SpectrumTalk

White Space Device Testing at FCC Lab

Docket 04-186 white space device (WSD) testing continues at FCC Lab. A big issue is whether it is exciting as "watching grass grow" or "watching paint dry"?

If you go watch it, you can copy down quantitative results as they are taken. But I will not give many details here as any numbers are subject to revision. (If you go, I recommend Ma's Kettle for lunch - a real taste of Howard County.)

One of the 2 Microsoft units is out of commission due to hardware problems (reportedly a power supply problem), but testing continues on the remaining one. The two I2R units from Singapore arrived broken after their difficult shipment and the engineer who came from Singapore was unable to repair them. He took one back with him and the repaired unit is expected shortly.

Oddly, Google has not submitted a unit yet but left their antenna at the Lab - perhaps as an indication of interest.

Only the Microsoft and Adaptrum units have both detectors and transmitters.

Three basic tests are underway now:

1. Detection with undistorted ATSC signal
2. Detection with a set of 14 recorded ATSC signals that are supposed to have realistic multipath propagation fading.
3. Detection of wireless microphone signals.
   

Other tests are expected but not know scheduled. Technical details of the other tests are not yet apparent other than the vague published test plan.

While many doubted that WSD could detect ATSC signals weaker than -114 dBm, more than one of the devices has consistently detected undistorted signals below -120 dBm. (For non techies, a bigger negative number means a smaller signal and -120 dBm is a signal with a strength 25% of a -114 dBm signal. These levels are about a thousand times smaller than what a DTV receiver can receive successfully through the magic of digital signal processing.) More than 1 of the WSDs has consistently detected recorded distorted signals with strengths less than -114 dBm and many detections of recorded distorted signals below -120 dBm have been made.

I do not have any data of the wireless microphone detection results. Personally, I think the wireless microphone issue is not one that should be addressed through obscure technologies but by reassessing the needs for such service, who the potential users are, and finding a spectrum solution for addressing their needs that is consistent with the general US spectrum policy of the last decade. Meanwhile an interim solution is also needed to address needs of present users, most of whom have stumbled into an illegal situation through circumstance often beyond their control. The FCC's UK counterpart, Ofcom, is seriously addressing the needs of all wireless microphone users (called PMSE in UK-speak). Ofcom recognizes that there is a legitimate need for wireless microphones for users other than NAB members and Hollywood moguls (e.g. churches and live theaters) - FCC rules don't.

I think FCC should look at the "forest, not the trees" and see that there is a real wireless microphone problem that has been swept under the carpet for too long and not get caught up in an esoteric technical diversion. Even if the WSD policy issue were to disappear tomorrow through some lightning stroke, there will be a real wireless microphone problem. Particularly when the 700 MHz auction winners ("$19,496,223,400 and counting") expect to use their expensive newly purchased spectrum in 363 days.

Now that -114 dBm has been demonstrated, the broadcast interests seem to be saying that that shouldn't be the criteria since the WSD's field strength sensitivity would depend on the detector's antennas and WSD manufacturer's would somehow get devices approved with one antenna and switch the antenna later. So stay tuned as we may get pressure for a "change of coordinates" from dBm for a unit of field strength as a dBu (dB re: 1 microvolt/meter) or perhaps power flux density. Just as you got used to big negative dBm numbers!