Major Leaps in Evolution of IEEE WLAN Technologies

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1 Major Leaps in Evolution of IEEE WLAN Technologies Thomas A. KNEIDEL Rohde & Schwarz Product Management Mobile Radio Tester

2 WLAN Mayor Player in Wireless Communications Wearables Smart Homes Smart Cities Healthcare Automotive Anything that benefits from network connection will be connected Smart Buildings LAN Retail Agriculture.. Evolution of IEEE WLAN Technologies 2

3 WLAN Standardisation IEEE Standard description Release date Mbit/s, GHz RF and IR All other standards below are Ammendments (Except f and t) a 54 Mbit/s, 5GHz, OFDM b DSSS, CCK, 11 Mbit/s, 2.4 GHz c Bridge operation procedures (not used) d International (country-to-country) roaming extensions e QoS and VoIP including packet bursting f Roaming with IAPP (Inter Access Point Protocol) g b OFDM for 2.4 GHz h DFS (dynamic frequency selection) and TPC (transmit power control) for a i Enhanced Security j Extensions for Japan, GHz, 10 MHz BW Incorporates all standards above 2007 The standard supersedes the standard released 1997 and incorporated all approved ammendments up to that point, ie a, g, j etc. Evolution of IEEE WLAN Technologies 3

4 WLAN Standardisation n-ad IEEE Standard description Release date n 600 Mbit/s, MIMO, Packet Aggregation, 40 MHz BW, OFDMA p WAVE / C2C (car to car), 10 MHz BW 2010 planned r Fast roaming s Mesh networking, Extended Service Set 2010 planned u Interworking with non-802 networks (for example, cellular) 2010 planned y 5 Km range, 3.7 GHz for the US aa Robust streaming of Audio Video Transport Streams 2011 planned mb Maintenance of the standard. Expected to become planned ac Very High Throughput <6GHz 2012 planned ad Extremely High Throughput 60GHz 2012 planned Evolution of IEEE WLAN Technologies 4

5 Mayor Steps in WLAN Evolution a b g n ac ax Evolution of IEEE WLAN Technologies 5

6 IEEE b Single Carrier Transmission a b g n ac ax Direct Sequence Spread Spectrum (DSSS) Complimentary Code Keying (CCK) 2.4 GHz Support of 4 data rates from 1 to 11 Mbps Evolution of IEEE WLAN Technologies 6

7 DSSS / Spreading with Baker Code 1 and 2 Mbps Occupied Bandwidth: 22 MHz 1 bit input 1 MBit/s 1 Mbps Phase change π DBPSK 11 BPSK chips 11 MHz Barker sequence +1, -1, +1, +1, -1, +1, +1, +1, -1, -1, -1 2 bits input 2 MBit/s 2 Mbps Phase change π/2 11 π 10 -π/2 DQPSK 11 QPSK chips output 11 MHz Barker sequence +1, -1, +1, +1, -1, +1, +1, +1, -1, -1, -1 Evolution of IEEE WLAN Technologies 7

8 DSSS / Spreading with Baker Code Intersymbol Interference Protection Chip rate: 11 Mcps Chip Size: 11 Chip duration: 90.9 ns Multipath delays between 1 and 10 chips (90.9 ns to 909 ns) are not of concern Assuming a propagation speed of m/s Path difference of about 27 to 272 meters The 11 Chip Baker code autocorrelation function High immunity of the system to multipath interference and collisions with other DSSS signals Code length of 11 Process gain: db 10 log (code length) Presence of information even below noise level Evolution of IEEE WLAN Technologies 8

9 CCK Complementary Code Keying 5.5 Mbps and 11 Mbps Bit stream 4 bit Block IEEE b DQPSK Phase Rotate Transmitter one of four, 8 bit code words Data 8 QPSK chips output at 5.5 Mbps Bit stream 8 bit Block Chip rate: 11 Mcps Chip Size: 8 Chip duration: 90.9 ns DQPSK Phase Rotate IEEE b Transmitter one of 64, 8 bit code words Data 8 QPSK chips output at 11 Mbps Evolution of IEEE WLAN Technologies 9

10 Up to 14 WLAN 2.4 GHz Band Evolution of IEEE WLAN Technologies 10

11 IEEE a/g Multi-Carrier Transmission a b g n ac ax Orthogonal Frequency Division Multiplexing (OFDM) 2.4 GHz / 5 GHz Support of 8 data rates from 6 to 54 Mbps g as an extension of b, additional 1, 2, 5.5 and 11 Mbps Evolution of IEEE WLAN Technologies 11

12 Single Carrier Modulation: Multipath Interference Sensitivity Problem of multipath interference with one carrier: delay Symbol C 0 Symbol C 1 Symbol C 2 delay Symbol C 0 Symbol C 1 Symbol C 2 Symbol C 0 Symbol C 1 Symbol C 2 Multipath interference when symbol duration shorter than delay spread t Transmitter Signal Receiver Signal Limitation of Single Carrier modulation as soon as symbol rate increases symbol interval becomes shorter than the delay spread. t Delay Delay spread t Solution: Multiple low-rate carriers instead of a single high-rate carrier Decreasing the symbol rate and increasing the number of carriers Evolution of IEEE WLAN Technologies 12

13 Multichannel System FDM System Conventional Multichannel System Non Overlapping Adjacent Channels. f Channels separated by more than their two sided bandwidth OFDM Multichannel System Higher Spectral efficiency compare to conventional FDM 50% Overlap of Adjacent Channels f Channels separated by Half their two sided bandwidth Evolution of IEEE WLAN Technologies 13

14 OFDM Orthogonal Frequency Division Multiplexing Principle of Orthogonality of Frequency Two signals f(t) and g(t) are called orthogonal, if the correlation integral is zero f ( t) g( t) dt = 0 f 0 f 1 f 2 1/T S f T S T S is the duration Single Carrier Symbol C 0 Symbol C 1 Symbol C 2 t Symbol time T s Characteristics of orthogonal waveforms: f 2 Symbol C 2 f Carrier = f 0 +n/t S where n is an integer The maximum of one carrier is at the zero crossings of all others The cross correlation of sine waves is zero This is obtained by the following setting f = 1/T S, therefore: f n = n x f Multi Carrier f 1 f 0 Symbol C 1 Symbol C 0 Symbol time T S t Evolution of IEEE WLAN Technologies 14

15 IEEE a/g: OFDM Sub-Carrier Structure 48 Subcarriers for Data 4 Pilot carriers for Reference Channel distance khz 12 unused carriers as guard bands (left, center and right) Channel divided into 64 sub-carriers Channel Spacing: 20 MHz Nominal/Occupied bandwidth of 16.6 MHz ( ) x khz = MHz 20 MHz OFDM Symbol Duration: 3.2 µs // additional Guard Interval 800 ns Data carrier modulation: BPSK, QPSK, 16QAM, 64QAM Coding Rate: ½, 2/3, ¾ Coded Data Rates: 6, 9, 12, 18, 24, 36, 48, 54 Mbps Center Carrier is not used Evolution of IEEE WLAN Technologies 15

16 SubCarriers 10 Short Training Sequence Symbols PLCP Preamble PCLP Header PSDU + Tail + Pad 2 Long Training Sequence Symbols SERVICE+Data SIGNAL Symbol Data Symbol Symbol Last Data Symbol Short Training Sequence only every 4 th carrier is used GI2 GI GI GI GI GI Start of Frame Detection Signal Strength Indication Frequency Offset Resolution Long Training Sequence Channel Estimate Fine Time Resolution Subcarrier Index (f c ) Pilots Pilot Signals Carrier Tracking Sample Clock Tracking R=1/2 BPSK Rate is indicated in SIGNAL symbol Time (in µs) BPSK Modulation used in Preambles, Signal Symbol and Pilot Signals Signal Detect. AGC, Diversity Selection Coarse Freq. Offset Estimation timing Synchronize Channel and fine Frequency Offset Estimation Rate length Service+ Data Data Evolution of IEEE WLAN Technologies 16

17 IEEE a/g 64QAM: I/Q Constellation Diagram Evolution of IEEE WLAN Technologies 17

18 OFDM Points of View Principles of OFDM is known for more than 30 years. Implementation of OFDM-Baseband processing, which use Fast-Fourier- Transformation (FFT) in Modulation and inverse FFT (IFFT) in Demodulation, requires powerful signal processing, which was not available for a long time. Advantages ı High resistance to Multi-path Fading ı Efficiently Deals With Channel Delay Spread ı Enhanced Channel Capacity (use of bandwidth) ı Adaptively Modifies Modulation Density ı Robustness to Narrowband Interference Disadvantages ı Sensitive to Small Carrier Frequency Offsets ı Higher Peak to Average Power Ratio (crest factor) ı Sensitive to High Frequency Phase Noise ı Sensitive to Sampling Clock Offsets ı Scalable data rate Equalization is simpler than in one carrier transmission Evolution of IEEE WLAN Technologies 18

19 Inter-Symbol Interference (ISI) Symbol Smearing Due to Channel x(t) h(t) y(t) x(t) h(t) y(t) Symbol t t Channel Distorted Symbol t Adjacent Symbols t t Evolution of IEEE WLAN Technologies 19

20 Guard Interval (GI) Elimination of ISI x(t) h(t) y(t) x(t) h(t) y(t) Symbol t t Channel Distorted Symbol t Symbol seperation by Guard Interval t t Evolution of IEEE WLAN Technologies 20

21 Cyclic Prefix (CP) Better Alternative to Null GI 0.8 µs 3.2 µs x(t) h(t) y(t) x(t) Symbol t h(t) t Channel y(t) Distorted Symbol t CP OFDM Symbol khz. Prefixing of symbol with a repetition of the end CP CP CP CP t t Evolution of IEEE WLAN Technologies 21

22 Up to 14 WLAN 2.4 GHz Band 22 MHz 20 MHz a / g (OFDM) 20 MHz Channel width MHz only used by Sub-Carriers Evolution of IEEE WLAN Technologies 22

23 IEEE n Multiple Antenna Systems a b g n ac ax MIMO Multiple Input, Multiple 2.4 GHz and 5 GHz 20 /40 MHz Bandwidth Physical Layer: data rate up to 600 Mbps Evolution of IEEE WLAN Technologies 23

24 IEEE n: OFDM Sub-Carrier Structure 52 Subcarriers for Data 4 Pilot carriers for Reference Channel distance 312.5kHz in case of 20 MHz bandwidth 8 unused carriers as guard bands (left, center and right) Channel Spacing: 20 MHz / 40 MHz Nominal/Occupied bandwidth of 16.6 MHz ( ) x khz = MHz 20 MHz OFDM Symbol Duration: 3.2 µs // additional Guard Interval: 400 ns or 800 ns Data carrier modulation: BPSK, QPSK, 16QAM, 64QAM MIMO up to 4 spatial streams Evolution of IEEE WLAN Technologies 24

25 Multi-Path Progagation - Fading Uncorrelaeted, fading channels are required to distinguish the data streams coming from different transmit antennas The higher the statistcal independence of the different fading channels, the better the achievable data transfer rate. Frequency shifts due to Doppler effects, caused by moving transmitters or receivers Receiver detects signals with different time delays, levels and phases. Evolution of IEEE WLAN Technologies 25

26 MIMO Systems Multiple Input, Multiple Output Spatial Diversity Spatial Diversity increases robustnes of data transmission SIMO Single Input, Multiple Output e.g. Alamouti space-time coding MISO Multiple Input, Single Output Spatial Multiplexing Multi-User Spatial Multiplexing increases data rates or channel capacity 2x2 MIMO MU MIMO Evolution of IEEE WLAN Technologies 26

27 SIMO Systems Rx Diversity Spatial Diversity x x increases robustnes of data transmission Received Signal Switched Diversity Maximum Ratio Combining MRC C = max (x, x ) C = (x + x ) Evolution of IEEE WLAN Technologies 27

28 SIMO Systems MRC Maximum Ratio Combining 1x2 MIMO SIMO TX Ant RX Ant 1 n 1 Spatial Diversity x x increases robustnes of data transmission x LO + = + RX Ant 2 y 1 y 2 MRC algorithm x e Estimates = x + Y = H x + N n 2 Improved Signal-to-Noise Ratio = Evolution of IEEE WLAN Technologies 28

29 MISO Systems Tx Diversity Spatial Diversity increases robustnes of data transmission e.g. Alamouti // Space Time Block Coding Tx 1 Tx 2 2x1 MIMO MISO Time t Time t + T Space-Time-Block -x 2 * x 1 TX Ant 1 TX Ant 2 RX Ant x e 2 x e 1 H H y 2 y 1 Estimates x e x 2 x 1 x 1 * x 2 LO = + + n = + + # = + + = + + # = + Improved Signal-to-Noise Ratio Y = H X + N Alamouti scheme has the same diversity as the two-branch maximum ration combining (MRC) Evolution of IEEE WLAN Technologies 29

MIMO Systems Spatial Multiplexing m transmit antennas n receive antennas 1 h 21 h 11 1 increases data rates or channel capacity 2 h 12 h 22 2 X h 1m h n1 Y

30 MIMO Systems Spatial Multiplexing m transmit antennas n receive antennas 1 h 21 h 11 1 increases data rates or channel capacity 2 h 12 h 22 2 X h 1m h n1 Y m h nm n Channel Matrix H = h 11 h 12 h.. h 1m h 21 h 22 h.. h 2m h.. h.. h.. h.m y = H x h n1 h n2 h n. h nm Evolution of IEEE WLAN Technologies 30

31 MIMO Systems Spatial Multiplexing h 21 2x2 MIMO increases data rates or channel capacity = + + = + + =H x " n Tx antennas 1 Channel 1 H = Rx antennas Evolution of IEEE WLAN Technologies 31

WLAN 11n Baseband Transmitter Model Spatial Streams Space-Time Streams TX antenna signals Interleaver Constellation mapper IDFT Insert GI and Window FEC encoder Interleaver Constellation mapper CSD -

32 WLAN 11n Baseband Transmitter Model Spatial Streams Space-Time Streams TX antenna signals Interleaver Constellation mapper IDFT Insert GI and Window FEC encoder Interleaver Constellation mapper CSD ns Direct Mapping Beamforming IDFT Insert GI and Window Data Scrambler CSD Cyclic Shift Diversity Encoder Parser FEC encoder Stream Parser Interleaver Interleaver Constellation mapper Constellation mapper STBC CSD ns CSD ns Spatial Antenna Mapping IDFT IDFT Insert GI and Window Insert GI and Window Evolution of IEEE WLAN Technologies 32

33 Space-Time Streams Beamforming Direct Mapping Beamforming Spatial Antenna Mapping Antenna map matrix % & TX antenna signals IDFT IDFT IDFT IDFT Insert GI and Window Insert GI and Window Insert GI and Window Insert GI and Window Beamforming steering matrix: % & is any matrix that improves the reception in the receiver based on some knowledge of the channel between the transmitter and the receiver n introduced implicit and explicit beamforming, but did not clearly defined It was not widely used Evolution of IEEE WLAN Technologies 33

34 IEEE ac Multi-User MIMO a b g n ac ax MU-MIMO Multi-User MIMO 5 GHz Channel Bandwidth: 20 /40 /80 /80+80 / 160 MHz Data carrier modulation: BPSK, QPSK, 16QAM, 64QAM, 256QAM Evolution of IEEE WLAN Technologies 34

35 IEEE ac: OFDM Sub-Carrier Structure 52 Subcarriers for Data 4 Pilot carriers for Reference Channel distance 312.5kHz in case of 20 MHz bandwidth 8 unused carriers as guard bands (left, center and right) Channel Spacing: 20 / 40 / 80 / / 160 MHz Nominal/Occupied bandwidth of 17.8 MHz ( ) x khz = MHz 20 MHz OFDM Symbol Duration: 3.2 µs // additional Guard Interval: 400 ns or 800 ns Data carrier modulation: BPSK, QPSK, 16QAM, 64QAM, 256QAM MIMO up to 8 spatial streams Physical Layer data rate up to Gbps (160 MHz; 8 SS) Evolution of IEEE WLAN Technologies 35

36 WLAN 11ac Channel Allocation 5170 MHz 5330 MHz 5490 MHz 5730 MHz 5735 MHz 5835 MHz IEEE channel # MHz 40 MHz 80 MHz 160 MHz Evolution of IEEE WLAN Technologies 36

Explicit Beamforming Announcement sending soon sounding frames 802.11ac focus on use of explicit beamforming and discarded possibility of implicit beamforming.

37 Explicit Beamforming Announcement sending soon sounding frames ac focus on use of explicit beamforming and discarded possibility of implicit beamforming. Null Data Packet (NDP) Sounding in various directions Measures the channel martices Report request Beamforming Feedback ' & -Matrix Re-calibration of phase shift for each of the transmitted signal from each antenna Reaching maximum signal strength at client ( Beamforming steering matrix: % & ) Implicit Beamforming AP measures the received upstream and based on the result derive the parameters for subsequent downstream beam Evolution of IEEE WLAN Technologies 37

maximize the received signal power in the direction of the intended receiver while substantially reducing the

38 MU-MIMO Systems Spatial Multiplexing based on Explicit Beamforming MU-MIMO beamforming addresses multiple users located in spatially diverse positions MISO Multi User MISO MIMO Null-steering transmit beamformers aim to maximize the received signal power in the direction of the intended receiver while substantially reducing the power impinging on the unintended receivers located in other directions. Evolution of IEEE WLAN Technologies 38

39 IEEE ax High-Efficiency Wireless a b g n ac ax Medium Access Control: CSMA/CA // OFDMA Orthogonal Frequency Division Multiplexing 2.4 GHz and 5 GHz Channel distance: khz (4 times less) // Symbol duration: 12.8 µs (4 times longer) Data carrier modulation: BPSK, QPSK, 16QAM, 64QAM, 256QAM, 1024QAM Evolution of IEEE WLAN Technologies 39

40 IEEE ax: OFDM Sub-Carrier Structure 234 Subcarriers for Data 8 Pilot carriers for Reference Channel distance khz 14 unused carriers as guard bands (6 left, 3 center and 5 right) in case of HE-SU 20 MHz bandwidth Channel Spacing: 20 / 40 / 80 / / 160 MHz Nominal/Occupied bandwidth of 17.8 MHz ( ) x khz = MHz 20 MHz OFDM Symbol Duration: 12.8 µs // additional Guard Interval: 0.8, 1.6, 3.2 µs Data carrier modulation: BPSK, QPSK, 16QAM, 64QAM, 256QAM, 1024QAM Coding BCC Binary Convolutional Code // LDPC Low-Density Parity-Check MIMO up to 8 spatial streams Physical Layer data rate up to Gbps (160 MHz, 8 SS) Evolution of IEEE WLAN Technologies 40

41 Medium Access Control: CSMA/CA Carrier Sense Multiple Access/Collision Aviodance AP STA 1 STA 2 DIFS Backoff Data SIFS Ack DIFS Backoff Data SIFS Ack DIFS STA 3 Backoff Data Distributed Coordination Function Interframe Space DIFS 50 µs (DSSS) 34 µs (OFDM) Short Interframe Space SIFS* 10 µs (DSSS) 16 µs (OFDM) * ) incl. 2.4GHz signal extention Backoff µs Ack 24 µs Evolution of IEEE WLAN Technologies 41

42 CSMA/CA extension: RTS/CTS Request-to-Send / Clear-to-Send AP CTS Ack CTS DIFS SIFS STA 1 Back off SIFS SIFS RTS Data DIFS SIFS SIFS STA 2 Back off RTS Data A C B Evolution of IEEE WLAN Technologies 42

43 IEEE ax: Multi-user Operations AP RTS STA1 RTS STA2 STA CTS ACK CTS ACK ½ BW => 2x duration AP MU- RTS STA1+2 OFDMA STA1+2 CTS ACK Time saved Simultaneous Response Evolution of IEEE WLAN Technologies 43

44 Evolution of IEEE WLAN Technologies 44 OFDMA = OFDM + FDMA WLAN 11ac: OFDM allocates users in time domain only WLAN 11ax: OFDMA allocates users in time and frequency domain Time domain Time domain Frequency domain Frequency domain User 3 User 3 User 2 User 2 User 1 User 1

45 From single-user to multi-user OFDMA Example: 20 MHz bandwidth Channel bandwidth is divided into resource units, RU One RU belongs to one user. In the next timeslot, the RU may be another user RU RU1 RU2 RU3 RU RU6 RU7 RU8 RU9 RU1 RU RU3 RU4 RU SU RU1 242 RU2 Each RU may have a different modulation scheme and/or coding rate RU size: x996 - SubCarriers Evolution of IEEE WLAN Technologies 45

46 Various Combinations ı RU sizes can be mixed: RU1 RU3 RU4 RU5 RU2 RU1 RU2 RU3 RU MHz RU 1 3 RU6 RU7 RU8 RU9 1 1 RU1 RU2 RU3 RU4 3 3 There are various combinations of how the frequency axis is divided into RUs. Which one is applied is given by control information, e.g. scheduling RU SU RU1 242 RU2 Evolution of IEEE WLAN Technologies 46

47 Multi-User DownLink AP MU RTS Data STA 1 STA 2 SIFS CTS CTS SIFS SIFS Ack Ack immediate UL OFDMA Ack OR SIFS Ack Block Ack Request Ack Block Ack Request STA 3 CTS Ack Ack Packet Protocol: HE-MU DL only Evolution of IEEE WLAN Technologies 47

48 Multi-User UpLink Synchronisation by Trigger Frame AP Trigger Frame Ack STA 1 STA 2 SIFS Data Data SIFS MU-STA Block Ack Multi-User Operations are controlled by AP Multi-User Uplink is initiated by Trigger Frame from AP Trigger Frame includes: Device IDs STA 3 Data RU allocations, MCS, Number of spatial streams, Packet Protocol: HE-TB UL only TB Trigger Based Power Control Evolution of IEEE WLAN Technologies 48

49 Time of Departure Accuracy Specified Tolerance: ± 0.4 µs AP Trigger Frame Ack STA 1 STA 2 SIFS Data Data SIFS MU-STA Block Ack STA 3 Data Packet Protocol: HE-TB UL only Evolution of IEEE WLAN Technologies 49

50 Dynamic Power Control STA 2 Power differences between STAs in a UL MU transmission results in a degradation of the performance Need for Transmit Power Pre-Correction Transmit Power Control (TPC) AP reports its used transmit power and the expected Target RSSI together with each data-package STA transmit signal with power equal to Target RSSI of AP plus calculated path loss. Arrival power of different STAs at AP should be roughly the same STA 1 Reference: Target Receiver Signal Strength Indicator (RSSI) at the AP side. STA measures RSSI of received datapackage and calculate its path loss AP If necessary AP send a appropriate command to each STA to increase or decrease their power levels Class A STA 3 Class B Absolute transmit ± 3 db ± 9 db Power accuracy RSSI measurement ± 2 db ± 5 db accuracy Evolution of IEEE WLAN Technologies 50

51 EVM Specification Transmitter Relative Constellation Error (RCE) Specification is independent of channel bandwidth Evolution of IEEE WLAN Technologies 51

OFDMA @802.11ax: Unused Tone Error Unused tone eror (In-band Emission) limit value for RU26.

52 Unused Tone Error Unused tone eror (In-band Emission) limit value for RU26. For other RU sizes, different limit values and step widths apply. Evolution of IEEE WLAN Technologies 52

53 MU-MIMO Systems Spatial Multiplexing Downlink and Uplink In the downlink, beamforming ensures targeted station coverage. In the uplink, the data streams can be separated without beamforming. Evolution of IEEE WLAN Technologies 53

54 Thank you for your attention! Evolution of IEEE WLAN Technologies 54

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