## 1 Introduction  
Exponential and phenomenal are the most suitable words to describe the increase in user traffic and smart devices in recent years. Such a situation, especially with the introduction of fifth-generation (5G) communication and beyond, has amplified the challenges of meeting high data rate demands and enhanced network coverage, without violating the bandwidth limitations. According to a survey conducted by CISCO, global mobile data traffic will increase nearly thirteenthd by 2022 [1]. This increment, together with the promises being made by 5G and beyond, shows that efficient bandwidth utilization only will not be enough, leading to comprehensive network restructuring and enhancement requirements. To cope with such issues, one way is to enhance the network heterogeneity by increasing the deployment of base stations (BSs) with different coverage areas, powers, and deployment costs (small-cells). In recent works, it has indeed been shown multiple times that heterogeneous networks (HetNets) can deliver more bandwidth-efficient communication by deploying low-power BSs called small-cells, i.e., mainly picocells and femtocells, commonly underlaid over a macrocell [2; 3; 4]. The concept of small-cells first emerged because of low coverage areas in cellular networks, e.g., basement parking, cell-edge areas, and elevators. Later, small-cells became popular because of their benefits of network traffic offloading and efficient spectrum utilization, especially when deployed in a co-channel environment in a multi-tier cellular network. Where there are advantages of co-channel deployment, at the same time, the main drawback is co-tier and cross-tier interference among multi-tier cells, generally referred to as inter-cell interference (ICI). Furthermore, as aforementioned, 5G and beyond requires increased deployment of small-cells, so dealing with ICI will become more complex and challenging, especially when small-cells are user-owned and mobile. One way to deal with this issue is to provide small-cell access to the interference, creating macrocell users (MUs). Currently, there are three access mechanisms for small-cells, i.e., open, closed, and hybrid-access [4]. The access mechanisms that allow MUs to handover to a small-cell are open and hybrid-access, wherein hybrid-access MUs have limited access to the small-cell. The hybrid-access mechanism is mainly for user-owned small-cells, where resource sharing is used for allowed access to the MUs in a way that they do not affect the quality of small-cell owners referred to as small-cell users (SUs). When it comes to resource sharing, recently, power domain non-orthogonal multiple access (NOMA) is being investigated in HetNets for its benefits [5]. Using NOMA for hybrid-access results in reduced cross-tier interference by letting interfering MUs connect to small-cell base stations (SBSs). This is achieved by forming NOMA pairs between SUs and MUs over the same channel, which leads to another benefit, i.e., very little compromise on SU resources. Some MUs, which may not be able to connect to the SBS using NOMA, can still cause ICI; for such cases, an efficient interference suppression technique is required. A number of interference suppression techniques have been investigated in recent years to handle ICI in HetNets, but very few require limited or no backhaul communication. In this work, we propose a joint strategy for the hybrid-access small-cells to cater to all the issues and scenarios discussed. The joint strategy is presented using the Walsh-Hadamard transform (WHT) with NOMA and the interference rejection combining (IRC) technique, to achieve high performance gains and suppress ICI. The use of WHT improves NOMA performance in terms of user throughput and reduced bit error rate (BER), whereas IRC manages the interference produced by MUs (cross-tier interference) who are denied access to SBS using NOMA. Interference rejection combining is generally used to efficiently combat ICI produced by the neighboring cells [6].