WINA Webinar Presentation - Reliability of Wireless Mesh in Ind Environs

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WINA Webinar Presentation - Reliability of Wireless Mesh in Ind Environs Powered By Docstoc
					The Reliability of
Wireless Mesh
Networks in Industrial
Environments
Brian Cunningham
                                             Agenda

 Modulation Techniques
  – Fixed Frequency Radio
  – Frequency Hopping, Direct Sequence and OFDM
  – Frequency Choices
 Range and Interference
  –   Comparing Radios
  –   How to Determine Range
  –   Software Propagation Studies
  –   Dealing with Interference
 Topologies and Mesh Performance
  – Topologies
  – Mesh Advantages and Disadvantages
  – Mesh Application Lessons

                                                      2
                                                   Fixed Frequency Radio


                                                                                Interference
                                                                                enters
                                                                                the bandwidth
                                                         100%



                                                 Percentage                            Signal integrity drops
                                                  of signals                           to zero almost
                                                                                       immediately when
                                                   with no                             interference enters the
    5         Interference
Watts           outside
                                                  collisions                           bandwidth of this radio
               bandwidth                         and errors
   4                                                       0%

                                Allocated Freq.                            Bandwidth (MHz)
   3
                                457.8250                        Interference Increases Across Bandwidth
                                Bandwidth 25KHz wide
   2                            (or 12.5KHz)


   1
                                   Bandwidth
                                   (MHz)
   0



        450              457.825           470
                      Bandwidth (MHz)

                                                                                                                 3
                               Multi-pathing



                         Original
                         Signal


                         Added to
Tx                       Reflection



                          Equal
 …now what if we could    s
 change frequencies…
                                               4
                  Spread Spectrum Introduction


 FCC allocated a portion of the 900MHz band, then
  later 2.4GHz and later 5GHz.
 Created Rules Manufacturers Must Adhere to:
   –   1W of Transmit Power
   –   FH or DS or OFDM
   –   FCC will not referee in case of interference from others
   –   Many other technical requirements
 Manufacturers Must Submit Prototype for Testing
 FCC then Certifies, and Assigns ID to Appear on
  Label
 Radio can then be Used by Anyone, Anywhere (in
  the US)

                                                                  5
                                           Frequencies

• Lower Frequencies:
   – propagate further
   – penetrate objects better
   – 900 band is 26MHz wide
• 2.4GHz:
                                  900MHz
   – used by microwave
     ovens (rain fade on
     longer links)
   – is license free around the
     world                        2.4GHz
   – 2.4 band is 81MHz wide
• 5.8GHz
   – brand new ISM band
                                  5.8GHz
                                                         6
                      Direct Sequence Spread Spectrum

                                                                            Interference
                                                                               enters
                                                                           the bandwidth


                                                               100%
   1 Watt


                                                         Percentage
                                                          of signals
                                                           with no
                                                         collisions &
                                                            errors

Transmit                               Interference
                                         outside
 Power
                                        bandwidth
(Watts)                                                          0%


                                                                        Interference Increases Across Bandwidth



                1 Watt of power “spread”
                 across wide bandwidth




   0 Watt
            902MHz                                    928MHz
                           Bandwidth (MHz)
                                                                                                           7   7
                                       Frequency Hopping


                                                           Interference
                                                              enters
                                             100%         the bandwidth



                                       Percentage
1 Watt                                  of signals
                                         with no
                                       collisions &
                                          errors




                                               0%


                                                      Interference Increases Across Bandwidth




0 Watt
   902MHz                     928MHz
            Bandwidth (MHz)                                                               8   8
                                                                              OFDM

                                                              Interference
                                                                 enters
                                                                  the
                                                 100%          bandwidth


   1 Watt                                  Percentage
                                            of signals
                                             with no
                                           collisions &
                                              errors




Transmit                                           0%
 Power
(Watts)
                                                          Interference Increases Across Bandwidth




   0 Watt
            902MHz                     928MHz
                     Bandwidth (MHz)

                                                                                              9
                                                    Who will Win?


           Direct Sequence Vs. Frequency Hopping Vs. Orthogonal Frequency
                                                      Division Multiplexing


 FREQUENCY                         BANDWIDTH
   HOPPING
      WAVE



      DIRECT
  SEQUENCE                                                          RF
    CHANNEL                                                         POWER
ORTHOGONAL
 FREQUENCY
     DIVISION
MULTIPLEXING
                                     FREQUENCY
         Interpreting Radio Specifications


 Ignore the range specs – there is no
  standard for comparison
 A well designed radio link has a 20dB fade
  margin to allow for degrading equipment
  and conditions
 For short range applications – this will
  give you the highest signal-to-noise ratio




                                               11
                            Transmit Power


 More power = greater range
 More power = strong S/N ratio
 Transmit power is only half the equation –
  receiver sensitivity is important
 Effective radiated power can be boosted
  by using a high gain antenna
 Does not require fancy antenna work, or
  critical antenna alignment
 Disadvantage is power consumption – if
  battery or solar powered

                                               12
                         Receiver Sensitivity


 Spec’d in –dBm (lower number = better
  sensitivity)
 Ask what the BER is? (bit error rate)
   – BER of 10^6 = 1 errored bit in 1 million
 For multiple over-the-air data rates – ask
  what the sensitivity is for each




                                                13
                802.11 Typical Specification


 802.11a:
     -88dBm @ 6Mbps    Note how the
     -71dBm @ 54Mbps   receiver sensitivity
                        gets worse as the
 802.11b:
                        data rate gets higher
     -95dBm @ 1Mbps
     -90dBm @ 11Mbps   Less time for a
 802.11g:              receiver to determine
     -90dBm @ 6Mbps    if a bit is a “0” or a
     -74dBm @ 54Mbps   “1”




                                                 14
            Range and Over-the-air Data Rate


 High



Baud
Rate




 Low
        Short                  Long
                   Distance
                                               15
                                Frequency and Range

 Lower Frequencies:
   – Propagate further
   – Penetrate objects better
     (air molecules are
     obstructions)
 Higher Frequencies:           900MHz
   – Loses more energy
     after each reflection
   – Results in increasingly
     shorter ranges in non       2.4GHz
     line-of-sight
     applications


                                 5.8GHz
                                                 16
                         How to Determine Range


 Use a functional radio
  system to test
 Should be the same
  model you intend to
  install
   – MUST be same frequency
   – Should be same transmit
     power
   – Should be set to same
     throughput required
 Sometimes antennas
  cannot be elevated as
  high as needed…
                                                  17
Pathloss Study




                 18
Pathloss Study




                 19
                                          Range and Propagation


                                           Circles of Success
Received Signal Strength




                                                  Performance Zone
                                                  Path Engineering Required
                                                  Wireless Conduits up to 20 miles

                                                  Common Sense Zone
                                                  Success with Experience
                                       Receiver   Wireless Conduits up to 1.5 miles
                                      Threshold

                                                  No Worry Zone
                                                  This is “Electricians’ Territory”
                           Distance               Wireless Conduits up to 1/4 mile



                                                                                  20
                                   Interference Mitigation
 Filtering! - the difference between high quality
  radios and the rest
 Single most expensive component on the
  circuit board - however because we’ve already
  done the engineering you need some other
  options:
   – Separation! Locate the antennas at least 6 feet
     vertically or 10 feet horizontally away from other
     antennas
   – Use high gain (narrow beam width) directional
     antennas
   – The higher the transmit power, the greater the
     source of interference - but signal strength drops off
     exponentially with distance
   – The closer to our operating frequency, the less
     effective the filter
   – Switch to another frequency (band)                       21
                                Mesh Topologies


 Point-to-point
 Star
 Mesh

 Mobil vs Fixed Applications
   – Mesh is the only practical method of Mobil
   – Mesh offers redundancy for Fixed Applications
   – More alternative paths = more redundancy = more
     reliability




                                                       22
                             Mesh Advantages


 Automatically re-route Data via Repeaters
 No predictions of which path need to be
  programmed
 Complete freedom to roam (mobile)
 If path degradation occurs due to foliage growth,
  or a new building constructed, re-routing takes
  place
 If background noise levels increase, radio can re-
  route to a closer node




                                                       23
                          Mesh Disadvantages


 Omni antenna use
   – Generally required to allow communication to nodes 360
     degrees
   – Opens that node to interference coming at it from 360
     degrees
   – Should use radio that employs good filters – will be
     expensive
      • Selectivity spec will determine filter quality, but
        rarely published in instrument world
 Traffic congestion at repeater nodes
   – Possible bottleneck of data
       • Slower response time
       • Requires good protocol that can deal with “report by
         exception”
   – If battery powered, reduced battery life                   24
                          Mesh Lessons Learned


 Background:
  – Large biotech company with multiple buildings on a
    campus
  – Thousands of temperature chambers (fridges, freezers
    and incubators) storing research material
  – Research material must be kept at specific temperature
  – Chambers on castor wheels, moved from lab to lab, to
    other buildings, sometimes to a freezer farm, at will of
    the lead researcher in charge
  – Desired alarming on temperature, plus monitoring of
    compressor currents, door open/closed, etc.
  – Hardwiring just not practical



                                                               25
                            Mesh Lessons Learned


 Dedicate some radios as repeaters
   – Random movement of chambers meant repeaters could
     not be guaranteed
   – Possible that some nodes could get overwhelmed with
     traffic
   – Boils down to reliability that a mesh will provide – if your
     repeater walks away, not so reliable
 Over-the-air Diagnostics are valuable (very)
   – Remote configuration, diagnostics and firmware
     upgrades
   – Some chambers could not be located
   – Campus large requiring travel time
   – Some areas were off-limits or buildings locked

                                                                    26
                         Mesh Lessons Learned


 High Transmit Power makes a Mesh more
  Reliable (and Simpler)
  – 50 or 100mW of transmit power could not go through
    many walls – take advantage of FCC’s allowable 1W
  – Short range required more repeaters, roaming area
    smaller
      • Left dead zones in basements and building shadows
  – 2.4GHz offering had shorter range than 900MHz or other
    lower frequencies and interfered with Wifi
 Do a Site Survey in Advance
  – Will catch any interference that would cause problems
      • Enables you to select a different frequency in
        advance
  – Shows up dead zones, allows planning for dedicated
    repeaters                                                27
                 Conclusion – Questions?


Contact Info:

Brian Cunningham
Applications Engineer
Port Coquitlam BC
866 713 4409 x 298
Brian.Cunningham@Cooperindustries.com




                                           28

				
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