Multi-DUT PXI approach reduces small cell manufacturing cost: Page 6 of 7

November 24, 2014 // By Thomas Deckert, National Instruments
Small cell base stations are a key technology that will increase capacity and coverage of today’s cellular mobile networks. In fact, the growth in the small cell industry is creating a new cost structure of base station manufacturing test.
Note that a true RF signal switch simply connects one of its input ports to one of its output ports. This topology allows engineers to take measurements on a single device at a time only. By contrast, products like a combiner/splitter can be used to feed the test signal simultaneously to multiple DUTs to verify their receivers in parallel. This is a common technique used in handset testing. However, generally, this is not possible for base station testing where the DUT – a cellular base station – dictates the timing of when it transmits and expects to receive signals, just as it would in a real cell. In that case, test engineers cannot reproduce the framework to make all the base stations under test align their frame timings. Consequently, it is typically not possible to use a single signal generator to test the receivers of multiple base stations in parallel.

Because base stations expect to receive signals at a time they dictate, one must ensure tight synchronization between the DUT and the signal generator for base station receiver tests. Base station designers can simplify manufacturing tests by providing an output port and a corresponding trigger signal to indicate the start of a frame or similar temporal structure. Then, the signal generator aligns its transmission timing with the DUT’s trigger without any need for a time-consuming and error-prone synchronization procedure between the base station and the test equipment. A multi-DUT base station test set should provide input ports for the trigger lines of all DUTs and/or switch between them.

Multi-DUT with PXI

Setting up a multi-DUT test set is relatively straightforward to do with a modular platform such as PXI. “Modularity” in this context refers to a user-defined selection of components where each component – called modular instrument – has a specific purpose. With modular instrumentation, engineers can match test capabilities to their needs much better than with a “one-size-fits-all” traditional instrument.

PXI/PXI Express is one of the most common platforms for modular instrumentation. Since its invention in 1997, PXI has developed into the most prevalent modular instrumentation platform, with over 1,500 modules available from more than 70 vendors. Using PCI bus technology, PXI offers high bandwidth and low latency data transfer to and from instruments, helping to improve test speed (Figure 6).

Figure 6: NI PXI modular instruments and extensive RF measurement software including 3GPP, WiFi and GPS testing lower the cost of test for small cell base stations.

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