reasing Number of LTE Deployments Following the introduction of LTE in Sweden and Norway, Verizon and Metro PCS in the United States also implemented LTE. Vodafone in Germany and Chinese car- rier CSL in Hong Kong are also early adopters. Interestingly, two different carriers in Uzbekistan also launched LTE. Carriers in other countries such as China and India are testing LTE or have announced their intention to use LTE. Factors promoting adoption include the need for more bandwidth and the need to replace outdated 2G equipment. These carriers can choose to skip 3G and implement LTE gear. Other carriers in some of these countries, such as China Mobile, are testing TD-LTE. The choices that a num- ber of carriers are making between TD-LTE and FD-LTE depend on the spectrum that they are able to obtain. In certain instances, countries have made one or the other type of spectrum available, but not always both. Fourth-Generation Advanced Mobile Services The Specifications for WiMAX Antennas and the Air Interface WiMAX is a competing pre-4G protocol to LTE. Although the IEEE defined the air interface, the WiMAX Forum specified protocols and further development on the core network. The WiMAX Forum also has a certification program which verifies that equipment meets WiMAX standards. Like LTE, WiMAX uses MIMO antennas and OFDM as an air interface. Prior to the availability of current mobile WiMAX (802.16e), WiMAX implemen- tations were used for fixed Internet access. The fixed version of WiMAX, 802.16d, is used in some rural areas as a lower-cost way for providers to deploy broadband Inter- net access. It is also used for business customers in metropolitan areas as a backup to Internet access over wired broadband in the event of a cable cut. Fixed WiMAX networks are an improvement over traditional microwave in that they do not require line-of-sight. Thus, buildings or trees in the path of WiMAX signals do not block those signals. Current pre-4G mobile WiMAX installations have been built using the 802.16e protocol for mobile