Research On The Key Technology Of Physical Layer With Gigabit Rate Coaxial Access

The access rate of China’s cable TV only has hundreds of megabits per second, and the highest spectrum utilization is only 7bps/Hz. It is difficult to meet the demand of millions of users. Therefore, how to improve the access rate of coaxial cables and the spectrum utilization is the primary problem. The article discusses the problems from the two aspects of the design of physical layer and researches on the key algorithms, and carries out the simulation of the physical layer system.First of all, this paper designs the reasonable scheme of the physical layer, including the division of time slots, the design of the pilot time slot, and the design of the conventional time slot. At the same time, this paper uses OFDM system and high-order QAM modulation, which can reach 4096 QAM. It effectively improves the spectrum utilization and the access rate of coaxial cables. The 128 M bandwith is the point where the access rate can reach 1126 Mbps and the spectrum utilization can reach 8.8bps/Hz.Secondly, this paper discusses some key algorithms, including the time and frequency synchronization, phase noise cancellation, channel estimation and so on. Time and frequency synchronization algorithm firstly uses the training sequence in the time domain to finish the coarse synchronization. Then the algorithm proposes a joint estimation algorithm to estimate the residual carrier frequency offset and the sampling frequency offset. Finally, the algorithm compensates the phase rotation caused by frequency offset and uses the resampling filter to correct the sampling frequency offset. When the signal-to-noise ratio is-2dB, the probability of detection can reach above 99%, and the false alarm probability maintains 510? When the signal-to-noise ratio is 32 dB, the normalized mean square error of the frequency estimation can go down 310? after smoothing. Channel estimation uses the the least square algorithm and the iterative algorithm When the signal-to-noise ratio is higher than 25 dB, the normalized mean square error of channel estimation can achieved 410? after smoothing. Phase noise cancellation algorithm can eliminate the fixed phase rotation and the inter-carrier interference, it has made some research results.Finally, this paper carries out the simulation of the physical layer with float data. When b0 E N reaches 29.5dB, the bit error rate reaches 710?. After scaling the float data, the simulation of the physical layer with fixed data losses 1 dB when the system reaches the same bit error rate.We must improve the physical layer transmission rate and spectrum utilization in order to satisfy the demands of millions of users. MIMO and OFDM will be combined and higher order modulation will be taken the next step. At that time, the expected access rate will reach 10 Gbps, and the spectrum utilization will reach 12bps/Hz in the future.