What is SCMA: Sparse Code Multiple Access

SCMA, Sparse Code Multiple Access, is a multiple access scheme that enables OFDMA to be combined with a CDMA code to enable more access to individual carriers within and OFDM signal.

SCMA Tutorial Includes

Sparse code multiple access, SCMA is a non-orthogonal multiple-access technique being developed for possible use with 5G and other advanced communications systems.

The aim is that SCMA, Sparse Code Multiple Access will improve spectral efficiency of wireless radio access.

In many respects, SCMA can be considered as a combination of CDMA, Code Division Multiple Access and OFDMA, Orthogonal Frequency Division Multiple Access.

Sparse Code Multiple Access, SCMA basics

With SCMA, different incoming data streams to be transmitted are directly mapped to code-words of different multi-dimensional cookbooks, where each code-word represents a spread transmission layer. This is effectively how the CDMA works

In this way the multiple data streams can share the same time-frequency resources of OFDMA signal.

The sparsity of code-words makes the near-optimal detection feasible through the iterative use of a Message Passing Algorithm, MPA.

In SCMA, coded bits are directly mapped to multi-dimensional sparse code-words selected from layer-specific SCMA codebooks.

SCMA enables overloading of the number of devices used. This occurs when the number of overlaid layers exceeds the code-word length. However the low complexity of multi-layer detection enables excessive code-word overloading.

As a result of the optimization of the overloading factor along with modulation-coding levels of layers, the system provides a more flexible and efficient link-adaptation mechanism.

Additionally, the signal spreading feature of SCMA can improve link-adaptation as a result of less coloured interference.

The complexity of detection of SCMA is controlled by two main factors:

  • The sparseness level of SCMA code-words.
  • The use of multidimensional constellations with a low number of projection points per dimension.

SCMA advantages

Sparse code multiple access, SCMA is a multiple access that promises some significant advantages. It is able to support large levels of connectivity, it provides reduced transmission latency and it is also able to provide energy saving.

By Ian Poole

. . . . | Next >>

Share this page

Want more like this? Register for our newsletter

Measuring up to the NB-IoT revolution Dr. Stamatis Georgoulis | Cobham Wireless
Measuring up to the NB-IoT revolution
There is a rapidly growing demand for making connections to all kinds of devices as the Internet of Things (IoT) starts to become a reality. Well over 10 different standards are already being proposed for these low-power machine-type communications (MTC) applications.
Online - Effective Vector Network Analyzer Measurements
How to make effective VNA measurements at RF and microwave frequencies

More training courses

Bringing the Internet of Things to Life
Silicon Labs looks at the fact that industry experts predict that the number of connected devices for the Internet of Things (IoT) will surpass 15 billion nodes by 2015 and reach over 50 billion by 2020. Learn how to overcome the challenges of connecting intelligent nodes to the Internet of Things.

More whitepapers

Radio-Electronics.com is operated and owned by Adrio Communications Ltd and edited by Ian Poole. All information is © Adrio Communications Ltd and may not be copied except for individual personal use. This includes copying material in whatever form into website pages. While every effort is made to ensure the accuracy of the information on Radio-Electronics.com, no liability is accepted for any consequences of using it. This site uses cookies. By using this site, these terms including the use of cookies are accepted. More explanation can be found in our Privacy Policy