rator Yota has also stated its intention to change from WiMAX to TD-LTE. Recognizing that a number of car- riers with WiMAX networks have announced they will convert to LTE when they upgrade, WiMAX manufacturers are now including LTE capability in their WiMAX base stations. WiMAX Technology Although both WiMAX and LTE are based on OFDM and use MIMO antennas, data within packets is arranged differently in LTE and WiMAX. For this reason, LTE and WiMAX devices can't roam on each other's 4G generation networks. They can roam on networks using 2G or 3G protocols such as GPRS or CDMA2000 if the WiMAX carrier provides its subscribers with devices with these air interfaces, as well. However, subscribers won't be able to achieve 4G speeds when roaming on 2G or 3G networks. In addition to the United States and Taiwan, carriers in Russia, China, India, Malaysia, Mexico, Spain, and other Asian countries have adopted mobile WiMAX. Some of these carriers have announced that they are switching to and testing LTE infrastructure SO that their networks will be compatible with more networks for roam- ing. There will also be more choices available for infrastructure and customer devices. Because WiMAX uses a time-division duplex version of OFDM, it is highly likely that carriers that change to LTE will adopt TD-OFDM rather than FD-OFDM. This because WiMAX and TD-LTE use the same spectrum bands, making the change less costly because new antennas are not required. Packetized Voice on LTE and WiMAX Networks LTE and WiMAX support only packetized voice and data; they do not support the cir- cuit-switched voice and Short Message Service (SMS) carried on 2G and 3G networks. Although LTE and WiMAX do support Voice over Internet Protocol (VoIP), there is no agreed-upon point protocol on how to carry the voice packets at this time. Therefore, mobile devices on current LTE and WiMAX networks handle voice by using 2G or 3G protocols in mobile handsets and networks. The disadvantage of using circuit-switched voice in combination with LTE and WiM