Testing TD-LTE with real world test technologies: Page 2 of 7

July 24, 2012 // By Erik Org, Azimuth Systems
Many wireless data networks were initially designed to offer symmetrical data capacities as the original killer wireless application, voice, required equal capacity for both uplink and downlink. Spectrum blocks were licensed and auctioned as paired spectrum suitable for Frequency Division Duplexing (FDD) protocols, which served carriers and subscribers well when voice was the primary application.

for real world testing of
TD-LTE systems and devices

MIMO protocols such as LTE are now impacted more than ever by the changing nature of the “real world” radio environment and are significantly affected by the degree of correlation exhibited by the channel models used during test. While basic conducted testing uses standard channel models, more advanced test solutions can enable test of TD-LTE solutions both over the air and with replicated radio field conditions in the lab.

Standard laboratory testing completed using wired connections produces repeatable results but lacks the “real world” and “through the antenna” aspect of over-the-air testing. While over the air tests (such as drive tests) represent the real world, testing such as drive testing lacks repeatability. This is because there are many variables which impact performance during a real world test, for example, channel conditions could change depending upon seasonality and network loading; real world testing such as drive testing is also expensive to perform.

To bridge this gap between laboratory and real world over-the-air testing, channel emulators are deployed in the laboratory testbed. Channel emulators replicate real world channel propagation conditions in a controllable and repeatable fashion through the use of complex channel models and multiple, programmable parameters (figure 1). Sophisticated channel emulators offer bi-directional operation (simultaneous activity in downlink and uplink directions) with independent programmability of channel characteristics in both directions. By using channel emulators, radio designs and performance can be verified, test coverage can be improved, test cycles decreased and higher quality products can be introduced to the market in a shorter period of time.

Figure 1: Schematic representation of a point-to-multipoint test case with channel emulation showing a fully bi-directional MIMO channel to each UE for realistic recreation of over-the-air conditions. Click image to enlarge.

Data communications technologies, as employed in TD-LTE, demand high system dynamic range and excellent RF fidelity. These radio systems often employ advanced digital modulation technologies to

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