Training-Based MIMO Systems: Part II—Improvements Using Detected Symbol Information

In this paper, the maximum achievable data rate performance is addressed for MIMO systems that employ transmission of known training sequences for channel estimation. In Part I of this paper, it was found that systems based on superimposed pilots (SIP) offer an increased performance over conventional time-multiplexed pilots for fast fading channels. In other cases, the performance gain is lost due the poor channel estimates that are attained when there is interfering data power present during the channel estimation process. By allowing channel reestimation using a decision-directed approach, this interfering data power can instead be utilized as additional training power, which significantly improves the quality of the channel estimates. As the channel estimates improve within the coherence interval, a higher coding rate can successfully be applied. These multiple coding rate schemes can also be applied to conventional time-multiplexed pilot schemes. However, our numerical examples show that a larger performance increase in maximum achievable data rate is attained if the decision-directed approach is applied to a SIP scheme.