1. Todd Stockert IEEE Northcon 2002 October 23, 2002 todd_stockert@agilent.comtodd_stockert@agilent.com Physical Layer and RF Testing Overview of Wireless LAN MODEMS

2. Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 Page 2 For more and updated information… Agilent WLAN & Bluetooth Links: WLAN & Bluetooth Information http://www.agilent.com/find/wlan WLAN & Bluetooth Webcasts & Courses http://www.get.agilent.com/bluetooth/mi/wc.shtml WLAN & Bluetooth Resource Library http://www.get.agilent.com/bluetooth/mi/library.shtml

3. Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 Page 3 WLAN: What and Why WHAT? An extension to, or a replacement for, wired LANs that offers: Ease of installation Flexibility Scalability Cost savings Mobility WHY? Eliminate physical constraints of wires Installing wires is expensive, time consuming, and disruptive

4. Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 Page 4 Topics Introduction to Wireless LAN Standards 802.11b PHYsical layer Overview of Spread Spectrum modulation 802.11b PPDU Structure 802.11a PHYsical layer Overview of OFDM 802.11a PPDU Structure Glance at 802.11g (Draft standard) Overview of WLAN Testing and Specification Measurements

5. Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 Page 5 Current WLAN Standards

6. Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 Page 6 IEEE 802.11b Incorporates 802.11 1,2 Mbit/sec modes, adds 5.5 and 11 Mbit/sec modes Most successful WLAN standard to date “Wi-Fi” standard 2.4GHz ISM frequency band

7. Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 Page 7 IEEE 802.11b: 2.4GHz Difficulties 802.11b Burst uWave Ovens Discrete Tone uWave Oven Splatter FHSS (Cordless Phone, Bluetooth...)

8. Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 Page 8 802.11B: Modulation Formats All modes incorporate “Spread Spectrum” modulation 802.11b extends 802.11 data rates to include 5.5 and 11 MBit/sec There are three rates to keep track of: Chip Rate: 11 MChip/sec -- always Bit Rates: 1 MBit/sec DBPSK 11 chip Barker sequence 2 MBit/sec DQPSK 11 chip Barker sequence 5.5 MBit/sec QPSK, 4 8-chip CCK spreading 11 MBit/sec DQPSK, 64 8- chip CCK spreading 5.5 MBit/sec BPSK PBCC (optional) 11 Mbit/sec QPSK PBCC (optional) Symbol Rates: 1 MHz (11/11) and 1.375 MHz (11/8) At all rates, the signal looks like an 11 MHz BPSK or QPSK waveform

9. Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 Page 9 Spread Spectrum Concepts: Simple Spreading 802.11B -- 1 MBit/Sec Map Barker Sequence +1, –1, +1, +1, –1, +1, +1, +1, –1, –1, –1 1 Bit In DBPSK For each single input bit, there are two possible 11 chip sequences that can be transmitted +1, –1, +1, +1, –1, +1, +1, +1, –1, –1, –1 –1, +1, –1, –1, +1, –1, –1, –1, +1, +1, +1 One sequence is simply the inverse of the other 11 Complex Chips Out

10. Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 Page 10 Spread Spectrum Concepts: Simple Spreading 802.11B -- 2 MBit/Sec Map Barker Sequence +1, –1, +1, +1, –1, +1, +1, +1, –1, –1, –1 2 Bits In For every two input bits, there are four possible 11 chip sequences that can be transmitted +1, –1, +1, +1, –1, +1, +1, +1, –1, –1, –1 +j, –j, +j, +j, –j, +j, +j, +j, –j, –j, –j –1, +1, –1, –1, +1, –1, – 1, –1, +1, +1, +1 –j, +j, –j, –j, +j, –j, – j, –j, +j, +j, +j 11 Complex Chips Out DQPSK

11. Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 Page 11 802.11B -- 11 MBit/Sec ?? Map Barker Sequence +1, –1, +1, +1, –1, +1, +1, +1, –1, –1, –1 11 Bits In 11 Complex Chips Out D2048PSK?

12. Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 Page 12 Spread Spectrum Concepts: Simple Spreading 802.11B -- 5.5 and 11 MBit/Sec 4 Bits In 1 of 4 8-chip sequence Selector DQPSK Rotate 8 Complex Chips Out 8 Bits In 1 of 64 8-chip sequence Selector DQPSK Rotate 8 Complex Chips Out d0-d3 d0,d1 d2-d7 d0-d7 d0,d1 d2,d3

13. Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 Page 13 IEEE 802 Protocol Acronyms *From Agilent 802.11b WLAN Signal Studio Software Product Note Physical Medium Dependent(PMD) PHY Convergence Layer Procedure(PLCP) MAC sublayer Protocol Data Units (MPDU) PHY Protocol Data Units (PPDU) PLCP Service Data Units (PSDU). *See IEEE802 standards for more detail

14. Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 Page 14 802.11B: Long PLCP PPDU Format *From Agilent 802.11b WLAN Signal Studio Software Product Note

15. Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 Page 15 Structure of IEEE802.11b CCK Frame (= Burst) PLCP Preamble PSDU PLCP Header 144 bits Fn(LENGTH,SIGNAL) bits 48 bits

16. Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 Page 16 Structure of IEEE802.11b CCK Frame (= Burst) PLCP Preamble PSDU PLCP Header PLCP Preamble 144 usec, (72 for ShortPLCP) 1MBit/s modulation Scrambled 1’s + SFD Signal detect, AGC, timing synchronization, frequency estimation.

17. Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 Page 17 Structure of IEEE802.11b CCK Frame (= Burst) PLCP Preamble PSDU PLCP Header 1MBit/s modulation (2MBit/s for ShortPLCP) CCITT CRC-16 Protects these fields SIGNAL --b2b3---b7 SERVICE b2: Locked clocks 0: Not Locked 1: Locked b3: Modulation Selection 0:CCK 1:PBCC b7: Length extension bit Solves LENGTH ambiguity 0x0A 1Mbps 0x14 2Mbps 0x37 5.5Mbps 0x6E 11 Mbps LENGTH 16bit Length of PSDU in µsec (Special Rounding)

18. Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 Page 18 Structure of IEEE802.11b CCK Frame (= Burst) PLCP Preamble PSDU PLCP Header PSDU Format varies with data rate Max symbols varies with data rate MAC layer starts here. MAC Header Payload Data FCS

19. Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 Page 19 802.11B: Short PLCP PPDU Format (Optional) *From Agilent 802.11b WLAN Signal Studio Software Product Note

20. Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 Page 20 Significant differences from 802.11b 5-6 GHz Frequency Bands (Less interference, more spectrum) OFDM Modulation 54 MBits/Sec in the same bandwidth RF Characteristics More precise RF design (<1/2 the wavelength) Much Higher Peak-to-Average Power Ratio More Sensitive to Phase Noise IEEE 802.11a

21. Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 Page 21 OFDM – Basic Concepts Slower symbol rate x multiple carriers = similar bits/sec/Hz Carrier spacing creates orthogonality. Less susceptible to: - single freq. interference - multipath dropouts - impulse noise IEEE 802.11a and HiperLAN/2 - 52 carriers - 250 kHz symbol rate - 312.5 kHz spacing - 18 MHz bandwidth...

22. Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 Page 22 Generating OFDM -2+2+10-3+3.. -24-25+2 5 +2 6 +2 4.. -26 carrier number: bits encode, interleave, map onto constellation load complex values into frequency bins.29 + j.85 1011 do inverse FFT to create time waveform add guard interval, clock out at 20 MSa/sec transmit as 1 symbol repeat 52 times repeat until data finished

23. Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 Page 23 OFDM vs. Single Carrier Modulation Frequency Domain View 1 carrier52 carriers BW = Sym(1+  ) BW = #carriers x spacing Adj Chan = Distortion Adj Chan = Normal Rolloff Carrier #0 always null

24. Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 Page 24 OFDM vs. Single Carrier Modulation Frequency Domain View 1 carrier52 carriers BW = Sym(1+  ) BW = #carriers x spacing Pilot Carriers -21, -7, +7, +21 always BPSK same amplitude, phase used as reference for vector demod.

25. Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 Page 25 OFDM vs. Single Carrier Modulation Time Domain View Data rate = 54 Mbits/sec @ ¾ coding = 72 Mbits/sec @ 64QAM = 12 MSym/sec 1 symbol = one point in time 1 point in time = 1 symbol SCM: OFDM: Data rate = 54 Mbits/sec @ ¾ coding = 72 Mbits/sec @ 48 carriers= 1.5 Mbits/sec @ 64QAM = 250 kSym/sec 1 symbol = 1 point in frequency and time 1 point in time = ~meaningless 1 Sym =.083 usec 1 Sym = 4.0 usec This is a sample; FFT(64 samples) gives 64 freq bins (48 carriers + 4 pilots + 12 zeros) This is a symbol = 6 bits

26. Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 Page 26 Structure of IEEE802.11a OFDM Frame (= Burst) Short Training …Data N SIGNALData 1 Data 2 Chan. Estimation 84444 usec... 8

27. Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 Page 27 Structure of IEEE802.11a OFDM Frame (= Burst) Short Training …Data N SIGNALData 1 Data 2 Chan. Estimation Short Training Seq. 8 uSec length Every 4 th carrier, equal amplitude/phase Signal detect, AGC, timing synchronization, coarse freq. estimation....

28. Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 Page 28 Structure of IEEE802.11a OFDM Frame (= Burst) Short Training …Data N SIGNALData 1 Data 2 Chan. Estimation Channel Estimation 8 uSec length Every carrier, equal amplitude and phase. Channel equalization, fine freq. estimation....

29. Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 Page 29 Structure of IEEE802.11a OFDM Frame (= Burst) Short Training …Data N SIGNALData 1 Data 2 Chan. Estimation SIGNAL Symbol 4 uSec length Always BPSK. Describes this frame’s rate, length. These parameters are read from signal under test....

30. Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 Page 30 Structure of IEEE802.11a OFDM Frame (= Burst) Short Training …Data N SIGNALData 1 Data 2 Chan. Estimation Data Symbols 1 symbol = 4 uSec length 1 FFT 52 carriers (48 + 4) 52 constellation dots Format varies Coding varies Max 4096 octets per frame. MAC layer starts here. 3/4 2/3 3/4 1/2 3/4 1/2 3/4 1/2 Coding Rate 216 192 144 96 72 48 36 24 Bits per Symbol Mod. Format Data Rate 64QAM54 64QAM48 16QAM36 16QAM24 QPSK18 QPSK12 BPSK9 6 Mbits/sec = 48 x 6 x.75...

31. Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 Page 31 IEEE 802.11a Payload Structure Address 4 Address 2Address 3 Sequence Control Address 1 Frame Control Duration/ ID Frame Chk Sequence User DataTail Bits Pad Bits 2266626 bytes 4 0-4061 bytes MAC Header...

32. Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 Page 32 IEEE802.11a versus HiperLAN/2 Similarities: 5-6 GHz frequencies 18 MHz bandwidth 52 subcarriers 250 kHz symbol rate BPSK, QPSK, 16/64QAM 6-54 MB/sec Differences: More choice of data services Preamble contents MAC contents Sync procedure Length of Guard Interval

33. Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 Page 33 IEEE 802.11g Mandatory: All mandatory 802.11b modes 802.11b ShortPLCP packet format All mandatory 802.11a modes using 802.11b channels Goals: Puts 802.11a rates into 2.4GHz band Creates 1-54 Mbit/sec variable rate WLAN standard Completely backward compatible to 802.11b Many implementation choices CCK-OFDM, PBCC-22, PBCC-33

34. Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 Page 34 802.11G: Rates and Modulation

35. Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 Page 35 802.11G: Draft CCK-OFDM Packet formats Long PLCP PPDU Packet Short PLCP PPDU Packet LongPLCP OFDM LONG SYNCOFDM SIGNALOFDM PSDUSignal Extension PSDU 8 µsec N sym x 4 µsec6 µsec 192 µsec ShortPLCP OFDM LONG SYNCOFDM SIGNALOFDM PSDUSignal Extension PSDU 8 µsec N sym x 4 µsec6 µsec 96 µsec

36. Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 Page 36 WLAN Measurements IEEE Specification Measurements Verify compliance of OEM components Grade components for different price-points Carry design-for-test from simulation to prototype to production Transient capture Troubleshoot conversation traffic Detect sources of interference Determine subtle DSP or analog impairments Analyze DUT without test mode requirements Multi-domain measurements Analysis in Demodulation/Time/Frequency domains required Most impairments have preferences for where they can be diagnosed Interactions exist between PvT/Spectral Mask/Modulation Quality

37. Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 Page 37 IEEE802.11b Transmitter Testing Measurement Specified by the 802.11B Standard 18.4.6.8 – TX spurious 18.4.7.1 – TX power level 18.4.7.3 – TX spectrum mask 18.4.7.4 – TX center freq. tolerance 18.4.7.5 – Symbol clock freq. tolerance 18.4.7.6 – TX power-time mask 18.4.7.7 – TX carrier leakage 18.4.7.8 – TX modulation accuracy

38. Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 Page 38 802.11B: TX Spectral Mask

39. Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 Page 39 802.11B: TX power-time mask : Power-Up Ramp 2 usec

40. Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 Page 40 802.11B: Power-Down Ramp

41. Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 Page 41 EVM: A Model For Signal Errors Ideal Signal Generator Error Signal Generator (e.g. noise, distortion, spurious, phase noise) Transmitter Ideal(t) error(t) actual(t) Ideal(t) Actual(t) Error(t) Magnitude Error(t) Error Vector Magnitude(t) Phase Error(t) I Q Carrier Leakage

42. Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 Page 42 IEEE802.11b Modulation Accuracy

43. Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 Page 43 IEEE802.11a Transmitter Testing Measurement Specified by the 802.11A Standard 17.3.9.1 – TX power level 17.3.9.2 – TX spectrum mask 17.3.9.3 – TX spurious 17.3.9.4 – TX center freq. tolerance 17.3.9.5 – Symbol clock freq. tolerance 17.3.9.6.1 – TX carrier leakage 17.3.9.6.2 – TX spectral flatness 17.3.9.6.3 – TX constellation error

44. Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 Page 44 802.11A: Measuring Center Frequency Leakage With Time Gating, Band Power, C/N Marker Time Gating selects just the short sync sequence. Band Power measures power during the short sync. C/N marker computes leakage at carrier #zero.

45. Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 Page 45 802.11A: Measuring Modulation Quality

46. Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 Page 46 802.11A: Modulation Quality

47. Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 Page 47 802.11A: Measuring Peak-to-Average Statistics With Time Gating, CCDF Plot CCDF results reveal the P.A. designer’s nightmare. Time Gating selects just the data portion of the frame (no preamble). Use appropriate trigger setup, delay, time length, etc.

48. Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 Page 48 802.11A: Channel Freq Response (Spectral Flatness) Equalizer-based Display as Amplitude Response, Phase Response, Impulse Response, or Group Delay.

49. Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 Page 49 802.11A: Transmit Spectral Mask

50. Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 Page 50 IEEE802.11 Receiver Testing Measurement Specified by the 802.11A Standard (Packet Error Ratio (PER) testing) 17.3.10.1 Receiver minimum input level sensitivity 17.3.10.2 Receiver adjacent channel rejection 17.3.10.3 Receiver non-adjacent channel rejection 17.3.10.4 Receiver maximum input level Measurements for Receiver Troubleshooting Quality of the test signal used for RX Sensitivity Testing Receiver Spurious Receiver Phase Noise Receiver EVM (distortion, noise, etc) Measurements at RF, IF and IQ Baseband Measurement Specified by the 802.11B Standard (Frame Error Ratio (FER) testing) 18.4.8.1 Receiver minimum input level sensitivity 18.4.8.2 Receiver maximum input level 18.4.8.3 Receiver adjacent channel rejection

51. Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 Page 51 IEEE802.11 Receiver Testing 802.11B: Uses FER (Frame Error Ratio) 802.11A: Uses PER (Packet Error Ratio) DUT uses demodulated CRC(11b) or FCS(11a) to determine failures. Ratio of unsuccessful frames to total is the FER or PER Requires software testpoint in receiver 802.11B Provides Test Mode to simplify legal transmit signals (Currently no 802.11A provision exists, but probably should). “Golden” TX Signal Level Adjust Interfering TX DUT Test Software Signal Level Adjust May substitute Source Instrument for this block (e.g. E4438C).

52. Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 Page 52 Summary Wireless LAN Standards - Interoperability is key to success. IEEE 802.11 standards are leading the way. 802.11b PHY Described the mandatory Spread Spectrum modulation formats Explored the 802.11b PHY packet structure 802.11a PHY Described some details about OFDM modulation Explored the 802.11a PHY packet structure Took a glance at 802.11g (Draft standard) Discussed WLAN testing methods and 802.11b/a Specification measurements

53. Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 Page 53 WLAN Measurement Setup