Todd Stockert IEEE Northcon 2002 October 23 2002

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

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 Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 2

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 Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 3

Topics • Introduction to Wireless LAN Standards • 802. 11 b PHYsical layer • Overview of Spread Spectrum modulation • 802. 11 b PPDU Structure • 802. 11 a PHYsical layer • Overview of OFDM • 802. 11 a PPDU Structure • Glance at 802. 11 g (Draft standard) • Overview of WLAN Testing and Specification Measurements Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 4

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

IEEE 802. 11 b • 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. 4 GHz ISM frequency band Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 6

IEEE 802. 11 b: 2. 4 GHz Difficulties u. Wave Ovens Discrete Tone Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 FHSS (Cordless Phone, Bluetooth. . . ) u. Wave Oven 802. 11 b Burst Splatter 7

802. 11 B: Modulation Formats • All modes incorporate “Spread Spectrum” modulation • 802. 11 b 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 Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 8

Spread Spectrum Concepts: Simple Spreading 802. 11 B -- 1 MBit/Sec Barker Sequence +1, – 1, +1, +1, – 1 1 Bit In 11 Complex Chips Out Map 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 One sequence is simply the inverse of the other Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 9

Spread Spectrum Concepts: Simple Spreading 802. 11 B -- 2 MBit/Sec Barker Sequence +1, – 1, +1, +1, – 1 2 Bits In 11 Complex Chips Out Map DQPSK For every two input bits, there are four possible 11 chip sequences that can be transmitted +1, – 1, +1, +1, – 1 +j, –j, +j, +j, –j, –j – 1, +1, – 1, +1, +1 –j, +j, –j, –j, +j, +j Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 10

802. 11 B -- 11 MBit/Sec ? ? Barker Sequence +1, – 1, +1, +1, – 1 11 Bits In Map 11 Complex Chips Out D 2048 PSK? Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 11

Spread Spectrum Concepts: Simple Spreading 802. 11 B -- 5. 5 and 11 MBit/Sec 4 Bits In d 0 -d 3 8 Bits In d 2, d 3 d 0, d 1 d 2 -d 7 d 0, d 1 Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 1 of 4 8 -chip sequence Selector DQPSK Rotate 8 Complex Chips Out 1 of 64 8 -chip sequence Selector DQPSK Rotate 8 Complex Chips Out Copyright Agilent Technologies 2002 12

IEEE 802 Protocol Acronyms 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 IEEE 802 standards for more detail Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 *From Agilent 802. 11 b WLAN Signal Studio Software Product Note Copyright Agilent Technologies 2002 13

802. 11 B: Long PLCP PPDU Format Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 *From Agilent 802. 11 b WLAN Signal Studio Software Product Note Copyright Agilent Technologies 2002 14

Structure of IEEE 802. 11 b CCK Frame (= Burst) 144 bits 48 bits PLCP Preamble PLCP Header Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 Fn(LENGTH, SIGNAL) bits PSDU 15

Structure of IEEE 802. 11 b CCK Frame (= Burst) PLCP Preamble PLCP Header PSDU PLCP Preamble • 144 usec, (72 for Short. PLCP) • 1 MBit/s modulation • Scrambled 1’s + SFD • Signal detect, AGC, timing synchronization, frequency estimation. Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 16

Structure of IEEE 802. 11 b CCK Frame (= Burst) PLCP Preamble PLCP Header 0 x 0 A 1 Mbps 0 x 14 2 Mbps 0 x 37 5. 5 Mbps 0 x 6 E 11 Mbps SIGNAL SERVICE - - b 2 b 3 - - - b 7 LENGTH b 2: Locked clocks 0: Not Locked 1: Locked b 3: Modulation Selection 0: CCK 1: PBCC b 7: Length extension bit Solves LENGTH ambiguity PSDU PLCP Header • 1 MBit/s modulation (2 MBit/s for Short. PLCP) • CCITT CRC-16 Protects these fields 16 bit Length of PSDU in µsec (Special Rounding) Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 17

Structure of IEEE 802. 11 b CCK Frame (= Burst) PLCP Preamble PLCP Header PSDU • Format varies with data rate • Max symbols varies with data rate • MAC layer starts here. • MAC Header • Payload Data • FCS Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 18

802. 11 B: Short PLCP PPDU Format (Optional) Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 *From Agilent 802. 11 b WLAN Signal Studio Software Product Note Copyright Agilent Technologies 2002 19

IEEE 802. 11 a Significant differences from 802. 11 b • 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 Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 20

OFDM – Basic Concepts • Slower symbol rate x multiple carriers = similar bits/sec/Hz • Carrier spacing creates orthogonality. . . . • Less susceptible to: - single freq. interference - multipathdropouts - impulse noise • IEEE 802. 11 a and Hiper. LAN/2 - 52 carriers - 250 k. Hz symbol rate - 312. 5 k. Hz spacing - 18 MHz bandwidth Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 21

Generating OFDM bits encode, interleave, map onto constellation load complex values into frequency bins carrier number: -26 -25 -24. . 1011 . 29 + j. 85 . . -3 -2 -1 0 +1 +2 +3. . repeat 52 times . . +2 +2 +2 4 5 6 do inverse FFT to create time waveform add guard interval, clock out at 20 MSa/sec Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 transmit as 1 symbol Copyright Agilent Technologies 2002 repeat until data finished 22

OFDM vs. Single Carrier Modulation Frequency Domain View 1 carrier BW = Sym(1+a) 52 carriers BW = #carriers x spacing Adj Chan = Normal Rolloff Adj Chan = Distortion Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 Carrier #0 always null 23

OFDM vs. Single Carrier Modulation Frequency Domain View 1 carrier BW = Sym(1+a) 52 carriers BW = #carriers x spacing Pilot Carriers • -21, -7, +21 • always BPSK • same amplitude, phase • used as reference for vector demod. Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 24

OFDM vs. Single Carrier Modulation Time Domain View This is a symbol = 6 bits SCM: 1 Sym =. 083 usec Data rate = 54 Mbits/sec @ ¾ coding = 72 Mbits/sec @ 64 QAM = 12 MSym/sec 1 symbol = one point in time 1 point in time = 1 symbol Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 OFDM: This is a sample; FFT(64 samples) gives 64 freq bins (48 carriers + 4 pilots + 12 zeros) 1 Sym = 4. 0 usec Data rate = 54 Mbits/sec @ ¾ coding = 72 Mbits/sec @ 48 carriers= 1. 5 Mbits/sec @ 64 QAM = 250 k. Sym/sec 1 symbol = 1 point in frequencyand time 1 point in time = ~meaningless 25

Structure of IEEE 802. 11 a OFDM Frame (= Burst) 8 Short Training Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 8 4 4 4 Chan. Estimation SIGNAL Data 1 Data 2 Copyright Agilent Technologies 2002 4 usec …Data N . . . 26

Structure of IEEE 802. 11 a OFDM Frame (= Burst) Short Training Chan. Estimation SIGNAL Data 1 Data 2 …Data N . . . Short Training Seq. • 8 u. Sec length • Every 4 th carrier, equal amplitude/phase • Signal detect, AGC, timing synchronization, coarse freq. estimation. Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 27

Structure of IEEE 802. 11 a OFDM Frame (= Burst) Short Training Chan. Estimation SIGNAL Data 1 Data 2 …Data N . . . Channel Estimation • 8 u. Sec length • Every carrier, equal amplitude and phase. • Channel equalization, fine freq. estimation. Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 28

Structure of IEEE 802. 11 a OFDM Frame (= Burst) Short Training Chan. Estimation SIGNAL Data 1 Data 2 …Data N . . . SIGNAL Symbol • 4 u. Sec length • Always BPSK. • Describes this frame’s rate, length. These parameters are read from signal under test. Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 29

Structure of IEEE 802. 11 a OFDM Frame (= Burst) Short Training Chan. Estimation SIGNAL Data Rate 6 Mbits/sec Mod. Format BPSK Coding Rate 1/2 Bits per Symbol 24 9 BPSK 3/4 36 12 QPSK 1/2 48 18 QPSK 3/4 72 24 16 QAM 1/2 96 36 16 QAM 3/4 144 48 64 QAM 2/3 192 54 64 QAM 3/4 216 Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 Data 1 Data 2 …Data N . . . Data Symbols • 1 symbol = 4 u. Sec length 1 FFT 52 carriers (48 + 4) 52 constellation dots • Format varies • Coding varies • Max 4096 octets per frame. • MAC layer starts here. = 48 x 6 x. 75 30

IEEE 802. 11 a Payload Structure 2 2 6 6 Frame Control Duration/ ID Address 1 Address 2 6 Address 3 2 Sequence Control 6 bytes Address 4 . . . MAC Header . . . 0 -4061 bytes User Data Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Tail Bits 4 Pad Bits Copyright Agilent Technologies 2002 Frame Chk Sequence 31

IEEE 802. 11 a versus Hiper. LAN/2 Similarities: • 5 -6 GHz frequencies • 18 MHz bandwidth • 52 subcarriers • 250 k. Hz symbol rate • BPSK, QPSK, 16/64 QAM • 6 -54 MB/sec Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 Differences: • More choice of data services • Preamble contents • MAC contents • Sync procedure • Length of Guard Interval 32

IEEE 802. 11 g • Mandatory: • All mandatory 802. 11 b modes • 802. 11 b Short. PLCP packet format • All mandatory 802. 11 a modes using 802. 11 b channels • Goals: • Puts 802. 11 a rates into 2. 4 GHz band • Creates 1 -54 Mbit/sec variable rate WLAN standard • Completely backward compatible to 802. 11 b • Many implementation choices CCK-OFDM, PBCC-22, PBCC-33 Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 33

802. 11 G: Rates and Modulation Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 34

802. 11 G: Draft CCK-OFDM Packet formats 192 µsec Long. PLCP PSDU OFDM LONG SYNC 8 µsec OFDM SIGNAL OFDM PSDU Signal Extension 8 µsec Nsym x 4 µsec 6 µsec Long PLCP PPDU Packet 96 µsec Short. PLCP PSDU OFDM LONG SYNC 8 µsec OFDM SIGNAL OFDM PSDU Signal Extension 8 µsec Nsym x 4 µsec 6 µsec Short PLCP PPDU Packet Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 35

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 Pv. T/Spectral Mask/Modulation Quality Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 36

IEEE 802. 11 b Transmitter Testing Measurement Specified by the 802. 11 B 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 Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 37

802. 11 B: TX Spectral Mask Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 38

802. 11 B: TX power-time mask : Power-Up Ramp 2 usec Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 39

802. 11 B: Power-Down Ramp Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 40

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

IEEE 802. 11 b Modulation Accuracy Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 42

IEEE 802. 11 a Transmitter Testing Measurement Specified by the 802. 11 A 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 Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 43

802. 11 A: Measuring Center Frequency Leakage With Time Gating, Band Power, C/N Marker Band Power measures power during the short sync. Time Gating selects just the short sync sequence. C/N marker computes leakage at carrier #zero. Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 44

802. 11 A: Measuring Modulation Quality Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 45

802. 11 A: Modulation Quality Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 46

802. 11 A: Measuring Peak-to-Average Statistics With Time Gating, CCDF Plot Time Gating selects just the data portion of the frame (no preamble). Use appropriate trigger setup, delay, time length, etc. CCDF results reveal the P. A. designer’s nightmare. Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 47

802. 11 A: Channel Freq Response (Spectral Flatness) Equalizer-based Display as Amplitude Response, Phase Response, Impulse Response, or Group Delay. Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 48

802. 11 A: Transmit Spectral Mask Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 49

IEEE 802. 11 Receiver Testing Measurement Specified by the 802. 11 A 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 Measurement Specified by the 802. 11 B 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 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 Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 50

IEEE 802. 11 Receiver Testing 802. 11 B : Uses FER (Frame Error Ratio) 802. 11 A : Uses PER (Packet Error Ratio) • DUT uses demodulated CRC(11 b) or FCS(11 a) to determine failures. • Ratio of unsuccessful frames to total is the FER or PER • Requires softwaretestpoint in receiver • 802. 11 B Provides Test Mode to simplify legal transmit signals (Currently no 802. 11 A provision exists, but probably should). “Golden” TX Interfering TX Signal Level Adjust DUT Signal Level Adjust Test Software May substitute Source Instrument for this block (e. g. E 4438 C). Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 51

Summary • Wireless LAN Standards - Interoperability is key to success. IEEE 802. 11 standards are leading the way. • 802. 11 b PHY • Described the mandatory Spread Spectrum modulation formats • Explored the 802. 11 b PHY packet structure • 802. 11 a PHY • Described some details about OFDM modulation • Explored the 802. 11 a PHY packet structure • Took a glance at 802. 11 g (Draft standard) • Discussed WLAN testing methods and 802. 11 b/a Specification measurements Physical Layer and RF Testing Overview if Wireless LAN MODEMS 23 October, 2002 Copyright Agilent Technologies 2002 52

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