by Marcus Weldon, CTO, Alcatel-Lucent
We
are at a defining moment in broadband network deployment. We are on the
verge of a transformation in behaviors so profound that what we think is
normal now will be viewed as quaint and amusingly antique in the same way
that the Model T Ford, or wooden-cabinet enshrouded black and white TVs,
or dial-up internet access are viewed today. And this behavioral change
will not be limited as before to a certain socio-economic class or age
demographic, or geography, or educational background - it will be
universal in extent, ageless and classless in adoption, and will
redefine economies and the nature of commerce.
What is the driving force behind this unparalleled new reality? A
device: the tablet. To understand how something that you are probably
holding in your hand or carrying in your backpack right now is going to
change our reality, consider what that device is and can become for
you. It is already a device on which you communicate (email, video
chat, messaging), you watch video content, you play games, you listen to
music, you read books, you navigate (in 2D and 3D), you view documents
and presentations, you surf the web, you monitor and control your home,
you record videos, you control your TV and more and more applications
appear every hour and every day. In essence, this device defines and
enables a new digital life - your life wherever and whenever you are.
But what has this got to with the future of wireless or networking?
Well it is this last observation - the 'whenever and wherever you are' -
that has truly profound consequences for networks, and in particular
wireless networks. But to fully appreciate this, it is first important
to realize that although the tablet is a remarkable device, it isn't
capable enough to store or process your life and it is unlikely that it
will be...at least for the next decade or so. In short, current tablets
have the processing power and storage capacity of an 8-10 year old PC.
And even a current PC hard drive doesn't have enough capacity to store
all our digital media objects, which is why we increasingly rely on
external storage and Cloud storage as a complement to local hard drive
storage. With the advent of Cloud storage we not only get access to
seemingly infinite storage capacity at the lowest cost per gigabyte, but
we can access the stored content from any device anywhere, without
having to replicate it on every device everywhere. So even as storage
density and processing power continue the seemingly inexorable march of
Moore's Law (doubling every 18 months), our demand will always exceed
the local supply on a mobile device, with its intrinsic power, size and
cost constraints.
The intrinsic connection between these two elements: the tablet and the
Cloud is the root of the manifest change in wireless networks that will occur, because without an ultra-high capacity wireless network
infrastructure this nascent demand and vision for a new digital
economy cannot be realized. In order to quantify this future demand,
Bell Labs have built a future demand model for the tablet generation
that predicts that by 2016, the intrinsic demand (unconstrained by
economics of supply) will be more than 80x today's average demand even
when averaged across different demographic age groups. So, in essence,
there are two central questions we must address to realize this future:
1)
How can we
increase the capacity of wireless networks by 80x (or more)?
2)
How can we
afford to do this?
I will exclusively focus on the first question here, and defer the
second critical question for another time. This question of the
ultimate capacity of wireless networks would, at first glance, seem to
require a futurist or information theorist to answer. But in reality,
the problem can be parameterized in a way that reduces the need for
technological clairvoyance or new theorems. In essence, there are 3
basic dimensions of capacity growth in wireless networks: A) More
spectrum, B) More spectral efficiency and C) More spatially efficient
use of that (efficiently-utilized) spectrum. And it is the product of
these 3 capacity elements from which one will derive the ultimate
wireless network capacity. Or, to put it simply:
Ultimate wireless
network capacity, U = A * B * C
So what are the right values of A, B and C? Interestingly, although
the answer to this question would require a detailed analysis for any
specific network or deployment scenario, the parametric, or limiting
(maximum) values are relatively simple to compute, and are summarized in
Figure 1.
If we start by considering the value of A), i.e. the maximum amount of
additional spectrum that will likely be made available, we have to
consider both licensed and unlicensed spectrum contributions. In terms
of licensed spectrum, approximately 500-600 Mhz of spectrum is currently
allocated (Figure 2) for commercial wireless services below 3Ghz (the
cut-off for commercial terrestrial deployments due to the non-line of
sight, superior propagation of this spectrum), and it is commonly
accepted that another 500-600 Mhz could be made available by various
refarming, repacking and reallocation schemes.
In addition to this,
approximately 500-600 Mhz of unlicensed spectrum is currently available
across the 2.4Ghz and 5Ghz bands and could be utilized to augment the
licensed spectrum, particularly for best effort, lower QoS services
delivery.
So,
this simple summary analysis suggests that a 2-3x increase in spectrum
is a realistic possibility, with a concomitant 2-3x increase in wireless
network capacity.
If we
now consider element B), the use of sophisticated physics and
engineering to increase the spectral efficiency, a number of approaches
have to be considered and quantified. But first, it is important to
recognize that we are already operating within 20% of the Shannon Limit
for a wireless communications channel, so the gains will largely come
from 4 factors:
1)
More efficient use of disjoint spectrum assets: Use
‘Carrier Aggregation’ to deliver higher peak capacity across the
aggregated bands
2)
More spatial paths: Use Higher-order MIMO with more
transmit diversity to improve received Signal to Interference + Noise
Ratio (SINR)
3)
Decrease interference: Use enhanced inter-cell
interference cancellation (eICIC) to reduce the received noise and
therefore increase SINR
4)
Coordinate transmission from multiple cells: Use
so-called ‘network MIMO’ (formally known as Coherent Multipath (CoMP))
techniques to improve the coherent signal strength at the receiver and
increase SINR
Although each of the four techniques can provide significant gains under
certain circumstances, such as at the cell edge or in lightly loaded
cells, when the average improvement is computed across all locations and
usage scenarios the gains are typically on the order of 20% per
technique, or a total of a factor of 2, if all techniques are employed
together.
So by
now it should be clear that if capacity growth by more than a factor of
6 is required, a new approach is required. And that new approach is to
increase the ‘spatial efficiency’ by deploying much smaller cells and
effectively reusing of all the spectrum assets of A), and the spectral
efficiencies of B), over much smaller areas and user groups. Therefore,
logically, the gain that can be realized using this approach is a factor
of ‘N’, if the inter-cell interference can be minimized and if users are
clustered in metrocell locations or ‘hotspots’, where N is the number of
small cells deployed per macro serving area. So, N could be 5, 10, 30
or even 100 or more, in the limit.
Now
returning to the predicted demand of the Tablet Generation with 80x
growth in demand over the next 5 years, the answer to the capacity
equation must be:
Tablet Generation Capacity Demand:
=
2.5x (More spectrum) * 2x (More spectral efficiency) * 16x (More spatial
efficiency)
So,
the future of wireless is small (cells), but it will drive very, very
big behavioral and socio-economic change.
About
the Author
 In 2000, Dr. Weldon started work on fiber-based Broadband Access technologies and, in 2005, became the CTO for Broadband Solutions business group in Lucent Technologies, with responsibility for wireline access networks and IPTV. He was subsequently appointed as CTO of the Fixed Access Division and the Wireline Networks Product Division in Alcatel-Lucent following the merger of Alcatel and Lucent in December 2006, with responsibility for xDSL and FTTH, IPTV, Home Networking and IMS. He was one of the primary architects behind the evolution of the Triple Play Service Delivery Architecture to the High Leverage Network™, now the widely accepted industry architecture centered around the principles of ‘all IP, converged wireline/wireless, intelligent, optimized networking’. Together with his CTO team he was also a primary driver behind the groundbreaking and multiple award-winning lightRadio™ architecture for next generation wireless networks. He continues to help drive the company in new portfolio directions, including defining new ‘Cloud-networking’ and ‘network as a platform’ paradigms, as well as the use of sophisticated analytics for optimizing the customer experience and service delivery. |
 With operations in more than 130 countries and one of the most experienced global services organizations in the industry, Alcatel-Lucent is a local partner with global reach. The Company achieved revenues of Euro 15.3 billion in 2011 and is incorporated in France and headquartered in Paris. For more information, visit Alcatel-Lucent on: http://www.alcatel-lucent.com |
