# AI Optimization-Based Heterogeneous Approach for Green Next-Generation Communication Systems
## 3 Proposed SDR-Based LTE-LAA Architecture and Its Resource Management Scheme
### Network Model  
The architecture of our SDR-based LTE-LAA system is illustrated in Figure 2. The system consists of macro base stations (MBSs), multiple SDR-based small-cell BSs, a control server, and end users. We represent the user set as \(\mathcal{J}=\{I_{1},I_{2},I_{3},\ldots,I_{N}\}\), indexed by \(j\), and represent the BS set as \(\mathcal{I}=\{I_{1},I_{2},I_{3},\ldots,I_{M}\}\), indexed by \(i\). Small cell BSs are assumed to support the LTE-LAA technique, where a BS uses the carrier aggregation concept and combines LTE carriers from both the unlicensed and licensed spectra [10]. Furthermore, these SDR-based BSs are distributed in consonance with a spatial Poisson point process (PPP) at a density of \(\varepsilon_{0}\) around the MBSs, where \(\varepsilon_{0}\) represents the median number of small-cell BSs per unit area [46; 47]. Thus, this system model presents a two-tier heterogeneous network where MBS are overlaid with multiple SDR-based small-cell BSs. In our system model, the MBS covers several SCBS and various users. Owing to the temporal and spatial dynamics of the mobility of users, some SCBSs are underutilized, and others are fully loaded with their native users. Hence, the underutilized SCBSs can offer, for a fee, their unused bands to the cognitive, radio-enabled users of the MBSs, accessed via the cognitive radio technique. Using SDR, the cognitive radio technique allows the device to scan various licensed bands to detect a free band or spectrum and send it to the control server. Once complete, the control server controls the user's association to the optimum base station for a fee. It is worth highlighting that in such a paradigm, if the primary user (i.e., operator customer) becomes available, then secondary users (i.e., not the operator customer) will be requested by the control server to leave the band. Accordingly, this is a win-win situation, where an underutilized BS which belongs to any operator can be utilized to earn more profit by serving secondary users from different operators for a fee. The SDR-based small-cell BSs scan the spectral environment continuously to find and generate two lists. Firstly, there is \(\mathcal{L}_{1}\), which is a list of unused or idle bands in both the licensed and unlicensed spectra in their coverage areas. This list is used as a base to establish the carrier aggregation for the LTE-LAA technique. Secondly, there is \(\mathcal{L}_{2}\), which is a list of the nearby macro-connected users and their utilized channel frequencies. This list represents the potential users to be offloaded to the SDR-based small-cell BSs. As illustrated in Figure 2, a control server is deployed and connected to all BSs in the area, including the macro BSs. This control server receives periodic updates from the BSs. These updates include \(\mathcal{L}_{1}\), \(\mathcal{L}_{2}\), the BSs' loads, radio element utilization, power consumption, and interference levels. These updates help the server to develop a comprehensive overview of the traffic load and its distribution all over the coverage area and to develop an interference map for this coverage area. The control server, which now has the knowledge of all the BS states in the entire coverage area, can easily recognize the best user allocation which maximizes the total throughput, minimizes the overall power consumption, and balances the load between BSs. Accordingly, it generates \(\mathcal{L}_{3}\), which contains the optimum user-BS association list along with the number of user-allocated carriers and notifies the SDR-based BSs to act accordingly. Using \(\mathcal{L}_{3}\) and the SDR capabilities, the BSs adjust their transmission parameters to perform carrier aggregation and provide LTE-LAA technology to the surrounding users. This aggregation provides users with faster data rates and a more responsive experience.