Wideband communication techniques in the HF channel

Because ionosphere allow for the signals to propagate through long distances, very long-distance communication is possible with relatively cheaper infrastructure. This type of communication allows is realizable between frequencies 3-30 MHz. Although ionosphere allows this very long-distance type of communication, communication in the HF band has many difficulties. First, HF bands are very busy and interference on the HF bands are intense. Amateur radio users, military and government transmission bands, HF radars and the radio stations on the HF bands are some of the interference sources. In addition to man-made interference, atmosferic noise being higher on lower frequencies, ionosphere changing with time and the HF channel changing as a result makes using the HF bands more difficult. In spite of all the harshness, research for understading the structure and movements of the ionosphere is ongoing for a long time. Measuring the total electron content with GPS satellites, using different interpolation techniques for different coordinates and modelling the electron densities and electron temperatures with International Reference Ionosphere (IRI) is some of the work which help us to estimate how the ionosphere will behave in a given coordinate and time. With all the ongoing research for understanding the ionosphere, it is now possible to estimate the propagation paths of the signals between transmitter-receiver pairs at the given coordinates and time. In this work, first we propose an algorithm which maximizes the bit rate of a given wideband communication system operating in the HF band. The proposed algorithm is built on the work given in the literature for estimating the electron densities in the ionosphere and estimating the propagation path of signals throughout the ionosphere. Algorithm uses the outputs of the ray tracing programs in order calculate the channel parameters and uses this parameters in order to optimize the parameters of the wideband communication system. Different optimization algorithms for multicarrier wireless communication systems like Orthogonal Frequency Division Multiplexing (OFDM), Filter Bank Multicarrier (FBMC) and Filtered Multitone (FMT) have been designed. With the help of the algorithm, it can be found which multicarrier system is more suited to the channel. Also, algorithm gives the best modulation index in the subchannels, transmitter power, number of subchannels, carrier frequency, subchannel bandwidth, cyclic prefix for OFDM, subchannel seperation for FMT parameters in order to maximize the bit rate. Also, the carrier frequencies produced by the algorithm are compared with the frequencies suggested by the VOACAP program. The parameter optimization algorithm can not suggest parameters for every channel. In these cases, the constraints of the multicarrier system can not be satisfied. So, for these cases, channel shortening filters or channel equalizers should be used before the multicarrier receivers. In this work, different channel shortening methods have been analyzed and proposed a new technique in order decrease the compexity of the Maximum Shortening Signal to Noise Ratio (MSSNR) method. It is shown that, the proposed technique can be used with the Minimum Mean Square Error (MMSE) method, too for some cases. Lastly, comparisons with the symmetric MSSNR method from literature are given.