A Novel Efficient Wireless Fronthaul (EWF) Method for the Common Public Radio Interface (CPRI) Signal Transmission

Unlike the classical common public radio interface (CPRI) where the in-phase and quadrature (I/Q) waveforms and the control words (CWs) are transmitted as a binary sequence, the proposed scheme transmits the I/Q waveforms and the quadrature amplitude modulation (QAM) signals that contain the CWs via time domain multiplexing (TDM) synchronously for the first time. A new adaptive equalization scheme is proposed for the time domain multiplexing (TDM)-EWF method to mitigate the impact of the multi-path effect. The bandwidth of the proposed TDM-EWF method is reduced by 47% compared with the digital CPRI compression method in the literature. We experimentally demonstrate the TDM-EWF transmission of one 20 MHz LTE signal with a CPRI equivalent data rate of 1.228 Gbps as a proof of concept. The test error vector magnitude (EVM) of the orthogonal frequency division multiplexing (OFDM)-64QAM LTE signals is below 1.6% from −51dBm to −39dBm received power and the CWs are recovered without error. The joint test results of the proposed EWF system and the baseband unit (BBU)/ remote radio unit (RRU) are reported for the first time in the paper. The EVM performance loss of the OFDM-64QAM LTE signals of the proposed method is less than 1% compared with the case where the BBU and RRU are connected by the fiber. The test results show that the proposed TDM-EWF method can efficiently transmit the CPRI signals without affecting the end to end LTE traffic.