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Here’s a thought concerning mobile power consumption in UMTS networks: In the uplink transmission direction, the power required to send data to the network depends on the amount of noise present in the channel. The more noise, i.e. the more other users are transmitting data to the cell at the same time, the higher the required power to send your data. That means that if there is a lot of activity from other people in the neighborhood, your own battery consumption increases when you transfer data yourself.  That doesn’t necessarily mean this has a significant impact on autonomy time but it should be measurable. Also, it should be taken into account that other factors have a similar or even bigger impact on uplink power requirements, e.g. if coverage is weak at the location where a mobile device is most of the time. But the idea remains: It’s not only you that decides how much power your device uses for communicating with the network.

At the recent CES a number of companies seem to have shown the first CDMA/LTE smartphones to be launched at some point later in the year. From a telecoms point of view the interesting thing is how these phones will do voice calls while connected to an LTE network. The issue here is that LTE doesn’t have a built in voice service like GSM and UMTS. While most of the press mostly commented around the design, screen size, processor and other features, this topic was completely overlooked.

Steve, over at the Voice over LTE blog, however, comes up with some interesting answers on how voice service is implemented. According to his post, these LTE phones will be connected to LTE and the CDMA network simultaneously so IP based traffic can use the LTE network while voice calls and text messages can be handled simultaneously by the CDMA network.

From a 3GPP GSM/UMTS engineer’s point of view this is, well, lets say, outmost sub-optimal. In the world of GSM and UMTS a lot of care is taken that voice calls and data sessions can move seamlessly between the two technologies. Ongoing calls will be handed over between the technologies when running out of UMTS coverage, for example, and the IP address and session contexts will also be preserved when hopping between the two radio networks. Voice and IP services even run concurrently, something that doesn’t work in the CDMA world at all. For LTE, the same mechanisms have been standardized for IP sessions and a number of different solutions exist to hand over ongoing LTE voice calls to GSM and UMTS.

So why are those phones not using these solutions? For one thing, they are designed for CDMA 2.5 / 3G network operators and from what I can tell they can’t use CS fallback, because that’s specified for fallback to GSM and UMTS only (please correct me if I’m wrong here). Also, Voice over LTE via GAN (VOLGA) is not an option for them as it is based on GSM and UMTS technology. That leaves them with VoLTE, which is an IMS solution with a specified feature set. Talked about in the industry for pretty much a decade it’s still nowhere to be seen and the announcement of dual-active-radio phones for LTE indicates that showtime for that technology won’t be anytime soon. Hence, their move to dual-active-radio phones.

Apart from the opinion of a 3GPP engineer, is a dual-active-radio device a solution that the customer could like? After all, the customer isn’t interested in sleek designs under the hood, but whether the device works well or not. So from my point of view, I as a customer want my smartphone to do two major things: It has to provide me with a highly reliable voice service anytime, anywhere and it has to provide me with a fast and reliable Internet connectivity for my IP based applications such as email, web browsing, Twitter, etc. etc.

So the question is, will those dual-active-radio phones provide that? From what I can tell the answer is yes, with some restrictions. The first one is the potentially higher power requirements to keep two radios listening to two networks at the same time. However, if I get a full day of use out of the device then I, as a user, don’t care to how many networks the device is connected to simultaneously. If those devices can do that is something yet to be seen. Secondly, voice service. Yes, the CDMA network layer provides that and as the radio is turned on all the time, my voice service in terms of availability and call setup time should be in the same ballpark as current 2G/3G phones. Furthermore, I wonder if the first generation of the CDMA/LTE networks and the devices themselves can switch the IP context  between the different networks. If not, then applications will loose their connection to the network every time a switch between LTE and CDMA is done for data services.

Loosing the IP context between CDMA and LTE might come in as a big argument against such a solution. But is it really an issue? Today, most smartphones can use both 3G and Wi-Fi for internet connectivity and automatically switch between the two radio technologies. Here, IP connectivity is also lost and applications have to re-connect to their server on the Internet each time the switch it made. Not very pretty from a design point of view but it seems to work in practice already today without anyone loudly complaining.

Oh, yes, and before I receive some comments on the Skype implementation on the phones that was reported, yes, I’ve seen that, too and I very much like it as an added goodie. However, I’d never rely on it as my main telephony service for a number of reasons. The most important one is that I often make calls while moving and often implicitly use, what I  think is the network operators biggest asset, the capability to hand over ongoing calls from 3G to 2G.

I find the thought around Wi-Fi very interesting. In effect, if the IP context can’t be taken over from LTE to CDMA, then the LTE network can be seen to do the same thing Wi-Fi already does today in 3G phones. So instead of having only a Wi-Fi chip, LTE smartphones have an LTE chip in addition that can also provide IP connectivity. And that, I think, is a crucial point in the discussion and way of thinking of whether it’s a good idea to have dual-active-radio LTE phones, which in fact will be triple-active-radio phones, as Wi-Fi is switched on all the time as well.

So the final train of thought for this post is whether this approach could and should work in the GSM and UMTS world as well!? Let’s first look at the “should”. From what I can tell, CDMA operators are keen on launching LTE because they depend on it as an upgrade path from their CDMA network technology that is not evolving anymore and is capable, from what I hear, to deliver around 1.5 MBit/s but not much more. Also, from a capacity point of view, it’s much more limited to what’s currently going on in UTMS networks. On the UMTS front, there’s a healthy evolution program in place. Many networks are already upgraded for speeds up to 7.2 or 14.4 MBit/s in the downlink, with 21 MBit/s in the downlink and dual-carrier 42 MBit/s on the way to reality. Also, network capacity keeps rising with more advanced devices coming to the market all the time that make better use of the resources, use of several carriers and densification of the network, all while preserving backwards compatibility with GSM and concurrent voice and IP based operation. So why go for the compromises of a GSM/UTMS/LTE phone that has to have two radios switched on at the same time? You can have it all on the evolution of UMTS for smartphones, while LTE is being used for non-voice devices such as netbooks, LTE USB sticks, pad computers, etc. For me, a GSM/UMTS/LTE phone only makes sense once voice over LTE works as good as voice over GSM/UMTS, including, and that’s most important, handover to GSM and UMTS. As an operator, anything less doesn’t cut it, Skype and others are here today. Whether an operator bets on IMS VoLTE or VOLGA, or a combination of both will be sorted out by competition.

And finally for today the “could” part. Running GSM/UMTS and LTE separately at the same time is going to be a bit of an engineering challenge. As per design, a single SIM card can only supply the credentials to be active in one radio network at the same time. So to be active in GSM and LTE at the same time would require two IMSIs (International Mobile Subscriber Identities). You can’t do that with standard SIM cards today. Of course one could think about solutions such as one SIM card having two IMSIs and two secret keys but why work on this when the real issue is to have Voice on LTE with seamless interworking with GSM and UMTS?

In summary, I think the answer for CDMA networks is to have dual-active-radio CDMA / LTE phones until they’ve got the voice question solved as they don’t have many other alternatives to evolve their networks and live with the downsides for the moment. For UMTS network operators, I think the equation is different as the strong evolution path of UMTS and using LTE for non-voice centric devices makes dual-active-radio designs not very attractive.

For those who travel the world a lot and don't have endlessly deep pockets, finding ways to economize spending for international calls and getting Internet access on the move is essential. Over the years I learnt a lot of tricks and at some point started the Prepaid Wireless Internet Wiki to share my information on getting local SIM cards for Internet access. The site has been quite successful and in the meantime many people contribute. 

But local SIM cards are only one piece of the puzzle. There are lots of other things one can do besides and on top of this but I never had the courage to write all that stuff down. Now Andrew Grill over at London Calling has done it and it's a great guide in 2 parts (here and here) on how to save on communication costs when traveling. Very well done, I don't have much to ad to it, except perhaps rebtel.com which I use frequently to make International calls from my mobile phone while in my home country.

O.k., the winter chaos in Europe has gotten to me as well and I was stuck in various places waiting for planes and trains like many others. So while the situation was far from comfortable I noticed that being connected and being able to get information from online sources not only proved to be entertaining and useful, as I could get some work done while waiting but also helped to keep my mood up. Here are some things I noticed:

Congestion: In airport lounges, free Wi-Fi is sometimes provided, but it is usually quite congested and slow due to many people using it at once. Good when one has a 3G dongle and can make oneself independent from the rest.

Flight Status: Flight status reports are not accurate at all, neither online nor at the airport. It's interesting to observe that a flight status on airport information displays and also online is marked as "on schedule" until just one hour before departure when it then suddenly changes to indicate a two hour delay. I wonder why this is done that way as airlines do know better!?

In my case for example, the plane that would take me to Frankfurt was coming from Frankfurt in the first place. Online, the delay for that plane was visible while for the outgoing leg the flight status remained "on schedule". Most people have better things to do than to spend time at the airport when a delay of several hours that is clearly predictable would allow them to do something else in the city. So perhaps the airlines want you at the airport so they can judge who shows up for a flight and who doesn't!? In the age of email, twitter, instant messengers and other methods to stay connected, even automatically, it's an archaic way of organization.

Abnormal situations also reveal how flight status displays at airports are working. The system used at Istanbul airport, for example, is not updated in real-time at all. For my flight, which was 3 hours late, somebody forgot to update the system so at the "theoretically correct time" the display showed "boarding" and then "final call". Very nice, except there was no plane at the gate to board and no ground personnel to inform people of what was going on. Quite a confusion. Once the theoretical time for "final call" was over the display went blank, still no plane and still no ground crew at the gate. You can imagine the confusion. Unless, of course, the online information on your mobile device from your airline tells you the real story.

Getting a Hotel at Midnight: And the best use of mobile Internet connectivity is when you are stuck at the airport, figure out from the online schedule of the train company that the last train home has just left despite a massive delay and you start wondering how and where you'll spend the night. Hundreds of people are around you with the same problem and the picture of camp beds in a big hall springs to mind. But your online hotel reservation system tells you that there are many hotel rooms close to the airport still available. It could be just as fake as the online schedule displays but a call to one of the hotels quickly revealed that rooms were indeed still available. Interestingly enough, the hotels shown did not take advantage of the situation but offered the standard rates per room. Much better than spending the night at the airport.

Stay in bed longer: And finally, the next morning your mobile is your best friend when it tells you that the train you want to take home is either on time or delayed, so you know it's worth getting out of bed or if there is no real rush to get up.

Entertainment and connectivity: And all the while it also plays your favourite music, keeps you informed about what's going on in the rest of the world and you can call people back home and wished your travels were as quick and easy as that of those electrons and waves that carry your voice through the maze we call a telecommunication network.

Are you already back from vacation? If so, you might want to have a look at the program of the Mobilware 2011 conference being held in London this year from the 22nd to the 24th of June. As you'll see in the scope and topics overview below it's about advances in communication middleware, mobile operating systems, networking protocols and applications. So just my thing 🙂

The call for paper ends February the 1st, so if you have an interesting paper to propose, you have a couple of weeks from now to send your proposal. It would be great to see you there!

Conference Scope

The advances in wireless communication technologies and the proliferation of mobile devices have enabled the realization of intelligent environments for people to communicate with each other, interact with information-processing devices, and receive a wide range of mobile wireless services through various types of networks and systems everywhere, anytime. A key enabler of these pervasive and ubiquitous connectivity environments is the advancement of software technology in various communication sectors, ranging from communication middleware and operating systems to networking protocols and applications.

Topics

The conference solicits original technical papers, not previously published and not currently under review for publication elsewhere. Topics of interest include but are not limited to:

• New middleware concepts for mobile devices
• Cross platform application development
• Open terminal and network APIs
• End-to-end architectures for seamless service provisioning and deployment
• Integration of heterogeneous wired and wireless networks and frequency bands
• Interworking of mobile applications in mobile cloud environments
• QoS awareness, adaptation, and fault-tolerance of mobile services
• Opportunistic and delay-tolerant mobile and wireless networking
• Location-aware and context-aware networking and computing
• Energy-efficient applications and services and OS air interface management
• Mobility and handoff management
• Location and tracking supports and services
• Human-computer interface and portable 3D graphics for mobile devices
• Novel applications and communication protocols for wireless sensor networks, vehicular networks, and home networks
• Modeling, simulation, and performance evaluation of mobile wireless systems and services
• Trustworthiness, security, and privacy of mobile and wireless systems

An interesting but probably not well known functionality of the SMS system are delivery reports. By default, requesting delivery reports is usually deactivated in the mobile device, so few people know about it. On Symbian phones, delivery reports can be activated in the SMS settings. Once active, the SMS Service Center sends a report back to the originator as soon as an SMS has been delivered, which is then displayed for a couple of seconds on the screen and also put into the "Delivery Reports" folder in the SMS application. So while this feature works well for SMS messages to other subscribers of the home network, I was wondering if it also worked when sending messages to other networks, both national and international?

The quick answer is yes. I tested this by sending an SMS to a SIM card of another national network operator and to SIM cards from network operators in Italy, Spain, and for the ultimate test, Thailand. To ensure the delivery report is not only sent in some cases once the SMS is received at the service center I only switched on the phone with the respective SIM a couple of minutes after the SMS was sent. In all cases the delivery report came in right after the SMS was delivered, i.e. right after the phone was switched-on and the SMS was delivered.

So in other words, SMS delivery notifications work even for international SMS transfers.

Back in 2006, I published my first book in English (Communication Systems for the Mobile Information Society) on the different network technologies available at the time (GSM, GPRS, UMTS, WiMAX, Wi-Fi and Bluetooth). I've been more than pleased with the success and the feedback I got over the years. But things have certainly moved on since then so it was about time to release a second edition.

And things have progressed well, the second edition, now titled "From GSM to LTE – An Introduction to Mobile Networks and Mobile Broadband" is almost ready for shipping. I'm enormously happy I've finally managed to do it because a lot of things have changed in the past 5 years. Consequently a lot of additional material made it into the new edition:

In the chapter on GSM, I've included up-to-date information on the MSC R4 Bearer Independent Core Network architecture to which many network operators have migrated their circuit switched voice and SMS infrastructure over the last few years or are in the process of doing so. Little has changed in the GPRS/EDGE chapter but the UMTS chapter has been almost a complete rewrite. 5 years ago, 3GPP Release 99 with its dedicated channels was state of the art and HSDPA was just on the horizon (but already described in the book). In the second edition, I rewrote the chapter to put HSDPA and HSUPA in the focus instead of R99 dedicated channels, which are nowadays only used for voice and video calls.

And then of course, LTE is a must, so I've added a full new chapter that gives a solid intro to the new radio access technology and the new core network architecture and its interfaces to various other network technologies (GSM, UMTS, CDMA). The book then goes on and has a look at WiMAX, where not a lot has changed since the last edition. Some significant additions can be found in the Wi-Fi chapter, with new material on 802.11n, Wireless Multi Media (WMM), significant additions to the security section, etc. etc. And finally in the Chapter on Bluetooth I brought the text up to date with enhancements such as the new pairing variants.

As you can see, the updates are plentiful and it has kept me quite busy in the last couple of months. So if you are looking for one single resource that gives you a solid introduction to all these technologies, then this is the book for you! At the moment it's listed on Amazon for pre-order and it should become available in the next two weeks. And should you attend the Mobile World Congress in Barcelona in February and can wait a bit longer, you can certainly pick up a copy from the Wiley booth there as well. I'll be there on one of the days as well so make sure you'll come by in any case! More details on that later.

A friend recently commented that Apple doesn't seem to be active in 3GPP (but they are a member), the standardization body responsible for the development and evolution of GSM, UMTS and LTE. That is an interesting observation as not participating at 3GPP meetings means they don't have much of a say in future advances of the cellular radio interface and so perhaps see cellular connectivity pretty much as a commodity for their business in a similar way as Wi-Fi and Bluetooth. What about HTC, how active are they in 3GPP? Any others, that could potentially be in the same category? And yet another question on this subject, which standards bodies is Apple active in?

Recently, I've been to Istanbul and as I've never been in Turkey before I was quite interested to see how well the mobile networks would perform there. After all, 3G only started in Turkey in late 2008 so they haven't had much time to play catch-up.

To my delight, the networks performed flawlessly and 3G coverage was good in all except one place I was throughout Istanbul. The hotel I was staying in the Maslak district even had dedicated 3G indoor coverage from one network operator so Internet access even on the 17th floor was quick. Quite interesting to see that towards the windows, 3G interference quickly grew and speeds slowed down. However, just a meter or two into the room and around a corner, the interference from outside cells was gone.

The one coverage exception mentioned above is metro line 2 from Taksim square to Maslak. There is 2G coverage in the underground stations and in some parts of the tunnels but no timeslots have been configured for GPRS or EDGE!? I tried all three operators and they all had their GSM networks configured for voice only (+SMS) in the metro system. I have to admit I don't quite understand that!? I don't think its for security reasons and I also can't imagine that the Istanbul underground authority has never heard of mobile Internet on phones. So why? Anyone? Capacity perhaps but if so, they are just doing it on the cheap as other cities are very well capable of having sufficient voice and data capacity in the metro, with 3G no longer only an "over ground" technology.

Initially, I wanted to buy a local SIM for Internet access as I usually do but this time I decided to use my Vodafone Germany prepaid SIM and daily Websessions. That worked very well but was a bit more expensive than a local SIM card. Next time perhaps.

Over Christmas, I was staying at a place away from home that had predictably little network coverage. Right at the place where I was staying the network operator's coverage map had a peculiar hole. So I took a UMTS power amplifier with me that is available, for example at these places, for a less than 200 Euros.

And indeed, at that place I had no 2100 MHz UMTS coverage at all that could be detected by my devices and even 900 MHz GSM coverage was very weak. The power amplifier I brought along has a directional antenna with an opening angle of 60 degrees and a total gain of 7 dbi. Pointed towards the next city with a UMTS base station, my coverage jumped from nothing to -89 dbm and an EcNo of -4. Throughput reached was beyond 6 MBit/s in the downlink direction and 2 MBit/s in the downlink direction. Incredible!

The picture on the left shows the setup. For local distribution I used my Huawei D100 I bought a couple of years ago, basically a 3G to Wi-Fi bridge that uses a 3G dongle for UMTS connectivity. The dongle itself is in the cradle of the power amplifier that induces the signal it picks up via the antenna (not shown) into the antenna of the stick and vice versa. The roll of cable on the right of the picture is the extension cable to the antenna, which I put on the cabinet above. No need to even put it outside the house, just directing it to the nearest UMTS base station was enough.

Over the days I've been at the place, the setup has proven its worth as the Wi-Fi signal of the D100 just perfectly received everywhere. Next time, I should bring a femto along as well so voice telephony also benefits from the setup 🙂