Design of troposcatter broadband link based on SCFDE

Abstract

Troposcatter communication link is essentially a broadband, multipath, highly frequency selective, slow fading, long hop, point to point link. Orthogonal Frequency Domain Multiplexing (OFDM) has been proposed for troposcatter link design [1]. However, OFDM being a multi-carrier transmission scheme suffers from high Peak to Average Power Ratio (PAPR) problem which leads to non-linear distortion by Power Amplifier (PA) and considerable SNR loss if input signal is backed off. Single Carrier Frequency Domain Equalisation (SCFDE) exhibits a low PAPR, due to single carrier transmission, while retaining the advantage of Frequency Domain Equalisation (FDE). We present a troposcatter link design based on SCFDE in this paper. The design incorporates all the components of a practical system and is hardware implementable. It employs Low Density Parity Check (LDPC) Forward Error Correction (FEC) coding for SNR gain, QPSK/ 16 QAM modulation, Solid State Power Amplifier (SSPA) model to analyse the effect of nonlinearity and Input Back Off (IBO), frequency and timing synchronisation using double sliding window packet detection and Moose algorithm, Zero Forcing (ZF) channel estimation with Minimum Mean Square Error (MMSE) equalisation and dual diversity with Maximal Ratio Combining (MRC) combining. A novel frame format has been presented suited to the link design. Simulation parameters are derived from parameters of actual troposcatter links located in North China and between Dallas and Austin, Texas (U.S.A). SCFDE achieves a link margin of 3.4 dB with QPSK modulation and 2.8 dB with 16 QAM modulation due to high IBO for OFDM.