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It is clear that in the near future much broader transmissions in the HF band will replace part of the current narrow band links. Our personal view is that a real wide band signal is infeasible in this environment because the usage is typically very intensive and may suffer interferences from all over the world. Therefore, we envision that dynamic multiband transmissions may provide better satisfactory...
We envision that dynamic multiband transmissions taking advantage of the receiver diversity (even for collocated antennas with different polarization or radiation pattern) will create a new paradigm for these links guaranteeing high quality and reliability. However, there are many challenges to face regarding the use of broadband reception where several out of band (with respect to multiband transmission)...
The reliability of bidirectional communication link can be guaranteed with Automatic Repeat Request Procedures (ARQ). The standard STANAG 5066 describes the ARQ procedure for HF communications that can either be applied to existing HF physical layers modems or adapted to future physical layer designs. In this contribution the physical layer parameters of an HF modem (HFDVL), developed by the authors...
Achieving reliable communication over HF channels is known to be challenging due to the particularly hostile propagation medium. To address this problem, diversity techniques were shown to be promising. In this paper, we demonstrate through experimental results the benefits of different diversity strategies when applied to multi-input-multi-output (MIMO) multicarrier systems. The performance gains...
Traditional use of the HF band is limited mostly to 3 KHz for both voice and data transmission, and therefore, most of the transceivers bandwidths are also adapted to this profile. However, there are some initiatives that clearly state that much broader bandwidths may be use with the corresponding data rate increase and performance improvement in the HF band [1,5]. Due to the increased bandwidth,...
Multi-carrier modulations are widely employed in ionospheric communications to mitigate the adverse effects of the HF channel. In this paper we show how performance achieved by these modulations can be further increased by means of CSI-based precoding techniques in the context of our research on interactive digital voice communications. Depending on communication constraints and channel parameters,...
Cognitive Radio principles can be applied to HF communications to make a more efficient use of the extremely scarce spectrum. In this contribution we focus on analyzing the usage of the available channels done by the legacy users, which are regarded as primary users since they are allowed to transmit without resorting any smart procedure, and consider the possibilities for our stations -over the HFDVL...
This paper addresses the real trials of a new OFDM modem specifically designed for data RADAR transmission that was promoted by the Spanish aeronautical authorities. The nature of this environment is very different of standard applications and has required some new features that will be described in the sequel. The data source is asynchronous depending on the appearance of new plots, and therefore...
This paper deals with the design of an integrated system that is able to transmit data with high data rate and also high quality. However, the main feature is not the enhanced performance but the objective of providing a nearly permanent and reliable communication over time. In order to overcome the long term fading, a probe modem is simultaneously monitoring all the available channels and ranking...
This paper describes a broadband (1MHz) digital HF transceiver for the HF band (3-30MHz) specifically designed for the transmission and reception of multicarrier and multichannel modulations. The wide modem bandwidth (1MHz) is not meant for the transmission of a single 1MHz wide signal, since the goal is to achieve flexible transmission and reception using several channels with a common standard bandwidth.
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