NOMA vs OFDMA: Key Differences in 5G Wireless

This page compares NOMA vs OFDMA and mentions the difference between NOMA and OFDMA used in 5G Wireless technology.

NOMA stands for Non-Orthogonal Multiple Access, and OFDMA stands for Orthogonal Frequency Division Multiple Access.

Introduction

Both NOMA and OFDMA are multiple access techniques. NOMA utilizes power domain or code domain, whereas OFDMA utilizes frequency/time resources to serve multiple users (i.e., UEs) in a cell by 5G-NB.

NOMA | Non-Orthogonal Multiple Access

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 have been 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 from 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.

OFDMA | Orthogonal Frequency Division Multiple Access

• In the OFDMA technique, the BS (Base Station) shares its resources by transmitting to UEs at different time instants and frequencies.
• OFDMA allocates subchannels and time slots to the users based on desired bandwidth or data rate. Each of the subchannels are mapped with a few number of subcarriers after permutations, and hence OFDMA is robust against fading.
• Technologies such as Mobile WiMAX, LTE, LTE-advanced, and 5G use OFDMA technique for resource sharing.

The following table summarizes the difference between NOMA and OFDMA.