Two Efficient Downlink Transfer Methods for Broadband Satellite Communication Systems with Large Capacity

Two specific continuous wave time division multiplexing (CWTDM) methods, i.e., adding frame overlapped (AFO) method and quasi-orthogonal time division multiplexing (QOTDM) method, are proposed to overcome the low efficiency and poor performance of the frequency division multiplexing (FDM) mode in the downlink of broadband satellite communication systems with large capacity based on the non-regenerative on-board processing (OBP). Both the proposed methods firstly samples and quantifies various baseband complex signals to be transferred; Then the AFO method divides the frames and overlaps them with the frame header to consist a multiplexing frame to transfer in the downlink, and the QOTDM method, interleaves sample sequences using the time division multiplexing mode and then transfers the sequences in the way of continuous signals by adding a synchronous sequence. The AFO method is simple in both multiplexing and de-multiplexing, while the QOTDM method is helpful for realizing larger capacity of onboard switching since it only needs to save one complex sample for each signal in multiplexing. Compared with the FDM downlink transfer method, both the proposed methods have higher power efficiency and better link performance. Simulation results show that the ratio of signal to inference of the QOTDM method improves 10 dB in 256 carriers compared with FDM transfer method, and the sub-channels isolation level meets a practical requirement. © 2017, Editorial Office of Journal of Xi'an Jiaotong University. All right reserved.