Research On New RF Receiver For Distributed 5G System

With the rapid development of mobile Internet,the indoor mobile communication services have taken a dominant position.The indoor wireless coverage performance and service support capabilities will be the priority design goals of 5G systems.As a key component in the indoor distributed base station system,the Radio Remote Unit(RRU)needs to have dynamic multi-beam shaping ability,in order to utilize the spatial dimension,improve the spectrum efficiency and power efficiency,and reduce the interference between users.In this paper,based on the characteristics and requirements of the indoor distributed base station RRU for the next generation mobile communication,a dualchannel indoor RRU RF receiver with low cost and multi-beam shaping function is developed.In an indoor environment,it is more convenient to use cable for distributed networking of RRUs,and the expansion is more flexible.The RRU system designed in this paper uses seven types of network cables(Cat7)with broadband transmission characteristics for data transmission and power supply,and simultaneously transmits data on the network cables through the multiplexer module,with a customized signaling protocol,which is to ensure the normal operation of the system.Multi-beamforming technology is one of the key technologies for future mobile communications.Based on a dual-channel indoor transceiver,this paper designs an eight-element integrated antenna array which supports two signal streams.The two signals are multiplexed with eight transceiver units,and the system has an array gain of 18 dB,which can significantly reduce the transmission power.The active integrated antenna array adopts the RF phase shifting architecture.In this paper,a 360° reflective phase shifter with small size,low cost and high linearity is specially developed as the RF phase shifting unit.In this paper,a RF subsystem consisting of a two-channel RF receiver,an active integrated antenna array and a control circuit is designed.According to the measured results of the conduction and air interface tests,the in-band noise figure of the RF receiver with 3.5 GHz center frequency and 100 MHz bandwidth is less than 5.5 dB.Moreover,the in-band gain flatness is less than 1 dB,the image rejection ratio is greater than 60 dBc,the out-of-band spur suppression is over 60 dBc,and the transceiver switching time is less than 1us.In addition,it achieves a wide dynamic range from-80 dBm to 0 dBm.The EVM of the 64 QAM and 256 QAM modulated signals with the code rate of 50 Mbps and a roll-off factor of 0.25 is 2.18% and 2.11%,respectively.The EVM of the 1024 QAM modulated signals with the code rate of 30 Mbps and a roll-off factor of 0.25 is 1.67%.In addition,based on the measured results of the active integrated antenna array,the single-channel transmit linear power is higher than 20 dBm and the maximum system transmit EIRP is 42 dBm.Moreover,the system receiving gain is about 32 dB.The phase shifting unit has 8 control bits,which can achieve stepping accuracy of 0.45°,and 360° shifting range.The beam-scan results indicate that the active antenna array has wide-beam scanning from-45° to 45° with gain fluctuations less than 2dB and its beam pointing error is less than 1°.The test results show that the RF receiver and the active integrated antenna array have excellent performance and meet the requirements of the system.