טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentRonen Yosef
SubjectIterative Channel Estimation and Decoding in Turbo Coded
Space Time Systems
DepartmentDepartment of Electrical Engineering
Supervisor Dr. Shraga Bross


Abstract

The design of coherent space-time codes (STC) and optimal detectors for the flat fading channel is often performed under the assumption that the additive noise is white and Gaussian, and that the receiver knows the exact realization of the fading process. However, recent studies quantify the impact of imperfect channel state information (CSI) at the receiver and show, via information-theoretic analysis, that the optimal coherent detector is not robust as long as the receiver exhibits errors in the estimation of the fading process.

In this work a multiple antenna coded communication system over both block fading and fast fading Rayleigh channel is considered, assuming that the channel state is unknown to both transmitter and receiver. Several iterative decoding strategies are investigated for space-time turbo coded (STTC) systems, which involve channel estimation based on known pilot symbols and a modification of the Expectation-Maximization (EM) algorithm. A new suboptimal joint receiver scheme is suggested which first improves the channel estimation, and then continues with channel estimation, demodulation and decoding through iterative steps.

The simulation results demonstrate the significant gain of STTC schemes and the effect that inaccuracy of the channel estimation has on the performance of the iterative decoding scheme, coinciding with the trends dictated by the recent information-theoretic analysis. The results emphasize the relevance of having both a good channel estimation and processing the modulation code inside the iteration.