Abstract
The authors have proposed Multi-Input Multi-Output (MIMO)-Constant Envelope Modulation (MIMO-CEM), as power and complexity efficient alternative to MIMO-OFDM, suitable for wireless backhaul networks. One of the major problems to withstand real application of MIMO-CEM is to estimate MIMO channel characteristics. The MIMO-CEM is based upon two contrary schemes; one is nonlinear Maximum Likelihood Sequence Estimator (MLSE), which needs accurate channel information to replicate the received signal passing through it. The other is a low resolution analog-to-digital converter (ADC), e. g., 1-bit in the default operation that removes the received signal amplitude fluctuation. This paper considers channel estimation problem in MIMO-CEM. First, we propose a MIMO-CEM adaptive channel estimator, in static and quasi-static channel conditions, based upon Code Division Multiplexing (CDM) preambles transmission, where channel parameters are iteratively estimated by observing the received MIMO preambles. Then, we extended the proposed CDM preamble method to Decision Directed Channel Estimation (DDCE) to track MIMO-CEM channel in high Doppler frequency conditions and clarify the effectiveness of MIMO-CEM in dynamic channel conditions.