Презентации / 1-2 Wireless Intro
.pdf
802.11n and 802.11ac
Скорость
ØСтандарты?
ØСкорости?
ØЧастоты?
ØПочему настолько отличаются скорости?
Evolution to MIMO Technology
qOld Wi-Fi systems used Single Input Single Output (SISO) technology
§Single transmit stream
§Single transmit antenna
§Single receive antenna
§Severely impacted by multipath signals
§Performance improved by diversity
Received Signals
Time
Combined Results
Time
Single-input Single-output (SISO)
Evolution to MIMO Technology
qMIMO requires at least 2 receivers or 2 transmitters per band
§Uses advanced signal processing to coordinate multiple simultaneous signals from multiple antennas
§Improved link reliability
|
|
Received Signals |
|
Transmitter |
Receiver |
Time |
|
Combined Results |
|||
|
|
||
The |
|
Time |
|
Wireless |
|
|
|
Channel |
|
|
MIMO Uses Advanced Signal Techniques to improve link reliability and efficiency
Maximal ratio combining (MRC)
•Performed by receiver
•Combines multiple received signals
•Increases receive sensitivity
•Works with MIMO and non-MIMO clients
message
message message
message
Half duplex
Evolution to MIMO Technology
q MIMO requires at least 2 receivers or 2 transmitters per band
?
MIMO Uses Advanced Signal Techniques to improve link reliability and efficiency
Maximal ratio combining (MRC)
•Performed by receiver
•Combines multiple received signals
•Increases receive sensitivity
•Works with MIMO and non-MIMO clients
Transmit beam forming (TBF)
•Performed by transmitter
•Ensures signal received in phase
•Increases receive sensitivity
•Works with MIMO and non-MIMO clients
Spatial multiplexing (SM)
•Transmitter and receiver participate
•Multiple antennas txmt concurrently on same channel
•Increases bandwidth
•Requires MIMO client
message
message message
message
message
message
message
me
ss
age
message
Advanced Techniques Improve Data Rates for All Clients
36 Mbps
54 Mbps
450 Mbps
(The same applies exactly to 802.11ac)
Пространственные потоки
3x4:3
3TX
4RX
3 пространственные
потоки
Пространственные потоки
Сдвиг фазы для Transmit beam forming
Фазированные решетки