The FCC has taken a first step toward re-auctioning the 700MHz “D block” in the 700 MHz band.
The FCC voted to ask for public comments (pdf) on how to re-auction the 10MHz piece of spectrum. Commissioners wanted to pair it with another 10MHz controlled by public-safety agencies to build a nationwide network shared by public-safety agencies and commercial users. But the public service band failed to receive the minimum US$1.3 billion bid it wanted.
The $1.3 billion reserve price and stringent build-out requirements are blamed for its lack of success at the 700 MHz auction earlier this year.
Now the agency is asking whether it is still appropriate to keep the public/private partnership, in which the spectrum winner would have worked with the Public Safety Spectrum Trust (PSST), a coalition of 15 public-safety groups that controls the second 10MHz block that would have been paired with the D block.
The FCC is seeking comment on issues like:
- The rules governing public-safety priority access to the network during emergencies
- The performance requirements and license term
- Whether to license the D Block and public-safety broadband spectrum on a nationwide or regional basis
- And auction-related issues such as whether to restrict auction participation and how to determine a reserve price.
Some advocacy groups criticized the PSST and advisor Cyren Call for suggesting they want an annual $50 million lease payment from the D block’s winner in exchange for use of their 10MHz. The FCC also asked whether for-profit organizations should be involved with the PSST.
Shortly after the agency’s 5-0 vote on the D Block, Rep. Jane Harman (D-Calif.) introduced legislation to authorize $4 million to begin funding the Public Safety Spectrum Trust Corp. To date, the PSST has been funded by loans arranged by its advisor — Cyren Call — and financed through the firm’s venture capital investors.
An issue that is not discussed often or at all is the fact that the spectrum mapping of 700MHz D block creates another interference problem just like what is happening with public safety today with Nextel.
Some of the technology that will be used in D block will be readily available today narrowband radio. The issue is these devices have very wide front ends that do not filter out adjacent spectrum blocks. This is done to keep noise figures to a minimum so that systems can be built to operate at the noise limit. The systems adjacent to this spectrum will be built for interference limits, thus the average signal levels are going to be much higher. Another driver of higher powers in these adjacent spectrum blocks is that OFDMA technologies need very high signal strengths to have the maximum throughputs, >-60dBm. Therefore, the high power sites that are broadband will create Intermodulation energy that will raise the noise floor of the PS radio receiver.
The intermodulation energy will cause dead spots throughout the PS operating areas. Just like how the Nextel system can create dead spots today. This will be considered unacceptable and the carriers will be forced to resolve the issues.
As a note, OOBE from transmitters is typically only about 10% of the issue with PS and Nextel. The IM issues were the main driver of the poor PS radio interference. In reality, the equipment used by the PS was not designed to handle the strong signals and would cause internal receiver blocking. Nextel was not doing anything wrong. Nextel worked hard to fix issues by retuning its channels to move the IM noise away from the PS carriers, putting on special transmit filters, and doing things like installing antennas upside down (Upper lobe suppression antennas upside down will keep the energy from blasting the ground at the tower).
If wide band signals were to be used, like CDMA, UMTS, or WiMAX/LTE, there would be no way to retune to fix the IM issue. Also the noise impacts are much wider as IM will basically raise the entire noise floor.
The FCC will need to put in a provision to ensure that the equipment makers of PS gear filter out the adjacent blocks, otherwise we will all be trying to figure out how to save PS once again in about 5 years.
Left by Wireless on May 15th, 2008