Effect of pilot ratio on channel estimation for spatial modulation

Spatial modulation (SM) is a single-stream multiple-input multiple-output (MIMO) technique which only activates one transmit antenna at a time. Apart from the complete avoidance of inter-channel interference, SM also exhibits a great energy saving in the radio-frequency (RF) chain. However, in contrast to multi-stream MIMO systems, channel estimation (CE) for SM becomes a challenge since the MIMO channel cannot be estimated in one transmission step due to the single RF chain. Motivated by this fact, a novel CE scheme has been recently proposed which exploits the channel correlation and jointly estimates the channels for different transmit antennas. Without needing feedback, this new method achieves the same estimation period as multi-stream MIMO schemes. In this paper, a varying pilot ratio has been investigated in SM for both the conventional and the novel CE methods. Balancing the accuracy and the amount of data, an optimal pilot ratio can be achieved for the peak throughput. Simulation results present that the novel CE approach significantly outperforms the conventional method with a much lower optimal pilot ratio.