One of the biggest barriers preventing widespread adoption of Enterprise small cells is that they are tied to a single network operator. Venues and many enterprises really want connectivity to multiple mobile networks. We explore half a dozen contrasting ways to achieve this, and discuss the pros and cons.
The requirement for universal seamless service
The fundamental requirement is that everyone’s mobile phone is supported regardless of which network operator they belong to.
Different terminology is used: “Neutral Host”, “Multi-Operator”, “Open access”.
DAS (Distributed Antenna Systems) and Wi-Fi can generally be used from any smartphone or device, regardless of which mobile operator subscription you have. Small Cells have been tied to a single network but there are several technical alternatives either available or coming soon to solve this issue:
- Multiple, independent small cells (one set per mobile network operator)
- Multi-radio small cells (dedicating one radio per mobile operator per unit)
- Network sharing using MORAN or MOCN
- Small cells in shared spectrum (e.g. 3.5GHz CBRS in USA)
- Small cells in independent licensed spectrum (3.5GHz in Europe)
- MulteFire (e.g. adapted LTE operating exclusively in unlicensed spectrum such as 5GHz)
Any of these can be connected directly to an independent commercial organisation who aggregates traffic from many businesses and interworks with multiple mobile network operators. Such organisations are commonly termed Neutral Hosts.
Multiple Independent Small Cells
With the cost of Small Cells being relatively low compared to other solutions, it can be less expensive to install separate units for each mobile network. While this may sound wasteful, a ratio of 1 small cell per 4 Wi-Fi access points is not unusual – the higher RF power, lower interference and lower frequency used significantly increases the range of a small cell vs Wi-Fi access point. Thus installing combined Wi-Fi/Small Cells with each operator having a quarter of total installation is quite feasible.
Mobile operators may have different requirements within the same building. They may have better or worse outdoor-in coverage, a different mix of 3G/4G devices to support, support for VoLTE or not, LTE Carrier Aggregation or MIMO. This leads to a different specification for their small cells, at least from a configuration perspective.
While it may be technically possible for several units to share the same antenna and hide equipment (e.g. behind a false ceiling/plenum), I suspect that it would be easier to use integral antenna within each separate small cell. The plethora of Wi-Fi access points deployed today, discretely disguised or hidden in many conference rooms, are a good example of what’s possible. In many cases, it should be feasible to combine both small cell and Wi-Fi products into a single unit.
Multi-Radio Small Cells
Several vendors now offer Enterprise small cells with two radios. These are commonly configured for either 3G/4G multimode, or to provide higher speeds using LTE Carrier Aggregation.
Another configuration would be to allocate each of the two radios to different mobile networks, operating in their respective frequency bands. Each network would have to choose either 3G or LTE and share the same RF footprint and deployment profile as each other.
A slight variation on this would be to use something like the Commscope (formerly Airvana) “toaster rack” approach, which combines four independent radio nodes into mini-rack connected to a common shared antenna.
My sense is that this approach hasn’t proved popular. At this stage either 3G/LTE multimode is still required or the tight integration between networks isn’t so common. Some consider the physical deployment to be awkward and bulky.
Network sharing through MORAN or MOCN
There are two different well-defined 3GPP standards for network sharing, which allow the spectrum of one mobile operator to be shared by others. MORAN is inherently available in distributed radio systems, such as Huawei’s Lampsite or Ericsson Radio DOT. MOCN is a core network feature with fewer constraints on the radio network.
Both are fully standardised but relatively rarely implemented for commercial reasons.
They could be attractive to those networks who already use them, extending their partnership indoors.
Small Cells in Shared Spectrum
The USA is actively debating how to share spectrum at 3.5GHz using several levels of priority access. Those who pay for a licence will have higher priority, while those who don’t will still get some access but at a lower level.
This spectrum could be used by independent operators (or building owners) to provide service available to all. Since this doesn’t interfere directly with licensed spectrum, mobile operators would be less concerned.
At this stage, the solution is not yet approved. It would require not just small cells but also a new version of smartphones capable of the new frequency band.
If successful, the method might be applied for use outside the US, probably in a different frequency band.
There has also been some unlicensed shared spectrum used for small cells in Europe – specifically a small piece of the 1.8GHz band. This has successfully been used in the Netherlands for GSM.
Small Cells in independent licensed spectrum
There are already several independent LTE networks operating commercially in the 3.5GHz band in numerous European countries. These are primarily providing a fixed broadband service using wireless modems rather than a fully mobile network with smartphones. However, once smartphones do support 3.5GHz bands, it would be possible for them to deploy small cells and offer roaming service to all other networks on a commercial basis.
We shared more insight on this opportunity from in a recent interview with Accelleran.
This would also have been possible for those fixed network operators who bought their own, such as BT (in the UK) who acquired their own 2.6GHz TDD spectrum. However, since they’ve recently bought the mobile network EE, this independent commercial model no longer applies.
MulteFire will initially focus on operating LTE standalone primarily in the 5GHz unlicensed band, adapted to co-exist with Wi-Fi through a “Listen Before Talk” mechanism.
It will require a new generation of smartphone/tablet devices and small cells to implement this in hardware. Building owners could in theory install their own standalone MulteFire networks but are more likely to connect through a neutral host to multiple external mobile networks. Seamless service continuity with external mobile networks is being designed to ensure full multi-operator interworking.