Application of Software-Defined Radio in Mobile Phones and Measurement Instrumen

by sales@dgaequipment.com | Classroom

Application of Software-Defined Radio in Mobile Phones and Measurement Instruments
In the field of wireless communications, both mobile phones and their testing equipment have increasingly adopted software-defined radio (SDR) technology. SDR provides flexibility for both test instruments and the wireless communication devices being tested. For instruments, different communication protocols can be tested by simply invoking different software. For communication devices, different protocols can be supported by downloading corresponding software. The software can run on various platforms - it can be installed on a computer’s hard drive or flash memory, or downloaded onto a DSP or FPGA. In mobile phones, the latter approach is more common, while test instruments often rely on Microsoft-Intel-based computer platforms.

Functional Testing via Simulated Calls
First, let’s review traditional wireless testing for mobile phones. Historically, a radio frequency (RF) test instrument equipped with a base station signaling protocol stack was used. This instrument established a simulated call with the device under test (DUT) through the wireless protocol's air interface, while simultaneously measuring the phone’s performance. Such an instrument is commonly referred to as a comprehensive tester.

The air interface here refers to the communication interface between the base station's transceiver and the terminal's (e.g., mobile phone's) transceiver as defined by the communication protocol. In real-world use, this interface operates over the air, but during testing, it is often connected via cable. This simulated call testing method relies on standardized protocol instructions, making RF testing independent of the internal design of the product. It can adapt to mobile terminals from any manufacturer operating under a specific protocol.

This simulated call approach long dominated the wireless testing industry. However, in recent years, declining profit margins in wireless terminal manufacturing have made it increasingly difficult to sustain the production costs associated with this method.

The cost pressure from test instruments mainly stems from the depreciation expense allocated to each unit tested. This includes the cost of necessary instrument upgrades to accommodate different device protocols. Assuming instruments have similar lifespans, production costs can be broken down into three main factors: instrument price, test speed, and upgrade expenses. Lower prices, faster speeds, and reduced upgrade costs lead to lower overall production costs.

Towards the end of the 20th century, cost control was achieved through lower instrument prices and parallelized testing processes. As mobile phone production volumes soared, instruments costing tens of thousands of dollars were no longer purchased one or two at a time, but in batches of dozens or hundreds. This increased demand reduced the design and manufacturing costs of comprehensive testers, leading to significantly lower actual selling prices.

Additionally, the RF testing process evolved from one instrument testing one device to one instrument testing 2-4 devices simultaneously. This optimization reduced idle time caused by device initialization and non-RF testing, thereby improving test efficiency.

However, in the last 3-5 years, wireless communication protocols have developed rapidly. Third-generation (3G) communication has become a reality, and fourth-generation (4G) communication is on the horizon. At the same time, the integration of multiple protocols into a single device has become a trend. A mobile phone must now support not only GSM, EDGE, and CDMA, but also WiFi and Bluetooth. Devices supporting 3G protocols must also remain compatible with GSM and EDGE.

Meanwhile, the upgradability of comprehensive testers appears to have reached its limit. Testing new protocols such as WiFi, Bluetooth, and WiMax requires additional dedicated instruments. Suddenly, the required investment for wireless production equipment over a 3-5 year period became highly uncertain. Large-scale production cannot be built on such uncertainty, prompting manufacturers to seek strategies to control production costs.

Although the concept of software-defined radio has existed for a long time, and SDR-based wireless terminals and test instruments have become mainstream, many production tests - especially in OEM factories - still rely on traditional functional testing that simulates actual communication signaling, often due to technology protection policies.

Fortunately, under market pressures, parametric testing based on SDR architecture has gradually taken shape. More and more instrument suppliers are opening up baseband data interfaces to users, and third-party RF test software is increasingly available on the market. This shift from black-box to gray-box testing not only brings economic benefits to manufacturers but also enhances the technical sophistication of wireless production. Open-architecture, modular SDR instruments have played a key role in this transition.

Application of Software-Defined Radio in Mobile Phones and Measurement Instrumen

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