Performing Tests On 4G Equipment

Sept. 21, 2010
Preparing 4G mobile handsets and network infrastructure equipment for operation requires test equipment that is capable of exceeding the performance limits set for emerging LTE and WiMAX systems.

Fourth-generation (4G) wireless networks, with their advanced modulation and antenna techniques, promise more services with better quality. They will feature infrastructure that takes advantage of multiple antenna paths and diversity techniques, and handsets called smart phones for their many applications and processing power. For it all to work, however, the networks and the handsets must be thoroughly tested, and test equipment suppliers have been far from lax to respond to the needs of both network equipment manufacturers and handset suppliers.

The technologies usually associated with 4G wireless networks are Worldwide Interoperability for Microwave Access (WiMAX) and the Third Generation Partnership Program (3GPP) Long Term Evolution (LTE) technology, although WiFi is also often included. First-generation (1G) wireless networks were all analog, devoted to voice communications. Emerging 4G networks are all digital, using Internet Protocol (IP) technology with packets data and concatenated forward error correction (FEC) to achieve high data rates with low bit-error rates (BERs). Even voice is transferred digitally in a 4G network, by means of voice-over-IP (VoIP) technology. A 4G network also uses multiple-input, multiple-output (MIMO) and single-input, single-output antenna architectures, and switching between them, to improve the data capacity and BER.

Testing the components of a 4G network, which include base stations, cell sites, and handsets, requires equipment that can exceed their performance. Test instruments intended to evaluate a 4G smart phone must not only emulate the transmit and receive characteristics of a 4G base station, but environmental conditions as well, such as signal fading and multipath.

For example, earlier this year, 4G handset supplier Novatel Wireless announced that it had chosen the Spirent 8100 LTE tester from Spirent Communications for evaluating the performance of all of its 4G LTE devices. The Spirent 8100 essentially emulates the network side of an LTE system, interacting with a handset to check performance under a wide range of signaling conditions.

Developed in collaboration with AT4 wireless, the Spirent 8100 checks LTE handset transmitter and receiver performance according to 3GPP guidelines. It offers dynamic channel models and can perform testing on the MIMO architectures that characterize LTE systems. The Spirent 8100 can be used in conjunction with the company's SR5500 Wireless Channel Emulator for fully exercising handsets with SISO and MIMO channels with dynamic path fading and interference. It includes the protocol test capabilities developed by AT4 wireless, which itself announced earlier this year that it had obtained ISO 17025 accreditation for its Taiwan LTE test laboratory.

Earlier this year, Verizon Wireless announced that it had selected Rohde & Schwarz as its provider of test solutions for certification of 4G LTE devices based on the upper 700-MHz C-block spectrum. Rohde & Schwarz offers test solutions for both LTE and WiMAX equipment. For LTE over-the-air (OTA) measurements, for example, the firm recently announced that the R&STS8991 OTA performance test system when equipped with options R&SAMS32-K30 and R&SAMS32-K29 could evaluate the quality of service (QoS) at the edge of LTE network cells. It performs spatial OTA testing on handsets, including simulations of the dielectric effects of a head and hands in close proximity to the handset. To use the R&SAMS- 2-K29 and R&SAMS32-K30 options, the R&STS8991 OTA performance test system hardware must be equipped with an R&SCMW500 wideband radio communication tester as an LTE base station emulator. The scalable system can be equipped for WiMAX RF and conformance testing on mobile devices.

For LTE signal generation, the AWG7000B arbitrary waveform generator from Tektronix supports sampling rates to 24 Gsamples/s and 10-b vertical resolution to create the complex waveforms used in both LTE and WiMAX transmissions, for either handset or infrastructure equipment testing. The waveform generator can produce one or two arbitrary waveform output signals to 9.6 GHz.

On the signal analysis side, Agilent Technologies offers the N9030A PXA signal analyzer (see figure) with models from 3 Hz to 3.6, 8.4, 13.6, and 26.5 GHz. The standard analysis bandwidth is 10 MHz, but the wider bandwidths (through 140 MHz) needed for LTE and WiMAX testing are available as options.

The company literally "wrote the book" on LTE testing, with the hardbound text, LTE and the Evolution to 4G Wireless, available for sale from the firm's web site. The book covers the LTE air interface, physical layer testing, upper-layer signaling, LTE system architecture, RF design and verification testing, and conformance testing. Educational materials on WiMAX measurements are available in the form of a white paper available from National Instruments.

Anritsu Company recently announced it has gained GCF approval from the Global Certification Forum (GCF) for numerous test cases for its ME7873L RF Conformance Test system as well as test cases for its ME7832L Protocol Conformance Test System. Mobile terminal manufacturers must gain GCF approval to ensure that their LTE terminals satisfy 3GPP standards. On a smaller scale, the firm's BTS Master MT8221B is a handheld tester with 20-MHz demodulation bandwidth in support of on-site testing at LTE and WiMAX sites. It includes a 30-MHz zero-span intermediate-frequency (IF) port for external demodulation.

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