[taichichuan]

Hmm... OK, I've read through the majority of the posts in this thread and I'm surprised that we haven't had any RF folks like the hams chime in. So, since I'm a ham operator of almost 40 years experience with antennas, I figure that I might as well open my big mouth and put in my $.02. Essentially, I think that there are several RF-related issues that could/should be taken into account.

The Dlink is a commercial, consumer wireless router designed for static mounting in a relatively benign RF environment. If we could characterize the Dlink's RF transmission pattern, I suspect that we'd find that the DLink is not a true omni-directional antenna. And, we're running it in an mobile, hostile RF environment. High-power motors, weird mounting angles, mounting near the cRio with lots of stray RF fields (unshielded PWM cables, the PDB, digital side car and more) and even mounting inside of signal-blocking structures like aluminum pillars all have the potential for interfering with RF signals. The only requirement for mounting the radio is that the inspector can see the status LEDs. But, the unit can be mounted in such as way that the RF transmission capabilities are seriously degraded while still having the LEDs visible.

There is a reason that most industrial WiFi units have small antennas protruding from them. It's because the little antennas the stick out have a higher RF gain and are more omni-directional than the small patch antennas found in the Dlink unit. In addition, IEEE 802.11n is capable of multi-in/multi-out (MIMO) operation that allows for antenna diversity so the antenna with the strongest signal can be selected and can support switching antennas on an as-needed basis during the match as the robot moves on the field.

So, I think that if you switch routers with ones that support multiple omni-directional antennas like the DIR-615 or DIR-655 as well as having Quality of Service (QoS) support (the ability to prioritize the DS packets and de-emphasize the video if bandwitdh is squeezed), perhaps even to support the remote mounting of the antenna on the center of the robot, that you might be able to address many of the loss of signal issues with the FMS. Additionally, mounting the receiver antennas *over* the center of the field instead of to the sides could also help.

As to licensing a section of the radio spectrum, that's not likely to be economically feasible. Companies like Verizon, Google and others spend literally billions of dollars to lease bandwidth in big government auctions run by the FCC. Even with 3000 new teams from the Boys & Girls clubs paying $5K a pop for registration, it's highly unlikely that FIRST could afford to license a chunk of the bandwidth for use -- let alone convince a radio manufacturer to create radios cheap enough for such a small market.

Of course, the lower the frequency, the the further the distance it will transmit. There are several, open ISM bands that do not require licensing. The 2.4 GHz and 5 GHz WiFi bands are examples. The early serial modems used several years ago where 900 MHz (another ISM band) modems I think. But, the field isn't so big that it justifies dropping to a lower frequency. And, we have to think about countries other than the US as well. The US 2.4 GHz WiFi band overlaps an Israeli military frequency if memory serves me correctly.

So, a dual-band (2.4 GHz/5 GHz) radio with MIMO support and multiple omni-antennas with antenna diversity support and some guidelines for mounting the radio would likely solve most of our FMS connection issues. These types of routers might cost an extra $100 or so more, but the ability to play the game without communications issues would be priceless, IMHO.

My $.02,

Mike