Optimised networks

With demand for 3G access in offices and public spaces often outstripping capacity, picocells may offer the best solution.

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By  Dr. Andy Tiller Published  March 11, 2009

With demand for 3G access in offices and public spaces often outstripping capacity, picocells may offer the best solution.

As enterprises turn to 3G for mobile voice and data services, operators will face a significant challenge: getting enough coverage and capacity into office buildings.

In the 2G world, picocells have proven themselves to be a cost-effective solution and are being widely deployed. But as the 3G enterprise challenge hits the radar screens of mobile operators, there is an apparent choice between using 3G picocells or alternatively adapting consumer-style femtocells to serve the enterprise.

Desktop PCs and laptop computers will undoubtedly remain the primary means of accessing data services in the office, but business users increasingly rely on their mobile handset during meetings and other occasions when the computer is not accessible.

Knowledge workers on the move are becoming familiar with 3G performance when using enterprise applications, downloading email attachments and accessing the internet from their smartphones and HSPA-enabled laptops.

As these workers get accustomed to 3G performance on their travels, they will expect and demand the same performance inside their offices. Unfortunately, that's a challenge for today's 3G networks. The walls and windows of office buildings absorb most of the radio energy transmitted by the outdoor network.

The energy that does make it through to the user is typically as little as a fortieth of the outside power (and often much less). This results in customer dissatisfaction with patchy voice coverage, and especially with poor data performance, because high-speed data requires a very good quality signal.

Mobile operators are vulnerable to losing business customers in places where their in-building coverage is poor - for example, T-Mobile cites this as the top reason its customers switch to rival networks.

To make matters worse, since all users in a 3G cell share the available base station transmit power, a few indoor users consuming data services can significantly reduce the capacity of the entire cell and compromise service quality for outdoor users as well.

Operators need a cost-effective way to deliver 3G coverage and capacity directly to enterprise users in their offices.

The enterprise 3G market is bound at the low end by small offices roughly the size of homes - in fact many of them are homes - where 3G coverage can be provided by a single femtocell designed for residential use.

A 4-channel femtocell could potentially serve an office of up to 10 mobile phone users. On the other hand, it might be sufficient for only four (or even fewer) handsets if mobile phone usage is heavy or if the quality of service needs to be better than the macro network outdoors.

At the high end of the market, the largest offices are covered by traditional in-building solutions such as distributed antenna systems and micro base stations, often complemented by picocells where a rapid solution is needed with minimal disruption.

The pay back from keeping important enterprise customers happy justifies the operator's investment in wireless solutions.

Between the two extremes is a large market consisting of offices housing up to 100 staff, which accounts for more than half of all office premises. Many of these smaller offices belong to large enterprises. The remainder belongs to Small to Medium Enterprises (SME).

Mobile and fixed operators are beginning to compete more aggressively for SME customers. As the trend to all-mobile office communications continues, mobile broadband has provided an entry point for mobile operators to target the SME market. But the fixed-line carriers are fighting back with their own enterprise FMC offerings based on dual mode WiFi handsets.

In this environment, it's especially important that mobile operators can offer a cost-effective way to guarantee 3G voice quality and data performance in smaller office buildings.

More than a third of SMEs have mobile phone coverage issues in their places of work, according to Quocirca's 2008 survey of the UK, France, Germany and Sweden. But historically, mobile operators have had no cost-effective way of in-building wireless solutions for the majority of this market.

A consumer femtocell lacks the capacity and range required to provide coverage in most of these offices, and the cost of DAS is prohibitive. Sometimes end customers try to solve in-building coverage problems for themselves by installing repeaters, which can cause a variety of problems for the outdoor network.

Operators getting to grips with the 3G SME opportunity are beginning to evaluate their alternatives. For all but the smallest and largest premises, the choice comes down to two approaches: either deploy multiple consumer-style 3G femtocells in each office, or deploy 3G picocells.

In principle, both options deliver compelling benefits. Not only do they bring a complete base station into the office, delivering targeted coverage and capacity exactly where it's needed, they also remove in-building users from the macro network, freeing up capacity and improving network performance for outdoor users.

They also use IP backhaul over a fixed-line broadband connection to significantly cut the cost of installation and operation, and they can be integrated to a local PBX, turning the mobile phone into a fixed line extension when in the office.

Drawbacks

Both solutions have traditionally had drawbacks. Early 3G picocells were large and expensive, requiring dedicated E1/T1 lines for backhaul and on-site installation by the operator.

Meanwhile, femtocells were designed for residential use - one per household - with insufficient capacity and range for offices. But recent developments are changing this picture, making both options potentially a lot more attractive for the SME market.

A new generation of 3G picocells builds on today's 3G femtocell technology. These picocells have higher capacity and range than femtocells, but they are based on low-cost femtocell technology platforms, and take advantage of auto-configuration techniques developed for femtocells to enable self-installation by the end customer.

They also share a common network architecture with femtocells, and they will conform to the new Iu-h standard for core network integration.

These next-generation picocells are sometimes referred to as "super femtocells". Some femtocell vendors are promoting the concept of an intelligent femtocell grid, which automatically configures itself to optimise performance in premises which require more capacity or coverage than can be provided by just a single femtocell access point.

These femtocells hand over calls between them as people move around the building, and support load balancing so that users are passed from one femtocell to another when one is at full capacity.

3G picocells and the femtocell grid

Several factors must be considered when comparing 3G picocells with the femtocell grid approach including: The number of femtocells it takes to equal the coverage and capacity of a single picocell; How femtocells and picocells handle the uneven distribution of users within the office at different times of day; How capacity, coverage and user experience are affected by interference between access points in the office.

The femtocell grid potentially offers greater data capacity (typically 7.2 Mbps per access point with today's femtocells versus 7.2 Mbps for the whole office with the picocell). However, interference between femtocells diminishes this advantage.

One final cost consideration is that the core network infrastructure for femtocells is designed for mass market scale. An operator without an existing consumer femtocell offering to build on might find the start-up costs for picocells are lower, especially for small scale deployments.

Access control

A picocell serves mobile phone users wherever they are in the office, so users are covered under all circumstances. Femtocells only cover a small, local area, so you would need to put more of them into hotspot areas to provide enough capacity, adding extra cost and creating more interference.

A standard feature of consumer femtocells is support for access control, giving the end customer control over which phones can use the network.

Most picocells will not be deployed at high power in closed access mode because this could potentially create coverage holes on the macro network for non-authorised users in the picocell coverage area. A low-power femtocell with a small coverage area has a potential advantage here if access control is important.

On the other hand, it is questionable if the sometimes non-existent IT department in a small business would want the hassle of administering the access control list for all members of staff, contractors and visitors.

It may be simpler to deploy picocells in open access mode with sufficient capacity to give passers by basic voice and internet services. This is the normal mode of operation for 2G picocells today.

Dr Andy Tiller is VP Marketing at ip.access, a manufacturer of picocell and femtocell infrastructure solutions for GSM, GPRS, EDGE and 3G. www.ipaccess.com

Guide to indoor networks

1. Consumer femtocells are a good solution for the small homes and offices market, where offices are similar size to homes.

2. The right approach to 3G coverage in SME offices (and branch offices of larger enterprises) is to use a next-generation picocell (or super-femtocell) with range and apacity appropriate to the size of premises.

3. A single wall-mounted picocell can provide coverage and capacity for the entire office.

4. Capacity is unaffected by users moving clustering in one area.

5. Interference issues can be significantly reduced.

6. Advanced management features give the operator control over service quality for important business clients.

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