Excellent capacity & scalability for IoT deployment

When IoT connectivity technologies are being considered, adopters rightly consider parameters like cost, battery life and range but it’s easy to overlook the importance of network capacity. And in the absence of empirical data from real world network deployments, we can be tempted to rely too heavily on theory rather than properly modelled scenarios which take into account the many factors impacting capacity in the real world. Capacity is not just about the number of simultaneously connected nodes, it is about mean data packet length, transmission time, frequency of transmissions and interference mitigation. Scaleability is also strongly impacted by the choices made in radio parameters from ultra narrowband at one end of the spectrum to spread spectrum at the other. Not surprisingly, both give rise to upsides and downsides and the capacity sweet spot is a compromise between the two. Narrowband channels offer the optimal capacity for uplink dominated traffic from a large number of devices with moderate payload sizes and typical transmission duty cycles so Weightless uses 12.5kHz channels. Weightless-P also offers flexible channel assignment which further enhances network capacity by enabling frequency reuse in large scale deployments while adaptive data rates from 200bps to 100kbps permit optimal radio resource usage to maximise capacity. Time synchronised base stations allow for radio resource scheduling and utilisation. Weightless-P operates across the entire range of licence exempt sub-GHz ISM/SRD bands for global deployment.

In any wireless system the data throughput determines the achievable network capacity. Higher data throughput enables larger data packets, more frequent transmissions and a greater number of end points. These fundamental parameters are the key factors in the scalability debate. Increase any one of these and you are stress testing the scalability of the network. Let’s look at a typical scenario.

Smart Meters

In the utility metering sector a 15 minute reading interval is the accepted default frequency of uplink transmissions. And a data packet of 200 bytes would be considered normal. What does this mean for an ultra narrow band, spread spectrum and narrow band technology?

200 bytes every 15 minutes is 800 bytes/hour or, alternatively, 1.78 bits per second. The MAC throughput divided by the end device data throughput will define for us the number of nodes that can be serviced - this is how data rate and capacity are linked.

Weightless can handle 2769 end points per base station with these uplink characteristics. A spread spectrum technology can manage 52 and an ultra narrow band technology can accommodate 789 end points.