Author: Martin

Dongle Upgrade Incentives

Here's a thought experiment about whether and how operators should encourage users to upgrade their 3G dongles to a newer model:

Most HSPA dongles currently 'in the wild' are are HSDPA category 6, i.e. they are capable of theoretical speeds of up to 3.6 MBit/s. Category 7 dongles with a maximum theoretical speed of 7.2 MBit/s are now also available and currently going over the counter. The speed increase between the two is mainly due to an increase of the number of spreading codes the device can handle simultaneously. In other words, from an overall network capacity point of view it does not matter a lot whether most of the devices used for high speed Internet access are category 6 or 7. In the future however, this is going to change.

Pretty soon, higher speeds in HSPA networks will be mainly achieved by more sophisticated 3G devices and networks. Receive diversity with several antennas helps during weak signal conditions (this Ericsson paper is a good starting point for further research) and MIMO while reception is good. In addition, more sophisticated mathematical approaches to separate noise from useful data will also help to increase data speeds. From a network point of view, this means that the more of those newer devices are in the network compared to the number of older devices, the higher the overall throughput of the network.

So should it be in the opreators interest to encourage users to upgrade to newer devices? And if so, how could that be done best? Is the higher speed achived with those devices incentive enough or should the base station scheduler also take the UE category into account to further boost data rates of newer devices? I could also imagine to offer a reduced rate to users with newer hardware as they use the air interface more economically than users with older hardware. Kind of a similar approach to taxing older cars with higher emissions higher than new cars (don't take the analogy too far…). Or maybe this is all overkill and the normal equipment replacement cycle of 2-4 years will do the job anyway!?

Three Italy won’t sell me a Prepaid SIM

Things can be simple when it comes to prepaid SIMs. You walk into a supermarket, get a
SIM and 2 minutes later you are set. Not so with mobile operator '3' in
Italy.

When I wanted to buy a prepaid SIM card from them this week they refused to sell me one. In the first store I went to at Roma Termini station, the shop assistant first doubted that it would work in my non Italian mobile phone. Once we cleared that they refused to accept my German identity card, which by the way is good enough for customs and for boarding airplanes as a valid identity. Hm, but not for buying a SIM card!? Ridiculous.

So in the afternoon, I went to another store in downtown Rome which was on my way, this time equipped with my passport. Just to make sure. Here, the same story again but I made it up to the Italian tax number, which they say is also required. I have one so I gave it to them. However, they insisted that they would only accept it on an official document. Again, no SIM card from me.  Ridiculous.

I have to say I am baffled. I could have understood one shop assistant being a bit difficult, but two in two different stores!? Note that this is a only a '3 Italy' attitude. Some days ago I got a SIM card from mobile operator WIND, my id card was good enough and no Italian tax number was required. Same with Vodafone Italia just three months ago just around the corner from the 3 store and I was not the only foreigner buying a prepaid SIM card while being there. As a matter of fact, I had to take a number and stand in line. Guess where the money is going.

Anybody in '3 Italy' reading this blog? Hello! Wake-up! How many millions of visitors are coming to your country each year who could be your customers!? Hm, but maybe that's one of the reasons why your market share is below 10%…

Virtual GSM in the Future?

While HSPA+ and LTE drive data rates higher and higher and have network operators and vendors discussing which is the right way to go, GSM for voice and low bandwidth data applications is unlikely to go away anytime soon. I've speculated in the past about when GSM would be switched off in Europe and elsewhere and wondered if maybe at some point Software Defined Radio (SDR) technology would allow to fold all radio access technologies into the same hardware and into a single digital and a single radio module in the base station.The more I think about it the more interesting such a combined option looks like to me.

With backhaul already converging to IP for GSM, HSPA and LTE, there will be nothing standing in the way from that side of the network in just a couple of years from now. From a handset perspective, GSM might also be the least costly and best technology for the foreseeable future for voice only devices. When I look at my 3.5G mobile stuffed with the latest technology and compare it to the simple GSM phone I use for voice calls only I can not only see a significant difference in size but also in price. After all, a 3G handset does not only have to contain more hardware but the license/patent fees are much higher than for 3G phones. And LTE will further increase the hardware and royalty costs, so there is no break from this perspective, either.

And while LTE and HSPA+ might be optimized for speed, they are definitely not optimized for voice and power consumption when compared to GSM.

A single digital / radio module in the base station would also have another interesting benefit: When only little capacity for GSM voice and GPRS/EDGE data is required in a region the base station could automatically reconfigure itself and use more of the bandwidth for LTE. During busy hour, when voice calls over GSM come close to the capacity of the current configuration, the LTE carrier bandwidth could be reduced and additional narrow band GSM carriers could be fired up within a few seconds. Currently, LTE bandwidths are defined at 1.25, 2.5, 5, 10, 15 and 20 MHz. Maybe not yet fine grained enough but that could be changed in future versions of the standard.

In the backhaul, everything will have converged on IP right up to the MSC Media Gateway and from there the phone call is also sent through the network over IP connections. The H.248 protocol between the Media Gateway and the MSC Call Server is also based on IP, as well as the link to the Home Location Register and all other equipment in the core network. In effect, the once circuit switched GSM network has become fully IP based and only higher layer protocols such as DTAP and MAP are still remaining from the original protocol stack to preserve the super efficient GSM air interface technology for voice.

Unconventional ideas, but who knows what the future holds.

8 SIM Cards and 3 Operators

In the days of prepaid SIMs and multiple phones many people carry, counting the Average Revenue Per User (ARPU) based on SIM cards has pretty much become irrelevant. I am the best example that this approach doesn't work anymore. Let's make it simple and only take a look at how I use mobile networks in a single country, Germany:

  • The 'currently used prepaid SIM card' in my primary phone which has good rates for telephony and small screen mobile Internet access. Network: T-Mobile, MVNO: Congstar.
  • My 'I always stay the same' prepaid SIM who's phone number is known by all my friends and via
    which they can reach me no matter in which country I am at the moment.
    When I am in Germany, I forward all incoming calls to the currently used SIM card since the price for Internet access is too high. Network: T-Mobile, MVNO: Simplytel.
  • My business SIM card, the only one that is postpaid. Network: T-Mobile
  • The prepaid SIM card in my car. I have a block heater which is connected to a GSM module. In the morning and evening, I call the car to switch on the heater so my windows are de-frosted and the interior is warm by the time I arrive. Network: T-Mobile, MVNO: Simplytel.
  • The prepaid SIM for notebook Internet access. I can activate 200 MB for 10 euros or 5 GB for 20 euros. Network: O2/Telefonica.
  • Two prepaid SIMs for notebook Internet access in Germany (€4.95 a day) or when I travel abroad and no local offer is available (€14.95 a day). Network: Vodafone. I have two so I can lend one to guests or colleagues traveling abroad.
  • One prepaid SIM to use in the mobile phone abroad for small screen web browsing and mobile e-mail in countries where I don't have a local SIM card. 19 cents for 100 kB is not exactly cheap but does the job well for mobile only use. Network: E-Plus, MVNO: Alditalk.

Altogether that's 8 SIMs and 3 mobile operators. Have fun calculating the ARPU! From a technical point of view all this is quite uneccessary, one sim card for the mobile phone, one sim card for the 3G USB notebook dongle, and one for the block heater in the car is all I would need.

3G Coverage on a Train Ride to Vienna

A1-on train
Recently I took the train from Linz to Vienna and I was quite surprised that Mobilkom Austria (A1) must have put a more or less dedicated 3G coverage alongside the railway track even in very rural areas. I've had 3G coverage for most parts of the trip and in the few places 3G coverage was lost, their EDGE network kicked in. I've reported on my experiences with non-optimized 3G HSDPA coverage on board of trains before (here and here), but this time, the experience was even better. The connection I established was maintained throughout the trip and high speed data transfers taking several minutes were performing very well as shown on the image on the left. I even dared to launch my IM client as connectivity was simply always there. I stepped out of the train very impressed by what is possible when operators decide to do a proper network planing and deployment.

Samsung D880 – Two SIM Cards Simultaneously

I've heard about dual-SIM phones before but only from not very well known Chinese manufacturers so my interest in them was not very high. Also, I assumed that while those phones could hold two SIMs, only one would be active at a time. While browsing the phones available at a mobile phone shop recently, I noticed that I've been wrong on both accounts.

Samsung has released two dual-SIM (GSM only) phones, the D880 at the end of 2007 and the D780 in the middle of this year, both capable of having both SIMs active simultaneously. Kudos for their courage, I am sure network operators are not very keen to see these phones.

For details see GSMArena:

Here are some technical details from the reviews above which hints how the dual-SIM functionality is implemented:

  • A master SIM card has to be declared which can be used in 900/1800 and 1900 MHz. This SIM is also used for GPRS/EDGE.
  • The secondary SIM card can be used for incoming and outgoing calls and SMS messages but only 900 and 1800 MHz.

To me this seems to indicate that each SIM card has its own GSM module and the second one is only dual band capable. Unfortunately, the review doesn't mention if an SMS can be received via the secondary SIM card while being in a voice call with the first SIM card. This would certainly prove it.

With the D880 available for around 200 euros and the D780 for even less, I can quite imagine that I will pick one up and give it a try myself. After all, it could reduce the number of phones I have to carry around with me these days by at least one. Not sure if they are a hit in sales statistics since I can't imagine network operators selling or even advertising them directly. In many countries, however, like in Italy and Germany for example, these phones can be bought from independent stores. If I were Samsung, I'd opt for a viral marketing strategy for those phones.

The LTE Frequency Gamble

A friend of mine pointed me to this document which gives an overview of which portions of frequencies have been allocated to which mobile operators in Europe. I've been looking for such a document for quite a while now as it can give interesting insights into which options mobile operators in Europe have when it comes to frequency bands in Europe. Here's what I think:

The 900 MHz band

In total, there are 35 MHz available in this band, which are typically shared for GSM today by two to four operators. Even if only two operators use this band, each operator has typically less than 10 MHz of consecutive bandwidth available here. For LTE that means that the best that an operator can do in this band is to deploy a 5 MHz LTE carrier. For most operators, that's unlikely though as the remaining 900 MHz chunks they already own are probably not enough to ensure GSM in-house coverage with enough capacity. So, most operators could only deploy a 1.25 MHz LTE carrier in this band. I wonder if that's attractive as the achievable bandwidth is severely limited. But maybe for deep in-house coverage, it's better than nothing!? Also, there's no possibility to buy additional chunks in this "prime" band, it's all allocated.

The 1800 MHz band

This game is a bit different as in total, 75 MHz were assigned to GSM here and many "second wave" GSM operators in Europe got assigned chunks of more than 10 MHz. Also, in many countries, not all of the 75 MHz have been sold so some operators might be thinking of acquiring some of the so far unused chunks to start with a 5 MHz or 10 MHz LTE carrier here.

The 2100 MHz band

This is the 3G UMTS band in Europe with a total of 60 MHz. In most countries, each operator has a 10 MHz chunk and probably only uses 5 MHz of that for a single 3G carrier. Also, there is some of that bandwidth still available, e.g. due to alternative 3G carriers having given up after they paid a bit too much for the licenses back in the year 2000. So scenarios for this band could be that some operators will start with a 5 MHz carrier in this band or try to by additional spectrum to be able to operate a 10 MHz carrier. Since there is not enough bandwidth left for all, let's see if a price fight breaks out again like in the early 3G days. Doubtful but I see more interested parties then available chunks.

The 2600 MHz band

In most countries, this part of the spectrum is still up for grabs. The issue here is that in-house coverage would be even more difficult to achieve than with the 2100 MHz band. Lots of space for 10 MHz+ carriers.

Do 5 MHz carriers make sense?

This is the big question. With MIMO, the performance of LTE with a 5 MHz carrier is similar as HSPA+ with MIMO. Even if operators do not choose to upgrade their HSPA networks to MIMO, I wonder if the speed difference is big enough to justify the expense to go to LTE compared to upgrading their already existing HSPA base station with a second carrier.

Multiband Devices

So there are four frequency options for LTE in Europe: 900, 1800, 2100 and 2600, each with benefits and drawbacks. Different operators will surely have different strategies, including using several bands at once, so it's likely that single band LTE devices are likely not to be a winner. Supporting all four frequency bands with MIMO, which requires at least two antennas per band in a single device, however, is going to be difficult to achieve. And on top of that we haven't even talked yet about the 700, 850, 1900 MHz band in the US.

I guess both first movers and followers in this space will have difficult choices to make when it comes to frequency bands. As always, comments are welcome.

3G Connection Sharing – Part 3: The D100

D100
While the software on the Fritzbox for 3G connection sharing over Wi-Fi is still an early beta, I have recently also tested the Huawei D100, a box dedicated for 3G connection sharing. So far, I've seen it advertised by 3 in the UK (with contract only) or by 3 in Austria, here unlocked for 99 euros. Needless to say I preferred the Austrian variant and went into a shop while in Austria recently to buy one. I have now used it for several days with a E220 3G USB stick in the Mobilkom A1network and I have to say I am very impressed by stability of both the Wi-Fi and the 3G connection and the ease of use of the box.

Once power is switched on and the power on button has been pressed, the box automatically attaches to the 3G network and establishes an Internet connection. What I've found a bit odd is that the power button has to be pressed for the box to start. This is a bit inconvenient after a power outage for example. Should the 3G connection drop while being online, the box is smart enough to figure out something is wrong and automatically re-establishes the connection within a couple of seconds. It happened two or three times in the course of a couple of days but it's hard to say if that was due to the D100, the 3G stick or the network.

The Austrian D100 comes preconfigured for all Austrian networks, but it's also possible to add configurations for SIM cards of other operators and countries. The page for this is a bit hidden but one found, it's pretty much straight forward.

While most people will probably use it for Internet connection sharing, Dean Bubley recently had a number of other interesting ideas of how to use what he calls 'the dongle dock'. Have a look here, especially the last paragraph. Now I need to get a femto to test his idea 🙂

HSPA State Change Measurements

A1-state-changes Last week I did some measurements to get an idea of the time required when switching between different HSPA air interface states. While data is transferred, the mobile is usually in Cell-DCH state on a High Speed Shared Channel. When only little or no data is transferred, the connection transferred to the Forward Access Channel, which is slow but has little overhead for both the network and the mobile device in terms of control measurements and power adjustments commands. If no data is transmitted for a longer duration (e.g. 30 seconds) the connection is put into Idle state. While the IP address is retained, the physical connection between the mobile and the network is severed.

As can be seen in the picture on the left, the round trip time to the first hop in the network of a ping packet is around 100 to 120 milliseconds while the mobile is using a high speed shared channel. While on the slower forward access channel, round trip time increases to 240 to 260 milliseconds. Moving from the high speed shared channel to the forward access channel is relatively quick, it takes around 550 to 600 ms (minus the actual round trip time of the packet itself). Going back to the high speed shared channel takes a little bit more time, around 1000 to 1500 milliseconds.

When using a 3G dongle with a notebook, a connection is rarely set into idle state as there is always one program or another such as an instant messenger, VoIP client, etc., that feels it needs to send a keep alive message to a server in the network before the idle time can expire. Therefore I haven't measured it this time. In the past, I've seen values around 2500 to 2800 milliseconds.

Some say that the effect of this state switching is that web browsing feels a bit more sluggish over HSPA than over a DSL line, which always offers Internet connectivity at full speed without the need of state switching. I use 3G connectivity a lot and quite frankly, while I can feel a difference, it's absolutely no problem to work and live with it.

And here's a quick overview of the test setup: Mobilkom Austria 3.5G HSPA network, a notebook connected via Wi-Fi to a D100 Wi-Fi/3G gateway, connected to a Huawei E220 3G USB stick, HSDPA category 6, no HSUPA.