Part Seven: Firmware Download

Being able to download firmware updates is a critical capability in virtually all applications we have encountered. 10-20 years is a long time to commit to a factory installed firmware image. This is another example of where the cellular folks were smart enough to bias the requirements inTR45.820 : Cellular system support for ultra-low complexity and low throughput Internet of Things (CIOT).  The problem is that the requirement governing code download size is far from realistic.

Fundamental Cellular Issue

Low data rate links are not able to support the amount of data to serially transmit particularly with an already overstressed downlink.  Cellular LPWA has no broadcast data channel capability.

Performance Impact

From TR45.820 : Cellular system support for ultra-low complexity and low throughput Internet of Things (CIOT), the simulated firmware size is a “[p]areto distribution with shape parameter alpha = 1.5 and minimum application payload size = 200 bytes with a cut off of 2000 bytes.”  This is a clever framing of the requirement, because at these sizes, the requirement can be satisfied naturally by standard serial downlink unicast transmissions.  However, from our experience, the distribution of firmware sizes are absurdly low relative to reality.

The upshot is that a firmware broadcast channel is required and that’s not something you can easily just bolt on.  As mentioned in An Overview of 3GPP Enhancements on Machine to Machine Communications published in IEEE Communications Magazine, broadcast firmware capability is an item for future study.  However, there is a chicken and egg problem looming:  how do you update endpoints to support broadcast firmware capability when the endpoints do not support broadcast firmware reception?

Perhaps devices could be upgraded by unicast once that capability is ready.  This may be feasible perhaps if their assumptions are off by one order of magnitude, however, modem firmware images are two orders of magnitude larger than their assumed distribution.  If this is a feasible approach, it means that uptake of the system is incredibly disappointing (especially given the better part of a decade it would take to commercialize a feature that is now only recently being considered).  An uptake rate this disappointing would likely signal the end of commercial service and another technology sunset.

How RPMA Solves the Issues

RPMA has authenticated, robust, and power-efficient multicast/broadcast channel.  It was a lot of work, but our customers demanded the capability and we listened.

This post is a part of the series Is the cellular standard roadmap (3GPP/GSMA) the answer to Low Power Wide Area (LPWA) Connectivity? Click a link below to learn more, or download our free eBook, How RPMA Works: The Making of RPMA.

If at any time, you would like a more detailed description of RPMA and how it stacks up in the competitive landscape, please take a look at the document How RPMA Works: The Making of RPMA.