on of arrival and departure. If antenna ports from different panels experience different large-scale fading, it causes the eigenvectors of New Radio Access Physical Layer Aspects (Part 2) 589 the channel matrix to become ill-conditioned (rank deficiency), resulting in inaccurate CSI for coherent MIMO transmission. Moreover, time-varying amplitude or phase calibration error among the panels may occur in practice, especially when the antenna panels have independent clocks and different operating temperatures. In addition, the frequency offset for different panels observed at the receiver may be different when there is a time-varying relative phase between different antenna panels. The reference signals transmitted from geographically separated panels may experience dif- ferent Doppler shift and Doppler spread, because the UE may move in a different directions relative to the panels. If the UE assumes the panels have the same Doppler shift and Doppler spread, the frequency offset estimation would be inaccurate, which results in per- formance degradation. The relative frequency offset between panels can be from 0 to 300 Hz, due to the following factors [59]: Doppler shift: For a UE moving with the speed of 30 km/h at the carrier frequency of 2 GHz, the maximum difference between the experienced Doppler shifts is 111 Hz. Frequency error: In LTE, the maximum tolerable oscillator inaccuracy is +1 0.05 ppm for the wide area base station classes; thus the maximum frequency error between two non-calibrated panels with independent oscillators at the carrier frequency of 2 GHz is about 200 Hz. Thus the total amount of relative frequency offset is around 300 Hz. As the carrier frequency increases, the frequency offset problem would be more severe. The same timing offset assumption for different panels may impact the accuracy of chan- nel estimation. With a timing offset, a random linear phase factor will be added to the channel coefficient on adjacent subcarriers, which is difficult to accurately estimate. The inter-symbol in