Training signal design for MIMO OFDM channel estimation in the presence of frequency offsets

All existing training signal designs for channel estimation in OFDM systems assume no frequency offsets. In practice, frequency offset is unavoidable and seriously degrades the performance of OFDM systems. In this paper, we address the problem of designing optimal training signals for the estimation of frequency-selective channels in MIMO OFDM systems with frequency offsets. The mean square error advantage of our proposed optimal training signals can be quite significant for moderate-to-high values of SNR and frequency offsets.

I. Introduction

Training signal design for channel estimation is a well-studied problem for SISO systems (e.g., see [1]–[6] and references therein) but a relatively new one for MIMO systems. For MIMO single-carrier systems, optimal design and placement of pilot symbols for channel estimation were presented in [4] while space-time-coded training signal designs were studied in [7]. Recently, optimal training signal designs for MIMO OFDM systems were addressed in [8]–[10].