Wednesday, August 22, 2012

The future of wireless is small, but very, very big

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 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
Marcus Weldon is Corporate CTO for Alcatel-Lucent and also a member of Bell Laboratories. In this position he is responsible for co-ordinating the technical strategy across the company and driving technological and architectural innovations into the portfolio. He holds a B.S in Chemistry and Computer Science and a Ph.D. degree in Physical Chemistry from Harvard University. He joined AT&T Bell Labs in 1995, winning several scientific and engineering society awards for his work on electronics and optical materials.

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.
About Alcatel-Lucent

The long-trusted partner of service providers, enterprises and governments around the world, Alcatel-Lucent is a leading innovator in the field of networking and communications technology, products and services. The company is home to Bell Labs, one of the world's foremost research centers, responsible for breakthroughs that have shaped the networking and communications industry. Alcatel-Lucent was named one of MIT Technology Review's 2012 Top 50 list of the "World's Most Innovative Companies" for breakthroughs such as lightRadio™, which cuts power consumption and operating costs on wireless networks while delivering lightning fast Internet access. Through such innovations, Alcatel-Lucent is making communications more sustainable, more affordable and more accessible as we pursue our mission - Realizing the Potential of a Connected World.

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.
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