Acta Polytechnica Scandinavica Mathematics, Computing and Management in Engineering Series No. 96 Receiver Structures Based on Self-organizing Maps

Dissertation for the degree of Doctor of Science in Technology to be presented with due permission for public examination and debate in Auditorium T2 at Abstract New adaptive receiver structures are studied to allow a more eecient compensation of the disturbances of the communication channel. This study concentrates on the use of the Self-Organizing Map (SOM) algorithm as a building block of new adaptive receivers. The SOM has been used both as an adaptive decision device and to follow up error signals. When the SOM was used as an adaptive decision device, comparisons with conventional equalizers such as the linear equalizer and the decision feedback equalizer were performed. The new structures were also compared with other neural methods like radial basis function networks and multi-layer perceptrons. The performances of the neural equalizers and especially the SOM have been found to be better in nonlinear multipath channels and about equal in linear channels. When the SOM was used to follow up error signals, the actual idea was to cancel interference. This task was divided between following up the error distribution and nding out the error estimate. The error was approximately the same as the interference. Other sources of error were noise, intersymbol interference, wrong error estimates and detection errors due to the reasons mentioned before. The error distribution can be followed up, but the problem is how to predict the error. Some solutions are presented in this thesis, but they do not provide satisfactory results. The performance has been compared with a pure detector without any kind of interference cancellation and with a receiver based on the radial basis function network. However, it was discovered that these neural receivers designed for interference cancellation perform better when nonlinear distortions are compensated. The receivers based on the SOM are slightly more complicated than conventional ones, but when a channel has nonlinear disturbances in particular, they ooer one possible solution.ogy and the Jenny and Antti Wihuri Foundation is gratefully acknowledged. Finally, I wish to thank my wife Virpi and son Mikko for providing pleasant and memorable moments outside the laboratory during the preparation of this thesis.