1. Radio Frequency Components
RF System Components:
Radiators
Isotropic radiation
Units of power level:
Decibels,
Decibels - milliwatt

2. 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

3. 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.

4. 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

5. 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.

6. Decibel dB
Telecom System IN
OUT

7. Decibel dB
Telecom System
1 Watt IN
2 Watts OUT

8. Decibel dB Telecom System 1 Watt IN 2 Watts OUT
This telecom system increases the signal level twice in magnitude or + 3 dB

9. 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

10. 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

11. Decibel Exercises Model the system into function blocks
Convert power values to decibels
Add or subtract

12. Example Microwave Radio
Antenna
Conductor Medium
Transmitter

13. Example Microwave Radio
Antenna Gain
Losses in coax cable
Transmitter

14. Example Microwave Radio
Antenna Gain
10 dB
+ 7 dB
Losses in
coax cable
- 3 dB
Transmitter
0 dB

15. Example Wireless Access Point
Losses in the air
Antenna Gain
Transmitter

16. 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

17. 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

18. RF Components Source Radiator Medium Receiver Transmitter of RF signal
Interface between system and medium
Medium
Air or vacuum
Receiver
Accepts incoming signal

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

20. 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

21. Antenna Transmission Function: radiates RF waves
Reception Function: absorb the RF waves
Reference: isotropic radiator

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

23. Antenna Output Antenna output can be manipulated by: Power Gain
Beam forming

24. 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

25. 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”…

26. Units of Power Level Watts, milli-watts Decibel dB
Decibel isotropic dBi
Decibel Dipole dBd

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

28. 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

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

30. EXERCISES

31. 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

32. 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

33. 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

34. 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

35. 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

36. 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

37. 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

38. 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?

39. 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

40. 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

41. 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

42. Obstacles Material Typical loss at 5 GHz Cubicle wall 2 dB Drywall
Brick or concrete
15 dB
Glass or windows
Concrete floor
11 dB

43. 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

44. rssi

45. 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

46. 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)

47. 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

48. Atheros dBm= RSSI – 95 Atheros makes – 95 dBm their 0% RSSI
-95 dBm is their card sensitivity
Atheros has a MAXRSSI of 60
Source:

49. Cisco Cisco assigns 101 values from 0 to 100
-10 dBm is considered 100 % RSSI
-113 dBm is considered 0 % RSSI

50. 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

51. 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.

52. 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.