Radisys has been active in the femtocell and small cell industry for some years. The company's CTO, Manish Singh, is a board member of the Small Cell Forum and the company won a Small Cell Forum award this year for best enabling technology.
Supplying software solutions to many customers for both 3G and LTE, they are well connected with the industry. I asked Manish for his views on the current market status.
What are operators asking for today?
Ideally, operators would like to see combined 3G and LTE running in the same small cell box with the ability to pick and choose either or both. Operators with an IMS core are less likely to go with dual mode. Rather, they will leverage VoLTE solutions that enable them to support both voice and data over LTE. Others will choose dual mode as they need Circuit Switched Fallback to support voice. Integrated Wi-Fi in the small cell is the common denominator. The nirvana is a low power, low cost tightly integrated solution which means it would be a SoC (System on a Chip) supporting both 3G and LTE with flexibility to select either or both. But that's not in production yet, so operators are first asking for standalone 3G or LTE today with the ability to upgrade to multi-mode at a later date.
Silicon vendors are actively developing products capable of dual PHY (physical layer) and with the raw horsepower to support both technologies. Our software products have both 3G Release 8 with extensions and LTE Release 9 (as used with Korea Telecom and South Korea Telecom in the world's first LTE small cells), so we are ready to support these new chipsets as they emerge.
We are also seeing an increase in capacity and scalability which comes with a demand for both indoor and outdoor products. The earliest 4 channel femtocells are making way for 16, 32 and even 64 channel small cells. We've seen operators become more confident with small cell technology now that it has been through several years of commercial deployment and thus are looking to apply small cells in multiple different locations beyond the home.
How do you expect LTE to grow compared to 3G?
We expect to see Asia grow LTE small cells volumes more quickly than elsewhere – all indications point to one of those big "hockey stick" growth curves. Elsewhere, especially in Europe, we think 3G investment will be more prominent while LTE macro network deployments move along at a slower pace.
LTE is perhaps still at an early stage in its lifecycle compared to 3G, and as such the standards and implementation code are changing more quickly with the results of real-world deployment. It may make more sense to allow LTE to finish this early stage before focusing too much on the tight integration with 3G.
However, in the medium to long term, both technologies will be widely used and combined in the same small cell units, together with Wi-Fi. This creates an opportunity for clever solution differentiation through combined Radio Resource Management (RRM) and Self Organizing Network (SON) functionality that spans all three air interfaces.
Is the LTE X2 interface ready to open up the small cell market for newcomers?
The X2 standard interface allows an operator to choose different vendors for their small cells and their (existing and larger) macrocells. It's already been defined within 3GPP Release 8 for eNBs with Release 9 extensions for HeNBs, but is not in commercial deployment today. The X2 interface allows cells of the same access mode to connect with each other (if an operator desires so) either directly or via the HeNB-GW as a proxy in later 3GPP releases.
The X2 interface can be regarded as a facilitator of two independent features. (a) X2 for the purpose of mobility and (b) X2 for the purposes of SON.
When we consider mobility, X2 in effect provides an "enhanced" relocation which otherwise is also possible via the S1 interface. By exploiting X2, the signaling is kept "local" and the Mobility Management Entity (MME) need not be disturbed unless it becomes a stipulation, say for reasons of access control. Mobility via X2 is also appreciably quicker and hence operators who adopt VoLTE will prefer to relocate voice bearers via X2.
When we consider SON, 3GPP has in consequence specified the interfaces (input and output), but not how that information can be utilized within the radio access network nodes. High interference indications, overload indications, narrow band transmit powers, subframe blanking patterns etc. can be exchanged between two peer nodes to ensure that the network can work in equilibrium. X2 becomes a fundamental requirement for HetNet deployments. X2 has evolved every release since 2008 and we can expect the X2 interface to offer even greater refinements going forward.
Undoubtedly there should be a big focus on IOT (Interoperability Testing) since "algorithms" that are invoked within an eNB (or small cell) in a multi-vendor environment are vendor dependent. This ensures that any gaps in the standards work are exposed and resolved at an early stage. As we speak, we are actively testing X2 in field trials that we are participating in throughout Asia and with collaboration and operator attention it is being leveraged to deliver both SON and mobility capabilities.
What differences are you seeing between indoor versus outdoor small cells?
We expect a lot of growth indoors, especially enterprise. Traffic forecasts show higher levels of demand indoors, especially where people are sitting. With greater reliance on wireless devices, we can expect substantial numbers of small cells to be deployed in these environments. It is also worth noting that indoor and outdoor cells, though deploying the same radio access technology, will instrument differing sets of algorithms as they are aimed at solving differing problems, in some cases orthogonal.
For example, a cell deployed in closed access mode, typically an indoor cell, will have to employ sophisticated uplink (reverse link) interference mitigation techniques because inbound mobility into such a cell is prohibited for non-members. While the same problem does not afflict the outdoor cell with the same intensity, the outdoor cell has differing sets of problems to solve. As an example, RACH capacity needs to be optimized as the number of users attempting access is several folds higher in the outdoor case.
From an outdoor perspective we're seeing demand for higher channel capacity with 32 being the minimum as well as a clear preference for open access. These small cells are focused on capacity augmentation in high traffic areas or "hot zones" and require tighter integration with the macro network for mobility and interference management. We have seen the majority of focus on LTE for outdoor deployments while more energy remains on 3G in the indoor enterprise segment.
Enterprise small cells will see local gateways installed at larger businesses. The mission critical nature of communication services means that these need to be very resilient with high availability.
Our ATCA platform is ideal for these carrier class enterprise applications, rather than relying on commodity web server machines. To address these requirements for lower capacity systems we also introduced RMS-220, our NEBS compliant, 19" deep, carrier-grade rack mount server which is ideally suited to meet these resiliency and high availability requirements. These platforms support load balancing and local breakout directly into the corporate networks and IPBX voice switches.
Finally, where do you see Wi-Fi fitting in?
Commercial, standards, and industry forum activity have been high in the past year for integrating Wi-Fi with operator networks. This has resulted in huge demand for infrastructure spanning security gateways and Wi-Fi access gateways supporting several aspects: Authenticating subscribers with a cellular SIM card with EAP-SIM/AKA, enabling secure access from partner or carrier deployed Wi-Fi, and supporting secure access over consumer Wi-Fi. Femtocell/small cell security gateways share many aspects with Wi-Fi security and access gateways.
This means we can expect to see integration of 3G, LTE and Wi-Fi throughout – in end user devices, small cells and core network gateways. Radisys is well positioned to address the security gateway requirements with our SEG product line which offers both security gateway as a standalone box or as SEG on an ATCA blade that can be easily integrated inside any core mobile network gateway.