Passive Intermodulation (PIM), an interference challenge for the radio Passive Intermodulation (PIM), an interference challenge for the radio Passive Intermodulation (PIM), an interference challenge for the radio Passive Intermodulation (PIM), an interference challenge for the radio access networks access networks access networks access networks John Miller
Smiths Interconnect � Kaelus is a new name company within the Smiths Interconnect group � We are a global company that designs and manufactures complex and technically sophisticated RF products for use in the rapidly growing wireless communications market. � Kaelus is the consolidation of four leading industry brands within � Kaelus is the consolidation of four leading industry brands within Wireless Telecoms: Triasx, Summitek, Allrizon and the commercial division of TRAK Microwave Ltd.
Global Technical Service & Support AMERICAS : EMEA : APAC :
What is Passive Intermodulation (PIM)?
What is Passive Intermodulation (PIM) ? PIM = Noise generated by the interaction between the multiple Tx signals and passive non-linear junctions in the RF path. Desired Interference Interference f 1 f 2 2f 1 -f 2 2f 2 -f 1 3f 2 -2f 1 3f 1 -2f 3f 1 -2f 3f 2 -2f 1 2 2 f 2 -f 1 4f 1 -3f 2 4f 2 -3f f 1 +f 1 2 2f 2 2f 1 PIM generated products will affect received band (UL) by Increasing the received Noise floor thus reducing base station sites coverage and capacity.
PIM is getting more complex with Indoor Area 1 Ant 1800/WCDMA Ant Ant Ant Ant Ant Ant 900/1800 PS PS PS PS PS PS Ant Ant PS PS Ant Ant Indoor Networks evolution towards : Area 2 PS PS Ant Ant Ant Ant Ant Ant PS PS PS PS Triplexer Indoor PS PS Ant Ant Area 3 • Indoor or outdoor complex DAS PS PS Ant Ant Outdoor Ant Ant systems (shared by several area PS PS Indoor Area 4 PS PS Ant Ant PS PS Ant Ant Indoor Area 5 operators) Load RF Output ports RF Output ports Combining Unit • Site sharing with multiple transmit WCDMA GSM 1800 GSM 900 carriers (same RF infrastructure for Node B Node B Node B OP 3 OP 2 OP 1 OP 3 BTS OP 2 BTS OP 1 BTS OP 3 BTS OP 2 BTS OP 1 BTS multiple operators) • Multi-technology sites (GSM 900 MHz, GSM 1800 MHz, UMTS 2100 and UMTS900 MHz, CDMA 450, CDMA850, LTE800, LTE2600, LTE2300)
PIM Sources Non-linear metal-to-metal contacts : • Loose RF connectors. • Poorly prepared RF cable terminations • Improperly mated / misaligned parts • Cracked / cold solder joints • Loose mechanical fasteners (screws, rivets) Traditional sweep (RL or DTF) testing many times does not identify these problems.
Sweep testing vs. PIM testing: Transmitted signals Incident signals Non-Linear Infrastructure Reflections caused by changes in impedance are Reflected + measured using sweep test equipment. interference (Efficiency of the signal propagation) signals Interference caused by non-linear junctions are measured by PIM test equipment (Interference created by the signal propagation)
PIM test specification IEC 62037 � First edition of IEC 62037 was published on 9/16/1999. (>12 years ago!) � Purpose: � To establish a standard test method for measuring Passive Intermodulation (PIM) � Provide a method to compare the PIM performance of different devices � Key recommendations of the specification: � Key recommendations of the specification: � Third Order IM products typically represent the worst case condition of unwanted signals; therefore measuring IM3 characterizes the DUT � PIM comparisons should be done at the same power level. (2x 20 W recommended for mobile communications systems) � Devices should be subjected to an “impact” or “movement” while PIM testing
How to test PIM? PIM Test Equipment TX TX TX 1 1 1 TX TX TX 2 2 2 PI PI M M PIM Source PIM Test equipment transmits 2 frequencies at high power into the system under test and measures the magnitude of the interference generated at the known IM3 frequency. The fault location is found by “tapping” on interconnections and components (dynamic test) during the test looking for spikes in PIM magnitude.
PIM Severity 3rd Order 5 th Order -60 dBm 7 th Order 9 th Order 11 th Order -93 dBm Outside PCS Metal flake Rx band for F1 & F2 selected selected Spectrum Analyzer Mode Repairing IM3 reduces ALL IM products.
PIM tests must be dynamic Poor RF Connection � IEC 62037 requires that devices be subjected to an “impact” or “movement” while PIM testing � This is referred to as “Dynamic” testing meaning “with motion” FAIL PASS � Loose mechanical contacts in the field may not generate PIM until subjected to a future environmental stress (thermal cycling, ice environmental stress (thermal cycling, ice loading, wind loading, etc.) � Dynamic testing finds these intermittent faults before they impact site performance � PIM level must stay below the specified maximum at all times during a dynamic test No Tapping tapping
Possible to have Same Band intermodulation issues • GSM900 • 890 MHz 890 MHz 915 MHz 915 MHz 935 MHz 935 MHz 960 MHz 960 MHz 900 GSM Rx band 900 GSM Rx band 900 GSM 900 GSM Tx Band Tx Band • GSM1800 • 3 rd order 5 th order 5 th order 7 th order 1710MHz 1710MHz 1785MHz 1785MHz 1805MHz 1805MHz 1880MHz 1880MHz 1800GSM Rx band 1800GSM Rx band 1800GSM 1800GSM Tx Band Tx Band • • UMTS2100 2110MHz 2110MHz 1920MHz 1920MHz 1980MHz 1980MHz 2170MHz 2170MHz 2100 UMTS Rx band 2100 UMTS Rx band 2100 UMTS 2100 UMTS Tx Band Tx Band
Also, Cross Band intermodulation issues involving UMTS 3 rd order � DCS1800 into UMTS2100 5 th order 1880MHz 1805MHz 1920MHz 1980MHz 1800GSM Tx band UMTS2100 Rx Band And with LTE there are multiple combinations nowadays
Where to look for PIM on statistics? � Main search focus on: � General – CDR, CSR, CSSR GSM UMTS � GSM Mean interference on Idle (IOI) � CDR data and voice � TCH Completion Rate and Drop % � RRC Success rate% � TRAFFIC RATE Erlangs � TRAFFIC RATE Erlangs � RAB Establishment Success % � RAB Establishment Success % � TCH Assignment Rate � Voice Traffic Erl � SDCCH Assignment rate and drops � PS Traffic (Mb) � HO Success Rate � Average Throughput � UL Quality � RTWP � Erlang Minutes Per Drop � RSSI � DROP_AFTER_TCH_ASSIGN � SDCCH_RADIO_FAIL
PIM test process at cell site:
Recommendations for Low PIM at site + + Use only high Well Trained staff Use correct grade products grade products who can assemble who can assemble tooling for the tooling for the <-150dBc Spc’n in a quality manner job = LOW PIM
KAELUS field trial evaluation This survey was based on the sites selected by our customers to do PIM tests and where they had UL interference issues
PIM Survey in EMEA by KAELUS KAELUS trials: • >390 feeder lines surveyed. 71.87% • 26 Operators and OEMs, 17 countries 28.13% • Many PIM problems recorded 2.56% • Few VSWR problems found Sites or sectors with Sites or sectors with Sites or sectors without PIM problems VSWR problems PIM Problems The sites were originally commissioned with Sweep test equipment so it is no surprise that the VSWR results are good
101 GSM900 PIM Survey in EMEA by KAELUS 50 50 GSM900/GSM1800/UMTS2100 44 GSM1800 25 GSM900/UMTS2100 24 UMTS2100 13 GSM900/GSM1800 GSM1800/LTE1800/UMTS2100 6 GSM1800/UMTS2100 6 technology feeder lines problems, different site UMTS900 4 On sites with PIM were tested. CDMA450 2 GSM900/UMTS900 2 LTE2600 2 CDMA850 2
PIM Survey in EMEA by KAELUS • The PIM defects found were primarily due to workmanship issues at the RF connections. 64.77% 70.00% 60.00% 50.00% 33.45% 40.00% • Many lines had multiple 30.00% defects 15.30% 14.23% 14.23% 20.00% 20.00% 10.00% 0.00% • KPI improvements reported Connectors Jumper Cables Other Passive Antennas Devices on the majority of sites that PIM was detected and repaired at site
Poor cable preparation Dirt / trash
Poor cable preparation
Cable damage Cable damage
External PIM Sources
KAELUS PPIM Solutions
PIM testing is not new! � Summitek Instruments has been producing “bench top” PIM test systems for more than a decade � Summitek has delivered more than 800 BPIM systems worldwide systems worldwide � These systems have been used by RF equipment manufacturers to reduce PIM in their component designs
What is relatively new is Portable PIM test equipment. � “Portable” PIM test equipment enables system level testing to be conducted at the cell site. � On site PIM testing reveals: � Installation workmanship issues � Installation workmanship issues � Component damaged during installation � Component damaged in transit
PIM test equipment: iQA Series � High Power – Premium � Adjustable power (2 – 20W) � Adjustable frequencies � Rugged construction � Integrated transit case � Panel PC with touch screen interface, on-board reporting
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