The R&S SMU 200A high-end vector signal generator from Rohde & Schwarz now has an option that supports real-time processing of feedback information in Long-Term Evolution (LTE) basestation receiver tests. Equipped with the R&S SMU-K69 option, the signal generator processes hybrid automatic repeat request (HARQ) feedback as well as uplink timing adjustment commands from the basestation. It then adapts the LTE signal dynamically in line with the 3GPP TS 36.141 test specification.

Previously, these tests required special test user equipment (UE) and fading simulators. But Rohde & Schwarz says that it now offers a unique one-box solution to replace complex test setups, as the R&S SMU 200A combines RF signal generation and fading simulation with real-time feedback processing capability all in a single instrument.

The 3GPP TS 36.141 conformance test specification defines a range of demanding closed-loop performance tests to characterize the performance of LTE basestation receivers. Basestations must be able to dynamically check the transmission of channel-coded data packets. As a result, signal generators not only need to send RF signals with the correct channel coding in compliance with the LTE standard, they also must be able to respond to the feedback information from the basestation. With the R&S SMU-K69 option (closed-loop basestation test), the R&S SMU 200A now supports real-time HARQ feedback information and uplink timing adjustment commands.

Using the HARQ function, the basestation signals to the mobile phone whether it received a data packet correctly or incorrectly. If the transmission was impaired, for example, by fading, the basestation requests retransmission of the packet with modified channel coding. The R&S SMU 200A behaves in a way that’s analogous to the HARQ processes of real user equipment.

The signal generator also can be installed with options that introduce fading and additive white Gaussian noise (AWGN) to simulate transmission conditions as stipulated by the test specification. This makes it possible to verify the basestation’s response to the received data packets with respect to the standard using a single instrument.

Basestations use uplink timing adjustment to adapt the timing of all transmitting mobile phones to prevent overlapping transmissions. Due to the R&S SMU 200A’s dual-path architecture, even the demanding uplink timing adjustment test can be performed with a single unit. The signal generator simulates a stationary UE on one path and a moving UE on the other. The moving UE can transmit with or without a time offset relative to the stationary UE.

According to the company, the R&S SMU 200A’s RF performance exceeds that of test UE, giving basestation developers more accurate and reliable results. The signal generator also can be used for many other basestation LTE receiver tests specified by the standard, minimizing test setup complexity.

The R&S SMU-K69 LTE closed-loop basestation test option for the R&S SMU 200A is now available. An LTE closed-loop basesation test option (R&S AMU-K69) is also available for the AMU200A baseband signal generator and fading simulator.

Rohde & Schwarz