Author: Martin

Solar Powered GSM in the Dominican Republic

Flexenclosure In the past two years I've seen a number of companies at the Mobile World Congress working on solar and wind powered GSM base station solutions targeted at countries where the power grid is unreliable and many base stations are powered by diesel generators. Looks like the industry is now slowly moving from the concept phase to practice.

Apart from environmental issues, diesel generators need fuel which is sometimes very difficult and expensive to get to rural areas. So if solar or wind power can partly or fully supply a GSM base station with power, that's good for the bottom line and for the environment as well.

Here's a link to a press release over at TeleGeography that Orange Dominicana has started rolling out solar powered base stations. The article concedes at the end that its only 30 base stations for now, but it's a start.

The press release doesn't mention which solution is being used. At the World Congress, I've seen VNL for example, that develops very low power GSM base stations with limited range and Flexenclosure who work together with, among others, Ericsson (see picture on the left).

Relative Cost of Voice over GSM, UMTS and LTE

The other day, a reader asked whether it is true that a voice call over a UMTS circuit switched bearer is less expensive than over a packet switched UMTS bearer. Good question and I guess very difficult to answer as there are many parameters. But nevertheless, let's expand the question and put GSM and LTE on top.

GSM

In the GSM world things were simple at first. There's a 200 kHz carrier and you can squeeze 8 timeslots into it. On the main carrier of a cell 6 out of those 8 timeslots can be used for voice, on all others, all timeslots can carry one voice call. Further, the adjacent carrier can't be used due to overlap, so the carriers bandwith is effectively 400 kHz. To increase the number of calls, the network operator can use AMR half rate, theoretically doubling voice capacity. Here it starts to get difficult as a half rate channel should not be used under weak signal conditions, i.e. some calls should fall back to a full rate channel so more redundancy and error correction information can be added to prevent the call from dropping. Anyway, a full rate channel voice coded streams at 12 kbit/s in each direction. Add error detection and correction bits and you end up with around 28 kbit/s.

UMTS Circuit Switched

In terms of resource use, things are similar as in GSM. The AMR full rate codec streams at around 12 kbit/s and redundancy information is added. I'd say resource use is similar as in GSM.

UMTS / HSPA Packet Switched

Packet switched means Voice over IP. Here, things start to get difficult because what is VoIP in practice? There's no standard solution as in the wireless circuit switched domain so there are different possibilities.

Let's look at standard SIP first that uses the 64 kbit/s uncompressed PCM codec. Add IP overhead and you stream at 80 kbit/s in each direction. Quite a difference to the 12 kbit/s used in the circuit switched wireless network. But wait, it's 28 kbit/s due to error detection and correction. However, that has to be added to the 80 kbit/s as well but how much, that's difficult to say. That depends how far the user is away from the base station, i.e. which modulation and coding is used. So to get realistic values, you have to calculate with a traffic mix. But no matter how you calculate it, there's no way to bring the 80 kbit/s down to the circuit switched value.

Some SIP implementations also use AMR if they detect that both ends support it. That brings down the data rate to 12 kbit/s + IP overhead to a total of 32 kbit/s. For details see this post. Still three times more than 'native' AMR. For users very close to the base station not a lot of redundancy needs to be added so I think we could come pretty close to GSM or be even better. But then, you switch-on half rate AMR and GSM is doing better once again. You could do that in VoIP as well but the IP overhead won't go down and it's already 2/3rds of the total bandwidth for full rate AMR.

Better spectral efficiency could also help to some extent to compensate for higher VoIP data rates as mobiles close to the base station do not only require less error detection and correction bits in the stream but can also use a higher order modulation, thus making the transmission more efficient than GSM circuit switched. But again, that's only for some but not all mobile devices.

Something that works against VoIP efficiency over wireless networks are channel assignments. While circuit switched timeslots are only assigned at the beginning of the call, bandwidth for VoIP calls over HSPA needs to be frequently re-assigned. There were some efforts in 3GPP to reduce the need by using static assignments but it starts getting messy quite quickly here (HS-SCCH-less operation).

But wait, there's IP header compression in UTMS, at least in theory. In practice, however, it's not used as far as I know, so I won't put that into the equation.

Over the top VoIP such as Skype uses pretty bandwidth efficient codecs that are in a similar bandwidth requirement range as AMR. There are lots of VoIP systems that could be used over wireless as well but I don't know what kind of bandwidth needs they have so I won't discuss them here.

LTE

There's a real pressure with LTE to switch to VoIP and similar dependencies on features such as modulation and coding, signaling overhead, etc. as in UMTS will have an impact. Robust header compression will probably make it into LTE much faster than in UMTS, be it for IMS, for VOLGA, or for any other network operator voice solution that will be used.

The Calculations

The book from Hari Holma and Antti Toskala on UMTS/HSPA has some interesting calculation on VoIP capacity. Their conclusion is that UMTS packet switched voice capacity can easily exceed that of GSM – if, and that's the big if, all optimizations are present and switched-on. For over the top VOIP, however, it's unlikely that these conditions will be met.

Summary

So as you have seen VoIP over UMTS or LTE can be more or less efficient than circuit switched voice over GSM depending on how you look at it. So maybe the question for the future will not be on efficiency but if mobile network operators will in the future continue to be the main provider of wireless voice calls or if over the top voice providers will take a bigger share of the market for which radio network optimizations are not working as efficiently.

3G Sticks Everywhere These Days

This is probably not big news to most but I just realized recently when walking through a German city how many people sit in cafes and restaurants with a notebook and a 3G USB dongle these days. I could swear it was still much different last year. Most people I saw were (still) using notebooks instead of the smaller netbooks, so I guess that trend is not yet as pronounced. I didn't talk to the people I saw so I don't know if they are using prepaid daily, hourly or monthly options or if they have a postpaid contract. Both are available in Germany. Also, it would be interesting if the connectivity is provided by the company they work for or if they are paying themselves. Would be quite interesting to find out.

LTE and UMTS Air Interface Comparison

There's a very interesting blog entry over at the 3G and 4G Wireless Blog by Devendra Sharma on the differences between the LTE and UMTS air interface beyond just the physical layer. By and large he comes to the conclusion that the LTE air interface and its management is a lot simpler. I quite agree and hope that this translates into a significantly more efficient power management on the mobile side (see here) and improved handling of small bursts of data of background IP applications (see here and here). I guess only first implementations will tell how much it is really worth. I am looking forward to it.

Symbian vs. Memo? – Some Thoughts

This week, the Financial Times Deutschland ran an article that Nokia is about to "change its strategy" ("Strategiewende") concerning their use of smartphone operating systems, that "they are loosing faith" in Symbian ("verliert Vertrauen") and are about to "abolish" ("verwerfen") Symbian in favor of Maemo.

Tough words which are immediately followed by the statement that in the future, Nokia will equip "many" of its new phones with Maemo. To me that doesn't quite sound like abolishment or loosing faith but more like continuing the path of working on more than one operating system.

The article only cites internal sources so it's difficult to verify the claim or the spin of the article. Other news websites have picked up the story (e.g. here, here and here) but I don't quite believe it yet.

Here's how I see things:

Something is going on behind the scenes at Nokia concerning their smartphones and I am not quite sure what it is. The innovation in the smartphone sector Nokia has so long driven with their Nseries range has notably slowed down. I have my Nokia N95 for almost 18 months now, and I am still waiting for a successor. Neither an iPhone nor the N97, that has just started shipping recently, are what I'm looking for. From that point of view, the speculation is understandable.

But the latest Maemo device, the N810, was released in the same timeframe as the N95, back in 2007. So Nokia has definitely not really pushed that OS with new hardware either. There are rumors of a new Maemo device to be released shortly, but I don't think that this is a change of strategy or loosing faith in Symbian.

The FTD article says Symbian is old, has 20 million lines of code by now and is difficult to extend. I would hold against it that Maemo, which is based on Linux, has probably similar complexity and Linux itself is not much younger either. But it's open source and well known by programmers which are two formidable advantages over Symbian. Symbian is going open source, too. How much that will draw programmers to it, however, still remains to be seen.

An advantage of Symbian over Maemo is it's integration of 2G and 3G network stacks, something Maemo does't have for any hardware with which it was released so far. On the other hand that seems to be something that can be overcome, as shown by Google's Android, which is based on Linux as well. 

Also, a change from Symbian to Maemo would not solve Nokia's challenges concerning platform popularity and an encompassing ecosystem such as a popular web store, synchronization to web services or to a PC, etc. These aspects have nothing to do with the operating system running on the mobile device itself.

The article further says that Nokia is loosing smartphone market share. After many years with little competition, I'd say this is not really surprising with strong competition coming from several directions now such as RIM, Apple and Google. That's not something that could be fixed by changing to another operating system.

But market share is not everything. I'd rather have a smaller market share of a big market than a big market share of a small market. I don't have the numbers here, so maybe someone can help me out with this, but I think there's a fair chance that with all the attention of companies with good products other than Nokia on the smartphone sector, the number of smartphones sold are probably increasing.

So without further facts I can't quite go along with the message of the FTD article that Symbian is going to be ditched. What do you think?

Vodafone and Petabytes

Another interesting number popped up on the Internet recently. Here, Teltarif quotes Georg Benzer, Chief Network Officer for Vodafone/Arcor in Germany, saying that Vodafone/Arcor (I assume he means both their DSL and mobile network Germany) transport 1.5 petabyte a day. No more details were given and there is only one more source on the net reporting the same number. But nevertheless, let's play around with this number a bit.

The 3UK CTO recently reported that at the end of 2008, they transferred around 1.000 terabytes (=1 petabyte) a month through their wireless network in the UK. Let's say most of that traffic was generated by 3G dongles. The exact 3G dongle subscriber number of 3UK is not known, I estimate it at around half a million at the end of 2008. That means every subscriber consumed about 1.000 terabytes / 500.000 subscribers = 2 GB of data a month.

Now lets say the 1.5 petabyte a day or 45 petabyte a month in the Arcor/Vodafone network were consumed by both fixed and mobile subscribers. Let's say Vodafone Germany has 2 million 3G dongle users (just an assumption, approximated from the 3UK number, no source for this) then out of the 45 petabyte, 4 petabyte would come from mobile subscribers. That means 41 petabytes are used by fixed DSL subscribers.

The number of fixed DSL subscribers of Vodafone/Arcor Germany is reported to be around 3 million. That makes 41 petabytes / 3 million subscribers = 13.6 gigabytes per subscriber per month on average. Note that both the 2GB above and the 13.6 GB are average values and there's no telling from those numbers how many users are at both ends of that figure (i.e. how many use much less and how many use much more).

Many of Arcor/Vodafone's DSL subscribers also use their DSL line for
VoIP (with a POTS to VoIP converter at home). That traffic should not
be counted either as it doesn't leave the network, at least not as IP packets. Let's say the average subscribers uses the fixed line phone
for 5 hours a month. VoIP produces 2*80 kbit/s (uplink + downlink) = 160 kbit/s of data
traffic = 72 MB per hour or 360 MB for 5 hours. Not very much compared to the 13.6 GB per month which are just reduced down to 13.3 GB per month.

A raw comparison of the two numbers would indicate that DSL subscribers are transferring 7 times more data through their connection than wireless subscribers. But I think that is a bit too simple a view. Most wireless subscribers are likely to also have a DSL line at home and fixed and mobile use might be different. Further, DSL lines at home are often shared with family members and several devices while a 3G dongle is mostly used by a single person with only one device at a time. Also, since most wireless offers have bandwidth caps, heavy users are much more likely to use a DSL line rather than a wireless modem, thus further distorting the direct comparison.

So despite the two numbers not being directly comparable they nevertheless give an interesting indication that mobile use is is not that far away from fixed line use.

Nokia Energy Profiler V1.2 now with 3G State Analysis Mode

A while back I reported on the Nokia Energy Profiler, a very useful utility from Nokia for S60 phones to measure power consumption. From the power consumption one can then deduct in which radio state the mobile is and how long it is kept there by the network during inactivity before a more power conserving state is selected. For details, see here. Now, Nokia has released V1.2 of the utility, which has a dedicated screen for showing the 3G radio states.

It's a bit hidden, though. First, it has to be activated in the preferences. Second, during recording only 0,1, 4 or 8 "CH" are shown. Not sure what "CH" means. Anyone? Anyway, 0 and 1 represents the Idle state, 4 the Cell-FACH state and 8 the Cell-DCH state (in HSDPA mode). The states are shown by stopping the recording and then using the 4-way navigation key to scroll back. In this mode, the application shows how long the mobile was in each state while you scroll back to the left.

I've tested the application in the T-Mobile network in Germany and the Orange network in France. T-Mobile keeps the connection in Cell-DCH state for around 20-25 seconds, including the (Opera Mini) page download time, which is around 2-3 seconds. The Cell-FACH state is keept quite long, somewhere between 1.5 and 2 minutes, before the connection is put into Idle state. In the Orange network, Cell-DCH state is kept for 10-15 seconds, and Cell-FACH state for around 30 seconds. A bit better for battery consumption one might argue, but T-Mobile's settings are better for the browsing experience if one remains on a page for more than 30 seconds.

Wi-Fi Sharing – The French Way

There is an interesting development in France concerning Wi-Fi sharing that I haven't seen anywhere else so far:

Fixed line network operators are now offering to their customers to share their DSL Internet connection over Wi-Fi with others in a number of ways:

  • FON is officially endorsed by SFR. They have upgraded the software of their customer based and operator managed DSL/Wi-Fi routers for the purpose.
  • SFR and Free now allow subscriber the use of DSL/Wi-Fi routers of other subscribers unless a customer specifically disables it.

While it is nice to be able to use someone else's Wi-Fi while being out and about there are two issues which are not addressed by this:

  • I am aware of FON for a number of years now but I have never seen one when I needed access. The number of FON hotspots might be impressive, but the range of the Wi-Fi signal is just too limited.
  • I imagine the same applies to the Wi-Fi sharing for French subscribers. As there is no way to ensure that one will find a suitable hotspot one can use for free the usability in practice is quite limited.

On the other hand, many locals might prefer such a kind of nomadity over 3G at the moment, as prices for 3G Internet access are still very high compared to other countries in Europe. With a bit of luck, though, that won't last forever. And once we have a situation like in Austria and other countries, where 50 euros buy you an unlocked 3G USB stick and a reasonable amount of data, I can't imagine that many people will go through the hassle of looking out for a suitable Wi-fi hotspot when it's much easier to just get connected over 3G.

This shows a bit of a dilemma with a future off-loading 3G traffic to Wi-Fi hotspots which might be a good thing in case we get a situation where cellular networks become too crowded: Today, users need to figure out themselves if there is a Wi-Fi hotspot close by and then use it instead of 3G. No way the majority will do that unless there is a severe price pressure or the 3G network is so loaded that the speed is not acceptable anymore.

So what is needed to make this work is an automatic means for a device to automatically use the network operator supplied Wi-Fi when found and to change back to 3G, seamlessly of course, when the user moves on. Not an easy task. In that regard, Femtos might be a better solution as they give extra capacity with a similar range without the hassle of installing software for network switching on mobile devices.

So in the end I think it's likely that we'll see a triumvirate with Wi-Fi and Femtos at home, Femtos in public hotspots, Wi-Fi in public hotspots for locals and travelers without a 3G subscription and 3G cellular for the general coverage.

Push and Pull, Keep-Alive and Wastefulness

O.k., here are some follow-up thoughts after my previous post on background applications that generate keep-alive IP packets which have a negative effect on radio interface efficiency. The “efficiency” issue here is that the ratio between the amount of data transferred and air interface radio signaling is very unfavorable for small bursts of data, especially in cellular broadband networks such as UMTS. So Dan asks in a comment to the post why mobile e-mail (push or pull) could be counted in the “wasteful” category. All right, here we go, this is my take on it:

There are two kinds of mobile e-mail delivery:

The first is push e-mail to mobiles, such as on the Blackberry. Here the server is likely to only communicate with the mobile device when there is an e-mail to deliver. I haven't tested it personally yet so I don't make a definite statement here. But I assume even if some keep-alive messaging is necessary, for example in cases when no e-mails are delivered for some time, it should not be that much. Also, IMAP push which is supported by more and more phones these days should also not generate keep-alive messaging.

Second is pull e-mail, which I use for example as I don't like the IMAP (push) implementation of my e-mail program. My polling timer is set to 10 minutes, so my N95 checks for e-mail 6 times per hour. Definitely more wasteful than push if there are less than 6 e-mail per hour. In case you receive more e-mails per hour however, it can even be more efficient than push.

So is mobile e-mail wasting air interface resources? I guess that depends on the definition. If the definition is that an application is wasteful that only transfers little data per radio bearer setup, then I guess the answer is yes. But then, small screen web browsing, like for example with Opera Mini, would have to be categorized as quite wasteful, too. Many pages I view are compressed to less than 20 kB. Ouch, that hurts, as it's one of my favorite applications…

So my own definition of “wasteful” would be:

Exchange of IP packets for frequent keep-alive messaging that do not contain data.

That excludes e-mail push, Opera Mini use and, depending on configuration and number of emails per hour, e-mail pull.

That still leaves us with a lot of other applications, especially when connecting the PC to the cellular network, that keep babbling away and provoke lots of bearer reconfigurations. But as I said in the previous post on this topic: For battery driven devices, always-on applications are quite likely to be optimized over time to talk less to increase the battery lifetime.

A Netbook, eeeBuntu and Mobility – Part 3

I've had my new netbook for about a month now (see here and here) so it's time now for an update on how things turned out. I was a bit skeptical at first whether I would keep Ubuntu Linux on the machine or revert back to the original Windows XP. A month later, I am pretty much convinced that Ubuntu is the right thing for me on the machine.

One of the most important things for me with is the startup time of the operating system and the applications. In both categories, Ubuntu does extremely well. Booting the system takes just around 60 seconds. Going to suspend mode and waking up again just takes 6 seconds. That's almost instantaneous and helps a lot if you just want do something quickly, like looking something up on Wikipedia for example.

The applications I use most are Firefox, Thunderbird, Open Office, GIMP, Pidgin (for IM) and Skype. Even when compared to my full notebook with Windows XP, most of them launch much quicker. Sometimes I even catch myself thinking that the netbook is faster than the notebook…

Some things especially noteworthy I haven't mentioned so far:

  • No drivers are needed for 3G phones or USB sticks. Both my Nokia N95 phone and the Huawei E220 3G USB stick worked right away. Not quite perfect as reported in part two, but it's a huge plus not having to install third party software, which often does more harm than good.
  • HP went out of their way to produce Linux drivers for their multifunction printers. The package is called HPLib and makes using my printer / scanner / fax over Wi-Fi very easy. I even dare say the software is much quicker than the PC version, especially the scanning part. No waiting for the next dialog box, no long program startup times, the scanner just jumps into action when the scan button is pressed. Conversion to JPEG and PDF works out of the box, too, very nice!

But where there is light, there is shadow, too. Here are the things that required under the hood tweaking to get it working:

  • The fixed line Ethernet chip was not detected automatically so I had to install the driver manually. It's not very complicated but for the average user compiling a driver is not a straight forward thing.
  • There seems to be a WPA2 problem with the Wi-Fi driver as I get lots of packet retransmissions. I've tried with several access points but the result is always the same. When going back to WPA encryption, everything is fine. I've searched the forums but haven't found anyone reporting this. Under Windows XP, WPA2 is working fine so it seems to be a driver issue.
  • The built-in video camera made some problems. I got it working for a while but it stopped once I've experimented with the screen resolution of the external VGA port and a second monitor. It seems the graphics driver can't handle advanced functions with a higher screen resolution. Also, desktop effects like windows zooming in and out when they are minimized only worked with the lower resolution. Getting the effects back requires manual intervention in the xorg.conf file as described here.
  • Automatic suspend when closing the lid did not work at first. Even worse, the processor utilization went to 100% and the netbook kept running. The root cause seems to have been a BIOS issue. After upgrading the Bios of my Acer Aspire One D250 to V1.07, suspend when closing the lid now works.

So even though it required some tweaking I've got a fully functional Ubuntu netbook now and I am very happy with the performance.