LTE is the 3GPP’s vision for ensuring that the evolution of UMTS network infrastructure remains the dominant cellular architecture going forward into the next decade. It targets data rates in excess of 100Mbit/s over the downlink and 50Mbit/s over the uplink when operating in 20MHz spectrum allocation, and climbing to peak rates of 300Mbps in the downlink for the highest category UEs.
LTE technology also ensures high performance for speeds up to 120km/h and mobility support across the cellular network for speeds up to 350km/h. As well as higher data rates, wide-area coverage is also being targeted. The throughput, efficiency and mobility targets must be met for 5km cells through to 30km cells and up to 100km cells. Reduced latency is also being addressed with a target for U-plane latency less than 5ms in unload conditions with small IP packets.
“LTE is based on a set of high-level requirements designed to deliver improved, high spectrum efficiency and coverage, but at a reduced cost per bit for both operators and users compared to 3G,” said Evan Gray, TM500 Manager. “Although LTE is designed as an evolutionary upgrade to existing networks, instead of using W-CDMA technology, it adopts the OFDM (Orthogonal Frequency Division Multiplexing) transmission scheme on the downlink and SC-FDMA (Single Carrier Frequency Division Multiple Access) on the uplink in order to provide flexible resource assignment. Furthermore, Multiple-Input Multiple-Output (MIMO) technology and higher order modulation (64QAM) are employed to improve the received signal strength and capacity needed to achieve the high rates and improved coverage. This represents a significant radio access technology shift, the deployment of which is a major challenge. Consequently, it is critical to have test equipment specifically oriented to LTE that can provide the new UE functionality as well as visibility of the physical and higher layer operation of the LTE radio access network components.”
The TM500 LTE incorporates test, logging and measurement features at all layers of the protocol. This includes advanced MIMO tests to verify that the network appropriately handles the MIMO related signalling and correctly applies the MIMO modes, which can be realised with or without the need for an external fading simulator. Graphical displays and charts give a visualisation of the signal quality and the system status enabling engineers to quickly characterise and isolate problems. It is also possible to override signaling, or even force data corruption, to enable simulation of abnormal conditions in order to test the system response and robustness or expose difficult problems.
In the early stages of LTE development, the higher layer protocol will typically not be available and engineers must configure the physical and lower layer tests using scripts that may incorporate hundreds of LTE parameters. The TM500 LTE enables incremental testing at Layer 1, Layer 2 or higher layer levels, and together with a powerful graphical user interface (GUI), engineers can easily configure parameters and scripts to execute complex tests scenarios at different layers.
The TM500 LTE also supports full local or remote automation of test scripts, which is essential when building extensive and repeatable testing. The TM500 LTE test script configuration tool enables the easy generation and management of scripts which can then be initiated manually or by an executive test entity. The TM500 also makes it possible to alter parameters in real time to extend test coverage across a wide range of different configurations used in a live system. This enables early detection of software bugs that may not otherwise be found until much later in the development cycle when diagnosing and rectifying errors is typically much more expensive.
“Structured development, integration and test programmes are essential for the implementation, verification, validation and optimisation of LTE infrastructure,” concludes Evan Gray. “TM500 LTE addresses all these issues through a suite of test components including the physical layer, protocol development and conformance, and multiple-UE operation, which support standalone testing of the base-station physical layer through to network level load testing.”