Optimal flashy transmission in training-based MISO TDD systems

We consider a flashy transmission scheme in multiple-input single-output (MISO) systems. In order to efficiently utilize the limited energy budget, only a portion of the available time is used for the actual transmission. For block-wise transmissions, we define the flashiness as the percentage of blocks used for the actual transmission. Each transmission block consists of a reverse training phase and a data transmission phase. Using a capacity lower bound as the figure of merit, we show that the optimal training and data transmit power does not change with the energy budget as long as the flashiness is strictly less than one. We provide a simple design guideline to obtain closed-form solutions for the optimal flashiness, training power, as well as data transmit power which maximize the capacity lower bound. Our numerical results demonstrate a significant rate improvement by using the optimal flashy transmission in the low signal-to-noise ratio (SNR) regime, compared to the non-flashy scheme which uses all blocks for transmission.