Preamble based Adaptive Beamformer for Hybrid Terrestrial-Satellite Mobile System
Ammar H. Khan, Muhammad Ali Imran, Muhammad Ali Imran, B.G. Evans · 2010
Convergence behaviour of beamforming in interference mitigation application is critical to overall system performance. In non-blind beamforming, the resources utilised to reach the steady state impacts the overall throughput. Traditionally in the downlink of Orthogonal Frequency Division Multiplexing (OFDM) based systems, a preamble formed of training sequence is transmitted prior to data for the purpose of channel estimation. While enabling superior estimation, the approach compromises on data throughput. On the other hand in the uplink, a preamble approach for channel estimation is not applicable due to interference issues. For beamforming, however, preamble transmission for the uplink becomes viable for improved detection performance. In this paper we propose a pilot reallocation based preamble solution for beamforming where dispersed pilots from OFDM symbols are reallocated to form a preamble at the transmission end. This preamble, transmitted prior to data OFDM symbols, guarantees faster convergence without affecting data throughput. Extending our previous work, we employ this solution in Hybrid Terrestrial Satellite Mobile System (HTSMS) with a channel model specific to the mobile-satellite scenario in order to yield practical results. We also study the impact of the preamble’s pilot density and its length on beamformer’s convergence behaviour and overall performance of HTSMS.