5G NR: The New Radio interface for 5G
The 5G air interface that scales from cellular to the mm-wave bands
5G builds on LTE and adds support for multiple sub-carrier spacings (15 KHz, 30 KHz, 60 KHz, 120 KHz,…). Cyclic prefix and sub-frame duration is also scaled with the sub-carrier spacing. With a scalable design, 5G NR scales from cellular to mm-Wave frequencies.
Beam forming in mm-Wave
In most wireless networks, mm-Waves (30 GHz to 300 GHz) have been restricted to direct line-of-sight links as these frequencies are easily blocked by foliage and buildings. Advanced beam forming techniques that can track the user help in increasing the gain for these frequencies. Quick handovers between cell sites also help mitigate the impact of blockage.
The following figure underscores the challenges in working with mm-Waves.
A Qualcomm study has found that 150m line-of-sight (LOS) and non-line-of-sight (NLOS) coverage is possible in dense urban outdoor deployment.
5G will support a very large number of antennas on the base station (gNodeB). This large number of gNodeB antennas coupled with multiple antenna at the UT help focus energy towards the UT, thus resulting in improvements in spectral efficiency. As a consequence, massive MIMO greatly increases the achievable throughput at the cell edge.
Advanced LDPC channel coding
5G NR uses LDPC (low density parity check codes) for channel coding on the downlink and uplink channels. The LDPC 5G NR codes have been designed so that they can be used in incremental redundancy schemes like HARQ.
The following figure shows how the base matrix in light blue color. Additional parity bits are generated by extending the matrix to include the dark blue squares.
Fine grain TDD
5G NR permits fine grain TDD within a single slot. A slot organization changes dynamically to adjust for the changing workload.
Low latency HARQ
5G NR will support low latency HARQ in TDD mode. The first transmission and the retransmission can be transmitted within a millisecond.
Ultra-Reliable Low-Latency Communication (URLLC)
5G AN will add support for URLLC services for applications that need very low latency and high reliability. These services would be targetted towards applications like autonomous driving and remote surgery.
Latency reduction and reliability improveents will be achieved by enhancements to the scheduler and channel coding:
- Downlink latency is reduced by letting URLLC packets preempt mobile broadband traffic.
- Uplink latency is reduced by advanced coding techniques that permit joint decoding of multiple uplink transmissions.
- Retransmission latency will be reduced using low latency HARQ.
- Reliability of the link is improved by use of diversity and channel coding support for short blocks.
5G networks are being designed to serve a wide variety of use cases. Optimizing a single network for all the use cases may not be practical. 5G networks will support core network and radio access network slices that can be optimized for one particular use case.
The following figure shows a possible optimized network for smart phones, MVNOs and IoT devices.