We have about a dozen instances of an M2M application deployed in testing for some weeks now. All have the MC7455 for the modem.
Most instances work reliably and in general we are almost satisfied. A single instance though has severe problems. The phenomenon is that the whole USB bus collapses affecting all devices on it, and this happens multiple times almost every day. This often happens in rapid successions so that the device would not be able to function properly for hours, after which it works again for some period, if we’re lucky for a day. We could not observe any patterns or regularity regarding when this occurs - it seems random.
Our best assumption is that the problem is related to power spikes drawn by the modem. This is the only instance where the modem is connected over LTE, all other deployments (which work perfectly without any problems) have UMTS connection, and the PTS tells us that consumption really can be higher when using LTE. All other aspects of the systems are completely identical, except for the network providers in use. In the problematic instance, the provider is AT&T in the Santa Monica region, and the modem is running AT&T-certified firmware (02.24.05.06_00_ATT_002.027_000).
Does our assumption about a power delivery problem sound plausible? Is there a chance the provider network also has a play in this (even though signal quality and strength in general seem to be good)?
And the real question:
What is the recommended way to reduce power consumption when using LTE? We’ve found !SARBACKOFF in the AT command reference, but there is no explanation of the backoff concept. What is the backoff state, and how is it set during runtime / what determines its value? Is it something we need to adjust for all 8 levels and what values (magnitude) should we choose? The example values in the AT-reference are all positive, but as they should be negative, am I right this is actually a negative offset?
Thank you for your help,