A Short Wait For LTE
06 August 2008
LTE (long term evolution) is a 3G modulation technique whereby GSM can carry on from HSPA (high-speed packet access) used for 3G mobile broadband. By CAROLINE HAYES
LTE-based services are causing quite a stir, as they could challenge WiMAX services for GSM technology
domination. It is certainly taking a foothold in the market, as companies are opting for LTE over WiMAX. It rivals WiMAX in that it is designed to meet carrier needs for highspeed data and media transport as well as
voice support, with high-speed data, multimedia unicast and broadcast services. Most recently, Nortel Networks announced that it is to concentrate on LTE over WiMAX, believing the younger technology is
accelerating at a rate exceeding WiMAX’s.
LTE is positioned at the enterprise market where the fast broadband access is attracting a lot of interest, even though it is expected to be available two years after WiMAX is available from carriers. The appeal is that wireless mobile broadband can be used in companies as an extension of the network, allowing increased productivity and flexibility in working practices.
LTE was defined by the 3GPP (third- Generation Partnership Project). It concluded that it was to have 100Mbit/sec in the downlink and 50Mbit/sec in the uplink, with a reduced latency of <100msec transition to active state from the camped state, of <50msec transition from dormant to active states and <5msec IP packet latency in the user plane in an unloaded system.
Accordingly, instrumentation companies are seeing the urgency in delivering LTE test equipment that meets the increase in downlink bit rates and improved spectrum capability of LTE.
Ericsson, for example, has developed a test bed around commercially available technology to develop layer-1 and layer-2 software functionality and in readiness for layer-3 (www.ericsson.com). It uses serial RapidIO and is based on ATCA (advanced telecomms computing architecture) and AMC (advanced mezzanine card) processing boards which form a processor cluster. The test bed connects to an application server and client, via TCP/IP over Ethernet.
The test bed is made up of an application server, radio basestation, user equipment and host. The radio sub-system hosts up to four transceivers and a configurable 4x20W power amplifier. The basestation can
support an additional radio sub-system of four transceiver units and configurable 4x20W power amplifier modules.
The basestation and user equipment are near-identical except that the antenna system of the former has lower RF output power. A host processor handles the software loading and debugging and is connected to the basestation and user equipment. A server is connected to the basestation and a client is connected to the user equipment allows for simultaneous applications, such as file transfer, VoIP and streaming. A scaleable timing and frequency reference can be synchronised using a GPS.
LTE test
While there is a lot of work being done to standardise 3G LTE, the main aim is to improve service provisioning and coverage while reducing the cost/bit for both operators and the consumer. One of the first
to demonstrate its LTE test prowess was Aeroflex (www.aeroflex.com) which supports the 3GPP LTE vision of global cellular 3G technology. The company has announced a pair of products, the TM500 and TM6401, the former supports physical layer testing of networks and the latter is for physical layer testing of mobile devices.
One of the latest to enter LTE is Anritsu (www.anritsu.com) with its MD8430A LTE network simulator for handheld testing. Like Aeroflex, there is also a user equipment version, an LTE user equipment simulator.
The MD8430A is in the beta stage with customers and complies with the 3GPP’s evolving LTE standards, 2x2 MIMO and 64QAM modulation to achieve 100Mbit/sec.
Library support
Agilent (www.agilent.com) has developed a wireless library that is designed to provide signal processing models and pre-configured simulation set-ups for its Advanced Design System EDA software.
The library allows the creation of test waveforms that are spectrally correct, claims the company and which comply with 3GPP requirements for LTE. The model and simulation test benches can be used as a golden reference for simulation and verification of baseband algorithms, digital basebands/IF systems and verification RF circuitry in 3GPP LTE.
Importantly, the library can be imported into the company’s RF Design Environment so that RFIC designers can access 3GPP LTE systems with Cadence’s Virtuo Custom IC platform using links developed as part of the EDA and the measurement companies’ alliance to develop a joint platform.
The wireless library allows users to create waveforms to measure EVM, PAPR, CCDF and ACLR performance of 3GPP LTE system RF components, such as power amplifiers, antennae and filters. It also provides receiver measurements, such as BER and supports FDD and TDD model and up to 20MHz
bandwidth. Modulation type is QSPK, 16QAM or 64QAM.
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