Space shift keying (SSK), conveying data symbols via only the antenna indices, is a new modulation technique for low-complexity implementation of multiple-input multiple-output (MIMO) systems. SSK can be combined with the orthogonal frequency division multiplexing (OFDM) technique to improve the capacity and reliability of transmission. However, the SSK MIMO-OFDM systems also inherit from OFDM systems the drawback of a high peak-to-average power ratio (PAPR) of the transmitted signal. To overcome this problem, in this paper, the special information-conveying mode of SSK is utilized and a fast-converged gradient-based PAPR reduction method which exploits the phase freedom of the transmitted SSK MIMO-OFDM signal in the frequency domain is proposed. Simulation results show that the proposed improved gradient-based method (GBM) achieves a superior PAPR performance, as compared to the promising discrete phase set based schemes such as selected mapping method (SLM) and flipping method. Besides the considerable PAPR reduction, the improved GBM also enjoys other advantages such as low complexity, and neglectable performance loss.

High peak-to-average power ratio (PAPR) and spectral leakage are two main problems of orthogonal frequency division multiplexing (OFDM) systems. For alleviating the above problems, this paper proposes a joint model which efficiently suppresses both PAPR and spectral leakage, by combining serial peak cancellation (SPC) and time-domain N-continuous OFDM (TD-NC-OFDM) in an iterative way. Furthermore, we give an analytical expression of the proposed joint model to analyze the mutual effects between SPC and TD-NC-OFDM. Lastly, simulation results also support that the joint optimization model can obtain notable PAPR reduction and sidelobe suppression performance with low implementation cost.

This letter presents an improved peak cancellation (PC) scheme for peak-to-average power ratio (PAPR) reduction in orthogonal frequency division multiplexing (OFDM) systems. The main idea is based on a serial peak cancellation (SPC) mode for alleviating the peak regrowth of the conventional schemes. Based on the SPC mode, two particular algorithms are developed with different tradeoff between PAPR and computational complexity. Simulation shows that the proposed scheme has a better tradeoff among PAPR, complexity and signal distortion than the conventional schemes.

In this letter, a low complexity transmitter is proposed for the downlinks of orthogonal frequency code division multiplexing (OFCDM) systems. The principle is based on a joint time-frequency spreading and inverse fast Fourier transform (TFS-IFFT), which combines the frequency spreading with partial stages of IFFT, so as to simplify the real-time processing. Compared with the conventional one, the proposed OFCDM transmitter is of lower real-time computational complexity, especially for those with large spreading factor or low modulation level. Furthermore, the proposed TFS-IFFT can also be applied to other frequency spreading systems, such as MC-CDMA, for complexity reduction.

Selected mapping (SLM) is a promising distortionless technique for controlling the high peak-to-average power ratio (PAPR) of orthogonal frequency division multiplexing (OFDM) systems. In SLM, phase sequence selection plays an important role for efficient PAPR reduction. Although some phase sequence sets have been proposed in past studies, we show that an optimal selection is still desired for the phase sequences from the same set. Therefore, this letter develops a measureable phase sequence selection criterion to optimally select the phase sequences from both the same and different sets, so as to achieve near optimum PAPR reduction performance in SLM-OFDM systems.