Cross Polarization Interference Cancellation (XPIC)

Topics of Discussion What is XPIC? Examples Design Considerations

General Comments Some carrier’s 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

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

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

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

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

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

What is XPIC? 4 Frequencies – Horizontal 4 Frequencies – Vertical Standard Frequency Assignments 4 Frequencies – Horizontal 4 Frequencies – Vertical XPIC Frequency Assignments 8 Frequencies – Horizontal 8 Frequencies - Vertical

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

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

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

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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