Data Compression in Base Transceiver Systems

Base transceiver systems transfer large amounts of sampled baseband signals over serial data links between base station processors and RF modules. To comply with evolving wireless communication standards, greater data rates on these serial links are needed. However, increasing the actual bit rate on the links or increasing the number of physical links is in conflict with the existing base transceiver constraints including power consumption, geographical characteristics, and cost. Furthermore, the above-mentioned link has become of a great importance recently with the emerge of distributed antenna systems and cooperative base station settings. This paper explores the compression of baseband signal samples prior to transfer over the serial data link between a base station processor and RF unit. We study and experiment lossy and lossless compression of baseband signals and analyze the cost and gain of each approach. Sample quantizing is proposed as a lossy compression scheme and it is shown to be effective by experiments. With QPSK modulation, sample quantizing achieves a compression ratio of 4 and 3 in downlink and uplink respectively. The corresponding compression ratios are 2.3 and 2 for 16-QAM modulation. Well-known lossless compression algorithms including arithmetic coding, Elias-gamma coding, and unused significant bit removal (USBR), and a recently proposed baseband signal compression scheme are analyzed and applied to real baseband signal samples. Our simulations and over the air experiments suggest that compression of baseband signal samples is a feasible and promising solution for increasing data rates on links between base station processors and antennas without enforcing much complexity and cost to base stations.