CSNT 180 Wireless Networking. Chapter 4 Radio Frequency (RF) Fundamentals for Wireless LAN Technology

Size: px

Start display at page:

Download "CSNT 180 Wireless Networking. Chapter 4 Radio Frequency (RF) Fundamentals for Wireless LAN Technology"

Toby O’Neal’
6 years ago
Views:

1 CSNT 180 Wireless Networking Chapter 4 Radio Frequency (RF) Fundamentals for Wireless LAN Technology Norman McEntire norman.mcentire@servin.com Founder, Servin Corporation, Technology Training for Technology Professionals TM Copyright (c) 2010 Servin Corporation. 1

3 Introduction RF = Radio Frequency RF consists of High Frequency Alternating Current (AC) Signals Passing over a coper wire Connected to an antenna RF units of measurement are important to know RF characteristics are important to know Copyright (c) 2010 Servin Corporation 3

4 Understanding Radio Frequency (RF) RF High Frequency Alternating Current (AC) Signals Passing over a coper wire Connected to an antenna See Figure 4.2 in Textbook Characteristics include (more info on following slides) Wavelength, Frequency, Amplitude, Phase Copyright (c) 2010 Servin Corporation 4

5 RF Requires Transmitter and Receiver See Figure 4.3 in textbook These always work as a pair The transmitter transmits The receiver receives Each has an antenna The antenna transforms the copper signals to/from radio waves Copyright (c) 2010 Servin Corporation 5

7 Frequency Frequency = number of complete cycles per second See Figure 4.5 in textbook Low frequency = longer waves High frequency = shorter waves Example 800 MHz cordless phone had 500 feet range 2.4 GHz had 250 feet range 2.4 GHz wavelength about ½ distance of 800 MHz Copyright (c) 2010 Servin Corporation 7

8 Amplitude Amplitude = height of the sine wave See Figure 4.6 in Textbook Same Frequency. Different Amplitudes. The voltage at the peak of the sine wave is used to calculate the amount of RF Power Increase in Amplitude = Increase in Power = Gain Increase in Power: Gain Decrease in Power: Loss Copyright (c) 2010 Servin Corporation 8

9 Phase Phase = difference in degrees designating the start and end of two different overlapping sine waves 0 to 360 degrees See Figure 4.7 in Textbook Signal #1 and Signal #2 are are 90 degrees out of phase If two signals are 180 degrees out of phase, they will cause a cancellation effect Copyright (c) 2010 Servin Corporation 9

11 FCC Unlicensed Frequency Bands Used by the IEEE Standards See Table 4.3 in Textbook 2.4 GHz ISM Band ISM Industrial, Scientific, Medical GHz 5 GHz UNII Bands UNII-1 UNII-2 UNII-2e UNII-3 Copyright (c) 2010 Servin Corporation 11

12 Channels 2.4 GHz ISM Frequency is divided into bands Bands are divided into channels 2.4 GHz ISM Band Total of 14 Channels Total of 11 Channels used in USA See Figure 4.8 Copyright (c) 2010 Servin Corporation 12

14 DSSS is 22 MHz Wide - Hence it overlaps multiple channels Example Step 1. Channel 1 = GHz = 2412 MHz Step Mhz + 22 Mhz = 2436 Mhz Step 3. What channel is greater than 2436? Answer: Channel 6: 2437 Mhz = GHz KEY POINTS 25 Mhz is required for channels to be NON overlapping Channels 1, 6, and 11 are 25 MHz apart and nonoverlapping Copyright (c) 2010 Servin Corporation 14

16 Range Range = how far the signal can travel Range based on Wavelength (distance of a single cycle) Lower the frequency, longer the range Higher the frequency, shorter the range At the same output power level A 2.4 GHz signal will travel 2x as far as 5 GHz Copyright (c) 2010 Servin Corporation 16

18 Coverage and Capacity Two key factors when designing/implementing WLAN Coverage Capacity Coverage Size of the RF cell Capacity Number of users who can connect and use RF cell Copyright (c) 2010 Servin Corporation 18

19 Coverage Coverage = size of RF cell Coverage depends on many factors Size of area Number of users Whether bandwidth intensive apps are in use Obstacles Radio Frequency WLAN hardware (2.4 GHz vs 5 GHz) Power output of Transmitter Copyright (c) 2010 Servin Corporation 19

21 Size of Area Manufacturers of WLAN hardware do not like to commit to a specific RF cell size Why? Answer: Too many variables NOTE: In Chapter 9 will will cover how to perform site survey Copyright (c) 2010 Servin Corporation 21

22 Number of Users How many users will access the RF cell? If a single RF cell has a single AP, how many simultaneous users can the AP handle? 10? 100? 1000? Recall the Apple ipad demo, with Steve Jobs asking the reporters to disconnect from Wi-Fi... Copyright (c) 2010 Servin Corporation 22

23 Type of Applications Does applications in user require much Wi-Fi bandwidth? Low bandwidth: Casual reading of static web pages Medium Bandwidth: YouTube High Bandwidth: CAD apps with huge image files Another high bandwidth example: Hospital Xray files Copyright (c) 2010 Servin Corporation 23

24 Obstacles What obstacles are in the area Walls, Doors, Windows, Furniture, etc. Thickness/Material of Walls, Doors, Windows, Furniture, etc. NOTE: More on this issue later in this chapter in section Environment: RF Behavior Copyright (c) 2010 Servin Corporation 24

25 WLAN Hardware and Output Power WLAN Hardware can impact coverage area Antenna Type Antenna Orientation Gain of the Antenna Higher the gain, higher the coverage Most enterprise-grade APs provide control of gain Copyright (c) 2010 Servin Corporation 25

26 Capacity Capacity = maximum users to can access AP without performance impact So many variables! How many users? Types of applications Bandwidth needs of applications Popular Option: Provide multiple APs! Copyright (c) 2010 Servin Corporation 26

27 Cannel Reuse and Colocation To handle increased capacity needs, add additional Aps See Figure 4.11 and Figure 4.12 in Textbook Figure 4.11 APs all set to Chanel 1 Figure 4.12 APs with proper channel reuse Channels 1, 6, 11 Very Key And Important to Know! 2.4 GHz ISM band has total of 3 NON- OVERLAPPING channels: 1, 6, 11 Copyright (c) 2010 Servin Corporation 27

30 Fresnel Zone Fresnel [fruh-nel] Zone The area of usable RF coverage between transmitter and receiver Must be clear of obstacles by at least 60 percent See Figure 4.13 in Textbook Copyright (c) 2010 Servin Corporation 30

31 Line of Sight Two types of Line of Sight Visual Line of Sight RF Line of Sight Visual Line of Sight Transmitter/Receiver see each other w/o obstacles RF Line of Sight Fresnel zone less due to obstacles Copyright (c) 2010 Servin Corporation 31

32 Interference Question: What is RF interference? Answer: The RF receiver hears two different signals on the same or similar frequency Result is signal distortion, which results in decreased data throughput Sources of Interference on 2.4 GHz WLAN Radio Control devices, Cordless phones, Microwaves, Medical devices, Industrial devices, baby monitors, other WLAN devices! (Whew!) NOTE: Later chapters will cover Site Survey! Copyright (c) 2010 Servin Corporation 32

33 Co-Channel/Adjacent Channel Interference Co-Channel/Adjacent Channel Interference When two devices in same physical area are tuned to same or close RF channel Example (causes interference) AP #1 set to channel 1 AP #2 set to channel 2 Example (does NOT cause interference) AP #1 set to channel 1 AP #2 set to channel 6 See Figure 4.14 and Figure 4.15 Copyright (c) 2010 Servin Corporation 33

34 WLAN/WPAN Interference WLAN = Wireless Local Area Network WPAN = Wireless Personal Area Network Example: Two iphone devices using Bluetooth to play a peer-to-peer game Example WPAN Technology Bluetooth 2.4 GHz frequency range Older versions of BT interfered with Newer versions of BT use AFH (Adaptive Frequency Hoping) to reduce interference Copyright (c) 2010 Servin Corporation 34

35 Bright Sunlight Interference Bright sunlight will NOT affect WLAN (Textbook mentions that Infrared (IR) impacted by bright sunlight but that is not part of CWTS exam.) Copyright (c) 2010 Servin Corporation 35

38 RF Reflection (think ping-pong) RF Reflection When an RF signal bounces off a smooth, non absorptive surface such as a tabletop Think ping-pong ball hitting ping-pong table See Figure 4.16 in Textbook Copyright (c) 2010 Servin Corporation 38

39 RF Refraction (think glass) RF Refraction When an RF signal passes between mediums of different densities, it may change speed or bend Example Glass is example material that may cause refraction See Figure 4.17 Copyright (c) 2010 Servin Corporation 39

42 RF Absorption RF Absorption When a material absorbs the RF signal Example Human body has high water content and will absorb RF signals This is issue with densely populated areas such as airports and conference halls See Figure 4.20 Copyright (c) 2010 Servin Corporation 42

43 RF Diffusion RF Diffusion RF signal naturally widens as it leaves the antenna Called Free Space Path Loss (FSPL) NOTE: FSPL is the greatest form of loss factor in an RF Link Copyright (c) 2010 Servin Corporation 43

45 Basic Units of RF Measurement Watt the basic unit of measurement for RF 1 Watt = 1000 milliwatts Example SOHO AP A SOHO AP may output 30mW of power 30mW = (30mW * (1W/1000mw)) = 30/1000 Watt Example - Enterprise AP A Enterprise AP may output 100mW of power 100 mw = (100 mw * (1W/1000mw)) = 100/1000 Watt = 1/10 W Copyright (c) 2010 Servin Corporation 45

46 Absolute Measure of Power The amount of power leaving an AP is one example of absolute measure of power Absolute measure is just that an absolute measure Not a ratio Not a relative value Examples of Absolute Measure of Power Watt Decibel Relative to a Milliwatt (dbm) Copyright (c) 2010 Servin Corporation 46

47 Decibel Relative to MilliWatt - dbm dbm = Decibel Relative to MilliWatt Power level compared to 1 milliwatt Based on a logarithmic function Rule of thumb: 0 dbm = 1mW Example (from USB N client device) RF Power 11n Mode: 13 dbm 11g Mode: 15 dbm 11b Mode: 19 dbm Copyright (c) 2010 Servin Corporation 47

51 Decibel Isotropic - dbi Decibel Isotropic dbi Gain in signal strength Isotropic = energy broadcast equally in all directions in a spherical fashion Isotropic radiator = an imaginary, perfect antenna Theoretical and used for reference calculations More on this in Chapter 6 Copyright (c) 2010 Servin Corporation 51

52 Decibel Dipole - dbd Decibel Dipole dbd Antenna gain with respect to a reference dipole antenna To quote from book The gain of most antennas used in WLANs is measured in decibel isotropic, dbi; however some manufacturers may reference gain in dbd Formulas dbi = dbd dbd = dbi Copyright (c) 2010 Servin Corporation 52

53 Chapter Summary RF Basics Transmitter, Receiver Wavelength, Frequency, Amplitude, Phase Unlicensed bands: 2.4 GHz ISM, 5 GHz UNII 2.4 GHz ISM Channels 14 total. 11 In use in USA. RF Characteristics: reflection, refraction, etc. RF Measurements: Watt, mw, db, dbm, etc. Copyright (c) 2010 Servin Corporation 53

54 Exam Essentials Know properties of RF Wavelength, Frequency, Amplitude, Phase Frequencies for WLAN 2.4 GHz ISM, 5 GHz UNII Coverage, Capacity Reflection, refraction, diffraction, scattering, absorption Absolute Measurements: W, mw, dbm Relative Measurements: db, dbi, dbd Copyright (c) 2010 Servin Corporation 54

Industrial Wireless Systems

Industrial Wireless Systems Application Considerations Don Pretty Principal Engineer Geometric Controls Inc Bethlehem, PA Sheet 1 Ethernet Dominates on the Plant Floor Sheet 2 Recognize Any of These? Sheet 3 Answers: 10 BASE 2 RG