However, as broadband data services have rapidly expanded, the demand on the network has become asymmetrical. In other words, the downlink and uplink loads on the network are no longer balanced as subscribers typically request (and download) much more content than they upload. With a symmetrically provisioned data service, the asymmetrical data demand will rapidly cause the uplink to become underutilized as downlink capacity is reached.
Time Division Duplexed (TD) protocols have an advantage in this situation since the relative allocation of bandwidth between uplink and downlink can be adjusted by adjusting the scheduling of uplink and downlink transmissions. With effective scheduling, carriers can operate their networks at a higher level of utilization than one which was built on a symmetrical model. TD-LTE allows bandwidth allocations to be dynamically modified and uplink and downlink transmission schedules within a single channel can be updated, depending on the particular needs of the network. This enables carriers to operate LTE networks at a higher level of utilization.
The key to a robust and reliable TD-LTE test methodology is to ensure that test equipment supports several key requirements. In the real world, the uplink and downlink coexist in the same spectrum, so effective test equipment designed to support successful TD-LTE deployments must also provide these same features. In particular, test equipment must support bidirectional testing and have phase and amplitude balanced uplink and downlink channels.
Advanced wireless test equipment such as a channel emulator can provide the real world environment necessary for TD-LTE Test. Integration of channel emulators within test solutions that support device and infrastructure testing provides test results that more closely reflect what happens in the real world. With the growing demand for bandwidth and the development of MIMO based protocols, channel emulators that can also support both the RF requirements for TD-LTE testing as well as implement the correlation models typical of real world activity are essential to effective testing.