LTE C-RAN / Fronthaul Architectures

Its been a while since I talked about C-RAN on this blog. Meanwhile on the 3G4G blog, a presentation by Orange labs have proved to be very popular. Netmanias have posted couple of slideshares on the C-RAN architecture. They are as follows:

The first one is NTT Docomo's advanced C-RAN architecture. I have posted a presentation on Slideshare as well on this topic. It can be viewed here for more details.

The next one is the Fronthaul and Backhaul architecture by SK Telecom. I have a slideshare on a similar topic by SK Telecom here. In fact a post on 3G4G blog from the iGR whitepaper here is an interesting read on this topic as well.

Small Cells and WiFi Forecast 2012 - 2018

I have been following and having some interesting discussions on a Linkedin group where the main argument is that Small Cells may never really take off as its not a good solution and doesn't make a good business case. I think that kind of discussion is best left to do on Linkedin.

ThinkSmallCell held a webinar recently inviting couple of leading experts to discuss their forecasts for Small cells. The webinar slides and videos are embedded below. Here is a quick comparison of what these independent leading experts had to show:

The main point to note above is that we will hopefully hit 1 million public access small cells probably around/after 2015. My view on why operators have been slow in deploying small cells have been mainly to do with interference management. As we know, Small cells are deployed for Coverage and Capacity and is mainly deployed in Co-channel (same carrier as Macro). If there is no or little coverage, Small cells deployment is not an issue. With higher frequencies, the reception in the houses goes down so deploying Femtocells make sense. With public access small cells, interference (especially on 3G) has to be managed. Surprisingly the practical results for co-channel public access outdoor small cells deployed for capacity purpose is not too bad but there is a no coverage area created as a result of interference at the edge of the small cell. This can cause handover issues.

In LTE-A, Interference techniques like (f)eICIC will help handle these situations so I wont be surprised if there are lots of deployments next year with this interference management capability.

The main thing to note is that WiFi will play a huge part for the connected devices of the future. Most of the small cells deployed with also have a WiFi capability so operators can use that to offload traffic from the cellular on Wi-Fi.

My understanding is that in future we will see Macro cells mainly serve high-mobility connections (including connected cars) and Small cells and WiFi will be used for low mobility and fixed access. I guess the real advantage of cellular over Wi-Fi in this low mobility scenario is that since Wi-Fi is unlicensed, there could be interference from many unpredictable sources. Licensed cellular bands dont generally have this issue.

Anyway, the presentation and video from webinar is embedded below:

Business case for Enterprise Small Cells

In our recent Cambridge Wireless SIG event where we discussed about Enterprise small cells, Simon Saunders from Real Wireless presented a business case on Enterprise small cells. David Chambers from ThinkSmallCell has also written an excellent summary that is available here.

The presentation from Real wireless is embedded below. A more detailed study from Small cell forum is available on Scf.Io here.

Enterprise Small Cells: The Business Case from Zahid Ghadialy

Quortus: Evolving architectures for Small Cells in the Enterprise

Continuing on our theme of Enterprise Small cells, here is slightly old presentation by Quortus from the Small Cell World Summit 2013

An Introduction to 'Enterprise Small Cells'

A nice presentation by David Chambers from ThinkSmallCell summarising Enterprise Small Cells from our recent Cambridge Wireless event 'Small Cells and the Enterprise'

Enterprise Small Cells from Zahid Ghadialy

Dual-connectivity, Bearer split and other Release-12 small cell enhancements

3GPP TR 36.842 has some interesting details on the small cells enhancements for Release-12. There is too much details for me to go through at the moment but there is some discussions. One of them is on the Dual connectivity and another is Bearer split. The concept of Master eNB (MeNB) and Secondary eNB (SeNB) seems to have been introduced. Here are some interesting definitions:

Bearer Split: in dual connectivity, refers to the ability to split a bearer over multiple eNBs.

Dual Connectivity: Operation where a given UE consumes radio resources provided by at least two different network points (Master and Secondary eNBs) connected with non-ideal backhaul while in RRC_CONNECTED.

Master Cell Group: the group of the serving cells associated with the MeNB.

Master eNB: in dual connectivity, the eNB which terminates at least S1-MME and therefore act as mobility anchor towards the CN.

Secondary Cell Group: the group of the serving cells associated with the SeNB.

Secondary eNB: in dual connectivity, an eNB providing additional radio resources for the UE, which is not the Master eNB.

Xn: interface between MeNB and SeNB. Since the current E-UTRAN architecture was selected as baseline in this study, Xn in this TR means X2.

There is also the concept of RRC diversity which can help mobility. as per 36.842

RRC diversity is a potential solution for improving mobility robustness. With RRC diversity, the handover related RRC signalling could additionally be transmitted from or to a potential target cell as illustrated in Figure 7.1.3-1.  RLF could in this case be prevented as long as the UE is able to maintain a connection to at least one of the cells.  This will eventually lead to a more successful handover performance (i.e. avoiding UE RRC re-establishment procedure). The RRC diversity scheme could also be applied for handovers from the macro to pico cells, between macro or between pico cells.

Finally, the security aspects for this Bearer split and dual connectivity is also being discussed. See the latest Rel-12 security update here.

Carrier Wi-Fi: Automatic handovers in the next generation Wi-Fi

Ericsson published a paper in their journal last month about how the next generation of Wi-Fi and its integration in the 3GPP core would help moving between Wi-Fi networks and the Cellular network seamlessly.

People who read the 3G4G blog regularly would know that this is done using the Access Network Discovery and Selection Function (ANDSF). For details see here.

Another post from the 3G4G blog explains the key challenges in moving between the Cellular and Wi-Fi technology. If not done properly, the QoE can be really off putting for the end user.

The Ericsson paper highlights the following as the top-three priorities for the next generation carrier Wi-Fi:

• Traffic steering 3GPP/Wi-Fi – to maintain optimal selection of an access network so quality of experience can be ensured and data throughput maintained;
• Authentication – to provide radio-access network security for both SIM- and non-SIM-based devices; and
• DPI, support for unified billing and support for seamless handover – achieved by integrating with the core infrastructure already deployed for 3GPP access.

3GPP has been working extensively in the new releases to come up with new features that would solve some of the issues and limitations that is affecting widespread deployment of carrier Wi-Fi and seamless roaming between the different technologies. Sometime back I provided the list of the features that are being released as part of different 3GPP releases, available here.

The Ericsson paper is available on Slideshare, embedded below:

More details on NTT Docomo's Xi Femtocell

Japanese operator, NTT Docomo recently published some more details about its Xi Femtocell service. The Femtocell is a dual mode LTE-WCDMA femtocell. WCDMA is mainly used as a CS Fallback option when used with LTE device. In this case if the WCDMA part stops working for some reason then depending on the macro availability, it may hand the UE back to Macro or just keep using the LTE only service.

I could not completely figure out but it also looks like the Femtocell operates in co-channel with the Macro. During the power on, SON algorithms device the codes, the power of the femtocell, etc.

The complete article is embedded below:

W-CDMA/LTE dual-mode Ultra-compact Base Station (Xi Femtocell) from Zahid Ghadialy

Enterprise Small Cells - Small Cell Forum Release Two

The long awaited "Release Two" from the Small Cell Forum is finally here.



Gordon Mansfield is explaining this Release two in the video above.

Small Cell Forum (SCF) also released a Small cell market update. As per the market report, as of October 2013, there were:

• 7.2 million residential femtocells deployed
• 168,000 indoor small cells deployed
• 2,700 outdoor small cells deployed

There is a good summary of this Release on ThinkSmallCell and TMN. Definitely worth a read.

There are a lot of documents released or revised as part of Release-2. You can access all the Enterprise related documents at http://www.scf.io/en/use_case_documents/Enterprise.php. You can also start with just the overview document at http://www.scf.io/en/documents/102_-_Release_Two_-_Enterprise_Overview.php

Finally, for more technical minded people, they can directly jump to the Enterprise small cell network architectures document at http://scf.io/en/documents/067_-_Enterprise_small_cell_network_architectures.php

LTE-U: First step towards 'Operator-neutral' Small Cells

3GPP member companies have decided to take the Small Cells vs WiFi fight back into the Wi-Fi camp by unveiling the initiative to have LTE in the unlicensed band (officially known as LTE-U but another interesting term uLTEA has been proposed unofficially too). 

Mike Roberts wrote an interesting post on ITM Blog:

Qualcomm has launched a radical initiative to deploy LTE Advanced in the unlicensed 5GHz band, which has traditionally been the preserve of Wi-Fi devices. If the initiative gains support, it could be a hammer blow to carrier Wi-Fi, though Qualcomm says it is still a strong supporter of all types of Wi-Fi, given its Qualcomm Atheros division, which is a leading producer of Wi-Fi chipsets. 

Qualcomm CEO Paul Jacobs unveiled the company’s initiative for LTE Advanced in unlicensed spectrum at its financial-analyst day in New York on Nov. 20. It was interesting timing, considering that the main annual carrier Wi-Fi event, the Wireless Broadband Alliance’s Wi-Fi Global Congress, was taking place on the same day on the other side of the world, in Beijing. 

The chipset giant followed the announcement by its CEO with detailed presentations on the initiative at Informa’s LTE North America event in Dallas on Nov. 21-22. The essence of Qualcomm’s proposal is that it is complicated to integrate LTE and Wi-Fi to create carrier Wi-Fi, so a better option could be to use LTE Advanced to extend LTE into unlicensed spectrum, thus eliminating the need for Wi-Fi in that context....So how does Qualcomm plan to square this circle and offer reliable mobile services in unreliable unlicensed spectrum? By using LTE Advanced to create a hybrid system operating in both licensed and unlicensed spectrum at the same time. Specifically, Qualcomm is proposing a system that uses the carrier-aggregation (CA) feature of LTE Advanced to aggregate licensed LTE spectrum with unlicensed spectrum in the 5GHz band. The unlicensed spectrum, which would be aggregated with licensed spectrum on the downlink only, would only be used for data services. The licensed spectrum would be used for uplink and downlink and would support network control as well as voice and data services. Given the power limits placed on devices using the unlicensed 5GHz band, uLTEA would be used mainly in small cells, similar to Wi-Fi.

'All about 4G' did a good quick write-up on this topic from standards perspective, as follows:

Qualcomm has recently floated the idea of deploying LTE in unlicensed bands, particularly focusing on the 5GHz band, which is currently used mostly for WiFi. According to a document (RP-131635) submitted to the upcoming 3GPP plenary meeting, the proposal is to deploy LTE as Supplemental Downlink (SDL) in 5725-5850 MHz in USA, with the PCell (Primary Cell) always operating on a carrier in a licensed band. Verizon has also submitted a Work Item Proposal (RP-131680) to to introduce the new band for SDL usage. There’s also a Study Item proposal from Ericsson (RP-131788) is the rapporteur to study the modifications necessary to the LTE radio.

One of the big issue (though small cell vendors often play it down) that has been delaying the rollout of Small Cells has been interference management in co-channel deployment cases. The operators are worried about ad-hoc small cells creating interference with the properly planned and optimized Macro cells (though in practice its not as bad as they think it is). With LTE-U, this issue can be put to rest.

I can see LTE-U, if adopted, can also help create new business models around Small cells. Neutral Small cells, deployed in the hotspots like stadiums, shopping malls, etc. can serve users of all networks. The signalling can take care of each user connecting to its own network using backhaul.

Femto as a Service (FaaS) and Small Cells as a Service (SCaaS) would probably become a common approach as there would be no concerns about which spectrum is being used. 

There would be a small concern about interference between Wi-Fi and Small cells. Most of the existing Wi-Fi and other devices that use unlicensed spectrum use the 2.4GHz band with a few using 5GHz band now. If LTE-U uses the 'Listen Before Talk' approach, other technologies can be enhanced to probably do the same. Another thing worth remembering is that there is nearly 300MHz of spectrum in 5GHz band available universally. In certain countries the available spectrum can be as much as 500MHz. This should be enough for LTE-U as well as other technologies in the unlicensed spectrum.

The complete Qualcomm presentation is embedded below and is available to download from here: