 of the world, including AT&T and Verizon, have implemented FD-LTE. Time Division Multiplexing www.TechnicalPDF.com Figure 7-11 Frequency Division-LTE compared to the Time Division air interface. In contrast to Frequency Division Multiplexing, TD- LTE uses the same set of frequencies for uplink and downlink transmissions. Time-Division Multiplexing (TD-LTE) is also referred to as Time-Division Duplex (TDD). TD-LTE does not require paired spectrum, and unlike FD-LTE, it is asymmetric; a different amount of spectrum can be used in the downlink and in the uplink. www.TechnicalPDF.com This is more spectrally efficient and flexible. For example, more spectrum can be allocated to the downlink than the uplink. China Mobile, the largest mobile carrier in the world, and some carriers in the rest of Asia use TD-LTE. Core networks are the same for both types of LTE. The same network core and backhaul support both Frequency Division and Time Division air interfaces. However, radios in users' devices must have chips to match the type of air interface for their devices to access the cell sites. Chip designers have integrated both TD and FDD into their platforms SO that carriers are able to support both types of LTE. Carriers able to support both FDD and TD-LTE support roaming for users with either type of handset. 4G Multiple-Input Multiple-Output Antennas LTE is designed to operate with Multiple-Input Multiple- Output (MIMO) antennas in base stations. MIMO antennas benefit by having more than one antenna and multiple receive/send channels. Thus, they can carry as many separate streams of voice or data as they have input/output channels. Each stream of traffic is carried on a separate frequency. An 8x8 antenna has eight antennas and handsets communicating with it also have eight antennas. This is analogous to multilane highways with eight lanes in each direction. MIMO antennas are available in 2x2, 4x4 and 8x8 send/receive channels. The 8x8 antenna is specified for LTE Advanced, the 100Mbps, true-4G air interface. As antennas 