LTE Challenges Test Gear Suppliers

The demanding requirements of LTE networks in terms of advanced modulation and MIMO techniques has pushed test suppliers to develop flexible, software-based environments for testing infrastructure and mobile units.

Long Term Evolution (LTE) wireless networks pose some challenges for test equipment suppliers. The LTE air interface, as defined by Release 8 of the Third Generation Partnership Program (3GPP), employs orthogonal frequency-division-multiple- access (OFDMA) techniques in the downlink and single-carrier-frequencydivision- multiple-access (SC-FDMA) methods in the uplink along with multiple- input, multiple-output (MIMO) antenna configurations to maximize data transfers. For test solution providers, the air interface represents an advanced measurement problem.

LTE networks are designed to operate around 700 to 3000 MHz, with IP-based data packets supporting all (voice, data, and video) services. The bandwidth allocations are flexible; in addition, each cell can be scaled for bandwidths of 1.5 to 20.0 MHz. By using OFDMA, available bandwidth is divided among multiple subcarriers using a variety of modulation formats, including quadrature phase shift keying (QPSK), 16-state quadrature amplitude modulation (16QAM), and 64-state QAM (64QAM). LTE systems can also be configured as paired frequencydivision- duplex (FDD) or unpaired time-division-duplex (TDD) systems.

Add the fact that LTE is an evolving standard, and test equipment manufacturers have their hands full. In some cases, test equipment for generalpurpose use can be adapted for LTE testing with the proper software. For example, the model N9030A PXA vector signal analyzer (VSA) from Agilent Technologies with model 89600 VSA LTE FDD and LTE TDD software can apply its 140- MHz maximum analysis bandwidth to LTE networks. The VSA (see figure) is available in various models covering a total frequency range of 3 Hz to 26.5 GHz.

Similarly, the MS269xA series of signal analyzers from Anritsu offer a standard analysis bandwidth of 31.25 MHz that can be extended to 125 MHz with options. Four models in the series cover a total range of 50 Hz to 26.5 GHz.

AT4 wireless has developed its E2010 Broadband Wireless Test Set as a flexible measurement system for wireless networks based on multiple radio access technologies (RATs), including LTE and WiMAX systems. The one-box solutions employ a software-definedradio (SDR) configuration to change measurement personalities.

The TM500 TDLTE test system from Aeroflex supports measurements on TDD LTE infrastructure equipment, notably under development in China. It can handle MIMO architectures and 20-MHz analysis bandwidth and coexist in the same unit as the firm's TM500 LTEFDD test solution for measurements on FDD-based LTE systems.

Rohde & Schwarz offers a variety of test solutions aimed at LTE, including its R&S CMW5500 HSPA+ and LTE protocol tester. For mobile units and infrastructure testing, the company's R&S SMU200A vector signal generator (VSG) is available in models covering a total range of 100 kHz to 6 GHz. The firm's R&S TS8980 LTE RF mobile test systems covers from 400 MHz to 3 GHz.

The growing number of LTE test solution providers includes Tektronix, with its real-time spectrum analyzers (RSAs), Keithley Instruments, with RF VSG and VSA products recently acquired by Agilent, and OSS Nokalva, with its S1 and X2 Protocol Stacks, UE Protocol Stack, and LTE-1Step testing and analysis tool.

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