An adaptive decision feedback equalizer with shaped training for mobile communication FM receivers

The paper describes an adaptive equalizer suitable for digital wireless systems. These systems are normally defined to work in indoor environments where channels show low delay spread values. For this reason, the possibility of signal equalization is not usually taken into account. Moreover, simplicity and cost are important parameters for these systems, and therefore simple and inexpensive receivers are used whenever it is possible. Because of their high capacity and low cost, it is interesting to study new applications based on these systems, for example, outdoor applications. However, these applications show higher delay spread values are necessary to perform an equalization process to maintain the communication quality. The problem appears when a limiter/discriminator receiver is used in the system due to the fact that this produces different distortions over the received signal which make the equalization process difficult. On the other hand, the modulation used in these systems may sometimes show modulation index variations that must be compensated for. The paper shows an equalization method that can perform the equalization process over the received baseband signal, compensating all distortions mentioned by using a shaped training sequence.