Category: Uncategorized

One information that is pretty hard to come by is which carrier in any one country holds what kind and how much spectrum. I've always been wondering if the coverage and speed situation in the US is perhaps due to too little spectrum available but the best I could do so far was summing up the available capacity per band. For details look here. How much each carrier has available, though, can't be derived from that. But recently, I've come across this interesting paper that shows how much spectrum each US carrier has available and in which band in table 5.

Let's take AT&T for example and compare that to the spectrum available to, lets say, Vodafone in Germany:

• In the 850 MHz band AT&T 2×12.5 MHz available, which compares directly to the 2×12.5 MHz (uplink/downlink) Vodafone has available in the 900 MHz band. While Vodafone uses the complete spectrum for GSM, AT&T runs both GSM and UMTS over the band.

• In the 1900 MHz band AT&T has 2×10 MHz available and uses it for GSM and UMTS service. This compares to the 2×10 MHz Vodafone has available in the 2100 MHz band it uses for UMTS services + 2×5 MHz in the 1800 MHz band used for GSM. In other words, Vodafone has a bit more spectrum, but not that much).

• AT&T has 2×7.5 MHz in the AWS (1700/2100) MHz band that I assume it doesn't use at the moment. 

• And finally, AT&T has 2×15 MHz in the 700 MHz digital dividend band. That compares to the 2×10 MHz Vodafone has in the 800 MHz band after the auction last year.

In other words, so far, the two carriers have about the same amount of spectrum in comparative frequency bands (and could hence offer the same quality in terms of coverage and speed).

Interesting twist relevant for the future: Vodafone has an additional 2×20 MHz in the 2600 MHz band it got during the spectrum auctions in 2010 for their LTE network. And I am sure they will put to good use.

Some time ago, I had a post on the many uses I have for a public VPN service today beyond just security aspects. But there is also an unwelcome downside to it that has hit me a few times now: Trust: When some websites detect the IP address of the VPN egress point they do strange things. Rebtel for example, that I use for international calls, immediately locks my account when I try to log in over the VPN as I recently discovered. Only an eMail to their support team unlocked the account again with a notice not to use them over the VPN. Great… Also, I suspect (but do not have complete proof) the credit card payment system of Thalys and SNCF (train operators) to refuse credit card payment requests with strange error messages if they come from an IP address of the VPN service. So it seems some companies have made bad experiences with traffic coming from such services. Fortunately, this behavior is not very common so far.

When reading this post on MocoNews recently I felt yet again reassured of the benefits of open mobile platforms where the user is in charge of what he wants to do with a device and which apps he either loads from one of several app stores or can install even directly onto the device if he wants to. According to the report, US lobbyists and lawmakers have pushed Apple to revise once again their app store rules, banning certain apps. Not that I don't like not seeing apps of this nature in an app store but once more, freedom and openness is further curtailed and I really have to wonder who will come next with what kind of demands. But fortunately there's choice and alternatives are available. Happy side-loading and app store choosing!

In the previous company I worked for, Instant Messaging was an integral part of office communication. Situated somewhere between a phone call and and email, one could quickly get information from someone without the full disturbance a phone call incurs and the long response times and explanations in an email. Moderate use of course was highly recommended and by and large it worked exceptionable well.

For two years now, however, I have to do without it as my current employer does have an Instant Messaging applications as part of its supported IT infrastructure and third party software is not allowed to be installed on the computer. And even after two years I miss it as a tool. Often, I don't want to call someone unless absolutely necessary but an eMail is too slow so I end up calling. Not very efficient.

Perhaps Instant Messaging on smartphones would be an alternative as most people in my environment are always-on these days anyway. Even critical mass might not be too hard to reach as Google Talk on Android phones gets activated by default anyway. But then the solution would lack the ease of a real keyboard thus making it clunky to use for most people. Also, exchanging company information over an unsecured channel is not the right thing to do.

One of the essential things that keep me glued to my Nokia N8 is Nokia maps for navigation and the possibility of downloading maps of whole countries for offline navigation. This is vitally important for me as I often travel to other countries and roaming charges are highly prohibitive for online mapping solutions such as Google maps. Over time, Google has added features to download mapping data but for navigation, that's not quite the same. But recently, there's been another report (link in German) that Google will soon release an offline component to Google Maps Navigation. Very good, I can't wait!

I have to admit that Skype's recent update behavior did not go down well with me. Yes, everybody has network and security issues that have to be dealt as quickly as possible. However, pushing down 20 MB updates without asking the user first just to fix a few things is not the right thing in every situation. When I am traveling, for example and have a 50 MB budget before I have to spend another 15 Euros, an uninvited Skype update is very annoying. Guys, at least you could give me the option to switch on a notification via your options menu. I fully agree that the average user shouldn't be concerned with this but an option for those who need it would be great. Oh and by the way, how about using delta updates instead of full blown installation packages? That would be great for my scenario above and I am sure it would reduce your update server load as well. Something really worth thinking about now that you seem to push one update per week…

I just had a look through my archive and found out that 2007 was the year Vodafone Germany introduced it's WebSession offer that I have used every since for Internet connectivity while traveling away from home when I didn't have a local SIM card. Since then the offer hasn't changed much, €15 for 50 MB a day with a nice little landing screen to invite you to spend another €15 when you exceeded the limit. At the time, I found the 50 MB quite sufficient and didn't have to control my usage to much. These days, however, the 50 MB are used up quite quickly and I have to watch my consumption. An interesting change! So Vodafone, no change in the tariff in 4 years!? It's about time, the world has moved on!

Here's an interesting thought I had the other day I'd like to throw at you to get some feedback. The main challenge faced by LTE is that the current GSM and UMTS voice infrastructure can not be used with LTE anymore as it is an IP only network. There are a number of solutions to the issue such as VoLGA, VoLTE and CS fallback but let's assume just for a minute that neither of them is able to get any traction due to one shortcoming or another. There is one more solution and that is dual-radio, the LTE radio is active at the same time as the GSM or UMTS radio.

Verizon, for example does this already, as shown with their HTC Thunderbolt. The Thunderbolt uses their CDMA 1xRTT network for voice calls and their LTE network for IP based traffic. For the CDMA part, CDMA credentials are used that are stored in a secure place in the device while the LTE security is handled by a SIM card.

So far so good. But what about countries that use GSM/UMTS? Here, a single set of security credentials, or, in other words, subscription is used so one can't be registered to, for example, GSM and LTE at the same time. At least that's what I thought so far. But is it really so? If, let's say, only a GSM circuit switched location update is performed, only the MSC is registered in the HLR/HSS. The packet switched part on the other hand is still open. Now the mobile device registers (only) the packet switched part over the LTE network. This would trigger the current MME to be registered with the HLR/HSS. In other words, there is no collision with the CS part of the network at all of this registration.

If the mobile runs out of LTE coverage it could then perform a routing area update in the UMTS network and also move the circuit switched connectivity from GSM. And once LTE coverage is available again, it could move the packet switched connection back to LTE while the circuit switched connectivity could either move back to GSM or stay on UMTS. From a network point of view I don't see anything that would speed against it. Do you?

Now how easily this could be implemented from a mobile device point of view is another matter. If there's an integrated GSM/UMTS/LTE baseband than that's likely to be difficult. But if there's just a UMTS/LTE chip for IP connectivity and a separate GSM chip for voice connectivity then the implementation would be straight forward, except for the physical access to the SIM card that would have to be multiplexed.

Obviously the power consumption of a dual radio device is higher than that of a single radio device. However, the power consumption of a GSM baseband while in idle is very small. While it would definitely have an impact to the idle standby time which is measured in the hundreds of hours these days, I think the impact it would have on total running time is much less, especially in smartphones. Most smartphone users make good use of their device today and regularly have to recharge it once per day anyway. So a hundred hours less standby time or so won't really matter very much.

Coming back to my question above. Perhaps I'm blind but I can't see any obstacle from a network point of view to have a mobile device CS attached only over the GSM network while PS only attached over UMTS or LTE. The HLR/HSS should not care at all. Let me know if you think I'm wrong.

One of the things I usually do when I go to meetings and conferences that are attended by more than 40 people or so is to get hold of a local SIM card for Internet access, as the public Wi-Fi at the conference venue and hotel is usually unusable. When I was in Seattle recently for a smaller meeting, though, I thought I'd give the Wi-Fi in the hotel a chance again. And indeed, things were working o.k at a steady 2 MBit/s. That changed, however, as soon as I got out of the hotel. Free Wi-Fi at Starbucks, so no problem you would think. Not really, the Wi-Fi was completely unusable. Next, I went to the airport, again depending on the Wi-Fi installation there. This time, it was sort of usable but still painstakingly slow. Very disappointing. And in Paris on the way back, the Wi-Fi in the lounge wouldn't even let me connect. Back to 3G then…

Back in August last year my last UTMS speed measurement at home resulted in a sustained peak data rate of 11 MBit/s. Since then, things have moved forward once again so it was time to perform another test, this time at 3 am in the morning once jet-lag caught up with me. And I was not disappointed, the sustained data rate was over 16 MBit/s as shown in the picture on the left. If you put the 10-15% of HARQ overhead on top that's just 2.5 MBit/s below the theoretical maximum speed of 21 MBit/s (again including HARQ). Performing the same test again in the morning resulted in around 14 MBit/s a second. Breathtaking values!