# A Comparative Analysis of Wi-Fi Offloading and Cooperation in Small-Cell Network
## 4 Comparison between Cooperation and Wi-Fi Offloading in Small-Cell Network
### Offloading in Co-Located Wi-Fi-Small-Cell BS
Constraint (16b) is the QoS constraint with \(R_{j}^{th}\) as the minimum data rate requirement of each UE \(j\). It ensures that the achievable data rate of each UE over both LTE and LTE-U links is above a threshold \(R_{j}^{th}\). Constraint (16c) is the user association on LTE and it ensures that a UE can be offloaded onto single SBS. Constraint (16d) is for user association on LTE-U. It also dictates that a UE can be at most associated with single Wi-Fi AP if it is present in its transmission range. Lastly, Constraint (16e) ensures that the maximum power constraint of each SBS is not violated. Similar to cooperative scenario, Wi-Fi offloading is also a MINLP and is hard to solve in polynomial time. As illustrated in (15), our objective function is a joint resource allocation problem with controlling variables \(y_{ij}^{k}\), \(z_{ij}\), \(P_{ij}^{k}\) and \(R_{ij}^{U}\). \(R_{ij}^{U}\) is continuous variable, it can take any value in between 0 and maximum leftover capacity, \(P_{ij}^{k}\) is also continuous variable and it can take any value between 0 and \(P_{max}\) whereas \(x_{ij}^{k}\) and \(z_{ij}\) are the binary variables. Constraints are also non-convex along with the objective function [33]. As this problem is also NP hard, we propose a heuristic to solve this problem also. Sequential Offloading Rate Enhancement (SORE) Algorithm for Small-Cell Network  
A SORE algorithm is proposed to solve the joint problem of SBS association and RB allocation, power allocation and leftover Wi-Fi rate allocation. Similar to SCRE, SORE is also centralized algorithm and is assumed to be aware of the channel state information for the each SBS \(i\) to UE \(j\). The problem is a joint problem of RB allocation, user-SBS association, power allocation and leftover Wi-Fi rate allocation. These four allocation variables are combined and then solved in a sequence to maximize the sum rate of the network. In this case, the preference is given to the resources of the SBS that a user becomes associated with on LTE band. In case the user's data rate is not satisfied, then Wi-Fi offloading is performed to satisfy the partial data rate requirement of the user (decision based on the presence of UE within Wi-Fi range). Algorithm 2 shows the steps of the centralized SORE algorithm. First, all the UEs are associate to a single SBS with which it has the best channel gain similar to SCRE and then RBs are assigned as represented in line 4. A significant proportion of the total power of each SBS \(\tilde{i}\) is then divided uniformly between associated UEs in line 5. The data rate requirement of each user is calculated and verified according to (8). Secondly, distance priority matrix \(I_{j}\) is made for all the UEs in which SBSs with minimum distance with user \(j\) are placed in ascending order as illustrated in line 7. Data rate of UEs in the network is required to be satisfied according to constraint (16b). If the value is below than rate threshold value, then it needs to provide more resources (RBs, Wi-Fi Offloading or more power) as mentioned in line 10. First, it lies on the first-priority SBS \(\tilde{i}\) for more resources. All the licensed resources must be exhausted before Wi-Fi offloading is done. Next it checks SBS for UE \(j\) from distance priority matrix, if UE lies within Wi-Fi range of that SBS and this SBS also has non-zero leftover capacity then it provides percentage of leftover rate depending on data rate requirement of UE \(j\). The remaining leftover capacity is reserved for other UEs that lie within its Wi-Fi range. One last way to enhance data rate is to provide more power from already associated SBS \(\tilde{i}\). After meeting all these requirements, the user data rate is adjusted and the central node is required to allocate power to the new RBs from the available power of the associated SBS, and it then again calculates the rate iteratively according to (11). Lastly, it will update number of RBs used, leftover capacity and the available power to each SBS. Each UE satisfies its QoS until all the resources are used.