Election Night 2008
The City of Chicago took extra care in securing Hutchinson Field in Grant Park for the 2008 Election Night festivities. The IBM DVS team was there (mostly Jim Jimenez and I) adding security cameras around the park using a Firetide wireless mesh and two long range Infrared monsters in a high rise building and an upper Hilton Hotel window.
I’ve received different instructions regarding the proper cabling of these new smart MIMO antennas. MIMO (multiple input, multiple output) is the new smart antenna technology for 802.11n wireless communications in which multiple antennas are used at both the transmitter and the receiver. These smart antennas are the reason we see bandwidth of 150Mbps + on 40Mhz channels.
I’ve created a diagram that shows that crossing cables 2 and 3, in a point to point configuration, can be beneficial, yet when doing this in the field, the RSSI did not reflect any change because I don’t believe these radios and their smart antennas have reach maturity. The biggest issue I’ve found with using the Firetide 7000 series MIMO radios, with their 19dBi 20 degree directional MIMO antennas is their back-lobes. Clearly, these back-lobes aren’t shielded enough as when working on linear meshes, these antennas cannot be back-to-back on the same pole – at all.
First of all, the RSSI is calculated based on connection #1 only, so testing bandwidth is the only way to confirm that the crossing of connection #2 and connection #3 would create any improvement. I’ve seen kinked cables on #2 & #3, without any effect on RSSI, but clearly visible in bandwidth tests.
When creating a point-to-point connection, front-to-front, the vertical polarization crosses the two angled polarization, and so it would be better to flip one antenna 180 degress (see diagram). Easiest method of remembering the proper configuration is having one vertical polarization arrow pointing up, while it points down at the other end.
Otherwise, chaos ensues as any other antennas pointing in the same direction create an even better (unintentional) connection front-to-back (where the polarizations match exactly), in close proximity, making it a problem to distinguish between radios and antennas without visual confirmation of the radios, antennas and cable connections.
Considering how the smart antenna is supposed to work, and the new proliferation of MIMO technologies, self-interference and network loops can become an issue without thorough design considerations. Just because you can’t see the link, doesn’t mean it isn’t there.
This is a comparison of an Axis 4CIF NTSC camera versus a Arecont 2MP camera within Genetec Omnicast Archive Player, using the digital zoom feature. Storage requirement increase substantially (the extra pixels need to go somewhere). Using H.264 compression, at 30 frames per second, 4CIF requires 10GB a day, while the 2MP needs 55GB per day. However, although the Arecont Megapixel cameras use a 1/2″ CMOS sensor, they are difficult to focus. The Pelco Sarix includes an initial autofocus feature, but are considerably more expensive.