Understanding RF Fundamentals and the Radio Design of ...

1 Fred Niehaus RF Fundamentals and the Radio Design of Wireless Networks 2010 Cisco and/or its affiliates. All rights PublicPresentation_ID2 Session Agenda -Objectives What is Radio how did we get here? Basic Radio Hardware & Terminology Antenna Basics Single & Diversity Antennas Interpreting antenna patterns Cisco Richfield Facility Diversity, Multipath, RF characteristics Choosing the right Access Point 2010 Cisco and/or its affiliates. All rights PublicPresentation_ID3 What is Radio ? How did we end up on these frequencies? 2010 Cisco and/or its affiliates. All rights PublicPresentation_ID4 Basic Understanding of How fast the AC current goes is its frequency AC is very low frequency 60 Hz (Cycles Per Second) Radio waves are measured in kHz, MHz and GHzThe lower the frequency the physically longer the Radio wave Higher frequencies have much shorter waves as such take more power to move them greater distances.

2 This is why GHz goes further then 5 GHz (given same amount of RF power) Popular Radio Frequencies:AM Radio 1100 kHz ( MHz)Shortwave 3-30 MHzFM Radio 88-108 MHzWeather Radio MHzCellular Phones 800-900 5 GHzBattery is DCDirect CurrentTypical home isAC Alternating CurrentAC Frequency 60 Hz or 60 CPS Cycles Per Second Waves travel back and forth so fast they leave the wireVintage RF Transmitter 2010 Cisco and/or its affiliates. All rights PublicPresentation_ID5A Radio needs a proper antennaCisco antennas are identified by colorBlue indicates 5 GHz Black indicates GHzAs the frequency goes up the radiating element gets smallerAntennas are custom made for the frequency to be used. Some antennas have two elements to allow for both frequencies in one antenna housingOmni-Directional antennas like the one on the left, radiate much like a raw light bulb would everywhere in all directions Directional antennas like this Patch antenna radiate forward like placing tin foil behind the light bulb or tilting the lamp shade Note: Same RF energy is used but results in greater range as its focused at the cost of other coverage areas 2010 Cisco and/or its affiliates.

3 All rights PublicPresentation_ID6 Complex Modulation SchemesRadio technology has a lot in common with that old twisted pair phone line that started out at 300 baud and then quickly increased In order to get faster data rates, (throughput) into the Radio signal, complex modulation schemes as QPSK or 64 bit QAM is speaking, the faster the data rate the more powerful signal needs to be at the receiver to be decoded. Take-away here is that is a method of using special modulation techniques and *not* specific to a frequency like or 5 can be used in either bandQAM or Quadrature Amplitude Modulation is one of the fastest modulation types actually sending two signals that are out of phase with each other and then somehow putting all the pieces back together for even greater throughput.

4 This is one of the advantages of Example of Modulation Coding Schemes 2010 Cisco and/or its affiliates. All rights PublicPresentation_ID7 The Radio spectrum in the USSource US Department of Commerce 2010 Cisco and/or its affiliates. All rights PublicPresentation_ID8Wi-Fi Radio Spectrum Wi-Fi is unlicensed so it doesn t show up in the overall spectrum allocation as a serviceBut it has beginnings in the ISM (industrial Scientific Medical) band where it was not desirable or profitable to license such short range devices. The first frequencies available for Wi-Fi use was in the GHz rangeAs Wi-Fi popularity and usage increased the FCC allocated additional spectrum in the 5 GHz spectrum we use today is also used by Amateur (Ham Radio ) and other services such as Radio location (radar).

5 There is more bandwidth in 5 GHz and mechanisms are in place to co-exist with services such as radar GHz5 GHz 2010 Cisco and/or its affiliates. All rights PublicPresentation_ID9Wi-Fi Radio Spectrum Even today many portable devices in use are limited to GHz only including newer devices but this is changing is GHz is 5 (can be either band) or 5 GHzThe GHz spectrum has only (three non-overlapping channels 1,6 and 11 (US)There are plenty of channels in the 5 GHz spectrum and they do not GHz and 5 GHz are different portions of the Radio band and usually require separate antennasMost if not all 5 GHz devices also have support for GHz however there are still many GHz only devices. 2010 Cisco and/or its affiliates. All rights PublicPresentation_ID10 Basic RF terminology and Hardware identification 2010 Cisco and/or its affiliates.)

6 All rights PublicPresentation_ID11 Common RF terms Attenuation a loss in force or intensity As Radio waves travel through objects or in media such as coaxial cable attenuation occurs. BER Bit Error Rate -the fraction of bits transmitted that are received incorrectly. Channel Bonding act of combining more than one channel for additional bandwidth dBd abbreviation for the gain of an antenna system relative to a dipole dBi abbreviation for the gain of an antenna system relative to an isotropic antenna dBm decibels milliwatt --abbreviation for the power ratio in decibels (dB) of the measured power referenced to one milliwatt of transmitted RF power. Isotropic antenna theoretical ideal antenna used as a reference for expressing power in logarithmic form.

7 MRC Maximal Ratio Combining a method that combines signals from multiple antennas taking into account factors such as signal to noise ratio to decode the signal with the best possible Bit Error Rate. Multipath refers to a reflected signal that combines with a true signal resulting in a weaker or some cases a stronger signal. mW milliwatt a unit of power equal to one thousandth of a watt (usually converted to dBm) Noise Floor The measure of the signal created from the sum of all the noise sources and unwanted signals appearing at the receiver. This can be adjacent signals, weak signals in the background that don t go away, electrical noise from electromechanical devices etc. Receiver Sensitivity The minimum received power needed to successfully decode a Radio signal with an acceptable BER.

8 This is usually expressed in a negative number depending on the data rate. For example the AP-1140 Access Point requires an RF strength of at least negative -91 dBm at 1 MB and an even higher strength higher RF power -79 dBm to decode 54 MB Receiver Noise Figure The internal noise present in the receiver with no antenna present (thermal noise). SNR Signal to Noise Ratio The ratio of the transmitted power from the AP to the ambient (noise floor) energy present. TxBF Transmit beam forming the ability to transmit independent and separately encoded data signals, so-called streams, from each of the multiple transmit antennas 2010 Cisco and/or its affiliates. All rights PublicPresentation_ID12 Identifying RF connectorsRP-TNC ConnectorUsed on most Cisco Access Points N ConnectorUsed on the 1520 Mesh and 1400 Bridge SMA Connector Pig tail type cable assemblies RP-SMA ConnectorUsed on some Linksys Products 2010 Cisco and/or its affiliates.

9 All rights PublicPresentation_ID13 Identifying different cable typesLMR-400 Foil & shieldLMR 1200 inch Heliax(Hardline)Leaky Coax shield cut away on one side 2010 Cisco and/or its affiliates. All rights PublicPresentation_ID14 Antenna Cables LMR SeriesThis is a chart depicting different types of Times Microwave LMR Series coaxial uses Times Microwave cable and has standardized on two types: Cisco Low Loss (LMR-400) and Cisco Ultra Low Loss (LMR-600). LMR-600 is recommended when longer cable distances are requiredLarger cables can be used but connectors are difficult to find and install 2010 Cisco and/or its affiliates. All rights PublicPresentation_ID15 Antenna CablesLMR-400 is 3/8 inch Cisco Low Loss LMR-600 is inch Cisco Ultra Low LossTrivia: LMR Stands for Land Mobile Radio 2010 Cisco and/or its affiliates.

10 All rights PublicPresentation_ID16 Antenna Cables -PlenumIf the cable is ORANGE in color it is usually Plenum Rated. Plenum is the air-handling space that is found above drop ceiling tiles or below of fire regulations this type of cable must burn with low smokeThe 3 Ft white cable attached to most Cisco antennas is plenum outdoor cable (black) is not PlenumPlenum cable is more expensive 2010 Cisco and/or its affiliates. All rights Antenna basics 2010 Cisco and/or its affiliates. All rights PublicPresentation_ID18 Antenna basics Antenna -a device which radiates and/or receives Radio signals Antennas are usually designed to operate at a specific frequency Wide-Band antennas can support additional frequencies but it s a trade-off and usually not with the same type of performance.