NOMA is a multiple access technique that enables multiple users to access the network simultaneously using the power domain. It allocates more power to cell-edge users and less power to near users. At the receiver side, near users perform SIC to decode and remove far users' signals before detecting their own signals. This allows NOMA to enhance reception capacity and throughput compared to the orthogonal multiple access schemes used in previous generations. NOMA is a promising technique for 5G networks to support massive connectivity.

1. NOMA –
NOMA
Non Orthogonal Multiple Access

2. Multiple Access Techniques -
• 1G – ?
• 2G – ?
• 3G – ?
• 4G – ?
• 5G – ?

3. Introduction -
• With the exponential growth in mobile broadband traffic attention has been
put on the development of different access technologies in order to enable the
anytime anywhere connectivity and satisfy the users’ increasing demands.
• These multiple access schemes are a key feature of the mobile wireless
communications systems that enable different users to gain access to the
network simultaneously.
• Therefore, researchers have been focusing on the design of the multiple access
schemes.

4. Introduction -
• Starting with the frequency division multiple access (FDMA) scheme, which was
used in 1G technology and is based on the analog frequency modulation.

5. Introduction -
• Whereas the 2G systems employed with time division multiple access scheme
(TDMA) to enable multiple access.
• TDMA makes use of time multiplexing and is based on the digital modulation.

6. Introduction -
• However, starting with the 3G systems a new multiple access scheme was
employed, such as code division multiple access (CDMA).
• CDMA makes use of the orthogonality of a spreading sequence to enable the access
of an increased number of users to the cellular system.

7. Introduction -
• Because of the existing problems on spectrum resources scarcity, the new 4G
systems introduced the use of orthogonal frequency division multiple access
(OFDMA).
• OFDMA is based on orthogonal frequency division multiplexing (OFDM) and makes
use of many orthogonal closed spaced carriers improving the spectral efficiency and
enabling an increased number of users connections.

8. Multiple Access Techniques -
• 1G – FDMA
• 2G – TDMA
• 3G – CDMA
• 4G – OFDM
• 5G – NOMA

9. OMA -
Advantages of OFDMA –
1. Intercell interference is eliminated by ensuring orthogonality between
subcarriers.
2. Compatibility with MIMO systems by employing the fast Fourier transform.
3. Interference within the cell is avoided by using a cyclic prefix.
4. The transmission power could be adjusted based on the users’ bit rates.
5. Frequency diversity is achieved by spreading the carriers across the available
spectrum.
6. Robust against inter symbol interference (ISI) and multipath distortion.

10. OMA -
Disadvantages of OFDMA –
1. The peak-to-average rower ratio (PAPR) is relatively high due to parallel
transmission of modulated symbols.
2. The limited spectral efficiency due to the cyclic prefix.
3. Highly sensitive to frequency offsets and phase noise.
4. Proper synchronization between transmitter and receiver is a must for better
performance.

11. What is NOMA -
• NOMA is defined as an intercell multiuser multiplexing scheme that proposes the use of an
additional domain, that is, the power domain, which has not been utilized in the previous
2G, 3G, and even 4G wireless systems.
• At the transmitter side, the user’s data is multiplexed on the power domain, which means
less power allocated for the user equipment (UE) located near the base station (BS) and
more power allocation for far (cell-edge) users.
• NOMA supports simultaneous connections, which is suitable to address the challenges
related to massive user connectivity.

12. What is NOMA -
• User multiplexing on NOMA is performed without relying on the knowledge of the
transmitter of the instantaneous channel state information (CSI) of each user.
• Successive interference cancellation (SIC) is employed at near users, which also has a good
enough channel to decode the far users’ data first and cancel out the interference.
• Studies have shown that NOMA enhances the reception, capacity, and cell-edge user (CEU)
throughput performance.
• Moreover, NOMA uses superposition coding (SC) for downlink transmission, where all the
users’ data is combined together and then transmitted.

13. OMA vs NOMA -

14. Features of NOMA -
1. NOMA introduces controllable interferences to realize overloading at the cost of a slightly
increased receiver complexity, which results in higher spectral efficiency and massive
connectivity.
2. The power domain is used for modulation processing and user multiplexing in NOMA.
3. NOMA increases the system capacity and coverage and supports mass user connectivity.
4. NOMA promises robust performance in practical wide-area deployments despite mobility
or CSI feedback latency.
5. NOMA retains the advantages of OFDMA and filter bank multicarrier (FBMC), because
basic carrier waveforms in NOMA can still be generalized from OFDMA or FBMC.
6. NOMA necessitates a careful design to schedule the right partners to share the same
resource block for performance optimization.

15. NOMA System Model -

16. NOMA System Model -
Downlink Transmission -

17. NOMA System Model -
Uplink Transmission -