# PS-CARA: Context-Aware Resource Allocation Scheme for Mobile Public Safety Networks
## 3 System Model  
We consider a two-tier HetNet UL scenario with underlayed mPC cellular network. A two-tier HetNet consists of a macrocell base stations (MBS) set \(\mathcal{M}\) with \(\mathcal{M}=\{1,...,M\}\), a set of \(\mathcal{K}=\{1,...,K\}\) mPCs that are randomly deployed in the coverage of each MBS, and a set of users \(\mathcal{U}=\{1,...,U\}\) with \(N\) and \(L\) are number of users attached per MBS and mPC, respectively. To clearly understand the system model, we plotted a single cell scenario with one BS and \(\mathcal{K}\) mPC are deployed in its coverage area in Figure 1. We consider the SDN enabled architecture where control and data planes are partitioned to easily and centrally manage the public safety scenario. In SDN based core network architecture, the control plane (CP) functions are moved to an application layer, where we have core network components for control purposes such as packet data network gateway (P-GW), serving gateway (S-GW), mobility management entity (MME), policy and charging function (PCC), and context-aware radio resource management (CA-RRM). The functions of each component are briefly explained as: \begin{table}
\begin{tabular}{c l} \hline \hline
**Symbol** & **Definition** \\ \hline \(\mathcal{M}\) & Set of macrocell base stations \\ \(\mathcal{K}\) & Set of mobile personal cell base stations \\ \(\mathcal{U}\) & Set of users involved in communication \\ \(\text{pr}_{m}^{u}\) & \(m\)-th macro base station transmit power \\ \(\text{pr}_{k}^{u}\) & \(k\)-th mobile personal cell transmit power \\ B & Bandwidth \\ \(R\) & Resource blocks \\ \(\psi_{u,j}\) & User association indicator for user \(u\) associated with \(j\)-th base station \\ \(L\), \(F\), \(S\) & Pathloss, fading, shadowing, respectively \\ \(P_{o}\) & Signal-to-noise-ratio (SINR) target control parameter \\ \(\alpha\) & Pathloss compensation factor \\ \(\eta\) & Mobile personal cell spectrum access ratio \\ \(\delta\) & Priority indicator \\ \(\rho\) & Load distribution \\ \(\psi\) & Call blocking probability \\ \(\gamma\) & SINR \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Table of symbols for PS-CARA scheme. P-GW: it is mainly responsible for users' IP address allocation, QoS provisioning, and charging based on the PCC rules. S-GW: the S-GW passes the IP packets of all users. The other functions of S-GW are to terminate the interface towards E-UTRAN, perform handovers among eNB, and to care about mobility interface to other networks. MME: it is the control node for LTE radio access. Some of the key responsibilities include user tracking, bearer activation and deactivation, P-GW and S-GW selection. PCC: the PCC consists of functions such as policy and charging rules function (PCRF), policy and charging enforcement function (PCEF), and online/offline charging system (OCS). The major functions of PCC include network control regarding service data flow detection, QoS control, and flow-based charging. Similarly, for user plane (UP) the functionality of the S-GW, P-GW is the same but will deal only with data and control will be managed centrally. The sidehaul links are considered to communicate among the mPC while backhaul link is to establish the link among the BS and mPC as shown in Figure 1.  
In this scenario, macro BS \(m\) transmits with a maximum power \(P_{m}^{\text{tx}}\), the mPC BS \(k\) transmits with maximum power of \(P_{k}^{\text{tx}}\), and the users \(u\) transmits with maximum power of \(P_{u}^{\text{tx}}\). We assume that each user \(u\) can associate with maximum one BS at a time. The total bandwidth (BW), \(B\), is divided into \(R\) resource blocks (RBs) in the frequency domain. Since, there can be different types of small cells in the 5G systems, so the possible interference situations after deploying mPC in HetNet is shown in Figure 2. There are five different uplink interference scenarios in a HetNet, as shown in Figure 2(a-e). From Figure 2, scenario (a) depicts the uplink interference at the small cell base station from the neighbor small cell users reusing the same frequency band.