Research On WFRFT Based Multi-component Signal Transmission Scheme

The rapid development of wireless network technology promotes the arrival of the Internet era.The Internet gradually integrates into people’s work and life,providing more efficient and convenient information transmission services.With the promotion of wire-less technology,the rapid increase in the number of users and the diversification of the environment lead to a rapid increase in network information.At the same time,informa-tion processing turns more complex,spectrum resources scarcer,and information security threats more serious.Therefore,how to ensure the stability,reliability and security of the wireless network has become a key research goal of researchers.The complex and diversified paths in the signal transmission process cause multipath effect,which causes channel frequency-domain selective fading.Whereas the Doppler shift caused by high-speed signal transmission leads time-selective fading.These fading results in signal distortion,seriously affecting the communication quality.Besides to the reliability of wireless networks,the security of information transmission in the wireless network cannot be ignored.Traditional wireless network security systems mainly rely on the cryptographic encryption system in the computer network,but the transmission open-ness of wireless network is often ignored,restraining its development.In recent years,it has been a research hotspot to use the underlying physical information characteristics of signals to maintain information security.However,most security technologies are stud-ied under ideal conditions(such as with powerful signal analysis capabilities),which are not easy to implement in actual wireless networks.Aiming at the above problems,the Weighted-type Fractional Fourier Transform(WFRFT)is adopted as the main research method in this paper.The WFRFT-based hybrid carrier(HC)communication system is a quite novel.The evenly distributed time-frequency energy of the hybrid carrier signal can achieve a smooth transition between single-carrier and multi-carrier systems,possessing strong anti-fading ability inharsh channels.At the same time,HC signals have the advan-tage of concealment,easy realization,low complexity,etc.,possessing great potential in physical layer security.A multi-component two-antenna transmission method based on 4-WFRFT is pro-posed in this paper,originating from 4-WFRFT multi-component signals.Through the waveform design of 4-WFRFT multi-component signals matched with multiple transmis-sion antennas,the system reliability is improved by the unique mathematical constraint relationship between the multi-component signals.According to different channel sce-narios,the multi-component signal design schemes in this paper include waveform design for 4-WFRFT hybrid carrier multi-component signals and cooperative transmission de-sign for 4-WFRFT time-frequency signal.The former designs two-channel hybrid carrier multi-component signals,using the characteristics of HC and the constraint relationship and compensation among the components to resist channel fading.The latter is to ob-tain a time domain component signal and a frequency domain component signal,relying on the cooperation of different waveforms to adapt to the channel fading scenario,there-by improving the systematic BER performance.The BER performance and computation complexity of the above design schemes are analyzed in this paper.It has been verified that the two schemes are suitable for different channel scenarios and effectively resist channel fading.As a general extension form of 4-WFRFT,the components of multi-fractional Fourier Transform(M-WFRFT(M>4))are with more quantity and complexity.Better conceal-ment of the signal is more applicable for research on systematic physical layer security.Taking advantage of the multi-channel characteristics of M-WFRFT,the self-interference characteristics within the same frequency band is used to improve systematic security performance by designing different multi-component signal schemes to match the anten-na number for transmission under scenarios with different antenna numbers.Since the2~n-WFRFT structure is more suitable for applications in digital communication systems,n=3 is taken as an example to study in this paper.Based on the analysis of the 8-WFRFT signal and its properties,the probability density function of 8-WFRFT signals is derived.In order to match the four-antenna scenario,an 8-WFRFT four-component signal form is designed and the systematic safe capacity distribution under Gauss channel consider-ing path loss is analyzed.The security capacity of the system is related to not only the energy of intercepted branch signals,but the transform order of the transmitter.When the antenna number at the transmitter increases to 8,the corresponding 8-WFRFT eight-component signal design is carried out with the self-interference among components to embed“artificial noise”at the modulation level.The energy of traditional“artificial noise”will not be consumed in that case.Simulation results show that the safety capaci-ty of the proposed scheme is higher than the traditional artificial noise scheme under the Rayleigh channel.3-WFRFT is a special weighted fractional Fourier transform.It cannot be converted with M-WFRFT according to the conventional equivalent relationship of other transform orders.Due to the particularity and the concealment,3-WFRFT signals can be used as a special waveform supplement for M-WFRFT applied in physical layer security.Based on the analysis of the 3-WFRFT signal waveform,the probability density function is derived and simulated in this paper.The security capacity of the 3-WFRFT physical layer com-pared with the artsecurity transmission scheme under Gaussian and Rayleigh channels is studied,which possesses higher security capacificial noise schemes.Due to the unclear relationship of different transform orders,simulation results show that the receiver cannot obtain the correct estimate signal when the transmitter adopts 3-WFRFT and M-WFRFT for signal processing.Therefore,3-WFRFT and M-WFRFT cannot replace each other.The particularity of 3-WFRFT degrades the detection and interception of illegal receivers and enriches the waveform diversity of M-WFRFT in physical layer security applications.