# A Mobility Management Using Follow-Me Cloud-Cloudlet in Fog-Computing-Based RANs for Smart Cities
## 3 Preliminaries
### System Architecture  
The fog-computing-based RAN system architecture evolution from cloud-radio access network (C-RAN) [1; 2; 3] is shown in Figure 1. To overcome the disadvantages of C-RANs with the fronthaul constraints, the user and control planes are decoupled in such networks and the high power nodes (HPNs) are mainly used to provide seamless coverage and execute the functions of the control plane, while remote radio heads (RRHs) are deployed to provide high-speed data rate for packet traffic transmission in the user plane. The fronthaul portion of a C-RAN telecommunications architecture comprising the intermediate links between the centralized radio controllers and remote radio heads (RRHs) at the edge of a cellular network [1]. One main difference between C-RANs and F-RANs is that the centralized control function is shifted from the BBU pool in C-RANs to the HPN in F-RANs [2]. To incorporate fog computing in edge devices, the traditional RRH is evolved to the fog-computing-based access point (F-AP) by being equipped with a certain caching, CRSP, and CRRM capabilities [2]. The main difference between C-RANs and F-RANs is that the centralized control function is shifted from the BBU pool in C-RANs to the HPN in F-RANs [2]. As shown in Figure 2a, the system architecture for our proposed follow-me cloud-cloudlet is modified from the system architecture of mobility using follow-me cloud approach from [PERSON] et al. 's work in [24], and its simplified architecture is given in Figure 2b. Consequently, our system architecture also contains the follow-me cloud controller (FMCC), decision making application module (DMAM), mapping information gateway (MIGW), inter domain mobility database (IDMD), and local mobility anchor (LMA) [24]. The service migration of follow-me cloud approach [24] is also provided and reviewed as follows. When an UE switches to a different region, FMCC then decides to initiate a service migration from the current serving data center to the new serving data center, and also initiate a handover procedure and re-calculate the shortest route from the new serving data center gateway (DCG) to the next LMA of the new serving F-AP. In our follow-me cloud-cloudlet approach, FMCC also pre-sends some packets to the cache of the new serving F-AP to reduce the total data transmission time. Figure 1: System architecture. In the paper, we propose a new mobility management using the follow-me cloud-cloudlet (FMCL) approach for the smart city. This main purpose of FMCL approach is to reduce the total transmission time and the packet loss rate, under a \(UE\) handover to a different area. The network architecture of the fog-computing-based RANs (or called as F-RANs) contains that there is a cloud set \(C=\{c_{1},c_{2},\cdots,c_{s},\cdots,c_{d},\cdots,c_{n}\}\), where \(c_{s}\) is the \(s\)-th serving data center or the \(s\)-th serving cloud, and cloudlet set \(L=\{l_{1},l_{2},\cdots,l_{s},\cdots,l_{d},\cdots,l_{n}\}\), where \(l_{s}\) is the \(s\)-th serving cloudlet, then a cloud-cloudlet (\(CL\)) set is defined as \(CL=\{c_{1}\to l_{1},c_{2}\to l_{2},\cdots,c_{s}\to l_{d},\cdots,c_{d}\to l_{s}, \cdots,c_{n}\to l_{n},\}\). In general, we assumed that an \(UE\) in the area with \(l_{s}\) moves to a different area with \(l_{d}\). Let \(c_{s}\to l_{d}\) represent as the packet transmission from cloud \(c_{s}\) to cloudlet \(l_{d}\) during our mobility management using the cooperation transmission of cloud-cloudlet. When the \(UE\) moves from a previous area with \(l_{s}\) to a different area with \(l_{d}\), the current serving \(c_{s}\) is performed the service migration operation to the new serving \(c_{d}\). The MAG of \(l_{d}\) sends out a proxy binding update (PBU), \(PBU\_message(UE\_id,prefix_{d},LMA_{d},TIM)\), to the inter domain mobility database (IDMD), where TIM (Traffic Information Message) is utilized to keep the receiving packet status of all packet transmissions during the handover procedure. The IDMD then creates an entry in its Binding Cache Entry (BCE) table.