Wavelet Transform Aided Single-Carrier FDMA With Index Modulation

Single-carrier frequency-division multiple access (SC-FDMA) is a well-known multiuser transmission method for uplink communications owing to its low peak-to-average power ratio (PAPR) characteristics. Simultaneously, index modulation (IM) has been widely studied owing to its flexibility for spectral-efficiency versus energy-efficiency trade-off. However, applying conventional IM schemes with SC-FDMA may affect the desirable characteristics of SC-FDMA signals, resulting in the increase of PAPR, for example. On the other side, Wavelet Transform (WT) has been shown to provide an improved performance over the fast Fourier transform (FFT)-based SC-FDMA, owing to WT's local focusing capability in both time and frequency domains. In this paper, we propose three IM schemes, namely Symbol Position Index Modulation (SPIM), Spreading Matrix Index Modulation (SMIM) and Joint Matrix-Symbol Index Modulation (JMSIM) schemes, which perform IM at the symbol vector level, spreading matrix level, or a combination of both. These IM schemes are implemented with the WT-based SC-FDMA for data transmission. We consider two spreading matrix design schemes, namely random dispersion matrix design and Gram-Schmidt (GS) orthogonalization matrix design. Correspondingly, we propose different detection schemes, including Maximum Likelihood Detection (MLD), Simplified Maximum Likelihood Detection (SMLD), and the Two Stage Index-QAM Detection (TSD). The performance of the proposed schemes is evaluated by simulations. Our studies and results show that all the three schemes can effectively reduce the PAPR encountered by the conventional IM-assisted SC-FDMA signals. Moreover, the method of GS matrices can provide a gain upto 20 dB compared with the method of random dispersion matrices. Furthermore, the GS-based system can employ the proposed low-complexity TSD, allowing to achieve a similar bit error rate (BER) performance as MLD, while requiring significantly low complexity.