Advanced HF Communications for Remote Sensors in Antarctica

The Antarctica is a continent mainly devoted to science with a big amount of sensors located in remote places for biological and geophysical purposes. The data from these sensors need to be sent either to the Antarctic stations or directly to the home country. For the last 15 years, La Salle has been working in the application of HF communications (3–30 MHz) with ionospheric reflection for data collection of remote sensors in Antarctica. We have developed and tested the several types of modulations, the frame structure, the radio-modem, and the antennas for two different scenarios. First, a long-range transequatorial (approximately 12,800 km) and low-power communication system is used as an alternative to satellites, which are often not visible from the poles. This distance is covered with a minimum of four hops with oblique incidence in the ionosphere. Second, a low-power system using near vertical incidence skywave (NVIS) communications provides coverage in a surface of approximately 200–250 km radius, a coverage much longer than any other systems operating in either the VHF or UHF band without the need of line of sight

Evaluation of Performance Improvement Capabilities of PAPR-reducing Methods

One of the major drawbacks of multicarrier modulation is the large envelope fluctuations which either require an inefficient use of high power amplifiers or decrease the system performance. Peak-to-average power ratio (PAPR) is a very well known measure of the envelope fluctuations and has become the cost function used to evaluate and design multicarrier systems. Several PAPR-reducing techniques have been proposed with the aim to alleviate back-off specifications or increase the system performance. Besides the fact that these techniques have varying PAPR-reduction capabilities, power, bandwidth and complexity requirements, it is interesting to notice that the performance of a system employing these techniques has not been fully analyzed. In this paper we, first, develop a theoretical framework for both PAPR and the distortion introduced by a nonlinearity, and then simulate an OFDM system employing several well known PAPR-reducing techniques from the literature. By means of the theoretical analysis and the simulation results we will show the relation between PAPR and the performance of OFDM systems when a clipping device is present and we will evaluate the real performance improvement capabilities of the PAPR-reducing methods. The agreement between the theoretical and the simulation results demonstrate the validity of the analysis

Reconfigurable Multiband Antenna Booster Architecture for Different Environments

A passive matching network cannot match a device for more than one specific scenario. For this reason, a new approach capable of matching a 50 mm $\times50$ mm Internet of Things (IoT) device at 698&#x2013;960 MHz and 1710&#x2013;2170 MHz, using a single SP4T (Single Pole 4 Throw) switch to provide good impedance matching ( \vert \text{S}_{11}\vert < &#x2013;6 dB), across five different environment cases (free space, metal, bricks, wood, and human body), is presented. To validate the capabilities of the proposed reconfigurable matching network to match the surrounding environments, two extreme scenarios have been considered: 1) at free space and 2) when the prototype is placed at three different $h$ distances of 7, 15, and 20 mm ( $0.016 \lambda$ , $0.035 \lambda$ , and $0.046 \lambda$ , respectively, at the lower frequency of operation of 698 MHz) from four different materials: metal, bricks, wood, and human body. The proposed method can compensate for the effects of the close environment variations by commuting between matched states of the reconfigurable matching network. To validate it, a prototype is implemented and tested in all the enumerated materials. By using the proposed reconfigurable architecture, total efficiency is maximized in all cases. The total efficiency increased by 0.8 dB for the on-wood case, by 1.7 dB for the on-body case, by 1.9 dB for the on-brick case, and by 3 dB for the on-metal case compared to a solution where the same matching network is used for all cases

Evaluation of Performance Improvement Capabilities of PAPR-reducing Methods

One of the major drawbacks of multicarrier modulation is the large envelope fluctuations which either require an inefficient use of high power amplifiers or decrease the system performance. Peak-to-average power ratio (PAPR) is a very well known measure of the envelope fluctuations and has become the cost function used to evaluate and design multicarrier systems. Several PAPR-reducing techniques have been proposed with the aim to alleviate back-off specifications or increase the system performance. Besides the fact that these techniques have varying PAPR-reduction capabilities, power, bandwidth and complexity requirements, it is interesting to notice that the performance of a system employing these techniques has not been fully analyzed. In this paper we, first, develop a theoretical framework for both PAPR and the distortion introduced by a nonlinearity, and then simulate an OFDM system employing several well known PAPR-reducing techniques from the literature. By means of the theoretical analysis and the simulation results we will show the relation between PAPR and the performance of OFDM systems when a clipping device is present and we will evaluate the real performance improvement capabilities of the PAPR-reducing methods. The agreement between the theoretical and the simulation results demonstrate the validity of the analysis