LTE-Advanced (LTE Release 10 & beyond) is a 4G (4th Generation) mobile communication system enhancing the basic LTE technology is specified in 3GPP Release 8. Carrier Aggregation (CA) is among the multiple features introduced with LTE-Advanced. In order to increase bandwidth and thereby bitrate, an LTE-Advanced capable UE (User Equipment) can be allocated 01 (Downlink) and UL (Uplink) aggregated resources comprising two or more carriers, wherein aggregated carriers are referred to as Component Carriers (CC).
Three different modes of CA are defined within LTE-Advanced:
intra-band contiguous CA,
intra-band non-contiguous CA, and
inter-band CA.
Intra-band CA relates to carrier aggregation wherein the component carriers belong to the same operating frequency band. For contiguous CA, contiguous component carriers are allocated while for non-contiguous CA carriers are allocated with one or more gaps between them. In case of inter-band CA, the component carriers belong to different operating frequency bands.
A component carrier can have a bandwidth of 1.4, 3, 5, 10, 15 or 20 Megahertz (MHz) and it is envisaged that a maximum of five component carriers can be aggregated, resulting in a maximum aggregated bandwidth of 100 MHz instead of at most 20 MHz without CA. However, according to Release 11 the maximum number of carriers in DL is 2, i.e., 2DL CA and therefore maximum aggregated bandwidth is 40 MHz. As an example, 3GPP IS 36.101 version 11.6.0 Release 11 may be consulted for further details on required UE transmission and reception characteristics.
It is envisaged that more than two, i.e., three downlink carrier aggregation (3DL CA), four downlink carrier aggregation (4DL CA), or five downlink carrier aggregation (5DL CA) will be introduced in the next releases to come. Current implementations are also restricted to one UL carrier. i.e., no CA on UL, while 2UL CA systems can be contemplated for future releases.
UEs can be said to support a specific functionality in case they have tested accordingly to verify proper functioning. The standard 3GPP IS 36.508 version 11.2.0, for example, defines a common test environment for UE conformance testing in Rel. 11 and 3GPP TS 36.521-1 version 11.2.0 Release 11 defines UE conformance specifications for radio transmission and reception for conformance testing Including measurement procedures for the conformance tests. Test cases are defined for testing UE capabilities such as reference sensitivity level, maximum input level, adjacent channel selectivity, blocking characteristics, etc, wherein test cases are defined without taking the CA feature into account, i.e., a single carrier is established only, while other test cases measure the UE capabilities when CA is active, i.e., for 2DL CA in case of Rel. 11.
“Testing LIE Advanced-Application Note” (accessible at http://www.rohde-schwarz.com/en/solutions/wireless-communications/lte/applications/applications_57855.html, also to be found on the Rohde & Schwarz web pages by searching for ‘Applications & White Papers for LIE/LTE-Advanced’) describes aspects of test environments for testing LTE-Advanced technology components and discusses various testing aspects of such technology components.
A test case for 2DL CA may comprise picking one of the DL component carriers as the measured carrier and keep the other DL component carrier active; assign an uplink to the band not containing the measured carrier; and then perform the measurements. For example, for selectivity and blocking tests, interferers may be assigned relative to the measured carrier. The test is then to be repeated by swapping the roles of the measured and non-measured carriers/channels.
It can be contemplated that with increasing number of CCs (up to 5) in CA, the number of test cases to be performed multiplies for comprehensive testing, as the tests are to be repeated according to the number of component carriers available.
In order to limit test resources or test efforts in terms of associated test factors (e.g., number of test cases, test time, etc.), sets or suites of test cases may be limited to cover random samples or combinations of tested parameter combinations. Such an approach, however, results in incomplete test coverage and for a given fixed test effort the coverage will decrease rapidly from 2DL CA to 3DL CA and further beyond.
There is a need, therefore, for an approach for testing LIE-Advanced CA receiver characteristics for 3DL CA and beyond, wherein the approach facilitates the limiting of test resources, such as test time, while at the same time optimizing test coverage.