Category: Uncategorized

Every now and then I have to sigh when using Android and wished they would have at least implemented telephony features half as intelligent as Symbian did in its days. But gone is gone and I have to make the best out of it. Activation of call forwarding is one such thing I kept sighing about because changing settings requires to go down several menu levels and waiting a couple of seconds for the device to read the current status from the HLR. But now I've found an interesting fix for that: USSD codes.

Yes, this 1990's technology to use special command codes in a dial string to interact with the HLR in the network in a standardized way speeds up a 2013 Android device. And here's how it works: As it's usually the same numbers I want to forward my calls to when my device is not reachable one can extend the entry of a person in the contacts by the phone number embedded in the USSD code to perform the desired call forwarding activation / deactivation procedure. The figure on the left shows how this is done for 'call forwarding when not reachable'.

The string starting with the '*' activates call forwarding when not reachable to this number and the entry with '#' at the beginning deactivates it again. Not shown in the image is the '#' sign that follows the phone number. Using the code is then as simple as selecting the entry in the address book and to 'dial' it. There's even feedback that the action has been performed.

Three months into Edward Snowden's revelations of PRISM and other government programs to monitor pretty much everything that flows through the Internet today and the news still get worse by the day. Now, first services are shutting down because they can't offer privacy anymore in the bounds of the laws of an open, free and democratic society. Instead they are shutting down because secret court orders they can't even talk about would force them to reveal private information on an unprecedented scale. I find that very disturbing and I feel that we need to speak up against this now as politicans word wide are still not willing to have a public discussion on the right balance between security, privacy and personal freedom.

Don't get me wrong, I am not at all against court sanctioned wiretapping when there is evidence  that someone is in the preparation of comitting a serious crime. What I'm against is monitoring everything. Lavabit's owner, Ladar Levinson, who used to run a secure email service that encrytped all data stored on his servers and could only decrypt it while the user was logged in seems to be of the same opinion. Being asked by reporters he stated that in the past he's always complied to court orders to give information out to government agencies on a case by case basis. But it seems the US government now wants to go much further and hence he's decided to shut down the service. Exactly what is going on he can't tell because he is bound to secrecy by law and threatened with imprisonment if he fails to do so. But from the public knowledge how his email service works and his statement that he complied with court orders for surrendering information from and about specific accounts before, it's pretty easy to discern that the latest order went much further, likely a tap for security agencies directly into his system. From a privacy and civil liberty point of view that's absolutely not acceptable.

Next in line was Silent Circle, another secure email provider, who shut down their email service without any notice because it suffers from the same shortcoming: There's no end to end encryption in email as per design. No matter how secure you make transmission, at some point it always has to be encrypted before transmission or storage. And finally Groklaw, a popular law website has shut down as the owner feared that the privacy and confidentiality of her sources was no longer ensured with the current practice of security agencies monitoring the whole Internet rather than only the traffic of persons for which they have a court order for surveillance.

All of these services could shut down because they are privately owned. That of course does not shed good light on the big service providers who have not spoken out against this and keep running their services without being able or wanting to tell their customers of how their private communication is monitored. Society needs trust in order to function. Where's the trust in this? This makes me wonder about the future of Internet companies in the US!? The current state of affairs simply means that it's impossible for customers to trust US companies or US owned companies abroad to securely and privatly handle their data. Secret court orders can force them to reveal sensitive data to governments and what is once out of their hands can then be easily used by governments for many purposes. If I owned a non-US company today the last thing I would do is to store or process any data I didn't encrypt on my own premisis on servers of such companies. Money's usually a strong argument and loosing business because of
run-away anti-terror laws is perhaps a strong incentive to pressure for
change. But trust is lost and it will take a lot to restore it. So perhaps we'll see an Exodus of tech companies from a country to which in the past people fled to because they wanted freedom. It would be ironic in the extreme.

Sure I'm trying everything to better protect my privacy. Those of you who follow my ongoing 'Raising the Shields' sequel know that I go far beyond what a normal user can do. But a lot of my communication is still exposed to mass surveillance and some of it always will be. Raising the shields is treating the symptions, it's not the cure. We need governments to clearly define what security agencies are allowed to do, what they are not allowed to do and to communicate that openly. Otherwise, a significant part of our civil liberties will remain lost.

Having friends and business partners around the world I frequently type texts in different languages and so far always struggled with non-standard Roman characters on my German keyboard. At some point I was so fed up that I spent a couple of hours to find a solution to make the process a bit less cumbersome.

While some non-standard Roman characters can be typed even on an German keyboard by using an "accent" modifier key, others such as for example the
'ç' are not directly reachable this way. As I need such characters quite frequently, however, I was looking for a possibility to assign such special characters to standard Roman alphabet keys together with the ALT or ALT-GR modifier key. The 'ç' for example should be reachable with the ALT or ALT-GR key (not available on a standard US keyboard) + the standard 'c' key.

On Ubuntu and I guess many other Linux based GUI's, the ALT key is already used for other purposes by the GUI so I focused on a solution with the ALT-GR key. As this key is not available on the standard US keyboard layout I am not sure if the following also works for this keyboard layout. But for all layouts that have an ALT-GR key here's the command to put the 'ç' on ALT-GR + c:

xmodmap -e "keycode 54 = c C c C ccedilla Ccedilla ccedilla Ccedilla"

54 is the code for the key on which the standard Roman "c" is located at on a German keyboard.

The current assignment of all keys is queried with the following command:

xmodmap -pk

and

xmodmap -pk | grep "(c)"

with the brackets around the character filters the output for the line with the code for key to which a specific character is assigned.

Non-standard Roman characters have a name that can be used in the assignment command above. The 'ç' character, for example like in 'François', is called ccedilla for the lowercase variant and Ccedilla for the uppercase variant. For the list of other special characters have a look here.

For each special character assignment a separate xmodmap -e… command is required. Changes are not persistent, however, i.e. a reboot returns the computer to the standard keyboard layout. To make the assignments persistent one can for example put all xmodmap commands in a shell script and execute it automatically during the login process.

So far, pretty much everyone in the industry measured channel bandwidths in what either the downlink or the uplink channel provides. A UMTS channel thus always had a bandwidth of 5 MHz despite twice the spectrum being used, 5 MHz for the downlink and another 5 MHz for the uplink. Sometimes this was also described as 2 x 5 MHz. But it seems some in the US are now adding uplink and downlink together as for example in this Gigaom article. A small 5 MHz LTE carrier now has a bandwidth of 10 MHz. Sounds nice when comparing it to other US network operators that in their words also use 10 MHz LTE carriers, which are, of course 2 x 10 MHz. So by those standards network operators in Europe using the 1800 or 2600 MHz bands already have 40 MHz LTE deployed! That sounds nice! After 4G, Real 4G, True 4G and LTE-Advanced it's the latest smoke bomb to confuse the world and make yourself look better than you really are. Sigh…

Over the years my use of Bluetooth for various purposes has significantly diminished. With the advent of Wi-Fi tethering that I wished for back in 2006 when the first phones with Wi-Fi connectivity were pioneered by Nokia (see here and here) and a few years later realized on the Android platform, my Bluetooth use became occasional at best. I tried Bluetooth headsets every now and then but was always disappointed with their range and I just don't listen often enough to music on my smartphone to have made it worthwhile to buy a Bluetooth enabled stereo headset. Also for transferring pictures or files from mobile devices to my PC or vice versa, Bluetooth was mostly not an option because I always needed a dongle on the PC side. The time this takes was usually the same as removing the SD card from the smartphone and inserting it into the PC or plugging in a cable to access the pictures from the simulated SD card provided by the generic SD card driver that Android provides. My new PC, however, now provides for the first time a built-in Bluetooth transmitter and due to no longer having to plug-in anything, I have found myself using Bluetooth again for quickly moving files and images back and forth if there is only one or two files or images involved in the transfer. A late renaissance of the technology as Wi-Fi direct still doesn't seem to take hold (see here, here and here).

Venturing down a bit on the frequency scale I've now also taken a closer look at DVB-T television signals with my DVB-T USB receiver stick and SDR-Sharp. The image on the left shows the right edge of an 8 MHz DVB-T signal that encodes 4 television stations. Like in the LTE signals I wrote about in a previous post, there are also vertical stripes that can be seen in the waterfall diagram. The stripes are much narrower, however, likely due to the 1 or 4 kHz carriers used in the C-OFDM modulation of DVB-T compared to the 15 kHz OFDM carriers used in the LTE downlink. Interesting to note is that parts of the channel on the frequency axis are broadcast with more power than others. Not sure why, my understanding of DVB-T signals is very limited.

I was also quite baffled with how little of the spectrum assigned to terrestrial television is actually used today. In Germany, DVB-T can be broadcast in the 177.5 – 226.5 MHz range (i.e. a total bandwidth of 49 MHz) and between 474 and 786 MHz (i.e. a bandwidth of 312 MHz). That's 361 MHz in total or enough for 45 DVB-T channels. Despite DVB-T being a single frequency technology in which neighboring transmitters can use the same channel, not all can be used simultaneously as different TV stations are broadcast in different parts of the country. But even if only every second channel is used, that spectrum could still hold an impressive 90 TV channels. In practice much less is broadcast today and when scanning through the spectrum in Cologne, most channels were empty.

360 MHz is quite a sizable chunk of spectrum and as the popularity of DVB-T and terrestrial TV broadcasting is on the decline I can see why there are moves to re-assign the 694-790 MHz range for wireless Internet connectivity, i.e. for use with LTE and perhaps other wireless technologies in the future. The Wikipedia article linked above indicates that the additional band could be brought into operation by 2026. This would give network operators access to an additional 96 MHz of spectrum that, with a duplex gap of 11 MHz, would offer 42 MHz for downlink and 42 MHz for uplink data transmission. That's a bit more than the current digital dividend spectrum in the 800 MHz band bundled in LTE band 20. Here, 30 MHz of bandwidth is available in each direction and used by three network operators in Germany today.

While in Europe, GSM, UMTS and LTE are used by all network operators, the US wireless landscape has always been much more diverse. This meant and still means that there always had and have to be several device variants to support different networks. But with the advent of LTE and advances in chip technology this may be about to change.

When Google recently introduced the 2013 version of the Nexus 7 tablet, it upgraded the cellular hardware to support 7 LTE bands. For details see Google's page on the Nexus 7 and AnandTech's mini review over here which has a somewhat different frequency listing. Apart from the stunning number of supported LTE bands it also supports the five major UMTS frequency bands.

The LTE band combination for the US is especially interesting, as band 13 is included for Verizon's LTE, band 17 for AT&T's LTE and band 4 for T-Mobile's LTE. This might very well become the future trend and will finally allow US consumers the same flexibility as in Europe to buy a device independent of the network operator or even change network operators over the life cycle of the device.

I'm not quite sure how Sprint fits into this equation!? From what I can tell they have LTE up and running in a 1900 MHz band and have taken over Clearwire's 2500 MHz TDD assets. While the 2500 MHz TDD band is not supported by the device I have no information which band Sprint uses with it's 1900 MHz assets. If you have some more information on that, please leave a comment.

Also interesting is the absence of CDMA support in the tablet. Probably not surprising for a tablet, as mobile telephony, if implemented on the user interface at all, is not a prime use case for a tablet. Also, unlike UMTS with it's great data rates, CDMA EvDo only offers limited speeds which are undesirable in a data heavy product as well. So why bother?

While in the US, network operators were perhaps struggling with the amount of spectrum they had for their 3G services and thus rushed to jump onto the LTE bandwagon, Europe continues to enjoy very good data rates over 3G UMTS to this day (for details have a look here for example) in addition to the massive additional capacity now available on other frequency bands with LTE. So I was wondering a bit how much for the UMTS 2100 MHz band 1 spectrum is actually used today.

Cologne is one of the bigger cities in Germany so it is fair to assume that it is also a place in which the highest number of UMTS carriers are needed to satisfy demand. In total, band 1 can host 12 individual UMTS 5 MHz carriers. In practice, however, SDR-Sharp and my DVB-T stick show quite clearly that only 7 of those are used today. In other words, 40% of the bandwidth available for UMTS in this band are still unused.

It's interesting to also look at how many 5 MHz slots each of the four network operators has in Germany in the prime UMTS band. The distribution is as follows:

• Operator 1: 2 channels
• Operator 2: 3 channels
• Operator 3: 3 channels
• Operator 4: 4 channels

Operator 1 has both channels on air and thus, LTE in other bands is the only way to increase available capacity.

Operator 2 and 3 also have two channels on air and in addition have deployed 10 MHz in band 20 for LTE. If necessary, they could still extend their UMTS capacity with one extra channel.

Operator 4 is only using one of its four channels so far! That's in line with that operator always trailing all other operators in speed tests by quite a bit. As that operator does not have spectrum for LTE in the 800 MHz band I would not be surprised if they started with LTE in the 2100 MHz band with a 10 or 15 MHz carrier.

After having taken a look at GSM and UMTS signals on the physical layer, this post is about how LTE signals are visualized by SDR-Sharp.

In Germany we are in the comfortable position to have three network operators offering LTE services in the 800 and 1800 MHz bands so it is not difficult to find an LTE carrier signal. Like for UMTS, it's not possible to show the full 10 MHz (800 MHz band) or 20 MHz (1800 MHz band) LTE channel as the hardware and software are only capable of showing around 2 MHz at a time. But one can observe the edges of the signal or any particular part in between. The first picture on the left shows part of an LTE signal on the 1800 MHz band. All LTE signals I have observed feature the vertical stripes. While the stripes make sense due to the OFDM modulation using many individual 15 kHz carriers that for a 10 or 20 MHz channel I am not quite sure why there are strips that are marked in yellow while other parts are blue (i.e. a lower signal energy). I first thought that perhaps this might have something to do with the reference signals but they are evenly distributed through the carrier and are not only present in particular spots!? Another particularly interesting thing in the image is the reddish bars in parts which is actual data transmission occurring while I downloaded a web page. In other words, it's pretty easy to see on layer 1 how loaded a cell is.

The second image on the left shows an LTE uplink transmission from my UE. Again, keep in mind that the image only shows a fraction of the total bandwidth used for uplink transmissions. The transmission starts in the lower part of the waterfall diagram and was again recorded while downloading a web page. Once the page was fully loaded one can see very nicely how uplink transmissions become spurious and at some later point, not shown in the image, cease completely. A further detail worth mentioning is the absence of the vertical strips compared to downlink transmissions. This is because in the uplink direction SC-FDMA modulation is used.

Incredible insight gained with a 20 Euro DVB-T receiver and the power of open source SDR-Sharp!

Two years ago I used a mobile phone that could show me the GSM frequency channels to find out whether all GSM network operators in Germany make use of the GSM 900 MHz band. While the original two GSM network operators obviously made good use of their beachfront property, the other two network operators that came later and at first only had 1800 MHz spectrum made little to no use of the 900 MHz spectrum. With my SDR-Sharp + DVB-T Stick Layer 1 utility I now revisited the topic to have a look at the complete band owned by the original 1800 MHz carriers in the 900 MHz band to see if I had overlooked something or if something had changed in the meantime.

The result is pretty much the same as two years ago. One of the two operators makes a bit of use, I could observe at least one or two carriers in their 5 MHz part of the spectrum in Cologne (i.e. in the city). This is very little compared to the two original GSM network operators that have many many cells on air in the same amount of spectrum.

The second original 1800 MHz operator still doesn't seem to make any use of GSM 900 in Cologne. I could only see very faint 200 kHz signals and I am not quite sure what they are. Perhaps echos of other carriers nearby shown here by my tracing hardware which has its limitations? Or perhaps cells used outside of Cologne that are still visible here?

In any case, both make so little use of it that I wonder if one day one of them might just start with either a UMTS 900 or an LTE 900 carrier in this part of the spectrum.