Research On Technology Of Self-interference Cancellation And High-frequency Effect Vector Quantization For Wireless Access Network

As an indispensable part of the communication system,the wireless access network has become one of the hot fields of mobile communication.In recent years,focusing on the goal of improving the spectrum efficiency,digitized radio over Fiber(DRo F)technology in the mobile fronthaul network,and the self-interference cancellation(SIC)technology in Co-frequency Co-time Full Duplex(CCFD)wireless communication has received widespread attention.On the one hand,although the DRo F system that transmits digital signals can improve the inherent shortcomings of non-linearity and chromatic dispersion in the transmission of analog signals on optical links directly,it will cause the amount of information generated by analog-to-digital conversion to increase dramatically.As the number of quantized bits increases exponentially,the spectrum utilization rate is greatly reduced.On the other hand,the CCFD system can theoretically double the existing wireless spectrum resources.However,this scheme of transmitting and receiving simultaneously in the same frequency band may cause the receiver to not work properly.This is because the receiving antenna may receive strong self-interference signals leaked from the transmitting antenna.The problem of work requires the use of SIC technology to eliminate strong self-interference signals in order to work normally and achieve efficient use of spectrum.In response to the above-mentioned problems,the main work of this article is as follows:In the first step,a multipath optical self-interference cancellation(M-OSIC)technology used in CCFD wireless communication is studied,which the technology was verified by simulation and experiment.The simulation verifies that the multipath self-interference signal of the OFDM signal with a center frequency of 28 GHz can be completely eliminated.Experimental results show that the proposed M-OSIC system can completely eliminate multipath self-interference signals with a center frequency of 8,10 GHz,and the elimination depth is greater than 40 d B.In the second step,a joint vector quantization based on two-dimensional discrete cosine transform(DCT-VQ)is proposed and verified.Aiming at the problem of low spectrum utilization of DRo F,this article starts with the quantization coding module at the transmitter,and uses two-dimensional DCT technology to preprocess the orthogonal frequency division multiplexing(OFDM)sampled signal.In this way,the information is concentrated in the head of signal to be transmitted.By discarding the nearly zero value at the end of the transmission process,the transmission rate can be increased,thereby improving the system’s spectrum efficiency.The experiment verified the 20 km 5 GBaud/λ PAM-4 IM/DD system transmission based on the proposed scheme applied in the digital mobile fronthaul link.Experimental results show that compared with the traditional k-means quantizer,when the error vector magnitude(EVM)value is the same,the proposed system has a lower compression ratio and higher frequency efficiency.At the same time,thanks to the cropping of transform coefficients whose tails are close to zero,the data set sent to the quantizer is smaller when the quantization bits is the same.Therefore,the quantization time is also significantly reduced.