Wireless System Design
An overview of how and why modern wireless systems are designed helps to develop a context for site acquisition work. RF engineers perform the task of system design. A clear understanding of system design objectives assists in finding locations that satisfy RF engineering criteria.
Coverage Sites vs. Capacity Sites
New cell sites are typically designed either to add more geographical coverage to a wireless carrier’s existing system or to increase capacity within existing system coverage. Therefore, new wireless sites are primarily considered coverage sites or capacity sites.
When cellular networks were first created, all sites were designed to provide coverage (which is not to say that each site didn’t add capacity to the system). At the time, a four-hundred-square-mile city metro area with a population of a million or more might have been adequately serviced by no more than a dozen sites. As the number of cellular customers increased, more sites were built to grow system capacity within the same areas covered by each of the original sites. Since new sites represent additional capacity, an area originally covered by one site can be split into multiple coverage areas or cells. This is called cell splitting and the new sites are referred to as capacity sites. Capacity sites add system capacity to an area that previously had adequate coverage, whereas coverage sites provide coverage to an area not serviced adequately with wireless.
Macro and MicroCell Sites
Traditional macrocell sites are the foundation of the wireless system infrastructure, also known as the wireless grid or ecosystem. Macrocell sites consist of elevated wireless antennas connected to associated equipment through cables placed vertically, known as the waveguide. Depending on the wireless carrier and the equipment manufacturer, the associated equipment may be in an on-site equipment shelter as large as twelve feet by thirty feet or in outdoor cabinets or on a 5 × 10 foot (or less) platform footprint on the ground surrounded by a security fence. Electricity is needed to power the facility, and telecommunication service connection(s) provides backhaul from the cell site to the public switched telephone network (PSTN) and the internet. While 3G wireless service could utilize twisted pairs of copper cables, 4G LTE service requires fiber-optic backhaul. Rooftop sites vary slightly.
The terms “macro” and “micro” with regard to cell sites refer to site configuration, coverage area radius, and placement within a wireless carrier’s system. Coverage and capacity site terminology refers to a site’s purpose or objective in the system.
DAS and Small Cells
Two primary categories of microcell facilities are implemented by the wireless industry. These are known as distributed antenna systems (DASs) and small cells.1 While both types operate small antennas, a DAS is available for sharing among competing wireless carriers, whereas a small cell system is utilized for the exclusive benefit of the one wireless operator developing the infrastructure project. Indoor DASs are common inside airports, public venues, office buildings, and shopping malls. Probably the biggest DAS growth today is in-building systems providing large office buildings quality service.2 Outdoor DAS applications are used for expanded geography such as outside public venues, college campuses, small historic towns, and ski areas. A DAS can offer all carriers equivalent access. If multiple wireless carriers each were to install their own small cell sites in the same venue, the result would be chaotic duplication of cable runs and antennas. As a result, large property owners and venue authorities prefer the DAS.
Backhaul and Fronthaul
The growth of the wireless industry and exponential diversification in small cells create great dependence on available fiber-optic transport systems as discussed in Module 1 Industry Structure. With traditional macro cell sites, backhaul to the mobile switching center was always a requirement. Until wireless networks evolved to 4G technology copper cable could be used for the backhaul. Once 4G/LTE service was deployed it became necessary to utilize fiber-optic cable for backhaul due to the greater volume of transport capacity required. As small cells and DASs have developed over the past ten years the transport links between microcell sites and macrocell sites have become known as front-haul.
Permanent and Temporary Facilities
Wireless carriers configure temporary infrastructure for additional service capacity to disaster areas and for large events such as conventions, state fairs, or cultural gatherings like the World Series, the Super Bowl, and the annual motorcycle rally in Sturgis, South Dakota. The short-term need for additional capacity may exist at these locations but without enough revenue per location throughout the rest of the year to justify the cost to build a new permanent macro cell site or micro cell sites.
