Noncoherent OFDM-IM and Its Performance Analysis

Abstract

In conventional orthogonal frequency division multiplexing (OFDM) with index modulation (OFDM-IM), the active subcarriers can convey information bits by modulated symbols as well as their indices. To detect modulated symbols, coherent detection is usually considered, which requires the channel state information (CSI) estimation for all subcarriers at a receiver. In OFDM-IM, however, since only a fraction of subcarriers are active, the overhead for pilot transmissions through all subcarriers to allow the receiver to estimate the CSI could be excessive, in particular, under a fast fading environment. To avoid this difficulty, we consider noncoherent OFDM-IM, where only the indices of active subcarriers are used to convey information bits. For a better performance, a transmit diversity scheme is also studied. We derive a closed-form expression for the probability of index error when no transmit diversity is considered under frequency-selective Rayleigh fading. We also derive an upper-bound when the transmit diversity scheme is employed. From the upper-bound, the diversity order is also clearly shown.