A novel feed-forward segmented digital automatic gain control algorithm for long-term evolution digital radio-over-fibre systems

This study describes a novel feed-forward segmented digital automatic gain control (FSD-AGC) algorithm for long term evolution (LTE) digital radio-over-fibre (DRoF) systems. It experimentally demonstrates the algorithm using a DRoF platform based on real-time field programmable gate arrays. The FSD-AGC algorithm is able to update power status accurately with a short delay (about 100 samples) and adjust the gain precisely by only one step. It can make full use of analogue-to-digital converter quantisation bits width without oversaturation and maintain a stable peak-to-average ratio to reduce the overall cost and energy consumption of digital links and to minimise the deterioration of error vector magnitude (EVM) in LTE systems. Compared with conventional solutions, the proposed algorithm shows significant improvement in the dynamic range (a 20 dB improvement is demonstrated experimentally) of 4G-LTE radio frequency signals in a DRoF system. This is a major step forward for the future commercialisation of DRoF systems for 4G and 5G network deployments. Meanwhile, FSD-AGC can be applied in both LTE time division duplexing and frequency division duplexing signals. Experimental results have shown a mean EVM of the DRoF system below 4.5%, which is well below the 8% required by 3rd generation partnership project.