Abstract
A low peak-to-average power ratio (PAPR) transceiver using a new parallel frequency-shift orthogonal keying (FSOK) technique is proposed for the multiuser uplink multi-carrier CDMA (MC-CDMA) system over multipath fading channels. By employing the frequency modulated and multiplexed FSOK techniques to combat the multiuser and parallel substream interferences, respectively, the system retains a low-PAPR transmitted signal and a low-complexity equalizer without any matrix inversion. At the basestation, a multiuser receiver is derived, which involves parallel FSOK despreading, demapping, and maximum likelihood decision rule to acquire M-ary modulation gain and frequency diversity gain. For higher link quality, a multiple input single output FSOK uplink system can flexibly be configured. Simulation results are included to demonstrate that the proposed system achieves the low-PAPR property, space-frequency diversity, and M-ary modulation gain. Compared to the existing MC-CDMA and SC-FDMA systems, the proposed system exhibits significant performance superiority.
Highlights
Low peak-to-average power ratio (PAPR) modulation schemes are highly recommended for uplink broadband wireless communications
A frequency-domain equalizer is adopted by the Single-carrier frequency division multiple access (SC-FDMA) receiver to mitigate the multipath interference (MPI) effect and obtain the frequency diversity gain
Each uplink user in the distributed or localized SCFDMA systems is assigned to utilize the partial spectrum. Such a constraint may deteriorate the PAPR property, as Horlin et al [6] have indicated that the localized SC-FDMA has a larger PAPR than the cyclic prefix (CP) CDMA system, and obtains a better link performance than the latter
Summary
Low peak-to-average power ratio (PAPR) modulation schemes are highly recommended for uplink broadband wireless communications. SC-FDMA systems with different subcarrier assignment schemes can preserve the orthogonality among users, which facilitates multiuser communications and combats multiple access interference (MAI). Based on the above discussion, to simultaneously achieve multiuser detection and low-PAPR, as well as obtain frequency diversity gain to the greatest possible extent, we propose a novel parallel frequency-shift orthogonal keying (FSOK) technique for multi-carrier CDMA (MC-CDMA) systems. To overcome the MPI and MAI problems, we continue the work started in [10,11] and propose a novel extension called the parallel FSOK MC-CDMA system to support robust multiuser uplink communications over multipath channels while preserving the low-PAPR property. Based on a single Chu sequence, the proposed sophisticated FSOK scheme can generate a group of spreading sequences for the parallel substreams of multiple users, while maintaining low PAPR and orthogonality between substreams and users, even in the presence of multipath fading channels. To achieve multiuser uplink and combat the MAI interference, different users are assigned to different sets of interleaved subcarriers, maintaining perfect orthogonality between multiple users
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