RF and Radio Technology Fundamen

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RF and Radio Technology Fundamen Powered By Docstoc
					Radio Frequency (RF) and Radio Technology
The Concept of Wireless Point-to-Point (PTP, PP)

     One location to one location
     Dedicated access
      > Full bandwidth between two locations

The Concept of Wireless Point-to-Multipoint

      One location to many locations;
       Many locations to one location
      Shared access
        > Shared bandwidth between multiple locations
                                                        Indoor Wireless LAN

    Outdoor Point-to-Multipoint

The Concept of Line-of-Sight (LOS)

     No obstructions between each end
       > No trees
       > No buildings
       > No mountains
           Can you go through a window?
                Probably, but with added losses that are hard to predict:
                   » Plan on 10dB as an initial guess, can be greater for
                     reflective (metallic) tinted glass

      Note: The lower the frequency, the better it will travel through obstacles

The Line-of-Sight Issue - raising one side

     A structure can be erected to establish line-of-sight over

The Line-of-Sight Issue – raising two sides

     Two structures can be erected to establish line-of-sight over

The Line-of-Sight Issue – using a repeater

     A system approach called a “repeater” can establish line-of-sight
      to go around or over obstacles
      > Active repeaters (two radio systems back-to-back)
      > Passive repeaters (one radio system redirected)

The Hertz Measurement of Frequency

     1 Hertz (Hz) = 1 cycle/second
      > 1,000 Hz = 1 kHz
      > 1,000,000 Hz = 1 MHz
      > 1,000,000,000 Hz = 1 GHz



 Directly related to frequency
 Wavelength = the distance required to complete one
  cycle at a particular frequency
    > The distance from Point A to Point B represents one
    > Wavelength is normally measured relative to meters
      (such as cm, or mm)

                                                     A      B


      The location of the traveling wave at a fixed point
       in time
      Measured in degrees or radians, related to Pi ()
      360 Degrees = 1 Cycle                               90°
        > 2 Radians = 360°
        > 57.3° = 1 Radian

                                                      0°     180°   360°


Watts & Decibels: Measurement of Power

      Watt (W)
      Decibel reference to 1 mW (dBm)
      Decibel (dB) - a ratio or difference in power
        > e.g. 20dBm is 3dB less than 23dBm

                   Conversion equations
                     x(dbm) = 10logy(mW)
                     y(mW) = 10x(dBm)/10

 Watts vs. dBm

                 100 W   50 dBm

                 10 W    40 dBm
                  2W     33 dBm
                  1W     30 dBm

             100 mW      20 dBm

                 1 mW    0 dBm
             100 uW      -10 dBm

            0.001 nW     -80 dBm
Power and Directivity

      Without obstructions and with high intensity and beam focus, RF can
       travel long distances
       > Power is measure of strength
       > Gain is measure of amplification

How Much Power is a Watt?

                        A standard microwave oven has an
                         output power of 700 to 1500 Watts
                        A typical cell phone has an output
                         power in the range of 0.1 to 0.2 Watts
                        Proxim's highest output power radio
                         devices are our outdoor radios that
                         operate at 2.4 GHz and have no
                         greater than 1 Watt output power
                        Proxim‟s indoor wireless systems and
                         our 5 GHz outdoor systems have
                         substantially less power, typically in the
                         range of 0.01 to 0.2 Watts

Concept: Microwaves Behave Similar to
Visible Light & Sound

                          They propagate in air similar to light and sound
                           > Reflect off surfaces
                           > Absorbed by surfaces
                           > Diffuse and refract through substances

 Transmitting source
 (e.g., car headlight)
                                                    Signal is more concentrated
                            Point A       Point B   at Point A than at Point B

RF Refraction and Scattering

      RF can pass through materials which will change it‟s direction of
       travel (called „refraction‟)
      RF can pass through materials which will diffuse the energy (scatter)
       to a wider beam

                                            Away from
                   Air (medium 1)          Perpendicular


                                              Water (medium 2)
                Actual Position

Reception:RF ~ Vision:Light

      Reception of RF can be affected by “vision-related” components
       > “Blinders”
       > Angle of attack
       > Focus
       > Obstructions
       > Weather

RF is Attenuated (Relative to Frequency)
by Rainfall

                             Signals above 11 GHz can be
                              severely affected
                             Most of Proxim‟s products operate
                              below 6 GHz and are virtually
                              unaffected by rainfall in most parts
 =7dB/mile                   of the world


Obstructions Will Stop or Seriously
Attenuate Signals

      Some RF can travel easily
       through walls, stone, etc. and
       some will be immediately
      Partial obstructions can
       dramatically reduce wave

RF Reflection and Multipath

                          RF can “bounce” off objects like
                           buildings and mountains, water
                           and atmosphere

                          Different paths of RF will arrive
                           at destination at different times -
                           this is called „multipath‟

The Importance of Signal Phase

     Best Case: Even number of ½ Wavelengths



               +                 =

      -x   _

 The Importance of Signal Phase

     Worst Case: Odd number of ½ Wavelengths



                 +                =
         x   _

        -x   _

Fresnel Zone

      The Fresnel zone is additional path clearance that is required to
       optimize radio reception
      There are an infinite number of points where reflected signal arrives
       exactly ½ wavelength out of phase for a given frequency

Earth Curvature and k factor

      One factor for line-of-sight includes earth curvature and the
       effects of the atmospheric refraction due to the curve of the
       earth‟s surface
        > The earth‟s bulge between the end points must be considered when
          determining if LOS and proper path clearance exists, including Fresnel
        > The k factor (refraction index) is a mathematical figure that will help
          determine the effect on path clearance
             Not much of a factor under 10 miles


      Polarization describes the orientation of the E (electrical) and H
       (magnetic) components of an RF wave front.
        > Linear polarization (horizontal, vertical, slant linear)
        > Circular polarization (right-hand, left hand)

      RF can be transmitted (and received) with dominant polarization

        > Polarization provides a level of discrimination (attenuation) against
          different polarization signals, especially “opposite” polarization (e.g.
          horizontal versus vertical)

      Weather and multipath can “de-polarize” RF

Terrain Effects on RF

                         Mountainous terrain is best
                           > Many multipath reflections will not
                             reach the other end, thus reducing
                             the potential for out-of-phase
                             reflected signals that may have
                             degraded the integrity of the direct

                         Flat, smooth terrain is worst
                           > Many multipath reflections may reach
                             the other end, thus increasing the
                             potential for out-of-phase reflected
                             signals that may degrade the integrity
                             of the direct signal

Climate Effects on RF

      Humid climate is worst
        > More moisture = more ducting and refraction = more attenuation

      Dry climate is best
        > Reduced moisture = less ducting and refraction = less attenuation

Overall Spectrum

               Radio          UHF TV         Remote Controls
           550 - 1700kHz    460-600MHz       100GHz-500THz Medical X-ray

     VLF    LF   MF   HF   VHF   UHF   SHF   EHF   Infrared   Visible   UV   X   Gamma   Cosmic

                   FM Radio
        Sound     88-108 MHz                              Light
     20Hz - 20kHz   VHF TV                           700THz - 1000THz
                  54-220 MHz

                             Cellular 800-900 MHz
                                 PCS 1.8-2 GHz
                        Terrestrial Microwave 1–18 GHz
                      Indoor Wireless 900 MHz, 2 & 5 GHz

USA Frequency Allocations

Types of Spectrum

      License-exempt
        > Anyone can use
        > No coordination or registration required
        > Opportunity for interference, which the user must work around
      Licensed (or „Leased‟)
        > Coordination required
        > Registration required
        > Interference is better controlled, but not completely eliminated
            Regulatory agency will assist with any interference cases
      Owned
        > Purchased spectrum, usually in a given region, usually by auction
        > Owner needs to self-coordinate intra-system interference potential
        > Some coordination may be needed with neighboring owners

 Primary License-Exempt Bands

      Three primary ISM (Industrial, Scientific, Medical) bands:
        > “900” MHz
            902-928 MHz
        > “2.4” GHz
            2400-2483.5 MHz
        > “5.7” or “5.8” GHz
            5725-5850 MHz
      Three primary U-NII (Unlicensed National Information Infrastructure)
        > “5.2” GHz (or “Lower 5”)
            5150-5250 MHz, indoor only
        > “5.3” GHz (or “Middle 5”)
            5250-5350 MHz, indoor and low-power outdoor
        > “5.7” or “5.8” GHz (or “Upper 5”)
            5725-5825 MHz (higher power, outdoor)
The Concept of Interference

      Interference is the reception of signals from sources other than the
       intended source
        > The source of the interference may be from a closer and/or stronger
          signal level compared to the desired signal impacting the ability of the
          system to receive the desired signal properly

      Interference can be caused by energy that is at the same frequency
       as the signal that you wish to receive, or can be at a nearby frequency
       with enough energy to „leak‟ into the receiver
      Interference can also be caused by energy that is a completely
       different frequency from that which you wish to receive. High-powered
       transmitters can radiate „harmonics‟ where they are also inadvertently
       transmitting energy that is a multiple of the intended transmitter

Methods of Two-Way Communications

      Frequency Division Duplex (FDD)
       > Communications in one direction are at a different frequency than in the
         other direction, transmitting and receiving in both directions at the same time
           Can establish high speeds in both directions (usually equivalent speed)
           No substantial time delays (latency) for communication, as no information
            is buffered
           The difference in frequency can be small (a few MHz) or large (100‟s of
            MHz), in the same frequency band or different bands altogether
      Time Division Duplex (TDD – or „Ping Pong‟)
       > Communications in one direction are at a different time than in the other
         direction, transmitting and receiving at the same frequency but in succession
           Can provide unbalanced communications when desired (e.g. more
             download than upload, or variable to demand)
           Has an impact on latency

Connected or Connectorized Antenna

      Some Proxim products have built-in antennas that cannot be removed
       or bypassed
      Some Proxim products have built-in antennas that can be bypassed
       and an alternate antenna connected instead
      Some Proxim products do not have a built-in antenna; an antenna
       must be connected, usually with a cable between the antenna
       connector and the radio

                                             Connectorized Antenna Configurations
         Connected Antenna Configurations

One-Piece and Two-Piece Construction

  For Proxim‟s outdoor wireless solutions,
   one end of the radio system is made up
   of one or two distinct boxes
     > One-piece radios are designed for all-indoor
       mounting (or mounting in a weatherproof
     > Two-piece radios give the flexibility of
       mounting part of the system closer to the             2-piece configuration
         In some cases, the antenna may be
          integrated as part of the radio to help ease
          cabling and minimize attenuation of the
          cable between the antenna and the radio
                                                         1-piece configuration

Antenna Performance Parameters

      Gain
      Beamwidth/Coverage Pattern
      Polarization

What Governs Distance or Coverage?

      The radio‟s technology (sometimes)
      The “strength” of the transmitted signal
      The radio‟s „threshold‟ specifications
      The radio‟s frequency of operation
      Output power regulations
      Obstacles between the end points
      Climate/Terrain
      The antenna pattern

Basic Distance Planning:
A Series of Gains and Losses

             Antenna     Path    Antenna
              (Gain)    (Loss)    (Gain)

 Transmission                           Transmission
   Line (Loss)                          Line (Loss)

           Radio                     Radio
       (Output Power)             (Threshold)

Understanding “System Gain” and “Fade

      System Gain
       > The difference between the output     Output
         power and the threshold               Power
      Fade Margin
       > The difference between the received
         signal level and the threshold


                       Received Signal Level (RSL)

Understanding “Availability”

      The predicted amount of time the system will be operating above
        > Availability is the primary design criteria for outdoor wireless

               99.999% = 5.26 minutes/year outage
               99.995% = 26.28 minutes/year outage
               99.950% = 262.8 minutes/year outage