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This paper presents a new approach to achieve optimal training sequences (OTS) in terms of minimizing the mean-square channel estimation error for spectrally efficient MIMO OFDM systems. It is shown that the OTS are equipowered, equi-spaced and position orthogonal. However, in special cases we can find that required conditions to achieve optimal pilot design are not satisfied, this means the optimum pilot is unachievable. In this paper, an algorithm is proposed to achieve suboptimum pilot design under time varying channels. To offer high throughput gains, we propose an adaptive pilot scheme in order to optimally use pilot tones over time varying channels.

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