The Anti-single-frequency-interference Technology Research And Realization In HINOC System

This paper is originated from a project named HINOC from National Natural Foundation of China(2009ZX01033-003-001) in Shanghai BWAVE Technology Co.,Ltd. HINOC (High performance Network Over Coax) access technology is a kind of broadband access solutions using CATV coaxial cable to achieve high performance bidirectional information transmission for Three-Networks-Convergence of China. In the HINOC access technology, we use the OFDM transmission mode. Due to the anti-interference characteristics which could be influenced by the adjacent Radio Frequency Interference of the OFDM systems itself or the non ideal characteristic of the RF device itself, in the channel it will be formed with the single frequency interference. The single frequency interference would cause the performance degradation and the HINOC system can’t work normally. And at the present HINOC system there is no any mechanism for single-frequency-Interference resistance. So in the HINOC system, how to weaken or eliminate single-frequency interference, which is related to the performance of the whole system, become one of the most critical issues.This paper analyzed the causes of single-frequency interference and the single-frequency interference modeling. According to the characteristics of single-frequency interference, and combined with its performance in HINOC system, we proposed the single-frequency interference detection scheme based on the threshold decision mechanism on the transform domain. Because of the sub carrier in the single frequency signal power is far greater than the average signal power, we will receive the signal through the fast Fourier transform, then compare the power of all the sub carriers, judge the existence of the single-frequency interference.If it exists, calculats the frequency and strength of the interference.According to the detection information from the single frequency interference detection scheme, we proposed the single-frequency interference suppression scheme based on combining of the time domain and frequency domain information. In time domain use a notch filter for filtering out the single frequency interference and adjust the signal power based on the automatic gain control mechanism; in frequency domain mask the sub carrier signal contaminated by interference. Made the software design and hardware design for the single frequency interference detection scheme based on the threshold decision mechanism on the transform domain and the single frequency interference suppression scheme based on combining of the time domain and frequency domain information.And also designed the corresponding test project.The software simulation and hardware test have been done for the scheme. The results showed that, in the actual HINOC system with single frequency interference of the intensity equivalent to the signal of10dB,when the single frequency interference and one of sub carriers were orthogonal, the performance of the system promoted about12dB; When the single frequency interference and anyone of sub-carrier were nonorthogonal, the performance of the system promoted about8dB. And the performance results of software simulation were even better.The results above show that this scheme we proposed can be very effective for the single frequency interference resistance. This topic will be a good guide to the design and debugging of HINOC system even OFDM system.