Spreading Sequence Estimation Based on Constant Modulus Property for QPSK-DSSS Signals
Ping Wei · Acta Aeronautica Et Astronautica Sinica · 2013
In this paper,a spreading sequence estimation algorithm based on constant modulus property is proposed for the QPSK-DSSS signals in low signal to noise ratio and non-cooperative scenarios.First,the single-user QPSK-DSSS signal can be equivalently represented as a two-user BPSK-DSSS signal,and then the two-dimensional signal subspace spanned by the in-phase and quadrature binary spreading sequences is estimated by the eigen-decomposition of the covariance matrix.Finally,to estimate the spreading sequences accurately,its constant modulus property is exploited to cope with the unitary matrix ambiguity resulting from eigen-decomposition.The proposed algorithm is simple and easy to implement,and has a lower computational complexity compared to existing methods.And simulation results demonstrate the significant performance gains of the proposed algorithm in low signal to noise ratio situations.