Cell phones go through the ringer

Code division multiple access (CDMA) cell phones manufactured by numerous companies, such as LG, Samsung, Audiovox, and Ericsson. All phones include a global positioning system (GPS) interface.

Develop a new test station to replace older stations that couldn't make all the necessary parametric measurements on a phone. Engineers must perform parametric tests on new handsets to verify that they operate properly with Verizon Wireless base stations. Tests include output power, frequency, transmitter/receiver isolation, and intermodulation distortion (IMD). Test conditions must emulate an actual network, including impairments such as fading and echoes. The new station must cut test time per phone from one week to one day.

Agilent Technologies (www.tm.agilent.com)

• 3-GHz spectrum analyzer
• wireless communications test set

Spirent Communications (www.spirentcom.com )

• CDMA network emulator
• wireless channel emulator
• interference modulator
• test configuration switch
• test executive software

Before Verizon Wireless (www.verizonwireless.com) approves a cell phone for connection to its code division multiple access (CDMA) network, test engineers put the phone through a series of parametric tests. When cell phones used analog technology only, engineers measured a few analog RF parameters such as transmitter power and frequency. With digital phones, though, engineers need to test for frame errors and analyze protocols. They must test for power consumption, global positioning system (GPS) performance, and transmitter/receiver isolation over a wide range of wireless-channel conditions.

An automated test system performs parametric measurements on cell phones.

Until recently, Verizon Wireless engineers needed a week to test a phone. Lou LaMedica, Verizon's director of CPE evaluation and development, needed to drastically cut test time. He also needed a test system that could test any phone and automatically perform all tests at one station. His engineers turned to Spirent Communications to integrate a complete automated test station.

The new test station emulates an RF channel and supports the protocols required to fully test a phone for voice and data communications as well as for GPS performance. A switch connects the phone under test to a CDMA network emulator or wireless communications test set though the wireless channel emulator and interference emulator. During a test, the network emulator and test set provide the protocols and messages needed to establish, conduct, and complete a call.

During test calls, the wireless communications test set measures transmitter output power, receiver sensitivity, frequency, and audio distortion. CDMA measurements include erased frames and rho factor (a measurement of signal power quality). For receivers, the instruments measure frame-error-rate, channel sensitivity, dynamic range, and audio frequency response. The channel emulator and interference emulator vary the channel conditions for a phone's transmitted and received signals in order to test the phone's ability to connect to the simulated wireless network.

A phone's transmitter must not overwhelm its receiver. Therefore, Verizon Wireless tests new phones for transmitter/receiver isolation. During this test, the handset must transmit at maximum power (23 dBm) while it receives a signal of –104 dBm. The receiver must properly receive a 13-kbps signal from the test set.

CDMA phones switch between transmit and receive modes, and that switching can produce harmonics that can impede performance. Thus, Verizon Wireless engineers measure intermodulation distortion (IMD) with the 3-GHz spectrum analyzer. The test tells engineers how well the phone's receiver rejects third-order harmonics.

Verizon Wireless engineers now test a cell phone in 24 hrs. Engineers run the automated tests overnight and review test results each morning before setting up the next phone's test. Two automated test systems run around the clock. Thus, engineers test two phones a day instead of one phone per week.