One key element of any cellular communications system is the multiple access technology that is used.
As a result the 5G multiple access schemes are being carefully considered and researched to ensure that the optimum technique or techniques are adopted.
There are several candidate 5G multiple access schemes that are in the running. Each has its own advantages and disadvantages and as a result, no single technique is likely to meet all the requirements.
5G multiple access schemes
There are several candidate systems that are being considered as the 5G multiple access scheme. They include a variety of different ideas.
- Orthogonal frequency division multiple access, OFDMA: OFDMA has been widely used and very successful for 4G and could be used as a 5G multiple access scheme. However it does require the use of OFDM and requiring orthogonality between carriers and the use of a cyclic prefix has some drawbacks. As a result other multiple access schemes are being investigated.
- Sparse Code Multiple Access, SCMA: SCMA is another idea being considered as a 5G multiple access scheme and it is effectively a combination of OFDMA and CDMA. Normally with OFDMA a carrier or carriers is allocated to a given user. However if each carrier has a spreading code added to it, then it would be able to transmit data to or from multiple users. This technique has been developed to use what are termed sparse code and in this way significant numbers of users can be added while maintaining the spectral efficiency levels.
- Non-orthogonal multiple access, NOMA: NOMA is one of the techniques being considered as a 5G multiple access scheme. NOMA superposes multiple users in the power domain, using cancellation techniques to remove the more powerful signal. NOMA could use orthogonal frequency division multiple access, OFDMA or the discrete Fourier transform, DFT-spread OFDM. .
There are several multiple access schemes that could be used with 5G. The one or ones used will be chosen as a result of the standardisation process which is currently onging.
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