Error floors in digital mobile radio systems due to delay distortion

The authors analyze the performance degradation of digital mobile communication systems due to delay distortions caused by filter imperfections and/or propagation anomalies of the channel. The analysis makes use of the error floor, which is defined as the lowest bit error rate (BER) the system can achieve in a very high C/N operated system. In addition to the conventional raised cosine filters, the performance of 'cube' and 'double jump' transfer function filters is studied. The results show that in the presence of delay distortion, the cube and double jump filters cause less BER degradation than the raised cosine filter. It is demonstrated that the 'linear rolloff' filter, a special case of cube and double jump filters, has the best performance. Computer simulations of channels with group delay distortion confirm these results.<>