Peak‐to‐average power ratio reduction in space–time coded MIMO‐OFDM via preprocessing

Abstract

In this paper, we propose a trellis exploration algorithm based preprocessing strategy to lower the peak-to-average power ratio (PAPR) of precoded MIMO-OFDM. We first illustrate the degradation in PAPR due to optimal linear precoding in MIMO-OFDM systems. Then we propose two forms of multi-layer precoding (MLP) schemes to reduce PAPR. In both schemes, the inner-layer precoder is designed to optimize system capacity/BER performance. In the first MLP scheme (MLP-I), a common outer-layer polyphase precoding matrix is employed. In the second MLP scheme (MLP-II), data stream corresponding to every transmit antenna is precoded with a different outer-layer polyphase precoding matrix. Both outer-layer precoders are custom designed using the trellis exploration algorithm by applying the aperiodic autocorrelation of OFDM data symbols as the metric to minimize. Simulation results indicate that both MLP schemes show superior PAPR performance over conventional MIMO-OFDM with and without precoding. In addition, MLP better exploits frequency diversity resulting in BER performance gains in multi-path environments.Algorithm 2 MLP-II: trellis exploration algorithm aided modified UCHT Require: M t , N P , L, and the number of iterations I, H, { l , l = 1, 2, · · · , L} Ensure: finding optimal P phases = [ (1), (2), · · · , (L)] H = V U H U n : UCHT D n = zeros(N P , N P ) for Tx = 1 to M t do for i = 1 to I do for m = 1 to N P do for l = 1 to L do D n (m, m, Tx) = phases(l) P(:, :, Tx) = 1 √ N P U n D n (:, :, Tx) δ(l) =cal δ(P(:, :, Tx), U, x(Tx, :)) end for [δ min(Tx), index min] =min(δ) D n (m, m, Tx) = phases(index min) end for end for P(:, :, Tx) = 1 √ N P