Enterprise Small Cells address any non-residential in-building. Businesses and offices, where a Small Cell system may be installed specifically for the benefit of staff, may find being tied to a single network operator is acceptable. The additional revenues from captive business subscribers justify and fund the installation of the in-building small cell system.
But many venue owners that serve the wider public are really looking for a solution that works with any network provider. The additional benefit they derive from good indoor coverage for everybody may mean they would contribute towards the cost of the system. Evidence for this includes the growth of so-called Amenity Wi-Fi, which is often paid for by venue owners as just another utility provided for visitors. The Small Cell Forum has looked into the options and published a paper on the topic.
The brute force method using duplicate Small Cells
Cellular systems operate on licenced spectrum bands, with each operator serving their own customers with their own spectrum. This would mean that to provide service for (say) four national mobile networks, you'd need to install four separate sets of Small Cells within the building.
By comparison, multiple Wi-Fi network operastors could also take this approach, installing separate Wi-Fi access points for each provider. This does happen, most visibly at conferences where every booth and display stand seems to have their own private network, but also in many multi-tenanted offices and tower blocks.
That's neither commercially feasible nor technically efficient, so other methods have evolved.
Broadly speaking, there are four ways of addressing the problem, of which three use Small Cells:
- National Roaming, a commercial arrangement where customers of one network can use the radio access of another
- Installing duplicate sets of small cells, one per network operator.
- Use Small Cells which support multiple networks, using either MOCN (Multiple Operator Core Network), a technical interworking where the small cells are connected to multiple networks and broadcast multiple network identities or GWCN (Gateway Core Networking), another technical interworking architecture but only at the core network level.
- Install a Distributed Antenna System (DAS) which can be powered by Picocells or Small Cells
This is perhaps the simplest technical method and quickest to implement, especially where there is poor coverage that encourages your phone to seek out a better signal. It's also quite common in the US, where many local operators have better in-building coverage than national operators in the more rural areas. It can also be commercially rewarding. One example from the Small Cells Americas conference quoted a rural operator who had seen a swing from a $5K to $10K monthly loss into a $5K to $10K profit by installing an outdoor Small Cell, switching outbound roaming costs into incoming roaming revenue.
This is also technically feasible in other countries, but rarely implemented. The UK regulator has made it clear there are no regulatory barriers – it's purely a commercial arrangement. The situation may vary in other countries.
In this approach the strongest beacon wins (i.e. the cellsite with the best signal received by the smartphone would be used, with preference to the home operator's cellsites). Smartphone SIM cards, core network and other systems would have to be remotely provisioned to allow and enable this function.
The option isn't open where different mobile radio technologies are used – Verizon and Sprint 3G CDMA customers can't share an AT&T or T-Mobile 3G UMTS Small Cell because CDMA and UMTS aren't compatible. This changes when all four migrate to the same common LTE technology.
Shared Operator Small Cells
You may be familiar with how a Wi-Fi access point can have multiple identities. Several different SSIDs (Service Set Identity) can be used for different purposes, such as one for private use versus a separate one for guests or paid access. Resources can be allocated and prioritised for each.
Small Cells could also operate in this way, with an existing standard allowing up to 6 different PLMN (Public Land Mobile Network) identities to be supported. The standards define two different network architectures for this:
- MOCN (Multiple Operator Core Network), where each small cell communicates directly with multiple core networks
- GWCN (Gateway Core Network), where the interworking is achieved at the core network level.
I am unaware of any deployment of this feature using Small Cells as yet although I have heard of at least one company developing it, and suspect this will come first in an LTE product.
Multi-Operator DAS System
Large buildings can be equipped with DAS, which pipes the RF signals around the building to multiple remote radio antennas. Typically a central machine room is fitted with one or more basestations from one or more operators. The DAS system combines the RF output and sends this using fibre or co-axial cabling to each floor, splitting the building into multiple sectors.
DAS is generally considered to be quite an expensive solution but does use the full spectrum available from each network. The low RF power used by active DAS systems (which include RF repeaters) means that some can be driven directly from Small Cells.
Some sharing issues
Where Small Cells are used more for coverage than capacity, it may often be sufficient to provide service using only one mobile network's spectrum. Savings come from installing and managing only one set of equipment. In cases where there is huge demand for capacity, perhaps it does make sense to install multiple Small Cells – one for each operator – to provide cost effective high traffic capability. Alternatively, you could just install more Small Cells and reuse the same spectrum.
Small Cell Management systems use the TR.069 standard with extensions. There are a few gaps and shortcomings in the specifications to configure a MOCN small cell which need to be addressed.
SON (Self Organising Networks) software handles the parameter management and optimisation for both Small Cell and Macrocell networks. The closer interworking with national roaming or MOCN Small Cells is an added complexity.
There remain some older featurephones and smartphones which don't implement the 3GPP Release 6 features to support MOCN. A technical workaround has been designed to cater for this.
The issue that Small Cells are locked to one network operator affect the business case and likely takeup, especially for public venues and amenities. Operators are bound to prefer being the sole provider, which would help fund investment to pay for the installation.
For business use this may be more acceptable, with the business owner and operator both benefitting from a wholesale arrangement. For public venues and those businesses where providing good connectivity to guests is important, multiple operator service is more critical. This may encourage the venue owner to subsidise or pay for the Small Cell installation.
National roaming provides a quick commercial solution whereas MOCN and GWCN are more technically complex. Issues such as network optimisation, smartphone compatibility and Small Cell remote management need to be addressed.
I liked this short article from Unwired Insights (2013) on the state of RAN sharing and 3GPP standards. For a more detailed analysis, read the 20 page Small Cell Forum document Enterprises and Multi-Operator Small Cells (069)