Category: Uncategorized

A couple of days ago I wrote the "LTE Voice Takes a Break" post musing on the fact that for some time there hasn't been a lot of news on any of the proposed voice over LTE solutions, potentially because everyone is waiting for devices with which they can demonstrate their solution. But it seems the VOLGA-Forum has pressed ahead internally and continued working on its specs. The latest update now includes SIM-less emergency calling over VOLGA, making the solution even more robust by not even requiring a circuit switched network for such emergency situations. Also, they've introduced means to use the VOLGA architecture over HSPA, introduced optimized voice bearer routing (have to take a closer look as to exactly what that is, or maybe someone can leave a comment below) and have defined some APIs for LTE handsets (also not sure yet what they will be used for). So its good to see these incremental additions coming while everyone is waiting for LTE handsets.

What do you do as a network operator in places where hundreds and hundreds of people waiting in line and potentially tens of thousands on people visiting that place every day? Right, you make sure you have excellent network coverage in that spot to keep your customers happy while they are standing in line. There's your chance, the people are bored while waiting in line so it's a good opportunity to sell some voice minutes or some bits of data when your subscribers make good use of the idle time. Maybe they even take a picture and send it to mom via MMS!? But in some places of the world, clocks are ticking differently.

Recently I was up the Empire State Building in New York, which exactly resembles this scenario, except…, well, there's no network coverage up there from any GSM operator. And it's not that you are just there for a couple of minutes. If you come at the wrong time you probably have to wait more than an hour in a no network coverage area. I am stunned, really! Ah hold on yes, there was some sort of coverage, AT&T UMTS coverage was indicated on the iPhone of my neighbor. Very good reception was indicated but each time he wanted to use the phone the bars went away. Not sure what that was but a coverage that is not working is even worse than no coverage at all. Yes, I am not amused.

Just went through the specs on EPS trusted non-3GPP networks to find some details on CDMA to LTE interworking when I suddenly wondered if there is anyone at the moment besides Verizon who will need this kind of interworking!? While lots of network operators require GSM/UMTS/LTE interworking (handover, cell reselection, voice handovers, etc) there seem to be only few CDMA operators who might require the functionality. Any others come to your mind besides Verizon?

When talking about signal strengths, values are usually expressed in dBm, which is, according to Wikipedia 'an abbreviation for the power ratio in decibels  (dB) of the measured power referenced to one milliwatt (mW)'. In other words, dBm is a value for the power or signal strength on a logarithmic scale.

In practice, signal strengths between -60 and -90 dBm are encountered at the receive antenna of a mobile device. So how much is that actually? On the high end of the scale, -60 dBm equals 0.000000001 Watts, while – 90 dBm are 0.000000000001 Watts.

I find two things quite remarkable in these numbers: First, both values are very small, definitely not enough to power anything and its amazing that receivers can pick up such small signals. And secondly, the wide range a receiver has to adapt to as the weakest signal compared to the strongest signal in this example is 1000 times weaker.

Interesting news from mobile network operator "3" in Austria: Heise reports in this article that their monthly data volume is now at 700 Terabytes per month. According to Wikipedia they currently have about 1 million subscribers which makes this number even more interesting, as on average that would be 700 MB  per subscriber per month. Of course many of their subscribers only use the network for voice calls and SMS so imagine what the number must be for the typical mobile Internet user in their network. With Austria being a super competitive mobile network country and usage numbers way ahead of those in other countries it's a good indicator of what is possible and of things to come.

One cool feature of UMTS compared to GSM is that you can't hear the interaction with the network when the mobile device is close to a radio or telephone conference equipment. This is because while GSM transmits bursts whose transmit on/off changes can be picked up by such equipment, UMTS transmits continuously in the uplink direction and as a consequence no annoying clicking sounds can be heard. With the introduction of Continued Packet Connectivity (CPC), however, this will change to conserve power. So I am wondering if CPC devices will again produce some sort of a clicking noise in other audio equipment!? I hope not… And in case it does it would be nice if CPC could be deactivated in the device. I know, highly unlikely that such an option will be put into devices but then one never knows. If a 'sexy' name can be attached to it someone might just do it. How about 'stealth mode' or 'undisturbed meeting mode'. I am sure marketing departments can come up with something better.

I was in New York for a couple of days recently and as my N95-8GB (yes, I am a traditionalist) can only do UMTS 2100 MHz my voice calls and small screen Internet connectivity had to be content with the GSM network layer. But there are interesting things to discover here as well.

It looks like AT&T consistently uses AMR Half-Rate in the center of the city to double their voice capacity. All calls I established were always set-up with this codec. Also, AT&T uses both the 850 and 1900 MHz bands and if the mobile detects both, the network always handed the voice call over to a 1900 MHz carrier, even when the signal in the 850 MHz band was 30 db stronger. That could have many reasons, maybe they use the 1900 MHz band as a capacity layer and reserve the 850 MHz carriers for difficult terrain and indoor connections.

Speaking of difficult terrain: AT&T when you have a minute, have a radio team look at your coverage in Penn Station. Even when standing still, my calls in the underground station frequently dropped. Despite a high signal level, audio quality was horrible, which points to interference, and every couple of seconds, the call was handed over between the 850 and 1900 MHz layer and the traffic channel bounced between AMR Full-Rate and Half-Rate. Quite a frustrating experience.

What I really miss on long-haul flights is Internet connectivity. A couple of years back, Boeing and its Connexion system was a cool option if you flew Lufthansa and a few other carriers but it seems the service was not profitable and Motorola discontinued the service. Too bad, long-haul is offline again since then. But it looks like things are going to change again, as Lufthansa has announced they will enter a cooperation with Panasonic and offer Internet connectivity again. Few details were available so far but now Heise has published an interesting article on the topic giving some details on the system and the general renewed interest in in-flight Internet and GSM connectivity. The original article is here and the Google translated version to English is here.

Like the earlier system, the Panasonic equipment is capable of downlink speeds in the double digit megabit per second range which should be sufficient even if a couple of dozen people are online at the same time. For the satellite connection the Ku-band (10-12 GHz) is used. In addition to Panasonic, there are two other companies in the business. OnAir uses a narrowband signal and the Heise article says the speed is limited to 400 kbit/s. That's too slow for full screen Internet connectivity in my opinion so maybe OnAir focuses more on voice calls, SMS and small screen (smartphone) connected applications. And then there is ROW44 with similar speeds as Panasonic but so far limited to the US market.

All very good signs that in-flight Internet might have a revival and personally, I hope it will be sooner rather than later.

It is always said that Quality of Service (QoS) mechanisms are important for VoIP, but what does it mean in practice? Well, as long as that Skype connection just works it doesn't really mean a whole lot. It suddenly means a lot though, when the call breaks up and the other end is barely understandable due to congestion that provokes rapid round trip time changes between 300 ms and 1600 ms in the course of just a few seconds.

This happened to me recently and at the time I wished I had some QoS preferring my VoIP packets over whatever else the other 99 participants of the meeting were transferring over that Wi-Fi link connected to a way too slow backhaul link at the time. It suddenly makes you aware of the benefits of network enforced QoS. And it must be the network because otherwise half the participants would immediately tweak their PCs to demand a better QoS for their packets irrespective of the application. Well, that's at least what I would do…

So in the end I resorted to making a call over GSM. Just another way of getting QoS, really, just not on an IP bearer.

Yes, I very much like my wireless mouse but I have just discovered the use for a cable bound mouse these days again: On an airplane! For long haul flights, if you have enough space to use a mouse it comes in very handy as wireless mice are not allowed to be used.

I wonder if that "suddenly" changes again once airlines introduce Internet access on some of their flights again (e.g. Lufthansa via satellite or American carriers via land based systems) but for now, the cabled mouse comes in quite handy.