51 Certified Wireless Network Professional :: CWNA-109 Basic Types of Modulation
52 Certified Wireless Network Professional :: CWNA-109 PSK Modulation Constellations Binary PSK (BPSK) Quadrature PSK (QPSK) 2 Bits 1 Bit BPSK – Two possible phases represent 1 data bit QPSK – Four possible phases represent 2 data bits Phase shift keying (PSK) modulation: Specific phase shifts applied to carrier wave to indicate bit sequence
53 Certified Wireless Network Professional :: CWNA-109 QAM Modulation Constellations 16-QAM 4 Bits 64-QAM 6 Bits 16-QAM – 16 possible phases - 4 data bits 64-QAM – 64 possible phases - 6 data bits QAM = Quadrature Amplitude Modulation: Phase and amplitude shifts applied to carrier to represent bit sequences.
54 Certified Wireless Network Professional :: CWNA-109 Chapter 3: RF Mathematics and Measurements Objectives Covered: 1.2 Apply the basic concepts of RF mathematics and measurement
55 Certified Wireless Network Professional :: CWNA-109 Units of RF Measurement Relative Units dB – decibel dBi – decibel relative to an isotropic radiator dBd – decibel relative to a dipole antenna Absolute Units mW – milliwatts W – Watts dBm – decibels relative to one milliwatt Know which measurements are absolute and which are relative units
56 Certified Wireless Network Professional :: CWNA-109 Absolute Power Measurement Milliwatts (mW) dBm 1 0 .1 -10 .01 -20 .001 -30 .0001 -40 .00001 -50 .000001 -60 .0000001 -70 .00000001 -80 .000000001 -90 .0000000001 -100 The relationship between dBm and mW is logarithmic 1 mW = 0 dBm Milliwatt – (1/1000 of a Watt) linear unit to measure energy transfer dBm – decibels (logarithmic unit) relative to a milliwatt
57 Certified Wireless Network Professional :: CWNA-109 Logarithms Logarithms utilize exponents to simplify large or small calculations Very small power quantities are difficult to work with using linear numbers • .0000000mW vs. -80 dBm • Decimals with several 0s are error-prone
58 Certified Wireless Network Professional :: CWNA-109 Relative Power Measurement Decibel (dB) – Basic unit of measurement that quantifies changes in power Connectors and Cable loss measured in dB / foot Antenna gain measured in dBi
59 Certified Wireless Network Professional :: CWNA-109 Change of RF Power Decibels can also be used to measure comparative amounts of amplitude. Quantifying gain and loss of a single signal Comparative measurements of different signals Before loss TIME FREQUENCY After loss AMPLITUDE Signal 1 Signal 2
60 Certified Wireless Network Professional :: CWNA-109 dBi and dBd dBi and dBd are used to measure antenna gain dBi Decibels relative to an isotropic radiator Used to measure passive antenna gain 0 dBi = no directivity / passive gain dBd Decibels relative to a half-wave dipole Lesser used unit to measure antenna gain Half-wave dipole = 2.14 dBi 0 dBd = 2.14 dBi Isotropic Radiator Half-Wave Dipole
61 Certified Wireless Network Professional :: CWNA-109 Basic RF Math dBm mW +20 100 +19 80 +16 40 +13 20 +10 10 +9 8 +6 4 +3 2 0 1 -3 0.5 -6 0.25 -9 0.125 -10 0.1 -13 0.05 -16 0.025 -19 0.0125 -20 0.01 Rule of 10s and 3s -3 dB = 1/2 power +3 dB = 2x power -10 dB = 1/10 power +10 dB = 10x power
62 Certified Wireless Network Professional :: CWNA-109 Conversion Chart (dBm/mW) 0 dBm 1 mW 10 dBm 10 mW 20 dBm 100 mW 1 dBm 1.25 mW 11 dBm 12.5 mW 21 dBm 128 mW 2 dBm 1.56 mW 12 dBm 16 mW 22 dBm 160 mW 3 dBm 2 mW 13 dBm 20 mW 23 dBm 200 mW 4 dBm 2.5 mW 14 dBm 25 mW 24 dBm 256 mW 5 dBm 3.12 mW 15 dBm 32 mW 25 dBm 320 mW 6 dBm 4 mW 16 dBm 40 mW 26 dBm 400 mW 7 dBm 5 mW 17 dBm 50 mW 27 dBm 512 mW 8 dBm 6.25 mW 18 dBm 64 mW 28 dBm 640 mW 9 dBm 8 mW 19 dBm 80 mW 29 dBm 800 mW
63 Certified Wireless Network Professional :: CWNA-109 RF Math Activity Transmitter +10 dBi -3 dB Antenna RF Cabling +3 dBi Rx Power -3 dB 17 dBm Antenna Receiver RF Cabling Free Space -10 dB Transmit Power Cable Loss Antenna Gain (Tx) Path Loss Antenna Gain (Rx) Cable Loss Received Power Change N/A -3 dB +10 dBi -10 dB +3 dBi -3 dB N/A Power 100mW 50mW 500mW 50mW 100mW 50mW 50mW
64 Certified Wireless Network Professional :: CWNA-109 RF Math Activity Transmitter +6 dBi -3 dB Antenna RF Cabling +16 dBi Rx Power 16 dBm -4 dB Antenna Receiver RF Cabling Free Space -13 dB* Transmit Power Cable Loss Antenna Gain (Tx) Path Loss Antenna Gain (Rx) Cable Loss Received Power Change N/A -3 dB +6 dBi -13 dB* +16 dBi -4 dB N/A Power 25mW 12.5mW 50mW 2.5mW 100mW 40mW 40mW *for practice only, not realistic
65 Certified Wireless Network Professional :: CWNA-109 RSSI – Received Signal Strength Indicator 802.11 measurement of signal strength RSSI values are relative for each vendor! 8-bit field (integers 0-255) Arbitrary “RSSI max” correlates with absolute dBm value or range
66 Certified Wireless Network Professional :: CWNA-109 Receiver Sensitivity 54 Mbps 36 Mbps 18 Mbps 6 Mbps Receiver sensitivity is the minimum signal strength at which data can be received at a specific data rate. How well a RF device can “hear” Device Specific Complex modulation and coding require better signals
67 Certified Wireless Network Professional :: CWNA-109 Signal-to-Noise Ratio (SNR) >25 db is very good 15-25 dB is OK <10 dB is poor
68 Certified Wireless Network Professional :: CWNA-109 IR and EIRP Intentional Radiator (IR) EIRP Intentional Radiator – Device that intentionally emits radio waves as its intended function (does not include antenna) Equivalent Isotropically Radiated Power – Energy measured at antenna output (intentional radiator & antenna gain)
69 Certified Wireless Network Professional :: CWNA-109 Link Budget Antenna Gain (Tx) Cables & Connectors Free Space Path Loss (Distance and Frequency) Tx Output Power Antenna Gain (Rx) Receive Sensitivity Cables & Connectors A Link Budget is an accounting for transmitter and receiver configuration as well as all gains and losses in the communication system. For links extending beyond 7 miles or 11.2 kilometers, earth bulge should be factored into the elevation calculations.
70 Certified Wireless Network Professional :: CWNA-109 Performing a Link Budget Factors Amount Result Receive Sensitivity (minimum goal) -74 at 54 Mbps Fade Margin (additional signal desired) 15 dB Transmit Power 26 dBm (400 mW) Tx Cable and Connector Loss -3 dB Antenna Gain 15 dBi Path Loss (FSPL) -104 dB Rx Antenna Gain 12 dBi Rx Cable and Connector Loss -3 dB Received Power -57 dBm
71 Certified Wireless Network Professional :: CWNA-109 Online RF Calculators
72 Certified Wireless Network Professional :: CWNA-109 Chapter 4: RF Antennas and Hardware Objectives Covered: 1.3 Identify RF signal characteristics as they relate to antennas 1.4 Explain and apply the functionality of RF antennas and antenna systems and the mounting options and antenna accessories available
73 Certified Wireless Network Professional :: CWNA-109 WLAN RF Components Antenna Transmitter/Receiver Connecting Cable Laptop with internal Radio and WLAN NIC Access Point with external antenna
74 Certified Wireless Network Professional :: CWNA-109 Antenna Function Radio Transceiver RF Cable Antenna Radios modulate a baseband signal onto an electrical current Antennas convert electrical current into RF waves. The electrical current is carried by a conductive RF cable. Antennas are connected to a radio transceiver via an RF cable, Antennas convert electrical current into RF waves, Antennas are bi-directional – they transmit and receive radio waves
75 Certified Wireless Network Professional :: CWNA-109 Electromagnetic Radiation Direction Electric Field Magnetic Field Electric and Magnetic fields are perpendicular to one another, moving into space away from the source Electric Field – E-Plane Magnetic Field – H-Plane
76 Certified Wireless Network Professional :: CWNA-109 Polarization Polarization determined by the E-field Polarization of Tx and Rx antennas should match • Linear (horizontal/vertical) • Circular Polarization describes the antenna structure or the orientation of an antenna’s wave oscillations
77 Certified Wireless Network Professional :: CWNA-109 Isotropic Radiator Antenna gain (directivity) is compared to an isotropic radiator (dBi) Isotropic radiator = 0 dBi Analogous to the Sun Isotropic Radiator is a perfect antenna in which energy is radiated equally in all directions.
78 Certified Wireless Network Professional :: CWNA-109 Passive Gain Antenna gain is measured in relative units Relative to an isotropic radiator (dBi) Relative to a half-wave dipole antenna (dBd) Antennas radiate energy in a specific pattern/direction They passively focus the energy; they do not actively add energy Different types of antennas provide different amounts of focus and directionality
79 Certified Wireless Network Professional :: CWNA-109 Beam Patterns Horizontal Beamwidth Vertical Beamwidth Vertical Beamwidth Horizontal Beamwidth
80 Certified Wireless Network Professional :: CWNA-109 Azimuth and Elevation Shows the antenna’s beam pattern from a topdown view, looking at the top of the antenna Also known as “Azimuth” 360° coverage with an “omni” antenna Shows the antenna’s beam pattern from a side view, looking at the side of the antenna Also known as “Elevation” Coverage varies with antenna gain
81 Certified Wireless Network Professional :: CWNA-109 Antenna Chart Details Beamwidth is measured in degrees at points where the main lobe decreases by 3 dB (60°) Antenna “polar” charts show antenna coverage patterns (antenna is in the center) Lobes (e.g. main, side, back) are plotted on the chart to show radiation Main lobe Side/back lobes
82 Certified Wireless Network Professional :: CWNA-109 Omni-Directional Antennas 360° horizontal coverage pattern Vertical coverage varies with antenna gain • High gain = small vertical beamwidth • Low gain omni = large vertical beamwidth Low Gain High Gain
83 Certified Wireless Network Professional :: CWNA-109 Omni-Directional Examples
84 Certified Wireless Network Professional :: CWNA-109 Omni-Directional MIMO Examples
85 Certified Wireless Network Professional :: CWNA-109 Semi-Directional Antennas Directional coverage pattern Vertical and horizontal beamwidth often varies between 180° and 15 ° depending on gain Patch, panel, Yagi, and sector are common semi-directional antennas Low Gain High Gain
86 Certified Wireless Network Professional :: CWNA-109 Patch/Panel Antenna Examples
87 Certified Wireless Network Professional :: CWNA-109 Highly Directional Antennas Highly directional signal pattern Used for long-range outdoor links Vertical and horizontal beamwidths usually less than 25° 24 dBi antenna gain
88 Certified Wireless Network Professional :: CWNA-109 Yagi and Sector Directional Antenna Examples
89 Certified Wireless Network Professional :: CWNA-109 Dish/Grid Antenna Examples
90 Certified Wireless Network Professional :: CWNA-109 Dish/Grid Examples (ctd.)
91 Certified Wireless Network Professional :: CWNA-109 Antenna Mounting Examples
92 Certified Wireless Network Professional :: CWNA-109 Antenna Mounting Accessories
93 Certified Wireless Network Professional :: CWNA-109 AP Mounting Enclosures
94 Certified Wireless Network Professional :: CWNA-109 Antenna Characteristics Summary Gain Beamwidths (horizontal/vertical) Polarization Cost Intended use Manufacturer Impedance, VSWR, and other electrical characteristics Connector type Available mounting gear Frequency Response Rear and side lobe coverage Evaluate these antenna characteristic prior to selection and use:
95 Certified Wireless Network Professional :: CWNA-109 Simply Diversity Systems Multiple antennas connected to same radio via a single radio chain Radio transmits or receives from one antenna at a time (switches back and forth) Provides different samples of RF medium, improving performance Antennas must be of same type, pointing in same direction 802.11a/b/g WLAN Radio Antennas Antenna Switch
96 Certified Wireless Network Professional :: CWNA-109 MIMO Diversity Systems Multiple antennas (2+) connected to same radio via individual radio chains Radio transmits or receives from multiple antennas at same time Major enhancement to simple diversity Antennas must be of same type, pointing in same direction 802.11n MIMO Radio Antennas
97 Certified Wireless Network Professional :: CWNA-109 Sectorized Antenna Systems
98 Certified Wireless Network Professional :: CWNA-109 Directional Antenna Arrays Antenna Array with Integrated APs Multiple integrated APs use directional antennas Directional antennas collectively provide 360° signal coverage in each frequency (2.4 & 5 GHz) similar to a sector antenna system Currently offered by Xirrus WLAN Array 2.4 GHz and 5 GHz Coverage
99 Certified Wireless Network Professional :: CWNA-109 Smart Antenna Arrays Wi-Fi radio is connected to multielement antenna array Array is controlled with smart switching that dynamically selects optimal antenna elements for each transmission
100 Certified Wireless Network Professional :: CWNA-109 Line-of-Sight (LoS) Short-range (e.g. indoor) RF LoS does not require visual LoS. Long-range RF LoS requires obstructionfree visual LoS. Obstructions in or near the LoS path will degrade or prevent RF communication.