Firstly, direct decoding for the x1 signal, then the concept of the SIC is applied as:
(7)
Now, direct decoding for the near user signal x2.
The SINR for decoding far user’s signal at near user is given by:
(8)
Hence the achievable rate(bps/Hz) will be:
(9)
After the far user's signal has been cancelled, the near user's SINR for decoding its own signal is:
(10)
The corresponding achievable rate(bps/Hz) is given as:
(11)
The three types of NOMA schemes that are now being employed in the broad spectrum are PD-
NOMA, waveform domain NOMA, and CD-NOMA, according to the survey and resources that are
currently accessible. The focus of most NOMA research is PD-NOMA, which necessitates a
substantial power differential between the signals allocated to various users. At the transmitter’s side
of a PD-NOMA system, superposition coding (SC) is used to create the signals of numerous users on
each subcarrier, which are dispersed over several users (In SC, although sharing the same time-
frequency-code resources, each user has their own power level. Each user's power level is determined
by the channel gain value; those with lower channel gain values receive greater power levels, and vice
versa. At the receiver side, the SIC approach is used to filter out extra user signals that interfere with
that band.
In terms of spectrum efficiency, NOMA's SIC method outperforms OMA. Between users 1 and 2, the
power is split. The power distribution to users has a considerable impact on the throughput of users in
the NOMA domain. The fairness of the users' Power allocation largely determines throughput.
3. FADING CHANNELS
During wireless propagation, fading refers to the degradation of the transmitted signal power caused
by a variety of factors. These variables include geographic location, time, radio frequency, and
atmospheric conditions like rainfall and lightning. There are different types of fading channels and
they are Rayleigh, Rician, Nakagami, Weibull fading channel, etc.
In this paper two fading channels Rayleigh and Nakagami are considered. Only NLOS components
between the transmitter and receiver are modelled in the Rayleigh. It is assumed that there is an
absence of Line-Of-Sight route between the transmitter and receiver. When multipath scattering occurs
with relatively high delay time spans and various groups of reflected waves, Nakagami fading takes
place. Table 1 shows a comparative study of Rayleigh and Nakagami fading channels taking few key
parameters into consideration.
y′
2
=h2Pα1x1+h2Pα2x2+w2−h2Pα1^
x1
1,2=
α1P h2
α
P h
2+σ2
1,2 =log21+
α1P h2
α2P h2
2+σ2
2=
α2P h2
2=log21+
α2P h2
σ2
https://doi.org/10.17993/3ctic.2022.112.183-193
3C TIC. Cuadernos de desarrollo aplicados a las TIC. ISSN: 2254-6529
Ed. 41 Vol. 11 N.º 2 August - December 2022
187