Introduction - Getting Started with Bluetooth Low Energy - page 8

So, in practice, a typical best-case scenario should probably assume a potential maxi‐
mum data throughpout in the neighborhood of 5-10 KB per second, depending on the
limitations of both peers. This should give you an idea of what you can and can't do with
Bluetooth Low Energy in terms of pushing data out to your phone or tablet and explain
why other technologies such as WiFi and classic Bluetooth still have their place in the
world.
Racing to Idle
In a world where things usually get faster with time, 10 KB/s might seem slow and
counterproductive, but it does highlight the primary design goal of Bluetooth Low En‐
ergy: low energy ! Even transmitting at these relatively modest data rates, 10 KB/s will
quickly drain any small coin cell battery, and the Bluetooth SIG made a clear, conscious
effort not to design yet another generic wireless protocol and slap the label low power
on it. Instead, they wanted to design the lowest power protocol possible, optimizing in
every way possible to acheive that goal. The easiest way to avoid consuming precious
battery power is to turn the radio off as often as possible and for as long as possible, and
that is achieved by using short burst of packets (during a connection event) at a certain
frequency (determined by the connection interval). In between those, the radio is simply
powered off.
This means low amounts of data transmitted in short bursts, with connection intervals
spread as far apart as possible to save battery life. The user-selectable 7.5 ms-4 s con‐
nection interval offers a sufficiently wide window to allow product designers to make
the right tradeoff between responsiveness (a short connection interval) and battery life
(a longer connection interval), without straying to far from the narrow design goals
behind BLE.
Operating Range
The actual range of any wireless device depends on a wide variety of factors (operating
environment, antenna design, enclosure, device orientation, etc.) but Bluetooth Low
Energy is unsurprisingly focused on very short-range communication.
Transmit power (typically measured in dBm) is usually configurable over a certain range
(usually between -30 and 0 dBm), but the higher the transmit power (better range), the
more demands are placed on the battery, reducing the usable lifetime of the battery
cell(s).
It's possible to create and configure a BLE device that can reliably transmit data 30 meters
or more line-of-sight , but a typical operating range is probably closer to 2 to 5 meters,
with a conscious effort to reduce the range and save battery life without the transmission
distance becoming a nuisance to the end user.