Training placement for tracking fading channels

The problem of training symbol placement in data packets for channel tracking is considered, where the channel is time-varying Rayleigh flat fading. We use the minimum mean-square error (MMSE) estimator for channel tracking. A minmax approach is considered. We optimize the placement by minimizing the maximum MSE over a packet. It is shown that training symbols should be scattered throughout the packet with equal space to achieve the optimal performance.