5G Fronthaul: Crosshaul & XHaul

I have written about Fronthaul as part of C-RAN in this blog as well as in the Small Cells blog. I am also critical of the C-RAN concept now that the Baseband Units (BBU) have become small enough to go on the cell cite. I have expressed this view openly as can be seen in my tweet below.

Someone finally said it - "Fronthaul is a manmade problem." #CRAN #5G https://t.co/B1uuJqLiQy

— Zahid Ghadialy (@zahidtg) September 1, 2016

While I am critical of the C-RAN approach, there are many vendors and engineers & architects within these vendors who are for or against this technology. I am going to leave the benefits and drawbacks of C-RAN in light of new developments (think Moore's law) for some other day.

The above picture from my earlier post explains the concept of Fronthaul and Backhaul for anyone who may not be aware. As data speeds keep on increasing with 4G, 4.5G, 4.9G, 5G, etc. it makes much more sense to use Fiber for Fronthaul. Dark fiber would be a far better choice than a lit one.

One thing that concerned me was what happens in case of MIMO or massive MIMO in 5G. Would we need multiple Fronthaul/Fibre or just a single one would do. After having some discussions with industry colleagues, looks like a single fiber is enough.

This picture above from an NTT presentation illustrates how WDM (Wavelength Division Multiplexing) can be used to send different light wavelengths over a single fiber thereby avoiding the need to have multiple of these fibers in the fronthaul.

There are 2 different projects ongoing to define 5G Fronthaul & Backhaul.

The first of these is 5G Crosshaul. Their website says:

The 5G-Crosshaul project aims at developing a 5G integrated backhaul and fronthaul transport network enabling a flexible and software-defined reconfiguration of all networking elements in a multi-tenant and service-oriented unified management environment. The 5G-Crosshaul transport network envisioned will consist of high-capacity switches and heterogeneous transmission links (e.g., fibre or wireless optics, high-capacity copper, mmWave) interconnecting Remote Radio Heads, 5GPoAs (e.g., macro and small cells), cloud-processing units (mini data centres), and points-of-presence of the core networks of one or multiple service providers. This transport network will flexibly interconnect distributed 5G radio access and core network functions, hosted on in-network cloud nodes, through the implementation of: (i) a control infrastructure using a unified, abstract network model for control plane integration (Crosshaul Control Infrastructure, XCI); (ii) a unified data plane encompassing innovative high-capacity transmission technologies and novel deterministic-latency switch architectures (Crosshaul Packet Forwarding Element, XFE).

The second is 5G XHaul. Their website says:

5G-XHaul proposes a converged optical and wireless network solution able to flexibly connect Small Cells to the core network. Exploiting user mobility, our solution allows the dynamic allocation of network resources to predicted and actual hotspots. To support these novel concepts, we will develop:

• Dynamically programmable, high capacity, low latency, point-to-multipoint mm-Wave transceivers, cooperating with Sub-6 GHz systems;
• A Time Shared Optical Network offering elastic and fine granular bandwidth allocation, cooperating with advanced passive optical networks;
• A software-defined cognitive control plane, able to forecast traffic demand in time and space, and the ability to reconfigure network components.

The well balanced 5G-XHaul consortium of industrial and research partners with unique expertise and skills across the constituent domains of communication systems and networks will create impact through:

• Developing novel converged optical/wireless architectures and network management algorithms for mobile scenarios;
• Introduce advanced mm-Wave and optical transceivers and control functions;
• Support the development of international standards through technical and technoeconomic contributions.

The differences are summarised in the document below:

5G Crosshaul vs 5G-XHaul from 3G4G

It remains to be seen if C-RAN will play a big role in 5G. If yes how much of Crosshaul and XHaul will help.

Further reading:

• Fronthaul and backhaul: Look out, a fusion is coming! - Alan Carlton, Interdigital
• RAN Evolution Project: Backhaul and Fronthaul Evolution - NGMN
• Examining the fronthaul opportunities for future radio access - Shigeru Kuwano, NTT Access Network Service Systems
• 5 Things You Need to Know About vRAN: “vRAN architecture: centralize or distribute” - Amir Atai, Parallel Wireless
• 5G-XHaul project looks at WDM-PON for mobile fronthaul, backhaul - Lightwave
• Why WDM is essential in C-RAN fronthaul networks? - Ultra high CPRI link capacity - Steve Shin and Dr. Harrison J. Son, Netmanias
• Fronthaul Evolution Toward 5G: Standards and Proof of Concepts

How much spectrum would 5G need?

The above picture is a summary of the spectrum that was agreed to be studied for IMT-2020 (5G). You can read more about that here. I have often seen discussions around how much spectrum would be needed by each operator in total. While its a complex question, we cannot be sure unless 5G is defined completely. There have been some discussions about the requirements which I am listing below. More informed readers please feel free to add your views as comments.

Real Wireless has done some demand analysis on how much spectrum is required for 5G. A report by them for European Commission is due to be published sometime soon. As can be seen in the slide above, one of the use cases is about multi gigabit motorway. If the operators deploy 5G the way they have deployed 4G then 56 GHz of spectrum would be required. If they move to a 100% shared approach where all operators act as MVNO and there is another entity that deploys all infrastcture, including spectrum then the spectrum requirement will go down to 14 GHz.

This is in addition to all the other spectrum for 2G, 3G & 4G that the operator already holds. I have embedded the presentation below and it can be downloaded from here:

The UK Spectrum Policy Forum (UKSPF) recently held a workshop on Frequency bands for 5G, the presentations for which are available to download on the link I provided.

Its going to be a huge challenge to estimate what applications will require how much amount of spectrum and what would be the priority as compared to other applications. mmMagic is one such group looking at spectrum requirements, use cases, new concepts, etc. They have estimated that around 3.1GHz would be required by each operator for 99% reliability. This seems more reasonable. It would be interesting to see how much would operators be willing to spend for such a quantity of spectrum.

Related posts:

• 5G Spectrum Discussions
• Feasibility Study on New Services and Markets Technology Enablers for 5G
• NTT Docomo's 5G Treasure Trove
• Some more thoughts on 5G

Some more thoughts on 5G

5G is often seen as a panacea for everything that is imperfect in mobile technology. Any issues with coverage, capacity, connectivity and speed are all expected to be solved with the arrival of 5G. While I don’t think we will be able to solve all the issues on the table, 5G will hopefully resolve quite a few of them.

Back in June I did an interview with the organizers of 5G World Series where I expressed my views for the questions that were posed to me. You can see this interview below.

Now that I have had time to think about the questions, here are a bit more detailed thoughts. As always, feedback, comments & suggestions welcome


Q: What will network architecture look like in the 5G era?

I have long argued that 5G will not be a single technology but a combination of multiple old and new technologies. You will often find various terms like Multi-stream Aggregation (MSA), Opportunistic Aggregation and Multi-connectivity being used to explain this. Not only will 2G, 3G and 4G have a role to play, Wi-Fi and other unlicensed technologies would be a part of 5G too.

I have had many discussions on this topic with respected analysts and many of them agree.

This #5G chart sums it up. Start from where we are, go in 4 different directions at once, give it all the same name https://t.co/ETldL8Sr8N

— Dan Warren (@TMGB) June 28, 2016

One of the approaches being proposed for the initial version of 5G is the non-standalone version of 5G which will use LTE as the control plane anchor and new 5G radio for user plane. Not only will this be easier to deploy along with the existing LTE network, it would be faster and hopefully less costly.

Related Post: Feasibility Study on New Services and Markets Technology Enablers for 5G

Q: To what extent is 5G dependent on virtualization?

Networks and Network Functions are progressively being virtualized, independently of 5G. Having said that, virtualization will play a big role in achieving the 5G architecture. Mobile operators can’t be expected to keep paying for proprietary hardware; virtualization would help with cost reduction and quick deployments.

Network slicing for instance will help partition the network for different requirements, on the fly depending on what is going on at any particular time.

Related post: 5G, NFV and Network Slicing


Q: What is your view on the interplay between standards and open-source developments?

Standards enable cost reduction by achieving economy of scale whereas open-source development enable innovation and quick deployment. They are both needed and they will willingly or unwillingly co-exist.


Q: What do you see as the 3 greatest technical uncertainties or challenges on route to 5G?

While there are many known and unknown challenges with 5G, some obvious ones that we can see are:

• Spectrum identification and harmonization.
• Getting to the right architecture which is backward compatible and future proof, without making it too complex
• SON – Once you have everything in place you have to make many different parts of the network work together with different kinds of loads and traffic. SON will play a crucial role here.

Q: What would 5G actually mean for consumers, business and IoT? / What will 5G allow me to do that I can’t right now with 4G?

There are a lot of interesting use cases being discussed like remote operations and remote controlled cars but most of them do not represent the general consumers and some of them are just gimmicks.



I really like the NGMN whitepaper that laid out some simple use cases.

If done properly, 5G will allow:

• Simplification of the network resulting in low latency – this means that your content will load faster and the delay between requests and responses are small. 
• Reasonable speed broadband everywhere - This will also depend on the operators’ rollouts plan but different technologies in 5G network would (should) enable a good speed reliable broadband not just in the middle of the cell but also on the edges. In fact, the concept of edges should be looked at in 5G and a solution to avoid data rates falling off should be found.
• Connectivity on the move – Whether we are talking about connectivity in trains/buses or from public safety point of view, it is important to define group connectivity, direct communications, etc.

Q: What will set companies apart in the development of 5G?

The days of vendor lock-ins are over. What will set companies apart is their willingness to be open to working with other companies by having open API’s and interfaces. Operator networks will include solutions from many different vendors. For them to be quick to bring innovative solutions to the market, they need vendors to work together rather than against each other.


Q: There is a lot of talk about the vision for 2020. What do you think the world will look like in terms of connectivity in 2030?

It would be fair to say that by 2030, connectivity would have reached a completely new dimension. One of the big areas of development that is being ignored by mainstream mobile community is the development of satellite communications. There are many low earth orbit (LEO) constellations and high-throughput satellites (HTS) being developed. These LEO and HTS combination can provide high speed connectivity with 4G like latency and high throughputs for planes/ships which cannot be served by ground based mobile technology. Broadband access everywhere will only become a reality with satellite technology complementing mobile technology.

Related Post: The role of satellites in 5G world

Disclaimer: This blog is maintained in my personal capacity and this post expresses my own personal views, not the views of my employer or anyone else. 

Dedicated Core Networks (DCN) for different traffic types

Looking at a paper (embedded below) from NTT Docomo technical journal where they talk about Dedicated Core Network (DCN) for handling different traffic type (M2M/IoT for example). Note that this approach is different from NFV based network sliced architecture. For the latter, the network functions should have been virtualized.

There will be some signalling overhead in the core network to handle the new core and reroute the traffic according destined for the new dedicated core. I would still hope that this would be minuscule in the grand scheme of things. Anyway, let me know what you think about the paper below.

Connected and Autonomous vehicles: Beyond Infotainment and Telematics

An interesting presentation from the recent Cambridge Wireless Future of Wireless International Conference 2016, delivered by David Wong of SMMT. The presentation and video of this talk is embedded below.

You can view many presentations from #FWIC16 at Cambridge Wireless page here and videos here.

3GPP Release-14 & Release-15 update

3GPP is on track for 5G as per a news item on the 3GPP website. In 5G World in London in June, Erik Guttman, 3GPP TSG SA Chairman, and Consultant for Samsung Electronics spoke about progress on Release-14 and Release-15. Here is his presentation.

According to 3GPP:

The latest plenary meeting of the 3GPP Technical Specifications Groups (TSG#72) has agreed on a detailed workplan for Release-15, the first release of 5G specifications.

The plan includes a set of intermediate tasks and check-points (see graphic below) to guide the ongoing studies in the Working Groups. These will get 3GPP in a position to make the next major round of workplan decisions when transitioning from the ongoing studies to the normative phase of the work in December 2016:- the start of SA2 normative work on Next Generation (NexGen) architecture and in March 2017:- the beginning of the RAN Working Group’s specification of the 5G New Radio (NR).

3GPP TSG RAN further agreed that the target NR scope for Release 15 includes support of the following:

• ■ Standalone and Non-Standalone NR operation (with work for both starting in conjunction and running together)
  • ■ Non-standalone NR in this context implies using LTE as control plane anchor. Standalone NR implies full control plane capability for NR.
  • ■ Some potential architecture configuration options are shown in RP-161266 for information and will be analyzed further during the study

• ■ Target usecases: Enhanced Mobile Broadband (eMBB), as well as Low Latency and High Reliability to enable some Ultra-Reliable and Low Latency Communications (URLCC) usecases
• ■ Frequency ranges below 6GHz and above 6GHz

During the discussion at TSG#72 the importance of forward compatibility - in both radio and protocol design - was stressed, as this will be key for phasing-in the necessary features, enabling all identified usecases, in subsequent releases of the 5G specification.


Telecom TV has posted a video interview with Erik Guttman which is embedded below:



Related posts:

• 5G Study Item (SI) for RAN Working Groups Approved
• NTT Docomo's 5G Treasure Trove
• Feasibility Study on New Services and Markets Technology Enablers for 5G
• 5G and Future Technologies from Johannesberg Summit
• Antenna evolution: From 4G to 5G

New whitepaper on Narrowband Internet of Things

Rohde & Schwarz has just published a new whitepaper on Narrowband Internet of Things (NB-IoT).

NB-IoT has been introduced as part of 3GPP Rel-13 where 3GPP has specified a new radio interface. NBIoT is optimized for machine type traffic and is kept as simple as possible in order to reduce device costs and to minimize battery consumption. In addition, it is also adapted to work in difficult radio conditions, which is a frequent operational area for certain machine type communication devices. Although NB-IoT is an independent radio interface, it is tightly connected with LTE, which also shows up in its integration in the current LTE specifications.

The paper contains the necessary technical details including the new channels, new frame and slot structure, new signalling messages including the system information messages, etc. It's a good read.

Its embedded below and can be downloaded from here:

Related posts:

• LTE-M a.k.a. Rel-13 Cellular IoT
• Cellular IoT (CIoT) or LoRa?
• LTE Category-0 low power M2M devices

Antenna evolution: From 4G to 5G

I came across this simple Introduction to Antenna Design videos that many will find useful (including myself) for the basics of Antenna. Its embedded below:


In the recently concluded 5G World 2016, Maximilian Göttl, Senior Director, Research & Development, Mobile Communication Systems, Kathrein gave an interesting presentation on Antenna Evolution, from 4G to 5G. The presentation is embedded below.

Please share your thoughts in this area in the comments section below.

Next Generation SON for 5G

There were quite a few interesting presentations in the recently concluded 5G World conference. One that caught my attention was this presentation by Huawei. SON is often something that is overlooked and is expected to be a part of deployment. The problem is that it is often vendor proprietary and does not work as expected when there is equipment from multiple vendors.

While the 4G SON in theory solves the issues that network face today, 5G SON will have to go much further and work with SDN/NFV and the sliced networks. Its going to be a big challenge and will take many years to get it right.

Here is the Huawei presentation from 5G World:

You may also be interested in:

• My old tutorial: An Introduction to Self-Organizing Networks
• Next Generation SON Free Whitepaper Download by Viavi

Feel free to let me know your thoughts as comments.

Two VoLTE Deployment Case Studies

Back in 2011, I was right in predicting that we will not see VoLTE as early as everyone had predicted. Looking through my twitter archive, I would say I was about right.

As I said earlier, CSFB for now and VoLTE around 2014 - RT @mitchellkp: LTE won't find voice anytime soon http://t.co/mn0EwAw

— Zahid Ghadialy (@zahidtg) September 7, 2011

Soon = before 2015. Ideally, if its working then never, until forced - RT @Gabeuk: I suspect VoLTE adoption will pick-up briskly in 2013.

— Zahid Ghadialy (@zahidtg) July 13, 2011

The big issue with VoLTE has always been the complexity. In a post last year I provided a quote from China Mobile group vice-president Mr.Liu Aili, "VoLTE network deployment is the one of the most difficult project ever, the implementation complexity and workload is unparalleled in history".

From a recent information published by IHS, there will only be 310 million subscribers by end of 2016 and 2020 is when 1 billion subscribers can make use of VoLTE. I think the number will probably be much higher as we will have VoLTE by stealth.

Below are couple of case studies, one from SK Telecom, presented by Chloe(Go-Eun) Lee and other from Henry Wong, CTO Mobile Engineering, Hong Kong Telecom (HKT). Hope you find them informative and useful.