The LPWA approach devised by Leti, uses its patented Turbo-FSK waveform, a flexible approach to the physical layer. It also relies on channel bonding, the ability to aggregate non-contiguous communication channels to increase coverage and data rates. The field trials confirmed the benefits of this approach in comparison to LoRa and NB-IoT, two of the leading LPWA technologies that enable wide-area communications at low cost and long battery life.
The results indicate the new technology is suitable for long-range massive machine-type communication (mMTC) systems. These systems, in which tens of billions of machine-type terminals communicate wirelessly, are expected to proliferate after 5G networks are deployed, beginning in 2020. Cellular systems designed for humans do not adequately transmit the very short data packets that define mMTC systems.
Designed to demonstrate the performance and flexibility of the new waveform, the field-trial results stem primarily from the system’s flexible approach in terms of the physical layer. This flexibility allows data-rate scaling from 3Mbit/s down to 4kbit/s, when transmission conditions are not particularly favourable and/or a long transmission range is required.
Under favourable transmission conditions, e.g. a shorter range and line of sight, the Leti system is able to select high data rates using widely deployed single-carrier frequency-division multiplexing (SC-FDM) physical layers to take advantage of the low power consumption of the transmission mode. Under more severe transmission conditions, the system switches to more resilient high-performance orthogonal frequency division multiplexing (OFDM).
When both very long-range transmission and power efficiency are required, the system selects Turbo-FSK, which combines an orthogonal modulation with a parallel concatenation of convolutional codes and makes the waveform suitable to turbo processing. The selection is made automatically via a medium access control (MAC) approach optimized for IoT applications.
“Leti’s Turbo-FSK receiver performs close to the Shannon limit, which is the maximum rate that data can be transmitted over a given noisy channel without error, and is geared for low spectral efficiency,” said Vincent Berg, head of Leti’s Smart Object Communication Laboratory. “Moreover, the waveform exhibits a constant envelope, i.e. it has a peak-to-average-power ratio (PAPR) equal to 0dB, which is especially beneficial for power consumption. Turbo-FSK is therefore well adapted to future LPWA systems, especially in 5G cellular systems.”
In the new system, the MAC layer exploits the advantages of the different waveforms and is designed to self-adapt to context, i.e. the usage scenario and application. It optimally selects the most appropriate configuration according to the application requirements, such as device mobility, high data rate, energy efficiency or when the network becomes crowded, and is coupled with a decision module that adapts the communication depending on the radio environment. The optimisation of the application transmission requirements is realized by the dynamic adaptation of the MAC protocol, and the decision module controls link quality.
