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Archive for the ‘Metro’ Category

Self-configuring Femtocells

Monday, November 10th, 2008

Rethink Wireless reports that picoChip has added cognitive capabilities to their femtocells. Related “sniffing” technology is used in White Spaces radios and in the UNII-2 band by Wi-Fi. The idea is to check to see how the spectrum is currently being used, and to arrange matters to interfere as little as possible. With White Spaces and Wi-Fi the sniffing is used to avoid spectrum occupied by a primary user. PicoChip uses it to create self configuring networks:

As well has handling configuration, synchronization and hand-off – and reporting metrics on the cell to help network planning – the sniff function will support entirely self-organizing networks of the type Vodafone has outlined in recent presentations. Currently, most of the interference management these require are handled in different ways by the femtocell OEMs, but each has its own proprietary algorithms, making mixed-vendor networks difficult. The picoChip designs also allow the femto silicon to run the manufacturer specific code.

White Spaces – why the resistance?

Monday, October 29th, 2007

It’s an amazing idea. Radio signals at less than 1 GHz pass easily through buildings. TV broadcast signals are below 1 GHz so you can use an indoor antenna. Anywhere in the US about half the TV channels are idle, so why not use these empty channels (White Spaces) for wireless broadband Internet access? The FCC has been pushing this idea since 2004. The IEEE has a workgroup (802.22) hammering out the technical details, and some of the mightiest companies in the technosphere are banding together to make it happen.

Even the broadcasting industry sees the merit of this idea – in a letter to Senators Stevens and Inouye, David Donovan, the president of MSTV (the Association for Maximum Service Television) says:

Ensuring that the United States is a global leader in the provision of broadband services is a worthy goal. We believe this goal can be accomplished, especially in rural markets, without causing interference to new digital television receivers and converter boxes… Our desire is to find a solution that will bring broadband to underserved Americans while ensuring that consumers’ and broadcasters’ investments in the DTV transition are protected.

Did you spot the catch? The broadcasters are worried that unlicensed use of their spectrum will interfere with their broadcasts. The chief executives of Disney, News Corporation, NBC and CBS sent a letter to the FCC saying:

As you know, current proposals based on “sensing” to avoid interference could cause permanent damage to over-the-air digital television reception.

There are two main categories of issue here: technical and compliance. Both must function correctly to avoid the outcome feared by the broadcasters.

On the technical side, if technologies can be developed that effectively eliminate the potential for interference, and regulations can be crafted that require the use of such technologies, the broadcasters have nothing to fear. This technical issue is relatively easy to debate, and while the broadcasters may seem overly cautious to some, their position is reasonable:

It has taken nearly a decade for government and industry to deploy digital television across this nation. A rush to place millions of unlicensed devices in the TV band without extensive real-world testing should not undermine these efforts.

But technical issues yield to engineers in time, and we can confidently expect cognitive radio to work properly in the end. Credible proponents argue that it is working correctly already. The FCC tested devices from Microsoft and Philips in July 2007 expecting to close this issue with hard data, but in a catastrophic blunder one of the tested devices was defective and failed the tests, leaving the issue open. The broadcast industry seized on this mistake and used it to characterize the technology in general as unripe. But the technical argument will eventually yield to conclusive experimental results, showing that cognitive radio works, and that unlicensed use of this spectrum as proposed by the FCC will not interfere with TV broadcasts.

The compliance and enforcement issue is far tougher to resolve, but it is separate from the White Spaces issue, and should be debated separately. This issue is actually more important, since it concerns not only the TV broadcast frequencies but the utility of the entire radio spectrum in the US. If devices that transmit on radio frequencies are badly engineered, defective or designed in such a way that they don’t conform to the regulations, it is possible that they might interfere with legitmate uses. As things stand, there is no guarantee that this will not happen, since the enforcement arm of the FCC is weak. Michael Marcus, in his “Spectrum Talk” blog goes into this issue and proposes some actions.

Muni Wi-Fi on the ropes?

Tuesday, September 4th, 2007

Wired has a story about the struggles of several municipal Wi-Fi deployments. Turns out that good coverage requires double the number of access points than planned, and that consumer subscriptons were an order of magnitude less than anticipated (1-2% instead of 10-25%).

The article holds out a few rays of hope: 802.11s for mesh deployments in residential areas, concentrate on high-traffic areas rather than trying to replace fixed broadband access, get the cities to become “anchor tenants.”

On the other hand, there still seem to be plenty of lower profile metro Wi-Fi deployments that are doing OK.