Cross Polarization Interference Cancellation (XPIC)

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Cross Polarization Interference Cancellation
(XPIC)
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Topics of Discussion

• What is XPIC?
• Examples
• Design Considerations

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General Comments

• Some carriers transport system designers are not
  aware that more than one RF channel may be
  assigned to a path
• Some also believe that if you do assign a second
  channel on a path that another antenna is
  required
• And most do not know about XPIC and what it
  allows a design engineer to accomplish

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Disclaimers

• This presentation is not a sales pitch for NEC
  equipment
• According to Dick Laine at Harris Corporation a
  similar capability is available for their
  Megastar Radio
• According to Floyd Brutout, Alcatel does not at
  this time offer a similar capability

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Disclaimers

• The presenter only has experience with NEC XPIC
  equipment
• Becky Holland and Bruce Blain of NEC wrote an
  article for RadioResourceMagazine
• Information from that article is presented
  with the permission of Bruce Blaine

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 What is XPIC?

• Cross Polarization Interference
  Cancellation (XPIC)
• How does microwave radio having XPIC capabilities
  effectively double the potential capacity of a
  microwave path?

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What is XPIC?

• It allows the assignment of the same frequency to
  both the vertical and horizontal polarization on
  a path
• Where available frequencies are limited then it
  is possible to assign the same frequency twice on
  the same path using both polarizations

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What is XPIC?

• Using standard microwave equipment from any of
  the major manufacturers, if a full block of eight
  frequencies were available for a 6 GHz lower band
  path then eight frequencies could be assigned in
  each direction on the path, four per polarization
  
• Using equipment with XPIC capability sixteen
  frequencies may be assigned each way on the same
  path, eight per polarization

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What is XPIC?

• Standard Frequency Assignments
• 4 Frequencies Horizontal
• 4 Frequencies Vertical

• XPIC Frequency Assignments
• 8 Frequencies Horizontal
• 8 Frequencies - Vertical

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Design Considerations

• The use of XPIC requires very high cross
  polarization discrimination antennas such as
  Andrew HSX-40 dB Cross Polarization
  discrimination
• XPIC should be considered in the initial system
  design retrofitting the equipment with the
  required intra bay cables is not easy after the
  equipment is installed, in fact NEC engineers
  told me that it cannot be retrofitted in the
  field

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Design Considerations

• NEC prefers to have ATPC operational on paths
  using XPIC equipment
• ATPC must be turned ON for both directions of a
  path
• Adjacent frequencies on a path should be
  receiving at nearly the same level in order for
  XPIC equipment to work properly

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Design Considerations

• For Example, if 13T requires ATPC to clear an
  interference case then 12T and 14T are also
  required to use ATPC at the same levels
• Designers must employ XPIC for the protection
  channel and the first operational channel for the
  remaining channels 2 through 7 XPIC may be
  applied on a per channel basis

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Design Considerations

• For circulator coupled XPIC equipment an
  additional 7.1 dB of loss for the transmitters
  and 7.2 dB of loss for the receivers must be
  taken into account in the path calculations
• XPIC equipment will work with one transmit
  antenna and if required a diversity antenna. The
  three-antenna configuration required by some
  equipment manufacturers because of
  intermodulation is not required

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Discussion, Questions, Comments