Investigations Of The RRU Transmitter For New-generation Mobile Communicationon

With the rapid development of mobile communication technology and the explosive growth of communication services,the base station of the next-generation communication system is facing the increasingly challenges to the higher performance and the faster data rate.The distributed base station Radio Remote Unit(RRU)is one of the vital units in these base stations.In order to achieve huge capacity and spectrum efficiency,the perfect multi-beam dynamic shaping function is needed in the RRU of the next generation mobile communication system.According to the requirements and characteristics of indoor distributed RRU,the thesis presents the development of a low-cost and high-performance dual-channel indoor RRU RF transmitter with 3.5 GHz.In the complex indoor environment,it is very economical and convenient to use the existing network cable for the layout of distributed RRUs.Therefore,the category 7 with high shielding is used to connect multiple RRUs to a center data processing unit.A set of custom signaling protocols and multiplexers are developed to simultaneously transmit baseband signals,clocks,control signals,etc.on the network cable.The RF transmitter adopts the single superheterodyne architecture to effectively suppress the image frequency and carrier leakage.The influence of the frequency response unevenness caused by the transmission medium is reduced with the equalized IF APC circuit.As one of the key technologies of the next generation mobile communication system,the multi-beamforming technology can not only effectively improve the spectrum efficiency,expand the data capacity of the communication system,but also reduce the system power consumption and the multi-user interference.A dual-channel transceiver is developed,each channel consists of an eight-element phased array.The two channels share 16 phase shifting cells by changing the phase of the signal of each cell,the electromagnetic waves are coherently superimposed on the mobile receiving end,achieving an array gain of 18 dB.Very high phase precision is achieved through the combination of digital phase shifter and reflective phase-shift analog phase shifter.Thus,more accurate mobile user tracking and positioning is achieved in wider beam range.The RF subsystem including transmitters,phased arrays and the power control circuit,is developed and tested according to system requirements.The subsystem operates in the 3.5 GHz band with a channel bandwidth of 100 MHz.There is no obvious outband spur.When the two transmitter channels operate in the maximum linear output power(20dBm),the image rejection is 64.113 dBc,61.827 dBc,and the carrier suppression is 58.702 dBc,58.647 dBc,and the ACPR is-45.3dBc,-45.2dBc;the in-band gain ripple is less than 1.5dB;the QAM16 EVM is 1.79%,1.51%,and QAM64 modulated EVM is 1.65%,1.77% respectively.In addition,the phased array is tested by indicators.When the single-channel linear power is 20 dBm,the maximum EIRP is 43 dBm.The phase shifter has a valid bit number of 10 bits,and the phase shift range of 360°,so the beam pointing step accuracy is 0.11°.The test results show that the RRU system has good performance,and the dual-channel transmitter and the eight-element phased array meet the system specifications.