d to avoid aliasing, equal to twice the highest frequency contained within the signal. Next Generation Mobile Communications Ecosystem Table 7.3 Link availability chart Link Availability Service Downtime 5 Nines = 99.999% Down 5 min/year 4 Nines = 99.99% Down 53 min/year 3 Nines = 99.9% Down 8.75 hrs/year 2 Nines = 99.8% Down 17.5 hrs/year 7.3.11.3 Power The power fed to the antenna determines the field strength across the antenna's terminals. This field strength is usually reduced due to atmospheric ionization. The ratio of the maximum available transmitted power and the minimum required signal power yields the acceptable propagation loss. Antenna heights should be chosen SO that the terrain at which reflection occurs supports dispersion of the energy to minimize the multipath effects. 7.3.11.4 Range Range or distance that a backhaul technology can provide in different topologies is a key component in the design of backhaul networks. In urban settings a range of 1-5 km is reasonable whereas in rural areas backhaul technologies need to support in tens of kilometers. Traditional microwave radio links are ideal for supporting these distances. The range for radio links depends on several factors, most importantly the equipment's system gain and the climate. The range of few kilometers in Norway and most places in Europe and down to a kilometer or two for countries with heavy rainfall. 7.3.11.5 Link Availability Link availability is the percentage of time over a year that a backhaul link will be operational. In a nutshell, the link availability is numerically defined with the digit "9" as shown in Table 7.3. Most of the microwave products can deliver 99.999% availability over radio links. The platforms typical MTBF (Mean Time Before Failure) is more than 20 years. 7.3.11.6 Atmospheric Attenuation Like excessive interference, service providers must engineer their backhaul solutions for local meteoro- logical conditions that can degrade the performance of their networks. Atmospheric attenuation occurs due to absorption