ITN 220

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ITN 220

• RF Basics

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This class

• This is the short compilation of a number of
  topics.
• No math (only hints at it)
• Some physics (mostly pictures)
• Stop me when it starts to hurt

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Peroid, Amplitude, Frequency
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The speed of light (or radio)

• 299,792,458 metres per second
• 1,079,252,848.8 km/h
• 186,282.397 mps
• 670,616,629.384 mph
• 983,571,056 fps
• 1 one foot per nanosecond
• 1 nanosecond 1GHz 1 foot antenna
• 2.4 Ghz .416 nanoseconds .409' 4.9

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Phase

• A comparison of two identical waves which denotes
  the amount of delay between them
• Expressed in degrees

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Propagation, Transmission and Radiation

• Propagation The spread of energy into an area or
  space
• Transmission The process of emitting a signal
• Radiation (noun) Energy that is radiated or
  transmitted
• Radiation (verb) The act of propagation

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Reflection

• The act of a propagating wave being thrown back
  from a surface. Involves a radiated pattern
  hitting a surface of another medium or object.

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Refraction

• Refraction The act of bending a signal as it
  passes from one medium into another.

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Diffraction

• The act of a wave pattern bending around an
  object or surface.
• Can create shadows
• Affected by angle
• Output doesn't necessarily contain an entire copy
  of the input (prism effect loss of content)

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Polarization

• The angle at which radio waves propogate. Can be
  expressed as an angle. The receiver must have
  the same polarization as the transmitter.

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Scattering, Absorption, and Polarization

• Scattering - The haphazard separation of a wave
  into components with differing frequences (can
  involve diffraction, reflection, refraction,
  etc.)
• Absorption the retention of radiated energy by
  an object (heat)

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Noise

• Noise the background electrical signals
  (within a specific bandwidth) generated by
  natural and synthetic sources (lightning, sun
  spots, other electronic equipment, radioactive
  decay, diffraction/reflection/refraction of other
  sources, your mom, etc.)
• Noise Floor The minimum level where a signal
  can be differentiated from noise
• Signal-to-Noise Ratio (SNR) A measurement of
  signal quality, expressed as a number

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Pro's/Cons

• Lower frequency signals tend to travel greater
  distances (for a given power)
• Lower frequency signals tend to travel through
  differing media (materials) better
• Higher frequency signals can carry more data
  (bandwidth)

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Gain

• The ratio of an output signal to an input signal.
  Expressed in decibels (dB)
• dBi - a relative measurement of gain as compared
  to an isotropic antenna. Normally used to
  describe the gain of antennas used to receive
  frequencies above 1 GHz.
• dBd - a relative measurement of gain as compaired
  to a half-wave dipole antenna
• dBm - a relative measurement of power, expressed
  in decibels above 1 milli-Watt
• dBm and dBd are used most often

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FHSS

• A spread-spectrum method of transmitting radio
  signals by rapidly switching a carrier among many
  frequency channels, using a pseudorandom sequence
  known to both transmitter and receiver.

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Direct Sequence Spread Spectrum (DSSS)

• A system for generating spread-spectrum
  transmissions. It generates a redundant pattern
  for each bit to be transmitted, called a chipping
  code. Using this, the signal is split over
  several frequencies, and the different parts are
  sent concurrently. This method is faster than
  FHSS, but is more sensitive to environmental
  factors.

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Modulation and Demodulation

• Modulation The process of manipulating the
  frequency or amplitute of a carrier signal so
  that it can carry information
• Demodulation The process of extracting
  information from a modulated signal
• Two Categories of Modulation Analog and Digital

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Analog Modulation

• Amplitude Modulation
• Frequency Modulation
• Phase Modulation
• Quadrature Amplitude Modulation (QAM)

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Amplitude Modulation (AM)

• Where a carrier signal has its amplitude
  modulated to carry information

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Frequency Modulation (FM)

• Where a carrier has its period (frequency)
  modified to carry information

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Phase Modulation (PM)

• Where a carrier has its phase modulated to carry
  information
• Similar to FM except the frequency of the carrier
  signal does not change
• Better suited for digital information

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Quadrature Amplitude Modulation (QAM)

• Where the amplitude of two carriers, 90 degrees
  out of phase with each other, is modulated to
  carry information
• Digital version of QAM combines AM and PM

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Pulse Amplitude Modulation

• The amplitude of a series of pulses carries a
  signal

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Digital Modulation

• Amplitude Shift Keying (ASK)
• Phase Shift Keying (PSK)
• Binary PSK (BPSK)
• Quadrature PSK (QPSK)
• Frequency Shift Keying (FSK)
• Orthogonal frequency-division multiplexing (OFDM)

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Amplitude Shift Keying (ASK)

• An AM signal where amplitude denotes a bit
• Signal/no signal or two different levels of signal

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Phase Shift Keying

• Where a carrier has its phase modulated to carry
  information
• Binary Phase Shift Keying (BPSK)

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Quadrature Phase Shift Keying (QPSK or 4PSK)

• Four phases
• Twice the through put as BPSK for the same
  carrier
• Break the stream into chunks (symbols) and
  indicate them by phase
• 4QPSK (2 carriers) used in Time Division Multiple
  Access (TDMA) 2G phones

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Constellation Diagrams

• Used to map symbols
• Used to describe a combination of digital
  modulations (for streams)
• Pro - more tolerant of noise as detector can be
  configured to choose the closest point
• Con Higher orders more difficult to detect -
  8PSK is normally the highest you will see

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Frequency Shift Keying (FSK)

• A (usually small) shift in carrier frequency
  denoting a binary state
• Used in the GSM mobile phone standard

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Digital QAM

• AM and PSK
• Pro - Even more throughput
• Con More sensitive equipment ()
• Less range
• Example here

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Digital QAM

• Most common forms
• 16-QAM
• 64-QAM
• 128-QAM
• 256-QAM

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Orthogonal Frequency Division Multiplexing

• For Wi-Fi, QAM is used as a modulation scheme for
  sub-carriers
• higher throughput for the same bandwidth (b vs.
  g)
• can be done with one radio
• Tolerant of multi-path and narrow-band
  interference
• Used in ADSL, 802.11g, WiMAX, MBWA, PLC

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Radios

• 802.11b
• CCK (a form of QPSK) 1, 2, 5.5, 11 Mbps
• 802.11a
• OFDM 6, 9, 12, 18, 24, 36, 48, 54 Mbps
• 802.11g
• CCK 1, 2, 5.5, 11 Mbps
• OFDM 6, 9, 12, 18, 24, 36, 48, 54 Mbps
• 802.16 (Redline, Proxim)
• 64 QAM, 16 QAM, QPSK, BPSK

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Antenna

• An arrangement of conductors that generate a
  radiating electromagnetic field in response to an
  applied signal or can be placed in an
  electromagnetic field so that the field will
  induce a signal between its terminals.

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Resonant Frequency

• Each antenna has a resonant frequency which is
  related to its electrical length.
• Antennas can be resonant on harmonic frequencies
  (1/2, 1/4, 1/8 - wave)
• Some antenna designs have multiple resonant
  frequencies and can be used over a wide range of
  frequencies
• Note resonant frequency is not limited to
  antennas (e.g., trees)

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Antenna Bandwidth

• The range of frequencies over which an antenna is
  effective
• High gain antennas have narrow bandwidth
  reception properties

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Radiation Pattern

• The radiation pattern is a graphical depiction of
  the relative field strength transmitted from or
  received by the antenna.

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Polarization

• The orientation of the electric field of the
  radio wave with respect to the Earth's surface.
• Determined by the physical structure of the
  antenna and by its orientation.
• A simple straight wire antenna will have one
  polarization when mounted vertically, and a
  different polarization when mounted horizontally.
• Can be expressed as an angle
• Transmitting and receiving ends must have the
  same polarization to work

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Basic Antenna Models

• Isotropic - A purely theoretical antenna that
  radiates equally in all directions.

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Dipole Antenna

• The most simple practical (real world) antenna.
  Comprised of two wires pointed in opposite
  directions arranged either horizontally or
  vertically, with one end of each wire connected
  to the radio and the other end hanging free in
  space. Alternate form the whip antenna.
• Also used as reference model for other antennas
  gain with respect to a dipole is labeled as dBd.

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The Electrically Short Antenna

• An open-end wire far less than 1/4 wavelength in
  length - in other words only one end of the
  antenna is connected to the radio, and the other
  end is hanging free in space. Electrically short
  antennas are typically used where operating
  wavelength is large and space is limited, e.g.
  for mobile transceivers operating at long
  wavelengths.
• Low gain but easy

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Loop Antenna

• Loop antennas have a continuous conducting path
  leading from one conductor of a two-wire
  transmission line to the other conductor

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Parabolic Antenna

• The parabolic antenna is a special antenna where
  a reflector dish is used to focus the signal from
  a directional antenna feeder.

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Fresnel Zone

• (Augustin-Jean Fresnel, France, 1788-1827) - the
  optimal area between a transmitter and a receiver
  that must remain clear for a true signal to be
  received (no diffraction, reflection,
  diffraction, etc.). Note the width of the zone
  is dependent on distance.