l w/o Turbo Far User - Turbo Near User - Turbo Far User - Uncoded Near User - Uncoded Eb/No (dB) FIGURE 5.8 BER performance of PD-NOMA w/o turbo under a Rayleigh fading channel. Non-Orthogonal Multiple Access Transmission Transmission Users Messages Users Decoding Messages Encoder FIGURE 5.9 Code-domain NOMA schematic diagram. algorithm (MPA) is a detection mechanism for multi-users used in SCMA decoding. The factor graph matrix includes two critical elements: (d f) which represents the total number of interfering users at a resource, and (dv) which represents the number of resources allotted to each user. With the number of users interfering with resources, the MPA complexity grows exponentially. The JK SCMA model in this research is 64 SCMA, which represents four resources shared by six users. In SCMA, the user's signals are transmitted over the resources. every user has a codebook containing M by K-dimensional constellations. Each code-word x X jm contains d non-zero complex components. The "log, (M)" data bits are mapped in the K-dimensional code-word. The received signal at ith user can be expressed as [21]: (5.6) where, h = is the channel gain vector, Pj is the power of each user signal, is the SCMA code-word of the jth user, Ni is additive white Gaussian noise (AWGN). The SCMA structure in a factor graph matrix shown in Figure 5.10 is our proposed structure with J = 6,K4, and the corresponding matrix indicator F as follows: Users Recourses FIGURE 5.10 SCMA factor graph presentation with K=4,J=6,6 dv = 2 and df = 3. 5G Wireless Communication System in Healthcare Informatics 111000 100110 (5.7) 001011 5.4.2.2 Message Passing Algorithm (MPA) The code book is based on [22]. With the help of the sparsity of code words, the user detection for the system can be performed by MPA [23]. In MPA, resources and users' nodes exchange messages from each other to collect the users' data. A diagram for MPA is shown in Figure 5.11. Below is an explanation of the steps for the SCMA Downlink system: Step 1: Initialization The