When it comes to NOMA technology, it is short for non-orthogonal multiple-access, and technology Geeks must be familiar with it: as a major research hotspot, it is in full swing in 5GNR. There are two advantages:
1. The uplink link-level traffic and the ability to support overload have been enhanced;
2. The packet arrival rate in the case of a given system interruption is enhanced.
NOMA technology is mainly aimed at uplink non-orthogonal multiple access, at least for the mMTC scenario.
In order to combat interference between non-orthogonal transmissions, the transmitter will use some spreading mechanisms (linear or non-linear, with or without sparseness) and interleaving techniques are often used to improve performance.
Regarding the main focus of NOMA in 3GPP, I have summarized the following points. If you are interested, please refer to 38.812
• NOMA can be applied to grant-based and grant-free transmissions.
• The advantages of NOMA, especially in the case of grant-free transmission, may complete a variety of use cases, including: eMBB, URLLC, mMTC.
• In the RRC-CONNECTED state, it saves the scheduling request process and assumes that the UE has completed uplink synchronization in advance.
• In the RRC-INACTIVE state, data can be transmitted without the RACH procedure.
• This way of saving signaling overhead will naturally save energy consumption, reduce delay, and increase system capacity.
• NOMA can benefit both Uu port and side link at the same time.
Explain a little bit about the concepts of grant-based and grant-free
Give a chestnut~
In the traditional LTE network, we assume that the process of an uplink access is as follows:
This is a grant-based process, that is, after the UE sends a scheduling request (SR) to the base station, it must wait for the scheduling grant (SG) of the base station to allocate resources to the UE. Correspondingly, the handshaking process in the grant-free network is omitted.
Continuing back to the topic of NOMA:
Transmit Processing:
Receiver Processing:
Main discussion points about NOMA:
• HARQ, including transmission scheme, feedback scheme and combination scheme.
• Link adaptive MA signature allocation/selection.
• Synchronous and asynchronous operation.
• Adaptation between orthogonal and non-orthogonal multi-channels.
• For link-level and system-level assessments, the benchmark for comparison is OFDM multiple access.
• For the actual TX/RX modeling, including potential PAPR problems, channel estimation errors, power control accuracy, collisions, etc.
For the specific details of the NOMA camp, each manufacturer has different technologies, as shown in the following table:
Japan’s 5GMF white paper envisions the future network as follows:
If you want to achieve such a smart IoT network that breaks the barriers of traditional communication networks, the research on how to reduce the time delay and other major indicators in the figure cannot stop. Therefore, about NOMA, all the things mentioned above are for research. 3GPP meetings are ongoing, and the conclusions of the topics are constantly updated, so stay tuned~
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