5G RSMA Explained: Advantages and Disadvantages

This article explains the basics of 5G RSMA (Resource Spread Multiple Access), its different types, advantages (pros), and disadvantages (cons). We’ll also touch on links related to LTE and other wireless standards.

Introduction to 5G RSMA

5G technology employs various multiple access techniques. Among them are CP-OFDM/OFDMA for downlink, SC-FDM/SC-FDMA for uplink, and RSMA specifically for the Internet of Things (IoT). RSMA is particularly useful in scenarios that require asynchronous and grantless access.

RSMA Basics and Types

Here’s a breakdown of RSMA’s core functions:

• RSMA spreads the signal across allocated time and/or frequency resources.
• It uses lower rate channel coding, resulting in low spectral efficiency as a trade-off for robustness.
• Signals from different users can be recovered simultaneously, even with mutual interference present.

RSMA’s robustness stems from:

• The coding gain provides Eb/No efficiency compared to orthogonal spreading or simple repetition.
• It can utilize more powerful codes than simple repetition methods, often combined with low-rate convolutional codes.

The two primary types of RSMA are:

• Single Carrier RSMA
• Multi-carrier RSMA (or OFDM-based RSMA)

Let’s delve into the differences between single-carrier RSMA and multi-carrier (OFDM-based) RSMA.

Single Carrier RSMA

Figure 1: Single Carrier RSMA

Figure 1 illustrates single-carrier RSMA. The transmitter includes a coder, interleaver, spreader/scrambler, and a cyclic prefix (CP) addition module. On the receiver side, you’ll find CP removal, despreader, deinterleaver, and a decoder.

Single-carrier RSMA is known for its better power amplifier (PA) efficiency. Furthermore, it eliminates the need for strict synchronization.

Multi Carrier RSMA | OFDM based RSMA

Figure 2: Multi Carrier RSMA, OFDM RSMA

Figure 2 depicts multi-carrier RSMA. The transmitter contains a coder, interleaver, spreader, serial-to-parallel (S/P) converter, IFFT, parallel-to-serial (P/S) converter, and a CP addition module.

The receiver includes CP removal, S/P, FFT, P/S, despreader, deinterleaver, and decoder modules.

Multi-carrier RSMA, leveraging OFDM, exploits wider bandwidths to achieve low latency. This makes it suitable for power-constrained applications such as M2M and IoT.

RSMA Advantages

• Single Carrier RSMA Advantages:

  • Allows asynchronous multiplexing
  • Grantless transmission with minimal signaling overhead
  • Link budget gain

• OFDM based RSMA Advantages:

  • Grantless transmission with minimal signaling overhead

RSMA Disadvantages

• Single Carrier RSMA Disadvantages:

  • Not suitable for higher spectral efficiency.

• OFDM based RSMA Disadvantages:

  • Requires synchronous multiplexing.