Multiband Carrier Aggregation in HF Communications

Background

High Frequency Communications (“shortwave”) in the frequency range 2-30MHz is still an important component in medium to long range communications where its used for airborne, maritime and emergency communications in particular in high latitudes where satellite communications fail. At HF frequencies signals are reflected In the upper layers of the earth’s atmosphere, the ionosphere, where solar radiation and particles (“solar wind”) create electrically charged layers. These layers are located at 100-400km height and allow for communication of up to 4000km in a single hop and globally through multiple hops. The electrical characteristics of these layers will change with location, time of day and the solar activity and can be difficult to predict in detail. Modern HF communications system use Automatic Link Establishment procedures where the system scans and probes the pool of available frequencies to find frequencies with favorable propagation and low interference. The communication channel is subject to severe multipath propagation as various wave-modes have differing path delay in the ionosphere. This gives rise to frequency selective fading, and conventional system are limited to a few kHz in bandwidth.

Purpose and goal

One possibility to increase the transmission bandwidth is to use parallel transmissions on many narrowband channels in different frequency bands and aggregating the bit streams. This also requires a fast link set-up procedure that can find frequency bands with favorable propagation conditions and “empty slots” in the spectrum, avoiding interference from other systems. Such a scheme has been proposed and simulated in [1]. Simulation results show that the capacity of a such a system can be increased by an order of magnitude compared to conventional HF systems. There are, however, several challenges that must be overcome. This includes the design of access protocols for multi-station networks, the efficient design of multi-carrier power amplifiers and efficient antenna systems for simultaneous transmission in several bands.

Expected outcome

The project aims at demonstrating the feasibility of a HF multi-band carrier aggregation scheme with simulation and a practical demonstration.

Planned approach and implementation

The project aims at demonstrating a real HF link over a few 100 km with an SDR-based system, using the Red Pitaya platform [2] and GNU-radio during 2022.

Duration

2021-2022

Contact person

References

[1] J. Zander, "Greedy Channel allocation in Meshed Wideband HF Radio Networks with Channel Aggregation," in EuCAP 2022 (submitted), Madrid, 2022.
[2] Red Pitaya, "SDRlab 122-16," [Online]. Available: redpitaya.com/product/sdrlab-122-16-standard-kit/ .