Optimization of the stop-and-go- and dual-mode-algorithms for real-time baseband transmission

This paper presents two optimized blind equalization algorithms, developed on a real-time digital signal processor (DSP) test bed. The most commonly used group of blind channel equalizers are those based on the Bussgang algorithm. By combining a joint algorithm (JA) with a dual-mode (DM) algorithm or a stop-and-go (SAG) algorithm exists the option for optimal matching to the channel behavior. The performance of a single algorithm like modified decision directed modulus (MDDMA), modified constant modulus (MCMA) or the modified decision directed (MDDA) algorithm can only be adapted by adjusting the step size for updating the equalizer tap vector or by changing the number of equalizer taps. Using SAG or DM algorithm introduces a flag (SAG) or a confidence zone (DM) to optimize the algorithm performance further. Combining the joint algorithm within the SAG or DM algorithm yields an optimized algorithm which offers the advantage of the different algorithms. The new algorithms lead to a decrease of the required transmit power by about 22 percent while achieving the same BER. Additional to this, a 6 percent reduction of the processing time is possible relative to MDDMA due to the possibility to reduce the equalizer length.