Sunday, 20 February 2011

Cure found for cell-site deafness – CTIA preview

Cure found for cell-site deafness – CTIA preview

Summitek has finally brought to market two user friendly truly portable PIM “diagnostic measurement” tools iMT and iQA for use in the field.  Both have the same high-power and effectiveness as their benchtop model which is the standard for laboratory PIM testing. It’s being demonstrated at CTIA (Central Hall C3, Booth 6221).
PIM often only shows up under full-power transit conditions. It is caused by a variety of factors such as arcing between surfaces that are not correctly prepared or where mating surfaces are not 100% clean or terminations not 100% torqued.
The route from transmitter to airwaves is a complex one – filters, diplexers, combiners, feeders, connectors, jumpers, and the antenna itself – and not only is every single component a candidate for causing  PIM, but so also is the way it was installed one, three maybe five or ten years ago.
VP Sales Interconnect technologies, “PIM is insidious, it slowly grows and the cell becomes more damaged, more ‘deaf’ – but no-one could investigate and explain why – until now.”
Conventional VSWR and ‘distance to fault’ testing are robust measurements in themselves, but incapable of finding PIM distortion and its causes; and even the low-power portable PIM testers are inadequate because they don’t have the power levels to simulate the system environments which cause the real-life PIM issues.
Summitek iMT and iQA field test units are both full 20w + 20w testers. Both are fully field ruggedized, capable of being dropped and stood upon (not that Summitek actively recommend such treatment) and can be easily taken by technician-in-van to any site and used to test and diagnose PIM issues, and once the suspect element has been replaced/repaired to test for a full “clean bill of health” on the entire RF system. There is even a small back-pack tester (iHA companion) which can be taken to the tower-top during identification and cure operations.
Engineers know that gaining an extra few dB of signal to noise ratio on the uplink receive path saves on lost calls and improves data thru-put. PIM cures effected with Summitek iMT and iQA portable field PIM testers have instances improving the noise floor by a massive 5dB delivering an environment which allows optimal receiver performance
Summitek forecasts a frightening rise in PIM issues as existing infrastructure is re-used for new technologies like 3G/UMTS and LTE.
Says Skinner “Feeders, filters and the like have been in-situ for years and they were built for either analogue or GSM single frequency operation. UMTS and LTE use wideband approaches so old empirical PIM solutions like using a different frequency are no longer an option. What’s more, because they are wideband instead of discrete transmission frequencies, the wideband carrier being transmitted creates a type of spreading effect of the third, fifth and seventh order intermods causing significantly raised noise floors for the uplink receivers.”
Although this is a potential minefield says Skinner, now with the Summitek iMT and iQA field testers it is possible to confirm end-to-end RF interconnection quality through the analysis of the presence of PIM – problems can be identified and rectified so that existing infrastructure can be re-used with the certainty of high quality operational use.

PIM-free RF components
From its leading position as the manufacturer of the laboratory standard Summitek PIM bench tester, the companies sister brands will also be on the CTIA booth (Central Hall C3, Booth 6221) showing:
Triasx HSPA proven Filters, Diplexers, triplexers, combiners and splitters
Triasx Sole supplier of RF products (Active solutions and Tower Mount Amplifiers) to the world’s fastest national mobile network
Allrizon radio receiver conditioning solutions, (filtering and amplification)
Allrizon Microwave broadband RF filter solutions from 2.4GH to 38GHz

Saturday, 19 February 2011

About MBNL

Mobile Broadband Network Limited (MBNL) is a 50/50 joint venture company owned by 3 UK and T-Mobile (UK). MBNL was formed following the ground breaking network consolidation agreement that was completed on the 18th December 2007. MBNL manages and delivers the combined 3G access networks of the two companies. This collaboration will lead to almost complete population coverage for 3G services across Britain by the end of 2008 with significant improvement to dense urban in-building coverage in 2009. As the world's largest known active 3G network consolidation agreement, this has significantly increased both operators' 3G network quality and coverage, accelerating the provision of new high-speed mobile broadband services and delivering substantial cost savings as well as environmental benefits by de-commissioning 5000 radio base station sites. By combining their 3G access networks (the mobile masts and infrastructure that connects to each operator's separate core network) T-Mobile and 3 UK will create Europe's most extensive high-speed downlink packet access (HSDPA) network. The agreement offers customers comprehensive mobile coverage in the first stage of joint development in 2008 and further improvements to quality of service in 2009. It furthers both companies' joint commitment to deliver true mobile broadband internet access in addition to reliable voice and text services

Passive Intermodulation

Passive Intermodulation
Common Misconceptions – Sweep vs PIM:

  • Sweep tests measure efficiency of signal propagation
  • PIM tests measure ability to propagate signals without generating interference.
  • Both tests are important and necessary to ensure quality site construction 
Measurable impact on network capacity
Correcting PIM issues on a site will have a measurable impact on the RF network. Not only quality but also capacity (especially in ‘noise floor dependent technologies like W-CDMA)
Root causes of PIM:
  • Loose RF connectors
  • Poorly prepared RF cable terminations
  • Improperly mated / misaligned parts
  • Deformed / rough mating interfaces
  • Metallic debris (flakes, chips)
  • Cracked / cold solder joints
  • Loose mechanical fasteners (screws, rivets)

Quotes from operators conducting regular PIM Testing:

PIM testing helps to find RF plumbing failures that are masked or not detected during sweep testing.”
We spent extra time on every connector so you wouldn’t make us look bad.
We thought we were good before [PIM Testing]. Now, we have had to become even better.”
PIM Testing changed everything. This [PIM testing] is my report card.
You can lie to me, but you can’t lie to the PIM Tester.
Two bad [PIM] reports, they get a warning. On the third [bad PIM Report], I send them home.

Summary:
  • Passive Inter-Modulation (PIM) degrades system performance.
  • Multi-band networks are susceptible to PIM internal and external to the infra-structure.
  • Multi-operator, passive DAS networks are susceptible to PIM problems.
  • Portable PIM test equipment is readily available to identify performance problems in both outdoor and indoor cellular infrastructure.
  • PIM testing and VSWR testing are necessary to verify site performance and installation quality.

PIM Generator, Bad factory connectors on jumpers.

PIM Generator

Poor workmanship on this connector was the cause of failing PIM.DSCN0707
DSCN0706

Bad factory connectors on jumpers.

Today we found 5 bad jumpers that were brand new. They all had connector issues.
Connector 1
Connector 2

Bad connector.

Bad connector.

Today we were having an issue with this connector and this is what we found when it was opened.

PIM Cause

Brand new jumper.

Brand new jumper.

Today we tested jumpers prior to sending them up the tower. Brand new out of the bag -121 dBc.

Missing washer in connector

Missing washer in connector.