With the demanding requirements being placed upon the new 5G mobile communications standard, a totally new radio interface and radio access network has been developed. Called 5G New Radio or 5G NR, the new radio interface provides for the growing needs for mobile connectivity.
The development of the 5G NR or 5G New Radio is key to enabling the 5G mobile communications system to work and it provides a number of significant advantages when compared to 4G.
5G NR has been developed from scratch taking the requirements and looking at the best technologies and techniques that will be available when 5G starts to be deployed.
5G NR utilises modulation, waveforms and access technologies that will enable the system to meet the needs of high data rate services, those needing low latency and those needing small data rates and long battery lifetimes amongst others.
The first iteration of 5G NR appeared in 3GPP Release 15. The draft specifications for Release 15 were approved in December 2017 and are expected to be finalized in mid-2019. Release 15 forms phase one of a 5G mobile communication standard. Release 16 will provide specifications for the second phase and this is expected to be finalized in December 2019.
5G New Radio, 5G NR Basics
The 5G New Radio has been developed to provide a significant enhancements in areas like flexibility, scalability and efficiency, both in terms of power usage and spectrum.
The 5G New Radio is able to provide communications for very high band with transmissions like streaming video as well as low latency communications for remote control vehicle communications as well as low data rate low bandwidth communications for machine type communications.
There are several cornerstones to the new radio used for 5G:
- New radio spectrum: Mobile communications usage is rapidly increasing, and the introduction of 5G will accelerate this trend with many more applications being accommodated by the technology. Whilst improvements in spectrum efficiency will be made these will not be able to accommodate the huge increases in usage, so more spectrum is needed.
Release 15 also outlines several groups of new spectrum specifically for NR deployments. These range in frequency from 2.5 GHz to 40 GHz. Two bands being targeted for more immediate deployment are in the regions of 3.3 GHz to 3.8 GHz and 4.4 GHz to 5.0 GHz.
The 3.3 GHz to 3.8 GHz spectrum has already been released in countries like the USA< Europe and certain Asian countries and they could see deployment as early as 2018. Other higher frequency bands but below 40 GHz are also being reserved for 5G but this is only the beginning as there is talk of usage of frequencies up to 86 GHz.
The advantage of the higher frequency bands is that they are much wider and they will be able to allow much higher signal bandwidths and hence support much higher data throughput rates. The disadvantage in some aspects is that they will have a much shorter range, but this is also an advantage because it will also allow much greater frequency re-use.
- Optimised OFDM: An early decision was taken to use a form of OFDM as the waveform for phase one of the 5G New Radio. It has been very successfully used with 4G, the more recent Wi-Fi standards and many other systems and came out as the optimum type of waveform for the variety of different applications for 5G. With the additional processing power available for 5G, various forms of optimisation can be applied.
The specific version of OFDM used in 5G NR downlink is cyclic prefix OFDM, CP-OFDM and it is the same waveform LTE has adopted for the downlink signal.
Read more about . . . . 5G waveforms: CP-OFDM & DFT-SOFDM.
- Beamforming: Beamforming is a technology that has become a reality in recent years and it offers to provide some significant advantages to 5G. Beamforming enables the beam from the base station to be directed towards the mobile. In this way the optimum signal can be transmitted to the mobile and received from it, whilst also cutting interference to other mobiles.
The move to higher frequencies allows for much smaller antennas and the possibility of programmable high directivity levels.
On frequencies above 24 GHz where antennas are smaller, there is the possibility of having high performance beamsteering antennas that are able to accurately direct the power to the mobile in question, and also provide receiver gain in this direction.
- MIMO: MIMO, multiple input multiple output has been employed in many wireless systems from Wi-Fi to the current 4G cellular system and it provides some significant improvements. Within 5G, MIMO will be one of the mainstay technologies.
5G will take full advantage of Multi-User- MIMO, MU-MIMO where it will provide multiple access capabilities to MIMO by utilising the distributed and uncorrelated spatial location of the various users.
In implementing this the gNB (5G base station) sends a CSI-RS (Channel State Information Reference Signal) to the different user equipment’s and then dependent upon the responses, the gNB computes the spatial information for each user. It uses this information to compute the required information for the pre-coding matrix (W-Matrix) where the data symbols are constructed into the signals for each of the elements of the gNB antenna array.
The multiple data streams have their own weightings which includes phase offsets to each stream to enable the waveforms to interfere constructively at the receiver. This maximises the signal strength to the user whilst also minimising the signal and hence interference to other users.
In this way the gNB is able to talk to multiple devices concurrently and independently by using spatial information. This means that 5G MU-MIMO enables the UEs to operate without need for knowledge of the channel or additional processing to obtain the data streams.
MU-MIMO on the downlink significantly improves the capacity of the gNB antennas. It scales with the minimum of the number of gNB antennas and the sum of the number of user devices multiplied by the number of antennas per UE device. This means that using 5G MU-MIMO the system can achieve capacity gains using gNB antenna arrays and much simpler UE devices.
- Spectrum sharing techniques: Much of the radio spectrum, although allocated, is not used in an efficient manner. One of the techniques being proposed is for spectrum sharing.
- Unified design across frequencies: With the 5G New Radio utilising a wade variety of frequencies, possibly 3.4 to 3.6 GHz below 6GHz and then 24.25 to 27.5 GHz, 27.5 to 29.5 GHz, 37 GHz, 39 GHz and 57 to 71 GHz range as possibilities for the mmWave radio. It is important to have a common interface across these frequencies.
- Small cells: As network densification is required to provide the required data capability more use of small cells and small cell networks are being proposed. A small cell network is a group of low power transmitting base stations which uses millimetre waves to enhance the overall network capacity. The 5G small cell network operates by coordinating a group of small cells to share the load and reduce the difficulties of physical obstructions which become more important at millimetre waves.
By utilising these techniques and many others, the 5G New radio, 5G NR will be able to significantly improve the performance, flexibility, scalability and efficiency of current mobile networks. In this way 5G will be able to ensure the optimum use of the available spectrum, whether it is licensed, shared or unlicensed, and achieve this across a wide variety of spectrum bands.
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