At present, high-speed and large-capacity data transmission technologies are mainly divided into wireless, cable and optical cable transmission technologies according to the transmission medium. Among them, the cable transmission features signal differential and channel coding, the advantages are reliability and low cost, and the disadvantage is the short transmission distance.
The advantages of optical fiber transmission are large bandwidth, long distance and large capacity, but the disadvantages are high complexity, high cost and large volume. Wireless transmission (OFDM, MIMO antenna) has the advantages of flexibility and good scalability, but the disadvantage is high delay and high complexity. The application of optical fiber and wireless transmission in multi-beam transmission will be introduced separately below.
Application of Optical Fiber Transmission Technology in Multi-beam
At present, almost all applications of medium and long-distance high-speed transmission of large-capacity data use optical fiber transmission. The main modules of a typical optical fiber transmission system include synchronization modules, framing/de-framing modules, variable speed modules, high-speed serial transceivers, optical modules, and optical fibers.
The multi-channel beam data at the antenna end is synchronized with the local clock through the synchronization module, and then processed in the framing module, such as recombination, checksum, and frame count to form one channel of parallel data, and then the variable-speed module adjusts parameters such as data bit width and clock. Complete the interface adaptation with the high-speed serial transmitter, and then drive the optical module, and transmit it to the optical module of the receiver through the optical fiber; After processing, the multi-beam signal is recovered.
Assume that the data rate of 5 geostationary orbit (GEO) beams is 5×5bit×62.5M, the 12 medium earth orbit (MEO) beams are 12×5bit×62.5MHz, and the 3 inclined geosynchronous orbit (IGSO) beams are 3×5bit×62.5M, which together form a data stream of 100bit×62.5M.
Considering that the internal coding of the high-speed transceiver is mostly 64B/66B or 128B/132B, and the digital frame interface is 64bit, then round to 128bit× 62.5M, after being processed by the variable speed module, a data stream of 64bit × 125M is formed. To meet 95% bandwidth utilization, the high-speed transmitter read clock should be higher than 131MHz. The advantage of using optical fiber to transmit multi-beam data is that the data rate is high and the transmission distance is long;
Application of Wireless Broadband High-speed Transceiver Modulation Technology in Multi-beam Transmission
Wireless transmission can reduce the requirements for wiring, but it is prone to external interference. If the wireless channel is changed to a wired channel, such problems can be avoided. After the wireless channel is changed to a radio frequency cable, the scheme of broadband high-speed wireless transceivers can also be applied to multi-beam data transmission.
The wireless transceiver scheme is very similar to the optical fiber transmission scheme. The main difference is that the optical transceiver is replaced by a wireless transceiver and multiplexer, and the optical fiber is replaced by a radio frequency cable. The interface between the high-speed serial transceiver and the wireless transceiver adopts the JESD204B/C standard, and the maximum rate exceeds 12Gb/s, which can meet the current multi-beam data transmission requirements.
Wireless transceiver chips such as AFE7799, ADRV902x and other models, which integrate IQ modulation, direct up and down conversion, channel correction, channel equalization and pre-emphasis and de-emphasis and other technologies, with the multiplexer can realize large-scale array antenna wired multiple. Input multiple output (MIMO), which can realize multi-beam data transmission on one RF cable, has flexible programmable characteristics, can adjust the frequency point according to the electromagnetic spectrum planning of the system, and improve the EMC and EMI performance of the system.
The function of the wireless transceiver solution is the same as that of the optical fiber solution, but the software and hardware systems are complex, and there are unfavorable factors such as occupying a large area of ??the printed board, which limit its application range.
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