  First of all if you receive TT’s of several down sites then

check your sites connectivity for any possible common links between the down sites.  If you find the down sites common link then site guard (both ends) directly to find out whether there is a power failure or not. If not then move immediately to one of the end.  Make sure that you have all the required cables and softwares in working conditions in your laptop and must take a rigger tech with you along with full toolkit.

Common troubleshooting steps.  If the IDU is powered off then check the front fuses of

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IDU using multimeter and if they are faulty then replaced them. If they are ok then check fuse . The fuses in fuse and power input/output of fuse . If fuse is not receiving input then check connections at rectifier. If fuse fuse is faulty then replace it. If every thing with power is ok then replace IDU.

Common troubleshooting steps.  Please note down that always visit both ends of the

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link before making any decission because mostly issue can not be judged from visiting one end of the link. If IDU is powered on then connect to it using your PNMT/PNMTj . Check for the current alarms and check event logs. Check RSL value and if RSL value is less than -45 dbm (i.e. towards -50 -60 -70 dbm) then improve the RSL value by making fine tunning in allignment. RSL should be between -32  -38 dbm approx.

Common troubleshooting steps.  BER : bit error rate/ratio  High BER/Low BER means that there is too much

noise and attenuation, it can be often due to some water penetration into the straight connectors. Check your connectors and make short test for IF cable.  If your IDU/ODU alarm on the IDU is blinking and there is a IDU/ODU link alarm in software then there is something wrong with the connection between IDU and ODU. Check your IF cable, L connector, straight connector etc.

Common troubleshooting steps.  If there are MOD and DEM alarms then either of your

ODU or IDU needs to be replaced. You have to troubleshoot by changing them one by one, that’s the best way to troubleshoot.  Please note that there are always two types of ODU’s. one is high and one is low. That’s why one end is called high and other end is called low. Care must be taken before replacing ODU to make sure that high band ODU is not mixed up with low band ODU.

Common troubleshooting steps.  IF the link is PASOLINK NEO then it has more clear

cut alarms then the older versions. E.g.  For short IF cable, there will be an alarm of IF cable short.  Similarly for OPEN IF cable, there is alarm of IF cable OPEN.  In Pasolink neo, you can change the cards and no need of replacing whole IDU e.g there is a modem card, an interface card, a control card.

IF cable Short Test.  Open the L and straight connectors from IDU and

ODU and short one end of it.  Take multimeter to the other end and select the short test option on multimeter.  Now put the two probs of MM on the inner and outer connection of the connector.  The MM should beep when the other end is short.

IF cable Short Test.  Now remove the short from the other end. Now mm

should not beep and cable path should be open. If it still beeps then either of your connectors are short and needs to be remade.  Make this test for atleast 5 to 10 times to get more confirm results.  If the behaviour of IF cable is sometime open and some time short even the other end is open and all connectors have been made fresh then check your IF cable it may have water penetrated inside it. in that case IF cable needs to be replaced.

Interference Test.  Send one team to one end and other team to far end.  Both should have laptops and softwares in it in

working conditions.  Now one team will turn off the IDU and the team at its far end will check RSL which should be -100 dbm. Take snap shot of RSL after a few seconds.  Similarly second team will turn off IDU and first team will take check RSL.  If RSL is not -100 then share the snap shots with your Regional Transmission Engineer along with dish sizes, dish heights, etc. for both ends.

RSL improvement/Link alignment.  Send your Rigger technician with multimeter to climb

the tower along with serial number of ODU. If the site is a major hub site then tell him to trace the IF cable too to avoid outage of another link. He must match serial number of ODU too before doing any thing.  When he find the right dish then he will get himself adjusted by fastening his safty belt.  Open multimeter and select 20VDC option.

RSL improvement/Link alignment.  Connect black wire to the tower by using neto tape.  Connect red wire to the back of ODU (option

available) now monitor the voltage values at MM.  If alignment is almost out then voltages will be 0.5 to 1.30 if RSL is improved to -30s then voltages will be 3.40 + - .  For RSL improvement activity on operational Links, never loose up and down as there can be chance that dish may get down and big sizes dishes are not easy to control then. Always check left right first to get max RSL, if no use then do fine tuning on up and down.

Safety measures and standard.  Grounding should be done properly.  IDU should be tight and balanced  There should be enough space between two IDUs min     

equal to 1U. All cables and tributaries should be tight and laid properly. Weather proofing should be done properly. Dishes should be locked properly after activities. Correct labeling should be done on everything from IDU to dish. Two meter IF cable should be looped on tower behind antenna .

Thanks & The end.  Software installations, software using, and HW details

will be taught during training and site visits.