On an ionospheric channel simulator driven by measurements of multipath and Doppler spread

Propagation simulators have been used for many years to evaluate the performance of data modems. They allow testing to be carried out using repeatable specified propagation conditions and allow performance comparisons to be made between different modems. Additionally they allow simulation of a wide range of propagation conditions, whilst avoiding the expense of extended on-air testing. Beyond line of sight (BLOS) high frequency (HF) signals propagate via the ionosphere. Because the ionosphere has a layered structure, multiple reflections of the transmitted signal may reach the receiver, each of which can arrive with a different time delay and may exhibit time dispersion. Furthermore, both frequency shifts and frequency spreads can be imposed on the transmitted signal by the temporal variability of the ionospheric channel. In order to accurately predict the bit error rate (BER) of a modem under a range of propagation conditions it is necessary for a simulator to be able to model all of these effects. In addition, to estimate the availability of modems it is necessary to have some knowledge of the statistics of the occurrence of multipath and Doppler effects. This paper describes how a parameterised version of the data collected by a pulse compression ionospheric channel sounder can be used to drive an ionospheric channel model. The result is a replay simulator that benefits from incorporating both an improved ionospheric channel model and real measurements of the channel