investigated in the literature. The most common approach is to estimate the channel response in the delay domain, and optimal pilots sent from different transmit antennas are typically assumed to satisfy the phase shift orthogonality condition in both the single-user case [@Li02Simplified; @Barhumi03Optimal; @Minn06Optimal] and the multi-user case [@Chi11Training]. Note that such phase shift orthogonal pilots (PSOPs) have been adopted in LTE [@Dahlman11LTE]. When channel spatial correlations are taken into account, optimal pilot design has been investigated for both the single-user case [@Tuan10Optimized] and multi-user case [@Tran12Training]. Although these orthogonal pilot approaches can eliminate pilot interference in the same cell, they do not take into account the pilot overhead issue, which is thought to be one of the limiting factors for throughput in massive MIMO-OFDM \[4\]. When such approaches are directly adopted in time-division duplex (TDD) massive MIMO-OFDM, the corresponding pilot overhead is proportional to the sum of the number of UT antennas, and would be prohibitively large as the number of UTs becomes large. This becomes the system bottleneck, especially in high mobility scenarios where pilots must be transmitted more frequently. Therefore, a pilot approach that takes the pilot overhead issue into account is of importance for massive MIMO-OFDM 