The late economist Herb Stein used to say that “if something cannot go on forever, it will stop.”
A profound economic truth lies behind that seeming flip statement. The world is forever on the verge of running out of vital commodities–oil, food, water, and many more–but somehow we never do. In the worst case, as a commodity grows scarce, its price rises and demand shrinks. The real world, however, human ingenuity triumphs over shortages. We find alternatives to whatever we are running out of, or, better, we find ways to use what we have much more efficiently. So it is with the spectrum we need to move ever-growing volumes of wireless data to our proliferating mobile devices.
In the short run, available spectrum is more or less fixed, creating an atmosphere of shortage. The established carriers, especially Verizon Wireless and AT&T, warn of “exponential”* growth in demand and use claims of shortage both to lobby for new allocations of spectrum for wireless data use and to justify data caps and higher rates. Critics argue that while dedicating more spectrum to wireless data is desirable, much can be accomplished through greater efficiency in the use of what we have.
In this an subsequent articles in this series on spectrum, I will examine the claims and look at possible solutions. Perhaps the biggest issue is just what is happening with demand for spectrum. The truth appears to be that it is still growing very quickly, but at a decelerating rate. Cisco’s Visual Networking Index, which has often been criticized for exaggerating the growth rate, indicates this clearly. It shows the growth rate for mobile data slowing from 133% in 2011 to an estimated 78% in 2014. A growth rate of nearly 80% is still staggeringly fast, but the effect of this deceleration is enormous. At a 133% compound annual growth rate, consumption would increase 240-fold over a decade; at 78%, just 60-fold. The difference: More than 100 exabytes of data per month.Stein’s Law: “If something cannot go on forever, it will stop.”
But even if we discount the more breathless and self-serving estimates of growth in wireless data use, it is clear that the amount of spectrum allocated to wireless data will be, at some point in the not too distant future will be inadequate to meet demand, based on today’s technologies. It is also clear that to meet this demand, we must both find additional spectrum and find ways to use it more efficiently. Fortunately, both are eminently doable.
The actions that can be taken to improve the availability of spectrum for data include:
- Auctioning spectrum currently used for other purposes. This is the course favored by the incumbent carriers and, to a considerable extent, by Congress and the Federal Communications Commission. The big problem is that it is extremely difficult to get anyone–public or private–who currently holds spectrum to part with it. Legislation passed last year provides for the auction of 100 MHz of unused or under-used television spectrum for data, with the current broadcast licensees sharing in the proceeds. The rules for these “incentive auctions” are extremely complex. No spectrum will actually be sold until next year at the earliest, and it seems unlikely that the amount freed will ever come up to 100 MHz. Prying spectrum from the vast hoard held by government agencies, particularly the Defense Dept., is even more difficult.
- Speeding buildout of unused spectrum. Even while complaining of spectrum shortages, the incumbent carriers still have a lot of spectrum in the bank. Neither Verizon nor AT&T has completed the build-out of LTE networks on the 700 MHz-band spectrum they bought in 2007, a Verizon has just acquired considerable additional spectrum in a deal with Comcast and other cable companies. The biggest chunk of barely used spectrum is nationwide coverage at 2.5 GHz held by Clearwire, whose financial woes have allowed only a small portion of the network to be built out. Both Sprint and Dish Networks are bidding for control of Clearwire with the fate of this spectrum in the balance.
- Spectrum sharing. A lot of spectrum is assigned to entities, usually government agencies, that sue it only sparingly. For example, Defense Dept. operates a scattering of military radars in the 3.5 GHz band. The FCC is currently implementing a plan that will allow commercial use of this spectrum by devices and base stations specially designed to operate only where and when they will not interfere with the radar.
- White spaces. This is a Wi-Fi-like spectrum-sharing variant that operates on unused portions of the television band. Unfortunately, white space is most available in rural areas and scarce in crowded cities where it is really needed. It is most likely to have its main impact as an alternative to wired broadband service in rural areas.
- Small cells. The basic principle of cellular communication is that limiting the range of base stations to fairly small areas allows spectrum to be reused, as long as the cells are far enough apart to avoid interference. Cell sizes, which depend on transmit power and the height of the antenna, range from a radius of 30 kilometers in the country to 1 km or less in dense cities. But reuse of spectrum can be increased greatly by using very small cells in the densest areas.
- Wi-Fi offload. Unlike other wireless technologies, Wi-Fi operates on spectrum that is free for anyone to use, and Wi-Fi access points serve areas with a radium of 100 m or less. The load on crowded cellular data networks can be reduced greatly if as much traffic as possible is shifted to Wi-Fi, and new technologies are enhancing the ability of this offload to be handled automatically and seamlessly.
- Smart antennas. While small cells reduce the radius of coverage, smart antennas can reduce the angle of the sector covered. Current cellular antennas typically cover a 120° sector. Smart antenna technology can allow base stations to beam their transmissions to the devices to which they are connected, again allowing for greater resuse of spectrum.
Most or all of these technologies are going to be needed in combination to deal with the growing demand for wireless data, but the fact is that the spectrum “crisis” is a challenge we can meet with a combination of sound policy and good technology. I’ll be looking at each of these options in more detail in coming articles in this series.
*–Truth in mathematics time. The essential characteristic of exponential growth is that it increases at an ever increasing rate. (For those of you who remember your calculus, all derivatives are positive.) This never happens in the real world, at least not for long, because growth is always constrained by something. As noted below, there is, in fact, evidence that the growth in demand for wireless data is already decelerating.