Research On Line Simulator For G.fast Systems

With the putting forward of “Broadband China” strategy and the rising of “Internet Plus” concept, the internet business is growing faster. However, the traditional copper access technology can only achieve fast access rate up to 100 Mbps, which is unable to meet the increasing bandwidth demands. New DSL technology must be put forward in order to reach the access rate of 1 Gbps. G.fast technology is responsible for this mission. It will bring new impetus to the development of “Broadband China” and “Internet Plus” industry. The signal spectrum has been expanded to 106 MHz. However, the line simulator up to 100 MHz is still not yet studied. This paper aims to develop a line simulator which can simulate the G.fast cable characteristic up to 106 MHz.Based on the transmission line theory, this paper analyzes the insertion loss property, crosstalk property and impedance characteristics of actual cable. Then, based on the existing theoretical models and circuit model, this paper uses the classical RLCG circuit model to simulate the insertion loss property of cable and use the capacitive coupling to simulate the crosstalk between different lines. The size of the coupling capacitor can be used to differentiate intensity of crosstalk. After the adoption of circuit simulation to verify the feasibility of circuit model, this paper designs a 48 lines simulation board. This board consists of insertion loss and crosstalk module, CPU system module, power modules, clock module and line switching module. The insertion loss and crosstalk module completes insertion loss and crosstalk circuit simulation between 48 lines. The CPU system module completes the communication function between simulation board and external module. The power module supplies power for whole board. The clock module supplies clock signal for CPU and network interface debugging PHY chip. The line switching module completes the switching of insertion loss and crosstalk module. The frame structure of the whole system adopts the frame structure of the "back board + interface board + simulation board + master control board". Master control board sends commands to control the the relay of simulation board to play, which achieves the different cable simulation length switching function.This paper achieves the hardware circuit design which can simulate insertion loss property and crosstalk property of 100 meters and 200 meters. This paper verifies the feasibility and accuracy of simulating the cable insertion loss by RLCG circuit and far-end crosstalk by capacitive coupling. The G.fast line simulator can be used for five kinds of line length switching. This line simulator achieves a breakthrough of circuit simulation from 30 MHz to 106 MHz. This line simulator has been adopted by the Equipment Ministry of company for research and development testing.