Channel estimation and adaptive MLSEs for wireless mobile communications

Abstract

In this thesis, for the reliable communications over fading environments, we discuss channel estimation issues in the pilot channel aided code-division multiple access (CDMA) systems and adaptive maximum likelihood sequence estimation (MLSE)-based receivers for time-division multiple access (TDMA) systems. For the channel estimation in the pilot channel aided CDMA systems, two new channel estimation algorithms using both pilot and traffic channels are proposed. First, we consider a linear prediction using both pilot and traffic channels. After deriving a new form of the optimal Wiener filter for the channel estimation, for its practical implementation, we propose the decision-directed adaptive linear prediction filter (DD-ALPF). To prevent from falling into the false lock, the proposed DD-ALPF uses the conventional channel estimate obtained only from pilot channel as a baseline for checking the reliability of the filter output. It will be shown through computer simulation that the proposed method can improve the receiver performance and performs better in the fast fading environments, compared with the existing ones. Second, as another technique to improve channel tracking performance in the fast fading environments, we propose a channel identification algorithm based on the linear modeling for the fading process. Its cost function is minimized by using the recursive least squares (RLS) algorithm and its stability is also analyzed. In addition, we propose three types of adaptive MLSE receivers for TDMA systems. First, as an approach to reduce the complexity of the per-survivor processing (PSP)-MLSE, so-called the hybrid-MLSE which employs both the tentative decision (TD)-MLSE and the PSP-MLSE and at each time selects one of them, is proposed. For this selection, we consider two criteria, which are based on the instantaneous received signal power and the instantaneous signal-to-noise ratio (SNR), respectively; in fact, the hybrid-MLSE based on the latter crit...