The fast pace of LTE development means that the implementation of early systems is, in a number of areas, running ahead of the formal 3GPP specifications. In particular, the early “proof of concept” systems have been developed in the period preceding the availability of the specifications. This has led to solutions incorporating substantial elements of proprietary assumption and customization. There also remain holes in the 3GPP specification. From the physical layer perspective, these undefined areas are mainly concentrated on the uplink and downlink control signalling. From a higher layers perspective the specifications are not expected to be ready for formal release until September of 2008. In the meantime, proprietary solutions continue to add more customization as required in order to enable the early higher layer operation. For these Long Term Evolution, LTE systems under development, it is essential that the test process and test equipment can support the latest core 3GPP specifications as well as the proprietary assumptions and customization. Thus the availability of 3G LTE test equipment is of paramount importance to assist in the swift location and cure of problems. LTE test equipment ranging from that required in the development laboratories to items such as an LTE test mobile for testing out in the field are all required.
The LTE/SAE architecture enables significant re-use of legacy infrastructure, especially in the core network. Within the air interface, the 3G LTE E-UTRAN borrows from earlier access technologies, but it is essentially new, thus requiring a significant development program. It will be important to gain early debug, test and validation of the key enabling features of the new specification. This includes MIMO, fast, low latency HARQ procedures, 64QAM and the broad set of RF band and BW combinations/ configurations that provide spectrum flexibility. Establishing the fundamental building blocks early on will enable LTE test and validation to proceed up to system level as quickly as possible
The LTE/SAE requirements to minimize the overall network architecture and protocol, and reduce latency, lead to significant differences between the E-UTRAN and the UTRAN architectures. The UTRAN employs relatively ‘dumb’ physical layer radio base stations (called NodeBs). These connect in a star topology into Radio Network Controllers (RNCs) which carry out the management of the radio resource and connect in turn to the core network. By contrast, in E-UTRAN, much of the radio resource management is devolved into the base stations (called eNodeBs or eNB). eNBs now connect directly into the core network gateway via a newly defined “S1 interface.” eNBs are also interconnected to adjacent eNBs in a mesh via the “X2 interface”. In addition to the new layer 1 and layer 2 functionality, the eNB will also handle radio resource control, admission control, load balancing and mobility. The high level of functionality and performance required from the eNB base station make it a complex and critical entity in the LTE architecture.
To achieve fast time-to-market of E-UTRAN infrastructure with evolving specifications, new technology, and different architecture demands an especially rapid and efficient development and test program. Having the right LTE test equipment, when it is needed, is a critical factor in this process. Building on a successful track record of providing such test equipment to mobile wireless programs, including HSPA and HSPA+, Aeroflex is already supplying equipment to a number of LTE developments. Advanced test equipment like the Aeroflex TM500 LTE test mobile and PXI 3000 Series of LTE test equipment have been specifically designed to address the challenges outlined above. The Aeroflex solutions employ both a powerful software defined radio platform (SDR) an, a fast and efficient software development process. This enables the equipment to support not only the core 3G LTE specification and its evolution, but also proprietary customization. Conclusion Being based on the highly successful GSM/UMTS ecosystem, there must be few who would bet against the future success of its long-term evolution. The rate at which momentum is currently building on Long Term Evolution trials and commercial programs reflects this opportunity. There will certainly be testing times ahead, but is seems clear that the “Long” in Long Term Evolution, LTE means that it will serve the mobile industry for the long term-and without delay. LTE is happening now.
——— Evan Gray has 20 years experience in the wireless communications industry. Currently based in Cambridge, UK, Evan is the TM500 General Manager for Aeroflex.
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