Martin – Page 287 – WirelessMoves

German Railway Extends Wifi On Trains Coverage

It looks like German Railways (Deutsche Bahn, DB) has had some positive feedback from their Wifi on Train pilot on the track from Dortmund to Cologne and has decided to expand the offer. Since 2005, seven high speed trains are equipped with on train Wifi which regularly run back and forth between the two cities. To connect to the Internet, Wifi to UMTS bridges were installed in the trains which used the 3G network of T-Mobile to backhaul the Internet traffic.

Now, DB has decided to extend the partnership with T-Mobile who will invest in new wireless base stations and tunnel coverage in 2007 on the tracks between Frankfurt – Hanover – Hamburg and Frankfurt – Stuttgart – Munich. The press release does not say if T-Mobile will use it’s UMTS network again or if they will deploy a new network based on Flarion’s Flash OFDM technology (now part of Qualcom) on the 450 MHz band as some rumors had it in the past (see here and here).

Deutsche Bahn will also increase the number of Wifi equipped trains to 50. Good news for me since I regularly use high speed trains between Munich and Stuttgart. Can’t wait to test it. After announcing to install power sockets at every seat this is yet another sign that DB has understood how to get new customers.

Carnival of the Mobilists over at AAS

This week, the Carnival of the Mobilists has arrived at All About Symbian. In it’s 66th edition, it’s as always a great roundup of what mobile bloggers had to say in the past week. Great job, Rafe, thanks a lot! So don’t wait and head over!

A Real Life Comparison of HSDPA and UMTS

These days I am totally unplugged but still always connected as I am staying in Italy for the moment, far away from my ADSL line back home. UMTS has kept me connected to the world in the past two weeks and I’ve been writing about my general experiences over at m-trends. So far, I’ve used a prepaid card from Wind to keep me connected. As Wind is not offering HSDPA (High Speed Data Packet Access) in their network yet the HSDPA card remained in the suitcase. Over the weekend, however, I’ve bought a prepaid card of Telecom Italia Mobile (TIM) where HSDPA is available. Their offer is not as good as Wind’s, giving me ‘only’ 500 MB for 20 euros over 30 days and an additional 1GB for an extra 20 euros should that not be enough. Still, for my purposes it should be more than enough. I am pretty much impressed by the speed increase HSDPA brings over plain UMTS. Also, responsiveness when clicking on a link in the web browser has noticeably increased as well. For the technical details read on.

The Hardware

HSDPA was standardized in a flexible way allowing data rates to grow as end user devices and networks become more capable. For my test, I used a Sierra Wireless Aircard 850, which supports HSDPA category 12 (inter-TTI of 1, QPSK only), i.e. a top speed of 1.8 MBit/s. Note that there are already category 6 mobiles and data cards available today promising speeds of up to 3.6 MBit/s by using 16QAM modulation in good coverage situations. However, my card is not capable of doing this yet. I am looking forward to compare the speeds of these two categories in a real network once I can get a hand on one. Enough about networks and terminal categories for the moment. For details you might want to take a closer look at my book 😉

Top Speed on Sunday Morning

There can be a big difference between theoretical maximum speeds and speeds that can be reached in a real environment. As I woke up early on Sunday morning I gave it a try when most other people were probably still sleeping, i.e. low overall radio network load from other people making phone calls and accessing the Internet. I was quite positively surprised in my first download test as the average speed for downloading a large file from the internet was about 1.5 MBit/s. Hey, that’s faster than my DSL line in Germany! It looks like TIM has not only upgraded their base stations to HSDPA but also ensured that the backhaul connection from the base station does not become the bottleneck.

I also downloaded the same file via the Wind UMTS network to be able to compare the behavior. As expected, the network load was also low and the download reached the highest possible UMTS download speed of 384 kbit/s. Also very nice but four times slower than via HSDPA.

The image above on the left shows a graph of the download as it happens. I started the download inside the apartment where radio coverage was far from ideal. Nevertheless, it can be seen in the graph that the download speed exceeded 1 MBit/s. Going to the balcony with the notebook after about half the download was finished improved the radio environment and the download speed even further.

Speeds at Other Times

To see how the network load impacts download speeds I ran the same test again at around noon on Sunday. This time my download speed was about 750 kbit/s or about 90 kbyte/s. The corresponding graph for the download is shown in the third image on the left. Note that I did not download the whole file which is why the download graph is not as long as in the previous image. Not quite as high in the morning but still quite respectable.

Web Browsing

The next test on my list was web browsing. I connected one notebook to the Internet via TIM’s HSDPA network and another one via Wind’s UMTS network. Then I surfed to a number of graphics intensive pages such as those from Nokia, CNN and a couple of German news magazines to compare first page display times and overall download times. While UMTS is by all means capable of delivering a good web browsing experience, HSDPA is by far quicker. All pages I tried always started to be shown a couple of seconds earlier on the notebook with the HSDPA connection than on the notebook with the UMTS connection. Needless to say that the time until the complete page is downloaded is also faster. I have to try again when at home with an ADSL connection in reach but I am pretty sure I would not be able to tell the difference between a DSL line and an HSDPA connection for web surfing except for the channel establishment delay described below.

Uplink Speed

TIM has also upgraded its radio network to support uplink speeds of 384 kbit/s. Note that this is not HSUPA (High Speed Uplink Packet Access) yet but plain 3G standards pushed to the limit. Even under average reception conditions, sending an eMail with a 2MB attachment was very quick with an average uplink data rate of about 350 kbit/s. Compare that to most 3G only networks today which usually support 64 kbit/s or 128 kbit/s at the most. 1 MBit/s ADSL connections usually have a 128 or 180 kbit/s uplink. So in this respect, current HSDPA even have a speed advantage in the uplink over a typcial 1 MBit/s DSL line.

Round Trip and Channel Establishment Delay

Round trip delays have also decreased a bit. While 3G connections usually have around 120-130 ms round trip delay times, I measured 90-100 ms to the first hop in the network over the HSDPA connection.

During the test it was also interesting to see that there is still a noticeable delay of 2.1 seconds in ping times or web page access time when no packets were transferred for some time. This is due to the fact that the network releases the HSDPA radio connection after some time of inactivity to reduce the power drain on the mobile’s battery and also the channel usage on the air interface. I experimented a bit and it seems TIM has set the transition timer to 15 seconds. Unless TIM has a stupid network implementation which drops the user to PMM IDLE state after this time, the 2.1 seconds are the time required for the transition from the FACH to HSDPA (DCH).

Summary

I am very impressed by the performance of HSDPA. Even my first generation category 12 data card exceeds a download speed of 1.5 MBit/s in a lightly loaded network and still over 700 MBit/s under normal network load conditions during the day. Uplink speeds beyond 350 kbit/s are very impressive as well. With further enhancements like category 6,7 and 8 handsets in the near future, multiple antennas in end user devices, enhanced receivers, improved signal processing, etc., etc., both end user speeds and overall wireless network capacity will continue to grow over the next couple of years. And beyond that, 3GPP Long Term Evolution is already in the pipe which ensures speeds will continue to rise. After all, the You-Tube generation needs as much bandwidth and speed as they can get!

Note: Click on the "HSDPA" category link below next to the date to see all articles on further tests which have followed afterwards.

Call Us Free By Skype

This is not a very mobile blog entry today unless you are using Skype via one of the third party clients now available. For many years I’ve heard people in the industry talking about how to integrate telephony functionality into web pages. Never saw a web site that actually did it until today. Take a look at the picture on the left. It’s part of a web page of Hotel Morgana in Rome, Italy. A Skype call button and the invitation to call them via Skype for free is placed neatly in the middle of the page. It makes total sense for them as they have guests from all over the world who would not be able to call national 0800 numbers. For them it also makes sense as the cost of offering the service for them is either zero as well or only very small in case they use Skype call forwarding to their fixed line phone. This is free for the caller and only costs a couple of cents to the hotel owner.

VoIP capacity over HSDPA

One of the main issues with VoIP over 3G networks is that the number of possible simultaneous calls per cell is much lower today than the number of calls that can be transported over 3G networks in circuit switched mode. This is due to the fact that the radio interface has been optimized on every layer to squeeze through as many circuit switched voice calls as possible. VoIP calls on the other hand are transported over IP which makes it impossible to specifically adapt each layer of the air interface for the application as each protocol layer is independent from the one above and below.

Another disadvantage to transport voice over IP is it’s requirement for real time data transmission. As voice data can be compressed quite well, the required bandwidth is quite small. In order to keep the delay acceptable a single IP packet only carries around 20 milliseconds of speech data. At this rate, the additional information generated by the air Interface, IP, UDP and RTP headers is almost the same as the actual voice data. This doubles the bandwidth required to transport a voice call over IP compared to transporting it over optimized circuit switched channels over the air interface.

As if this was not enough there is yet another problem that plagues VoIP over wireless: While most other IP applications benefit from retransmission of lost or damaged air interface frames, this is most unwelcome for VoIP as it’s better to loose a couple of frames rather than to wait for the retransmission. As the lower layers are not application aware, however, it’s not possible to carry voice and data of other applications over the same connection and treating them differently on the air interface.

HSDPA And Intelligent Scheduling Come To The Rescue

While I knew all this for some time now and was thus a bit pessimistic about mid-term success of VoIP over 3G and WiMAX networks, Harri Holma and Antti Toskala describe in their book about HSDPA, or 3.5G as sometimes called in the press, that VoIP capacity is not necessarily lower than 3G circuit switched capacity per cell. Compared to an average of around 64 simultaneous circuit switched calls per cell as referenced in their book, they present a study which results in at least equal or even higher VoIP capacity in an HSDPA enabled cell. So how’s this possible with all the difficulties mentioned before? Here are the main principles they used for their calculations:

HSDPA Capacity

Due to the use higher order modulation for mobile stations with good reception conditions, better error coding and fast re-transmission, total capacity of an HSDPA cell is twice as high compared to a 3G UMTS only cell.

Use of AMR

Many VoIP implementations today use the G.711 codec for digital voice transmission which requires a bandwidth of 64 kbit/s. For HSDPA cell capacity, the authors used the AMR codec instead, which is also used for circuit switched wireless calls today, which only requires around 12 kbit/s to achieve the same voice quality.

Header Compression

Compressing IP headers of VoIP frames is absolutely essential for capacity. Thus the authors have assumed the use of Robust Header Compression (ROHC) for their simulation. This is quite realistic for the future as ROHC between the mobile station and the RNC is already in the 3GPP standards.

Intelligent Scheduling

HSDPA packets have a transmission duration of 2 milliseconds. A 2ms packet, however, can hold several VoIP packets. To achieve the highest cell capacity the traffic scheduler has to hold enough packets destined for a user to fill up a full air interface frame before they are sent. While this increases the total VoIP capacity of the cell it also has the disadvantage to introduce unwanted speech delay. For their simulation the authors did not queue more than three VoIP packets for a single user. This introduces a maximum additional delay of 60 milliseconds.

Fast HSDPA retransmission

The retransmission problem for VoIP described above is reduced by HSDPA by it’s fast retransmission scheme. A faulty packet can be retransmitted within 10 milliseconds. If air interface parameters are used to ensure that at most two retransmissions are required before the packet can be deciphered correctly on the other end, a maximum additional delay of 20 milliseconds can appear.

Summary

Based on the assumption that an additional latency of 80 milliseconds is acceptable to the user, the authors show that HSDPA network can have the same or even better voice capacity than 3G networks have today for circuit switched calls. It’s still some way to go until we are at this point as enhancements have to be made on all parts of the network. But this study impressively guides the way forward!

Anti-Creativity: Let’s Help Some MVNO’s To Invent Additional (Roaming) Fees

This year has started with a lot of positive creativity on the operator side in Germany and elsewhere. Examples: Affordable prepaid mobile data is now available in a number of countries (Germany, Austria, Italy for example). Also, Vodafone has introduced a €15 euro a day roaming for data on prepaid SIMs and Three has even scrapped roaming charges for mobile voice and data altogether. It seems, however, that there is also some anti-creativity on the operator side these days when it comes to inventing new fees for so far free services. As reported by Teltarif in this article, Arcor and 1&1, two Mobile Virtual Network Operators (MVNO) of Vodafone Germany, have silently put fees for incoming SMS message while roaming into their fine print. Prices for incoming SMS messages are foreseen to range between 59 cents and 1.49 euros depending on the country. Charging for incoming SMS messages will start by mid of this year.

The problem with charging for incoming SMS messages is that the user can not stop receiving SMS messages while roaming today. So if these MVNO’s really start doing this, then the least I would expect of them is to offer the possibility for the user to block incoming SMS while roaming. Also, I would expect them not to charge users for sending SMS messages which are then blocked by the receiver. Well, let’s see what happens, I am still not convinced that they will prevail with this.

I am not sure yet if this is a move intended as a threat against current activities of the EU to lower roaming charges or if this will be another nail in the roaming coffin which will inflame decision makers in the EU even more and push them to reduce roaming charges even further.

More Anti-Creativity Suggestions

It seems some operators are getting desperate these days to compensate for falling prices for voice minutes. Here are some suggestions from my side in case you need more destructive ideas for your business:

Charge users for switching their mobiles on and off
Charge users making a call which is never answered
Charge users for switching voice mail or call forwarding on and off.
Charge users for the time their mobile is switched on per day
Charge users for mobility, i.e. charge them when they don’t leave the phone at home but instead carry it in the pocket while roaming out and about.

All these events require network interaction and all of them are recorded. No problem to forward these records to the billing server. I am getting goose bumps…

So all jokes aside dear operators. Instead of this roaming SMS anti-creativity why are you not considering some positive creativity like your competitors as shown at the beginning of this entry to increase your revenue by offering interesting services at affordable prices?

Vodafone Data Roaming With Websessions

It’s CeBIT time and wireless operators in Germany have been keen these days to announce new price plans for mobile data. One of the most exciting announcements for me is Vodafone Germany’s announcement of lowering the price for their WebSessions data price plan while roaming. So far, they were charging 30 euros a day for Internet access to roaming customers in one of their partner networks. Now, they’ve lowered the price to 15 euros. While still too expensive for private use, it will help business travelers a lot.

And the cream on top: WebSessions also work with Vodafone Germany prepaid cards and a 24 hour web session can be bought either via the monthly phone bill (post paid), via the prepaid account or via credit card. Credit card payment is especially useful for business travelers needing a receipt for their company.

A WebSession is started by establishing an Internet connection via the "event.vodafone.de" apn. Afterwards, web access is redirected to a portal page on which the payment method can be selected. The fine print: The session duration is 24 hours and there is no limit on the number of reconnects during that time. The data volume, however, is limited to 50 megabytes after which access is blocked. For most people, that should be more than enough. More on the technical details when I had a chance to try it in practice.

I had a quick look at the web site of Vodafone U.K. (the mother ship…) to see if they have similar offers. I came up empty handed!? So it looks like the national divisions have quite some power when it comes to price plans. Let’s hope other Voda subsidiaries follow the good example.

Nokia Maps Review Part 2: Navigating in Rome

A couple of days have passed since I posted the first entry on the Nokia Maps / Smart2Go application and how it fares for car navigation. In this post I’ll take a look at how well the application fares while being on foot in an unknown city. I am in Rome at the moment and since I don’t know the city very well, a great opportunity to use the application. Be warned, there are quite a number of things to be described so this blog entry is not going to be a short one.

The Tools

In the past days I’ve been using the Nokia Maps application on a Nokia N93 together with an external GPS receiver connected to the phone via Bluetooth. In addition, I downloaded a map of the metro system of Rome as a pdf file to the phone and archived a couple of eMails on the phone containing addresses of places I wanted to go and phone numbers of people I wanted to meet. As a backup I also printed out all of this information since I am a strong believer of always having a plan B. Having all information on the phone turned out to be much better than the paper version as the information is instantly available without having to open the backpack or going through half a dozen sheets of paper to find what one is looking for.

Preparation Phase

Before going on a trip I usually do some preparation work at home to ensure I have all the information I require and to get an idea of where the hotel, work place, train station, airport etc. is located. I usually do this on the PC with an Internet mapping application such as Map24 or Mappy or the PC application of my ‘old’ navigation system. This time I additionally located the places I wanted to go in Nokia Maps on the phone and saved them as landmarks for quick retrieval later on. I felt that the step on the PC is still required as the mobile phone screen is too small for getting an overall view of the situation. Also, the mapping application behaves quite slowly when zooming to a resolution that covers a couple of kilometers on the screen. Scrolling through the map in this resolution is quite frustrating. Scrolling through the map while only showing a few streets around a location, however, is very quick. Since this is the view which is later on also required for navigation it’s still tolerable.

Warning: Being in an unknown city and not knowing exactly where to go is a stressful situation. Trying out new things while already being overwhelmed by external impressions is not advisable. Thus, knowing how to use the mapping application before one has to rely on it takes a lot of stress out of the situation.

Navigation vs. ‘Free’ Walking

For street navigation on foot two application modes can be used. If you’ve paid for navigation you can use the on-foot navigation option to plot a course from the current GPS position to the selected place. While this works great for car navigation I found it quite awkward to use for street navigation on foot. When walking into the wrong direction for example, the application re-calculates the route instead of just asking the user to turn around. Also, the application constantly switches back to car navigation for which routing rules are quite different. For the moment, I therefore prefer the standard mode as shown in the image on the left in which the user saves a destination as a landmark which is then displayed on the main map. The current GPS position is shown as a cross and the location is updated as the user walks down the street. As destinations are usually in walking distance (less than 2 km for most occasions I would say) it’s easy to zoom in and out at the beginning to find the right direction and keep the zoom level low for the final turns. In practice this mode worked well for me and on top is even free of charge.

Usage Scenario 1: Airport to Hotel

It’s midnight and the plane touches down at Ciampino airport. After waiting endlessly for the baggage to finally show up on the transportation belt there is only one thought left for the day: How long does it take to get to the hotel!? A Taxi is found quickly and somewhere in the twilight zone between being aware and asleep I manage to start the mapping application on the mobile phone to observe the progress to the hotel. The GPS receiver takes a couple of minutes to find the satellites but one locked I see the distance shrinking and shrinking. It’s also a good tool to see if the driver takes you on a sightseeing tour to increase the fare. In my case the driver was honest, tired or both as he took the direct route to the hotel. Great!

Usage Scenario 2: From Work To The Train Station To The Apartment

Getting picked up by a local in the morning for work at an unknown place has its benefits. Being dumped on the street after work to find your way home through a foreign city is less fun. But hey, I’ve got a navigation system now, so finding my way from work to the next rain station worked like a charm. Off I went with the metro to the station closest to the apartment I’ve rented for the next weeks. I’ve never been at this place before either, so the mapping application has to prove itself once again. Now that the GPS receiver has kind of understood that I am in Rome, it usually takes less than 15 seconds for getting a first position. Again, finding the apartment is easy as walking in the wrong direction immediately becomes obvious on the mobile’s screen.

Usage Scenario 3: A Ride To The City Center And The Search For A Bookstore

I am sure you’ve been in a similar situation as this. You are in a foreign city and somebody tells you to take this or that bus to ride into town to go to a certain place, a book store in my case. Great, you are on the bus but you are not really sure when you should get off. Be it because instructions where not quite that detailed or be it that the bus stop signs are not really very well visible. No problem with a navigation system in your hand. I’ve created a landmark in the mapping application for the book store I wanted to visit and was following the progress of the bus towards my destination. No more anxiety of when to get off or to miss the right stop. Once it looked close enough on the phone’s map, I got off and walked the last meters to the book store. I am impressed. Wandering through the narrow streets of Rome I noticed that the GPS receiver has some problems now and then giving me a precise position. Sometimes the position fix is lost altogether. In practice this is not much of a problem as reading names of crossing streets is good enough to follow your progress on the map.

Summary

I have to say that I am impressed by the possibilities of Nokia Maps. Similarly to car navigation, using the application for navigating through a city on foot takes some of the uncertainties and detours out of the equation. Finally, I have a feeling of direction which I was so desperately missing when wandering through unknown cities. Not all people feel as disoriented when coming to a foreign city as me. For those who do, however, this application will be a real help. As processing power increases on mobile platforms, some hiccups described above will surely be fixed as well, improving the experience further. And looking even more into the future a total navigation solution with voice commands and instructions is quite imaginable. But that’s for another post.

Deep Inside the Network: T-Mobile starts using GPRS NOM-1

Quite recently T-Mobile has started to make use of the GPRS Network Mode of Operation (NMO) 1 feature in southern Germany. I haven’t seen any other operator using NMO-1 in Germany so far and only few in other countries so this came as quite a surprise. In this network operation mode, the circuit switched part of the network used for voice calls and SMS and the packet switched part of the network used for GPRS and EDGE data transmissions are connected via a signaling interface. This interface, referred to as the Gs interface, has a number of subtle but important advantages:

During an ongoing GPRS / EDGE data transfer (TBF established), mobiles can’t detect incoming voice calls and SMS messages as they are focused on receiving packets and thus can not observe the paging channel. In NMO-1 (sometimes also abbreviated as NOM-1), the circuit switched part of the network forwards the paging message to the packet switched side of the network which then forwards the paging message between the user data blocks while a data transfer is ongoing. Mobiles can thus receive the paging message despite the ongoing data transfer, interrupt the session and accept the voice call or SMS.

Location/Routing area updates when moving to a cell in a different location/routing area are performed much faster as the mobile only communicates with the packet switched part of the network. The packet switched network (the SGSN) then forwards the location update to the circuit switched part of the network (to the MSC) which spares the mobile from doing it itself. This is especially important for ongoing data transfers as these are interrupted for a shorter period of time.

Cell reselections from UMTS to GPRS can be executed much faster due to the same effect as described in the previous bullet. Whithout NOM-1 an Inter RAT (Radio Access Technology) cell reselection with Location and Routing Area update requires around 10 to 12 seconds. With NOM-1 the time is reduced to around 5 to 6 seconds. An important difference as this reduces the chance to miss an incoming call during the change of the radio network. Also, ongoing data transfers are interrupted for a shorter time,an additional benefit that should not be underestimated.

Talkline Launches Try And Buy Offer for Mobile Internet Access

Recently, a number of German MVNOs have slashed prices for prepaid mobile Internet access. Now, mobile network reseller Talkline has launched a 60 day try and buy offer for mobile Internet connectivity for people with a usage that makes a contract more attractive than prepaid. During this time the two year contract can be canceled at any time.

Other offers by the competition, except for the prepaid data mentioned above, always bind customers two a two year contract without the possibility to cancel the contract for reasons such as lacking coverage at the places of use.

Included in the offer is a free PCMCIA or USB 1.8 MBit/s HSDPA modem. A 27 Euro activation fee is charged when signing up (which is probably not refundable) and a monthly basic charge of 8 Euros applies for the duration of the contract. The first six months, however, are free. On top of the basic charge, users can select a data offer either based on volume or time:

200MB: €20.-
400MB: €35.-
5GB: €50.-

The SIM card can also be used to make voice calls, but prices are not attractive with 39 cents a minute to the national fixed line network and 69 cents to other national mobile phone networks.