5G RSMA vs SCMA | difference between RSMA and SCMA in 5G

This page compares 5G RSMA vs SCMA and mentions difference between RSMA and SCMA used in 5G. RSMA stands for Resource Spread Multiple Access and SCMA stands for Sparse Code Multiple Access.

Both are multiple access techniques used in 5G wireless technology. Figure-1 depicts resource allocation of both RSMA and SCMA.


As shown these techniques spread the user signal across time/frequency.

RSMA | Resource Spread Multiple Access

RSMA-Resource Spread Multiple Access

There are two types of RSMA viz. single carrier RSMA and multi carrier RSMA. The figure-2 depicts block diagram of transmitter part of RSMA types.
Refer RSMA basics >> which describes block diagram, advantages and disadvantages of single carrier RSMA and multi carrier RSMA.

SCMA | Sparse Code Multiple Access

SCMA-Sparse Code Multiple Access

SCMA is based on low density signature (LDS) CDMA. It offers low density spreading like LDS CDMA. But it uses multi-dimensional constellations unlike LDS-CDMA.

The figure-3 depicts block diagram of LDS-CDMA and SCMA transmitter part. Here each user has unique codebook which maps each of M codewords to a length N constellation. The length N constellation is extended to length L by insertion of (L-N) zeros. It requires iterative multi-user joint detection technique at the receiver.


The figure-4 depicts SCMA transmit part. As shown, input bits to be transmitted are directly mapped to codewords and are spread over multiple subcarriers. In this technique, codewords are assigned to same UE or different UEs.

It has following functionalities.
• Non-orthogonal: Multiplexes code layers
• Over-Loading: Increases overall rate and connectivity
• Sparsity: Limits receiver complexity for detection
• Spreading: Provides robust link adaptation and coverage
• Multi-dimensional: codewords with shaping gain

Advantages and disadvantages of SCMA

Advantages of SCMA are as follows.
➨When there are less number of users, it allows low complexity iterative message passing multi-user detection.
➨Users occupy the same resource blocks in a low density way
➨Affordable low multi-user joint detection complexity
➨Less collision even for large number of concurrent Users
➨Better coverage due to spreading gain

Disadvantages of SCMA are as follows.
➨It offers high PAPR in comparison to SC RSMA.
➨It requires synchronous multiplexing.
➨It offers lack of scalability/flexibility to the users which need different spreading factors.
➨This technique does not exploit full diversity.

TDMA, FDMA, CDMA related links

Refer difference between TDMA vs FDMA vs CDMA
To know more on FDMA refer satellite tutorial
To know more on TDMA refer GSM tutorial
To know more on CDMA refer CDMA tutorial
For comparison between FDM and TDM multiplexing techniques, READ MORE

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