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Bulging SuitcaseWhile it is the prerogative, and perhaps the duty, of Network Operators to stretch the capabilities of equipment manufacturers, we risk delaying the wide scale deployment of small cells, and their associated capacity and user experience benefits, if the MNOs and vendors spearheading its adoption are unable to make some choices. 

Cost and ease of deployment in city environments are both critical requirements for metrocells but to achieve these we will have to be selective about other highly desired attributes. 

We can't risk demanding too many requirements and asking too much of developers.

Key deployment considerations for the physical design of metrocells

Many of the environmental and operational requirements for metrocells can be transferred directly from existing RRH (Remote Radio Head) and outdoor microcell products.  However, the scale of metrocell deployments and the use of below rooftop locations will make some requirements, such as fan free operation, mandatory and will also introduce some additional considerations for these products.

Ease of deployment and operation

A previous ThinkSmallCell article “Metrocells-Is now the time for a landgrab?” discussed agreements with Local Authorities and the use of street furniture to deploy metrocells. Lamp Posts (or Light Poles) are likely to be widely used to house metrocells but, in addition to hard requirements, such as meeting the weight and wind-load capabilities of the host pole, the more subjective and highly variable requirement of aesthetics becomes a critical factor.

Security

As metrocells will be deployed in areas which could be accessed relatively easily by the public they must be tamper proof and be secured at the point of installation.  At the same time the installation needs to be quick and simple to keep down deployment costs.  One key consideration is whether metrocells need to provide the capability for a technician to access the unit in the field or whether a “return to base” support model is employed. The latter would allow for more secure sealing of the metrocell enclosure and would also reduce the required skill level of the deployment staff, which could be more cost effective than field repairs.

What’s in the box?

The quantity and variety of radio modules within a metrocell, as well as their specified transmit power levels, will have the greatest impact on the unit’s physical specification. The products being offered today range from around 6kg for the smallest single mode unit to around 12kg for a metrocell housing  three radio modules (these are the figures for the metrocell excluding external components such as antennas or covers). In order to provide flexibility, a number of vendors are taking a modular approach to their design; developing an enclosure capable of supporting a mix of technology combinations through plug-in radio modules. While this flexibility could also be used to enable upgrades, in practise it is more likely that technology advancement would make replacement of the complete metrocell more attractive than upgrading internal modules only. To understand the implications of including a wide range of capabilities on the physical attributes of the metrocell let’s look at some of the key functions which need to be considered.

Access Technology

Although not universally accepted, there is broad consensus that metrocells are data oriented. This still leaves 3G, LTE and Wi-Fi as potentially valuable access technologies. The webinar “The Compelling Business Case for 3G/LTE Multi-Mode Small Cells” discussed some of the implications for multimode small cells and the potential upgrade benefit of multimode chipset based solutions. 

When operating in concurrent mode (multiple access technologies in operation simultaneously), to provide higher capacity and/or serve multiple RAT types, each access technology requires additional PA and filtering hardware.  This significantly increases the requirements relating to volume, weight, power consumption and heat dissipation.  Typically, each technology is also mapped to a different frequency, with lower frequencies requiring larger RF front end components.

Backhaul and Power

Where readily available, wired Ethernet connectivity can adequately serve the backhaul requirement of a metrocell.  It may also be possible to power single radio metrocells through the same cable using PoE+ (Wikipedia: Power_over_Ethernet, IEEE 802.3at-2009 ), but due to the limited power available via PoE+ (currently 50W max in the specification referenced above) this is more likely to be applicable to indoor or low Tx power small cells only.

Where wired Ethernet is not available at the preferred deployment location, there are a number of wireless backhaul solutions which can provide a quickly deployable alternative.  Integrating the wireless backhaul module within the metrocell enclosure provides a single box solution but it adds another radio which, as discussed above, significantly increases the size of the unit.  An external backhaul unit gives the Network Operator more flexibility in their choice of vendor but the total amount of equipment to be deployed increases in both quantity and volume, and an external connection from the metrocell to the backhaul unit (typically a single Ethernet connection providing connectivity and power – subject to the 50W limitation referenced above) will be required.

Antenna solutions

Given the variety of options for Radio Access and Wireless Backhaul solutions, which may include both directional and omni-directional antenna patterns, designing an unobtrusive antenna solution is challenging.  This is complicated further with inclusion of additional radio modules such as GPS; which is required to provide location information in certain markets.  Techniques such as incorporating antennas into the enclosure of the metrocell or use of an external shroud to hide the metrocell and its external components are being employed to improve the aesthetics of these solutions.

Summary

The business case for small cells requires them to be competitive with existing cell sites in terms of both CAPEX and Opex and to be easily deployable in high volumes.  If lamp posts and other street furniture are to be widely used, a discreet design is a mandatory requirement in most markets. Perhaps we need to look beyond the traditional box shaped form factor and think more broadly and creatively as to how the metrocell integrates with its intended environment.

The quantity and variety of radio modules has the greatest impact on the physical specification for a metrocell. Building too much functionality or flexibility into the mechanical design, to support multiple configurations or potential upgrades, carries a cost in relation to form factor which is likely to severely impact ease of deployment. Selecting the correct access technologies will, therefore, have the greatest impact on the ease of deployment of the metrocell network, its utilisation and on the ROI of the metrocell program.  In making this assessment we should also consider the cost of deployment and the required service life to achieve ROI targets.

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