# A Comparative Analysis of Wi-Fi Offloading and Cooperation in Small-Cell Network
## 2 Related Work
### Cooperative Small Cells  
BS cooperation is being considered for 5G and beyond 5G (B5G) for efficient coverage and high throughput. For B5G, cell-free system is being proposed where a group of base stations cooperatively serve the users without creating autonomous cells while intelligently identifying the user's communication environments [11; 12; 13; 14]. Base station cooperation technologies are also critical for providing reliable cell-edge service in the millimeter wave bands, even for high mobility scenarios. In [15], SBS cooperation is implemented with digital beamforming in millimeter wave band.  
For 5G/B5G systems data are cooperatively transmitted by multiple License-assisted access (LAA) SBSs through the unlicensed spectrum [16]. To improve the access to unlicensed spectrum, a coordinated access to the unlicensed spectrum is proposed using learning-assisted clustering of densely deployed SBSs. The CSI of LAA users in unlicensed band is fed back to the control plane of the (5G/B5G) system, and data are cooperatively transmitted by multiple LAA SBSs. [PERSON] et al. [17] analyzed small-cell base station (SBS) cooperation for software-defined hetnets using different metrics including connectivity probability, load balancing and energy efficiency. [PERSON] et al. [18] proposed a joint transmission coordinated multipoint (JT-CoMP) technique that addresses the time synchronization issue. As described earlier, CoMP is a form of SBS cooperation, and it is being actively explored for implementation in 5G/B5G systems. [PERSON] et al. [12] analyze coordinated beamforming/scheduling scheme for massive MIMO small-cell network and their analysis shows 2-4.5 times higher average sum-rate compared to non-cooperative massive MIMO network. This signifies SBS cooperation for future systems that are likely to have massive MIMO-based SBS.  
In [19], by controlling user association, resource and power allocation, the authors aim to maximize the sum rate while also considering intercell interference coordination. In [20], the authors solve non-convex sum-rate maximization problem while considering limited backhaul capacity of small-cell BSs. In [20], the authors solve maximization problem related to the proportional fairness of cooperative multi cell network. The author of [21] optimizes association of user for load balancing by using CoMP techniques in cellular networks. A joint user association with JP-CoMP scheme for proportional fairness maximization among users of a network within a small-cell cluster using hybrid self-organizing network (SON) is proposed in [22]. It is argued that the proposed scheme is effective (in terms of reducing the intercell interference) in handling the load balancing of the network. In [23], a mathematical framework for a user-centric small-cell network is proposed. The authors argue that Poisson Point Process is not a rigorous model when cooperation of small cells is involved. They also compute an optimal number of small cells for each user that maximizes the energy efficiency.  
The cooperative small-cell concept has also been explored for enhancing caching in small-cell networks. The authors in [24] propose a high-performance architecture for fast content delivery using femto caching along with femto BS cooperation. If a user requests certain video file that is cached, then the femto BSs with the file cached will cooperate to transmit the information to the user. An energy efficient caching for a cooperative small cell is proposed in [25]. A file placement strategy is investigated such that the cooperation can enhance the overall energy efficiency of the network.