Testing Upstream and Downstream DOCSIS 3.1 Devices

Transcription

1 Testing Upstream and Downstream DOCSIS 3.1 Devices April 2015 Steve Hall DOCSIS 3.1 Business Development Manager

2 Agenda 1. Decoding and demodulating a real downstream DOCSIS 3.1 signal and reporting key metrics such as MER and BER. 2. Combining powerful trigger and recording techniques to detect, identify and repair issues that cause BER. 3. Understanding the complexities of demodulating and measuring low frequency, small grant upstream signals. 4. Generating in-channel and out-of-channel upstream and downstream DOCSIS 3.1 signals. Technologies 2015 Page 2

3 Agenda 1. Decoding and demodulating a real downstream DOCSIS 3.1 signal and reporting key metrics such as MER and BER. 2. Combining powerful trigger and recording techniques to detect, identify and repair issues that cause BER. 3. Understanding the complexities of demodulating and measuring low frequency, small grant upstream signals. 4. Generating in-channel and out-of-channel upstream and downstream DOCSIS 3.1 signals. Technologies 2015 Page 3

4 DOCSIS 3.1 Signal Format Physical Layer Link Channel (PLC) OFDM Channel Descriptor (OCD) Downstream Profile Descriptor (DPD) messages Technologies 2015 Page 4

5 DOCSIS 3.1 Signal Format NCP Fields Data Fields Technologies 2015 Page 5

6 Automatic Demodulation of Downstream signals in VSA - New DOCSIS3.1 Downstream measurement option BHM for 89601B VSA (BHM)Key features: - Automatic setup for downstream configuration by demodulating and decoding: Physical Layer Link Channel (PLC) OFDM Channel Descriptor (OCD) Downstream Profile Descriptor (DPD) messages - Decode the NCP and locate the codewords for each profile - Demod the data for each profile - MER - Post-process MER & BER/PER measurements to accumulate over successive acquisition. Technologies 2015 Page 6

7 Result Traces DOCSIS3.1 Downstream Step 1 detect and decode PLC Physical Layer Link Channel Step 2 detect and decode OCD OFDM Channel Descriptor (not necessarily sent every frame as per standard) Step 3 detect and decode DPD Downstream Profile Descriptor Technologies 2015 Page 7

8 Result Traces DOCSIS3.1 Downstream Initial performance results Technologies 2015 Page 8

9 Description of Results Result Traces DOCSIS3.1 Downstream Report Profile Results Report NCP Results Technologies 2015 Page 9

10 Result Traces DOCSIS3.1 Downstream Technologies 2015 Page 10

11 Result Traces DOCSIS3.1 Downstream Technologies 2015 Page 11

12 MER Measurement Hardware Positioning $ Max 510 MHz Demod BW + RF Measurements Max 160MHz Demod BW + RF Measurements Max 750 MHz Demod BW MER Technologies 2015 Page 12

13 Introducing the N9040B UXA Signal Analyzer 8.4/13.6/26.5 GHz Up to 510 MHz analysis BW Streamlined touch driven interface Full BW RTSA Industry Leading Phase noise VSA & N9068C Phase Noise App Technologies 2015 Page 13

14 Hardware Platforms: U5303A digitizer or X-Series Spectrum Analyzer U5303A PCIe High-Speed Digitizer PCIe rack mount expansion chassis Desktop PC OR 89601B Vector Signal Analyzer UXA N9040B Signal Analyzer Install VSA software on Windows 7 OS or on an external PC Technologies 2015 Page

15 Hardware Platforms: U5303A digitizer and X-Series Spectrum Analyzer Personal Cpmputer Preserve your X-Series investment! Combine the power of the PCIe Digitizer Modulation Measurements with the power of the PXA/UXA RF Measurememts. Technologies 2015 Page 15

16 Agenda 1. Decoding and demodulating a real downstream DOCSIS 3.1 signal and reporting key metrics such as MER and BER. 2. Combining powerful trigger and recording techniques to detect, identify and repair issues that cause BER. 3. Understanding the complexities of demodulating and measuring low frequency, small grant upstream signals. 4. Generating in-channel and out-of-channel upstream and downstream DOCSIS 3.1 signals. Technologies 2015 Page 16

17 To BER or not to BER: BER says everything is working nicely or that it is NOT! Hours of testing complete yet BER fails! How do you determine WHY your Bit Error Rate is failing? DOCSIS Frame Generator M8190A Device Under Test CMTS (single ended) Optical Transport Amplifier BER Golden Receiver Cable Modem What causes bit errors? Clipping? Noise? Compression? Interference? How and where do they show up other than in an accumulated over-time BER test? Rapid fire in-channel and adjacent-channel energy spikes? Increased unexpected signal amplitude? Spurious emissions? Reduced Adjacent Channel Power performance? Technologies 2015 Page 17

18 How do DOWNSTREAM events manifest themselves? These events show up at various times and places and are distinguishable as perturbations in the frequency domain! By building a very flexible mask around the spectrum, these perturbations can be trapped, recorded, analyzed and subsequently questions answered! Technologies 2015 Page 18

19 The test steps Monitor Transient Spectral Behavior in Real Time Determine Root Cause and Repair Issue Trigger on Transient Spectral Behavior in Real Time Determine if the Transient Spectral Behavior Caused Bit Errors Record Transient Spectral Behavior Including Behavior Leading up to the event Technologies 2015 Page 19

20 Watch for the transient event The Tools: How are transients found? Real Time Spectrum Analysis Technologies 2015 Page 20

21 Watch for the transient event The Tools: How are transients found? Real Time Spectrum Analysis Technologies 2015 Page 21

22 Watch for the transient event The Tools: How are transients found? Real Time Spectrum Analysis Frequency Mask trigger Catches the transient Technologies 2015 Page 22

23 Watch for the transient event The Tools: How are transients found? Real Time Spectrum Analysis + Vector Signal Analysis Set up frequency Mask Trgger in VSA Technologies 2015 Page 23

24 Watch for the transient event Multiple Domain Insight Technologies 2015 Page 24

25 Watch for the transient event Multiple Domain Insight Note spectral behavior of transient event Technologies 2015 Page 25

26 The Tools: How are transients found? Impact on Constellation Transient Event Impact on MER Technologies 2015 Page 26

27 The test steps M8190A (DOCSIS 3.1 Frame Generator) Monitor Transient Spectral Behavior in Real Time DUT (Amplifier/Optical Transport or CMTS) Trigger on Transient Spectral Behavior in Real Time Real Time Spectrum Analyzer uses frequency Mask Trigger to detect unwanted energy in and around the desired signals. Record Transient Spectral Behavior Including Behavior Leading up to the event Vector Signal Analyzer begins recording triggered by a violation detected by the Real Time Spectrum Analyzer including a pre-trigger window Technologies 2015 Page 27

28 Determine if the Transient Spectral Behavior Caused Bit Errors Determine Root Cause and Repair Issue Calculate and analyze BER results for the entire gap-free recorded frames in order to answer the question: Did THIS event cause bit errors? Study demodulation test results for the gap free recording to answer questions like: Was signal quality impacted buy the event that caused the recording to be triggered? Technologies 2015 Page 28

29 Automating the process Monitor Transient Spectral Behavior in Real Time Determine Root Cause and Repair Issue Test Controller Create scripts to automate and record events. Trigger on Transient Spectral Behavior in Real Time Determine if the Transient Spectral Behavior Caused Bit Errors Record Transient Spectral Behavior Including Behavior Leading up to the event Technologies 2015 Page 29

30 Testing for the Real Upstream Environment Environmental Interference How tolerant is this system of this signal? CM 1 CM 2 CMTS Node FIBER Node CM 3 CM n Technologies 2015 Page 30

31 Testing for the Real Upstream Environment Environmental Interference How tolerant is this system of this signal? Real Time Spectrum Analyzer Plus VSA Node FIBER Node Upstream Generator Plus Impairments Technologies 2015 Page 31

32 Real Time Spectrum Analysis and Event recording Step 1: RTSA Trigger Mask Step 2: Initiate Signal recording! Step 4: Post-process Multimeasurements Show recovery after the event the event Step 3: Post-process using Multimeasurements to show impact during the event Technologies 2015 Page 32

33 Agenda 1. Decoding and demodulating a real downstream DOCSIS 3.1 signal and reporting key metrics such as MER and BER. 2. Combining powerful trigger and recording techniques to detect, identify and repair issues that cause BER. 3. Understanding the complexities of demodulating and measuring low frequency, small grant upstream signals. 4. Generating in-channel and out-of-channel upstream and downstream DOCSIS 3.1 signals. Technologies 2015 Page 33

34 Stability of MER Measurements at Low Grant % 1 Cable Modems 2 CMTS OFDMA 96MHz Channel Hybrid Fiber Coax (HFC) Network 4 3 OFDMA: Low-grant signals are those where less than about half of the subcarriers are active, and the remainder are transmitted as nulls. 5 96MHz Channel Spectrum Technologies 2015 Page 34

35 Stability of MER Measurements at Low Grant % Measurement Challenge: Vector Signal Analysis synchronization algorithms are optimized for signals with a relatively high grant percentage. 96 MHz Acquisition BW 5% grant 96 subcarriers DC Sample Freq MHz Center Freq. 53 MHz 2048 point FFT Technologies 2015 Page 35

36 Stability of MER Measurements at Low Grant % Measurement Approach: Reconfigure existing measurements to zoom in on the active subcarriers only. Thus, rather than analyzing a small percentage of a large FFT block, the demodulator processes a smaller FFT block that is almost fully-populated! Smaller acquisition BW improves SNR to the sync algorithms, stabilizes MER readings. Mathematically, the two approaches are identical there is no effect on the calculation of MER, carrier frequency error, symbol clock error, or other measurement results. 96 MHz Acquisition BW ~5 MHz Acquisition BW 5% grant 96 subcarriers Mathematically equivalent to: Automatic Bandwidth Translation Compliments of Optimizer Macro! 100% grant 96 subcarriers DC Sample Freq MHz Center Freq. 53 MHz 2048 point FFT Sample Freq. 6.4 MHz Center Freq. 8 MHz 128 point FFT Technologies 2015 Page 36

37 Stability of MER Measurements at Low Grant % Optimize VSA Macro Technologies 2015 Page 37

38 Results Comparison Identical hardware, identical input signal: Demod config: 2K FFT 5% grant Demod config: 128 FFT 100% grant Avg. MER: ~37 db Variance: ±5 db Sync stability: 50% Avg. MER: 53.8 db Variance: ±1 db Sync stability: 100% Technologies 2015 Page 38

39 Stability of MER Measurements at Low Grant % 1 Cable Modems 2 CMTS OFDMA 96MHz Channel Hybrid Fiber Coax (HFC) Network Small Grant 1 Small Grant 2 96MHz Channel Spectrum Setting the grants side by side creates a challenging measurement scenario. Technologies 2015 Page 39

40 Reconfiguring OFDM for Synchronized ACP The DOCSIS 3.1 PHY specification requires that Adjacent Channel Power be measured in the spectrum regions directly adjacent to the transmitted signal, starting at one subcarrier spacing (25 or 50 khz) from the outermost active subcarriers. However, even well-windowed OFDM signals will have significant sinx/x modulation sidebands that extend into this region which are visible when viewed on a traditional swept spectrum analyzer. Technologies 2015 Page 40

41 Reconfiguring OFDM for Synchronized ACP The ACP specification is not meant to include these sidebands, but rather to measure only the unwanted noise and distortion that may accompany them. In order to separate these components, the spec requires that ACP measurements at offsets of 2 MHz or less be performed synchronously - that is, sampled at the same frequency and in phase with the underlying OFDM modulation clock. This suppresses all orthogonal (modulation-related) energy, leaving only the non-linear distortion to be summed. Technologies 2015 Page 41

42 Reconfiguring OFDM for Synchronized ACP Optimizer Adds extra null subcarriers to the OFDM demod configuration. VSA Configure analyzer to display the null subcarriers. Read ACP from VSA spectrum display using band power markers. Technologies 2015 Page 42

43 Agenda 1. Decoding and demodulating a real downstream DOCSIS 3.1 signal and reporting key metrics such as MER and BER. 2. Combining powerful trigger and recording techniques to detect, identify and repair issues that cause BER. 3. Understanding the complexities of demodulating and measuring low frequency, small grant upstream signals. 4. Generating in-channel and out-of-channel upstream and downstream DOCSIS 3.1 signals. Technologies 2015 Page 43

44 M8190A Main Features Breakthrough performance Up to 90 dbc SFDR for Reliable and repeatable measurements 14 bit 8 Gsa/s or 12 bit 12 Gsa/s Variable sample rate from 125 Msa/s to 8/12 Gsa/s 2 GSa memory for Long play time 5 GHz analog bandwidth For today s and tomorrows apps Operation with leading software platforms Technologies 2015 Page 44

45 M9099T Waveform Creator - Downstream Page

46 M9099T Waveform Creator - Upstream Page

47 SystemVue Libraries Technologies 2015 Page 47

48 ATP PHY 31 Spectrum Loading Cable Load Signals Notch Cable Load Signals Technologies 2015 Page 48

49 ATP PHY 31 Interfering spectrum Technologies 2015 Page 49

50 Output of M8190A as per settings described above DOCSIS 3.1, 1901 active subcarriers DOCSIS 3.0 = 158 channels, 6 MHz spacing Technologies 2015 Page 50

51 Questions? 1. Decoding and demodulating a real downstream DOCSIS 3.1 signal and reporting key metrics such as MER and BER. 2. Combining powerful trigger and recording techniques to detect, identify and repair issues that cause BER. 3. Understanding the complexities of demodulating and measuring low frequency, small grant upstream signals. 4. Generating in-channel and out-of-channel upstream and downstream DOCSIS 3.1 signals. Technologies 2015 Page 51