LTE/LTE-A Signal Compression on the CPRI Interface

C-RAN (Centralized, Cooperative, Cloud Radio Access Network) is a next-generation wireless access network architecture based on Centralized processing, Collaborative Radio, and Real-time Cloud Infrastructure. In this architecture, different access technologies (GSM / TD-SCDMA /WCDMA / LTE) can be supported on the same hardware platform in a baseband pool system, which can largely reduce system costs. LTE (Long Term Evolution) and LTE-A (Long Term Evolution - Advanced), which are based on Orthogonal Frequency Division Multiplexing (OFDM) and Multiple-Input Multiple-Out-put (MIMO) technologies, are regarded as the main wireless access technologies in the evolution from 3G to 4G. A variety of novel technologies have been introduced in LTE/LTE-A to improve the system performance especially in C-RAN architecture, such as Multi-antenna MIMO, Carrier Aggregation (CA), and Coordinated Multi-point (CoMP). However, one of the technical challenges for C-RAN architecture is the fiber bandwidth required for data transmission between RRU (remote radio unit) and BBU (baseband unit). To solve this problem, a low-latency baseband signal compression algorithm is proposed to reduce the fiber data rate. Based on the characteristics of LTE signal data, redundancy in the spectral domain is removed. Next, block scaling, together with linear or nonlinear (non-uniform) quantizer, are designed to minimize quantization error. This algorithm effectively reduces the amount of data transmitted between BBU and RRU, and facilitates the deployment of LTE in the C-RAN architecture. The algorithm has been verified by simulation and demo system lab test. It is observed that the proposed algorithm yields good system performance under 1/2 compression rate and 1/3 compression rate in a practical propagation environment.