Saturday, October 2, 2010

Wi-Fi Tip: 802.11n Outdoor Bridge Links

In order to achieve 300 Mbps raw data link rates on outdoor 802.11n line-of-sight bridge links, polarize one antenna chain horizontally and one antenna chain vertically.

Due to the use of MIMO (multiple input, multiple output) in 802.11n, multiple spatial streams are required in the same time domain. Indoor networks rely on sufficient multipath in the environment in order for the receiver to distinguish separate data streams. Outdoor bridge links cannot provide sufficient multipath in order accommodate multiple independent spatial streams due to fundamental differences in design to prevent fresnal zone blockage and to ensure link stability and reliability. Thus, they require opposite antenna polarization to sufficiently distinguish the streams at the receiver.

Theoretically, two spatial streams "should" be the maximum supported for outdoor point-to-point bridge operation. But with the innovation in advanced antenna design being done by many companies today (Ruckus, MPAntenna, etc.), I think someone is bound to find a way to support 3 or possibly even 4 stream 802.11n on outdoor links.



  1. Have you had a chance to work with the Ruckus Outdoor ZoneFlex Bridge products? I have a few clients that want to replace their older bridges to get higher throughput but Cisco seems to be dragging their feet. I'm trying to find a good solution.

  2. Hi Chad,
    I have worked with the indoor Ruckus gear, but not their outdoor mesh gear. Novarum did run comparison tests with Ruckus, Cisco, and BelAir for outdoor mesh performance and Ruckus came out looking pretty good. I can't speak to the accuracy of their results or their testing methodology, you'll have to draw your own conclusions.

    Here is the link: