Advantages of NOMA | Disadvantages of NOMA | Non-Orthogonal Multiple Access
This page covers advantages and disadvantages of NOMA (Non-Orthogonal Multiple Access). It mentions NOMA advantages or benefits and NOMA disadvantages or drawbacks or limitations. It also describes NOMA basics.
What is NOMA or Non-Orthogonal Multiple Access?
The NOMA is a multiple access technique employed in 5G cellular wireless network. The main function of NOMA is to serve multiple UEs (User Equipments) using single 5G-NB (Node B or Base Station). It serves multiple users on same time/frequency resources.
There are two main techniques employed in NOMA for multiple access.
• Power domain: Here NOMA achieves multiplexing based on different power levels.
• Code domain: Here NOMA achieves multiplexing based on different codes.
Transmit side: NOMA uses superposition coding at the transmitter end. The different power levels have been assigned to users. As shown in the figure-1, Base Station transmits superposed signals to User#1 and User#2. Here User#2 uses high gain and User#1 uses low gain as shown.
Receive side: NOMA uses SIC (Successive interference cancellation) technique to retrieve data of both the users. At receiver, User#2 (Strong User) substracts signal of user#1 through SIC and later decodes its own signal. User#1 (Weak User) treats signal of User#2 as noise and decodes its own signal directly.
Benefits or advantages of NOMA
Following are the benefits or advantages of NOMA:
➨It offers higher spectral efficiency due to use of multiple users on same frequency resource.
➨It offers massive connectivity by serving more uses simultaneously at the same time.
➨It offers lower latency due to simultaneous transmission all the time rather than dedicated scheduled time slot.
➨It offers better QoS (Quality of Service) to all the users using flexible power control algorithms. It helps in increasing cell-edge throughput and better user experience at cell-edges.
➨The NOMA along with MIMO delivers enhanced performance.
Drawbacks or disadvantages of NOMA
Following are the disadvantages of NOMA:
➨Each of the users within the cluster need to decode information of all the other users even one having worst channel gains. This leads to complexity in the receiver. Moreover energy consumption is higher.
➨If error occurs in single user due to SIC, decoding of all the other users information will be erroneous. This limits maximum number of users to be served by each of the clusters of the cell.
➨In order to achieve desired functionalities of power domain concept in NOMA at the receiver, channel gain difference between users should be adequate. This limits effective number of user pairs served by clusters.
➨Each users required to provide channel gain informations back to Base Station as feedback and hence NOMA is sensitive enough to obtain these measurements.