By David Swift, senior product marketing manager, Wireless Networks Marketing & Strategy, Alcatel-Lucent

Mobile data is growing at such an unprecedented rate that traditional macro-only mobile networks cannot meet demand, either economically or operationally. This is because it is hard to make spectral efficiency improvements as we get closer to the theoretical limits of spectrum predicted by Claude Shannon; and it will be impossible to put macrocells everywhere capacity is needed due to regulatory and cost constraints.

The solution for providing massive capacity is the effective segmentation of radio frequency (RF) into smaller geographical “bins” or coverage areas. (See Simon Saunders’ post on managing interference).  There are a number of ways to do this: one way is to deploy active array antennas (AAA). Another is to utilize metrocells, a type of small cell which operates within the public network.

Metrocells appeal to mobile operators for a number of reasons. They let operators strategically and cost-effectively add capacity to traffic hotspots to improve the quality of experience (QoE) for end users. Simply put, more bandwidth and a better throughout and connection time, means a happier customer.

In addition, they extend network coverage to indoor locations that have traditionally been challenging to cover with a macro-only solution

Bell Labs compared the total cost of ownership (TCO) of a macro-only solution to that of a macro and metro cell solution, with and without the early introduction of LTE. The Bell Labs study showed that a W-CMDA macro and metro cell solution provides a 38% TCO savings compared to a W-CDMA macro-only solution. When LTE macrocells are deployed with W-CDMA and LTE metrocells, the five-year TCO is reduced by 45%, compared to deploying W-CDMA macrocells only.

Why and when should they be deployed?

When to deploy metrocells depends on whether metrocells will be used for capacity or coverage.

As a capacity solution, metrocells are usually deployed in high-traffic locations to offload traffic from heavily loaded or saturated macro sites. To better understand when high-density W-CDMA networks will become saturated, with and without the launch of LTE, Bell Labs conducted a five-year network simulation with a Tier 1 operator in Western Europe. The simulation showed that approximately 2% of all W-CDMA macrocell sites are already saturated. Therefore, if you have a high-density network and are planning on launching LTE late, you  would benefit from deploying W-CDMA metrocells as a capacity offload solution right now.

If LTE is to be launched early, the you can start to deploy metrocells now on a more selective basis, then increase the volume of deployment in 2013 or 2014, as the macro sites begin to saturate. LTE metrocells, on the other hand, should be incorporated into the LTE network design from the onset, especially for high traffic-density zones that are expected to saturate quickly after service launch.

Where do  they make the most sense?

Metrocells are used to provide capacity for urban hotspots, improve coverage in indoor locations and extend network coverage and capacity to rural locations. When used to provide capacity to urban hotspots, metrocells are deployed in selected high-traffic locations, such as city centers, train stations or shopping malls.

When used to improve coverage for indoor locations, metrocells can be deployed within indoor convention centers, hotel lobbies, shopping malls, hospitals or office buildings. And they can be targeted at areas with poor or non-existent macro coverage. In summary, metrocells can be deployed where they offer a lower TCO than other methods of extending coverage to in-building locations.

For coverage and capacity extension to rural areas, metrocells are deployed in villages and other rural areas to deliver cost-effective voice and packet data services to locations with poor or non-existent macro coverage. Ideally this will be in one of the lower spectrum bands such as the Digital Dividend 800MHz band or refarmed 900MHz GSM spectrum (refarmed for use in 3G).

Iuh or Iub?

Adopting an Iuh (3GPP-defined macro) architecture for the integration of metrocells into a W-CDMA network offers operators several advantages over an Iub (Home NodeB) architecture. These include multi-vendor support, easier deployment of metro cells, relaxed backhaul requirements, efficient metro-to-metro handovers, IP traffic offload, subscriber group control and massive scalability. Soft-handovers (SHOs), supported by the Iub architecture, is an important feature for maintaining circuit-switched voice calls during macro-to-macro handovers, but is not essential for metrocells that are mainly used in shared carrier only for HSPA services.

Should a dedicated or shared carrier be used?

The economic return of a metro network is driven by the percentage of traffic that it offloads from the macro network — and this percentage is heavily influenced by which frequency is allocated to the metro layer. Metrocells can be deployed using a dedicated frequency or by sharing a frequency with the macro network

With a dedicated carrier, you reserve a carrier for the exclusive use of metrocells in geographies that have been specifically targeted as needing extra capacity. In all other areas, macrocells can use this same carrier. With shared-carrier deployments, metrocells use one of the same carriers assigned to the macro layer, which would nor­mally have one or more additional dedicated carriers. The coverage range and offload effectiveness of metrocells deployed with shared carrier are lower than those using dedicated carriers. Also, with this type of deployment, metrocells cannot be placed too close to high-power macrocells.

Our Bell Labs simulations demonstrate that with typical shared carrier implementations, approximately 20% of the traffic can be offloaded from the macro layer, whereas with dedicated carrier, 70%  of the traffic can be offloaded. This is why we prefer dedicated carrier deployments over shared carrier ones. The high economic return of using a dedicated carrier for metro cell deployments suggests that, when it comes to metro cells, operators need to change their way of thinking and not use all available spectrum to add capacity on the macro network.

To help you successfully introduce metro cells, we created a solution called Metro Cell Express  to find out more how to overcome  the challenges of building a metro cell network and address the issues beyond the radio, including power, backhaul, installation, commissioning, provisioning, configuration, network optimization, site selection and acquisition — and regulatory and policy compliance go to this website.

This post was originally published on Wilson Street’s blog.