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Lesson 1 - WiFi Performance Principles
TC Leeon 30 July 2014
Transcript of Lesson 1 - WiFi Performance Principles
1. Downlink: Getting signal from AP to client
3. Signal BETWEEN clients
Client must be able to receive good, stable signal from the AP. Good signal means higher data rates and throughput.
This is achieved with AP transmission power and/or directivity.
provides better downlink signal and SNR to clients.
2. Uplink: Getting signal from client to AP
AP must be also able to receive good, stable signal from the client.
But clients have weaker radios than APs. And we cannot change that.
The only way is to have better reception on the AP.
improves the AP reception. Allows the AP to pick up signals of weak clients in any orientation.
Better reception means higher data rates on the uplink.
WiFi uses CSMA/CA as the media access method. Shared bandwidth concept.
Clients on the same AP (actually frequency) takes turns to transmit. Like using walkie talkie.
But this depends on clients being able to "hear" each other.
If clients is unable to "hear" each other, collision occurs at the AP. Retransmission occurs. Throughput drops.
Achieved by designing proper AP locations such that within the coverage area, clients are able to "hear" each other.
In order for WiFi to work well, three things must happen:
1. Get good signal from AP to client.
2. AP must receive good signal from client.
3. Clients must be able to "hear" each other.
Ruckus products addresses the first two challenges.
Proper design will address the third challenge.
Allows Ruckus AP to focus the signal towards the client
Creates a stronger signal to the client without additional transmit power
Like a reflector of a light bulb - it focuses light in a specific direction
Who can hear better?
Low power client device
Better reception with Ruckus
Design Exercise 1
Design Exercise 2
Design Exercise 3
Rooms are separated by thin walls.
Obstructions between bedrooms are two thin walls.
Rooms are mostly separated by three walls.
Master bedroom and BR4 separated by bathroom.
BR2 and BR3 separated by three, almost four walls.
Master bedroom and BR3 separated by multiple walls.
Polarization Diversity - Maximal Ratio Combining
Carrier Sense Multiple Access / Collision Avoidance
Every (overlapping) frequency is a collision domain.
Like an Ethernet hub.
This is why WiFi best practice says to use Channels 1, 6 and 11 - to get 3 collision domains (3 hubs) for better performance.
Clients in different rooms are separated by thin walls.
So it is highly likely that clients can all "hear" each other.
Clients in Master bedroom or BR2 may not be able to "hear" clients in BR3 and BR4.
Better to partition the coverage area to be served by two APs instead of having one single coverage area.
Clients on one side of the corridor will not be able to "hear" clients on the opposite side of the corridor.
This will result in high collision environment causing throughput to be lower than it should be.
Better to partition the coverage area and treat each side of the corridor separately.
Certified Wireless Technology Specialist
In order for WiFi to work well, three important conditions must be met:
1. Good signal from AP to client
2. AP must receive good signal from client
3. Clients must be able to "hear" each other
WiFi Performance Principles
Radio Power Comparison
Understanding Data Rates
High data rates - like speaking fast
It takes shorter time to complete transmission.
Low data rates - like speaking slow
It takes longer time to complete transmission.