8/14/2019 Footprint Part 5 of 6 Case Studies

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FootprintChanging the RF cost performance paradigm

Further information visit our websiteswww.summitekinstruments.com

www.triasx.com

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Introduction

Through extensive testing with operators in Australia, Africa, Asia/Pacific, USA and Europe, we estimate morethan 60% of existing sites have some form of PIMproblem, of which around 80% are connector related.

The following are a small selection of examples we havediscovered in the field.

Case Study 1 - South East Asia

Located in a major South-East Asia capital, this site is aGSM900 macro cell, using 6 main feeders with pre-combined Transmit/Receive Units (TRUs) for channelcapacity and a 47m tower.

The carrier has a required system PIM threshold of -130dBc. Jumper cables from the combiner were >-120dBc. The combiners were using resistive loads which

measured at >-130dBc. (Individually the loads were>-70dBm.)

Dirt was found in the combiner connectors giving >-80dBc.

A factory manufactured jumper cable from acombiner to a load was >-120dBc due to a badcrimp.

To rectify the problems:- Two connectors were cleaned, checked and re-

mated. Two connecters within the cabin were re-terminated. A masthead connector which had suffered lightning

damage (visible burn) was cut back 6 inches and newconnector fitted.

All the resistive loads where replaced with low IMcable loads.

Upon completion of testing, all 6 sectors were in the range-150dBc to -145dBc. With just a few hours of rectificationwork, Dropped Calls improved by greater than 50% in firstweek.

Case Study 2 Australia

An Australian carrier operating a WCDMA850 network overlaid on a GSM900 network had an in-buildingdistributed antenna system suffering from high DroppedCall Rates (DCR).

Figure 1

The DCR was logged over a period of time and plotted inFigure 1. There is a significant increase in July 2004 whenthe CDMA equipment at the site was switched on.

Figure 2

Configuring a spectrum analyser for Maximum Hold,capture, wide band noise resulting from the presence of PIM in the RF interconnection over time could be seen(Figure 2).

Case Studies (Part 5 of 6)Through previous articles in this series we have presented the concept of system transparency, and how PassiveIntermodulation (PIM) and Noise can affect Base Station coverage and capacity. In this article we review some of thepractical issues found in the field.

8/14/2019 Footprint Part 5 of 6 Case Studies

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FootprintChanging the RF cost performance paradigm

Further information visit our websiteswww.summitekinstruments.com

www.triasx.com

Page 9 Footprint Five - 2

In this case the GSM900 and WCDMA800 were co-locatedwith resulting PIM products degrading the receivernoise floor to as high as -95dBm/30kHz. This loss inreceiver sensitivity is a loss in coverage and capacity.Using the Triasx test set the operator was able to locate

numerous faulty connections, correcting these to producean excellent result.

Figure 3

After all PIM generating connections were reworked thereceiver noise floor was reduced to -112dBm (Figure 3).This improvement allowed the receiver to provideoptimum performance without interference. The increasein the number of successful calls is evident.

As evolving technologies utilizing wider channelbandwidths are overlaid on existing systems, the presenceof PIM becomes increasingly important in receiverperformance.

Case Study 3 - USA

During a visit to a series of mid-western US base stationsites, 4 out of 5 failed PIM in some capacity.

A six sector site using a Lucent compact 4 BTS, with roof mounted EMS antennas was investigated more closely dueto its repeated diversity alarms. A relatively new site, ithas been installed within the last 18 months, and used5/8 Andrew AVA copper mainline and jumpers.

Checks on the main feeder of sector g revealed:

Return Loss (RL) and Distance to Fault (DTF) sweepswere acceptable (pre-post).

A BTS jumper failed PIM.

Checks on the diversity feeder of sector g revealed:

RL and DTF sweeps were acceptable (pre-post). The main feeder failed PIM tests. An antenna jumper failed PIM tests. A 5/8 connector was spinning under

weatherproofing. Water poured out of the feederwhen the connector was removed.

The relevant connectors and jumpers were replaced, andthe system passed PIM measurements.

Figure 4

Monitoring of site statistics after repair showed adownward trend in the Dropped Call Rate (DCR), in Figure4, and Diversity alarm HEHs were no longer produced.

Summary

Utilizing a PIM test as an RF infrastructure performancemetric is now being used or reviewed by wireless network operators around the world.

Testing for PIM at the BTS, in conjunction with ReturnLoss (RL) and Distance to Fault (DTF) measurements is

proving to be the most effective way to eliminate orsignificantly reduce problems with the RF interconnection.

With the series of portable PIM test equipment developedby Triasx and Summitek Instruments, it is now possible tocarry out complete RF interconnection testing at the BTSreceiver input with ease.