Software-defined and multi-user LPWAN radios : towards preventing the obsolescence of IoT devices
(2022)
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- Abstract
- With the exponential deployment of Internet-of-Things (IoT) connected devices, massive networks relying on first-generation low-power wide-area network (LPWAN) protocols begin to reach their limits. Although more scalable LPWAN protocols are expected to be commercialized, LPWAN radios are typically implemented in hardware and tied to a single protocol. Upgrading an IoT network to a newer protocol hence requires the replacement of functional devices, which implies a high environmental cost. We study in this thesis two approaches to prevent the disposal of existing IoT devices that could arise from technological obsolescence. The first part of this thesis tackles the challenge of designing LPWAN software-defined radios (SDRs) on ultra low-power microcontrollers. In particular, we target SDR implementations of the LoRa and Sigfox protocols. We initially design, thanks to an accurate analytical model of unsynchronized LoRa signals, a Nyquist-rate LoRa receiver chain with a low-complexity iterative synchronization procedure. We then conduct a hardware/software co-design of a microcontroller architecture for LPWAN SDRs on IoT devices. This architecture includes a general-purpose low-power processor for the protocol-specific baseband computations and a hardware digital front-end for the generic signal processing. The LoRa and Sigfox SDRs are evaluated with an ultra low-power prototype of the microcontroller architecture and attain a sub-mW power consumption for the baseband processing. The second part of this thesis studies the design of multi-user receivers for LoRa gateways. Since LoRa devices are not synchronized in time, collisions between uplink frames limit the scalability of LoRaWAN networks. As a first attempt, we derive from the maximum-likelihood criterion a two-user detector capable of decoding two colliding frames. We demonstrate the practicality of this approach thanks to an SDR implementation of the proposed detector, along with an interference-robust synchronization algorithm. To overcome the intrinsic limitations of this first detector, we then design a successive interference cancellation two-user receiver that explicitly leverages the interleaving and channel code of LoRa with soft decisions. Network-level simulations show that a LoRa gateway employing our two-user receiver may serve 4.7 times more devices than a conventional gateway.
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Xhonneux, M. (2022). Software-defined and multi-user LPWAN radios : towards preventing the obsolescence of IoT devices. https://hdl.handle.net/2078.5/27850