Key management scheme of distributed IoT devices based on blockchains

Abstract

High-frequency systems (HF) are still used in many communication applications, especially at long distances, due to their robustness. Data can be sent for hundreds of kilometres at a low power cost with only one drawback, low bitrate. To increase the bitrate, several methods were reported using the single-tone modulation with 24 kHz bandwidth, but still not practical in real-time applications because, the 24 kHz is unavailable due to the instability of the ionosphere layer. Here, a structured method built on the non-orthogonal multiple access technique (NOMA) is proposed to increase the bit rate per HF narrowband channel. To increase the data rate, two parts of the data are divided and sent to one user over two different power levels. Since the ionosphere conditions prohibit the use of single-tone channels most of the time, spread narrowband channels are used instead. The NOMA technique is used on the receiver's side to recognize the two parts of data. The results show a significant improvement (up to 45%) using NOMA in narrowband 3 kHz channels. The bit rate at the receiver has increased up to 200 kb/s concerning, while the maximum bit rate recorded by conventional methods used in previous studies is 138 kb/s. Combined with multichannel algorithms such as HF XL, the total increase in bit rate can be considerable. The system is built on the SDR platform and tested in multiple channels, weather, and power conditions in real-time experiments to validate its reliability.