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25th Anniversary of FCC Decision Enabling Wi-Fi and Bluetooth

25th Anniversary of FCC Decision Enabling Wi-Fi and Bluetooth
A series of posts describing how this all came about. (Click on picture above)

Thursday, February 26, 2009


CTIA, NENA, APCO, and NPSTC Ask FCC to Act on Wireless Microphones and 700 MHz

On 2/23 CTIA - The Wireless Association®, the National Emergency Number Association ("NENA"), The Association of Public-Safety Communications Officials - International ("APCO"), and the National Public Safety Telecommunications Council ("NPSTC") filed a joint letter with FCC in WT Docket No. 08-167 asking it to act on the issues of wireless microphones' continued use of 700 MHz.

(Oddly the letter is not on the CTIA website even today, but was reported by FierceWireless.)

The letter stated,
"Harmful interference from unauthorized low-power devices operating in the 700 MHz band threatens to prevent licensees from realizing the benefits to public safety that the 700 MHz band promises. We understand that there is an item currently before the Commission to address low-power devices in the 700 MHz band and urge you to take action to curb the harmful use of these low-power devices.

It is of critical importance that low-power auxiliary devices do not cause harmful interference to critical communications - and the commercial communications that enable ordinary Americans to reach public safety in their moments of need. As both public safety and commercial licensees begin to utilize spectrum from broadcasters who have completed their digital transition, we ask that the Commission take action to clear the 700 MHz band of unauthorized low-power auxiliary users. By clarifying in an Order that low-power auxiliary devices must not interfere with authorized public safety and commercial licensees, and that those devices must accept all interference from licensed users, the Commission sends a strong signal to all users of these devices that the public safety benefits of the 700 MHz spectrum outweigh any - licensed or unauthorized - use of the band."
The joint parties then said they
"urge the Commission to require that operation of all low-power auxiliary devices in the 700 MHz band cease no later than one year from the adoption of an Order and issue a Consumer Advisory informing the public. Additionally, in order to speed the deployment of public safety and commercial systems in the 700 MHz band, the Commission should require low-power users to cease operation within 60 days of notice that a licensee intends to initiate or change its wireless operations such that the low-power devices will likely cause interference."
As we pointed out previously, this 60 day issue - originally proposed by NAB, MSTV and Shure - has the practical problem that almost all wireless microphones in use are illegal and hence not in any public database. (Perhaps Shure has such a database internally and might be willing to share it in exchange for immunity from criminal prosecution of their clients?)

So far Shure and fellow travelers have not addressed the points raised in this joint filing.

2 comments:

Henry Cohen said...

As FCC 08-188 already states all Part 74 devices must cease operating after the final DTV transition date, and Part 74 Subpart H (specifically 74.802) is currently being revised to reflect this, what is the point of the joint PS community letter?

Further, and already addressing in substance the concerns of the letter, the vast majority of Part 74 users are in fact aware of these changes, the wireless mic manufacturers have had informational campaigns regarding these spectrum and regulatory changes underway for a year now, and have ceased selling 700MHz equipment in the US market for nearly that same time period.

Whereas it's certainly possible a 100mW wireless mic transmitter next to a PS radio could desense that radio when at the very fringe of its coverage area, the reality is that once these PS systems begin testing, much less before they come on line, the Part 74 devices operating in 700MHz will experience intolerable interference and will no longer be used. It's important to understand the necessary SNR (resultant audio quality) for Part 74 device audio is far more critical than that of two-way radio voice communications.

Lastly, wireless mics (and coms, in ear monitors, and cueing) are commodity items; they are sold through dealer networks, box houses, resold used on the open market, stolen and thrown out: There's no real database kept by anyone or small group that could provide accurate geographical versus user deployment information at any given time.

MJM said...

The potential wireless microphone/public safety interference is asymmetric because the most public safety systems are frequency division duplex (FDD) - they have uplinks on one frequency and downlinks on another.

If the wireless mic is on a PS downlink channel and is in a weak PS signal area it could cause interference to PS without receiving interference.

If the wireless mic is on a PS uplink channel it is unlikely to cause interference to PS except in the very unlikely case that it is next to a public safety repeater. (This might happen if a church using 700 MHz wireless mics is adjacent to a police station or firehouse that is the location of a repeater.)

In the PS uplink frequency case, PS radios would not cause interference to wireless mics unless a PS radio was transmitting in the theater or church.