NOMA: Advantages and Disadvantages

This page covers the advantages and disadvantages of NOMA (Non-Orthogonal Multiple Access). It mentions NOMA advantages, benefits, disadvantages, drawbacks, and limitations. It also describes NOMA basics.

What is NOMA or Non-Orthogonal Multiple Access?

Introduction: NOMA is a multiple access technique employed in 5G cellular wireless networks. The main function of NOMA is to serve multiple UEs (User Equipments) using a single 5G-NB (Node B or Base Station). It serves multiple users on the 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. Different power levels are assigned to users. As shown in Figure 1, the Base Station transmits superposed signals to User #1 and User #2. Here, User #2 uses high gain and User #1 uses low gain.

Receive side: NOMA uses SIC (Successive Interference Cancellation) technique to retrieve data of both users. At the receiver, User #2 (Strong User) subtracts the signal of User #1 through SIC and later decodes its own signal. User #1 (Weak User) treats the 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:

• Higher Spectral Efficiency: Due to the use of multiple users on the same frequency resource.
• Massive Connectivity: By serving more users simultaneously at the same time.
• Lower Latency: Due to simultaneous transmission all the time rather than a dedicated scheduled time slot.
• Better QoS (Quality of Service): To all the users using flexible power control algorithms. Helps in increasing cell-edge throughput and better user experience at cell-edges.
• Enhanced Performance with MIMO: The NOMA along with MIMO delivers enhanced performance.

Drawbacks or Disadvantages of NOMA

Following are the disadvantages of NOMA:

• Increased Receiver Complexity: Each of the users within the cluster needs to decode information of all the other users, even the one having worst channel gains. This leads to complexity in the receiver. Moreover, energy consumption is higher.
• Error Propagation with SIC: If an error occurs in a single user due to SIC, the decoding of all the other users’ information will be erroneous. This limits the maximum number of users to be served by each of the clusters of the cell.
• Channel Gain Difference Requirements: In order to achieve the desired functionalities of the power domain concept in NOMA at the receiver, the channel gain difference between users should be adequate. This limits the effective number of user pairs served by clusters.
• Feedback Sensitivity: Each user is required to provide channel gain information back to the Base Station as feedback, and hence NOMA is sensitive to the accuracy of these measurements.