Low Complexity Channel Estimation for MIMO-Constant Envelope Modulation

摘要

MIMO-Constant Envelope Modulation, MIMO-CEM, with Low Resolution ADC receiver (1-bit ADC in the default operation) is considered as one of the alternative candidates to the well known MIMO-OFDM, suitable for wireless backhaul network in which relay nodes are fixed in their positions. Due to the low resolution ADC, MIMO-CEM channel estimation is considered as one of the major problems to withstand its real application. The authors have proposed an adaptive MIMO-CEM channel estimator based upon replicating the received preamble signal to exactly estimate the non-linear effect of the low resolution ADC. Because MIMO-CEM ADC is Intermediate Frequency (IF) sampled, the authors replicated the whole IF MIMO-CEM transceiver to exactly replicate the received preamble signal. Although this channel estimator has an excellent performance, its computational complexity is very high. This high complexity comes from the IF (high frequency) calculations. In this paper, we introduce a low complex MIMO-CEM adaptive channel estimator based upon linearly modeling the quantization error occurred at the low resolution IF sampled ADC, using linear curve fitting, in baseband. Hence, a baseband adaptive channel estimator can be designed, which has a much lower complexity than the IF estimator (previously designed by the authors). We prove the effectiveness of the proposed estimator under different channel scenarios using MSK and GMSK modulations.