# PS-CARA: Context-Aware Resource Allocation Scheme for Mobile Public Safety Networks
## 3 System Model
Similarly, scenario (b) is the uplink interference at the MBS uplink communication from the neighbor small cell user. Moreover, in scenario (c) there is an uplink interference from the neighbor mPC user to the mPC base station. Furthermore, we also have an uplink interference from mPC user to MBS in scenario (d). Finally, in scenario (e) there is an uplink interference from the neighbor device-to-device (D2D) user to the MBS. From the mentioned scenarios, we only focus on scenario (c) and (d) where we have UL interference from mPUE \(\to\)\(m\)-th BS and from MUE \(\to\)\(k\)-th mPCs for backhaul, sidehaul, and access links. The major difference among the conventional small cells and mPC interference is the rapidly changing environment which in turn needs context-aware resource allocation schemes to counter this interference. Figure 2: Illustration of various kinds of inter-cell interference after mPC deployment in a HetNet. In the literature, numerous user association schemes are discussed. For instance, in [32] authors proposed the user association and power allocation scheme for mmWave networks. This scheme jointly considers load balancing, energy efficiency, QoS requirements, and energy harvesting constraints to model this problem. However, unfortunately, this scheme cannot be adopted for the public safety prioritized mobile scenario because they ignored the mobility and the PS user prioritization. Therefore, in this paper, we modeled the user-association problem as the public safety priority-based user association [14] that can be represented as  
\[\psi_{u,j}=\arg\max_{k\in\{1,2,\ldots,K\}}\delta_{u,j}L_{u,j}^{\min}, \tag{1}\]  
where \(L_{u,j}^{\min}\) is the minimum pathloss of user \(u\) from BS \(j\), and that BS can be either macro BS (MBS) or mPC and \(\delta_{u,j}\in\{0,1\}\) is the priority indicator. Since all users \(u\in\mathcal{U}\) are randomly distributed in the coverage area of MBS. Hence, there is a possibility that some users would exist at the cell edge, which in turn will cause high co-channel interference. Thus, to reduce interference, _fractional power control_ (fpc) [33] is implemented for public safety (PS) and non-PS users transmissions, where user transmit power \(P_{u}^{\text{tx}}\) can be calculated as  
\[P_{u}^{\text{fpc}}(dB)=\min\{P^{\text{max}},P_{0}+\alpha L\}, \tag{2}\]  
where \(P_{0}=P_{0}^{\text{cell}}+P_{0}^{\text{UE}}\) is the signal-to-interference-plus-noise-ratio (SINR) target control parameter, with \(P_{0}^{\text{cell}}\) and \(P_{0}^{\text{UE}}\) being the cell-specific and user specific parameters, respectively. These values can be selected within the specified ranges as \(P_{0}^{\text{cell}}=[-126,24]\) dBm and \(P_{0}^{\text{UE}}=[-8,7]\) dB. In addition, \(\alpha\in[0,1]\) is the path loss compensation factor, which is selected as \(\alpha=0.7\) from the interval because it provides good coverage and better signal-to-interference-and-noise-ratio (SINR). The UL received signal from the \(u\)-th transmitting (tx) user (mPUE/MUE) to \(k\)/\(m\)-th receiving (rx) BS (mPC/MBS) is written as  
\[y_{u\to k}^{\text{rx}}(j,r)=h_{u\to k}(j,r)\sqrt{P_{u\to k}^{\text{tx}}(j,r)}x_{u \to k}+\sum_{u=2,u\
eq 1}^{U}\] \[h_{u}(j,r)\sqrt{P_{u}^{\text{rx}}(j,r)}x_{u}(j,r)+n_{u}. \tag{3}\]  
In (3), \(x_{u\to k}\) is the transmitted data, \(h_{u\to k}(j,r)\) is the channel gain between the u-th tx user and the \(k\)-th rx user during the \(j\)-th subframe and on the \(r\)-th RB. Furthermore, \(P_{u\to k}^{\text{tx}}(j,r)\) is the transmitted power of the \(u\)-th user to \(k\)-th BS, whereas \(h_{u}(j,r)\) is the channel gain of the \(U-1\) interfering users, and \(n_{u}\) is the additive white Gaussian noise (AWGN) at the receiver with variance \(\sigma^{2}\) for the u-th user. Similarly, (3) can be adopted to model the SH and BH received signals.