Measurements of the Doppler and multipath spread of HF signals received over a path oriented along the mid-latitude trough

The presence of the midlatitude trough can severely impact on HF radio systems since the electron density depletion within the trough reduces the maximum frequency which can be reflected by the ionosphere along the great circle path. Furthermore, the associated horizontal gradients in the electron density distribution frequently result in propagation well displaced from the great circle path. The signal characteristics associated with this type of propagation have been investigated for a 1400 km link oriented along the midlatitude trough between Sweden and the UK. As anticipated, the observed delay and Doppler spread characteristics are strongly dependent upon time of day and season since the trough is a nighttime feature which occurs predominantly during the winter. In particular, the Doppler spread is often large when great circle propagation has been suppressed and reflections are from the north of the great circle path (i.e., from the poleward wall of the trough or from gradients and/or irregularities associated with the auroral zone)

Nighttime sporadic E measurements on an oblique path along the midlatitude trough.

Observations of nighttime sporadic E (Es) made within the HF band on a 1400 km path that lies approximately along the midlatitude trough are presented. Although the probability of occurrence of Es (PEs) is generally below that predicted by the ITU-R model, a significant increase in PEs is found when Kp ≥ 6. The signal parameters (azimuth, elevation, and Doppler spreads) also increase for high values of Kp. This behavior is consistent with the character of the propagation changing from midlatitude to auroral as the polar cap expands and the trough moves equatorward with increasing Kp

The influence of high latitude off-great circle propagation effects on HF communication systems and radiolocation

The influence of high latitude off-great circle propagation effects on HF communication systems and radiolocatio

The effect of the mid-latitude trough on the direction of arrival and time-of-flight of HF radio signals

The effect of the mid-latitude trough on the direction of arrival and time-of-flight of HF radio signal

The synthesis of travelling ionospheric disturbance (TID) signatures in HF radar observations using ray tracing

Characteristic signatures are often observed in HF radar range-time-intensity plots when travelling ionospheric disturbances (TIDs) are present. These signatures, in particular the variation of the F-region skip distance, have been synthesised using a ray tracing model. The magnitude of the skip variation is found to be a function of the peak electron density perturbation associated with the TID and radar frequency. Examination of experimental observations leads to an estimate of the peak electron density perturbation amplitude of around 25% for those TIDs observed by the CUTLASS radar system. The advantage of using the skip variation over the radar return amplitude as an indicator of density perturbation is also discussed. An example of a dual radar frequency experiment has been given. The investigation of the effect of radar frequency on the observations will aid the optimisation of future experiments

Measurement and modelling of HF channel directional spread characteristics for northerly paths

The northerly ionosphere is a dynamic propagation medium that causes HF signals reflected from this region to exhibit delay spreads and Doppler shifts and spreads that significantly exceed those observed over midlatitude paths. Since the ionosphere is not perfectly horizontally stratified, the signals associated with each propagation mode may arrive at the receiver over a range of angles in both azimuth and elevation. Such large directional spreads may have a severe impact on radio systems employing multielement antenna arrays and associated signal-processing techniques since the signal environment does not comprise a small number of specular components as often assumed by the processing algorithms. In order to better understand the directional characteristics of HF signals reflected from the northerly ionosphere, prolonged measurements have recently been made over two paths: (1) from Svalbard to Kiruna, Sweden, and (2) from Kirkenes, Norway, to Kiruna. An analysis of these data is presented in this paper. The directional characteristics are summarized, and consideration is given to modeling the propagation effects in the form of a channel simulator suitable for the testing of new equipment and processing algorithms

A comparison between the measured and predicted parameters of HF radio signals propagating along the midlatitude trough and within the polar cap

Prediction of the propagation characteristics of HF signals is an important aspect in the planning and operation of radio systems operating within that frequency band. Various computer codes have been developed by a number of organizations for this purpose. These prediction techniques assume that propagation is along the great circle path and ignore the effects of various large-scale ionospheric structures that can be present in the northerly ionosphere and result in propagation well displaced from the great circle path. This paper reports on a statistical analysis of observations of the direction of arrival and signal strength, and their comparison with VOACAP predictions for four paths, two roughly tangential to the midlatitude trough, one trans-auroral, and one entirely located within the polar cap

Time of flight and direction of arrival of HF radio signals received over a path along the midlatitude trough: Observations

Measurements of the time-of-flight, direction of arrival, and Doppler spread are presented for HF radio signals radiated on six frequencies between 4.6 and 18.4 MHz received over a subauroral path oriented along the midlatitude trough between Sweden and the UK. During the day, the signals usually arrived from the great circle direction whereas at night, especially during the winter and equinoctial months; the signals on frequencies between 7.0 and 11.1 MHz often arrived from directions well displaced from the great circle direction. In summer the deviations tended to be smaller (<5°) than those observed during the other seasons (several tens of degrees). The deviations were mainly to the north and often lasted all night, with the time of flight initially decreasing and then increasing, showing an approach and then recession of the reflection point. Southerly deviations were much less coherent and less frequent

The simulation of off-great circle HF propagation effects due to the presence of patches and arcs of enhanced electron density within the polar cap ionosphere

Observations over recent years have established that large-scale electron density structures are a common feature of the polar cap F region ionosphere. These structures take the form of convecting patches and arcs of enhanced electron density which form tilted reflection surfaces for HF radiowaves, allowing off-great circle propagation paths to be established. Numerical ray tracing has been employed to simulate the effects of these structures on the ray paths of the radiowaves. The simulations have reproduced the precise character of experimental observations of the direction of arrival over a propagation path within the polar cap and of oblique ionograms obtained over the same path

Observations of 5.9 GHz radio propagation and 802.11p network performance at road junctions

The propagation of 5.9‐GHz radio signals and performance of an 802.11p network were measured at three road junctions each having a different density of buildings. The maximum range for which acceptable performance (defined as where the packet delivery ratio was greater than 90%) was dependent on the junction but lies in the range of 45–70 m. While reflections from transient vehicles were often found to have a small positive impact on network performance, this could not be relied upon to provide a reliable improvement in communications. The received signal strength was dependent on the junction type with the strong reflections from buildings located on the opposite side of a T‐junction leading to higher signal strength. Finally, an empirical relationship between the packet delivery ratio and the received signal strength has been established that will allow modelers to link signal strength to network performance for field conditions