Simultaneous Channel Estimation in MIMO OFDM Systems Using Constant-Amplitude Sequences

Constant-amplitude (CA) sequences are efficacious in the construction of multicarrier sounding waveforms in order to facilitate simultaneous channel estimation (SCE) in uplink multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems. The permissible single-root length-N Zadoff-Chu sequences that are cyclically shiftable with a minimum cyclic shift distance (CSD) (sic)(min) in time domain are widely adopted to enable the separation of simultaneously received sounding OFDM waveforms and thus achieve accurate SCE when at most left perpendicular N/(sic)(min) right perpendicular MIMO channels are estimated simultaneously. To enable the large-size SCE of more than left perpendicular N/(sic)(min) right perpendicular MIMO channels, nonorthogonal multiple-root Zadoff-Chu sequences have to be adopted and this degrades the SCE performance remarkably due to heavy inter-sequence interference (ISI). In this paper, various CA sequence families are thus investigated for performance prevalence in the large-size SCE over independent Rician multipath channels. It is analytically shown that the large-size SCE can be achieved with less influence from ISI when the adopted CA sequence family is composed of orthogonal sequence subfamilies, each containing as many permissible cyclically-shiftable CA sequences as possible.