NVIS Multicarrier Modulations for Remote-Sensor Applications

Abstract

The number of Internet of Things (IoT) devices has experienced a large growth during the last decade, as well as the data volume gathered from remote sensors. Satellites are still a suitable communication method and may be preferable for a remote ubiquitous sensor network (USN), which sometimes are located in places without much communications infrastructure where coverage is the principal drawback. Alternatively, the proposed solution for this article aims at a near-vertical incidence skywave (NVIS) channel for high frequencies (HF) with a low-cost platform, allowing a low-power transmissions coverage area up to 250 km for USN. The HF standards are focused on generic communication channels not being robust for NVIS communications. In this article we study and test an alternative based on orthogonal frequency-division multiplexing (OFDM) modulations to make them more robust and less dependent on the channel NVIS communications. For that purpose, we test the HF standard modulations and a designed OFDM modulation to prove the robustness of each. This study has been tested between Barcelona and Tarragona, using different transmission power levels and modulation orders.

SC-FDE Layer for Sensor Networks in Remote Areas Using NVIS Communications

“…In other NVIS studies, such as [8,9,[49][50][51], narrowband modulations have proven that communications are quite reliable in a wide range of scenarios. So far, HF standards (military or otherwise) have used 3 kHz channels with single-carrier modulations such as PSK and QAM.…”

“…The SC-FDE design follows almost the same structure as OFDM, only the SC-FDE concept distributes the symbols shorter in the time domain but longer in the frequency domain. The symbol length was calculated by simply dividing the symbol length defined in [20] by the number of subcarriers defined due to the coherence bandwidth. We kept the same CP due to the maximum delay spread of 3 ms.…”

“…In Table 1, all the parameters of the SC-FDE design are summarized. Additionally, they are compared to the OFDM design proposed in [20] since they have a similar configuration.…”

“…For the tests, we decided to first check the success rate of the SC-FDE and decided to optimize the transmission power by adopting the clipping technique. In addition, we compared the BER/E b N 0 with the OFDM, FSK, and QAM from the study performed in [20].…”

“…Considering these modulations in the context of ionospheric communications, the study performed in [19] compared SC-FDE with OFDMA and SC-FDMA with ionospheric communications in an oblique way. In [20], an alternative solution with an OFDM transmission was proposed to avoid the complex equalization (OFDM requires frequency-domain equalization) for NVIS communications using the Zero Forcing (ZF) equalization method. The main drawback is that the subdivision of the bandwidth into subcarriers presents peaks in the envelope that cause a reduction in amplification capability.…”