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Control-Data Separation With Decentralized Edge Control in Fog-Assisted Uplink Communications
Kang, Jinkyu,Simeone, Osvaldo,Kang, Joonhyuk,Shamai Shitz, Shlomo IEEE 2018 IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS Vol.17 No.6
<P>Fog-aided network architectures for 5G systems encompass wireless edge nodes, referred to as remote radio systems (RRSs), as well as remote cloud center (RCC) processors, which are connected to the RRSs via a fronthaul access network. RRSs and RCC are operated via network functions virtualization, enabling a flexible split of network functionalities that adapts to network parameters such as fronthaul latency and capacity. This paper focuses on uplink communications and investigates the cloud-edge allocation of two important network functions, namely, the control functionality of rate selection and the data-plane function of decoding. Three functional splits are considered: 1) distributed radio access network, in which both functions are implemented in a decentralized way at the RRSs; 2) cloud RAN, in which instead both functions are carried out centrally at the RCC; and 3) a new functional split, referred to as fog RAN (F-RAN), with separate decentralized edge control and centralized cloud data processing. The model under study consists of a time-varying uplink channel with fixed scheduling and cell association in which the RCC has global but delayed channel state information due to fronthaul latency, while the RRSs have local but more timely CSI. Using the adaptive sum-rate as the performance criterion, it is concluded that the F-RAN architecture can provide significant gains in the presence of user mobility.</P>
Time-Asynchronous Robust Cooperative Transmission for the Downlink of C-RAN
Seok-Hwan Park,Simeone, Osvaldo,Shitz, Shlomo Shamai IEEE Signal Processing Society 2016 IEEE signal processing letters Vol.23 No.10
<P>This letter studies the robust design of downlink precoding for cloud radio access network (C-RAN) in the presence of asynchronism among remote radio heads (RRHs). Specifically, a C-RAN downlink system is considered in which nonideal fronthaul links connecting two RRHs to a baseband unit (BBU) may cause a time offset, as well as a phase offset, between the transmissions of the two RRHs. The offsets are a priori not known to the BBU. With the aim of counteracting the unknown time offset, a robust precoding scheme is considered that is based on the idea of correlating the signal transmitted by one RRH with a number of delayed versions of the signal transmitted by the other RRH. For this transmission strategy, the problem of maximizing the worst-case minimum rate is tackled while satisfying per-RRH transmit power constraints. Numerical results are reported that verify the advantages of the proposed robust scheme as compared to the conventional nonrobust design criteria as well as noncooperative transmission.</P>