Fifth Generation (5G) Cloud-Radio Access Networks (C-RANs) are about to exploit both optical and Millimeter Wave (mmWave) technology to meet the ever-increasing traffic demands. In this new type of converged Fiber-Wireless (FiWi) systems efficient Medium Transparent-Medium Access Control (MT-MAC) protocols should be designed, able to satisfy the very strict 5G service requirements. To this end, in this paper, we propose an MT-MAC protocol for mmWave Analog Radio-over-Fiber (A-RoF) C-RANs, which employs gated service, according to which users are granted transmission windows equal to the number of bytes contained in their buffer. An analytical model is also proposed for the mean packet delay, which is verified by means of simulation for different fiber length values, network load conditions and optical capacity values. Our results not only prove the accuracy of the proposed model but also the suitability of the proposed MT-MAC protocol to meet the sub-ms delay challenge of latency-critical 5G network requirements. Index Terms-5G, Centralized-radio access network (C-RAN), delay analysis, fiber-wireless (FiWi), fronthaul, millimeter wave (mmWave), passive optical network (PON), radio-over-fiber (RoF).

A. Mesodiakaki 1[0000−0001−9309−0524] , P. Maniotis 1 , G.Abstract. Next generation, i.e., fifth generation (5G), networks will leverage both fiber and wireless (FiWi) technology to meet the challenging 5G traffic demands. Moreover, a Cloud-Radio Access Network (C-RAN) architecture will be mainly adopted, which places the BaseBand Units (BBUs) at centralized locations, thus offering cost-efficient energy supply and climate control. To this end, efficient Medium Transparent-Medium Access Control (MT-MAC) protocols are needed to ensure the optimal exploitation of both media. In this paper, we propose a gated service MT-MAC protocol (gMT-MAC) for Millimeter Wave (mmWave) Analog Radio-over-Fiber (A-RoF) C-RANs. GMT-MAC grants a transmission window to each user equal to the time needed for its requested traffic to be successfully sent. A mean packet delay model is also proposed and verified by means of simulation. The performance of gMT-MAC is evaluated for different network load conditions, number of Remote Radio Heads (RRHs) and optical availability values. The provided results prove the suitability of gMT-MAC to meet the sub-ms delay requirements of latency-critical 5G services.Keywords: Fifth Generation (5G) networks · mean packet delay model · fiber-wireless (FiWi) · millimeter wave (mmWave) · cloud-radio access networks (C-RANs) · analog radio-over-fiber (A-RoF) · medium transparent-MAC (MT-MAC).