How to remove degraded RNA fragments from my samll RNA sequencing data

Question

[wang.qiang.prc]

Hi,

It is the first time for me to process the small RNA data. After adapter-trimming, quality-filtering, mapping to the reference genome and removing rRNA and sRNA, I was stuck at the step how to remove degraded RNA fragments. The purpose of this experiment is to find the different expression level of different sRNAs.I want to get high-quality sRNAs to make the normalization. So How can I do next? Thanks