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5G – Need for Harmonized Spectrum

Posted on | by Matt Walker

Optimistic 5G forecasts assume that telcos’ spectrum needs are met

Ericsson recently predicted that by 2024 5G subscriptions will reach 1.9 billion, 35 percent of traffic will be carried by 5G networks and up to 65 percent of the global population could be covered by 5G. This is one of the many forecasts that predict the success of 5G, however there are many variables attached to it. A key one is the availability of suitable, affordable and importantly harmonized radio frequency spectrum, which is the focus of this blog.

Harmonized spectrum is key for 5G success

At the upcoming World Radiocommunication Conference (WRC), the overall goal of the telecommunication world at is to secure a sizeable chunk of harmonized spectrum for 5G.

Spectrum harmonization drives economies of scale, better battery life (as phones don’t need multiple radio modules and to toggle between frequencies), less cumbersome roaming and lesser cross border interference. It’s essential for 5G to succeed.

Government policymakers want to auction or license this harmonized spectrum to cover their current and future budgets. Telecom network operators on the other hand are interested in getting this harmonized band(s) at a reasonable cost from governments in order to meet operational excellence requirements and achieve their business targets in partnership with their vendors.

Background on spectrum

Wireless communications require airwaves to provide services. Airwaves, or electromagnetic spectrum, consist of a range of all types of electromagnetic radiation, from radio waves to gamma rays. The range of frequencies that are used for providing mobile and WiFi connectivity falls under the radio frequency (RF) portion of the electromagnetic spectrum. RF spectrum ranges from 3 kHz to 300 GHz (Figure 1).

Figure 1: Range of frequencies in wireless communications

Source: Nasa (https://imagine.gsfc.nasa.gov/science/toolbox/emspectrum1.html)

Mobile communications – a subset of wireless communications – primarily takes place in the range of 600 MHz to 42 GHz. The lower frequency bands are suitable for addressing communications between mobile phones and base stations (radio towers) while the high bands are used for supporting backhaul connectivity between radio towers. Fronthaul, which is a much newer concept, connects remote radio heads mounted on towers to baseband units located in a centralized location. Fronthaul requires much higher bandwidth and minimal latency and thus for the most part it is supported with optical fiber. However, in case fiber is not available, a wireless medium can be used (e.g. microwave). (Figure 2).

Figure 2: Use of radio waves in cellular networks

Source: MTN Consulting

The electromagnetic spectrum requires proper management, allocation, assignment and harmonization at a global level. That’s because wireless communications isn’t limited by national boundaries, and a global approach helps facilitate economies of scale. This huge function is performed by the ITU (International Telecommunication Union), which is the United Nations’ specialized agency covering information and communication technologies (ICTs). More specifically, the ITU’s Radiocommunication sector (ITU-R) takes care of this obligation at the global level.

ITU-R allocates spectrum through the pivotal World Radiocommunication Conference (WRC), which takes place once every 3-4 years. WRC is the most significant inter-governmental event related to the frequency spectrum. WRC has a mandate to review, and, if necessary, revise global Radio Regulations, the international treaty governing the use of the radio-frequency spectrum and the geostationary-satellite and non-geostationary-satellite orbits. This treaty is the basis for the harmonization of spectrum worldwide.

WRC allocates frequencies to everything that needs airwaves for execution – from as small as garage door openers all the way to space satellites, and everything in between (terrestrial, aviation, maritime, etc.).

Once spectrum is allocated at the WRC, national regulatory bodies such as the FCC and can assign specific bands to specific service providers (such as AT&T, Sprint, etc.) through a license for a specific number of years.

To predict the future, you have to understand the past

The focus of this blog is three-fold: (a) to provide a brief summary of the key activities that took place at WRC-15 (b) to give a sneak preview of the upcoming WRC-19 and (c) to analyze the cost and global implications of spectrum for 5G.

Recap from WRC-15

The demand for wireless connectivity and applications on the go is continuously on the rise. The wireless industry requires quick access to frequency spectrum and a lot of it, on a worldwide basis. Back in 2014, the ITU-R predicted that the world would need an additional 1340-1960 MHz for broadband services by 2020. The aim of the world body was to get harmonized spectrum in the range suggested by ITU-R, preferably on a global scale, if not then at least to some extent on the regional basis.

To keep the story short, WRC-15 can be considered as the first major international event that looked into allocating frequency spectrum for 5G. However due to some geopolitical challenges and presence of many existing services, the WRC-15 was only able to allocate 51 MHz for IMT (International Mobile Telecommunications) systems on the worldwide basis. In addition to this 51 MHz allocation which was made in the L-band (1-2 GHz), sizeable additional allocations were made on a regional basis. The total allocation was over 1500 MHz, satisfying the regional requirements for the most part (Table 1).

To clarify, IMT is the flagship project of the ITU-R and covers 3G, 4G and 5G systems. The ITU-R doesn’t allocate spectrum for a specific mobile generation but rather in generic terms of MOBILE and IMT. This capitalization means that the service has been allocated on a primary basis and no other service can interfere in its operations.

In the past, the identification of spectrum as MOBILE for cellular/broadband systems (including 2G) was sufficient. However, the advent of 4G/5G has the brought the concept of IMT systems to the limelight and now even if a service is already allocated for MOBILE, it doesn’t necessarily mean that it can be used for it unless it has been identified as IMT in the footnotes.

Table 1: IMT allocation at WRC-15

Band (MHz) Regions (or parts thereof) * Bandwidth (MHz)
450-470 2 20
470-698 2 & 3 228
694/698-960 1, 2 & 3 (not worldwide) 262
1427-1452 Worldwide 25
1452-1492 2 & 3 40
1492-1518 Worldwide 26
1710-2025 2 315
2110-2200 2 90
2300-2400 2 100
2500-2690 2 190
3300-3400 1, 2 & 3 (not worldwide) 100
3400-3600 1, 2 & 3 (not worldwide) 200
3600-3700 2 100
4800-4990 2 & 3 190

Sources: 5G Mobile Communications: Concepts and Technologies, and the ITU.
*Region 1 comprises of Europe, Africa, the former Soviet Union, Mongolia, and the Middle East west of the Persian Gulf, including Iraq. Region 2 includes Americas including Greenland, and some of the eastern Pacific Islands. Region 3 covers non-FSU (former Soviet Union) east of and including Iran, and most of Oceania.

WRC-15 also identified several bands as study items for their potential usage for IMT. The range covers various bands from 24.25 GHz to 86 GHz. These bands are already providing a number of services particularly backhaul and satellite. The specific services in these bands also can differ by region to some degree. Therefore, spectrum sharing and compatibility studies were required to look at their applicability of co-existence with IMT.

WRC-19 Preview

Before diving into WRC-19 it is worthwhile to look into the work executed by 3GPP in this regard after WRC-15. 3GPP, the flagship organization for 4G and 5G specifications, identified the following two frequency ranges:

  • Frequency Range 1 (FR1): 410 MHz to 6000 MHz with channel bandwidths in the range of 5 to 100 MHz with increments of either 5 or 10 MHz. This frequency range is applicable for both frequency and time division multiplexing modes.
  • Frequency Range 2 (FR2): 24.25 GHz to 52.60 GHz with channel bandwidths of 50, 100, 200 and 400 MHz supporting operations only in time division multiplexing mode.

3GPP focuses more on the nitty gritty of spectrum which has been identified in broad terms by ITU-R. 3GPP works more on the lines of identifying channel bandwidths and duplexing modes to support the underlying mobile services.

In preparations for WRC-19, the ITU-R as per its practice executed the two Conference Preparatory Meeting (CPM) sessions. In February 2019, the ITU-R issued a close to 1,000-page “CPM 19-2” report, designed to assist in preparations for and deliberations at WRC-19. It can be said that hundreds of resources, thousands of workforce hours and millions of dollars have been spent to study the subject frequency range.

The upcoming WRC-19, scheduled to take place later this quarter, has two major tasks when it comes to the allocation for MOBILE/IMT.

First to conclude on the applicability of the identified bands for MOBILE / IMT as required by agenda item 1.13 (Table 2). The CPM 19-2 report forecasted that IMT will require 0.33 GHz to 12 GHz of spectrum in the ranges of 24.25-33.4 GHz, 37-52.6 GHz and 66-86 GHz, depending upon the metrics, assumptions and frequency range. The problem is that all the bands listed in Table 2 are already in use. Further identification for IMT on a primary basis could face stiff opposition particularly from the satellite community at the WRC-19. Opposition from satellite is even more an issue than 2015 as many new players have entered this space, including some deep-pocketed companies like Amazon and Facebook.

Table 2: Applicability of identified bands for MOBILE/IMT (WRC-19 conference prep, Agenda item 1.13)

Band (GHz) Bandwidth (GHz) Key Current Primary Allocation Services Potential Additional Services
24.25 – 27.5 3.25 FIXED, FIXED-SATELLITE,

EARTH EXPLORATION-SATELLITE, MOBILE, INTER-SATELLITE

 Identified by CPM to be used for IMT
31.8 – 33.4 1.6 FIXED, INTER-SATELLITE, SPACE RESEARCH, RADIONAVIGATION Has not been identified by CPM for IMT
37 – 40.5 3.5 FIXED, FIXED-SATELLITE, SPACE RESEARCH, MOBILE, MOBILE-SATELLITE Identified by CPM to be used for IMT .
40.5 – 43.5 3.0

 

 FIXED, FIXED-SATELLITE, BROADCASTING, BROADCASTING-SATELLITE Identified by CPM to be used for IMT
45.5 – 50.2

 

 4.7

 

 FIXED, FIXED-SATELLITE, MOBILE Identified by CPM to be used for IMT
50.4 – 52.6

 

 2.2

 

 FIXED, FIXED-SATELLITE Identified by CPM to be used for IMT
66-76

 

 10 FIXED, FIXED-SATELLITE, BROADCASTING-SATELLITE, MOBILE, MOBILE-SATELLITE, RADIONAVIGATION, RADIONAVIGATION-SATELLITE Identified by CPM to be used for IMT
81-86 5 FIXED, FIXED-SATELLITE Identified by CPM to be used for IMT

Source: ITU (https://www.itu.int/dms_pub/itu-r/opb/act/R-ACT-WRC.12-2015-PDF-E.pdf, and https://www.itu.int/dms_pub/itu-r/opb/act/R-ACT-CPM-2019-PDF-E.pdf)

Second, WRC-19 will need to look into spectrum allocation issues affecting several other big markets as listed in agenda items 1.11, 1.12, 1.14 and 1.16 and their implications on existing and future IMT systems:

  1. Railway radiocommunication systems between train and trackside within existing mobile service allocations – RSTT
  2. Intelligent Transport Systems (ITS) under existing mobile-service allocations
  3. High-altitude Platform Stations (HAPS), within existing fixed-service allocations, and
  4. Radio local area networks (RLAN), in the frequency bands between 5.150 GHz and 5.925 GHz

A brief summary of the key bands under consideration for these services is provided in Table 3 below. There are several bands that are already in use for IMT and thus any allocation to any new service needs to be justified and obtain consensus from administrators.

Table 3: Key bands for RSST, ITS, HAPS & WLAN

Potential Service Key Bands Under Consideration
RSST 138-174, 335.4-470, 703-748, 758-803, 873-925, 918-960, and 1770-1880 MHz; 43.5-45.592 GHz and 92-109.5 GHz
ITS 5850-5925 MHz
HAPS 6.44-6.52, 21.4-22, 24.25-27.5, 27.9-28.2, 31-31.3, 38-39.5, 47.2-47.5 and 47.9-48.2 GHz
RLAN 5150 – 5925 MHz

Source: MTN Consulting


Big battles lie ahead

At this stage, the telecom industry is not close to achieving its target of harmonized, adequate 5G spectrum resources. Basically, there are two camps – one is favored by China and other by the USA. Disagreements are not settled easily at this stage as there is a first mover advantage in the development of mobile wireless generations. The market leader can set the stage for future infrastructure development, product development and specifications. In this context, three ranges of spectrum bands have been considered namely:

• low band (sub 1 GHz) which is used heavily for broadcasting and wireless services.
• mid band (1 GHz to 6 GHz) which is primarily used for wireless services.
• millimeter wave or mmWave (24 GHz to 100 GHz) which is used for many non-mobile services (Table 2)

The battle hovers around the sub 6 GHz and mmWave bands. China is looking towards 3.5 GHz whereas the USA is focusing on multiple millimeter bands. The mid band, particularly the 3.5 GHz band that ranges from 3.3 to 3.8 GHz, is the most sought after band for use as a core band for 5G. That’s because of this band’s availability and lower deployment costs as compared to mmWave bands. China already assigned 200 MHz in this mid band. By contrast Japan and South Korea are working in both mid and mmWave bands. The rest of the world for the most part is playing catch-up on 5G spectrum assignments (Figure 3)

Figure 3: 5G spectrum bands by region

Source: https://www.everythingrf.com/community/5g-frequency-bands

The US faces a unique problem in the mid-band. Namely, the US Department of Defense currently holds roughly 500 MHz in the 4 GHz range and thus it cannot be used for commercial operations. According to a DoD report, the estimated time required to clear spectrum (relocate existing users and systems to other parts of the spectrum) and then release it to the civil sector, either through auction, direct assignment, or other methods could take 10 years. Spectrum sharing between entities is another option and is a slightly faster process, but it could still take five years according to the same DoD report. Thus, the FCC has focused on the mmWave band. It had to auction out 24 GHz and 28 GHz bands and is planning to offer 37, 39 and 47 bands as well in the future. This is one of the key factors behind the limited coverage launches of 5G in USA. Verizon’s 5G network is based on the 28 GHz and 39 GHz bands, AT&T uses 39 GHz, and T-Mobile is planning 28 GHz. Sprint is eyeing the 2.5 GHz band as it doesn’t have any spectrum assets in the mmWave range.

A study conducted by Google for DoD found severe limitations in the mmWave band. It concluded that for the same number of cell sites (macro cell sites and rooftops), 1 Gbps can only be provided to 3.9% coverage area at 28 GHz (US model) as compared to 21.2% at 3.4 GHz (Chinese model). The same study also estimated that it will require approximately 13 million utility pole-mounted 28-GHz base stations (one of the key choices of US operators for mmWave) and $400B in capex to deliver 100 Mbps edge rate at 28 GHz to 72% of the U.S. population, and up to 1 Gbps to approximately 55% of the U.S. population. Figure 4 illustrates the problem, showing the propagation difference between 28 GHz and 3.4 GHz deployments on the same pole height in a relatively flat part of Los Angeles.

Figure 4: Propagation difference in Los Angeles: 28GHz vs 3.4GHz

Source: “The 5G Ecosystem: Risks & Opportunities for DoD,” April 2019.

In a nutshell, mmWave bands will likely have a detrimental impact on operators’ budgets, at a time when they are not eager to ramp up capex. At the end of 2018, Verizon held ~$120B in debt with ~4% dividend yields, while AT&T held ~$175B in debt with over 6% dividend yields. T-Mobile holds ~$25B in debt, and Sprint holds ~$40B in debt. These companies are at the forefront of the U.S. effort to develop 5G, but their balance sheets suggest that they may struggle with the cost of a full mmWave network roll-out and the infrastructure it would require.

Conclusion

The wireless world’s technology leadership role will be at stake at WRC-19. History has proven that having access to the right set of spectrum assets can deliver a competitive advantage in the overall supply chain for years to come. The implications are vast both from the commercial and strategic point of views, impacting governments, operators, vendors, and ultimately jobs.

As of today, the industry lacks harmonized frequency bands for 5G. Perhaps at the end of WRC-19 the world will be closer to achieving this goal.

Stay tuned for more news from MTN Consulting on RF Spectrum and WRC-19!

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*Saad Asif is a Contributing Analyst for MTN Consulting and a recognized industry expert in wireless communications. He has worked in the field of telecommunication for over 21 years, and has authored three books and multiple peer-reviewed technical papers. Saad has been granted multiple patents and is a senior member of the IEEE.

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5G and Data Center-Friendly Transmission Network Architectures

Posted on | by Matt Walker

Introduction

In the last few years the demands from webscale network operators (WNOs, Figure 1) on transmission network architectures have changed considerably. From pure raw capacity requirements and lower costs, webscale players now prioritize highly scalable and advanced point to point bandwidth bundling interface technologies.

Figure 1: List of Webscale Network Operators (WNOs)

Source: MTN Consulting, LLC

Webscale operators’ field of expertise is the data center, and most planned at least initially to rent capacity as leased lines from telcos (or telecommunications network operators, aka TNOs). However, many TNOs did not have the end to end transmission networks able to support webscale needs in terms of capacity, latency, cost objectives. Further, telco networks were not flexible enough to follow rapidly WNOs’ needs for modifications, additions, and changes of the services they needed.

Hence several years ago, WNOs themselves decided to build their own backbone and regional transmission networks, sometimes linking continents. Undersea, the WNOs either leased capacity from existing submarine consortia systems or started to build submarine cables for their own dedicated use. The largest WNOs, such as Microsoft, Facebook and Alphabet, have increasingly favored the latter (self-build) approach. With these initiatives, WNOs seek to have full control of the transmission network, and adequate time to market for their needs.

As webscale players have built out their networks, they have become more influential across the industry.  Their buying power alone is a major reason; Figure 2 shows how webscale operator capex has grown dramatically since 2012, while telco capex has stagnated.

Figure 2: Capex – telco vs webscale (US$B)

Source: MTN Consulting, LLC

At the same time, the telco market is far larger, and the largest integrated telcos spend well over 10% of capex on their transport networks. These telcos are heavily investing in the transformation of their transport networks, and supporting 5G is a central goal.

In the past, mobile services have been sold on the back of convenience of use. With very little considerations beyond coverage and without a capacity objective, there was never a firm commitment to service quality. 5G is probably the first access network with services subject to a wide variety of SLAs, from best effort to non-congested, and very low latency services with limits as low as 1ms. 5G will help operators to move from best effort services for all, to a tiered service level agreement (SLA)-based portfolio. Telcos hope this will help them to be more profitable, at least for the more sophisticated services.

Network slicing poised to play important role

The big change in direction in the strategy of transmission networks is that the planning, design, engineering and operations of a telecom operator will soon be subject to much tighter contracts and commitments.

For years, wild overbooking levels have been the norm, especially for mobile services, and networks were in most cases engineered for coverage alone. This won’t be possible for the next generation of services, which will require more than a 10x increase in bandwidth, and 10x less latency than the current generation.

In addition, webscale operators and large enterprises have demanding network KPI requirements. To serve this market, telcos must develop their transmission network end to end with enough flexibility to satisfy the capacity growth needs and resiliency requirements of these customers.

TNOs and WNOs both accept that the demanding requirements on bandwidth, latency and operational scalability to ensure short time to market for 5G services cannot be supported with existing network architectures.

A potential solution is “network slicing”, which starts with adding more TDM capabilities in the data plane to be able to provide a hard separation in the way services with different KPIs use network resources. This separation is orchestrated by an SDN centralized control and management plane.

Network slicing brings improvements to traffic engineering, with clear KPIs for bandwidth, latency and packet congestion. That helps to support all types of services over the same network infrastructure. Low priority services such as web browsing are effectively separated from network resources dedicated to services with demanding SLAs such as low latency leased lines or 5G inter-vehicle communications.

Operators pursuing FlexO technology to help cope with looming Shannon limit

Historically the main requirements telcos have standardized for transmission network architectures and platforms are high resiliency, powerful operations administration maintenance features, multiservice support, and backwards compatibility with legacy platforms.

This makes a lot of sense as most of the costs of running the network are operational in nature, such as repairs and maintenance. Further, multiservice capabilities can facilitate the migration of legacy services to newer platform. This reduces the need to support overlaid networks, and also avoids the cost of capacity expansions on older platforms at or near their end-of-life (EOL) dates.

In recent years, technological developments have pushed transmission networks towards the limit in the bandwidth per distance product, or the “Shannon limit”. The transmission technology is starting to hit the limits of the fiber medium.

One way to cope with this comes from the ITU, with its Flexible OTN, or FlexO, standard (G.709.1/Y.1331.1). FlexO allows client OTN handoffs above 100Gbps by defining an “OTUCn” modular structure: “an aggregate OTUCn (n ≥ 1) can be transferred using bonded FlexO short-reach interfaces as lower bandwidth elements.” FlexO also supports standard 100GbE optical modules.

FlexO has led telcos to consider how to fully exploit the flexibility of coherent transmission systems, allowing very high capacity transmission on non-regenerated short links, say 400Gbps links over 300Km distances, and lower capacity transmission over longer links, for example 100Gbps over 1500Km distances (figures for illustration only).

FlexO can bundle a number of lower rates at the TDM level to serve a higher capacity service for very long distances. For instance, by using inverse multiplexing or bundling a 400G service interface, capacity could be carried over four 100G links over (for instance) 1500kms without regeneration.

True to their backwards compatible requirements, telcos have made sure that FlexO supports 100G transmission requirements, and is an extension of existing OTN standards. This should simplify the roll out of FlexO on existing platforms.

FlexE to improve utilization, end-end manageability and router-transport connectivity

Operators – both telco & webscale – have also been exploring breakthroughs in the interfaces between transmission systems and servers and routers.

Aligned with FlexO, the Optical Internetworking Forum’s Flexible Ethernet (FlexE) supports similar schemes of bundling and multiplexing of interfaces between routers and transmission systems. FlexE offers a way to transport a range of Ethernet MAC rates whether or not they correspond to existing physical (Ethernet PHY) rates. Network utilization should improve, as should end-end manageability. One key element of FlexE was that Ethernet would grow within a TDM frame. This may pave the way to network slicing through the use of hard boundaries between tranches of services with different SLAs.

Most webscale operators lack an access link to the end user, making them rely heavily on telcos. And smaller webscale players like Netflix rent their clouds from other providers. Maintaining control of the user experience is an uphill battle. FlexO and FlexE help achieve this, in theory. On the UNI side, a WNO transmission network would now use FlexE interfaces with data platforms and servers and storage. On the NNI side, towards the fiber and other transmission systems, the WNO would use FlexO interfaces and standards.

Transmission interoperability improving due in part to the webscale push

Interoperability is something that transport engineers always wish for but never achieve due to network management interfaces’ lack of interoperability. Further, with coherent transmission, there is a problem with transmission interface incompatibility between vendors, each of whom can be more interested in higher performance and features differentiation than simplicity.

The telco response to the interoperability challenge has generally been to achieve subnetwork level interoperability rather than network element interoperability outright.

Things will change, though, as FlexO could be called the first optical standard that thrives on multivendor equipment operations.
Furthermore, webscale operators have designed simple transmission platforms and aimed to use cheap components already available from larger industries. Examples include the use of Ethernet interfaces components at 25G and 50G that were originally proposed for intra data center connectivity and rack cablings between servers and top rack unit switches. These will also be used in 5G base stations and mobile cloud engine platforms that require a transmission network to interconnect.

Conclusions

There is a growing alignment in the requirements for transmission network architectures across telecommunications and webscale network operators. They both need more flexible ways to grow their networks and manage them on an end to end basis. They want to benefit from low cost, open source components and procurement, but adapt technology to suit their customer base. They need to be able to support different classes of service and traffic. Even when providing free services, operators need to deliver a high quality of experience in order to monetize.

5G transport and data center interconnectivity services pose such a challenge to both TNOs and WNOs that work-arounds will not make up for limitations in either the data centers nor the network. For many operators, building a transmission network that supports network slicing principles will require a fresh start and new investments.

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Source of cover image: CommScope.

[Note: a condensed version of this article first appeared at Telecomasia.net.]