1.RF principle

1.RF Specturn sl

..... wave propagate to a receiver which receive eneryg

Frequency slide sl

. 7.Decible to miliwatt

wave take dfff tume to tro ravel what cycle, depend on its length

the shorter the wavelength, the higher the frequency

3, Wavelength slide

Ex: when car play loud music, the first you hear are drums and the base coz lower freq travel father than higher freq

.... the shape is same as signal that antena rediate

Greeek symbol lamda is the distance, it define the physcal distance

diff didstance has diff property as diff environment can affect the wave

Ex: AM radio can use wavelenth 400 - 500 long

Wife use a few centimeter

  1. Amplitude slide

seen as distance between highest and lowest crests of cycle

The symbol GAmma Y represent amplitue

the higher amplitude, higher energy

Example:if have rope tie to fence to swing harder to cover wider scope

5.free path loss slide

Energy dissipate from all direction

the radio wave have higher crest (peak of the wave) close to center and the crest will reduce the size

it is not due to distance

It is due to small circle energy is higher, big circle energy has to distribute to more points

6.RSSI and SNR slide

RSSI is relative and range from -0 ( no signal or no reference) to a max of 255

Many verndor use max value that is lower than 255 (such as 100 or 60)

can compare RSSI of diff vendor

click to edit

For cisco, good RSSI is -67Dbm or lower

(DT)Future standard will use RCPI (received channel power indicateor)

SNR above 20db is good

  1. Describe Decibel and Watt (Cont)

0 dbM send the same miliwatts as reference source

..... power reference for slide is 1mW, so means device send 1 mw

this explain the bracket

Power in the sl means sent from source, type of AP, & type of antenna

Power relative means with reference of 1 volt

extra

on WLC can config minimum r(RSSI) require for the client to associate to an access point.

If the client’s average received signal power dips below this threshold, reliable communication is usually impossible. Therefore, clients must already have found and roamed to another access point with a stronger signal before the minimum RSSI value is reached.

Not in sl

the first unit of power meansurement is watt

watt means energy spent per send

DB

logarithm unit of

antena power (= antena gain =dbi)

WLC can statically set the transmit power of AP antenna based on 802.11abg

we change the DBi because we want to change the EIRP

EIRP

Most countries will specify Max transmit power and Max EIRP

WLC allow you to configure transmit power

default trasmit power is dynamically adjust to reduce interference

antena

omnidirection

radiate on all angle

Azimuth

horizontal plane

as seen from top

Elevation plane

as seen from side

celling mount

provide good average for side but not so good on top and bottom

install by pointing downward

integrated antenna

work well for 1 floor

Yagi antenna

large corridor or warehoue

Spatial multiplexing

support by cisco wave 2 such as 1830, 1850, 2700, 3700

Controller can show SNR and RSSI between client and AP

antenna gain configurable ? (DT)

High-gain antennas have a more focused radiation pattern in a specific direction. The antenna gain is measured in 0.5 dBi units, and the default value is 7 times 0.5 dBi, or 3.5 dBi.


If you have a high-gain antenna, enter a value that is twice the actual dBi value (see Cisco Aironet Antenna Reference Guide for antenna dBi values). Otherwise, enter 0. For example, if your antenna has a 4.4-dBi gain, multiply the 4.4 dBi by 2 to get 8.8 and then round down to enter only the whole number (8). The Cisco WLC reduces the actual equivalent isotropic radiated power (EIRP) to make sure that the antenna does not violate your country’s regulations.

dual band dipole antenna

they operate in both the 2.4 GHz and 5 GHz frequency bands.

spatial multiplexing

data requested by the user) is split into two or more independent data streams that are transmitted over multiple antennas, called spatial streams. A common configuration is the previously mentioned 2×2 MIMO system. In this case the throughput is theoretically doubled compared to the single antenna configuration

This is to increase data rate

mu (MULTIPLE USER)-mimo

Can transmit multiple frames to up to 4 client at the same time and same spectrum

EXAMPLE: Maximize the energy to user 1 in the direction of user2 and user 3