A new small cell approach is required for large indoor buildings

Tower BlockBehind the hockey stick growth charts showing rapid wireless data traffic increases, there is a behavioural change taking place inside our workplaces. Voice calls previously using fixed wired telephone extensions are more often being taken on mobile phones. Checking email is no longer constrained to the desktop, or even laptop. These days your email is more likely to be read on a Blackberry, smartphone or tablet – as evidenced by those little "sent from my iPhone" footnotes on the reply.

This trend is present in all sizes of business, large and small, and across both public and private sector. Competitive advantage is to be gained by anticipating and addressing this change in user behaviour.

Mobile operators have traditionally addressed their large enterprise customers through a direct sales channel, signing deals for thousands of employees in return for low rates and subsidised phones. This market segment can contribute as much as 30% of their total revenue. Often, the arrangement will require the operator to provide adequate coverage and capacity inside the office building to handle the traffic demand.

In the past, large buildings would be equipped with Distributed Antenna Systems (DAS) which distribute the wireless signal throughout using bulky and expensive RF feeder equipment. Installations may take weeks, involve RF technical specialists and have significant costs. This restricted these solutions to the top tier of customers and left many corporate customers less than happy with the service provided.

New technical architecture required

At Small Cells Global Congress 2012, Huawei stated that "DAS is simply not good enough anymore" – new technical solutions are required. Their approach is to expand a nearby macrocell, connecting it using fibre to a distributed array of radio access nodes inside the building. However, the need for a dark fibre connection between the two (at a sensible price) cannot be assumed, even in urban areas. The cost of the system is based on macrocell technology, rather than purpose designed small cell approach.

Also speaking at the conference were SpiderCloud, who have perfected their high capacity enterprise solution which they call an Enterprise Radio Access Network (E-RAN), specifically architected to meet the needs of large scale enterprise deployments.

A third approach evolves from residential femtocells, but using more powerful and higher capacity. Ubiquisys offer a femto-grid which allows small clusters of enterprise femtocells to co-ordinate between themselves and shift the capacity and coverage of each cell to adapt to measured traffic demand.

Today, NEC currently resell and deploy both SpiderCloud and Ubiquisys systems.

While the needs of SOHO businesses could be met by 1 or 2 small cells, and small to medium businesses might require up to 10, large businesses could justify anything up to 100 or more.

Key attributes of a large enterprise small cell solution

There are a number of factors that need to be designed into a small cell enterprise solution targeted at the larger corporate premises.

  1. Seamless Mobility. A residential or small office femtocell user may leave the building only two or three times a day, and is unlikely to be mid-call. Large offices, equipped with many small cells, frequently have people walking around mid-call or mid-session. There are several issues with this:
    • Calls/Sessions need to be seamlessly transferred between the small cells and by default would be handled by the core network. This places a heavy load that could better be handled locally.
    • Frequent hard handovers require additional processing and transmissions with the mobile device, increasing battery consumption and reducing battery life.
    • There may also be a greater risk of call drops.
  2. Consistently high throughput. One issue with DAS systems is that they distributed a fixed amount of capacity around the building – improving coverage but not necessarily capacity. Each extra small cell provides substantial extra throughput, essential to meet the growing demand and avoid wide variations in data rates.
  3. Enterprise-Centred Management. An operator should be able to manage each enterprise small cell system as a single entity, rather than having to manage individual small cells. This reduces operational costs and allows the operator to offer and report on SLAs (Service Level Agreements) to its enterprise customers.
  4. Rapid deployment. The cost of an enterprise installation impact both parties – businesses can't afford periods of long or disruptive downtime, while the operator needs the cost to be low to remain viable and competitive. The system should be smart enough not to require specialist technical planning or deployment staff, use commonly available wiring/cabling, and be self-organising and self-optimising to adapt to each individual corporate environment.
  5. Efficient use of Backhaul. Dedicated transmission between the customer site and the operator's core network can be costly, but is likely to be justified to ensure good QoS. Optimising the traffic on this link by reducing unnecessary signalling overhead, routing calls and intranet traffic locally within the building improves system efficiency, security and reduces cost. A by-product is the reduced transaction load on the core network.
  6. Scalability. A solution needs to be able to cope with the largest enterprise buildings and campuses of anything up to 500,000 square feet. It also needs to handle the forecast growth in higher traffic demand either by subsequent addition of extra small cells and/or use of Wi-Fi and/or LTE within the same radio heads.
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