In its open meeting on September 23, the Federal Communications Commission will be voting on a Second Memorandum Opinion and Order allowing the use of unlicensed wireless technologies operating in unused parts of TV spectrum. The idea termed "TV White Space" transmission has been on the table for years, and it holds the promise of shaking the wireless industry to its roots.
Radio spectrum is the most basic commodity in wireless, and it is the major limiting factor in expanding the range and capacity of wireless services. Managing the allocation of radio spectrum in the US is one of the major responsibilities of the FCC. At the most basic level, that radio spectrum is classed as either licensed (i.e. dedicated to specific users, for specific purposes, in specific areas) or unlicensed (open to all users but subject to regulations to minimize interference). Large portions of the spectrum are allocated to licensed bands that are used by the cellular operators, radio/TV broadcasters, and a variety of government agencies.
Securing licensed frequencies involves buying them either at FCC auctions or from other license holders, and prices are measured in millions or billions of dollars. Hence the appeal of unlicensed technologies like Wi-Fi and Bluetooth; however there is relatively little unlicensed spectrum available in the US (see Table below).
When it comes to finding new radio assets, the TV broadcast bands stand out as having the widest swath of desirable but underutilized spectrum available.
The broadcast TV spectrum runs non-contiguously in the band between 54 MHz to 698 MHz (TV channels 2 through 51); other services like FM radio are interspersed among the TV channels. At 6 MHz per channel, the current broadcast band represents 300 MHz. of radio spectrum, and industry estimates hold that 75% of that is unused in most markets. Importantly, this spectrum has the same low-loss, high-penetration characteristics as the 700 MHz channels the FCC auctioned in 2008; in that case they sold roughly 60 MHz of spectrum for $19.6 billion.
The big question is: what is this going to mean to me, the user? As in most cases, the devil is in the details, and there are some key issues we’ll be keeping an eye on:
* Protocol Specifications/Deployment Plans: Most of the reports we’ve seen on the FCC proposal thus far have used meaningless terms like "Wi-Fi On Steroids" (yeah, that's the same term they used to describe WiMAX--not a lot of imagination in the wireless camp) and there is talk of ranges up to several miles. We won't really know the potential range or data rate until we get a closer look at the specs. Those 700 MHz frequencies do have better loss characteristics than the 2.4 G or 5 GHz frequencies we use for Wi-Fi, but the actual range will be based on the allowable transmit power or equivalent isotropically radiated power (EIRP).
The protocol will likely be based on the IEEE 802.22 standard for Wireless Regional Area Networks, in which they will spell out the radio link (Layer 1) and MAC (Layer 2) specifications. That will define how the signal can be encoded (i.e. maximum bits per second) and how the channel will be shared. TV channels are only 6 MHz wide versus 20 MHz or 40 MHz for Wi-Fi, so the theoretical maximum should yield a relatively modest 1.5 Mbps downstream and 384 Kbps upstream; those transmission rates will decrease with range. Longer ranges also mean that there can be more people sharing the channel. On the other hand, there is the potential for bonding multiple 6 MHz channels together to increase the potential transmission rate. So the "real answer" will be a factor of the standard and the deployment decisions.
The other major feature in 802.22 is interference control. There are other systems that run in the TV band like the wireless microphones used in theaters, and bringing those users into the fold has been one of the major factors that has delayed the deployment. Originally a solution based on frequency sensing and avoidance had been proposed, but the current plan seems to lean in the direction of a location-based approach using either maps or GPS to avoid interference. Either option would address interference within a single city, but a GPS-based solution could also solve the problem of roaming users.
* Devices: As there are virtually no devices that support IEEE 802.22 today, so we will need chip sets that can be built into laptops, smartphones, or tablets to access the service. USB dongles or Wi-Fi routers would also allow user devices to attach to the network. Given the potential market, we do not anticipate a shortage of devices, but those things won't appear overnight.
* Applications/Markets: The real question is where will white space fit in the overall wireless market, and what existing services will it compete with? Given WiFi's dominance in both the home and office markets, it is unlikely that white space is going to supplant Wi-Fi for true wireless LAN applications. However, open area or metro area Wi-Fi has now become an alternative to 3G and 4G cellular data services, and that is where white space could have the biggest impact. Free municipal Wi-Fi systems looked like a failure a few years ago, but the second round of offerings (like the one from my local cable TV provider here on Long Island) are turning out to be a real crowd pleaser.
Conclusion
While the full picture of how white space will change the wireless market is still foggy, the addition of the TV white space to the unlicensed spectrum is a major development and potentially a major challenger to the nascent 4G offerings from the cellular operators. With just 83.5 MHz, Wi-Fi in the 2.4 GHz band revolutionized people’s ideas about mobility. Wireless technologies have improved enormously since the introduction of IEEE 802.11b, so throwing another 200+ MHz of unlicensed spectrum into the mix with a greater range potential can only spell good things for the consumer.
I’ll have more to say about this after the FCC makes its announcement next week, and as the whole white space picture comes into a clearer focus.
