S8HR: Standardization of New VoLTE Roaming Architecture

VoLTE is a very popular topic on this blog. A basic VoLTE document from Anritsu has over 40K views and my summary from last years LTE Voice summit has over 30K views. I assume this is not just due to the complexity of this feature.

When I attended the LTE Voice summit last year, of the many solutions being proposed for roaming, 'Roaming Architecture for Voice over LTE with Local Breakout (RAVEL)' was being touted as the preferred solution, even though many vendors had reservations.

Since then, GSMA has endorsed a new VoLTE roaming architecture, S8HR, as a candidate for VoLTE roaming. Unlike previous architectures, S8HR does not require the deployment of an IMS platform in VPLMN. This is advantageous because it shortens time-to-market and provides services universally without having to depend on the capability of VPLMN.



Telecom Italia has a nice quick summary, reproduced below:

S8HR simplicity, however, is not only its strength but also its weakness, as it is the source of some serious technical issues that will have to be solved. The analysis of these issues is on the Rel13 3GPP agenda for the next months, but may overflow to Rel14. Let’s see what these issues are, more in detail:

Regulatory requirements - S8HR roaming architecture needs to meet all the current regulatory requirements applicable to voice roaming, specifically:

• Support of emergency calls - The issues in this context are several. For example, authenticated emergency calls rely on the existence if an IMS NNI between VPLMN and HPLMN (which S8HR does not provide); conversely, the unauthenticated emergency calls, although technically feasible in S8HR, are allowed only in some Countries subject to the local regulation of VPLMN. Also, for a non-UE-detectable IMS Emergency call, the P-CSCF in the HPLMN needs to be capable of deciding the subsequent action (e.g. translate the dialed number and progress the call or reject it with the indication to set up an emergency call instead), taking the VPLMN ID into account. A configuration of local emergency numbers per Mobile Country Code on P-CSCF may thus be needed.
• ­Support of Lawful Interception (LI) & data retention for inbound roamers in VPLMN -  S8HR offers no solution to the case where interception is required in the VPLMN for inbound roamers. 3GPP is required to define a solution that fulfill such vital regulatory requirement, as done today in circuit switched networks. Of course VPLMN and HPLMN can agree in their bilateral roaming agreement to disable confidentiality protection to support inbound roamer LI but is this practice really viable from a regulatory point of view?

Voice call continuity – The issue is that when the inbound roamers lose the LTE coverage to enter into  a 2G/3G CS area, the Single Radio Voice Call Continuity (SRVCC) should be performed involving the HPLMN in a totally different way than current specification (i.e. without any IMS NNI being deployed).
Coexistence of LBO and S8HR roaming architectures will have to be studied since an operator may need to support both LBO and S8HR VoLTE roaming architecture options for roaming with different operators, on the basis of bilateral agreement and depending on the capability.
Other issues relate to the capability of the home based S-CSCF and TAS (Telephony Application Server) to be made aware about the VPLMN identity for charging purposes and to enable the TAS to subsequently perform communication barring supplementary services. Also, where the roaming user calls a geo-local number (e.g. short code, or premium numbers), the IMS entities in HPLMN must do number resolution to correctly route the call.
From preliminary discussions held at Working Group level in SA2 (architecture) and SA3 (security) in April, it was felt useful to create a new 3GPP Technical Report to perform comprehensive technical analysis on the subject. Thus it is expected that the discussions will continue in the next months until the end of 2015 and will overheat Release 13 agenda due to their commercial and “political” nature. Stay tuned to monitor the progress of the subject or contact the authors for further information!

NTT Docomo also did some trials back in February and got some brilliant results:

In the trials, DOCOMO and KT achieved the world's first high-definition voice and video call with full end-to-end quality of service. Also, DOCOMO and Verizon achieved the world's first transoceanic high-definition VoLTE roaming calls. DOCOMO has existing commercial 3G and 4G roaming relations with Verizon Wireless and KT.

The calls were made on an IP eXchange (IPX) and network equipment to replicate commercial networks. With only two months of preparation, which also proved the technology's feasibility of speedy commercialization, the quality of VoLTE roaming calls using S8HR architecture over both short and long distances was proven to be better than that of existing 3G voice roaming services.

In fact, NTT Docomo has already said based on the survery from GSMA's Network 2020 programme that 80% of the network operators want this to be supported by the standards and 46% of the operators already have a plan to support this.

The architecture has the following technical characteristics:
(1) Bearers for IMS services are established on the S8 reference point, just as LTE data roaming.
(2) All IMS nodes are located at Home Public Land Mobile Network (HPLMN), and all signaling and media traffic for the VoLTE roaming service go through HPLMN.
(3) IMS transactions are performed directly between the terminal and P-CSCF at HPLMN. Accordingly, Visited Public Land Mobile Network (VPLMN) and interconnect networks (IPX/GRX) are not service-aware at the IMS level. The services can only be differentiated by APN or QoS levels.

These three technical features make it possible to provide all IMS services by HPLMN only and to minimize functional addition to VPLMN. As a result, S8HR shortens the time-to-market for VoLTE roaming services.

Figure 2 shows the attach procedure for S8HR VoLTE roaming. From Steps 1 to 3, there is no significant difference from the LTE data roaming attach procedure. In Step 4, HSS sends an update location answer message to MME. In order for the MME to select the PGW in HPLMN (Step 5), the MME must set the information element VPLMN Dynamic Address “Allowed,” which is included in the subscribed data, to “Not Allowed.” In Step 6, the bearer for SIP signaling is created between SGW and PGW with QCI=5. MME sends an attach accept message to the terminal with an IMS Voice over PS Session Support Indication information element, which indicates that VoLTE is supported. The information element is set on the basis of the MME’s internal configuration specifying whether there is a VoLTE roaming agreement to use S8HR. If no agreement exists between two PLMNs, the information element will not be set.

The complete article from the NTT Docomo technical journal is embedded

A tale of two Smart Cities

Over the last few months I heard quite a few talks about Smart Cities. Here are two that I thought its worth posting and a very good TEDx talk at the bottom



I think we all agree that more and more people will move from rural to urban areas and the cities will not only grow in population but also in size. The infrastructure will have to grow to be able to cope with the influx of people and increased demand on services.



I guess in most developed nations we have the 1.0 Era Digital City which is long way away from the 3.0 Era Smart City.



To be a full fledged 3.0 Smart City, every aspect of our life may need to evolve into "Smart". Anyway, here is the complete presentation:

How China Telecom is Shaping the Smart City Concept in China from Zahid Ghadialy

While IoT would be important, access, big data, applications, etc. all will have a role to play.

Milton Keynes Future Cities Conference - March 2015 from Zahid Ghadialy

If you want to find out more about the Milton Keynes smart city, also see this video on Youtube. There are driverless pods and other autonomous cars which may be considered as initial step towards smart cities, see this interesting video here.

Finally here is the TEDx talk about designing these smart cities for future:

LTE-M a.k.a. Rel-13 Cellular IoT

Some months back I wrote about the LTE Category-0 devices here. While Rel-12 LTE Cat 0 devices are a first step in the right direction, they are not enough for small sensor type of devices where long battery life is extremely important. As can be seen in the picture above, this will represent a huge market in 2025.

To cater for this requirement of extremely long battery life, it is proposed that Rel-13 does certain modifications for these low throughput sensor type devices. The main modification would be that the devices will work in 1.4MHz bandwidth only, regardless of the bandwidth of the cell. The UE transmit power will be max of 20dB and the throughput would be further reduced to a maximum of 200kbps.

The presentation, from Cambridge Wireless Future of Wireless International Conference is embedded below:

The IoTopportunity from Zahid Ghadialy

See also:

• LTE Category-0 low power M2M devices

Broadband Access via Integrated Terrestrial & Satellite Systems

Last week I attended an event in the University of Surrey that was about providing high speed connectivity to un-served and under-served areas in future. While there is no arguing that satellites are a great option for unserved areas, the underserved areas can really benefit by such initiatives.

The way this is being proposed is to have a specialised Intelligent User Gateway (IUG) that can connect to ADSL, Mobile and Satellite. The assumption is that in areas of poor conectivity, ADSL can provide 2Mbps and the mobile could do something similar, upto 8Mbps. The satellites can easily do 20Mbps.

Evolution path of Satellite Broadband: 2005: 2 - 3Mbps 2010: 10 - 20 Mbps 2015: 30 - 30 Mbps 2020: roughly 100 Mbps

— Zahid Ghadialy (@zahidtg) June 11, 2015

While the satellite broadband has the advantage of high speeds, they often suffer from high latencies. ADSL on the other hand has very small latency but may not be good enough for streaming kind of applications. Mobile generally falls in between for latency and speed. Using Multipath TCP and some intelligent routing algorithms, decisions can be taken to optimise for latency and speeds.

I did see some impressive demo's in the lab and it did what is says on the tin. The real challenge would be the business models. While ADSL can offer unlimited internet, both Mobile and Satellite broadband will have caps. I was told that limits could be imposed so that once the Mobile/Satellite data allowance is over, only ADSL would be used. Maybe a more complex algorithm could be implemented in future that can include cost and priority of the application/service being used.

An example would be that sometimes I want to watch some long videos over Youtube but I am happy to start buffering an hour in advance. Its not critical that I have to watch that now. I would be more than happy to save my Mobile/Satellite broadband data allowance for some other day when I need to watch things more urgently. If the end of month is coming and I have a lot of data allowance left then maybe I dont mind using the quota otherwise I will anyway lose the allowance. Its always challenging to put this intelligence in the routing decision algorithms though.

Anyway, the combined presentations are embedded below and you can download them from the BATS project page here:

BATS Dissemination Day at University of Surrey - June 2015 from Zahid Ghadialy

Have researchers moved on past 5G on to 6G Wireless?

As I am active on multiple social networks including blogs, twitter, facebook, linkedin, etc., Its always tricky to be able to share information from one on to another. Some time back I tweeted about the 6G research that seems to have started according to an article in FT.

While everyone is focusing on 5G, research has already started on 6G :-) http://t.co/FvxJvXaxXS via @FT pic.twitter.com/g50hYqsnrN

— Zahid Ghadialy (@zahidtg) May 3, 2015

While I had a few retweets and interactions, I realised that its always challenging to search the tweets so I decided to add this in the blog post, always easier to look it up.

So the FT Article states that:

Even as 5G remains a distant prospect for most mobile users, some scientists have already begun to work on plans for 6G services in the future.

To an extent, terms such as 4G and 5G have become as much about marketing equipment as any single technology breakthrough, with incremental improvements to technical specifications often arbitrarily given names such as 3.5G or 4.5G.

But that has not stopped people from thinking about what 6G could look like — and in the UK at least, the prediction is for a “quantum” leap.

Britain has created a “national quantum strategy” to identify areas where advances in technology will have the greatest impact on daily lives in the future. The strategy was developed by the Quantum Technologies Strategic Advisory Board, a government funded agency, which oversees the £270m programme. 

One of the key goals will be the development of faster communications for mobile devices. The advisory board predicts that the market for quantum products and technology has the potential to become a £1bn industry, even if details of how mobile technology can use quantum theory — science at an atomic level — are thin on the ground.

So why did I suddenly think about 6G? Because I have had a few discussions where the research community feel that they should focus on technologies beyond 5G, something that would be a game changer and would change the way we do communications. To be honest, new ways of communications have been found (like LED-Fi / Li-Fi ) but they have not really been ground breaking.

Do you have any ideas or suggestions, add it as comments.

Using 8T8R Antennas for TD-LTE

People often ask at various conferences if TD-LTE is a fad or is it something that will continue to exist along with the FDD networks. TDD networks were a bit tricky to implement in the past due to the necessity for the whole network to be time synchronised to make sure there is no interference. Also, if there was another TDD network in an adjacent band, it would have to be time synchronised with the first network too. In the areas bordering another country where they might have had their own TDD network in this band, it would have to be time synchronised too. This complexity meant that most networks were happy to live with FDD networks.

In 5G networks, at higher frequencies it would also make much more sense to use TDD to estimate the channel accurately. This is because the same channel would be used in downlink and uplink so the downlink channel can be estimated accurately based on the uplink channel condition. Due to small transmit time intervals (TTI's), these channel condition estimation would be quite good. Another advantage of this is that the beam could be formed and directed exactly at the user and it would appear as a null to other users.

This is where 8T8R or 8 Transmit and 8 Receive antennas in the base station can help. The more the antennas, the better and narrower the beam they can create. This can help send more energy to users at the cell edge and hence provide better and more reliable coverage there.  



How do these antennas look like? 8T8R needs 8x Antennas at the Base Station Cell, and this is typically delivered using four X-Polar columns about half wavelength apart. I found the above picture on antenna specialist Quintel's page here, where the four column example is shown right. At spectrum bands such as 2.3GHz, 2.6GHz and 3.5GHz where TD-LTE networks are currently deployed, the antenna width is still practical. Quintel’s webpage also indicates how their technology allows 8T8R to be effectively emulated using only two X-Polar columns thus promising Slimline antenna solutions at lower frequency bands. China Mobile and Huawei have claimed to be the first ones to deploy these four X-Pol column 8T8R antennas. Sprint, USA is another network that has been actively deploying these 8T8R antennas.

There are couple of interesting tweets that show their kit below:

Sprint's John Saw showing of TD-LTE 8T8R and Network Vision. Room for expansion. pic.twitter.com/Mydzasg3F6

— Walt Piecyk (@WaltBTIG) June 23, 2014

Sprint's 8T8R antenna (on left) is actually smaller than 4T2R on 1.9 GHz and 1T2R for 800MHz.(on right) #tdlte $S pic.twitter.com/q26IhZmDie

— Walt Piecyk (@WaltBTIG) June 23, 2014

In fact Sprint has very ambitious plans. The following is from a report in Fierce Wireless:

Sprint's deployment of 8T8R (eight-branch transmit and eight-branch receive) radios in its 2.5 GHz TDD LTE spectrum is resulting in increased data throughput as well as coverage according to a new report from Signals Research. "Thanks to TM8 [transmission mode 8] and 8T8R, we observed meaningful increases in coverage and spectral efficiency, not to mention overall device throughput," Signals said in its executive summary of the report.

The firm said it extensively tested Sprint's network in the Chicago market using Band 41 (2.5 GHz) and Band 25 (1.9 GHz) in April using Accuver's drive test tools and two Galaxy Note Edge smartphones. Signals tested TM8 vs. non-TM8 performance, Band 41 and Band 25 coverage and performance as well as 8T8R receive vs. 2T2R coverage/performance and stand-alone carrier aggregation.

Sprint has been deploying 8T8R radios in its 2.5 GHz footprint, which the company has said will allow its cell sites to send multiple data streams, achieve better signal strength and increase data throughput and coverage without requiring more bandwidth.

The company also has said it will use carrier aggregation technology to combine TD-LTE and FDD-LTE transmission across all of its spectrum bands. In its fourth quarter 2014 earnings call with investors in February, Sprint CEO Marcelo Claure said implementing carrier aggregation across all Sprint spectrum bands means Sprint eventually will be able to deploy 1900 MHz FDD-LTE for uplink and 2.5 GHz TD-LTE for downlink, and ultimately improve the coverage of 2.5 GHz LTE to levels that its 1900 MHz spectrum currently achieves. Carrier aggregation, which is the most well-known and widely used technique of the LTE Advanced standard, bonds together disparate bands of spectrum to create wider channels and produce more capacity and faster speeds.

Alcatel-Lucent has a good article in their TECHzine, an extract from that below:

Field tests on base stations equipped with beamforming and 8T8R technologies confirm the sustainability of the solution. Operators can make the most of transmission (Tx) and receiving (Rx) diversity by adding in Tx and Rx paths at the eNodeB level, and beamforming delivers a direct impact on uplink and downlink performance at the cell edge.

By using 8 receiver paths instead of 2, cell range is increased by a factor of 1.5 – and this difference is emphasized by the fact that the number of sites needed is reduced by nearly 50 per cent. Furthermore, using the beamforming approach in transmission mode generates a specific beam per user which improves the quality of the signal received by the end-user’s device, or user equipment (UE). In fact, steering the radiated energy in a specific direction can reduce interference and improves the radio link, helping enable a better throughput. The orientation of the beam is decided by shifting the phases of the Tx paths based on signal feedback from the UE. This approach can deliver double the cell edge downlink throughput and can increase global average throughput by 65 per cent.

These types of deployments are made possible by using innovative radio heads and antenna solutions.  In traditional deployments, it would require the installation of multiple remote radio heads (RRH) and multiple antennas at the site to reach the same level of performance. The use of an 8T8R RRH and a smart antenna array, comprising 4 cross-polar antennas in a radome, means an 8T8R sector deployment can be done within the same footprint as traditional systems.



Anyone interested in seeing pictures of different 8T8R antennas like the one above, see here. While this page shows Samsung's antennas, you can navigate to equipment from other vendors.

Finally, if you can provide any additional info or feel there is something incorrect, please feel free to let me know via comments below.

Nuggets from Ericsson Mobility Report

Ericsson mobility report 2015 was released last week. Its interesting to see quite a few of these stats on devices, traffic, usage, etc. is getting released around this time. All of these reports are full of useful information and in the old days when I used to work as an analyst, I would spend hours trying to dig into them to find gold. Anyway, some interesting things as follows and report at the end.

The above chart, as expected, data will keep growing but voice will get flatter and maybe go down, if people start moving to VoIP

Interesting chart showing the breakdown of usage from heavy mobile data users to light mobile data users. pic.twitter.com/ew2Z0rWzlZ

— Ben Bajarin (@BenBajarin) June 3, 2015

Application volume shares, based on the data plan. This is interesting. If you are a heavy user, you may be watching a lot of videos and if you are a light user then you are watching just a few of them.

Good chart looking at how device screen size impacts certain mobile tasks more than others. Video mainly. pic.twitter.com/DcuS1rJway

— Ben Bajarin (@BenBajarin) June 3, 2015

How about device sizes, does our behaviour change based on the screen size?

ICYMI: #Ericsson appears to backtrack on 50B connected device vision http://t.co/uLS63BQJ9C #MobilityReport #IoT #M2M pic.twitter.com/YARPqjxpYI

— Mobile World Live (@mobileworldlive) June 3, 2015

What about the 50 Billion connected devices, was it too much? Is the real figure more like 28 billion?

Anyway, the report is embedded below.

'The Future Inter-connected Network' and Timing, Frequency & Phase requirements

I had the pleasure of doing a keynote at PhaseReady 2015 in London today. My presentation is embedded below along with some comments, followed by tweets some of which I think are important to think about. Finally, I have embedded a video by EE and Light Reading which was quoted and maybe its important in the context of this event.

The Future Inter-connected Network from Zahid Ghadialy

My main focus during this presentation has been on how the networks have evolved from 3G days with the main focus (unconsciously) on speeds. While the networks are evolving, they are also getting more complex. The future ecosystem will consist of many Inter-connected (and in many cases inter-operable) networks that will work out the requirements in different situations and adapt to the necessary network(technology) accordingly.

An example of today's networks are like driving a manual car where we have to change gears depending on the traffic, speed required and fuel efficiency. Automatic cars are supposed to optimise this and achieve the best in all different cases. The future inter-connected networks should achieve the best based on the requirements in all different scenarios.

While it is easy to say this in theory, the practical networks will have many challenges to solve, including business and/or technical. The theme of the conference was timing, frequency and phase synchronisation. There are already challenges around them today, with the advanced LTE-A features. These challenges are only going to get bigger.

The following are the tweets from the day:

Finally, here is the link to video referred to in the last tweet. Its from last year but well worth listening.

'5G' talks from Johannesburg Summit 2015

The annual Johannesburg Summit took place May 10th-12th 2015. While it seems like there is a 5G related event every week, most of the events focus on different themes, use cases, applications and possibilities.

While there were some quite futuristic grand visions, there were a few technical presentations that would be a treat to the audience of this blog. I would especially recommend the presentations from Qualcomm and Samsung. Here is a video of all the presentations:


Some of the presentations from this summit, in PDF format are available here.

The path from 4.5G to 5G

In the WiFi Global Congress last week, I heard this interesting talk from an ex-colleague who now works with Huawei. While there were a few interesting things, the one I want to highlight is 4.5G. The readers of this blog will remember that I introduced 4.5G back in June last year and followed it with another post in October when everyone else started using that term and making it complicated.

According to this presentation, 3GPP is looking to create a new brand from Release-13 that will supersede LTE-Advanced (LTE-A). Some of you may remember that the vendor/operator community tried this in the past by introducing LTE-B, LTE-C, etc. for the upcoming releases but they were slapped down by 3GPP. Huawei is calling this Release-13 as 4.5G but it would be re-branded based on what 3GPP comes up with.

Another interesting point are the data rates achieved in the labs, probably more than others. 10.32Gbps in sub-6GHz in a 200MHz bandwidth and 115.20Gbps using a 9.6GHz bandwidth in above 6GHz spectrum. The complete presentation as follows:

Huawei: Paving the Way to 5G from Zahid Ghadialy

Another Huawei presentation that merits inclusion is the one from the last Cambridge Wireless Small Cells SIG event back in February by Egon Schulz. The presentation is embedded below but I want to highlight the different waveforms that being being looked at for 5G. In fact if someone has a list of the waveforms, please feel free to add it in comments

Research challenges in #5G #IEEE #Bangalore #5GTechnologyWorkshop pic.twitter.com/CQhwGfVb8T

— Amod Anandkumar (@amodjaiga) May 22, 2015

The above tweet from a recent IEEE event in Bangalore is another example of showing the research challenges in 5G, including the waveforms. The ones that I can obviously see from above is: FBMC, UFMC, GFDM, NOMA, SCMA, OFDM-opt, f-OFDM.

The presentation as follows:

Huawei: Forward 2020 -> 5G from Zahid Ghadialy