Thank you for a nice article... The “energy per bit” is any day a better indicator of power efficiency than other metrics and this has been raised in other areas like design of high speed motherboards for 100Gb/s ethernet.
One issue that doesn't seem to have been addressed above with respect to power efficiency in a M2M context is the issue of multipath fading...
Replay available now: A handful of emerging network technologies are competing to be the preferred wide-area connection for the Internet of Things. All claim lower costs and power use than cellular but none have wide deployment yet. Listen in as proponents of leading contenders make their case to be the metro or national IoT network of the future. Rick Merritt, EE Times Silicon Valley Bureau Chief, moderators this discussion. Join in and ask his guests questions.