Unlocking the Benefits of C-RAN with OTN Mobile Fronthaul

Author: Scott Wakelin

Ever since 1987, players from the winning Super Bowl team have been asked the question, “You’ve just won the Super Bowl, what are you going to do next?”  They respond, “I’m going to Disney World!”  This led me to wonder how the U.S. Treasury would answer the same question after the conclusion of the latest AWS-3 auction in which Mobile Network Operators bid almost $45B to secure new licenses – a number that easily surpassed analysts’ estimates of between $10B and $20B.

Why? As highlighted by the December 2014 edition of the Ericsson Mobility Report, mobile subscribers are expected to drive a nearly 8x increase in mobile data (particularly mobile video) between 2014 and 2020. As a result, mobile networks need more capacity, and the way to get more capacity is to 1) deploy more spectrum, perhaps in conjunction with carrier aggregation and 2) densify with more cell sites, especially small cells.

The question for mobile network operators now becomes, “How do you deploy your costly new spectrum in a way that ensures you have the highest capacity and lowest cost network possible.” After spending a record $45B on spectrum, it is now time for mobile operators in North America to give serious consideration to the C-RAN architecture, and in particular, a C-RAN architecture enabled by an OTN-based fronthaul network.

Deploying capacity in the traditional distributed manner, where the baseband for each sector is located at the cell site has serious disadvantages in the LTE-A era and is most certainly counter to the requirements of 5G. The disadvantages include:

  1. Inefficient use of the baseband. On average, utilization is only around 30 percent because they need to have enough processing capability to handle the peak load for the area served.
  2. Limited, if any, ability to take advantage of new LTE-A features like Coordinated Multipoint for interference reduction.
  3. High power consumption, up to 46% of which is for non-radio-related items like air conditioning.
  4. Challenging site dynamics and increased costs, including where to put the new radios and baseband, site preparation and on-going lease expenses.

…and the list goes on.

On the other hand, the C-RAN architecture not only alleviates each of these considerations, but it enables operators to take the first and perhaps most important step toward a cloud-enabled mobile network. The fundamental concepts behind C-RAN are 1) move the baseband processing resources for all cell sites and small cells within an area to a centralized location, and 2) (eventually) leverage NFV/SDN to virtualize the baseband processing onto cloud infrastructure.

CRAN Model

Figure 1 – Advantages of the C-RAN Model

C-RAN has several important technical advantages. For example, by co-locating baseband units, support for interference busting techniques like Coordinated Multipoint (CoMP) can be employed. In the paper, “Recent Progress on C-RAN Centralization and Cloudification,” China Mobile has shown uplink CoMP gains of up to 100 percent at the cell edge.  As a mobile operator, you may have just spent billions to acquire new spectrum. Doesn’t it make sense to make the most efficient use of that spectrum throughout your footprint, including at the cell edge (which, as the network is densified, there will be more of)?

My next post will focus on why an OTN-based mobile fronthaul solution is the best choice for unlocking the advantages of C-RAN and how PMC’s HyPHY family is enabling this important network transition on the path to 5G.

This post was also published on Wireless Week.

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