Joint equalization and channel coding for channels with multipath propagation

Multipath propagation of radio waves as a result of reflections at the ionospheric layers and the associated superimposition of wave trains arriving at the receiver with different delays is the main source of impairment to radio data transmission. Great efforts are needed to achieve the required data transmission quality under these conditions. The shortwave channel using the ionosphere as a transmission medium is used as an example for a time-variant channel with frequency- and time-dispersive fading. The long distances between transmitters and receivers and the varying channel characteristics are a general problem when testing the transmission components. This article deals with measurements of the transmission and receiving components and with methods for data protection under real transmission conditions. An optimal combination of Viterbi detection and channel coding is the main theme of our investigations. The results of practical tests in the radio channel are compared with results obtained from simulation. The comparison shows that the so-called on-the-air measurements yield essential information for performance assessment of transmit and receive algorithms. Since the model characteristics correspond to real channel characteristics only at certain points, the selection of a real transmission medium is of utmost importance especially for investigating the interplay of the different system components, as shown in this article