progress of the standardisation work for 3G LTE is based on a set of high-level requirements, the principal aim of which is to further improve service provisioning and coverage but at a reduced cost per bit compared to 3G for both operators and users. All this is to be achieved within the context of an enhanced user experience, operational flexibility that covers both existing and new frequency bands, improved data rates and reduced latency. As such, 3G LTE will provide the major leap forward, all of which brings with it significant testing challenges.
In order to obtain the all-important performance advantage for higher data rate mobile applications, the 3G LTE specification will be based on a switch from W-CDMA to OFDM (Orthogonal Frequency Division Multiplexing) modulation technology. This represents a significant change at the very lowest level of the radio communications and achieving synchronisation will be a major challenge.
Aeroflex is designing a pair of test products, the Aeroflex TM500 LTE and Aeroflex 6401 LTE, which will support the physical layer testing of networks and mobile devices respectively. The complete visibility into the very lowest layers of the radio modem will allow users to diagnose the actual cause of a synchronisation problem rather than just knowing that synchronization has failed.
Without the higher layer protocol, it is necessary to completely configure the physical layer using test scripts. As a consequence, many early test failures may not be the result of real problems but rather by a mismatch in the setup between the prototype under test and the test equipment. With 100’s of parameters that need to be selected, the risk of a mismatch is significant. Aeroflex has developed a powerful graphical user interface to allow both the TM500 LTE and the 6401 LTE to be easily configured without the need to write software to execute the test. The GUI facilitates parameter configuration through dialogue boxes which allows users to select their values using engineering terms and units.
A further implication of physical layer testing when the higher layer protocol is not available is that test automation is essential to ensure extensive and complete testing. The TM500 and 6401 have been designed from the start to be integrated into an automated test environment. The incorporation of test script configuration tools will allow the easy generation of all scripts needed to select the different configurations and tests. These various scripts can then be initiated by a test controller as required to synchronise control of the prototype under test and the test equipment. It will be possible to alter parameters in real time to enable test coverage to be extended across the wide range of different configurations used in a live system both in relation to test of the 3G LTE network and test of early 3G LTE prototype mobile devices. This will allow the early detection of software bugs associated with particular parameter values that will not otherwise be found until much later in the design cycle when diagnosing and rectifying errors tends to be much more expensive.
The implementation of Multi-In Multi-Out (MIMO) antennas to improve the signal strength received by mobile devices from the network is a key new feature of 3G LTE. Aeroflex will be developing test features especially for MIMO to ensure that both the network and mobile devices are able to get the signalling right and then transmit and receive in full synchronisation with the signalling.
As 3G LTE is an evolution of existing UMTS systems based on W-CDMA and will also be fully integrated with existing GSM/GPRS/EDGE networks, seamless handovers will be critical to the gradual roll-out of the first 3G LTE networks and deployment of the first LTE mobile devices. Such handovers might simply be inter-cell between neighbouring 3G LTE cells or they could be handovers to W-CDMA or GSM/GPRS/EDGE as a user moves in or out of LTE coverage. The TM500 and 6401 will allow testing of these handovers both at an early physical layer only test stage and then eventually at the system test stage as Aeroflex develops protocol development test and protocol conformance test options for LTE based on the TM500 and 6401 LTE test platforms.
“Historically, new technology roll-outs have been subjected to delays, often due to problems experienced when the new technology mobile devices are tested against the new technology networks,” concluded Phil Windred. “Aeroflex will be providing powerful test tools to support both network and mobile device testing at the very earliest development stages of 3G LTE products. Experience shows that the earlier problems are detected, the lower the cost of correcting them. The TM500 and 6401 can play a major role in the mobile test industry in terms of providing diagnostic data geared specifically to the needs of 3G LTE that will not only ensure the early detection of implementation problems but also help accelerate the rate at which they are resolved.”