Introduction to Flexible LTE Test Technology

Long-term evolution (LTE) wireless networks present several challenges to test equipment vendors. The LTE air interface defined by 3GPP uses orthogonal frequency division multiple access (OFDMA) technology in the downlink and single-carrier frequency division multiple access (SC-FDMA) technology in the uplink, and multiple-input multiple-output (MIMO) antenna configurations in both uplink and downlink to maximize data transmission rates. For test solution vendors, this air interface presents complex measurement challenges.

LTE networks operate at approximately 700 to 3,000 MHz with IP-based data packets, supporting all (voice, data and video) services. It features flexible bandwidth allocation, and each unit bandwidth is adjustable from 1.5 to 20.0 MHz. By using OFDMA technology, the available bandwidth can be allocated to multiple carrier frequencies using a variety of modulation formats including Quadrature Phase Shift Keying (QPSK), 16-state Quadrature Amplitude Modulation (16QAM) and 64-state Quadrature Amplitude Modulation (64QAM). LTE systems can also be configured as paired frequency division duplex (FDD) or unpaired time division duplex (TDD) systems.

Adding to the LTE testing problem is the fact that LTE is an evolving standard that test equipment manufacturers are keeping busy. In some cases, general-purpose test equipment can be used for LTE testing with the right software. For example, Agilent offers the N9030A PXA vector signal analyzer (VSA) with the 89600 VSA LTE FDD software module and LTE TDD software, which can apply its maximum analysis bandwidth of 140 MHz to LTE networks. Agilent's VSA is available in a variety of models, covering the range of 3 Hz to 26.5 GHz (Figure).

Similarly, Anritsu's MS269xA series of signal analyzers offer a standard 31.25MHz analysis bandwidth that can be optionally extended to 125MHz. The four models in the series together cover the range of 50Hz to 26.5GHz.

AT4 wireless has developed the E2010 Broadband Wireless Test Set, a flexible measurement system that can be used for wireless networks based on a variety of wireless access technologies, including LTE and WiMAX systems. The solution uses software-defined wireless configuration to change measurement properties.

Aeoflex's TM500 TD-LTE test system supports measurements of TDD LTE infrastructure equipment, which, as is well known, is being developed in China. It can handle MIMO architectures and 20MHz analysis bandwidth, and shares a unit with the company's TM500 LTE-FDD test solution for measuring FDD-based LTE systems.

Rohde & Schwarz offers a range of test solutions for LTE, including its R&S CMW5500 HSPA and LTE protocol tester. For mobile unit and infrastructure testing, the company's R&S SMU200A vector signal generator (VSG) models cover the 100kHz to 6GHz range, and the R&S TS8980 LTE RF mobile test system covers 400MHz to 3GHz.

In addition, some other test solution suppliers are also involved in LTE testing, such as Tektronix (real-time spectrum analyzer RSA), LitePoint (new test system IQxstream for 3G/4G large-scale manufacturing industry), and OSS Nokalva (S1 and X2 protocol stacks, UE protocol stacks and LTE-1Step test and analysis tools).

Figure: Agilent's VSA covers the range from 3Hz to 26.5GHz.