In our introduction to how system design enhances the quality and reliability of measurements, we hinted at a myriad of key factors that have an effect on end-user experience, one of them being the device itself and the technologies it supports. In this post, we will look at the evolution of phone design and how it impacts the engineering and designing of Rohde & Schwarz mobile network testing solutions powered by SwissQual.
Since the foundation of SwissQual 16 years ago, the design of cellular devices has changed enormously. In 2000, phones, such as the Siemens S25, were state-of-the-art. With one antenna, they supported dual band GSM (Global System for Mobile Communication) and the use of voice call and SMS (Short Message Service). Today, in 2016, phones supporting all current cellular technologies are state-of-the-art, namely 2G GSM, 3G UMTS (Universal Mobile Telecommunications System), and 4G LTE (Long Term Evolution).
This includes dozens of frequency bands, several band combinations, and the support of technologies, including carrier aggregation, antenna diversity, MIMO (Multiple Input Multiple Output), to only name a few. Multiple cellular antennas are necessary. The capabilities of a modern smartphone include voice call, video call, video player, music player, gaming console, video streaming, video camera, personal computing, and so on.
Obviously, a lot has changed in phone design, and we, at Rohde & Schwarz mobile network testing, have developed our systems to fulfill customer needs and meet all requirements of the latest phone generations.
In the beginning, cellular phones were big and bulky. With time, they became smaller, fitting into jacket and trouser pockets; step by step, they transformed into the handheld devices we know now. The quest for a slimmer and sleeker design brought about major changes in the manufacturing process: non-removable batteries and flexible PCBs (Printed Circuit Boards) superseded replaceable batteries and static PCBs; today, mostly glue is used instead of screws and bolts. With devices being so slim, the audio jack has become the biggest connector, which is why some phone manufacturers no longer consider them in their designs.
In the following, we will discuss three specific changes in phone design and their impact on our system design.
Until recently, phone batteries were replaceable, presenting us with several opportunities for modification. We replaced the battery with an AEC (Accumulator Emulator Component), which is a PCB specifically engineered for a dedicated phone model, adding the following main features:
- Controlled voltage/power and energy
- Hardware reset of device
- Physical fixation of device by AEC
- No aging effect at power source
With the evolution of batteries, however, controlled voltage/power and energy lost its significance, and the design trend towards slimmer phones pushed manufacturers to use non-replaceable batteries. Consequently, the use of an AEC was no longer an option; therefore, to ensure our systems’ reliability, for which we are known and valued, we development a software watchdog running on the phone.
For the physical mounting, the FMK (Freerider Mounting Kit) was designed to ensure shock resistance and stability; it holds and secures the devices. Most FMKs can hold different kinds of phone models; if required, we customize the FMK according to the requested device.
In the beginning, a mobile phone might have supported one technology and one frequency, for example GSM 900MHz. The phone had one antenna, which depending on the model was detachable, and usually there was a 50 Ohm test connector for attaching an external antenna. During drive tests, the external antenna would be placed on the car roof. To fulfill the needs of this generation of phones, we designed the MCM (Mobile Containment Module).
With new technologies, the number of cellular antennas per phone increased. Additional antennas were added to support more frequency bands and antenna diversity. Within no time, two cellular antennas became state-of-the-art. The ASM (audio slide-in module) was designed to support up to four antennas per device. To reduce the number of roof antennas to an acceptable level, power splitters (combiners) were used.
As manufacturers stopped equipping their phones with antenna connectors, correctly attaching an external antenna became a difficult task. In addition, latest technologies, such as MIMO and carrier aggregation, further increased the number of antennas per phone. Now, four cellular antennas are state-of-the-art.
Fact is, the external antenna approach became a dead end. ETSI (European Telecommunications Standards Institute) no longer recommends external antennas, because in MIMO environments they don’t deliver results that represent the true end-user experience of the original device.
In a visionary step and after prolonged and intensive research, we decided to change the way we measure: we began using the internal antennas of the device. A bold decision with its share of tricky challenges; inside the car, exposure to electromagnetic fields would reach critical levels after a certain amount of devices had been in use.
Therefore, it was decided to host the devices outside the car. This also eliminated the issue of chassis attenuation, specified by the vehicle type, which can greatly vary depending on where in the vehicle the device is located. Outside placement, however, created new challenges, for example temperature control.
Our answers to these challenges are the TCM (Test Device Containment Module) and the VRB (Vehicle Roof Box). Together, they make up a cutting-edge cellular measurement system for up to 16 devices, each using their individual internal antenna designs to reflect the true end-user experience.
When GSM was introduced, data transmission was not yet possible; the most demanding applications for an embedded computing module were voice analyzing algorithms. At the time, our processing module hosted Intel Pentium M. It was the optimal choice to bridge calculating performance on the one hand and limited power availability (drive test) on the other hand. With the extension of GSM to GPRS (Global Packet Radio Service) and EDGE (Enhanced Data Rates for GSM Evolution), phones began transferring other data than only voice and could connect to the Internet. Offering 55 kb/s (GPRS) and 220 kb/s (EDGE), throughput was quiet moderate and the Pentium M sufficient.
With the introduction of the third generation of cellular technologies (3G), data rates of up to 384 kb/s (UMTS) were achieved. We replaced the Intel Pentium M in our processing module with an Intel Core Duo. An SSD (Solid State Drive) replaced the HDD (Hard Disk Drive) to increase write performance when throughput rose up to 42 Mb/s with HSPA (High Speed Packet Access, Cat 20). New and more efficient CPUs and batteries with high-energy density allowed designing a benchmarking system in the style of a backpack, the Diversity Ranger. Its processing modules first supported Intel Core 2 Duo for throughputs up to 60 Mb/s. To process even higher data rates, drive test systems and walk test systems were equipped with Intel Core i7 CPUs for throughputs of 300 Mb/s and higher.
At the same time, the calculation performance of phones increased and it became possible to let them analyze their data streams. With this, the calculation performance of the processing modules became free for other tasks. The combination of the R&S TSME scanner and our processing modules for drive tests (CSM2) and walk tests (NCM) was a perfect fit, ready for current and future throughputs of LTE-Advanced.
In the next post of this series, we will take a closer look at how temperature affects system design: where and when temperature is a concern and how Rohde & Schwarz mobile network testing solutions handle and control temperature-related issues.