  The future wireless network, such as Centralized Radio Access Network
(C-RAN), will need to deliver data rate about 100 to 1000 times the current 4G
technology. For C-RAN based network architecture, there is a pressing need for
tremendous enhancement of the effective data rate of the Common Public Radio
Interface (CPRI). Compression of CPRI data is one of the potential
enhancements. In this paper, we introduce a vector quantization based
compression algorithm for CPRI links, utilizing Lloyd algorithm. Methods to
vectorize the I/Q samples and enhanced initialization of Lloyd algorithm for
codebook training are investigated for improved performance. Multi-stage vector
quantization and unequally protected multi-group quantization are considered to
reduce codebook search complexity and codebook size. Simulation results show
that our solution can achieve compression of 4 times for uplink and 4.5 times
for downlink, within 2% Error Vector Magnitude (EVM) distortion. Remarkably,
vector quantization codebook proves to be quite robust against data modulation
mismatch, fading, signal-to-noise ratio (SNR) and Doppler spread.
