# Joint User-Slice Pairing and Association Framework Based on H-NOMA in RAN Slicing
### Contribution  
Utilizing the recent prosperity of using the matching theory to solve combinatorial optimization problem is proposed for eMBB UEs/uRLLC UEs association and pairing in HetNets in this paper. A scenario where eMBB and URLLC UEs with different requirements can be associated with different BSs and pair with each other is investigated. The main point of this paper can be summed up as follows in Figure 1:  
* Joint user-association and pairing algorithms are considered for eMBB and uRLLC users in HetNets while considering the different association and pairing metrics required for each user type.
* In our system architecture, eMBB users are treated as downlink (DL) data-rate-hungry users and uRLLC users as latency and reliability-constrained users. The user-slice association and pairing processes are expressed as a multi-objective optimization problem to optimize the DL data rate for UEs and reduce the DL transmitted latency for uRLLC UEs whereas considering the users' data rate-dependent QoS requirements and ensuring the intra-isolation for each slice by applying orthogonal frequency multiple access (OFDMA) technology between the similar service's users; meanwhile, the inter-isolation between slices is assigned a DL threshold rate for each slice.
* We suggest a system model in which eMBB traffic is transmitted over long TTIs \(\mathcal{T}\), whereas uRLLC traffic is transmitted over short TTIs \(\delta\) by superimposing the ongoing eMBB transmissions. Here, transmitting the incoming uRLLC traffic in the short TTI guarantees its delay demand. The data rate of eMBB traffic is picked up by Shannon's capacity considering the effect of uRLLC transmissions, while uRLLC depends on the finite block-length capacity model due to its small packet size nature.
* We separate the multi-objective optimization problem into UE-slice association and UE-slice pairing sub-problems. Moreover, we improve a framework based on a one-to-many matching game to find a solution for the UE-slice association sub-problem in which BSs and UEs rate each other based on clear preference measures that define UEs' and BSs' needs. Meanwhile, the UE-slice pairing sub-problem is optimized by a one-to-one matching game in which the associated uRLLC and eMBB UEs with the same BS rank one another through some mini slots. To our knowledge, no matching game has been researched in HetNet to solve the eMBB UEs and uRLLC UEs association and pairing problem.
* We represent utility functions for UEs and BSs that consider the UEs' different demands in terms of attained data rate, DL latency reliability, the threshold rate of each slice, dynamic criteria for limiting the number of attached UEs in HetNet, and the number of paired uRLLC UE with eMBB UEs (i.e., quota matching game), to achieve a reference rate for UEs.
* The joint UE-slice association and UE-slice pairing algorithms are proposed to solve this game. Then, the proposed algorithms are proven to arrive at a stable matching. As well as the computation complexity study for the suggested algorithms is given. Simulation results illustrate that our submitted algorithms outperform the comparable approaches, especially regarding DL latency performance for uRLLC UEs and DL rate performance for eMBB and uRLLC UEs. To illustrate the effectiveness of the proposed algorithms, we also compare their performance with other search schemes.