# Clustering Approach for Reliable Wireless Communication
###### Abstract  
Multiple access techniques for 5G systems are based on principles related to security, efficiency, and performance increase. Multi-user shared access (MUSA) is included in code-domain non-orthogonal multiple access (CD-NOMA) techniques with multiple benefits including multiple-access interference minimization and system capacity increase. The additional benefits of MUSA include its grant-free nature, which makes it applicable to scenarios involving random access channels, minimal latency communications, etc. Depending on the high-frequency diversity of the fading-affected channels, this technique is also used to lessen their effects. This paper illustrates the concept of code correlation used in MUSA by proposing a method to allocate MUSA codes to active users in an uplink data transmission system based on clusters. This clustering approach (grouping of 3 GPP TR 38.812 spreading codewords) enables performance improvement in different system configurations by implementing various scenarios and providing reliable results. It is demonstrated that four-length spreading code selection from 3 GPP family codes is a satisfactory solution, and this cluster grouping can be designed in a less overloaded multi-user system. The challenges, advantages, and limitations of the proposed method are outlined throughout the study. M +
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higher capacity systems due to its limitations in resource allocation and user pairing, which lead to error propagation in successive interference cancellation (SIC) [18; 19; 20]. Code-domain NOMA aims to multiplex several users using non-orthogonal unique sequences with low correlation properties [19]. Under this category, interleave division multiple access (IDMA) [21; 22], low-density spreading CDMA (LDS-CDMA) [23; 24], low-density spreading orthogonal frequency-division multiplexing (LDS-OFDM) [25], sparse code multiple access (SCMA) [26], and MUSA [27; 28; 29; 30; 31; 32; 33; 34; 35] demonstrated efficient performance in multiple transmission scenarios. Compared to the classic CDMA technique, IDMA provides better efficiency because multiple access interference (MAI) is used at the interleaving block level and there is a higher throughput [36]. The performance of a multi-carrier IDMA (MC-IDMA) system relies on its capacity in terms of user numbers and relays, making this technique unsuitable for a MIMO system [37]. Better results can be obtained using the LDS-CDMA technique [38], and practical implementations demonstrate that using transmission on multiple carrier frequencies makes LDS-OFDM a dependable candidate for wideband communication [39; 40]. Lately, the MUSA technique was highly implemented to avoid or minimize interference in the system (also with a role in the reliable detection and reception of user data) through various SIC techniques. In [28], short MUSA low-correlated codes were designed starting from the real and imaginary sets of values [0, 1, 1 + j, \(-\)1 + j, \(-\)1 - j, \(-\)1 - j]. Using an SIC receiver, their approach enables grant-free access and increases traffic load. Thus, in our paper, we implemented small-length low-correlated MUSA codes to observe the system's behavior. The authors in [41; 42] state that MUSA manages to ensure massive connectivity among multiple users in 5G systems by providing users with access to Internet of Things (IoT). In [41], it is stated that a MUSA pattern can make use of quantized elements within the spreading sequences, which are elements achieved from typical digital modulations like quadrature amplitude modulation (QAM) and quadrature phase shift keying (QPSK). Since researchers at ZTE and Nokia have successfully used this technique, we considered implementing it in our experimental study.