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**Radio Frequency Components**

RF System Components: Radiators Isotropic radiation Units of power level: Decibels, Decibels - milliwatt

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Signal Level Unit Telecommunications has a standard unit for measuring signal level This unit has been used for a very long time Initially, it was drawn up by the study of the way that the human ear responds to sounds The human ear respond to sound in a non-linear way, but rather a logarithmic way

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**Signal Level Unit: the Decibel**

Decibel is a logarithm of a ratio. The ratio could be calculated between a number and an arbitrary reference number. The reference number could be 1, for example. The ratio could be calculated between the power measured in two different places.

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**Signal Level Unit: the Decibel**

Telecom System IN OUT When the ratio is calculated between the output of a system with respect the input the resulting decibel is a measure of either gain or loss of the system

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decibel dB The decibel is the fundamental unit to express signal level or amplitude in telecommunications systems. Signal level, signal loss (attenuation) and signal gain (amplification) are all expressed in decibels. Loss is expressed in negative terms. Gain is expressed in positive terms. Decibels are added and subtracted. Numbers smaller than 1 yield negative decibels.

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Decibel dB Telecom System IN OUT

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Decibel dB Telecom System 1 Watt IN 2 Watts OUT

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**Decibel dB Telecom System 1 Watt IN 2 Watts OUT**

This telecom system increases the signal level twice in magnitude or + 3 dB

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**Some decibel values 1 10 0.1 -10 2 + 3 - 3 4 +6 8 +9 Power Output (W)**

Power Input (W) dB Meaning 1 No Gain, no loss 10 10 times gain 0.1 -10 1/10 loss 2 + 3 Doubles - 3 Halves 4 +6 Twice, twice 8 +9 Twice, twice, twice

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Some decibel values Power Output (W) Power Input (W) dB Meaning 1 No Gain, no loss 10 10X 100 20 100X 1000 30 1,000X 10,000 40 10,000X 100,000 50 100,000X 2,000 2 1,000 1,000 times

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**Decibel Exercises Model the system into function blocks**

Convert power values to decibels Add or subtract

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**Example Microwave Radio**

Antenna Conductor Medium Transmitter

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**Example Microwave Radio**

Antenna Gain Losses in coax cable Transmitter

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**Example Microwave Radio**

Antenna Gain 10 dB + 7 dB Losses in coax cable - 3 dB Transmitter 0 dB

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**Example Wireless Access Point**

Losses in the air Antenna Gain Transmitter

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**Example Wireless Access Point**

Transmitter - 10 dB Losses in The air - 6 dB (Depends on distance and objects in path) PC receiver gets -16 dB

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**Example Wireless Access Point**

Receiver Sensitivity - 70 dBm @ 54 Mbps Losses in the air ? Antenna Gain 5 dBi The IR transmits 20 dBm while a receiver with a sensitivity of – 70 dBm leaves a power budget of 90 dB with no reserve Transmitter 15 dBm @ 54 Mbps

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**RF Components Source Radiator Medium Receiver Transmitter of RF signal**

Interface between system and medium Medium Air or vacuum Receiver Accepts incoming signal

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The transmitter Signal is delivered to medium by the interface (antenna) Modulator Signal Amplifier Input Information Local Frequency Oscillator

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**Transmitters in 802.11 Notice this specification from Linksys**

DSSS or FHSS 2.4 GHz 802.11a OFDM 5 GHz 802.11b HR-DSSS 2.4 GHz 802.11g ERP 2.4 GHz 802.11n OFDM MIMO 5 GHz Notice this specification from Linksys 11b uses two spread spectrum techniques DSSS and CCK But the specs describe PSK which is a modulation system

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**Antenna Transmission Function: radiates RF waves**

Reception Function: absorb the RF waves Reference: isotropic radiator

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Isotropic Radiator A perfect (ideal) point source that radiates RF energy with the same intensity for all directions

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**Antenna Output Antenna output can be manipulated by: Power Gain**

Beam forming

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**Intentional Radiator FCC Code Federal Regulations Part 15:**

…”A device that generates and emits radio frequency energy by radiation”… IR includes: transmitter, connections, grounding, amplifiers, but not the antenna. Power level reference is typically the dBm

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**Equivalent Isotropically Radiated Power**

FCC defines EIRP as…”the product of the power supplied to the antenna and the antenna gain in a given direction relative to an isotropic antenna”…

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**Units of Power Level Watts, milli-watts Decibel dB**

Decibel isotropic dBi Decibel Dipole dBd

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dBi The gain of an antenna as compared to an ideal isotropic radiator

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**dBd The reference of the gain is a Dipole Antenna**

Standard dipole has a gain of 2.14 dBi To convert dBd to dBi just add 2.14 dBi = dBd

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Dipole Antenna Check this out: www-antenna.ee.titech.ac.jp/.../index.html

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EXERCISES

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Typical Model For WLAN The typical model for a complete telecommunications system includes a source, a path, and a receiver end. If an obstacle is present in the path, then it is added to the model. Path Loss RF out Obstacle

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**Intentional Radiator IR**

Typical Model For WLAN The typical model for a complete telecommunications system includes a source, a path, and a receiver end. Path Loss RF out Receiver Intentional Radiator IR Antenna Signal out Obstacle

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Typical Model For WLAN This is the simplified model of the telecom system in functional blocks. Now, the whole system can be evaluated in terms of gain and losses in decibels. Source (Transmitter) Path Obstacles Receiver

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**Data for Exercises Card Name Power Senao/Engenius NMP-8602+**

400mW (b,g), 100mW (a) 1stWave Wavemaxxpro 100 mW 3com AirConnect 30 mw 3e-110 200 mw AddtronCard 30mw Belkin F5D6001 version 2 31dBm Belkin F5D6020 (Ver. 1) 13 dBm ~ 20 dBm (50mW) (max) Belkin F5d6020 Ver.2 17 dBm (50mW) Belkin F5D6020 Ver.3 16 dBm - 18 dBm (40 mW - 63 mW) Belkin F5d6050 (Ver.1) 13dBm

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Data for Exercises Specifications The receive sensitivity of the Aironet mW card is: 1Mbps 2Mbps 5.5Mbps 11Mbps The receive sensitivity of the Aironet 4800B 30mW card is: -90 1 Mbps Mbps Mbps Mbps

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**Intentional Radiator IR**

Exercise The Signal out is 100 mW The antenna has a gain of 10 dBi What is the value of RF out in dB? RF out Antenna Intentional Radiator IR Signal out

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**Intentional Radiator IR**

Exercise The Signal out is 200 mW The antenna has a gain of 10 dBd What is the value of Antenna Gain in dBi? What is the value of RF out in dBm? RF out Antenna Intentional Radiator IR Signal out

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**Exercise Aironet PCI4800 (Cisco 340) wireless card**

The IR output power is 100mW The card has a 2dBi rubber antenna What is the value of RF out in dB and dBm?

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**Intentional Radiator IR**

Exercise The Signal out is 31 dBm The antenna has a gain of 2 dBi What is the value of RF out in dBm? RF out Antenna Intentional Radiator IR Signal out

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**Intentional Radiator IR**

Exercise Frequency = GHz Signal out is 30 mW Antenna gain is 3 dBi Find RF out in dBm RF out Antenna Intentional Radiator IR Receiver in Signal out

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**Intentional Radiator IR**

Exercise Frequency = GHz Signal out is 30 mW Antenna gain is 3 dBi Receiver sensitivity is Mbps Find maximum distance for link to work RF out Receiver in Antenna Intentional Radiator IR Signal out

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**Obstacles Material Typical loss at 5 GHz Cubicle wall 2 dB Drywall**

Brick or concrete 15 dB Glass or windows Concrete floor 11 dB

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**Intentional Radiator IR**

Exercise Frequency = GHz IR Signal out is 30 mW Antenna gain is 3 dBi Receiver sensitivity is Mbps Add a brick wall Find maximum distance for link to work RF out Antenna Intentional Radiator IR Receiver in Signal out

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rssi

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**Radio Signal Strength Indicator RSSI**

PHY sub-layer energy RSSI arbitrary, optional parameter Vendors can do whatever they want with their RSSI value A value from 0 to a maximum

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Power Levels in WLAN In Wireless communications, strong power is not the issue. It is never that strong. Small received power is the main concern. Wireless clients can detect and work with extremely low power (nanowatts and picowatts)

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Small Power From 0 dBm to – 100 dBm there is a delta power of only watts (1 mW – 0.1 picoW = Watts) Most receivers have no problem listening to signal power higher than 1 mW

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**Atheros dBm= RSSI – 95 Atheros makes – 95 dBm their 0% RSSI**

-95 dBm is their card sensitivity Atheros has a MAXRSSI of 60 Source:

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**Cisco Cisco assigns 101 values from 0 to 100**

-10 dBm is considered 100 % RSSI -113 dBm is considered 0 % RSSI

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**Cisco RSSI 101 values 0 = -113 1 = -112 2 = -111 3 = -110 4 = -109**

5 = -108 6 = -107 7 = -106 8 = -105 9 = -104 10 = -103 11 = -102 12 = -101 13 = -99 14 = -98 15 = -97 16 = -96 17 = -95 18 = -94 19 = -93 20 = -92 21 = -91 22 = -90 23 = -89 24 = -88 25 = -87 26 = -86 27 = -85 28 = -84 29 = -83 30 = -82 31 = -81 32 = -80 33 = -7 34 = -78 35 = -77 36 = -75 37 = -74 38 = -73 39 = -72 40 = -70 41 = -69 42 = -68 43 = -67 44 = -65 45 = -64 46 = -63 47 = -62 48 = -60 49 = -59 50 = -58 51 = -56 52 = -55 53 = -53 54 = -52 55 = -50 56 = -50 57 = -49 58 = -48 59 = -48 Etc, etc … 80 = -27 81 = -25 82 = -24 83 = -23 84 = -22 85 = -20 86 = -19 87 = -18 88 = -17 89 = -16 90 = -15 91 = -14 92 = -13 93 = -12 94 = -10 95 = -10 96 = -10 97 = -10 98 = -10 99 = -10 100 = -10

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RSSI RSSI is intended to avoid using decibels (for people who do not understand dB) Personally, I rather use decibels than some arbitrary, un-scientific, non-sense, ridiculous number. Many vendors have reverted to use dBs. Just learn and use decibels.

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Signal Level The measurement and description of signal levels is fundamental for WLAN communications. The unit system is based in the decibel. Understanding decibels requires some thinking about it since the decibel is not a lineal unit but rather logarithmic.

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