New Radio is a new air interface that is not backward compatible with LTE, LTE⁃Advanced or LTE⁃Advanced⁃pro.
Without depending on 2G, 3G or 4G networks, NR networks can be independently deployed. In order to be able to work independently, NR should have a complete set of RAN functionalities.
Just like the previous mobile generation networks, NR should have a main framework, numerology, access proceedings, and scheduling for operation.
In a way, these main elements for 5G NR system may take lots of design of past generations, especially 4G standards.
It seems that multiple access schemes for NR would be based on OFDMA (Orthogonal Frequency Division Multiple Access).
Moreover, the fundamental waveform of NR is cyclic prefix⁃orthogonal frequency division modulation (CP⁃OFDM), while the frame structure and numerology would share some characteristics of LTE.
Innovations of multiple access, MIMO, and channel coding will have important tasks in fulfilling 5G performance requirements.
The framework of NR physical layer technologies is shown in the figure below.
New multiple access schemes like those based on non⁃orthogonal elements would allow a “scheduling⁃light” and/or “light initial access” mechanism to highly decrease the control overhead and access latency to strengthen mMTC efficiently.
New channel coding schemes like low⁃density parity check (LDPC) and polar codes can extremely reduce the decoding complexity for scenarios with large block sizes and/or high coding rates. Also, it can improve the performance of those with short block sizes. Moreover, a lot of processing power of a receiver is consumed by the decoding of channel codes.
The design and specification for URLLC are enabled by fast decoding. With the super⁃wide bandwidth foreseen for 5G up to 1 GHz, channel codes efficient for large block sizes become a must, not an option. the frame structure of NR without it will be only a hollow place holder.
In many ways, MIMO techniques distinguish NR from 4G. NR would operate up to 100 GHz bands. Thus, MIMO or beamforming is an indispensable feature.
Therefore, the beamformed transmission will be greatly used not only for traffic channels, but also in other areas such as random access signal, control signaling, synchronization signal, and broadcast channels carrying system information.
References:
- J. M Meredith,“Study on channel model for frequency spectrum above 6 GHz,” 3GPP TR 38.900, Jun. 2016.
- J. Krause,“Study on scenarios and requirements for next generation access technology,”3GPP TR 38.913, Sept. 2016.
- ZTE Corporation.