Carrier Aggregation (CA) and Dual Connectivity (DC)

This topic keeps coming up every few months with either someone asking me for clarifications or someone asking us to make a video. While I don't think I will mange to get round to making a video sometime soon, there are some excellent resources available that should help a new starter. Here they are in an order I think works best



The first resource that I think also works best is this webinar / training from Award Solutions. It covers this topic well and the image at the top of the post is a god summary for someone who already understands the technology.

It may also help to understand that in the 5G NSA can have 4G carrier aggregation as well as 5G carrier aggregation in addition to dual connectivity.

If you saw the video earlier, you noticed that DC actually came as part of LTE in Release-12. We covered it in our Telecom Infrastructure blog here. NTT Docomo Technical journal had a detailed article on 'Carrier Aggregation Enhancement and Dual Connectivity Promising Higher Throughput and Capacity' that covered DC in a lot more technical detail, albeit from LTE point of view only. The article is available here. A WWRF whitepaper from the same era can also provide more details on LTE Small Cell Enhancement by Dual Connectivity. An archived copy of the paper is available here.

Another fantastic resource is this presentation by Rapeepat Ratasuk and Amitava Ghosh from Mobile Radio Research Lab, Nokia Bell Labs. The presentation is available here and details the MCG (Master Cell Group) Split Bearer and SCG (Secondary Cell Group) Split Bearer, etc. This article from Ericsson also provides more detail on this topic while ShareTechNote takes it one level even deeper with technical details and signalling here and here.

So hopefully this is a good detailed starting point on this topic, until we manage to make a simple video someday.

SCF Releases 5G Functional API to Enable Open Small Cells Ecosystem

The Small Cell Forum (SCF) announced the publication of documents focused on stimulating a competitive ecosystem for vendors of 5G-era small cell hardware, software and equipment. The expanded set of specifications contained in these documents are:

• SCF222 - 5G FAPI: PHY API Specification
• SCF223 - 5G FAPI: RF and Digital Frontend Control API
• SCF224 - 5G FAPI: Network Monitor Mode API

According to the press release:

Expanding upon the 5G Physical Layer API specification, published in July 2019, the new specifications enable small cells to be constructed piece-by-piece using components from different vendors, in order to address the diverse mixture of 5G use cases relatively easily, a common goal to all of the specifications made by Small Cell Forum.

The new release also includes two completely new specifications, SCF223: 5G NR FAPI P19 FrontEnd Interface Specification and SCF224: Network Monitor Mode API for Small Cells.

According to Dr. Prabhakar Chitrapu, Chair of SCF, “FAPI helps Equipment Vendors to mix PHY & MAC Software from different suppliers via this open FAPI interface. So, FAPI is an 'internal' interface.”

“5G-nFAPI (network FAPI) is a 'network' interface and is between a Distributed Unit and Centralised Unit  of a Split RAN/Small Cell network solution. An open specification of this interface (nFAPI) will help network architects by allowing them to mix distributed and central units from different vendors.”

SCF nFAPI is enabling Open RAN ecosystem in its own way by allowing any small cell CU/DU (S-CU / S-DU) to connect to any small cell radio unit (S-RU)

Here is a video playlist from SCF that explains the new API's



Related Posts:

• Telecoms Infrastructure Blog: Small Cell Forum Releases 5G FAPI API Specifications
• The 3G4G Blog: A quick tutorial on Open RAN, vRAN & White Box RAN
• Telecoms Infrastructure Blog: SuperMicro's 5G Pole-Mounted DU Server Solution

Update on UK's Emergency Services Network (ESN) from #BAPCO2019

I have discussed about the UK's Emergency Services Network (ESN) multiple times but I manged to hear about the progress first hand this week. Bryan Clark, ESN Programme Director, Home Office gave a keynote address at BAPCO on Day 2 and the title of his presentation was "2019: The year vision becomes reality"

British APCO or BAPCO Annual Conference and Exhibition 2019 was going to be a big launchpad for the ESN network. The ESN LinkedIn post said "Representatives from ESN and EE will be on hand to discuss coverage and ESN Assure. See an installation of the ESN Gateway solution within a police car, plus a live demonstration showing how ESN coverage can be extended from a vehicle into a building. We’ll also have a ‘Motorola Zone’ where you can watch demos of Kodiak and the ESN self-service portal – and a large touchscreen demo of the Samsung ESN Galaxy"

Bryan started by cracking a joke about people referring to 'ESN' as 'ES When' programme because it has been delayed multiple times. He said straight in the beginning that he going to talk about what the ESN programme is doing now and what comes next.

He started with this short video, embedded below but detailed info available on this LinkedIn post

x

So here is a short summary of the talk:

• There are roughly 350,000 customers of this service
• There are 137 separate organizations that will take advantage of this new this new technology. 
• There are couple of vehicles in the display area (pic on the top and video below) and roughly 50,000 vehicles that need to have a kit
• Over 100 aircraft need to have an air network access that currently isn't there. 
• There are nearly 30 direct suppliers to the program and that doesn't include the whole supply chain through each of those suppliers.
• Looking at the coverage, there is a commitment to providing a signal along half a million (0.5 million) kilometers of roads in England, Scotland & Wales. It extends 12 nautical miles out to sea and 10,000 feet in the air right across England, Scotland & Wales.
• In London alone there are over 400 kilometres of tunnels that were actually almost finished cabling out.
• 300 masts are being built as part of the ESN programme to extend services into remote areas.
• EE has extended their network by adding 700 additional masts. 
• Thousands of special locations will need to have effective access to ESN network
• ESN is a large programme so it's hardly surprising that it's very late. It's Bryan's job over the past 10 months to work out how to get it back on track. 
• People are going through quite a detailed review of where ESN has got to in terms of next steps. 
• The programme now has a very clear and approved plan to complete the technical element of the work, most of it should be done by late summer next year.
• One of the first products, Assure, is a way of testing the effectiveness of the network in the field. 
• A demonstration of Push-To-Talk (PTT) on a 4G network will be demoed within 3 weeks.
• This is the first generation end-to-end solution
• Emergency services is critical national infrastructure so any new solution can only replace the legacy once we are absolutely confident that we've got an effective replacement
• Even though the technical piece is quite challenging, when you compare it to the business change that follows, the technical part looks pretty simple. 
• To ensure that everything works effectively operationally, plans are in place but more detailed plans are going to follow in the coming three to four months.
• Individual components are already being tested in the field
• Programme deployment should start by the end of 2019 in terms of having basically completed laying the core components and a clear plan will be in place for how to test in an operational context. 
• The ESN programme is not only responsible for the replacement solution but also for operations to date based on the Airwave contract with Motorola currently
• The number one priority is to provide critical voice communications of sufficient quality that people can rely on in the field and enable them to move away from the TETRA technology that served them so well. So we aren't going anywhere until we've got rock solid critical voice communications. It's our number one priority, simply because people's lives depend on it.

The following are various videos from the ESN demo area. The Gateway device (which is a mobile small cell) is supplied by Parallel Wireless*.



In case you missed BAPCO, Ken Rehbehn, a very well known Industry Analyst who works as a Principal Analyst at Critical Communications Insights and is also Montgomery County Firefighter/EMT, shared his observations and reflections from conference. Very grateful for his interview which is embedded below



Further Reading:

• Building a new critical communications network that keeps you safe - Bryan Clark, Programme Director, Emergency Services Network

Related posts:

• 3G4G Small Cells Blog: Meshing for BYOC (Bring Your Own Coverage)
• The 3G4G Blog: Quick tutorial on Mobile Network Sharing Options
• The 3G4G Blog: A practical use of MOCN in ESN
• The 3G4G Blog: EE's vision of Ultra-Reliable Emergency Network
• The 3G4G Blog: Update from 3GPP on LTE & 5G Mission Critical Communications

*Full Disclosure: I work for Parallel Wireless as a Senior Director in Strategic Marketing. This blog is maintained in my personal capacity and expresses my own views, not the views of my employer or anyone else. Anyone who knows me well would know this.

5G Top-10 Misconceptions

Here is a video we did a few weeks back to clear the misconceptions about 5G. The list above summarizes the topics covered.



The video is nearly 29 minutes long. If you prefer a shorter version or are bored of hearing me 😜 then a summary version (just over 3 minutes) is in 3G4G tweet below.

Based on the comments received, here is our shorter version of "5G: Top 10 Misconceptions" video #UK5G #HWMBBFhttps://t.co/7lxE3ekDPM

— 3G4G (@3g4gUK) November 21, 2018

The slides can be downloaded from our Slideshare channel as always.

As always, we love your feedback, even when you strongly disagree.

Other interesting recent posts on 5G:

• 5G NR Radio Protocols Overview
• Overview 3GPP 5G NR Physical Layer
• 5G Development and Progress in Singapore
• 5G Network Architecture Options (Updated)
• Automated 4G / 5G HetNet Design
• Optus launching commercial 5G Fixed Wireless Access services in January 2019
• Benefits and Challenges of Applying Device-Level AI to 5G networks
• 5G New Radio Standards and other Presentations
• Base Station Antenna Considerations for 5G
• End-to-end Network Slicing in 5G
• ITU 'Network 2030': Initiative to support Emerging Technologies and Innovation looking beyond 5G advances

Automated 4G / 5G HetNet Design

I recently heard Iris Barcia, COO of Keima speak after nearly 6 years at Cambridge Wireless CWTEC 2018. The last time I heard her, it was part of CW Small Cells SIG, where I used to be a SIG (special interest group) champion. Over the last 6 years, the network planning needs have changed from planning for coverage to planning for capacity from the beginning. This particular point started a little debate that I will cover in another post, but you can sneak a peek here 😉.

Embedded below is the video and presentation. The slides can be downloaded from SlideShare.

Automated HetNet Design from 3G4G

Related posts:

• Twitter et al. for Small Cell Planning
• Radio Challenges and Opportunities for Large Scale Small Cell Deployments
• Summary of Cambridge Wireless Event on Small Cells, 3rd Oct. 2012
• Introduction to Fixed Wireless Access (FWA)
• 5G Network Architecture Options (Updated)

LiFi can be a valuable tool for densification

LiFi has been popping up in the news recently. I blogged about it (as LED-Fi) 10 years back. While the concept has remained the same, many of the limitations associated with the technology has been overcome. One of the companies driving LiFi is Scottish startup called pureLiFi.

I heard Professor Harald Haas at IEEE Glasgow Summit speak about how many of the limitations of LiFi have been overcome in the last few years (see videos below). This is a welcome news as there is a tremendous amount of Visible Light Spectrum that is available for exploitation.

While many discussions on LiFi revolve round its use as access technology, I think the real potential lies in its use as backhaul for densification.

For 5G, when we are looking at small cells, every few hundred meters, probably on streetlights and lamp posts, there is a requirement for alternative backhaul to fiber. Its difficult to run fiber to each and every lamp post. Traditionally, this was solved by microwave solutions but another option available in 5G is Integrated Access and Backhauling (IAB) or Self-backhauling.

A better alternative could be to use LiFi for this backhauling between lamp posts or streetlights. This can help avoid complications with IAB when multiple nodes are close by and also any complications with the technology until it matures. This approach is of course being trialed but as the picture above shows, rural backhaul is just one option.

LiFi is being studied as part of IEEE 802.11bb group as well as its potential is being considered for 5G.

Here is a vieo playlist explaining LiFi technology in detail.




Further reading:

• O2 uses light to transmit data in latest network trial
• IEEE Task Force Works on Standard for Light Communications
• Learn How Li-Fi Works from Its Inventor, Harald Haas
• Light Communications for Wireless Local Area Networking
• LiFi can bring enhanced connectivity to your workspace, while also enhancing data security

Tutorial on Network In a Box (NIB)

Made a short video explaining what Network In a Box is. Slides and video embedded below.

Beginners: Network In a Box (NIB) from 3G4G

Small Cells, Macrocells, Backhaul, Infrastructure and other connectivity solutions from #MWC18

Well, it was officially 3G4G's first Mobile World Congress so I took time to go through the different booths, demos, etc. and compile a small presentation

Our first official #MWC18 thanks to @Parallel_tw. Do wave to @zahidtg when you see him around pic.twitter.com/ETR9oU21z9

— 3G4G (@3g4gUK) February 26, 2018

The presentation (embedded below and can be downloaded from Slideshare) covers the following companies:

Acceleran
Action Technologies
Airspan
Altiostar
Azcom
BaiCells
BravoCom
CBNL
CCS
Ceragon
Comba Telecom
Commscope
Fingu
Gemtek
IP.Access
JMA Wireless
Kleos
MitraStar
NuRAN
Parallel Wireless
Polaris Networks
Qualcomm
Qucell
Raycap
Ruckus
SOLiD
SpiderCloud
Vodafone
Zinwave

Small Cells, Macrocells, Backhaul, Infrastructure and other connectivity solutions from #MWC18 from 3G4G

Do let me know if you found it useful


Related Posts:

• Quick summary of Mobile World Congress 2018 (#MWC18)
• LoRa is quietly marching on...

5G Network Architecture, Design and Optimisation - Jan 2018

Prof. Andy Sutton, Principal Network Architect, Architecture & Strategy, TSO, BT, provided an update on 5G Network Architecture & Design last year which was also the most popular post of 2017 on 3G4G blog. This year again, he has delivered an update on the same topic at IET '5G - State of Play' conference. He has kindly shared the slides (embedded below) that are available to download from Slideshare.

5G Network Architecture, Design and Optimisation from 3G4G

The video of this talk as follows:


There are many valuable insights in this talk and the other talks from this conference. All the videos from the IET conference are available here and they are worth your time.

Related Links:

• [Video] The UK’s first end-to-end 5G network test - EE
• [Video] 5G Network Architecture Options - 3G4G
• [Video] Beginners: 5G Terminology - 3G4G
• 3GPP-VRIF workshop on Virtual Reality Ecosystem & Standards in 5G
• Ultra Reliable Low Latency Communications (URLLC) 2017 Conference summary

Macrocells, Small Cells & Hetnets Tutorial

I blogged about it on the Small Cells blog but cross posting here, just in case you missed it. I am making some videos sharing basic information about mobile technology. Its on YouTube here.

Recently I made some videos looking at all kinds of cellular infrastructure; playlist is embedded below. If you need slides, get it from 3G4G slideshare channel here.

Connecting Rural Scotland using Airmasts and Droneways

This week EE has finally done a press release on what they term as Airmasts (see my blog post here). Back in Nov. last year, Mansoor Hanif, Director of Converged Networks and Innovation BT/EE gave an excellent presentation on connecting rural Scottish Islands using Airmasts and Droneways at the Facebook TIP Summit. Embedded below are the slides and video from that talk.

Driving Connectivity in the Scottish Islands: Droneways and Airmasts from 3G4G

In other related news, AT&T is showing flying COWs (Cell On Wheels) that can transmit LTE signals

Their innovation blog says:

It is designed to beam LTE coverage from the sky to customers on the ground during disasters or big events.
...
Here’s how it works. The drone we tested carries a small cell and antennas. It’s connected to the ground by a thin tether. The tether between the drone and the ground provides a highly secure data connection via fiber and supplies power to the Flying COW, which allows for unlimited flight time.  The Flying COW then uses satellite to transport texts, calls, and data. The Flying COW can operate in extremely remote areas and where wired or wireless infrastructure is not immediately available. Like any drone that we deploy, pilots will monitor and operate the device during use.

Once airborne, the Flying COW provides LTE coverage from the sky to a designated area on the ground.  

Compared to a traditional COW, in certain circumstances, a Flying COW can be easier to deploy due to its small size. We expect it to provide coverage to a larger footprint because it can potentially fly at altitudes over 300 feet— about 500% higher than a traditional COW mast.  

Once operational, the Flying COW could eventually provide coverage to an area up to 40 square miles—about the size of a 100 football fields. We may also deploy multiple Flying COWs to expand the coverage footprint.

Nokia on the other hand has also been showcasing drones and LTE connectivity for public safety at D4G Award event in Dubai

Nokia's Ultra Compact Network provides a standalone LTE network to quickly re-establish connectivity to various mission-critical applications including video-equipped drones. Drones can stream video and other sensor data in real time from the disaster site to a control center, providing inputs such as exact locations where people are stranded and nature of the difficulty of reaching the locations.

Related Posts:

• Flying Small Cells are here...
• Facebook's Attempt to Connect the Unconnected
• An Update from the TIP Summit
• Drone cells are becoming a reality
• When COWs Fly: AT&T Sending LTE Signals from Drones
• Nokia demos drones with LTE connection to conduct rescue operations

Facebook's Attempt to Connect the Unconnected

I am sure that by now everyone is aware of Facebook's attempt to connect the people in rural and remote areas. Back in March they published the State of Connectivity report highlighting that there are still over 4 billion people that are unconnected.

The chart above is very interesting and shows that there are still people who use 2G to access Facebook. Personally, I am not sure if these charts take Wi-Fi into account or not.

In my earlier post in the Small Cells blog, I have made a case for using Small Cells as the best solution for rural & remote coverage. There are a variety of options for power including wind turbines, solar power and even the old fashioned diesel/petrol generators. The main challenge is sometimes the backhaul. To solve this issue Facebook has been working on its drones as a means of providing the backhaul connectivity.

Recently Facebook held its first Telco Infra Project (TIP) Summit in California. The intention was to bring the diverse set of members (over 300 as I write this post) in a room, discuss ideas and ongoing projects.

There were quite a few interesting talks (videos available here). I have embedded the slides and the talk by SK Telecom below but before I that I was to highlight the important point  made by AMN.

As can be seen in the picture above, technology is just one of the challenges in providing rural and remote connectivity. There are other challenges that have to be considered too.

Embedded below is the talk provided by Dr. Alex Jinsung Choi,  CTO, SK Telecom and TIP Chairman and the slides follow that.

View more on edocr

For more info, see:

• TIP Summit 2016
• An update from TIP 2016 summit
• The race to 5G gets a whole lot more social - An interview with Subbu Subramanian, engineering director at Facebook
• Inside Facebook’s First Efforts to Rain Internet from the Sky

Download the TIP slides from here.

5G and Evolution of the Inter-connected Network

While there are many parameters to consider when designing the next generation network, speed is the simplest one to understand and sell to the end user.

Last week, I did a keynote at the International Telecom Sync Forum (ITSF) 2015. As an analyst keynote, I looked at how the networks are evolving and getting more complex, full of interesting options and features available for the operator to decide which ones to select.

There wont just be multiple generations of technologies existing at the same time but there will also be small cells based networks, macro networks, drones and balloons based networks and satellite based networks.

My presentation is embedded below. For any reason, if you want to download it, please fill the form at the bottom of this page and download.

Just after my keynote, I came across this news in Guardian about 'Alphabet and Facebook develop rival secret drone plans'; its an interesting read. As you may be aware Google is actively working with Sri Lanka and Indonesia for providing seamless internet access nationally.

It was nice to hear EE provide the second keynote which focused on 5G. I especially liked this slide which summarised their key 5G research areas. Their presentation is embedded below and available to download from slideshare.

5G: The Future of Mobile Communications - EE from Zahid Ghadialy

The panel discussion was interesting as well. As the conference focused on timing and synchronisation, the questions were on those topics too. I have some of them below, interested to hear your thoughts:

• Who cares about syncing the core? - Everything has moved to packets, the only reason for sync is to coordinate access points in wireless for higher level services. We have multiple options to sync the edge, why bother to sync the core at all?
• We need synchronisation to improve the user’s experience right? - Given the ever improving quality of the time-bases embedded within equipment, what exactly would happen to the user experience if synchronisation collapsed… or is good sync all about operators experience?
• IoT… and the impact on synchronisation- can we afford it? - M2M divisions of network operators make a very small fraction of the operator’s revenue, is that going to change and will it allow the required investment in sync technology that it might require?

HetNets and Ultra Dense Networks

When I did my 5G presentation back in Feb., I explained about Ultra Dense Networks (UDN) that will be a main feature of future traffic hotspots. I have also blogged about Qualcomm having tested 1000 small cells in a square km. Some operators are already running out of spectrum with traditional deployments in hotspots. They are already making their cells smaller (but not yet using Small cells) thereby having less users in each cell. This may not be enough so the approach likely to be taken is:

• Offload to WiFi
• Aggregate WiFi with LTE (different approaches including LTE-U, LAA and LWA)
• Use Small cells and C-RAN
• Multi technology Carrier Aggregation
• Beamforming (and massive MIMO)

The above picture is from a presentation (embedded below) by ZTE in the LTE World Summit. Its a good attempt to show different technologies, the year they are expected to go mainstream, whether they are TDD or FDD and if they will form part of 5G.

Anyway, here is the presentation. There is some interesting information on C-RAN, D-RAN results and fronthaul too.

5G: A 2020 Vision

I had the pleasure of speaking at the CW (Cambridge Wireless) event ‘5G: A Practical Approach’. It was a very interesting event with great speakers. Over the next few weeks, I will hopefully add the presentations from some of the other speakers too.

In fact before the presentation (below), I had a few discussions over the twitter to validate if people agree with my assumptions. For those who use twitter, maybe you may want to have a look at some of these below:

5G is coming, maybe much earlier than you expect it to. There is a race to be first. Come... http://t.co/BQUR5p3bpk pic.twitter.com/z3cOD7Xv2O
— eXplanoTech (@eXplanoTech) January 30, 2015

@disruptivedean @ericsson Re 2% only cellular, I was discussing this the other day. Too many competing techs. pic.twitter.com/Z7s6wqxkBM
— Zahid Ghadialy (@zahidtg) January 26, 2015

Spectrum Bands Summary - Can anyone point me to a better picture? (Cc @open_spectrum @StevenJCrowley @elenaneira) pic.twitter.com/IkBhtQubSj
— Zahid Ghadialy (@zahidtg) January 19, 2015

Anyway, here is the presentation.

 

5G: A 2020 Vision from eXplanoTech

LTE Deployment Dilemma

Earlier this month during our Cambridge Wireless Small Cells SIG event, I presented a small quiz in the final session. The first part of the quiz was titled "LTE Deployment Dilemma" and it generated lots of interesting discussions. After the event, I did a more detailed writeup of that and Cisco has kindly published it in their SP Mobility Blog. Since many people have told me that they cannot anonymously post comments there, I am now bringing it to this blog. I am interested in hearing what others think.

Here is the complete post

LTE Deployment Dilemma from Cisco Service Provider Mobility

3GPP Rel-12 and Future Security Work

Here is the 3GPP presentation from the 9th ETSI Security workshop. Quite a few bits on IMS and IMS Services and also good to see new Authentication algorithm TUAK as an alternative to the widely used Milenage algorithm.

3GPP Rel-12 Security, and Future 3GPP Security Work from Zahid Ghadialy

M2M, Cellular and Small Cells

I have written a post on this topic in the Cisco Service Provide Mobility blog here. The article is embedded as follows:

Feel free to add any comments you may have on the blog post here.

Small Cells Enhancements for 3GPP Release-12

The following presentation is by 3GPP in the not so long ago, Small Cells World Summit 2013.

Enhancements for Small Cells in 3GPP Release-12 from Zahid Ghadialy

Related Post:

• Small cell standardization in 3GPP Release 12

The 'Phantom Cell' concept in LTE-B

One of the LTE-B proposals by NTT Docomo is this 'Phantom Cell' concept. A recent article from the IEEE Communications Magazine expands this further:


Phantom Cell Concept — In the current deployments, there are a number of capacity solutions for indoor environments such as WiFi, femtocells, and in-building cells using distributed antenna systems (DAS). However, there is a lack of capacity solutions for high-traffic outdoor environments that can also support good mobility and connectivity. Thus, we propose the concept of macro-assisted small cells, called the Phantom Cell, as a capacity solution that offers good mobility support while capitalizing on the existing LTE network. In the Phantom Cell concept, the C-plane/U-plane are split as shown in Fig. The C-plane of UE in small cells is provided by a macrocell in a lower frequency band, while for UE in macrocells both the C-plane and U-plane are provided by the serving macrocell in the same way as in the conventional system. On the other hand, the Uplane of UE in small cells is provided by a small cell using a higher frequency band. Hence, these macro-assisted small cells are called Phantom Cells as they are intended to transmit UE-specific signals only, and the radio resource control (RRC) connection procedures between the UE and the Phantom Cell, such as channel establishment and release, are managed by the macrocell.

The Phantom Cells are not conventional cells in the sense that they are not configured with cell specific signals and channels such as cell-ID-specific synchronization signals, cell-specific reference signals (CRS), and broadcast system information. Their visibility to the UE relies on macrocell signaling. The Phantom Cell concept comes with a range of benefits. One important benefit of macro assistance of small cells is that control signaling due to frequent handover between small cells and macrocells and among small cells can be significantly reduced, and connectivity can be maintained even when using small cells and higher frequency bands. In addition, by applying the new carrier type (NCT) that contains no or reduced legacy cell-specific signals, the Phantom Cell is able to provide further benefits such as efficient energy savings, lower interference and hence higher spectral efficiency, and reduction in cellplanning effort for dense small cell deployments.

To establish a network architecture that supports the C/U-plane split, and interworking between the macrocell and Phantom Cell is required. A straightforward solution to achieve this is to support Phantom Cells by using remote radio heads (RRHs) belonging to a single macro eNB. This approach can be referred to as intra-eNB carrier aggregation (CA) using RRHs. However, such a tight CA-based architecture has some drawbacks as it requires single-node operation with low-latency connections (e.g., optical fibers) between the macro and Phantom Cells. Therefore, more flexible network architectures should be investigated to allow for relaxed backhaul requirements between macro and Phantom Cells and to support a distributed node deployment with separated network nodes for each (i.e., inter-eNB CA).