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Best Practices for Achieving Low PIM Performance in DAS Networks Slide 1.

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Presentation on theme: "Best Practices for Achieving Low PIM Performance in DAS Networks Slide 1."— Presentation transcript:

1 Best Practices for Achieving Low PIM Performance in DAS Networks Slide 1

2 Agenda What is Passive Intermodulation (PIM) Sources of PIM in a DAS environment Reasons why PIM is particularly problematic in DAS How a PIM tester works Best practices for mitigating PIM Anritsu MW82119A product features Slide 2

3 Passive Intermodulation (PIM) Slide 3 F1F2 TX Signals at site Passive Intermodulation (PIM) PIM = interference PIM = new frequencies generated by TX Signals at a cell site when they encounter non-linear junctions or materials in the RF path PIM falling in an operators uplink can elevate the noise floor: Dropped calls Access failures Slower data rates 2*F2–1*F1 3*F2–2*F1 4*F2–3*F1 5*F2–4*F1 2*F1–1*F2 3*F1–2*F2 4*F1–3*F2 5*F1–4*F2 IM 3 IM 5 IM 7 IM 9 IM 3IM 5 IM 7 IM 9

4 What does PIM look like at the site? Slide 4 PIM Mobile uplink signal

5 What does PIM look like to the operator? Slide 5 High average noise level Lower average noise level QUIET BUSY QUIET BUSY PIM Repair

6 What is a non-linear junction? Slide 6 Current increases linearly with applied voltage High pressure, metal-to-metal contacts Welded or soldered connections Current Voltage Linear junctions Non-linear junctions Current Voltage Current does not increase linearly with voltage. Low pressure, metal-to-metal contacts Oxide layers on metal surfaces Arcing across small air gaps or cracks

7 What is non-linear in a DAS? Slide 7 Damaged / poorly made components Broken cracked solder joints Loose internal fasteners Braided cables with crimp connectors Nickel plating Shipping damage

8 What is non-linear in a DAS? Slide 8 High power RF terminations BTS #1 Input Out Notorious for poor PIM Impact depends on frequencies being combined BTS #2 Input

9 What is non-linear in a DAS? Slide 9 Metal flakes inside RF connectors Worse when touching inner or outer conductor

10 What is non-linear a DAS? Slide 10 Poor cable termination Loose metal flakes Rough / irregular metal edges

11 What is non-linear a DAS? Slide 11 Metal flakes inside cables Plenum rated cables have no foam to prevent metal flakes from falling inside

12 What is non-linear in a DAS? Slide 12 Loose RF connectors Must be torqued with a torque wrench

13 What is non-linear in a DAS? Slide 13 Type-N connectors Easy to damage contacting surfaces if over torqued Tend to loosen over time 7/16 DIN connectors better 4.1/9.5 or 4.3/10 mini DIN connectors also better

14 What is non-linear in a DAS? Slide 14 External PIM Sources Fire suppression pipes Air handling ductwork Metal hangers Lighting fixtures Ceiling tile frames Etc., etc., etc. Antennas flush mounted to ceiling

15 And… there are many opportunities for PIM! Floor 1 Slide 15 Radio 1 Radio 2 Floor 2 Floor 3 63 RF connections 31 cable assemblies 15 antennas 14 power dividers 1 hybrid combiner 1 RF termination In this simple example:

16 Where does PIM occur? F1F2 IM 3IM 5 IM 7 IM 9 IM 3IM 5 IM 7 IM 9 2*F2–1*F1 3*F2–2*F1 4*F2–3*F1 5*F2–4*F1 2*F1–1*F2 3*F1–2*F2 4*F1–3*F2 5*F1–4*F2 PIM occurs at mathematical combinations of the Tx frequencies F1 = 1930 MHz F2 = 1945 MHz IM3 = (2*1930) – (1*1945) = 1915 MHz IM3 = (2*1945) – (1*1930) = 1960 MHz IM5 = (3*1930) – (2*1945) = 1900 MHz IM5 = (3*1945) – (2*1930) = 1975 MHz IM7 = (4*1930) – (3*1945) = 1885 MHz IM7 = (4*1945) – (3*1930) = 1990 MHz IM9 = (5*1930) – (4*1945) = 1870 MHz IM9 = (5*1945) – (4*1930) = 2005 MHz BTS DownlinkBTS Uplink Slide 16

17 Where does PIM occur? (the easy way) F1F2 IM 3IM 5 IM 7 IM 9 IM 3IM 5 IM 7 IM 9 15 MHz BTS Downlink BTS Uplink Slide 17

18 Where does PIM occur? (the easy way) F1 F2 IM 3 IM 5 IM 3 IM 5 30 MHz BTS DownlinkBTS Uplink Slide 18 Wide frequency spacing moves IM products farther apart Increases probability that low order IM product will fall in uplink band

19 Neutral Host Systems Increase Probability that IM Products Will Fall in Rx Band Slide 19 Multiple operators / bands: Different story! IM 3 falls in E / F block uplink IM 5 falls in A-block Single PCS operator: FCC did a good job! IM 11 first product that falls in A-block uplink

20 What is the bandwidth of PIM signals? F1 F2 IM 3IM 5 IM 7 IM 9 IM 3IM 5 IM 7 IM KHz 600 KHz 1 MHz 1.4 MHz 1.8 MHz 600 KHz 1 MHz 1.4 MHz 1.8 MHz PIM bandwidth increases as carrier bandwidth increases PIM bandwidth increase with PIM order BTS DownlinkBTS Uplink Slide 20

21 Can one wide band carrier generate PIM? IM 3 IM 5 IM 7 IM 9 5 MHz YES ! Signal is composed of individual sub-carrier frequencies BTS DownlinkBTS Uplink Slide 21

22 What is the solution? Slide 22 Eliminate non-linearity so that multiple frequencies can peacefully co-exist! LTE GSM UMTS CDMA

23 Slide 23 How do we measure linearity? With a PIM tester! Inject two CW test signals at a known magnitude Measure 3 rd order intermodulation product (IM3) IM3 characterizes the linearity of the system If IM3 is low = linearity is good If IM3 is high = linearity is poor Load IM products F1, F2 PIM Test lead PIM tester PIM

24 Low IM3 = good linearity Low IM3 drives higher order products below the noise floor Slide 24 Reducing IM3 Reduces all IM Products A A F1F2 IM 3 IM 5 IM 7 IM 9 IM 11 IM 3 IM 5 IM 7 BTS Uplink (Rx) BTS Downlink (Tx) Noise Floor

25 Best Practices for Achieving Low PIM performance in a DAS Slide 25

26 1) Start with high quality components Slide 26 Only use RF components that: Are designed for low PIM performance Proper material selection No loose metal-to-metal junctions IEC provides more extensive list of design guidelines From companies that: Own PIM test equipment Have their manufacturing processes under control 100% test to verify performance (-150dBc with 2x 20W test tones )

27 2) Use crews that are PIM certified Slide 27 Understand the importance of cleanliness Use alcohol swabs to clean mated pairs of connectors Vacuum end of cables before attaching connectors Understand the importance of proper cable preparation Cut plenum rated cables with razor blade cutter (not saw) Use sharp cutting tools Use the correct tools for the type of cable in use Understand the importance of tight connections Always use a torque wrench (DIN) Do not over/under tighten (Type-N) Have experience operating PIM test equipment

28 3) PIM test as you build Antenna location tests Branch test Floor test Slide 28 Radio 1 Radio 2 Sector test System test

29 3) PIM test as you build (cont) Problems are identified and corrected before being replicated throughout the DAS Faster to locate PIM sources when testing smaller sections Easier access to antennas / splitters to troubleshoot and correct problems Tools, materials, man-lifts, still on hand Reduced re-work at antenna locations (when antenna locations are pre- tested) Slide 29

30 Antenna Location Testing Place antenna as close to design location as possible using low PIM pole Perform PIM test Low test power ( dBm typical) Lowest frequency only (700 or 850 MHz) Pass/Fail limit (depends on test power) Find passing location within 1 m of design location Small movements = big changes in PIM! Slide 30 PIM tester

31 Things to Avoid Around Antennas: For every rule there is an exception This is why it is important to test! Try to avoid placing antennas within 1m of: Metal seams (ductwork, etc.) Concrete with obvious signs of rust Lighting fixtures Electronic devices Products containing RF ID tags Slide 31

32 PIM Master MW82119A Features Slide 32

33 Key Specifications / Capabilities for DAS Slide 33 * - Weight varies by frequency option

34 Battery Operation = Enhanced Portability Slide 34

35 PIM magnitude vs. time Tap on all RF connections while performing the PIM test Visual indication of PIM stability Peak PIM held for Pass/Fail Slide 35 PIM vs. Time Capability Tapping on RF connections Limit Line

36 Distance-to-PIM (DTP) Capability Slide 36 The fastest way to locate PIM PIM magnitude vs. distance Eliminates guess-work Able to see PIM beyond antenna 6 markers + marker table to identify multiple sources

37 Wide Range of Test Accessories Slide R - Hard Case Accessory Kit R - Backpack Accessory Kit R – Transit case (Holds MW82119A plus accessories) (accessories not included) R – Transit case (Holds MW82119A only)

38 Conclusion PIM is a challenge in DAS environments Many potential sources More harmful frequency combinations Best practices for mitigating PIM include: Using high quality components Using trained installation crews PIM testing as you build (starting with antenna locations) Anritsu PIM Master is well suited for PIM testing in a DAS environments Exceptional portability Fully integrated, Distance-to-PIM (DTP) technology Slide 38


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