A digital RF transmitter prototype for the future massive MIMO system

In this paper, a novel architecture of a digital RF transmitter for the future massive MIMO system is proposed, which features flexible deployment, low cost, small volume and power efficiency. The comparison with a traditional architecture is also provided. To evaluate the feasibility of the proposed architecture, a prototype of one radio channel is implemented. The prototype consists of a BBU (Base Band Unit) and a RRU (Remote Radio Unit) which are connected by the well developed digital fiber interface, such as SFP (Small Form-Factor Pluggable) optical module and multi-gigabits transceiver in Xilinx FPGA. The core of the BBU is a 4 order BPSDM (Band Pass Sigma-Delta Modulator) which convert the downlink signal of 10MHz symbol rate and 500MHz carrier to a high speed binary 1-bit data stream of 2Gbps. In the RRU, the 500MHz RF signal is retrieved from the 1-bit data stream by bandpass filtering. To extend the RF frequency, the first image signal at 1.5GHz could be exploited. The measurement results show that EVM (Error Vector Magnitude) performance of the 500MHz and 1.5GHz RF output signal is 1.62% and 3.64% respectively.