1. An Overview of ax
Greg Kamer – Consulting Systems Engineer

2. Image from an article on IEEE Spectrum
25 Years of WiFi
Image from an article on IEEE Spectrum

3. WiFi Evolution
“We need to know where we are coming from to appreciate where we are going”
802.11
(Legacy)
802.11b
802.11a
802.11g
802.11n
(HT)
802.11ac
(VHT)
802.11ax
(HE)
Year Ratified
1997
1999
2003
2009
2014
2019 (Expected)
Operating Band
2.4 GHz/IR
2.4 GHz
5 GHz
2.4/5 GHz
Channel BW
20 MHz
20/40 MHz
20/40/80/160 MHz
Peak PHY Rate
2 Mbps
11 Mbps
54 Mbps
600 Mbps
6.8 Gbps
10 Gbps
Link Spectral Efficiency
0.1 bps/Hz
0.55 bps/Hz
2.7 bps/Hz
15 bps/Hz
42.5 bps/Hz
62.5 bps/Hz
Max # SU Streams 1 4 8
Max # MU Streams NA
4 (DL only)
8 (UL & DL)
Modulation
DSSS, FHSS
DSSS, CCK
OFDM
OFDM, OFDMA
Max Constellation / Code Rate
DQPSK
CCK
64-QAM, 3/4
64-QAM, 5/6
256-QAM, 5/6
1024-QAM, 5/6
Max # OFDM tones 64
128
512
2048
Subcarrier Spacing
312.5 kHz
kHz

4. Image from an article by Eddie Felmer published in Hiddenwires
MU-MIMO
Image from an article by Eddie Felmer published in Hiddenwires

5. IEEE ax

6. IEEE 802.11ax 802.11ac 802.11ax 2.4GHz, 5GHz radio 1024-QAM
160MHz bandwidth
Support 8 SS
Transmit Beamforming
Multi-user MIMO (MU-MIMO)
Multi-User OFDMA
802.11ac
802.11ax
BANDS
5 GHz
2.4GHz / 5GHz
CHANNEL BANDWIDTH
20MHz, 40MHz, 80MHz, MHz, 160MHz
FFT SIZES
64, 128, 256, 512
256, 512, 1024, 2048
SUBCARRIER SPACING
312.5kHz
78.125kHz
OFDM SYMBOL DURATION
3.2us+ 0.8 / 0.4us CP
12.8us / 1.6 / 3.2us CP
HIGHEST MODULATION
256-QAM
1024QAM
DATA RATES
433 Mbps (80MHz, 1SS)
6933 Mbps (160Hz, 8SS)
600.4 Mbps (80Hz, 1SS)
Mbps (160Hz, 8SS)

7. Key Features of ax
Bigger number on the box and better performance in high-density/outdoor environments
Feature
Description
Benefits
1024-QAM
10-coded bits loaded on each tone (compared to 8 in 11ac)
Contributes to 25% increase in peak PHY data rate
Long OFDM Symbol
OFDM symbol duration increased by 4x, to 12.8 us from 3.2 us, with guard interval (GI) ranging from 0.4 to 3.2 us
Increased resilience to longer delay spread
Higher PHY throughput due to reduced GI overhead
MU-MIMO (UL & DL)
Concurrent transmission to and from multiple clients exploiting spatial separation of clients
Higher capacity and higher network throughput
Higher throughput for 1x1 and 2x2 clients
OFDMA (UL & DL)
Concurrent transmission to and from multiple clients allocating different subsets of tones to different clients
Reduced medium occupancy with short packets
Increased range through lower BW signaling
Reduced power consumption through lower BW signaling
Mitigate OBSS issues through tone allocation
Outdoor
Sensors

8. Long OFDM Symbol OFDM Symbols in 11g/n/acGI
(Multipath Immunity)
“Useful” Portion of OFDM Symbol
3.2 us
OFDM Symbols in 11ax (Indoor – Increased Throughput Due to Reduced GI Overhead)
12.8 us
“Useful” Portion of OFDM Symbol GI
(Multipath Immunity)
OFDM Symbols in 11ax (Outdoor – Increased Multipath Resilience Due to Longer GI)
12.8 us GI
(Multipath Immunity)
“Useful” Portion of OFDM Symbol

9. OFDM vs OFDMA
OFDM
OFDMA

10. Multi-User OFDMA Multi-User OFDMA
The ax standard borrows a technological improvement from 4G cellular technology to multiplex more users in the same channel bandwidth: Orthogonal Frequency-Division Multiple Access (OFDMA). Building on the existing orthogonal frequency-division multiplexing (OFDM) digital modulation scheme that ac already uses, the ax standard further assigns specific sets of subcarriers to individual users. That is, it divides the existing channels (20, 40, 80 and 160 MHz wide) into smaller sub-channels with a predefined number of subcarriers
将一条大的车道划分成多条小的车道

11. Short Packet Problem OFDM Transmission
OFDMA Transmission -- Reduced Medium Usage and Latency for Short Packets

12. OBSS Problem
OFDMA allows smart tone allocation between links to mitigate OBSS interference

13. OFDMA vs MU-MIMO
Complementary techniques to serve multiple users concurrently
OFDMA
MU-MIMO
Useful when multiple users have small amount of data
Useful when multiple users have full buffer traffic
Number of concurrent clients can be as high as 74
Number of concurrent clients limited to 8
Network xput gain of TBD assuming certain traffic pattern
Network throughput gain of ~4 assuming 8x8 AP & 1x1 client
Effective at all ranges (close, mid, and far)
Effective at close- to mid-range, not effective at far range
UL OFDMA improves UL range
No range improvement
No sounding overhead for either DL or UL OFDMA
Sounding required for DL MU, but not for UL MU
Tends to decrease latency
Tends to increase latency
Can be used to mitigate OBSS interference issues
No interference mitigation

14. Miscellaneous Features
Description
Benefits
Triggered Access
AP sends out “Trigger Frame” to assign UL OFDMA resource units to specific clients and/or for random access
Reduced collision in dense environments
Client Power Control
AP commands clients to increase/decrease Tx power
Avoid near-far issue with UL MU-MIMO/OFDMA
Mitigate interference
Dynamic CCA
CCA threshold varied dynamically based on channel conditions
Improved performance in dense environments
Increased Block ACK (BA) Window Size
BA window size increased to 128 from 64
Transmit larger aggregates (improved throughput)
Multi Client Bursting
Frames within a burst sent to different clients
Improved medium utilization