  In this work the modeling and calibration method of reciprocity error in a
coherent TDD coordinated multi-point (CoMP) joint transmission (JT) system are
addressed. The modeling includes parameters such as amplitude gains and phase
differences of RF chains between the eNBs. The calibration method used for
inter-cell antenna calibration is based on precoding matrix indicator (PMI)
feedback by UE. Furthermore, we provide some simulation results for evaluating
the performance of the calibration method in different cases such as varying
estimation-period, cell-specific reference signals (CRS) ports configuration,
signal to noise ratio (SNR), phase difference, etc. The main conclusion is that
the proposed method for intercell antenna calibration has good performance for
estimating the residual phase difference. Keywords-LTE-Advanced; TDD; CoMP; JT;
reciprocity error; phase difference; inter-cell antenna calibration
