[1] Our research group in Electromagnetism and Communications is involved in a project dealing with the channel characterization of an ionospheric radio link from the Spanish Antarctic Base (62.6°S, 60.4°W) to the Observatori de l'Ebre (40.8°N, 0.5°E) in Spain. Since the link was established for the first time on December 2003, the sounder and measurement techniques have been improved on the basis of the preliminary results. In this paper, the final results of the project corresponding to the 2006/2007 sounding survey are presented. First the hardware and measurement techniques used to probe the channel are described. Then the results in terms of channel availability (and its daily, hourly, and frequency variation), multipath and Doppler spreads, and signal-to-noise ratio are discussed. These results are being used to design the physical layer of a low data rate transmission system intended to send the information acquired by a geomagnetic sensor in the Antarctica.

[1] Since 2003, our group has been investigating the performance of different transmission techniques for low-power low-interference High Frequency (HF) ionospheric communication systems. Specifically, we have focused on the link between the Spanish Antarctic Station (SAS) Juan Carlos I in Livingston Island and Ebro Observatory (OE) in Spain, in order to transmit the data gathered from some geomagnetic sensors. These transmission techniques require a valuable knowledge of the channel behavior, thus a comprehensive narrowband and wideband sounding of the ionospheric channel is needed. Some significant improvements both in the system and in the signal processing have been done to achieve this goal. The analysis time and the frequency band have been extended to 24 hours per day and to the whole HF band (2-30 MHz). Moreover, new measurements of the absolute propagation time and the Doppler frequency shift are introduced. In this paper, the sounding results obtained using the new system are presented.

This paper presents two digital transmission techniques for long haul ionospheric links. Since 2003 we have studied the HF link between the Antarctic Spanish Base, Juan Carlos I, and Spain; and we have described the link in terms of availability, signal-to-noise ratio, and delay and Doppler power profile. Based on these previous studies we have developed a test bed to investigate two digital transmission techniques, i.e., Direct-Sequence Spread Spectrum (DSSS) and Orthogonal Frequency Division Multiplexing (OFDM), which can provide a low power, low-rate ionospheric data link from Antarctica. Symbol length, bandwidth, and constellation are some of the features that are analyzed in this work. Data gathered from the link throughout the 2010/2011 and 2011/2012 Antarctic surveys show that the spread spectrum techniques can be used to transmit data at low rate when the channel forecast is poor, but when the channel forecast is good multicarrier techniques can be used to transmit sporadic bursts of data at higher rate.

Fractal geometry has been proven to be useful in several disciplines. In the field of antenna engineering, fractal geometry is useful to design small and multiband antenna and arrays, and high-directive elements. A historic overview of the most significant fractal mathematic pioneers is presented, at the same time showing how the fractal patterns inspired engineers to design antennas.

La Salle and Ebro Observatory have been involved in remote sensing projects in Antarctica for the last 11 years (approximately one solar cycle). The Ebro Observatory has been monitoring and analyzing the geomagnetic and the ionospheric activity in the Antarctic Spanish station Juan Carlos I (ASJI) (62.7• S, 299.6• E) for more than eighteen and ten years, respectively. La Salle has two main goals in the project. The first one is the data transmission and reception from Antarctica to Spain to obtain a historical series of measurements of channel sounding of this 12,760-km ionospheric HF (high frequency) radio link. The second one is the establishment of a stable data low power communication system between the ASJI and Cambrils, Spain (41.0• N, 1.0 • E), to transmit the data from the remote sensors located on the island. In this paper, both narrowband and wideband soundings have been carried out to figure out the channel availability performed using a frequency range from 2 to 30 MHz with 0.5 MHz step during the 24 h of the day, encompassing wider channel measurements than previously done, in terms of hours and frequency. This paper presents the results obtained for the austral summer in 2014, using a monopole antenna at the transmitter and an inverted V on the receiver side. These results led us to the final physical layer design for the long Remote Sens. 2015, 7 11713 haul link, dividing the day into two parts: daytime, with low data throughput design, and nighttime, reaching high data throughput.