Author: Martin

The 14.4 Psychology

A little anecdote today: In the "old" days I had a 14.4 kbit/s fixed line modem for quite a number of years. Even though new and shiny 28.8 kbit/s modems came on the market, I was stuck with my '14.4' because the new modems were expensive and as a student my monetary resources forbade an upgrade. So for me, the number '14.4' has a bit of a negative touch attached to it ever since.

Fast forward to today to the "megabit" era. In wireless, HSPA 7.2 Mbit/s downlink is currently pretty much state of the art. Some network operators have announced further upgrades and in due time, top speeds of 21 MBit/s and beyond will be reached. On the way to double digit speeds, there's also a 14.4 step. No, not kbit/s, but Mbit/s. Still it kind of reminds me of my 14.4 kbit/s days and has a negative "psychological" touch to it to me.

Strange strange, because I'd really like to have this 14.4 this time around 🙂 Any numbers in telecoms that have a psychological edge for you?

The HSUPA RTD Delight

When discussing High Speed Pack Uplink Access (HSUPA), or E-DCH, to use the correct term, the major focus usually lies on the improved uplink speeds. Seldom is it mentioned, however, that E-DCH also improves the latency, i.e. the time it takes for an IP packet to be sent to a server and a response packet to arrive back to the source. But is this relevant in practice?

So far, I used an HSDPA 3.6 non E-DCH capable 3G stick and my round trip delay times (RTD) to a number of web sites I visit most were around 110 milliseconds. Over a DSL link, the same sites can be reached with an RTD of around 45 ms. In other words, a difference of 55 ms. In practice this can be felt especially during web browsing, as web sites take a bit longer to load over 3G compared to a DSL link with a similar bandwidth. Not that this is a showstopper but it can definitely be felt.

A few days ago, I ran some tests with a Cat 8 HSDPA + HSUPA 3G stick and was quite surprised that the RTD times to those web sites were just around 65 ms. In other words, that's only 20 ms more compared to DSL. The difference to the HSDPA only 3G stick are quite remarkable. I compared backwards and forwards with my DSL line but I couldn't "feel" the difference anymore. Stunning!

The one thing E-DCH does not do away with, however, are the delays incurred when radio states are switched. The 300 ms or so delay when switching between a full DCH and the less power and resource intensive FACH are still there. In practice, however, background traffic from applications such as my Instant Messengers usually keep the link in DCH state so I rarely come into contact with it anyway.

Google Books and the Hardcopy on the Table

Book-search There are lots of political discussions around Google books these days but this short blog just focuses on a cool feature I just found. I've got lots of good books on wireless topics at home but when searching for a specific piece of information it often takes a long time to find it, even if I know in which book I could find the answer. So I usually turn to Google first to see what the search engine can come up with before I start flipping through and index or the table of contents of a book.

So one of these days I wanted to find out what the A1 event in LTE is all about. So I typed "LTE A1 event" into the Google search engine and one of the first entries in the result list was a book on Google books which had the answer. Google books gives me a page number and a preview of the page. In this particular case I had the book on the bookshelf already so I could go directly to the page and read the whole subsection on the topic. Excellent!

Ericsson says 1GB can be had for 1 Euro

Here's an interesting article from Ericsson on the business case of mobile broadband. Taking CAPEX, OPEX for both access and core network into account, the article comes to the conclusion that once an economy of scale is reached in terms of the number of broadband subscribers, the network can deliver 1GB of data for one Euro.

While this is the main outcome of the paper, there are a number of other pieces of information in there on which the calculation is based which are quite interesting. Here are some which I noted:

  • 20% of the cells carry 50% of the traffic. I've heard of similar numbers before and I think it's a good thing because the network operator can focus on upgrading a subset of all cells rather than having to work on the whole network simultaneously.
  • 3-5% of the cells carry very heavy load. The article doesn't say where such cells are usually located. It would be interesting if this load is mostly generated in-house, for example in shopping centers, train stations, airports, etc. and if femtos would provide a cheap future capacity extension for those places.
  • The technical evolution of 3G networks is all about keeping pace with higher user demand for capacity. Fully agree to that.
  • Going from 7.2 MBit/s to 21 MBit/s adds a cost of around 10-15% but increases capacity around 70%. An interesting statement because 7.2 -> 21 MBit/s is about a 3x theoretical speedup while from a practical point of view it is much less. The article says its 70% or 0.7x.
  • 70% of overall CAPEX is spent on base stations.
  • 50% of overall OPEX is spent on base stations.
  • The €1 per GB seems to be a number over a 5 year period. At the end of the article it is stated that the networks that Ericsson looked at for the study are not quite there yet. However, the first network, after 2 years of operation, reported that they have reached €2 per GB.
  • For the study, a base station price of €40k was assumed. Looks like they have gotten quite a bit cheaper than what was calculated with just a couple of years ago.

And just to get a bit more aggressive, this Ericsson presentation states that mobile broadband is even cheaper than DSL (cp slide 13 ff.). I assume that leaves IPTV delivery out of the equation, but still it's an interesting way of looking at things.

Spectrum Use Today of Wi-Fi and 3G Compared

Here's an interesting comparison of how much spectrum is used today for 3G vs. Wi-Fi. In Europe, UMTS/HSPAS is assigned a 60 MHz uplink + 60 MHz downlink = 120 MHz. Out of that only 20+20 = 40 MHz are in active use today even in dense urban areas except for a few exemptions. For details, see here and here. In the future, the digital dividend band in the 800 MHz band (2×35 MHz), and the IMT extension band in 2.6 GHz (2×70 MHz) will be added.

Wi-Fi 802.11b and g use the 2.4 GHz band spanning 80 MHz. Especially in dense urban areas, I'd say that's already used quite intensively these days. In addition, some 802.11n kit can also use the 5 GHz band, where almost 400 MHz is allocated for Wi-Fi and other short range wireless systems. It's probably still not used a lot but with more and more 5 GHz band enabled equipment appearing that will certainly change.

So, what's the message here? There are several. 3G only uses a fraction of the spectrum that is already allocated today without suffering massive bandwidth bottlenecks. The same applies to Wi-Fi although the original 2.4 GHz band is already quite busy. But if your gut feeling told you that cellular networks probably had much more spectrum available than Wi-Fi, then that was not quite accurate.

I Need Opera Mini for the N900

Yes, like many others, I am waiting for the release of the Nokia N900 and I have lots of good reasons for it. But there's one thing I really need on that device before I can use it: Opera Mini. True, in all the videos, the browser looks great. However, try using the browser with EDGE and frequent loss of signal. Quite a different experience under such circumstances.

I've used Opera Mini for years now and just under such circumstances, which happen more often than not when traveling, it really excels. But I am afraid that with the N900 we have to wait a bit for the browser as it is a Java ME application, an environment the N900 does not support (yet). So anyone heard of Java ME being added to the N900 software repository or Opera working on a port of their Mini for Maemo Linux?

HSDPA now with 28 Categories and Speeds up to 84 Mbit/s

Hsdpa categories Almost exactly two years ago, I wrote a post in which I reported my first sighting of new HSPA+ device categories. The top at the time were category 14 and 16 with 64-QAM modulation and MIMO respectively and speeds up to 28 Mbit/s. This was Release 8 of the 3GPP standards. Now in Release 9, 28 device categories are listed in 3GPP TS 25.306 (see table 5.1a) with top speeds under ideal radio coverage of up to 84 Mbit/s if everything is combined, i.e. 64-QAM, MIMO and Dual Carrier. For almost every combination of options there's a category now. Breathtaking…

As I found no good overview of which device category goes up to which speed, I took the liberty of updating the HSDPA article on Wikipedia and add device classes 16-28 in the table. A screenshot of it can be seen on the left.

Now where can I get a Category 28 device and a suitable network please? 🙂

P.S. 1 – Important: Note that all indicated speeds are top speeds under ideal signal conditions. See here for further details and a reality check!

P.S. 2 – I left out cat 17 and 18 as they are a bit special and I am not sure that they will be relevant. If you have an opinion on this one, please let me know. Also, feel free to add them to the table on the Wiki yourself and while you are at it, have a go at the coding rates for the higher categories as well.

The 1000ms SIP Delay Mystery

Here's a mystery I can't quite figure out so I thought I'd write about it to see what you think: There are a number of VoIP services I use frequently over a DSL link and they all work well. Over a 3G wireless connection, however, SIP via Sipgate.de isn't working as it should. While there is almost no noticeable delay in the speech path in downlink direction, the uplink speech path has a delay of almost 1000 ms!

One might argue, that's a 3G issue, but it definitely is not, as the delay in Skype in both directions is just fine. O.k. so maybe it's a combination of the mobile device I use for my SIP calls, a Nokia N95, and the 3G router that's causing this. No, I can rule that out, too, since I've tried it with a Huawei D100 3G router as well as with my Fritzbox DSL/3G router from AVM. I also use the Fritzbox over DSL and the N95 works well over that backhaul link, so that can't be the issue either.

My final idea: Maybe something is done in the network!? Possible but unlikely as the behavior is the same in Vodafone's network in Germany, the Mobilkom A1 network in Austria and Wind's network in Italy.

Other ideas, anyone?

The Economist on Mobile Banking in Africa

Here's an interesting article I've recently discovered in The Economist on mobile banking solutions in Africa and Asia such as MPesa and others. In my opinion the article contains good information on how such services work, how people benefit from them and the issues encountered with the local banking system and regulators. Also quite interesting are the many comments which contain quite different points of view so be sure to check them out as well.