The emerging wireless communications standard, Long Term Evolution-Advanced (LTE-A), is specified as part of Release 10 of the Third-Generation Partnership Project (3GPP; www.3gpp.org) specifications. Though largely building upon existing LTE parameters, it also incorporates new features. Through carrier aggregation, for example, LTE-A specifies spectrum allocations to 100 MHz by aggregating two or more component carriers. In an application note titled, "Solutions for LTE-Advanced Physical Layer Design and Test" (5990-9138EN), Agilent Technologies details how to use signal generation and analysis to overcome the challenges associated with such carrier aggregation.
For most operators, 100 MHz of contiguous bandwidth is difficult to find among available spectrum resources. As a result, LTE-A defines three carrier-aggregation scenarios: single-band (or intra-band) contiguous; single-band non-contiguous; and multiband (inter-band) non-contiguous. Contiguous carrier aggregation is the least complex of the three types. In the Release 10 User Equipment (UE) specification, it will not exceed two component carriers of 40 MHz maximum. This configuration could possibly be supported with a single wideband transceiver in the UE. In contrast, the UE must use multiple transceivers or one very wideband transceiver for non-contiguous allocations.
One can imagine the number of test cases for carrier aggregation if all types and combinations have to be explored. With multiple simultaneous transceiver chains, simultaneous tests will have to be performed for multiple transmitters. With inter-band aggregation, however, test challenges will be encountered because of synchronization for frequency error between the multiple frequency bands, simultaneous error vector magnitude (EVM) on multiple transmitters, and out-of-band tests.
According to the five-page application note, the testing of carrier-aggregated signals calls for instruments that can generate and analyze multiple component carriers simultaneously. Such tools must be able to capture all component carrierswhether they are inter-band or intra-bandand conduct analysis at the same time. As an example, the firm points to its own suitable offerings while detailing features that could tackle LTE-A carrier aggregation. Currently, no signal analyzer on the market offers a sufficiently wide bandwidth to test inter- band carrier aggregation. Engineers can instead use two synchronized signal analyzers, which are each tuned to a relevant frequency band, with vector-signal-analysis (VSA) software. The VSA will acquire the inter-band signal from the two analyzers and perform simultaneous analysis on all component carriers.
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