# AI Optimization-Based Heterogeneous Approach for Green Next-Generation Communication Systems
## 3 Proposed SDR-Based LTE-LAA Architecture and Its Resource Management Scheme
### Resource Management Problem Formulation  
The resource management scheme for the SDR-based LTE-LAA system has two main targets. The first one is to boost the aggregated throughput of the users, and the second one is to minimize the power consumption of battery-constrained devices. For the users' throughput, the small-cell BSs assign more subcarriers to users to maximize their overall throughput. These subcarriers are selected from both the licensed and unlicensed spectra using LTE-LAA technology. For users to reduce power consumption, they need to be offloaded from the macro BS to their nearest small-cell BSs. However, this offloading process can lead to congestion in some BSs, which may result in traffic delays and a decrease in the data rate. Accordingly, a user association technique needs to be used to avoid this situation. The proposed technique is explained in more detail later in the following subsection. Once the throughput and power consumption figures for the users are calculated using the traffic and energy models, the subsequent step involves associating the users to their optimum small-cell BSs so that the two targets are achieved. This is where the small-cell BS scans the surrounding users and selects the optimum set of nearby users for connecting. This decision will be based on the total throughput the user can have byutilizing the unlicensed spectrum and the total power consumed in this process. This can be expressed as a network utility function as follows:  
\[z=\sum_{i\in I}\sum_{j\in I}(D_{ij}^{eff}+\beta\cdot(1-\frac{P_{ij}}{P_{j_{max}}})) \tag{19}\]  
where \(P_{j_{max}}\) is the user's maximum affordable transmission power, \(P_{ij}\) is the power consumed to connect to the SCBS, and \(D_{ij}^{eff}\) is the users' effective data rate (i.e., throughput). The users' gain is calculated by the first term, and the users' power consumption represents the users' cost and is calculated by the second term. Furthermore, \(\beta\) presents a trade-off coefficient, which is set by the user when choosing the power performance modes in his or her smartphone (i.e., normal, power saving, or ultra power saving modes). Accordingly, \(\beta\) is responsible for adjusting the relation between users' power consumption and their overall throughput. In order to maximize the overall network benefit, taking into consideration both the user throughput and power consumption, we formulate an optimization problem where \(x_{ji}\) is a binary decision variable which takes on the value 1 if a user \(j\) is connected to a BS \(i\) and is 0 otherwise. Hence, the objective function \(z\) expresses the aggregated benefit and is written as follows:  
\[\text{maximize }z=\sum_{i\in I}\sum_{j\in I}(D_{ij}^{eff}+\beta\cdot(1-\frac{P_{ ij}}{P_{j_{max}}})) \tag{20}\]  
subject to  
\[\sum_{i=1}^{I}x_{ij}\leq 1,\qquad\forall j\in\mathcal{J} \tag{21}\]  
\[\sum_{i=1}^{I}D_{ij}^{eff}\geq D_{th},\qquad\forall j\in\mathcal{J} \tag{22}\]  
\[y_{ij}\leq x_{ij},\qquad\forall i\in\mathcal{I} \tag{23}\]  
\[\sum_{j=1}^{I}x_{ij}\leq N_{l}^{i},\qquad\forall i\in\mathcal{I} \tag{24}\]  
\[\frac{\sum_{j=1}^{I}x_{ij}}{N_{u}^{i}}\leq y_{ij},\qquad\forall i\in\mathcal{I} \tag{25}\]  
\[P_{ij}\leq P_{j_{max}},\qquad\forall i\in\mathcal{I} \tag{26}\]  
\[\varphi_{i}\leq\varphi_{i_{max}},\qquad\forall i\in\mathcal{I} \tag{27}\]  
\[x_{ij}\cdot\alpha_{ij}\geq\alpha_{jmin},\qquad\forall j\in\mathcal{J} \tag{28}\]  
\[\text{maximize }z=\sum_{i\in I}\sum_{j\in I}(D_{ij}^{eff}+\beta\cdot(1-\frac{P_{ ij}}{P_{j_{max}}})) \tag{20}\]0  
Here, the following apply:  
* Equation (21) makes sure that each user can be assigned to only one small-cell BS. * Equation (22) indicates that only users who have data demands over a certain threshold are allowed to be offloaded and become connected to another suitable BS to avoid congestion in the network. * Equation (23) makes sure that users cannot be associated with BSs which have only carriers in the unlicensed band.