The ‘small cell’ era has arrived!  Well, at least it arrived officially with the rebranding of the “Femto Forum” as the “Small Cell Forum” last week.  But as the good folks at the ABI Research point out (here) most vendors have already moved past the ‘femto’ terminology and have embraced the ‘small cell’ terminology in much of their marketing and, and very soon, their product line-ups.

The momentum is clearly there as demonstrated by some of the recent weeks’s announcements.   ip.access, the maker of AT&T’s MicroCell, announced plans to build a combination of 3G, 4G, and WiFi upgradeable small cell targeted for the enterprise indoor market based on the Freescale QorIQ Converge PCS9132 processor.   Similarly Mindspeed, who recently completed its acquisition of PicoChip, took the opportunity to announce their first joint product, a dual-mode LTE/3G System-on-Chip for small cells.

The tide of hype is rising and it will reach its first crescendo at the upcoming Mobile World Congress where many Tier 1 and Tier 2 OEMs are expected to make small cell product announcements.   As with all new technologies the initial euphoria needs to be tempered with some old fashioned pragmatism.  Are service providers really looking for a multi-mode solution?  Or will they deploy best in class products to address each market of network needs separately and on different frequencies?  WiFi offers a viable option for data offload while avoiding the issues of inter-cell interference.  Companies like Alcatel-Lucent have already taken steps to address the dual mode WiFi / Cellular access from the Core and Access perspectives.  How will the backhaul, one of the key operator OPEX cost drivers, be addressed as it may now need to be extended to thousands of small cells within the operator network?   This question alone has created a cottage industry of backhaul startups and established microwave vendors have also stepped up to address the backhaul issue.   These are cursory and high level issues, so it’s a good thing that the Small Cell forum has as its mandate to develop consensus on common approaches, standards, best practices for small cells.

But finally, how does one build a small cell?  Is a small cell just a ruggedized Femtocell with a higher power amplifier?  If so, how many users should it support and how much power does it need?  If it needs to support a few hundred users and 2W-5W of transmit power as some outdoor deployments will require, how does one scale up the Femtocell to meet the small cell requirements? Alternatively, does one try to scale down a Macrocell into a small form factor?  Fundamentally this presents its own challenges since the macrocells were designed primarily for coverage and scalability.  In contrast, a small cell needs to address operator requirements for capacity, quick and versatile deployment, and low cost and seamless network integration.   Low cost and easy to deploy backhaul is of course a table stake, and it will be addressed with a variety of methods, but this is a topic for another post.

At TEKTELIC we believe that a small cell must strike a balance between user capacity, transmit power, size and cost.   In order to maximize the transmit power and keep the size small one must start with an integrated custom design optimized for the key performance indicators.  The RF subsystem in particular must be designed to include a highly efficient Power Amplifier to minimize power consumption, thus reduce the overall product size, cost and weight.   Simply put, this means that the Power Amplifier must incorporate high efficiency design topologies and the overall system must support Digital Pre-distortion, Crest Factor Reduction and other technologies.  These capabilities are certainly widespread in Tier 1 vendor macrocellular systems,  but they have not been utilized in Femtocell systems due to much lower transmit power and higher barriers to these technologies.

Many issues need to be addressed before small cells, especially powerful outdoor models, become a reality.   At TEKTELIC we are well aware of these challenges and are applying our technology and experience to designing and building the solutions which optimize the small cell equation of power, cost and size.    Get in touch with us if you would like to learn more about how we solve some of these challenges..