Compression method to remove unnecessary MSBs of IQ data frames in C-RAN

Abstract

Smart phones are growing rapidly with the support of Over the Top (OTT) service and multimedia streaming service as well as existing Internet service. In the conventional Distributed-RAN (D-RAN) structure, a Base Band Unit (BBU) and a Remote Radio Head (RRH) are configured at one cell site. However, C-RAN, which is a new RAN structure, is composed of separated base stations in which BBU and RRH are separated. RRH is left in cell sites where radio signals are transmitted and received, and BBUs are collected and managed in different places. When the bandwidth of the LTE signal is 20 MHz and the 2 × 2 Multiple Input Multiple Output (MIMO) antenna is used, the CPRI requires 2.5 Gbps transmission. Since there is a limit to handle mobile traffic that is continuously increasing with the current transmission rate, several techniques for compressing IQ data before transmission have been proposed. In this paper, we apply the compression technique to remove unnecessary parts in the Most Significant Byte (MSB) of a basic frame after applying the existing Up/Down sampling and Non-linear Quantization. We measured the error vector magnitude (EVM) to measure the compression rate and the quality of the signal after compression to confirm the compression performance. Also, it was confirmed whether the experimental results satisfied the compression requirement of Open Radio Interface (ORI).