## 2 Reflective In-Band Full-Duplex with NOMA in beyond 5G
### System Model  
Figure 2 shows the system model for R-IBFD with a D2D cooperative communication for a Downlink (DL) communication system. The proposed system model contains a transmitter (Alice), total \(N\) users (_Bobs_) and a passive Eve. Near user/s ( _Bob\({}_{1}\)_, _Bob\({}_{3}\)_, \(\cdots\)_) and far users (_Bob\({}_{2}\)_, _Bob\({}_{4}\)_, \(\cdots\)_, _Bob\({}_{N}\)_) are considered to have similar channel conditions. Alice, Bobs and Eve contains a single antenna excluding _Bob\({}_{1}\)_. Alice uses \(P_{T}\) as the total transmission power. Power domain NOMA is used for the allocation of power to each users' signal. \(\alpha_{1}\), \(\alpha_{2}\), \(\alpha_{3}\), \(\alpha_{4}\),, \(\alpha_{N}\) where \(\alpha_{1}+\alpha_{2}+\alpha_{3}+\alpha_{4}+\cdots+\alpha_{N}=1\). The power coefficients are allocated with respect to the distances \(d_{1}<d_{3}<d_{2}<d_{4}<\cdots<d_{N}\) and the channel power gain \(g_{4}\approx g_{2}<g_{3}\approx g_{1}\) of each Bob from Alice, statistically and with machine learning. As per consideration, each Bob is facing a Rayleigh fading channel and their CSI are known by [PERSON] and _[PERSON]\({}_{1}\)_. [PERSON] does not have CSI information of the legitimate user/s. The [PERSON]'s channel is considered as worse than two near users conditions; therefore, [PERSON] is unable to detect their signals. \(g_{4}\approx g_{2}<g_{e}<g_{3}<g_{1}\). [PERSON] is capable of detecting the signal of _[PERSON]\({}_{2}\)_ and _[PERSON]\({}_{4}\)_. The other channels included in the transmission are \(g_{12}\) and \(g_{11}\) are the channels for the R-IBFD communication in the IBFD mode, from _[PERSON]\({}_{1}\)_ to _[PERSON]\({}_{2}\)_ and the SI channel from _[PERSON]\({}_{1}\)_ to itself. [PERSON] modulates road 1, [PERSON] signal on the real component, and road 2, Bobs' signal on the quadrature component of the 16-QAM modulation constellation. This is because real and quadrature components do not interfere with each other, therefore Bobs' signals of road 1 do not interfere with Bobs' signals of road 2. It assists in reducing interference as compared to NOMA signals. Figure 2: The system model with an Alice, four Bobs and an Eve. Each Bob is modulated differently following the proposed algorithm, for the reduced NOMA interference. _Bob\({}_{1}\)_ shows the IBFD nature and assists _[PERSON]\({}_{3}\)_ with an R-IBFD transmission. The given system involves self and co-channel interference. \(Bob_{1}\) and \(Bob_{4}\) on road 1 are modulated on the real component and the remaining Bobs of road 2, \(Bob_{2}\) and \(Bob_{3}\), are modulated on the quadrature components of the modulation. Therefore, both Bobs of road 1 face the co-channel interference with each other only, as shown in Figure 2. Ideally, there is no interference between the Bobs of different roads. This is to avoid the interference between two high power signals (far users \(Bob_{2}\) and \(Bob_{4}\)) with each other. Therefore, far users ideally do not interfere with each other, rather faces minor interference due to very low power signal, which can be considered as noise. According to the system model, the near IBFD mode user \(Bob_{1}\) receives high power signals of far users therefore it can assist far user \(Bob_{2}\) with R-IBFD. To decode its signal, \(Bob_{1}\) performs SIC by decoding \(Bob_{4}\)'s signal and removing the combined AN \(A_{1}\) of \([PERSON]_{2}\) and \(Bob_{4}\), then subtracting it from the total received signal. \([PERSON]_{1}\) decodes its own signal from the total received signal and adds AN \(A_{2}\), null space of \(g_{12}\), forward the signal of \([PERSON]_{2}\) and \([PERSON]_{3}\), using R-IBFD, like a reflector, to assist \([PERSON]_{2}\). \(Bob_{3}\) cannot decode the signal received from \([PERSON]_{1}\) due to the addition of \(A_{2}\) which is a null space of \([PERSON]_{2}\)'s channel. For forwarding the signal, \([PERSON]_{1}\) uses the power \(P_{c}\).