In this paper, we investigate channel acquisition for high frequency (HF)
skywave massive multiple-input multiple-output (MIMO) communications with
orthogonal frequency division multiplexing (OFDM) modulation. We first
introduce the concept of triple beams (TBs) in the space-frequency-time (SFT)
domain and establish a TB based channel model using sampled triple steering
vectors. With the established channel model, we then investigate the optimal
channel estimation and pilot design for pilot segments. Specifically, we find
the conditions that allow pilot reuse among multiple user terminals (UTs),
which significantly reduces pilot overhead. Moreover, we propose a channel
prediction method for data segments based on the estimated TB domain channel.
To reduce the complexity, we are able to formulate the channel estimation as a
sparse signal recovery problem due to the channel sparsity in the TB domain and
then obtain the channel by the proposed constrained Bethe free energy
minimization (CBFEM) based channel estimation algorithm, which can be
implemented with low complexity by exploiting the structure of the TB matrix
together with the chirp z-transform (CZT). Simulation results demonstrate the
superior performance of the proposed channel acquisition approach.Comment: 30 pages, 4 figure