Simultaneous Channel Estimation in Multicell Multiuser MIMO OFDM Systems

In multicell multiuser multiple-input multiple-output orthogonal frequency-division multiplexing (OFDM) cellular environments, simultaneous channel estimation (SCE) is achieved by first separating multiple received sounding OFDM signals carrying different constant-amplitude (CA) pilot sequences from all cells and then estimating channel responses jointly at each base station receiver. Multicell least-square-based SCE is analytically studied herein in terms of average mean-square-error for each base station receiver operating under independent uplink Rician/Rayleigh multipath channels and in the presence of time offsets among multiple received sounding signals. The SCE system is shown to suppress the mutual interference among various received sounding signals effectively when the pilot sequence subset for each cell consists of all CA sequences that are cyclically shiftable with a minimum cyclic shift distance ϖ<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">min</inf> in time domain (namely, ϖ<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">min</inf>-permissible CSCA sequences), and CA sequences from different subsets are mutually orthogonal. Thus, a modified phase-model-assigning (MPMA) sequence family is constructed herein of orthogonal ϖ<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">min</inf>-permissible CSCA sequence subfamilies, and compared with Zadoff-Chu and Yu-Lee sequence families which are both comprised of nonorthogonal ϖ<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">min</inf>-permissible CSCA sequence subfamilies. The system adopting the MPMA family is demonstrated to provide higher estimation accuracy in SCE than the systems adopting Zadoff-Chu and Yu-Lee families.