Sunday, 18 September 2016

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.

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:

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:


Anonymous said...

Hello sir.

I would like to comment something. You write in this blogpost:

"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."

If by C-RAN do you mean Cloud RAN and not centralized RAN, then I don't think that the size of the BBUs was ever the reason why the community considered the Cloud RAN architecture at first place. The reason in my view was the cost reduction attributed to the BBU gathering and virtualization, the corresponding statistical multiplexing gains, and the ability to apply coordinated multi-point (CoMP) transmission / reception schemes (well, CoMP technology has its flaws, mainly due to the uncoordinated out-of-cluster interference, but still I think that cooperation is a useful concept).


Zahid Ghadialy said...

News just in - Telcos unite to demonstrate 5G Crosshaul technology

"More than 20 telcos, including Orange, Telecom Italia, Telefónica, Ericsson, Nokia and NEC, have partnered to trial an integrated fronthaul and backhaul technology demonstration..."