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Due to the deluge of data driven largely by smartphones and tablets, it is urgent to put into agenda the upgrade of the current 3G/4G wireless networks to a future 5G network with a thousand times increase of throughput. One promising candidate solution to fulfill the above throughput requirement is cloud radio access network (C-RAN), which was initially proposed by China Mobile.
As shown in the figure, unlike the base stations (BSs) in conventional cellular networks which encode/decode users’ messages locally, the relay-like remote radio heads (RRHs) in C-RAN are connected to a central unit (CU) via high-speed fronthaul links, e.g., fiber, and thus can serve mobile users cooperatively under the coordination of CU.
Despite the centralized processing architecture, the practically achievable throughput of C-RAN is significantly constrained by the fronthaul links between the CU and RRHs. According to China Mobile's recent report, the fronthaul traffic generated from a single user signal of MHz bandwidth could be easily scaled up to multiple Gbps. In practice, a commercial fiber link with tens of Gbps capacity could thus be easily overwhelmed even under moderate mobile traffic.
I have been working on practical fronthaul compression/quantization techniques, e.g., uniform scalar quantization, to improve the end-to-end performance of C-RAN. We hope that our research can lead to efficient design of C-RAN in the forthcoming era of 5G.
Publications:
- L. Liu, and R. Zhang, “Optimized uplink transmission in multi-antenna C-RAN with spatial compression and forward,” IEEE Trans. Signal Process., vol. 63, no. 19, pp. 5083-5095, Oct. 2015.
- L. Liu, S. Bi, and R. Zhang, “Joint power control and fronthaul rate allocation for throughput maximization in OFDMA-based cloud radio access network,” IEEE Trans. Commun., vol. 63, no. 11, pp. 4097-4110, Nov. 2015.
- L. Liu, and R. Zhang, “Downlink SINR balancing in C-RAN under limited fronthaul capacity,” in Proc. IEEE International Conference on Acoustics, Speech, and Signal Processing (ICASSP), Shanghai, China, 2016.
- L. Liu, P. Patil, and W. Yu, “An uplink-downlink duality for cloud radio access network,” in Proc. IEEE International Symposium on Information Theory (ISIT), Barcelona, Spain, 2016.
- L. Liu, and W. Yu, “Joint sparse beamforming and network coding for downlink multi-hop cloud radio access networks,” in Proc. IEEE Global Communications Conference (Globecom), Washington D.C., America, 2016.
- L. Liu, and W. Yu, “Cross-layer design for downlink multi-hop cloud radio access networks with network coding,” IEEE Trans. Signal Process., vol. 65, no. 7, pp. 1728-1740, Apr. 2017.
- L. Liu, P. Patil, and W. Yu, "Channel diagonalization for cloud radio access," IEEE Wireless Commun. Lett., vol. 7, no. 4, pp. 622-625, Aug. 2018.
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