Interference and the beer analogy
Controlling interference in mobile networks can have the same effect as a team of big guys taking on smaller opponents in a contest to drink a keg of beer.
The theory goes the larger team wins because they have more capacity, in this case thanks to interference cancellation.
Michael Thelander, chief executive and founder of Signals Research group, used the analogy to explain the importance of minimizing interference. “We know interference exists. [We] can’t get rid of it, but [we] can control it,” he told journalists and analysts attending Qualcomm’s first Modem Performance Workshop, which took place in San Francisco late last week.
Because interference increases with signal strength, having five bars on your phone is an indication of signal strength “not quality,” Thelander said, adding the display means there is “a lot of RF energy.”
Thelander explained that networks aren’t always to blame for poor reception. “[The] device can influence network performance,” he said, adding that network efficiency can be improved by up to 32% by deploying interference cancellation on devices.
Tests of mobile modems reveal a “big difference in the performance of chipsets as well as devices,” Thelander said, citing research in early 2013 of the performance of LTE chipsets from eight vendors. The chips “generally all perform the same” while stationary and with ideal network conditions, but there was a 28% difference between the best and worst performing when tested on the move.
Knowing the network conditions is key to testing mobile modems, Thelander explained, noting that he tests devices at all times of the day to account for differences in network loads and performance. It is also important to know all devices in a test are using the same cell site, he noted, citing a test in which each device was accessing a separate tower. “Device placement is critical and the behavior is unpredictable.”
The unpredictable nature of real world networks makes it easier to replicate them in laboratories and test modems there, Michael Barrick, senior business development manager at test and measurement firm Anritsu, told the workshop.
Barrick says standards groups have not eliminated differences in the performance of modems from different manufacturers. He says variations are caused by factors including proprietary baseband features, RF performance, manufacturing processes, the way optional features are integrated, and interactions with the network.
Speaking for the modem designers, Sandeep Pandya, senior director of product management at Qualcomm Technologies, said the component is one of the pillars of user experience, affecting users’ perception of network quality, battery life, and even if a handset gets too hot to handle.
A well designed modem takes the network environment and applications users are likely to access into account, and is capable of reducing network interference, Pandya explained.
Alex Katouzian, senior vice president of product management at Qualcomm Technologies, explained there are now at least 700 device designs based on its Gobi modem, and the firm is moving into power amplifiers, transceivers, and antenna tuners to improve its power management capabilities.
Battery life is an increasingly scarce resource in smartphones, which often have a GPS chip, processor, and camera among other things to power. However, Katouzian says the modem remains the key to a connected life. “The more data capability we have, the more access we have, the easier life is going to be.”