The document discusses key enhancements in 802.11n including: - Increased throughput through wider channel bandwidth of 40MHz, higher order modulation like 64QAM, and multiple-input multiple-output (MIMO) with up to 4 antennas. - MAC layer improvements such as aggregate MAC protocol data units (A-MPDU) and aggregate MAC service data units (A-MSDU) that bundle frames to improve efficiency. - Modulation and coding scheme (MCS) indexes that specify data rates up to 600Mbps depending on configuration.

1. Generation of Wireless Local Area Networks
802.11n Over all view
Presented By,
Arun.N

2. Contents
 Key PHY Level 802.11n Features
 Key PHY Changes which accounts for high throughput
 20MHz and 40MHz bandwidth transmission
 MCS rates
 Short Guard Interval (400ns)
 IEEE 802.11n MIMO OFDM
 MAC level enhancements
 A-MPDU
 Block ACK
 A-MSDU
 Long NAV Protection
 RIFS
 IEs for 802.11n

3.  HT: High Throughput
 A-MPDU : Aggregate MAC Protocol Data Unit
 A-MSDU : Aggregate MAC Service Data Unit
 MCS : Modulation and Coding Scheme
 RIFS : Reduced Inter frame Space
 BA : Block Ack
 L-LTF : Non-HT Long Training Field
 L-STF : Non-HT Short Training Field
 L-SIG : Non-HT Signal Field
 HT-SIG : HT Signal Field
 HT-GF-STF : HT Greenfield Short training field
Acronyms

4.  Bandwidth expansion
 Use of 4 more sub-carriers in 20MHz, increase rate by 8%
 Maximum code rate increased to rate 5/6
 increase data rate by 11% over .11a/g code
 Channel Bonding
 use 40Mhz channel and 108 data carriers increases rate by a factor of 2.25
 Reduced Inter frame Spacing (RIFS)
 Allows for a 2 use interval between successive transmissions from the same device
 Short Guard Interval
 Optional shortening of GI from 800 nsec to 400 nsec
 Results in data rate increase of 11%
Some of the KEY PHY Changes

5.  3 modes of operation in 802.11n (distinguished by PLCP header)
 Non-HT (Legacy)
 Mixed Mode (mandatory)
 Legacy portion of the preamble provides built in PHY protection
 Allows mixture of legacy and 11n packets in one network
 Avoids hidden node issues
 However, the preamble length is increased
 Greenfield Mode (Optional)
 No Backward compatibility
 Short and more efficient PLCP header
802.11n: Modes of Operation

6. PLCP header for different Modes
LEGACY COMPATIABLE
New in 11n

7. PLCP header for Legacy and 11n rates.

8. SiSo vs MiMo
Spatial Multiplexing
Independent paths between multiple antennas can be used to much greater effect than simply for
diversity to overcome RF loss
Spatial multiplexing uses independent spatial paths to send independent streams of information at
same time over the same frequencies
Streams will become combined as pass across channel
Receiver will separate and decode

9. Multiple Antenna Techniques
 Adding antennas can increase capacity even though
antennas transmit and receive on same frequency band
simultaneously
 Changes fundamental relationship between power and
capacity per second per Hz
 2 techniques can be used to take advantage of multiple
streams.
Spatial Diversity
 Spatial diversity techniques increase reliability and range
by sending/receiving redundant streams in parallel along
different spatial paths between transmit and receive
antennas
 Use of extra paths improves reliability because unlikely all
of the paths will be degraded at the same time
 Spatial diversity can also improve range and some
performance increase (gather larger amount of signal at
receiver)
802.11n PHY Layer Spatial Multiplexing

10. Modulation Technique:
Quadrature Amplitude Modulation (QAM)
The creation of symbols that are some combination of amplitude
and phase can carry the concept of transmitting more bits per symbol further.
This method is called quadrature amplitude modulation (QAM).
For example:
 8-QAM uses four carrier phases plus two amplitude levels to transmit 3 bits per symbol.
Other popular variations are 16QAM, 64QAM, and 256QAM,
which transmit 4, 6, and 8 bits per symbol respectively.

11. MCS
Index
Number
of
spatial
streams
Modulation
(Stream 1/ 2/ 3/
4 )
Codin
g rate
Data Rate (in
Mbps)
(GI = 800ns)
Data Rate (in
Mbps)
(GI = 400ns)
20MH
z
40MHz 20MHz 40MH
z
0 1 BPSK 1/2 6.5 13.5 7.2 15.0
1 1 QPSK 1/2 13.0 27.0 14.4 30.0
2 1 QPSK 3/4 19.5 40.5 21.7 45.0
3 1 16-QAM 1/2 26.0 54.0 28.9 60.0
4 1 16-QAM 3/4 39.0 81.0 43.3 90.0
5 1 64-QAM 2/3 52.0 108.0 57.8 120.0
6 1 64-QAM 3/4 58.5 121.5 65.0 135.0
7 1 64-QAM 5/6 65.0 135.0 72.2 150.0
8 2 BPSK 1/2 13.0 27.0 14.4 30.0
9 2 QPSK 1/2 26.0 54.0 28.9 60.0
10 2 QPSK 3/4 39.0 81.0 43.3 90.0
11 2 16-QAM 1/2 52.0 108.0 57.8 120.0
12 2 16-QAM 3/4 78.0 162.0 86.7 180.0
13 2 64-QAM 2/3 104.0 216.0 115.6 240.0
14 2 64-QAM 3/4 117.0 243.0 130.3 270.0
15 2 64-QAM 5/6 130.0 270.0 144.4 300.0
Modulation and Coding Scheme - MCS Index Table
MCS index for two spatial stream
•MiMo 1x1 – 1 spatial stream
•MiMo 2x2 – 2 spatial stream

12. Modulation and Coding Scheme - MCS Index Table
MCS index for two spatial stream
•MiMo 3x3 – 3 spatial stream
•MiMo 4x4 – 4 spatial stream
MCS
Index
Number
of
spatial
streams
Modulation
(Stream 1/ 2/
3/ 4 )
Coding
rate
Data Rate
(in Mbps)
(GI =
800ns)
Data Rate (in
Mbps)
(GI = 400ns)
20
MHz
40
MHz
20
MHz
40
MHz
16 3 BPSK 1/2 19.5 40.5 21.7 45.0
17 3 QPSK 1/2 39.0 81.0 43.3 90.0
18 3 QPSK 3/4 58.5 121.5 65.0 135.0
19 3 16-QAM 1/2 78.0 162.0 86.7 180.0
20 3 16-QAM 3/4 117.0 243.0 130.0 270.0
21 3 64-QAM 2/3 156.0 324.0 173.3 360.0
22 3 64-QAM 3/4 175.5 364.5 195.0 405.0
23 3 64-QAM 5/6 195.0 405.0 216.7 450.0
24 4 BPSK 1/2 26.0 54.0 28.9 60.0
25 4 QPSK 1/2 52.0 108.0 57.8 120.0
26 4 QPSK 3/4 78.0 162.0 86.7 180.0
27 4 16-QAM 1/2 104.0 216.0 115.6 240.0
28 4 16-QAM 3/4 156.0 324.0 173.3 360.0
29 4 64-QAM 2/3 208.0 432.0 231.1 480.0
30 4 64-QAM 3/4 234.0 486.0 260.0 540.0
31 4 64-QAM 5/6 260.0 540.0 288.9 600.0
802.11n allows up to 4x4:4
Common configurations of 11n devices are
2x2:2, 2x3:2, 3x3:2
3x3:3 is becoming common because higher
throughput due to additional data stream
Improvements beyond 3x3 are small

13. Data Rate comparison for 802.11 a/b/g/n

14.  Channel divided into 0.3125 MHz subcarriers
 802.11a/b/g 20MHz channel widths- divided into 52 subcarriers (4 pilot carriers)
 802.11 a/b/g/n 40 MHZ channel widths- divided into 128 subcarriers (6 pilots carriers).
 802.11n doubles channel width to 40 MHz channels by using 2 adjacent 20 MHz channels
merged into 1 40 MHz channel
 802.11n - only 4 guard subcarriers at each edge of the channel
 Different modulation schemes (BPSK, QPSK, QAM-16 and QAM-64).
802.11 PHY Comparison
20 MHz and 40 MHz Channel Width

15. MAC Enhancements
 Interface spacing
 SIFS
 DIFS
 PIFS
 RIFS
 AMPDU
 AMSDU
 Block-Ack
 MCC Concurrency
 SCC concurrency
 Self -CTS

16. MAC Frame Format

17. WLAN Call Flow Diagram

18. Inter frame spacing(Time parameters)
Short interframe space (SIFS)
The SIFS is used for the highest-priority transmissions, such as RTS/CTS frames and positive
acknowledgments.
PCF interframe space (PIFS)
It is used by the PCF during contention-free operation. Stations with data to transmit in the
contention-free period can transmit after the PIFS has elapsed and preempt any contention-
based traffic.
DCF interframe space (DIFS)
The DIFS is the minimum medium idle time for contention-based services. Stations may have
immediate access to the medium if it has been free for a period longer than the DIFS.

19. Contention-Based Access
If the medium has been idle for longer than the DIFS, transmission can begin Immediately.
If the medium is busy, the station must wait for the channel to become idle.
802.11 If access is deferred, the station waits for the medium to become idle for the DIFS and prepares
for the exponential back-off procedure.

20. General MAC Frame
MAC Address of
wireless host AP RX
this frame
MAC Address of
wireless host AP TX
this frame.
Used only in AD-
HOC mode..

21. Management Frames

23. Beacon IE
Packet Info
Packet Number: 1
Flags: 0x00000000
Status: 0x00000000
Packet Length: 166
Timestamp: 12:20:21.404043500 01/09/2014
Data Rate: 2 1.0 Mbps
Channel: 11 2462MHz 802.11b
Signal Level: 100%
Signal dBm: -45
Noise Level: 100%
Noise dBm: -51
802.11 MAC Header
Version: 0 [0 Mask 0x03]
Type: %00 Management [0]
Subtype: %1000 Beacon [0]
Frame Control Flags: %00000000 [1]
0... .... Non-strict order
.0.. .... Non-Protected Frame
..0. .... No More Data
...0 .... Power Management - active mode
.... 0... This is not a Re-Transmission
.... .0.. Last or Unfragmented Frame
.... ..0. Not an Exit from the Distribution System
.... ...0 Not to the Distribution System
Duration: 0 Microseconds [2-3]
Destination: FF:FF:FF:FF:FF:FF [0-5]
Source: 00:A0:C6:E9:C1:F5 [6-11]
BSSID: 00:A0:C6:E9:C1:F5 [12-17]
Seq Number: 111 [18-19 Mask 0xFFF0]
Frag Number: 0 [18 Mask 0x0F]
802.11 Management - Beacon
Timestamp: 4198784 Microseconds [20-27]
Beacon Interval: 100 [28-29]

24. Capability Info: %0000010000100001 [30-31]
0....... ........ Immediate Block Ack Not Allowed
.0...... ........ Delayed Block Ack Not Allowed
..0..... ........ DSSS-OFDM is Not Allowed
...0.... ........ No Radio Measurement
....0... ........ APSD is not supported
.....1.. ........ G Mode Short Slot Time [9 microseconds]
......0. ........ QoS is Not Supported
.......0 ........ Spectrum Mgmt Disabled
........ 0....... Channel Agility Not Used
........ .0...... PBCC Not Allowed
........ ..1..... Short Preamble
........ ...0.... Privacy Disabled
........ ....0... CF Poll Not Requested
........ .....0.. CF Not Pollable
........ ......0. Not an IBSS Type Network
........ .......1 ESS Type Network
SSID
Element ID: 0 SSID [32]
Length: 10 [33]
SSID: Arun_kumar
Supported Rates
Element ID: 1 Supported Rates [44]
Length: 8 [45]
Supported Rate: 1.0 Mbps (BSS Basic Rate)
Supported Rate: 2.0 Mbps (BSS Basic Rate)
Supported Rate: 5.5 Mbps (BSS Basic Rate)
Supported Rate: 6.0 Mbps (Not BSS Basic Rate)
Supported Rate: 9.0 Mbps (Not BSS Basic Rate)
Supported Rate: 11.0 Mbps (BSS Basic Rate)
Supported Rate: 12.0 Mbps (Not BSS Basic Rate)
Supported Rate: 18.0 Mbps (Not BSS Basic Rate)

25. Aggregate-MSDU (A-MSDU)
All sub frames shares the common MAC header, AMSDU Frames considered as a single MPDU by the PHY-
Layer.
No check sum for individual sub frame, re-TX of complete sub frame is not possible.
An A-MSDU consists of multiple sub frames. Each sub frame of an AMSDU
has a sub header (Destination address, Source Address, Length), MSDU, and padding bytes.

26. All the sub frames share a common MAC header and frame check sequence (FCS)
which is calculated over all the sub frames and a common MAC header and then appended as the trailer.
Since there is no checksum for the individual sub frames, selective retransmission of corrupted sub frames is
not possible.
sub frames have the same sequence number & traffic identifier (TID) [2-3].
The maximum length of an A-MSDU frame can be 3839 or 7955 bytes.
This capability information is exchanged during the time of association.
Aggregate-MSDU (A-MSDU)

27. Aggregate-MPDU (A-MPDU)
First 4 bits in delimiters are reserved & currently not used.
MPDU length sub-field consist of 12 bits that are used for representing the length of current MPDU.
CRC calculation include reserved & length sub field.
Unique pattern is used to find next delimiter with minimal, computation is case of complete delimiter.
Padding append at end of each MPDU to make size a multiple of 4-bytes and padding bytes not necessary for
last MPDU.
Appending at the end of each
MPDU. Make size multiples of
4-bytes.

28. Aggregate-MPDU (A-MPDU)
In noisy environment it yields poor performance due to the lack of an individual FCS for each sub-frame.
On the other hand, A-MPDU is robust against errors due to the presence of individual CRC per MPDU and the
aggregated frame size can be up to 64 KB.
Advantage:
A-MSDU is very effective in ideal channel conditions due to lesser protocol overheads.