In this paper, a cooperative single-carrier transmission scheme considering a distributed quasi-orthogonal space-frequency block code (QOSFBC) that provides improved peak-to-average power ratio (PAPR) performance is constructed for uplink communications. Focused on reducing the size and computational complexity, the source node, i.e., the mobile devices, is equipped with two transmit antennas, while only one antenna is required at the relay node in order to collaboratively generate a distributed QOSFBC signal using four transmit antennas. To achieve full diversity, a phase rotation strategy is proposed at the relay node. In addition, since single-carrier schemes considering SFBCs re-permute the spectral components of the transmitted signal and induce high PAPR value, a modified SFBC coding technique is proposed that allows the high-PAPR problem to be mitigated. Consequently, the designed distributed single-carrier frequency-division multiple access (SC-FDMA) QOSFBC scheme is able to provide full transmit diversity over frequency-selective fading channels, with a lower PAPR value on mobile devices when compared with a conventional SC-FDMA QOSFBC scheme.

In this paper, an amplify-and-forward cooperative single carrier-frequency domain equalizer system for spectrum sharing is proposed to improve the performance of the primary user (PU) and allow the secondary user (SU) to transmit its information simultaneously. To achieve this purpose, a modified data-dependent superimposed training (DDST) scheme is employed. In the original DDST scheme, a part of the frequency bins of the information signal is discarded to insert pilots. In the proposed approach, after receiving PU's data SU firstly serves as a relay and amplifies PU's data. Following, the modified DDST scheme is utilized to discard a part of the subcarriers to insert SU's data. The overall signals are transmitted to the destination. At the destination, the signals from PU and SU are combined for detection by maximizing the signal-to-noise ratio in the frequency domain. Furthermore, the signal-to-interference plus noise ratio of the primary system is analyzed. If the BER of the primary system is given, the number of subcarriers shared to the SU can be determined. The simulation results reveal that the proposed approach is more suitable for spectrum sharing compared with cooperative orthogonal frequency division multiplexing system.

In data-dependent superimposed training (DDST) scheme, the data-induced interference in channel estimation is eliminated at the sacrifice of data distortion. Unfortunately, data distortion causes data identification problem (DIP) for DDST scheme, which results in error floor phenomenon in bit error rate (BER). Although some literatures have analyzed the DIP, the DIP is still an open problem without solution. In this work, we firstly review the data identification problem from the view of sub-space. The analysis result inspires us to introduce a precoding matrix for resolving the DIP in DDST scheme. In order to prevent the advantages in DDST scheme being reduced by the precoding matrix, we introduce several constraints on the precoding matrix. Subsequently, we derive the requirement of the precoding matrix for solving the DIP in DDST system by using singular value decomposition. Furthermore, an appropriate precoding matrix is developed based on Zadoff-Chu sequence, which is shown to satisfy all conditions derived in this work. Finally, simulation results are conducted to verify that the precoding matrix removes the error floor in BER for DDST scheme.

Multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems with space-frequency block coding (SFBC) have a high computational complexity since the number of inverse fast Fourier transforms (IFFTs) required scales in direct proportion to the number of antennas at the transmitter. This paper proposes to generate the SFBC encoded signals of the various antennas in time domain by exploiting the time-domain signal properties and signal correlations among the various transmitter antennas, achieving a significant reduction in computational complexity. In particular, it is demonstrated that the time domain SFBC encoded signals of the various antennas can be obtained from the time domain signal of the first antenna. Therefore, the proposed scheme requires only one IFFT irrespective of the number of transmission antennas. In addition, a low-complexity peak-to-average power ratio (PAPR) reduction scheme is presented based on the proposed transmitter architectures.