Guest columnist Lindsay Harris from Rohde & Schwarz UK says there is nothing "long-term" about the Long Term Evolution (LTE) test challenge.
With revenue opportunities for bandwidth-intensive mobile services continuing to blossom and many new applications on the horizon – such as multiplayer gaming, videoconferencing and streaming high-definition video, all on the move – next-generation cellular technology development has moved quickly, with the result that both Long-term Evolution (LTE) and Wimax are now fully-fledged wireless standards.
LTE, which was introduced as the 3rd Generation Partnership Project (3GPP) Release 8 last year, is being designed into numerous new mobile devices. TeliaSonera launched one of the first LTE networks in Stockholm and Oslo in December 2009, and more are planned in 2010.
LTE is not just about providing a high-speed communications interface; it is as much about raising call/data transmission quality and capabilities, increasing efficiency and decreasing cost to operators.
As an IP-based network that supports IPv4 and IPv6, LTE was initially regarded as a data-centric set of technologies.
However, recent moves by a group of operators and OEMs to improve its voice-handling capabilities mean that LTE now looks set to gain wider appeal. The group has agreed on the ‘One Voice Profile’ standard, a way of incorporating traditional circuit-based switching voice and SMS services on IP-based networks.
LTE supports frequency-division duplex (FDD) and time-division duplex (TDD) radio interfaces, suiting it to many frequency band allocation arrangements and enabling LTE to co-exist with earlier 3GPP radio technologies.
High data throughput
Data throughput is much higher than existing solutions, with LTE capable of more than 100Mbit/s in download and 75Mbit/s upload per cell, when using 20MHz channel bandwidth in both instances. This considerable increase in data throughput can be attributed to the evolution of an all-IP architecture as the core architecture.
Referred to as System Architecture Evolution (SAE), this also accounts for LTE’s minimal latency and network complexity.
With the specification having evolved so quickly and voice services not having been fully defined until of late, among the first LTE-user equipment to become available will be dongles and PC communications cards, though LTE-capable mobile phones are now in development. Whatever the user device, developers will be under pressure from network operators to demonstrate adequate data throughput, as well as handover capabilities, to and from existing networks such as CDMA2000, HSPA, 3G and 2G.
Throughput testing
The protocol conformance tests for LTE are still being defined, but developers can already run some conformance test cases and demonstrate the data throughput capabilities of an LTE device.
Using a test unit that allows developers to perform throughput testing, protocol and RF testing in one is imperative nowadays. Notably, LTE involves sending high data rates over various radio channels, involving complex protocol-layer processes to correct errors and handle multiple data streams in parallel. Without the right RF and protocol-level characteristics, data throughput will not be at the optimum level.
When testing any high-speed communications interface, it is invariably necessary that the test unit’s own component specification is well above the range of the device under test. The tester, for example, should offer a sampling rate up to 100MHz, a key requirement for those all important data throughput measurements for LTE.
Various multiple input multiple output (MIMO) schemes have been adopted by LTE, including transmit diversity, single user-MIMO, multiuser-MIMO, closed-loop rank-1 precoding and dedicated beamforming. Developers will need to be able to simulate these features, hence it is advisable to choose test equipment that, if not already capable, will offer an upgrade path to MIMO 2x2 and MIMO 4x2.
Ultimately, MIMO or no MIMO, it is a device or network’s quality of service performance that will determine its fate. The bar is set high with LTE, but a comprehensive test routine will really make the difference.
Author is Lindsay Harris, an account manager at Rohde & Schwarz UK