Design And Implementation Of 3Gbps Satellite Adaptive Transmission System Transmitter

Because of wide range of communication coverage,large capacity and many other advantages,satellite communication is essential to information construction of country.For example,high-throughput communication satellite can achieve communication rate of up to tens of gigabits per second or more,which meets the needs of aviation,high-speed rail and remote areas.In order to achieve high throughput of satellite communication system,we need adaptive transmission technology,which can match channel state change.The traditional Adaptive Modulation and Coding(AMC)technology relies on channel estimation and cannot smooth the adjustment rate,and is not suitable for long delay satellite communication.In this paper,based on Random Projection Code(RPC)and Hybrid Automatic Repeat reQuest(HARQ)technology,an adaptive transmission system transmitter for satellite communication is designed,which can realize the transmission rate of 3Gbps.At first,we analyse the characteristics of satellite communication and propose the scheme of adaptive transmission based on RPC and HARQ.The design principle and the function of each module of transmitter are analyzed emphatically.Then,the paper designs an adaptive transmission control protocol.In order to reduce the overhead of the frame and increase the utilization rate of the channel,we propose the large packet as the downlink transmission unit.We also give the definition of the packet composition and the packet head field and introduce adaptive transmission realization process.Group frame is introduced for the sake of decreasing the number of instructions in transmitter,which can reduce the number of instructions to the original 1/G.Simulation results show that the system throughput decreases only 3% under G equals to 2,4,6,8.Finally,the scheme of high-speed encoding circuit is proposed.In order to achieve the target of 3Gbps,coding circuit encodes 4 frames at the same time.In the channel coding circuit,each frame takes 8 CRC and BCH parallel coding based on the recursive principle and 64 LDPC parallel differential coding using parity check matrix double diagonal characteristics.Test shows that the coding circuit can achieve 3.8Gbps throughput running at 230 MHz.Using the coding matrix sparse quasi-cycle characteristics,we design 4-way RPC encoding circuit based on the two-level lookup table that are matrix lookup table and code result table.Test shows that the coding circuit can achieve 1.6Gsps throughput running at 180 MHz.Taking full account of the satellite communication scene and characteristics,the proposed 3Gbps adaptive transmission system transmitter can achieve high system throughput,which meets the needs of large-capacity broadband satellite communication.