Design and verify 5G systems, part 1

EDN

JULY 28, 2020

BY LAURO RIZZATTI, RON SQUIERS AND MIKA CASTREN

Starting in the 1980s, the mobile industry has been upgrading the wireless technology at the rate of one new standard every decade. The first-generation (1G) cell phones launched in the ’80s, although they were not referred to as 1G at the time, were based on an analog technology that supported only voice communication with poor quality.

The second generation (2G) mobile phones introduced in the ‘90s upgraded analog voice transmission to digital voice communication, added support for short message service/multimedia messaging service (SMS/SMM), and dramatically expanded network capacity. At the turn of the century, 3G mobile phones introduced internet access for web browsing, email communication, video downloading, and picture sharing. In the 2010s, 4G smartphones permitted wireless internet access at high speeds to execute desktop applications.

Table 1 summarizes services, key differentiators and weaknesses of the four wireless generations.

All four wireless standards have addressed only one market with one goal: the creation of super-smart phones to provide an increasingly enriching user experience from simple mobile voice calls to all-encompassing internet enjoyment.

Why 5G?

In recent years, a confluence of factors commanded a new wireless standard to replace the aging 4G specifications. They include dramatic growth of mobile users demanding more and faster delivery of data, proliferation of Internet-of-Things (IoT) devices, increasing deployment of drones, popularity of mobile augmented reality, and tough requirements imposed by autonomous driving cars.

In response to the pressure of these demands, the International Telecommunications Union (ITU) crafted the IMT2020 standard, commonly referred to as 5G, to address three mobile markets each with unique requirements.

The first market, referred to as extreme mobile broadband, is primarily concerned with communication services for human-centric use cases that enable users to access multimedia content, services, and data addressed by 3G/4G standards. 5G will better serve increasing demands of new applications and bit rates, for example.

The critical machine communication segment serves machine-to-machine (M2M) applications where ultra-reliable and low-latency communication is compulsory. Examples include vehicle-to-vehicle (V2V) communication for autonomous or semi-autonomous vehicles, wireless control of industrial manufacturing or production processes, remote medical surgery, distribution automation in a smart grid, and transportation safety services.

5G’s third market sector, formally known as massive machine communication, serves what has come to be known as the IoT. In this role, 5G is expected to provide the wireless web that ties together large numbers of connected devices, each transmitting a relatively low volume of non-delay-sensitive data. Devices that support these applications are required to be low cost and operate for many years on a small battery pack.

The 5G standard is the first to support all these markets under one umbrella. For the end user, 5G will be an ecosystem of connected applications. Each application will adaptively manage data speed, latency, and reliability based on the tasks required. For example, a self-driving car requires reliable, instant response and a secure link at highway speeds. To support this, 5G networks will provide wide coverage, low latency, and an encrypted communication link.

5G networks will allow service providers to meet all of their end-users application needs by consolidating multiple communication systems under a single standard that provides data, voice, video, IoT, and crucial communications.

5G extreme specifications

Even a quick glance at the 5G specifications reveals a wealth of new specifications, from one to two orders of magnitude improvements in speed, bandwidth, latency, capacity, density, spectrum efficiency, network efficiency, reliability, coverage, and more. Figure 2 provides an overview of how the new standard supports greater amounts of information transfer between all sorts of devices faster than ever before, and with a high level of security over a wide coverage range.

Table 2 compares the five generations of wireless communication standards based on speed, bandwidth, latency, and data transfer rate.

5G technical requirements

The European Telecommunications Standards Institute (ETSI) enumerates eight 5G requirements:

  1. Peak data rate (Gbit/s)
  2. User experience data rate (Mbit/s)
  3. Latency (msec)
  4. Spectrum efficiency
  5. Mobility (km/h)
  6. Connection density (devices/ km2)
  7. Network energy efficiency
  8. Area traffic capacity (Mbit/s/m2)

The spider chart in Figure 3 compares the 4G (IMT-Advanced) and 5G (IMT-2020) specifications.

Several emerging technologies are being employed in order to meet the 5G standard’s challenging requirements, including:

  • millimeter waves,
  • beamforming,
  • massive multiple input, multiple output (MIMO),
  • carrier aggregation, and
  • small cells.

The technical challenges involved with their commercial implementation are significant, and some are keeping the design community up at night. To understand why, let’s examine each technology.

Millimeter waves

All wireless standards that preceded 5G shared the radio spectrum with other services (radio, HDTV, police/fire/EMS, government, military, etc.), occupying various licensed and unlicensed bands between roughly 1 GHz through 30 GHz. Sometime after the turn of the 21st century, the last few bands of what we had considered to be the usable spectrum were either auctioned off or assigned for other applications, leaving no more bandwidth for 5G expansion below 30 GHz. To solve this, technologists began to consider the block of spectrum covering the frequency range between 30 GHz and 300 GHz, often referred to as the millimeter wave (mmWave) spectrum, which remains largely unoccupied.

Figure 4 shows the electromagnetic frequency/wavelength spectrum split by band.

Until recently, mmWaves had limited use because of the difficulty managing them and the inadequacy of electronics to process them. It was mostly confined to radio astronomy and satellite communications. All that changed in recent years, as technological advances pushed the mmWaves to the forefront for mobile communications, replacing the centimeter wave spectrum saturated by the broad adoption of 4G mobile communications.

A few data points to consider: First, the entire mmWave spectrum is about 10 times wider than the centimeter wave spectrum (300GHz – 30GHz = 270 GHz), providing abundant room for expansion. As a result, mmWave networks can support many simultaneous high-bandwidth channels, each transmitting and receiving immense amounts of data.

In addition to high capacity, 5G systems have been architected to provide significantly lower latency than earlier generations of wireless networks (latency = the delay between when data is transmitted and when it is received). The minimum latency in 4G networks hovers around 70 ms. Today’s early 5G networks can deliver latencies as low as 10 ms and it’s expected to eventually reach down to 1 ms. This dramatically reduced latency will reduce or eliminate the frustrating lags in wireless calls and video chats. In some scenarios, such as driverless cars and telemedicine, the fast responses made possible by the near-instantaneous connections may avert unnecessary injuries or deaths.

More to the point, propagation beamwidth of mmWaves, a measure of how a transmitted beam spreads out as it gets farther from its point of origin, is narrower than in centimeter waves. While the wider beamwidth of centimeter wave signals reduces the reuse of transmission of the same signal within the local geographic area because of interference, the narrower beams of the mmWaves alleviate interference and support multiple transmissions in close proximity using the same frequency ranges.

Unfortunately, mmWaves have drawbacks, including their limited transmission range. The laws of physics dictate that the shorter the wavelength, the shorter the transmission range is for a given power, an effect mostly due to atmospheric attenuation. In addition, mmWave signals attenuate quickly because they cannot easily travel through buildings or obstacles and can be absorbed by trees, foliage, and rain. Because of their poor propagation characteristics, mmWave signals require an enormous amount of radio units (RUs) to achieve the desired coverage.

Beamforming

Beamforming is a technique used to reduce the amount of transmitter power required to support a channel, as well as to increase network capacity. While conventional radios transmit their signal in all directions, wireless beamforming narrows the focus of the transmitter signal, focusing its energy into a tight beam aimed directly at the receiver. This increases the strength of the signal at that receiver while minimizing the surrounding signal interference.

In 5G, beamforming plays a major role to control the power in the system and concentrate power on the user via special multiplexing. Further, the short millimeter wavelengths make it practical to build multi-element, dynamic beamforming antennas small enough to fit into handsets.

Massive MIMO

Multiple-input and multiple-output (MIMO) radios use multiple antennas in the transmitter and receiver to increase the capacity of the antenna links and, ultimately, the efficiency of a network while reducing transmission errors. The method, already used in 3G (Evolved High Speed Pack Access or HSPA+) and 4G (LTE or Long-Term Evolution) wireless standards, has been limited to a few (single digit) antennas.

The extremely short wavelengths of mmWaves make it feasible to use an array of small antennas to concentrate signals into highly focused beams with enough gain to overcome propagation losses and dramatically increase efficiency and throughput of the communication. The more antennas, the higher the efficiency of the communication.

Massive MIMO can push the technology up to hundreds of antennas. In 5G, massive MIMO may require up to 256 antennas on the transmitter side and up to four antennas and two layers on the receiver side. All signals from all the antennas on the receiver side are combined to improve the robustness of a link and increase the bit rate of the system up to 10 Gbps (3.2 Gbps per layer, up to four layers).

The drawback to this approach is that the complexity of the radio’s baseband processor grows exponentially with the number of antennas and modulation orders in the system.

Carrier aggregation

Carrier aggregation augments the efficiency of a communication. In general, the broadcasting spectrum is expensive and in 4G it is becoming more and more congested. It is therefore critical to get smarter in using the available spectrum. Carrier aggregation can involve using one band in 4G, and another band in 5G. By combining them, the transmission data rate can be significantly increased.

Small cells

The infrastructure supporting all standards up to 4G consisted of big cell phone towers that propagate cellular signals throughout a geographical area. 5G will alter this approach. Rather than building big towers, service providers will install their equipment (called small cells) on existing telephone poles, buildings, and other structures. These cells typically have a range of around 250 meters (820 feet).

The shorter propagation characteristics of mmWave signals are encouraging service providers to create a denser infrastructure, i.e. more base stations in closer proximity, to ensure broad and consistent service.

Quality of service

An important requirement for 5G communication is enhanced quality of service (QoS). All previous wireless standards focused on delivering higher data rates to customers but QoS had not been a priority. This changed with the emergence of IoT devices and, more so, with driverless cars. In these applications, and many others, QoS is now a critical requirement.

If a call drops in a 4G communication, the system selects another frequency, another channel, or changes to another modulation scheme. The limited power in current devices forces them to operate at the link layer higher in the protocol stack to switch to a new frequency or modulation scheme, stretching the time to complete the switch and recover from the failure.

In a 5G environment, a selection must be performed within milliseconds, compelling the system to operate at the physical layer. When the communication degrades, switching to a new frequency or another modulation scheme must be accomplished within a few milliseconds.

It is important to handle the QoS closer to the physical layer to also enable the connection of different types of devices to the network.

The 5G standard is a leap forward from all four previous wireless standards, promising faster speeds, higher data transfer rates, and lower latency with wider coverage. Cumulatively, 5G will put an end to congestion and latency issues hampering the aging 4G standard.

Stay tuned for Part 2 of this series, which outlines a verification strategy for a 5G system and the need for hardware emulation.

Dr. Lauro Rizzatti is a verification consultant and industry expert on hardware emulation.

Mika Castren is a senior engineering and product development manager with Mentor, a Siemens Business.

Ron Squiers is a solution networking specialist at Mentor, a Siemens Business.

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