Network capacity is a big problem for IoT industry; networks will connect a very large number of devices. These problems are more significant in the limited bandwidth in licence exempt ISM/SDR spectrum with only about 100kHz typically available. Uplink dominated traffic from a very large number of devices with moderate payload sizes will be typical for the majority of IoT use cases and this means that the network will require a large number of independent communication channels.

Wide band modulation schemes occupy the entire spectrum and so must use time or code division multiplexing. This quickly limits capacity calling for a larger number of smaller cells and bases stations. Wide band modulation for uplink is not the right approach for even moderate network capacity deployments.

Ultra narrow band schemes enable a large number of simultaneous communications but at a far lower data rate. Network capacity for large scale deployments is improved by minimising the channel separation but this is difficult to achieve as the low complexity and cost of end devices does not allow for extremely accurate frequency synchronisation. The limitations of some ultra narrow band schemes lead to longer transmission times, less capacity, increased energy consumption and lower network performance.

Narrow band offers the best compromise between wide band and ultra narrow band with channels in the region of 10-20kHz wide optimising performance for the majority of applications. Weightless adopts a 12.5kHz channel spacing which delivers the best compromise for typical IoT use cases offering optimal throughput, transmission time, channel separation and selectivity, number of channels and capacity and occupied bandwidth.

But Weightless is a true bidirectional technology offering optional full acknowledgement of 100% of uplink traffic. The downlink using 100kHz as a single channel offers far better spectrum and energy efficiency since there is no contention on this channel and so no need for multiple simultaneous transmissions. Weightless-P is easy to deploy when available spectrum is scarce whilst offering optimal performance.