The Spectrum Is Not Enough
This article is not about a new James Bond movie (see “The World Is Not Enough”) protecting the world from the takeover of all spectrum resources by a power-crazed tycoon. It is time to emphasize that spectrum alone is not sufficient. There are too many statements flying around of the kind, “The Internet is going wireless,” or “We know that broadband connections will become wireless.”
Neither statement is true, nor can they ever become true if meant to indicate that as in voice communications it will be possible for individuals, if they so wish, to rely entirely upon broadband wireless or mobile access and not bother with a fixed access subscription. Until and unless the current laws of physics are invalidated in ways that remove current limits on spectrum capacity such as are embodied in Shannon’s Law, the future will see:
(a) The vast majority of broadband traffic continuing to be carried over fixed access networks; and
(b) Demands for broadband traffic from wireless or mobile subscribers outstripping the capacity of all the bandwidth available for radio access networks to handle it, even with the use of new spectrum that can be allocated and the deployment of more spectrally efficient technologies. It should be noted that a single mode fiber has a bandwidth of as much as 100,000 GHz, whereas total valuable spectrum for mobile communications provides bandwidth of no more than at most 3 GHz.
Two other “Laws” (neither of them derived from basic science) and one forecast are relevant in this context, namely (1) Nielsen’s Law of Internet bandwidth, that a high end user’s connection speed grows by 50% per year; (2) Moore’s Law, that the number of transistors on a computer chip, which is a rough measure of computer processing power, doubles every 18 months; and (3) Cisco’s forecast, that the volume of mobile data traffic will increase by almost 40 times over the 5 year period from 2009 to 2014 (or about 110% per year).
If we assume that Nielsen’s Law will hold for 5 more years, then high end connection speeds will increase by a factor of about 7.6 over this period, and 58 times if it holds for the next ten years. Over the same period, if Cisco’s forecast is accurate, mobile data traffic will grow by about 40 times over 5 years, and by over 200 times over a period of 10 years if the annual average growth rate in traffic slows to a “mere” 40% per year over the second 5 year period. Under these conditions there is no way that a combination of additional spectrum and the deployment of more spectrally efficient wireless technologies will be able to handle the volume of mobile broadband traffic that may be generated within the next decade.
There are of course counter-arguments to refute the expectation of a looming and substantial shortage of spectrum to accommodate mobile broadband traffic in the locations of highest demand. Another “Law” can be invoked, namely Cooper’s “Law” about wireless capacity, an observation by the mobile phone pioneer Martin Cooper. This Law refers to the number of “conversations” (voice or data) that can theoretically be conducted over a given location in all useful radio spectrum. It turns out that this number has doubled every two-and-a-half years for just over a century.
Several technological approaches have fueled this remarkable increase in the capabilities of wireless communications, but now spectrum re-use as in cellular technology is the only one with the theoretical potential for further expanding wireless network capacity by orders of magnitude. If broadband wireless links could be constructed between any two points, with independent connections to points separated by only a few feet, then ultimately every user could have access to up to one to a few GHz of bandwidth.
This line of reasoning may justify the conclusion that with a combination of new technologies and regulatory approaches to the use of spectrum there should be no spectrum shortage to carry even the huge amounts of broadband traffic that each user may generate and receive in a future as envisioned by Cisco. However, other realities – economic, operational, timing, and competitive – must also be taken into account, as well as the observations that: (1) Much mobile use actually takes place within buildings in fixed or nomadic modes, and (2) A small proportion of users account for a disproportionately large amount of the traffic.
It seems highly improbable that a combination of drastically new design and regulatory principles for the allocation and use of spectrum could be implemented in time to handle the already rapidly rising tide of broadband traffic even if the new technologies were to become commercially available and affordable in the near future, which is itself highly improbable. Nor is this scenario li
kely to be realizable in a way that is competitive with the deployment of new fixed access networks, with intrinsically much greater capacity in terms of Mbps/km2, to cover the majority of user locations.
If new radio access networks alone are not sufficient, mobile operators have several other ways in which they can mitigate the risks of congestion to complement their access to greater bandwidths and the deployment of more spectrally efficient technologies. However the only approach with long term continuing impact is off loading of mobile traffic onto the fixed network via Wi-Fi, other short range (in-building, in-room) wireless, and femtocell connections
Any credible long term broadband plan at the level of a country or of an operator must carefully coordinate the deployment and interworking of new fixed broadband access as well as broadband wireless access networks. The heavy emphasis and excitement in investment of the past decade or more on mobile networks must be rebalanced towards placing a greater weight on new fixed access infrastructure as well, if the aspirations of countries, innovators, and users with respect to broadband are to be realized.
The Spectrum Is Not Enough << Comments and views
Loading ...