Intro to 5G NR

5G, the next (fifth) generation in wireless smartphone communications, has been heavily promoted in the consumer world as a level up for mobile devices. But what does 5G entail in the eyes of the engineers who develop these devices?

In this article, we will dive deeper into 5G NR and explore the multiple-use models and multiple frequency bands covered by this emerging standard. We will also take a look at some of the advanced technologies associated with 5G NR.

 

5G Standards

Standards for 5G are being developed by the 3rd Generation Partnership Project (3GPP) which consists of partners from seven different global standards organizations. The standards for 5G began with “Release 15” in December of 2017 and are being expanded upon in subsequent releases as new features, functionality, and requirements are added. 

Within 3GPP are Technical Specification Groups (TSGs) that work to define the 5G NR systems in increasing levels of abstraction. Example levels include, but are not limited to:

• Radio Access Network (RAN): Responsible for defining the lower levels (1-3) of the radio performance specs which include:
  • The physical layer
  • Modulation
  • Frequency-division duplexing (FDD)
  • Time-division duplexing (TDD)
  • Beamforming
  • Error detection
  • Correction
• Services & Systems Aspect (SA): Oversees the overall architecture and service capabilities which includes charging, accounting, network management, and security
• Core Network & Terminal (CT): Defines the specifications for the user equipment, handoff between networks, quality of service mapping, etc.

 

Three Frequency Bands of Tiered 5G Service

As wireless telecommunications technologies have advanced, the frequencies and bandwidth have steadily increased. As illustrated in Figure 1, the newer generations retain some backward compatibility with existing networks but expand into more frequency bands.

 

Figure 1. Evolution of frequency spectrum allocations for 2G, 3G, 4G, and 5G networks. Image used courtesy of Ericsson

 

This trend is taking a huge leap forward with 5G as it moves up into the millimeter-wave (mmWave) frequencies above 30GHz. This allows 5G NR to support ultra-wide bandwidths of up to 100MHz at frequencies below 6GHz and up to 400MHz at higher frequencies.

5G can generally be divided into three bands:

• FR1
  • Lower Frequencies: MHz–1 GHz
  • Mid Frequencies: 1–7 GHz
• FR2
  • Higher Frequencies: 24–48 GHz

As Figure 2 illustrates, the three bands are designed to work together to meet different needs for bandwidth, latency, and coverage.

 

Figure 2. Relationships between bandwidth, latency, and coverage for the 3 bands of 5G NR. Image used courtesy of Advantech

 

The initial deployments for 5G are in the lower frequency range (FR1), with two bands (referred to as low and mid) that span the more traditional frequencies used for smartphones of 450 MHz to 6 GHz. These lower frequencies provide the greatest coverage range.

The higher frequency range (FR2) moves up towards and into the mmWave region with frequencies from 24 - 100 GHz to support faster download speeds and enable new applications that require ultra-low latency.

 

Orthogonal Frequency-division Multiplexing for 5G NR

5G transmission for both the uplink and downlink connections is based on OFDM (orthogonal frequency-division multiplexing). OFDM combines quadrature amplitude modulation (QAM) and frequency division multiplexing (FDM) to enable high data rate communications.

Because the subcarrier frequencies are orthogonal to each other, the individual peaks all line up with the nulls of the other subcarriers (Figure 3).

 

Figure 3. The frequency spectrum of orthogonal frequency-division multiplexing. Image used courtesy of Keysight

 

This minimizes interference and allows the receiver to efficiently recover the signal. These modulated subcarriers can be used to support many independent signals (like FM radio channels), but in 5G applications are typically combined to increase the data rate for a single channel.

The NR specification supports an adjustable carrier spacing of 15 kHz, 30 kHz, 60 kHz, 120 kHz, 240 kHz, or 480 kHz with a maximum of 3300 subcarriers. In addition, the subcarrier modulation can be QPSK (quad-phase shift keying) or 16-, 64-, or 256-QAM. These options provide versatility that allows operators to optimize the communication scheme to meet the environments and applications.

 

5G Performance Compared to 4G

As we have come to expect from each new generation of smartphone technology, 5G is faster and provides more capacity than its predecessor 4G. 5G is expected to support peak data transfer rates of up to 10-20 Gb/s and average data rates in excess of 100 Mb/s. 5G is also designed to support a 100x increase in capacity through improvements in network efficiency and a 10x decrease in latency to as low as 1 ms.

Beyond those basic improvements, 5G is being designed as a more diverse telecommunications standard than 4G to support applications beyond standard mobile broadband including:

• Mission-critical communications with low latency
• Massive connectivity for Internet-of-Things (IoT)
• Support for all spectrum types (licensed, shared, unlicensed) 
• Expanded deployment models including hotspots
• New communication models such as device-to-device and multi-hop mesh.

 

5G Use Models

Typically when we hear about 5G, we immediately think of better smartphones, and that is, indeed, an aspect of the 5G NR specifications. However, the standards are being developed to support much more than just better smartphones. Specifically, there a three major use models as illustrated in Figure 4:

• eMBB (Enhanced Mobile Broadband): loosely better smartphones, consumer apps 
• URLLC (Ultra-reliable and Low-latency Communications): mission-critical services
• mMTC (Massive Machine Type Communications):  think Internet of Things

 

Figure 4. Example applications of the three 5G NR use models. Image [modified] used courtesy of 3GPP

 

eMBB (Enhanced Mobile Broadband)

The initial focus of 5G NR network development is focused on eMBB for the improved download and upload speeds and reduced latency. eMBB is expected to improve mobile video streaming and enable applications that include mobile augmented and virtual reality (AR and VR). emBB is anticipated to provide enhanced access to wireless broadband in densely populated urban areas, sporting or concert venues, and smart offices.

 

URLLC (Ultra Reliable Low-Latency Communications)

As the name suggests, URLLC is designed to provide very low-latency communications for “real-time” applications including autonomous vehicles, industrial automation, and remote surgery. Clearly, each of these applications will require robust network connections with low error rates and imperceptible latency (theoretically as low as 1 ms). These requirements are vastly different than for a voice call or streaming your favorite new show.

 

mMTC (Massive Machine Type Communications)

mMTC is the third use model and is also quite a bit different from the first two. mMTC will take advantage of the wide bandwidth available with 5G NR to support communication to a “massive” number of low data rate devices. Applications will include the Internet-of-Things and Smart Cities where a large number of nodes will require narrow bandwidths for remote sensing, monitoring, traffic and parking management, logistics and fleet management, and electronic billboards. 

 

Technologies that Enable 5G

There are many technological advancements that are coming together to enable 5G communications. This section will touch on a few key technologies that are likely of interest to electrical engineers working in the hardware.

 

Advanced Transistor Tech

The continual march of silicon CMOS technology to finer geometries is obviously important to increase the processing power necessary in handsets, base stations, and the network backbone. Additionally, as 5G expands into the millimeter-wave region of the frequency spectrum, improvements in advanced transistor technology are taking center stage.

As Figure 5 illustrates, silicon germanium (SiGe), gallium arsenide (GaAs), gallium nitride (GaN), and silicon carbide (SiC) are all suitable for operation in the high-frequency FR2 bands above 6 GHz. In particular, GaN and SiC devices are widely used in the base stations where both high frequencies and high powers are necessary. 

 

Figure 5. Power vs. frequency of wide bandgap (WBG) materials. Image used courtesy of Analog Devices

 

Beyond just the transistors themselves, external connections from the chip to the printed circuit board (PCB) require technology advancements in packaging and advanced design techniques. Something as simple as a 1 mm bond wire inside a package becomes a potential antenna at millimeter-wave frequencies and can have a complex impedance that makes it difficult to achieve a 50 Ω impedance match to the PCB. Moving to flip-chip assembly using solder balls can help, but the impedance matching challenge may still remain.

 

Massive Multi-Input Multi-Output Antennas

Because of the very short wavelengths, phased array antennas become feasible for the 5G millimeter-wave frequencies. For example, the millimeter-wave handset prototype demonstrated by Qualcomm in Figure 6 appears to have three 4x2 phased array antenna sections. The phased array antennas can support beamforming for improved antenna gain. 

 

Figure 6. 5G NR mmWave handset prototype. Image [modified] used courtesy of Qualcomm

 

In the base stations, the use of phased arrays is expected to explode to what is referred to as massive multi-input multi-output (MIMO) systems. Using a large number of antennas and complex algorithms a massive MIMO system can employ adaptive beamforming and spatial diversity for:

• Spectral efficiency through the focusing of narrow beams toward each user 
• Energy efficiency through antenna gain for reduced total radiated power
• Improved data rates and capacity through gain and spatial diversity
• Tracking of mobile users via adaptive beamforming

A combination of digital and analog processing at the base station creates unique transmission channels for individual users. The individual users may also employ multiple antennas to enhance communication in the presence of fading, multipath, and interference.

 

Figure 7. Massive multi-input multi-output communication for millimeter-wave 5G. Image used courtesy of Alemaishat et al

 

Summary

5G NR is so much more than simply an improved network for mobile smartphones. The three major use models of enhanced mobile broadband, ultra-reliable low-latency communications, and massive machine-type communications will likely result in many new applications in the coming years.