Low complexity channel estimation technique for MIMO-Constant Envelope Modulation

Low-resolution ADC MIMO-Constant Envelope Modulation, MIMO-CEM, is one of the alternative candidates to the well-known MIMO-OFDM, suitable for wireless backhaul networks. One of the major problems withstands the real application of MIMO-CEM is the channel estimation. This comes from the low resolution ADC used in MIMO-CEM receiver. Intermediate Frequency (IF) based Adaptive channel estimator was previously proposed for MIMO-CEM. This channel estimator is based upon replicating the received preamble signal to exactly match the effect of high quantization error ADC upon the received MIMO signal. Because MIMO-CEM ADC is IF sampled, the whole IF MIMO-CEM transceiver is replicated to exactly replicate the received preamble signal. Although this channel estimator has an excellent estimation performance, its computational complexity is very high. This high complexity comes from the IF (high frequency) calculations. In this paper, a low complexity MIMO-CEM adaptive channel estimator is introduced. The proposed channel estimator is based upon linearly modeling the quantization error occurred at the low resolution IF sampled ADC in baseband. Hence, a baseband adaptive channel estimator can be designed, which has a much lower complexity than the IF estimator (previously designed). The effectiveness of the proposed estimator is proven under different channel scenarios using Minimum Shift Keying (MSK) and Gaussian MSK (GMSK) modulations.