Wireless Networks Past Paper PDF

Handout 4 Radio Frequency Signal and Antenna Concepts Course Name: Wireless Networks Course Code: CSN 405 Notes appended and modified to those accompanying “CWNA Certified Wireless Network Administrator: Official Study Guide”, D. Coleman & D. Westcott, John Wiley & Sons - Sybex, 6th Ed., 2021, Ch....

Handout 4 Radio Frequency Signal and Antenna Concepts Course Name: Wireless Networks Course Code: CSN 405 Notes appended and modified to those accompanying “CWNA Certified Wireless Network Administrator: Official Study Guide”, D. Coleman & D. Westcott, John Wiley & Sons - Sybex, 6th Ed., 2021, Ch. 5 Chapter 5 Overview • • • • • • • • Active and Passive Gain Azimuth and Elevation Charts Interpreting Polar Charts Beamwidth Antenna Types Visual Line of Sight RF Line of Sight Fresnel Zone Certified Wireless Network Administrator: CWNA – PW0-108 2 Chapter 5 Overview (continued) • • • • • • Earth Bulge Antenna Polarization Antenna Diversity Multiple-Input Multiple-Output (MIMO) Antenna Connection and Installation Antenna Accessories Certified Wireless Network Administrator: CWNA – PW0-108 3 Isotropic Radiator  An isotropic radiator is a point source that radiates signal equally in all directions.  The sun is probably one of the best examples of an isotropic radiator. It generates equal amounts of energy in all directions. 4 Electromagnetic 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 Electric Field Direction Magnetic Field 5 Passive Amplifier Antenna Radios modulate a baseband signal onto an electrical current Radio Transceiver RF Cable The electrical current is carried by a conductive RF cable. Antennas convert electrical current into RF waves. 6 Passive Antenna Gain: dBi and dBd Isotropic Radiator dBi - Decibels relative to an isotropic radiator  Used to measure passive antenna gain  0 dBi = no directivity / passive gain HalfWave Dipole 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 7 Azimuth and Elevation  To assist potential buyers with their purchasing decisions, antenna manufacturers create azimuth charts and elevation charts, commonly known as radiation patterns, for their antennas.  These radiation patterns are created in controlled environments, where the results cannot be skewed by outside influences and represent the signal pattern that is radiated by a particular model of antenna.  These charts are commonly known as polar charts or antenna radiation envelopes. 8 Azimuth and Elevation omnidirectional Elevation semidirectional Azimuth Elevation Azimuth Azimuth chart = H-plane = top-down view Elevation chart = E-plane = side view 9 Azimuth and Elevation Charts • Commonly known as radiation patterns • Created in controlled environments • Also known as polar charts Certified Wireless Network Administrator: CWNA – PW0-108 10 Azimuth and Elevation Charts (continued) • • • • • Azimuth chart = H-plane = top-down view Elevation chart = E-plane = side view Outer ring usually represents strongest signal Scale of chart is in dB from outer ring inward Therefor chart is logarithmic not linear Certified Wireless Network Administrator: CWNA – PW0-108 11 Interpreting Polar Charts • Often misinterpreted and misread • dB aspect of chart is often misunderstood • If you have 4 boxes and each is double the previous, it is simpler to represent them as the first image versus the second 1 2 4 8 16 32 64 128 256 512 • However many people do not realize that the first image is a logarithmic representation, not the actual linear coverage Certified Wireless Network Administrator: CWNA – PW0-108 12 Interpreting Polar Charts (continued) • Left images show logarithmic and linear representation of an omnidirectional antenna • Right images show logarithmic and linear representation of a directional antenna • Remember the 6 dB rule when creating a normalized view of a polar chart Certified Wireless Network Administrator: CWNA – PW0-108 13 Beamwidth • Measurement of how broad or narrow the focus of an antenna is • Measured both horizontally and vertically • Measurement from the strongest point on polar chart to the half power (-3 dB) points • Measured in degrees Certified Wireless Network Administrator: CWNA – PW0-108 14 Beamwidth  Beamwidth is the measurement of how broad or narrow the focus of an antenna is— and is measured both horizontally and vertically. Main lobe 60º Side/back lobes  It is the measurement from the center, or strongest point, of the antenna signal to each of the points along the horizontal and vertical axes, where the signal decreases by half power (–3 dB).  These –3 dB points are often referred to as half-power points. 15 Beamwidth (continued) • Start at the strongest point (1) • On each side, move along the antenna pattern to 3 dB closer to center of polar chart (2) • Draw a line to these points and measure the degrees between the lines (3) Certified Wireless Network Administrator: CWNA – PW0-108 16 Beamwidth (continued) Certified Wireless Network Administrator: CWNA – PW0-108 17 Antenna Types • Omnidirectional – radiates in all directions, provides general coverage • Semidirectional – wide directional focus • Highly directional – narrow directional focus • Antennas focus both transmitted and received signals Certified Wireless Network Administrator: CWNA – PW0-108 18 Antenna Types  Omnidirectional: Antennas that radiate RF in a fashion similar to the way a table or floor-lamp radiates light. They are designed to provide general coverage horizontally in all directions.  Semidirectional: Antennas that radiate RF in a fashion similar to the way a wall sconce radiates light away from the wall or the way a street lamp shines light down on a street or a parking lot, providing a directional light across a large area.  Highly directional: These highly directional antennas radiate RF in a fashion similar to the way a spotlight focuses light on a stage or a sign. 19 Omnidirectional Antennas • • • • • Dipole antenna is typical Coverage pattern is bagel shaped Typically used for point-to-multipoint networks Top view (azimuth) is circular Side view (elevation) is shown below, varies with gain Certified Wireless Network Administrator: CWNA – PW0-108 20 Half-wave dipole antenna Improperly installed Note: For this antenna, Lambda = λ = C/F λ = 3 * 10^8 / 2.4 * 10^9 = 3/24 = 1/8 = 0.125 (m) and λ/4 = 0.03125 (m) = 3.125 cm Certified Wireless Network Administrator: CWNA – PW0-108 21 Semidirectional Antennas • Directs signal in a specific direction • Short to medium distance communications • Three types of antennas Patch – Patch – Panel – Yagi • Planar Antennas (Patch & Panel) • Horizontal beamwidth < 180 degrees Yagi Certified Wireless Network Administrator: CWNA – PW0-108 22 Highly Directional Antennas • Most focused, narrow beamwidth • Strictly point-to-point communications • Two types of antennas – Parabolic Dish – Grid • Grid antenna less susceptible to wind load Grid Certified Wireless Network Administrator: CWNA – PW0-108 23 Sector Antennas • High-gain, semidirectional • Generates very little RF signal behind the antenna (back lobe) • Pie-shaped coverage – 60 to 180 degrees • Sectorized array – multiple sector antennas installed as a group to provide 360 degrees of horizontal coverage • Narrow vertical beamwidth – 7 to 17 degrees (slight downtilt) Certified Wireless Network Administrator: CWNA – PW0-108 24 Antenna Arrays • Group of two or more antennas integrated to provide coverage • Perform beamforming – concentrating RF energy • Three types of beamforming • Static • Dynamic • Transmit Certified Wireless Network Administrator: CWNA – PW0-108 25 Static Beamforming • Using directional antennas to provide a fixed radiation pattern • Another term for sectorized array • Slight overlap between antenna patterns can improve roaming Certified Wireless Network Administrator: CWNA – PW0-108 26 Dynamic Beamforming • Focuses the RF energy in a specific direction and particular shape in the direction of an individual client • Broadcast frames are sent omnidirectionally • Pattern can change on a frame-by-frame basis • Uses an adaptive antenna array • Known as smart antenna technology or beamstearing Certified Wireless Network Administrator: CWNA – PW0-108 27 Transmit Beamforming (TxBF) • Multiple phase-shifted signals are transmitted to arrive in-phase at the location of the receiver • A digital signal processing technology • Technically not an antenna technology • 802.11n amendment defines two types – Implicit TxBF (uses an implicit channel-sounding process to optimize the phase difference of the transmitted chains) – Explicit TxBF (uses feedback from the user station to determine the amount of phase shift required for each signal) Certified Wireless Network Administrator: CWNA – PW0-108 28 Visual Line of Sight (LOS) • Perceived straight line that light travels along • Due to refraction, diffraction, and reflection, there is a slight chance that it is not • Has no bearing on successful RF transmission Certified Wireless Network Administrator: CWNA – PW0-108 29 Indoor Antennas – Directional  It is common for patch antennas to be connected to access points to provide directional coverage within a building.  Because Omnidirectional antennas often have difficulty providing effective RF coverage in areas with shelving.  MIMO patch antennas, such as the one shown, can be used effectively in libraries, warehouses, and retail stores with long aisles of shelves. 30 Indoor Antennas – Directional Another common use case for deploying MIMO patch antennas indoors is in very high- density (VHD) environments.  The use of directional antennas reduces Cochannel Interference, CCI, especially when a 40 MHz channel reuse pattern is deployed.  Directional antennas are often used in very high density environments to sector the coverage.  Examples: lecture halls, gymnasiums, libraries, cafeterias, etc. 31 Outdoor – Semidirectional  Yagi and sector antennas  Used for building-to-building WLAN communications 32 Downtilt 0° Angle of Downtilt  Antenna downtilt is a vertical alignment principle designed to point the antenna’s main lobe in the proper direction  The downtilt angle is determined by the antenna height (at both locations, if bridging two radios) and distance 33 Outdoor – Highly Directional Root bridge Non-root bridge  Dish and grid antennas  Used for long-distance point-to-point bridge links 34 Polarization  Describes the antenna structure or the orientation of an antenna’s wave oscillations  Determined by the E-field  Polarization of Tx and Rx antennas should match When discussing antennas, the proper term is antenna polarization, which refers to the alignment or orientation of the waves. The use of the term polarity is incorrect. Polarity refers to positive or negative voltage, which has no relevance to antenna orientation. 35 Antenna Polarization • Orientation of the amplitude of the RF waves – Vertical – Horizontal • Transmitting and receiving antennas must have the same orientation • “Antenna Properties.wmv” from the book’s website www.sybex.com/go/cwna3e presents this well Certified Wireless Network Administrator: CWNA – PW0-108 36 RF Line of Sight • Required unobstructed LOS between two antennas • Additional area needed around the visual LOS • Additional area = Fresnel zone Certified Wireless Network Administrator: CWNA – PW0-108 37 Fresnel Zone • Imaginary American football-shaped area that surrounds the visual LOS between two point-to-point antennas • Theoretically an infinite number of zones • Closest zone is the first Fresnel zone • First two zones are most relevant • Only frequency and distance affect size of Fresnel zone (unaffected by antenna gain) Certified Wireless Network Administrator: CWNA – PW0-108 38 Fresnel Zone (continued) • Obstruction of first Fresnel zone will negatively influence the integrity of the RF communication • Obstruction decreases the energy of the received signal • Ideally no obstructions at all • > 40 percent obstruction will likely make the link unreliable Certified Wireless Network Administrator: CWNA – PW0-108 39 Fresnel Zone Formula (at midpoint) Radius of first Fresnel Zone radius = 72.2 x [D÷ (4 x F)] D = distance of the link in miles F = transmitting frequency in GHz Minimum clearance formula (60% unobstructed) radius (60%) = 43.3 x [D ÷ (4 x F)] D = distance of the link in miles F = transmitting frequency in GHz Certified Wireless Network Administrator: CWNA – PW0-108 40 Fresnel Zone Formula (at any point) Radius of first Fresnel Zone at any point radius = 72.2 x [(N x d1 x d2) ÷ (F x D)] N = which Fresnel zone you are calculating (usually 1 or 2) d1 = distance from one antenna to the location of the obstacle in miles d2 = distance from the obstacle to the other antenna in miles D = total distance between the antennas in miles (D = d1 + d2) F = frequency in GHz Certified Wireless Network Administrator: CWNA – PW0-108 41 Fresnel Zone – RF Line of Sight  The first Fresnel zone is technically the area around the point source, where the waves are in phase with the point source signal.  The second Fresnel zone is then the area beyond the first Fresnel zone, where the waves are out of phase with the point source signal.  All the odd-numbered Fresnel zones are in phase with the point source signal, and all the even-numbered Fresnel zones are out of phase. 42 Fresnel Zone Entire Fresnel zone - 100% Fresnel zone - 60% clearance 43 Earth Bulge • Curvature of the earth • Must be considered if link is > 7 miles H = D2 ÷ 8 H = height of the earth bulge in feet D = distance between the antennas in miles • Overall antenna height formula H = obstacle height + earth bulge + Fresnel zone Certified Wireless Network Administrator: CWNA – PW0-108 44 Earth Bulge When you are installing long-distance point-to-point RF communications, another variable that must be considered is the curvature of the earth. FZ3 FZ2 FZ1 H = D2 ÷ 8 H = height of the earth bulge in feet D = distance between the antennas in miles 455 Antenna Diversity • Exists when wireless device has two antennas and receivers functioning together • Pre-802.11n radios use switched diversity • Listens with multiple antennas but only processes the signal with the best amplitude – known as receive diversity • When transmitting, the device will the antenna that was last used to receive – known as transmit diversity Certified Wireless Network Administrator: CWNA – PW0-108 46 Simple Antenna Diversity  Legacy APs: 802.11a/b/g use switched antenna diversity to minimize the negative effects of multipath. 802.11a/b/g WLAN Radio Antennas Antenna Switch Multiple antennas connected to same radio via a single radio chain  When receiving incoming transmissions, switched diversity listens with multiple antennas. Multiple copies of the same signal arrive at the receiver antennas with different amplitudes.  The signal with the best amplitude is chosen, and the other signals are ignored.  This method of listening for the best received signal is also known as receive diversity. 47 Simple Antenna Diversity 802.11a/b/g WLAN Radio Antennas  Switched diversity is also used when transmitting, but only one antenna is used.  The transmitter will transmit out of the diversity antenna where the best amplitude signal was last heard. Antenna Switch Multiple antennas connected to same radio via a single radio chain  The method of transmitting out of the antenna where the last best-received signal was heard is known as transmit diversity. 48 Multiple-Input Multiple-Output (MIMO) • More sophisticated form of antenna diversity • Radio architecture that can receive or transmit using multiple antennas concurrently • Uses complex signal-processing techniques • Enhances – Reliability – Range – Throughput • Used by 802.11n and 802.11ac radios Certified Wireless Network Administrator: CWNA – PW0-108 49 MIMO Antennas • Indoor MIMO Antennas – Typically not much choice – Usually 3 omnidirectional antennas – One antenna vertical, other two slightly tilted • Outdoor MIMO Antennas – Usually 2 antennas per radio – Multipath is provided by using different polarization – Special pairs of omnidirectional antennas provide horizontal and vertical polarization – Directional MIMO antennas incorporated two antenna elements within one physical antenna Certified Wireless Network Administrator: CWNA – PW0-108 50 MIMO Antenna Diversity 802.11n/ac MIMO Radio Antennas  Multiple-input, multiple-output (MIMO) is more sophisticated form of antenna diversity that takes advantage of multipath.  MIMO is a wireless radio architecture that can receive or transmit using multiple antennas concurrently. Multiple antennas connected to multiple radio chains 51 Antenna Connection and Installation • Voltage Standing Wave Ratio (VSWR) • Signal Loss • Antenna Mounting – Placement – Mounting • Indoor mounting considerations • Outdoor mounting considerations – Appropriate use and environment • Ingress Protection Rating (IP Code) • National Electrical Manufacturers Association (NEMA) Enclosure Rating • "Appareils destinés à être utilisés en ATmosphères Explosives" (ATEX) Directives • National Electrical Code (NEC) hazardous locations Certified Wireless Network Administrator: CWNA – PW0-108 52 Antenna Connection and Installation (continued) • Antenna Mounting (continued) – Orientation and alignment – Safety – Maintenance Certified Wireless Network Administrator: CWNA – PW0-108 53 Antenna Accessories • • • • Cables Connectors Splitters Amplifiers – Fixed-gain – Fixed-output • Attenuators • Lightning arrestors • Grounding rods and wires Certified Wireless Network Administrator: CWNA – PW0-108 54 RF Connectors 55 RF Cabling Outer jacket Braided shield Inner Conductor  Cable introduce signal loss into a communications link.  Higher the grade of cable, the less the loss.  Cable must be rated for proper frequency response. 56 Impedance  Access Point connectors  Cabling  Connectors  Antennas 50 Ohms 50 Ohms  Impedance is a value of ohms of electrical resistance to an AC signal.  Impedance must match when connecting RF equipment. 57 Regulatory Compliance • For an access point manufacturer to sell its product within a country or region, it must prove that its product operates within the rules of the relevant regulatory domain, such as the FCC. • The FCC does allow an antenna to be substituted with a different one, providing two key conditions are met: The gain of the new antenna must be the same or lower than the antenna that the system was certified with. • The new antenna must be of the same type, which means that the antenna must have the same in-band and out-ofband characteristics. • Certified Wireless Network Administrator: CWNA – PW0-108 58 VSWR  Voltage standing wave ratio (VSWR) is a measurement of the change in impedances to an AC signal. 50 Ohms  Voltage standing waves exist because of impedance mismatches or variations between devices in an RF communications system.  When the transmitter generates the AC radio signal, the signal travels along the cable to the antenna. Some of the energy is reflected back toward the transmitter because of impedance mismatch. 75 Ohms 59 VSWR VSWR is a ratio measurement of an impedance mismatch:  1:1 (no impedance) being optimal but unobtainable.  Typical values range from 1.1:1 to as much as 1.5:1.  VSWR military specs are 1.1:1. 50 Ohms Negative effects of VSWR:  Decreased signal amplitude (return loss)  Erratic signal amplitude  Transmitter or amplifier failure 75 Ohms 60 Lightning Arrestors  Bi-metal conductors or gas discharge tubes  Detect incoming over-voltages induced by nearby lightning strikes  Shunt the current to earth ground  Cannot fully protect against a direct lightning strike Coaxial Gas Discharge Tube Surge Protectors 61 Lightning Protection WLAN Bridge Lightning Arrestor Antenna Partially Protected Network Segment Copper Copper / Fiber Transceiver Fiber Fully Protected Network Segment Ground Wire Copper / Fiber Transceiver Grounding Rod 62 FCC Certified System  Regulators require wireless systems to be authorized as a system  Use of non-certified equipment with an intentional radiator must follow specific guidelines  Third-party antennas may be used (in FCC) with restrictions  The FCC maintains public documents about authorized equipment 63 Indoor AP and Antenna Mounting 64 Chapter 5 Summary • • • • • • • • Active and Passive Gain Azimuth and Elevation Charts Interpreting Polar Charts Beamwidth Antenna Types Visual Line of Sight RF Line of Sight Fresnel Zone Certified Wireless Network Administrator: CWNA – PW0-108 65 Chapter 5 Summary (continued) • • • • • • Earth Bulge Antenna Polarization Antenna Diversity Multiple-Input Multiple-Output (MIMO) Antenna Connection and Installation Antenna Accessories Certified Wireless Network Administrator: CWNA – PW0-108 66 Questions Home Work 1. Open your book and go through all the review questions at the end of the chapter. 2. Review the answers by using Appendix A. 67