Dynamic Channel Estimation for MIMO-Constant Envelope Modulation

The Multi-Input Multi-Output (MIMO)Constant Envelope Modulation MIMOCEM is introduced as power and complexity efficient alternative to MIMO-OFDM for wireless backhaul networks. Due to a low resolution ADC (1-bit in the default operation) employed in the MIMO-CEM receiver, MIMO-CEM channel estimation is considered as one of the major challenges toward its real application. A block based adaptive channel estimator was proposed by the authors to estimate MIMO-CEM channel in static and quasi-static channel conditions. In this scheme, channel parameters are iteratively estimated by replicating the received preamble signals. In addition, to accurately estimate MIMO-CEM channel in presence of severe quantization errors caused by a low resolution ADC on the receiver side, the authors proved that Code Division Multiplexing (CDM) preambles transmission is effective in estimating MIMO channel state information. Although wireless backhaul channel is generally assumed to be static and quasi-static, it suffers from channel fluctuations in actual situation. Therefore, the objective of this paper is to present a decision directed channel estimation (DDCE) to track MIMOCEM channel fluctuation in high Doppler frequency conditions, and clarify the effectiveness of MIMO-CEM adaptive estimator in time varying channel conditions. The performance of proposed DDCE is compared with that of Pilot Assisted (PAS) linear interpolation dynamic channel estimation. For performance evaluations, different Doppler frequencies are assumed to prove the effectiveness of the scheme even in high channel variations. Simulation results prove that MIMO-CEM is applicable to dynamic channel conditions with various Doppler frequencies.