How mmWave bolsters real-world 5G networks - Embedded.com

How mmWave bolsters real-world 5G networks

mmWave technology can help address of the limitations of sub 6 GHz 5G networks, but there are still challenges ahead.

Expectations from 5G are huge. However, a major challenge facing 5G deployment is that the available sub-6-GHz spectrum does not support the latency and throughput needed to deliver the optimal performance required by advanced applications and simultaneous users. While current sub-6-GHz 5G networks provide marginal improvements over existing 4G LTE networks, they fail to deliver on the promise of 5G coverage, performance, and latency in dense urban environments and crowded event venues.  mmWave technology can help address this, but there are also challenges. This article looks at the key factors to consider in addressing these 5G deployment challenges.

Cellular technologies are always evolving to meet the growing data demands of the modern age. GSM led to 2G which allowed text messaging and basic data transfer. 3G allowed effective mobile internet browsing and 4G allowed users to stream video more reliably and enjoy stable VoIP calls. 5G promises much more, being up to 100 times faster than its predecessor, with higher bandwidth, lower latency, more reliable coverage, and greater availability.

We expect much more from 5G, especially in data-intensive scenarios where real-time processing is essential. Upcoming 5G rollouts will bring innovations such as autonomous driving, and other emerging use cases include vehicle-to-vehicle (V2V) communications, smart buildings, cities, telemedicine, medical robotics (for surgical consults and training, for example), and virtual and augmented reality (VR/AR) solutions.

The number of connected devices for the internet of things (IoT) will also increase, especially in areas such as supply chain monitoring and in the industrial IoT (IIoT) where monitoring of critical systems is a top priority.

However, given 5G’s technical requirements (and native limitations), early adopters of true 5G will include smart factories, warehouses, and sports arenas.

There are different types of 5G networks

Converting the entire cellular network infrastructure to handle 5G is a massive undertaking and many carriers are using the existing infrastructure to provide what they call “5G,” but are falling far short of the download speeds promised by actual 5G.

Essentially, there are two types of 5G networks:

  • The first operates on mid (3.4 to 6 GHz) and low-frequency bands (less than 1GHz). It generally relies on 4G infrastructure. 4G offers download speeds from 35 to 50+ Mbps. While the ‘5G’ solutions offered by these carriers exceed 4G download speeds, they fall dramatically short of the promised benefits of 5G. As a result, such solutions are unlikely to convince consumers to upgrade.
  • Super-fast millimeter wave (mmWave) offers the 5G we all want and operates on high-frequency bands from 24 to 40GHz. With speeds of up to 5Gbps, it’s possible to download an entire HD movie in seconds.

Understanding the differences and synergies between each 5G network is crucial to addressing deployment challenges. In terms of user experience, mmWave has the greatest potential benefits, but setting it up is not without complications.

The pros and cons of mmWave and 5G deployment challenges

Real-world mmWave network speeds vary greatly depending on range, signal blockers, and proximity to the nearest 5G tower or small cell. While mmWave 5G networks are ultra-fast, they’re also very short range. To receive mmWave signals, users must be within a block or two of a 5G tower with no line-of-sight (LOS) obstructions.

High-frequency mmWave signals are easily blocked by buildings, walls, windows, and foliage, further reducing the available 5G range. To optimize coverage, carriers are faced with installing numerous small cells in high densities, driving up the cost of deploying mmWave networks at scale.

Because of its coverage and line of sight limitations, mmWave technology is better suited for dense urban environments. Due to its range limitations, mmWave is not a practical choice for suburban and rural areas, which are best served by easier-to-deploy, more affordable 4G LTE and sub-6 GHz 5G networks. Widespread deployment of mmWave 5G networks will require extensive underground installation of fiber cable. Until this happens, carriers will continue to rely on existing network infrastructure while the market transitions to 5G.

Although range, signal propagation, and LOS limitations are mmWave’s drawbacks, advanced technologies developed by companies like Movandi, such as massive MIMO (multiple-input multiple-output), miniaturized antenna arrays, adaptable beamforming, and smart active repeaters can effectively address these challenges

Smart active repeaters solve 5G signal propagation challenges by amplifying mmWave signals and extending the range and coverage of mmWave-based networks in outdoor environments and inside buildings. Active repeaters work by boosting mmWave signals, enabling them to penetrate walls and other blockers and bend around buildings to overcome LOS issues without the need for bulky antenna designs or costly fiber backhaul. When deployed inside a building, a smart repeater amplifies a weak beamed signal and can light up an entire room, improving end user and application connectivity experiences (figure 1).

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Figure 1: Smart active repeaters solve 5G signal propagation challenges, extending the range and coverage of mmWave-based networks in outdoor environments and inside buildings.

Widespread use of active repeaters throughout 5G networks enables service providers to launch indoor, outdoor and mobile enhanced 5G mmWave services at 50 percent lower costs.

All major U.S. carriers are now testing mmWave networks, providing availability in selected major cities and neighborhoods. Sub-6 GHz 5G is currently more widely available than mmWave, with major carriers rolling out lower frequency 5G networks to many customers in urban areas.

Tier 1 operators are migrating to mmWave technology to meet network capacity requirements as customer demand is expected to exceed sub-6 GHz capacity by 2023, with multiple operators already deploying mmWave-based 5G networks.

While critics of mmWave argue that sub-6 GHz networks offer better coverage than mmWave and require fewer base stations (next-generation radio nodes — gNBs), a limited sub-6 GHz spectrum will eventually require the deployment of more gNBs. High bandwidth mmWave can help relieve growing network congestion in crowded urban areas, sports arenas, concert venues, and airports. This deployment means you’ll have a stable high-speed connection in places you’ve come to expect little to no connection.

While the transition to 5G networks is underway, there’s still a long path forward until 5G replaces 4G LTE. For the time being, most users are getting by with 4G and limited sub-6 GHz 5G service, with the promise of ultra-fast mmWave speeds and low latency just over the horizon.

Three technical challenges to unlocking the potential of 5G

To achieve 5G’s ambitious goals of low latency, high bandwidth, faster speeds, and broad coverage; major carriers and mmWave solution providers are working to overcome these fundamental challenges:

  • Traditional approaches to high-frequency RF design and costly, bulky, and inefficient antennas pose barriers to achieving the performance goals of mmWave 5G networks.
  • Mass deployment of small cells and relays to support mmWave networks at scale can drive up 5G infrastructure costs.
  • mmWave frequencies can lead to greater transmission losses caused by distance, signal blockage, and non-line-of-site conditions.
  • Beamforming antennas and advanced beam management technologies are required to achieve a longer range for mmWave networks, adding to system complexity.

To accelerate the deployment of mmWave networks at scale, carriers and 5G equipment makers must address these three technical challenges:

  • Higher propagation loss at high frequencies with a single antenna: This is a well-understood technical challenge with a thoroughly analyzed and well-defined solution. The use of steerable phased arrays can overcome this challenge by building large antenna apertures through the co-phasing of many small antenna elements.
  • The need for a trackable LOS path or a strong reflective path between the transmitter and receiver: The lack of refraction/diffraction in high radio frequencies limits the availability of links to the LOS path or strong, mirror-like reflective paths. This is a major constraint in delivering mmWave connections that must be available anywhere, anytime.
  • High transmittance loss through materials at high radio frequencies: compared to sub-6 GHz radio signals, mmWave signals exhibit very high transmittance losses when propagating through materials such as glass, tinted windows, brick, wood, and drywall. Even conventional glass windows can attenuate mmWave signals by 6 dB, and multi-pane Low-E glass can result in a loss of nearly 40 dB. Signal blockage is a major constraint limiting the availability of mmWave, anywhere and anytime.

The first challenge (propagation loss with a single antenna) is well understood and successfully mitigated by deploying large phased-array antennas. However, until recently, there have been no widely agreed upon or standardized solutions to the line of sight and transmittance loss issues.

How an active repeater solution works

There are three deployment scenarios in which a smart active repeater can mitigate LOS link availability challenges:

Lack of LOS or a strong reflective path: this deployment challenge includes cases where there is no line-of-sight or strong reflective path between the gNB (think next-generation base station) and end-user equipment (UE). Given the reflective propagation properties at high frequencies, the natural/passive reflectors need to create a mirror-like path between the source and destination. This mirror-type path requirement further limits the deployment scenarios that rely on natural reflectors in the environment to close the mmWave link.

Very high transmittance loss: this deployment scenario involves a very high transmittance loss due to signal-blocking objects between the gNB and UE. For example, transmission loss through a tinted glass window can be as high as ~40 dB, which is very challenging to compensate for in a single hop.

Untrackable changing environment and/or reflectors: ideally, beam tracking algorithms are expected to track and adapt to movements and changes in the environment, reflectors, and UE. Typical changes in the environment, such as blockage of LOS or a change in orientation of the UE may prove very difficult to track without losing the connection. However, additional mitigation methods and architectural improvements are required to provide more robust, reliable connections for mobile and varying environments.

Instead of tracking rapid changes in the environment or reflectors by adjusting narrow beams pointing at the gNB and UE, an active repeater can generate wide beams in the vicinity of mobile devices. Once these quasi-stationary wide beams are created, there is no need for immediate tracking of fast changes in the mobile device’s location or orientation.

Active repeaters can be designed to mitigate mmWave link availability and address LOS challenges. To minimize latency, cost, and complexity, a repeater based on a “demodulator-less” architecture maximizes available signal strength and eliminates the need for conventional demodulation and re-modulation techniques.

By enabling multiple access options via time slots, frequency, and physical space or range, a single active repeater can support several types of end-user equipment under the following scenarios:

Static single-beam: the repeater receives a single stream that covers the full frequency channel and retransmits the stream over a single narrow beam that can cover all end-user equipment (figure 2).


Figure 2: Example of a static single-beam deployment.

Switching multi-beam: the repeater beam setting is switched on a time-slot basis. The repeater receives a single stream and retransmits the stream over switching beams. The beam profile during each time slot is associated with the end-user’s equipment assigned to that time slot (figure 3).


Figure 3: Example of a switching multi-beam deployment.

Concurrent multi-beam: the repeater can be configured to concurrently retransmit the full bandwidth mmWave signal over multiple beams covering all end-user equipment.

An active repeater can be designed to dynamically support all three types of beams by reconfiguring the beamforming engine resources within the repeater equipment. Beam reconfiguration can be applied at installation or during operation. Given the reconfigurable and dynamic nature of this multiple-access architecture, a single repeater can support several types of end-user equipment.

Consider an active repeater scenario in which four hops are configured between the gNB and the last repeater in the chain. These hops extend the range between the gNB and the last repeater to more than 2 km. This is achieved with nearly zero latency over the hops since each demodulator-less node doesn’t need to perform de-modulation/re-modulation. Analysis of the gradual degradation of error vector magnitude (EVM) as the mmWave signal propagates through the repeaters shows that a target signal-to-noise ratio (SNR) of ~23 dB is still maintained at the very last repeater node.

The complexity of beam search and refinement at the repeater is manageable because the beam configurations for the link between the gNB and repeater are static. Once the beams between the gNB and repeater are optimized and fine-tuned (at power-up or periodically at a slow rate), there are only two beams to be optimized dynamically, e.g., the beams between the repeater and UE. This results in a highly efficient beam search implementation comparable to a direct link between a gNB and UE.

Conclusion

It is worth noting that there are additional commercial and end-user requirements for 5G adoption. These include fiber-only data center upgrades to handle increased traffic, data transfer and storage requirements that complement the high speeds demanded by 5G. 5G-compatible devices are another consideration, whether mobile or on a fixed LAN, especially if you plan to use 5G to ensure business continuity when your fixed broadband is down.

A major challenge facing 5G deployment is that the available sub-6-GHz spectrum does not support the latency and throughput needed to deliver the optimal performance required by advanced applications and simultaneous users. While current sub-6-GHz 5G networks provide marginal improvements over existing 4G LTE networks, they fail to deliver on the promise of 5G coverage, performance, and latency in dense urban environments and crowded event venues.

5G networks based on mmWave frequencies in the 24 GHz to 40 GHz range hold the most promise for high-bandwidth, low-latency 5G connectivity. However, mmWave technology also poses signal propagation, blocking, and path loss challenges. We’ve seen similar technical challenges before in the areas of satellite TV and in Wi-Fi; and we’ve solved them using solutions such as additional access points, boosters, repeaters, and satellite alignment.

Similarly, by holistically tailoring the 5G radio and beamforming antenna as a complete system, the performance issues of mmWave solutions can be solved to a far greater degree than ever before. Mobile technology providers are responding to this challenge by delivering the first mmWave RF front-end solutions, large phased-array antenna designs, and smart active repeaters that enable the high performance, broad coverage, and high availability end-users expect from 5G networks. Thus, enabling service providers and industry partners the ability to launch indoor, outdoor, and mobile enhanced 5G mmWave services at 50 percent lower costs. Companies like Movandi have developed solutions that help improve both performance and economics for global 5G operators that cut deployment costs by half.

Once carriers handle the necessary upgrades and provide sensible data caps (avid gamers and streamers can use up a monthly allowance in a few days), then we can all enjoy 5G as it should be.

— Reza Rofougaran is CTO and co-founder of Movandi

>> This article was originally published on our sister site, EE Times.


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