Zhenduo Wang

Joint suppression of PAPR and sidelobe of hybrid carrier communication system based on WFRFT

A novel joint suppression method of peak to average power ratio (PAPR) and sidelobe power of hybrid carrier (HC) system based on weighted-type fractional Fourier transform (WFRFT) is proposed in this paper. PAPR and sidelobe power are restrained through pulse shaping in frequency domain and windowing in time domain respectively. Undesired peak regeneration emerges as a result of time windowing for out of band radiation suppression and pulse shaping is applied as a united technique to suppress PAPR with scarcely affecting on system performance. Flexible selections of WFRFT parameter α, shaping parameter β, and windowing parameter γ are employed for multi-objective optimization of the proposed HC framework. A multichannel model is then proposed according to the parameter analysis.

Bit error rate analysis of generalised frequency division multiplexing with weighted-type fractional Fourier transform precoding

Generalised frequency division multiplexing (GFDM) as a non-orthogonal waveform candidate is posed to reduce the high out of band radiation of orthogonal frequency division multiplexing system via pulse shaping. In this study, an analytical model of introduced interference from neighbouring subcarriers caused by pulse shaping is firstly proposed. Signal-to-interference-plus-noise ratio (SINR) is calculated according to related GFDM models with different weighted-type fractional Fourier transform (WFRFT) precoding orders. Approximated bit error rate (BER) expressions are derived for the low complexity GFDM system over additive white Gaussian noise and fading channels based on the analysis of SINR. Particularly, the BER superiority of WFRFT precoding is highlighted over the fading channels. Furthermore, peak-to-average power ratio and out of band power suppression performances are simulated at different WFRFT orders to illustrate the advantages of WFRFT precoding.

WFRFT precoding for generalized frequency division multiplexing

This paper presents a generalized frequency division multiplexing (GFDM) communication scheme based on 4-weighted fractional Fourier transform (WFRFT) precoding. The proposed scheme as well as its low complexity version achieves flexible multi-object optimization of system performance such as bit error rate (BER) and peak to average power ratio (PAPR). Compared to traditional GFDM scheme, the improved system based on weighted parameter selection brings about combined performance advantages.

On the probability density function of the real and imaginary parts in WFRFT signals

Recently a Hybrid Carrier (HC) scheme based on Weighted-type Fractional Fourier Transform (WFRFT) was proposed and developed, which contains Single Carrier (SC) and Multi-Carrier (MC) synergetic transmission. The wide interest is primarily due to its appealing characteristics, such as the robust performances in different types of selective fading channels and a great deal of potential for secure communications. According to the literatures, the HC signal and SC or MC signal probability distributions are different. In particular, some benefits of this HC scheme are brought by the quasi-Gaussian distribution of WFRFT signals. However, until now researchers have only presented statistic properties through computer simulations, and the accurate expressions of signals are not derived yet. In this paper, we derive the accurate and rigorously established closed-form expressions of Probability Density Function (PDF) of WFRFT signal real and imaginary parts with a large number of QPSK subcarriers, and this PDF can describe the behavior of data modulated by WFRFT, avoiding the complex computation for extensive computer simulations. Furthermore, the components of PDF expression are described and analyzed, and it is revealed that the tendency of signal quasi-Gaussian changes with the increasing of the parameter α (α in [0,1]). To validate the analytical results, extensive simulations have been conducted, showing a very good match between the analytical results and the real situations. The contribution of this paper may be useful to deduce the closed form expressions of Bit Error Ratio (BER), the Complementary Cumulative Distribution Function (CCDF) of Peak to Average Power Ratio (PAPR), and other analytical studies which adopt the PDF.

BER analysis of STBC hybrid carrier system based on WFRFT with frequency domain equalization

The inherent characteristic of hybrid carrier (HC) scheme based on the weighted-type fractional Fourier transform (WFRFT) is revealed. The proposed linear combination of single carrier (SC) and multicarrier’s (MC) characteristics is helpful to balance the conflicting requirements and achieve the comparative analysis of SC/MC. As an example, analytical SER/BER expressions of HC system with zero forcing (ZF) and minimum mean square error (MMSE) equalization are derived. In addition, the derived BER expressions are extended to multi-input systems. A unified framework of space time block code (STBC) HC scheme is proposed with two WFRFT modules at the transmitter or receiver, where STBC-SC and STBC-MC systems are the special cases of the novel structure.

Performance of uplink WFRFT-based hybrid carrier systems with non-orthogonal multiple access

In this paper, the performance of hybrid carrier (HC) systems based on weighted fractional Fourier transform (WFRFT) is investigated in an uplink non-orthogonal multiple access (NOMA) scenario. NOMA is a promising technology to improve the system capacity, in which two users (far-user and near-user relative to a base station) are allocated to use the same time-frequency resources, and the successive interference cancellation (SIC) technique is implemented to decode signals at the receiver. Considering the actual error decoding in the SIC process (i.e. imperfect SIC), NOMA cannot avoid the inter-user interference (IUI) and residual interference (or error propagation). Therefore, firstly IUI and residual interference are analysed, and signal to interference plus noise ratio (SINR) of the far-user is expressed mathematically considering the residual interference. Then, based on the analysis of IUI, considering different WFRFT orders, a near-user BER expression over additive white Gaussian noise (AWGN) channels is derived. Furthermore, the optimal WFRFT order selection to minimise the interference influence in the uplink is formulated and solved efficiently. Simulation results have verified the mathematical expression of SINR, the near-user theoretical BER expression, and the proposed optimal WFRFT order selection to obtain the maximum sum spectral efficiency.

A novel analysis of PAPR of FRFT-OFDM system

As is shown that the multicarrier system based on fractional Fourier transform (FRFT) has advantages over orthogonal frequency division multiplexing (OFDM) system in performance of peak-to-average power ratio (PAPR). In this paper, precise expressions of PAPR of FRFT-OFDM scheme and traditional OFDM scheme are derived and verified by simulations, as an effective proof for lower PAPR of FRFT-OFDM system. Furthermore, compared to OFDM system, PAPR inhibition techniques such as selected mapping (SLM) and iterative clipping and filtering (ICF) also apply to FRFT-OFDM system. Flexible selection of the order of FRFT-OFDM scheme brings facile PAPR performance, which can be deeply reduced through jointing with SLM and ICF. View of combined multi-object optimization of FRFT-OFDM system is considered in the end of the paper.