Low Rate High Frequency Data Transmission from Very Remote Sensors

Abstract

This chapter deals with the difficulties of transmitting data gathered from sensors placedin very remote areas where energy supplies are scarce. The data link is established bymeans of the ionosphere, a layer of the upper atmosphere that is ionized by solar radiation.Communications through the ionosphere have persisted, although the use of artificialrepeaters, such as satellites, has provided more reliable communication. In spite of beingrandom, noisy and susceptible to interference, ionospheric transmission still has favorablecharacteristics (e.g. low cost equipment, worldwide coverage, invulnerability, etc.) thatappeal to current communications engineering.The Research Group in Electromagnetism and Communications (GRECO) from La Salle -Universitat Ramon Llull (Spain) is investigating techniques for the improvement of remotesensing and skywave digital communications. The GRECO has focused its attention on thelink between Antarctica and Spain. The main objectives of this study are: to implementa long-haul oblique ionospheric sounder and to transmit data from sensors located at theSpanish Antarctic Station (SAS) Juan Carlos I to Spain.The SAS is located on Livingston Island (62.7◦S, 299.6◦E; geomagnetic latitude 52.6◦S) in theSouth Shetlands archipelago. Spanish research is focused on the study of the biological andgeological environment, and also the physical geography. Many of the research activitiesundertaken at the SAS collect data on temperature, position, magnetic field, height, etc.which is temporarily stored in data loggers on-site. Part of this data is then transmittedto research laboratories in Spain. Even though the SAS is only manned during the australsummer, data collection never stops. While the station is left unmanned, the sets of dataare stored in memory devices, and are not downloaded until the next Antarctic season. Theinformation that has to be analyzed in almost real-time is transmitted to Spain through asatellite link. The skywave digital communication system, presented here, is intended totransmit the information from the Antarctic sensors as a backup, or even as an alternativeto the satellite, without depending on other entities for support or funding.Antarctica is a continent of great scientific interest in terms of remote sensing experimentsrelated to physics and geology. Due to the peculiarities of Antarctica, some of theseexperiments cannot be conducted anywhere else on the Earth and this fact might obligethe researchers to transmit gathered data to laboratories placed on other continents for intensivestudy. Because of the remoteness of the transmitter placed at the SAS, the system suffers frompower restrictions mainly during austral winter. Therefore, maintaining the radio link, evenat a reduced throughput, is a challenge. One possible solution to increase data rate, withminimal power, is to improve the spectral efficiency of the physical layer of the radio linkwhile maintaining acceptable performance. The outcomes and conclusions of this researchwork may be extrapolated to other environments where communication is scarcely possibledue to economic or coverage problems. Therefore, the solutions presented in this study maybe adopted in other situations, such as communications in developing countries or inanyother remote area.