But how about the technologies involved gsm mobility management pdf their role in the delivery of wireless communications services that we rely on every day? To understand how cell towers and base stations work, start by taking a look in your own home. American neighbors, you own a cordless phone system that plugs into your home telephone line.
Except, of course, that they are built to withstand the elements, cover a far greater geographic area than your home, simultaneously support hundreds of handsets, operate in different radio frequencies, and allow users to maintain their connections while traveling from one base station to another, even while driving at highway speeds. We’re not launching into a discussion about life in medieval Europe. Rather, towers, cells and hexes are key building blocks for the design and operation of wireless communications networks. In the wireless world, a cell is the geographic coverage area enabled by a tower. Locations are carefully selected to ensure that individual cells form a tightly knit mesh without coverage holes or unnecessary overlap. Engineers use hex schemes to design cellular networks and pinpoint tower locations to meet service demand.
Wires run from the tower antennas to base station equipment, typically located at ground level in sealed telecom equipment cabinets. Components of the base station include transceivers, which enable the transmission and reception of radio signals through the antennas, plus signal amplifiers, combiners, and a system controller. To ensure antennas are tall enough to cover a targeted cell area, cell towers are typically 50 to 200 feet in height. Towers can be standalone structures, such as steel poles or lattice frame, or affixed to other structures. In the latter category, cell towers are attached to buildings, water towers, bridges, tunnels, street lights, traffic lights, stadium lights, and billboards, among other things. To accommodate community aesthetic concerns, towers are increasingly camouflaged to resemble trees or flagpoles, or concealed in purpose-built structures, such as church bell towers or steeples.
The factors affecting cell tower site selection are complex and plentiful. At a basic level, the site must be adjacent to a road for physical access, with availability of electrical power and telecommunications network connectivity. Local zoning ordinances must accommodate tower height requirements to ensure signal coverage across the terrain. Sources of electromagnetic interference need to be avoided to ensure radio signal integrity. Environmental and wildlife impacts must be considered, in addition to architectural historic preservation and aviation requirements.
The primary driver for cell tower locations is the service delivery needs of wireless carriers. Simply put, they want to be sure they are investing in infrastructure where it is needed most. When considering a tower placement, they will evaluate population and demographic data, plus the profiles of nearby businesses, pedestrian traffic, and the proximity of roads and highways. This mix helps carriers understand how many potential wireless users live or work in the area each day, plus those that will be passing through on the way to another destination. Additionally, wireless carries carefully study the voice and data traffic traversing their networks in each cell area. If utilization begins to near the capacity limits of the antennas on a given tower, they need to evaluate options to increase capacity.
Likewise, if local population and demographic data is favorable, before a carrier begins aggressively marketing wireless service in a given geographic area, they want to be sure they have enough capacity in place to serve the new subscribers that will be added to the network. On the super-size side of the scale are macrocell towers. These standalone or structure-attached cell sites literally tower over the target area, offering a range of 10 miles or more in rural settings. Microcells are the mid-sized option, frequently employed in urban and suburban areas, covering cell areas less than a mile in diameter. Tiny picocells typically cover less than 250 yards and are used in office buildings, airports and business centers.
The newest arrival, femtocells, are personal devices intended for home or office use and offer a coverage range similar to a cordless phone base station. It is the foundation for the delivery of all mobile services and applications, just like physical networks constructed of fiber-optic and copper wiring enable telephone, data and TV services to homes and businesses. CDMA and GSM are designed to offer faster data access speeds and network efficiencies for mobile Internet and multimedia applications. Worldwide, GSM is the most widely used 2G wireless communications technology. UMTS requires that carriers completely replace their existing base station equipment to offer 3G services, while EDGE does not.
Cell towers are configured with antennas to support services in these frequencies. 25 MHz each, one from 824-849 MHz and the other from 869-894 MHz. The PCS Band, also known as 1. When auctioning these Cellular and PCS frequency blocks to carriers, the FCC placed strict limits on the amount of spectrum an individual carrier could purchase in a given geographic area. As a result, limited wireless spectrum was available to each carrier to offer services. As more customers were added to their networks, carriers needed to find ways to stretch the finite RF spectrum they had available.
1710-1755 MHz and 2110-2155 MHz bands. The forced transition from analog to digital broadcast television services freed up a swath of additional spectrum in the 700 MHz band, which the FCC auctioned to wireless carriers in 2008. A limited number of simultaneous mobile calls can be carried within a given frequency. Wireless carriers have taken the reduce and reuse approach a step further with the use of directional antennas, illustrated in Figure 5. Rather than using a single omni-directional antenna that covers a circular radius around a tower, carriers introduced directional antennas, to further segment cell sizes and enable the reuse of additional frequencies. Besides squeezing every last drop of available capacity from their available spectrum, major wireless carriers have leapt at opportunities to increase their spectrum holdings each time the FCC has offered new frequency blocks for sale. Interestingly, with the additional spectrum available from auctions and carrier consolidation, plus the introduction of more efficient digital protocols associated with 3G and 4G technologies, some wireless providers are now actually looking to recombine cells.