Evaluating 4G Testing Needs

Aiming for increased bandwidth efficiency, fourth-generation (4G) wireless communications networks offer some complex technical issues for test equipment suppliers.

Fourth-generation (4G) wireless communications systems are under development to meet the ever-insatiable appetites of consumers for more voice, video, and data services over their portable handsets. These emerging systems include fixed and mobile WiMAX as well as the 4GPP Long Term Evolution (LTE) system. As with any new system, testing is a critical issue because of the use of advanced technologies in 4G wireless networks, including multipleinput, multiple-output (MIMO) antenna schemes and orthogonal-frequencydivision- multiplex (OFDM) modulation. Test equipment manufacturers are already responding to 4G measurement requirements with both single instrument and integrated system solutions.

At the system level, Verizon Communications recently announced details on the company's LTE-based 4G wireless network, scheduled to deploy in 2010. Verizon will begin testing the service this year and launch it commercially in at least 25 to 30 markets in the US. According to Verizon Chief Technology Officer (CTO) Dick Lynch, "We are modeling the rollout after our EV-DO deployment. So we expect to get to about the same level in the first year of deploying LTE that we got with EV-DO, which is about 25 or 30 markets."

Given the use of multiple signals and complex modulation schemes found in 4G wireless networks, most measurement solutions incorporate a vector signal generator (VSG) and vector signal analyzer (VSA) as well as some form of software-defined-radio (SDR) architecture for flexibility.

Anritsu, for example, recently introduced its BTS Master MT8221B, a handheld base station analyzer that supports emerging 4G standards as well as existing secondgeneration (2G) and third-generation (3G) wireless network standards. It combines a number of different measurement functions within a portable package, including a power meter covering 10 MHz to 7.1 GHz, a cable and antenna analyzer spanning 400 MHz to 4 GHz, and a spectrum analyzer operating from 150 kHz to 7.16 GHz. A VSG option allows the portable instrument to generate two modulated signals from 10 MHz to 6 GHz plus noise for receiver testing. The battery-operated BTS Master MT8221B measures just 315 x 211 x 94 mm and weighs only 4.9 kg, making it easy for technicians to use it anywhere at a cell site.

German test equipment supplier Rohde & Schwarz recently launched its R&S ROMES 4.30 drive test software in support of both frequency-divisionduplex (FDD) and time-division-duplex (TDD) versions of LTE. The software is written to analyze large amounts of data collected during drive testing of LTE networks and to identify weak spots and gaps in network coverage. The latest version of the drive test software, R&S ROMES 4.30, supports the LTE standard, mainly on the R&S TSMW universal radio network analyzer. With the analyzer, it provides CDMA2000 1xEV-DO position estimation, a new route-tracking map tool, and improved graphical user interface (GUI).

Several years ago, Keithley Instruments anticipated the need for MIMO testing, developing a MIMO test system based on the firm's model 2920 VSG, model 2820 VSA, model 2895 MIMO synchronization unit, and MIMO test software. It supports 4-input, 4-output (4 x 4) MIMO testing for a wide range of standards. The system features 1 ns signal sampler synchronization and better than 1-deg. peak-to-peak signal sample jitter. It can support MIMO measurements on a variety of signals, including IEEE 802.11n 40-MHz WLAN MIMO and 802.16e Wave 2 Mobile WiMAX, and can be upgraded via software for 4G LTE testing. The model 2920 VSG is available with a frequency range of 10 MHz to 4 GHz and 10 MHz to 6 GHz while the model 2820 VSA comes in 4- and 6-GHz versions with 40-MHz instantaneous measurement bandwidth.

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