Author: Martin

Several years after the start of 3G and some operators still
struggle with their 3G network engineering. Unbelievable but true.

Latest
example: Wind in Milano, Italy. I’ve been using the Wind network already last
year in Roma for several weeks and enjoyed great 3G coverage and performance. A year
later, I am in Milano, a city in Northern Italy, and the situation is
completely different. Last week when I was here the 3G network was completely
unusable, due to packet drop rates of 30% or more. This week the situation has
improved but it still is nowhere where it should be.

Over the weekend I had some time to take a closer look what was
going on. While at first I suspected that they had some timer and threshold
problems that makes the connection switch between dedicated and common
channels, I quickly saw that this was not the case. Instead, there is frequent
measurement control messaging, traffic channel reconfiguration and active
setup updates. Every time the channel is reconfigured, packets are either lost
or delayed for a second or two which slows down the connection considerably.
After a while this starts a chain reaction as sometimes web page downloads
become so slow that the network decides to switch the connection onto a common
channel. This again provokes packet delays. It doesn’t seem to be a single
mobile issue as it happens with three different phones. Very strange as I am in
a place with excellent network coverage. So Wind, please get out there and fix
this!

But then, Wind’s also got EDGE coverage in Milano, which
works very well… Shame I have to fall back on 2.5G because their 3G network
engineering is flawed…

Let’s timewarp to 2012. I am in a small foreign town somewhere out in the countryside. I want to check my eMails and browse the net a bit. What kind of wireless access will I find in that place five years from now? 3G? Hopefully. Wifi? Well could also be, but at what price? Or even WiMAX? Why not with Intel pushing the technology and promising to get chipsets out the door soon which can do both Wifi and Wimax (Rosedale 2?). Let’s stay with WiMAX for a second. How will my experience look like? I can imagine several scenarios:

The 3G-like scenario: I open my notebook and I detect a local WiMAX network. Unfortunately, just like most 3G networks today, access is restricted to users with a valid SIM card. No other way to access the network. Too bad for me, as I can’t use the network and too bad for the network operator as he is missing out on potential revenue.

The Hotspot-like scenario: Again, I open my notebook and detect a local WiMAX network. Local users have a SIM card just like with 3G and access is seamless. However,the network is clever and sees that I am a roamer without a SIM and permanent subscription. Thus, it allows me restricted access and guides me to a web page where I can buy some volume or time credit. Prices are moderate and I am only billed for the time or volume I really use. Excellent. Maybe the network is even clever enough to detect my device whenever I log on again afterwards. Instead of having to type in my credentials again, I am just shown a page which welcomes me and tells me that network access for the prices as agreed last time has been granted again without further ado.

But maybe 3G operators have learnt their lesson in the meantime and are now offering affordable roaming prices to access the Internet. No need for the WiMAX network then. I wonder if the WiMAX competition has helped in this change of mind or if new EU regulation gave the gentle push!?

The Smartphone Scenario: So will my smartphone in 5 years from now support 3G with fallback to GPRS/EDGE for the really remote parts of this world, Wifi for home, and WiMAX (because 3G operators still won’t allow me to roam abroad and connect to the Internet at a reasonable price)?

I think we won’t see a several network technology everywhere world by 2012 so I hope WiMAX networks will be as open and reasonably priced as possible and devices to have enough wireless technologies built in to allow true roaming worldwide.

As bizare as it sounds but I think only a healty competition of different wireless technologies and mindsets will ensure the best possible network coverage for each technology.

Other Ideas? Anyone?

I was not sure if I should post my “TFO and
TrFO introduction” here as there are probably only a handful of people on the
globe who are interested in this topic. Also, some prior knowledge is
required on how GSM and UMTS networks handle circuit switched calls and how
things change with the introduction of 3GPP Release 4 BICN functionality. A
good intro on this topic can for example be found in my book (take a look on
the left). Most of my blog entries require no such in-depth prior knowledge but
this one definitely does. I decided to do it anyway as I didn’t find any other
usable overview on the web.

Tandem Free Operation (TFO) and Transcoding
Free Operation (TrFO) Overview

Voice calls from mobile phones today always involve several voice transcoding steps
in GSM and UMTS Release 99 networks. This is done mainly to transport a voice
call, which uses sophisticated compression in the radio network, through the
core network with the standard G.711 PCM (Pulse Code Modulated) codec over 64
kbit/s circuit switched links. Furthermore, transcoding a voice data stream to the
64 kbit/s G.711 PCM codec is necessary in order to call fixed line phones.
Another advantage of voice transcoding in the network is to be able to process
the voice data stream and to compensate for unwanted effects such as echo in
the speech path.

With the introduction
of the Bearer Independent Core Network functionality in the 3GPP Release 4
standards, core network connections are based on high bandwidth ATM or IP links
rather than on 64 kbit/s TDM links. In such networks it is therefore possible
to transmit a voice data stream in the core network with other codecs than 64 kbit/s G.711. This
also has the additional benefit of removing transcoders from the speech path which
reduces speech path delay and improves speech quality to some degree as the
speech signal is no longer degraded by the transcoding process. Furthermore,
not having to convert to the narrow voice band G.711 codec allows the use of
AMR Wideband (AMR-WB) codecs. These codecs are not backwards compatible to
G.711 without loosing their much better audio quality which they achieve by
encoding twice the frequency range as previous Full Rate, Enhanced Full Rate,
AMR and G.711 codecs. A general downside of not using a transcoder in the
network is that it is no longer possible to process the voice data stream to
remove effects such as echo.

Transcoder Free Operation (TrFO)

In UMTS
Bearer Independent Core Networks (BICN), PCM links which require the use of the
G.711 codec are no longer used. Instead, connections to RNCs in the radio
network and connections to other Media Gateways are based on ATM and IP.
Therefore, the MSC servers involved in a call can establish a bearer path
without activating voice transcoders in the media gateways between two mobile phones. For a mobile to landline call the connection remains transcoder free up to
the media gateway which connects the wireless network to the fixed network.
Here, the transcoder is used to convert the compressed audio signal to G.711.

In mobile
to mobile calls, both handsets report their codec capabilities to the MSC
servers involved in the call as part of the signaling before the bearer path is
established. Thus, an AMR-WB codec is automatically used if supported by both
terminals. This greatly improves the voice quality of the call. If not
supported on both ends, a standard narrow band AMR codec will be used for the
connection instead. This is called Transcoder Free Operation (TrFO) and the out
of band transcoder control performed by MSC servers is described in 3GPP TS
23.153.

While TrFO
works well while both ends of the connection remain in the UMTS network, it has
to be deactivated if one of the two parties is handed over to a GSM network
during the connection. This happens, for example, if the subscriber roams out
of the UMTS coverage area or in case the UMTS coverage is temporarily weakened
by obstacles while GSM network coverage remains acceptable. This can happen for
a number of reasons like because of different locations of the UMTS and GSM
base station sites or due to better GSM in-house coverage. If AMR-WB was used for the call, deactivating TrFO
also requires a fallback to AMR which results in an abrupt voice quality
degradation of the call in case the GSM network does not support Tandem Free
Operation which is described next (see also 3GPP 23.153, chapter 6.5).

To
communicate with services in the networks such as a voice mail system, or a
prepaid top up voice server, DTMF (Dual Tone Multiple Frequency) tones are used
to send passwords and commands to the system. If a call is established from a
UMTS terminal, DTMF tones are sent as out of band signaling messages to the MSC
Server. The MSC Server is then responsible to forward the message. If the
service platform which analyzes the DTMF tones is BICN compatible, the tone
is delivered as a message. If the service platform is still using PCM links and
the G.711 codec, the DTMF tone is inserted into the voice connection at the Media
Gateway at border to the PCM network. If a call is established from an external
PCM network to a service in BICN network, DTMF tones are not sent as messages
but inside the voice bearer. In this case, 3GPP 23.153, 5.9 requires the
gateway at the border of the BICN network to discover the inband DTMF tone,
remove it from the voice stream and send a DTMF signaling message to its MSC
Server which then forwards the DTMF message out of the voice band to the
destination.

Tandem Free Operation (TFO)

For GSM
networks, TrFO can not be used even if the core network uses BICN media
gateways and MSC-servers. This is because the A-Interface, which connects the media
gateway to the BSC/transcoding unit is based on PCM. Thus, voice calls from GSM
radio networks always arrive at the media gateway as a PCM G.711 64 kbit/s
circuit switched stream. Unlike in UMTS, where the transcoding is a
functionality of the media gateway, GSM uses a dedicated transcoding unit
between the BSC and the media gateway. This is necessary in order not to change
the radio network architecture when the core network is upgraded to BICN. As a
consequence, a mobile to mobile GSM call will always have two PCM links in the
connection, one to and from each transcoder and thus a GSM call is always
established using the G.711 codec. The two transcoders of the connection are
also called a tandem. In order to remove the transcoder tandem from such a connection,
in band codec negotiation between the two transcoders can be attempted once the
call is established. Instead of sending signaling messages via the MSC-servers
through the network, the two transcoder units send their information embedded
in the G.711 link. This is done by using a special bit pattern as part of the
voice stream which is recognized by the other end as a transcoding control message
and not as a part of the voice signal. If both transcoder units support at
least a single common codec like AMR 12.2 or an AMR-WB codec, the 64 kbit/s
G.711 connection is used to tunnel the compressed and encoded voice stream. As
the audio stream is compressed most of the bits of the transparent 64 kbit/s
stream are not used. This effectively removes the transcoder tandem from the
voice connection and is thus called Tandem Free Operation (see 3GPP TS 23.053
and 3GPP TS 28.062). While audio quality and delay times can be improved this
way, no bandwidth savings can be achieved in the core network unlike with TrFO.

Some events
in the network can temporarily interrupt TFO and the speech path in the core
network automatically falls back to standard G.711 encoding. This is the case
for handovers for example in which the call is handed over to a cell which is
controlled by a different TRAU. This is the case for an inter-BSC handover for
example. Once the handover is complete, TFO has to be negotiated again between
the two TRAUs (see 3GPP TS 23.053, 6.5.7). TFO is also temporarily interrupted
when the MSC inserts DTMF tones or announcements. As the MSC is not aware of
TFO it overwrites the compressed speech information in the circuit connection.
This is detected by the terminating transcoder and transcoding elements are
automatically reinserted into the speech path. Especially for AMR-WB, TFO has
to be started again as soon as possible in order to avoid speech quality
degradation.

Conference
bridges are another network feature which automatically disable TFO. This is
because standard conference bridges mix G.711 voice signals from several
parties to produce a combined signal which also overwrites the TFO data stream.
This again forces the TRAUs to introduce a transcoder in the speech path again.
While this has little impact on narrow band speech calls from a voice quality
perspective, it is not possible to use AMR-WB when a conference bridge is
inserted unless the conference bridge also supports TFO and the AMR-WB codec.

There we go, if you have made it up to here, please consider leaving a comment 🙂

For the previous Nokia Open Studio in New York, Nokia invited Martin Varsavsky, CEO of FON (A Wifi hotspot company) for the panel discussion. A clever move for both which I understand even better now that I’ve bought an N93 with built in Wifi support.

New Wifi Possibilities

I’ve been using the phone quite a lot since then over my Wifi network at home. This alone saves me a ton of money since I can now use my Wifi/DSL connection while at home instead of more expensive 3G connections. Also, using Wifi opens up a range of new things beyond eMail and Web browsing which I would have never thought about doing over 3G:

• Podcasts: Downloading podcasts directly to the mobile instead of first downloading them to the PC and then sideloading them to the phone via a memory card works like a charm over Wifi. I haven’t done that in the past because as even with a cheap 3G price plan, downloading  30 MB podcasts was never an option. No problem over Wifi though. Nokia’s got a great podcast catcher program which can download several podcasts simultaneously and automatically resumes after a paused or interrupted download without having to start from scratch. In addition it lets you listen to the first couple of minutes of a podcast so you can find out easily if it’s worthwhile to download the rest.

• Blog reading with an RSS Reader: I’ve been doing this over 3G already but my blogroll is quite comprehensive and a complete update generates about 1.5 MB of traffic. No problem over Wifi. Luckily, Resco has just released a version of RescoNews for S60 3rd edition. I’ve already reviewed RescoNews a couple of months ago for 2nd edition phones and it is still my favorite mobile blog reader. The version for 3rd edition phones works almost the same way as the version for 2nd edition. Some enhancements have been done, though: First of all it can be used in both normal and landscape mode on the N93 and the configuration menu now also allows the user to choose which browser to use in case posts contain links or in case you want to see the original post on the web site. Wifi integration works well but configuration is still not straight forward. When setting the connection type to "always ask" the program just shows the configured 3G connections and leaves out Wifi connections. If you go to the settings menu however, it’s possible to set the connection to use to a preconfigured Wifi profile. That’s good enough for me as I only want to update when I am at home anyway.

• Flickr Uploads: Shozu is a great program to upload pictures to Flickr and other picture sharing sites. The latest version also supports video uploads to sites which support video. With image sizes almost reaching 1MB with the N93, uploading images gets easily expensive over 3G. So in case I can wait with the upload until I am back home, I pause Shozu and just hit a button when I am back home to upload the pictures automatically. Excellent!

It’s Not About Technology it’s About Money

Don’t get me wrong, all of the things mentioned above can easily be done over 3G as well both from a technical and a practical point of view. What keeps people from doing it is price, especially when roaming to other countries. I think this will change in the future but for now that’s how things are. So this is where Martin and FON come back into the picture. If he succeeds then a FON Wifi hotspot will be close in the future no matter where you go in the city so you can update your blogroll or download a podcast even while you are waiting for the bus.

Mixed 3G / Wifi Usability

Each application can be configured separately how to connect to the net. While I’ve configured the web browser to always ask which connection to use, I’ve set the blog reader and podcast catcher to always use my Wifi access point at home. Here’s a wish to Nokia: A third option which assigns a priority to configured connections would be a cool feature. I’d use this for the web browser for example. In case my Wifi access point at home is detected, the browser automatically uses this connection. If it can not be found, the configured 3G profile would be taken instead without my intervention.

So, my thumbs are both up for the N-series Wifi integration!

It had to come this way, I am a proud owner of a Nokia N93 now. Many reviews have been written about the phone so I have no intention of adding another one. Instead, I will write down my impressions about what I like and also about what I don’t like about the phone beyond what is said in the numerous reviews.

This entry is about the new Nokia Web Browser: I was quite sceptical if it could do better than the Opera browser which I have been using on my N70. A lot has been written about the browser on the web already, including the fantastic minimap feature which shows you where you are on the page while scrolling. What I always wondered about and was never really able to get out of the reviews was how one is able to read web pages if they are not reformatted. After using the browser myself for a couple of minutes, the answer came quickly: While the page is shown on the minimap approximately as it would be rendered by a desktop browser, the page and especially the text is reformated in the main window. This works surprisingly well. I’ve tried many web sites and only once did the reformating of the text blocks of the page to the width of the screen fail. Congratulations to the S60 browser team, the browser really gives me the best mobile web browsing experience I ever had!

While I have already come to love the browser I’ve discovered two rather nasty issues as well:

The first one is its memory consumption. On the N93 which is supposed to be Nokia’s flagship product, the browser quickly takes all available memory and the OS in turn closes other applications. Very bad behaviour which I hoped would be a thing of the past after I switched from the 6680 to the N70. It seems that there is a software update that might fix this issue but I haven’t been able to download it so far.

The second issue is stability. Even though my software version is quite up to date (*#0000#) shows 12.07.06 the browser crashes quite frequently when browsing on normal web pages. Still some work to do here… Not a big issue for me at the moment, though, as most web sites I access on the mobile have a mobile friendly version of their content.

So much about the browser for the moment, stay tuned for further impressions.

A couple of weeks ago I wrote about 3G licensing fees and their impact on end user prices and network deployments in different countries today. I got magnificent feedback on this story and this podcast with Peter Curwen, visiting professor for telecommunications strategy at Strathclyde University in the U.k. is a direct sequel. In the podcast we discuss:

• Licensing fees were free in Finland compared to 50 billion Euros in Germany. Yet, end user prices in Germany and Finland for 3G are pretty similar. How is this possible?
• Network Coverage is also very different from country to country. Which factors influence this?
• Why is the French mobile market so uncompetitive?
• Austria and Italy are far ahead in terms of network deployment and end user prices. What was done differently and by whom?
• While WiMAX be a threat for 3G in the next 5 years?

The Podcast, 26 minutes, MP3, 25MB

Here’s a feature request for Nokia or the developers over at S60 (because they develop my favorite phones…): Have you ever been asked to help someone over the phone with the configuration of his or her phone or to explain a seemingly simple task such as writing and sending an SMS? If so, you probably know how difficult these seemingly simple things are to explain over the phone. Since we have 3G and video calls now how about extending the video call feature to alternatively send over what the other side sees on the screen!? Remote support would be dead simple then: You could see what the person on the other side sees on the screen and give directions what to do next. Remote keyboard support would be the cream on top but I know that this would be more difficult to do.

I couple of years ago I thought EDGE (Enhanced Data Rate for GSM evolution) would not have a big chance on the market with new technologies like 3G and later on HSDPA entering the market. An yet, EDGE has made it into many networks around the world. In some countries, 3G hasn’t made it beyond big cities yet and I have come to value EDGE quite a lot in my frequent travels which often bring me to smaller towns or even the countryside. Interesting to see that work is underway in 3GPP to push EDGE forward once again.

Evolved EDGE

Today, EDGE for GPRS mainly increases user data rates by using new modulation and coding schemes which go far beyond the original GPRS specification. Effectively, EDGE increases GPRS speeds about four times. In practice, speeds of about 220 kbit/s can be reached under good radio conditions. Evolved EDGE sets out to increase the user data rate once again to a level around 1 MBit/s with the following enhancements:

Multiple Receiver Chains: Today, GSM mobile phones use once receiver chain. By adding a second one which analyzes the incoming signal (with a different polarization or different phase I am not sure) independently, chances to decode the data stream correctly increases. This means that higher modulation and coding schemes can be used in the same conditions as if the mobile phone only had one receiver chain. Note that this is a receive diversity scheme and not a MIMO (multiple input, multiple output) which will be used in 4G systems like LTE, WiMAX and also in the next generation of Wifi (802.11n).

Higher Order Modulation: EDGE uses 8PSK modulation which encodes 3 bits per transmission step. Evolved EDGE introduces 16QAM modulation which can encode 4 bits per transmission step and 32QAM modulation which encodes 5 bits per step. In practice, however, 32QAM is difficult to use for average transmission conditions on the air interface.

Two Simultaneous Radio Channels: Since 1992 the principle of GSM has been to use only a single carrier frequency to receive data. With E-EDGE, mobiles can now receive data on two frequencies. This could in effect double the data rate available to a single user.

Independent Transmission and Reception Chains: Another principle that E-EDGE is about to lift is the use of only a single transmission and reception chain which so far restricts mobiles to only sending or receiving at a time. By introducing independent transmission and reception chains, data rates are increased as the mobile phone does not have to switch between transmission and reception. This doesn’t only free up the timeslots used for the reverse direction but also frees up adjacent timeslots which are not usable with a combined transmitter and receiver which needs some time to switch between transmission and reception mode. While most EDGE mobiles on the market today are still restricted to four timeslots per carrier due to this phenomenon, having independent transmission and reception chains could allow mobiles to use all eight timeslots of a carrier.

Speed Calculation

When putting it all together, speed can be increased as follow: Higher order modulation can increase transmission speed by 1/4, so 220 kbit/s become 293 kbit/s. Use of twice the number of timeslots per carrier increases the top speed to 2 * 293 kbit/s = 586 kbit/s. Using two carriers could again double the speed to about 1.173 kbit/s. Not bad for a 15 year old technology that was originally intended for a transmission speed of 12 kbit/s for voice communication.

While this all sounds quite fascinating, there will be a number of downsides in practice as well:

Availability

E-EDGE will not be around for quite some time. Taking past developments as a reference, I expect that it will take at least another two to three years before networks are upgraded and for mobiles to be available (if such a decision is made).

Spectrum Efficiency

E-EDGE, in contrast to EDGE, only modestly increases spectrum efficiency. Thus, the total available bandwidth per sector per cell will still be in the range of "only" 1.5 MBit/s for a typical base station which uses three carriers per sector. In addition, the base station is also used for voice communication which further limits transmission speeds. Compare this to a full blown UMTS 3.5G HSDPA base station which uses 2 carriers per sector to reach a total bandwidth beyond 20 MBit/s and the difference becomes quite obvious. Thus, to say that E-EDGE drives data rates up to HSDPA levels is true as far as per user speeds are concerned but certainly not as far as the overall base station capacity is concerned. In addition, data rates of HSDPA in two to three years from now will have certainly moved on to beyond 3.5 MBit/s per user. Therefore, statements saying that E-EDGE is en par with HSDPA is pure marketing nonsense… Additionally, the number of E-1 links (2 MBit/s each) which connects the base station to the network also has to be increased to support the new modulation and additional timeslots which will be usable for voice.

Terminal Support

Most of the enhancements of E-EDGE will have a strong impact on current GSM terminal design. Independent receiver and transmitter chains have been standardized already since the first days of GPRS (GPRS class A). However, up to this date there are no such mobiles on the market. This seems to be a hard nut to crack. I am not sure if this is for technology reasons or simply due to the price or increased packaging requirements.

Other radio systems

Today, one of the main issues that keeps many operators from deploying 3G in rural areas is the use of the 2100 MHz spectrum which requires a higher number of base stations due to the smaller range compared to what can be achieved in the 900/850 MHz band used currently used by many GSM operators. At least in North America it looks, though, as if UMTS 3G will also be used in the 850 MHz band in the near future thus leveling this advantage of GSM/EDGE today. Furthermore, UMTS has now also been standardized for the 900 MHz band but it remains to be seen if regulators in Europe will allow deployments in that band in the near future. Also, other technologies such as WiMAX should also not be underestimated as a competition in the rural area in three or four years from now. With data rates over ten times higher per base station site then what an E-EDGE cell could deliver it seems doubtful to me that the technology would compete very well.

Summary

So will this technology get deployed and will it be successful? With this one, my crystal ball remains clouded. E-EDGE has many good ideas and will certainly increase data rates somewhat but it will not compete very well with other 3.5G and 4G technologies, which are also evolving to higher data rates. The best I therefore expect is that todays gap between 2.5G on the one hand and 3.5G and 4G networks on the other hand does not further increase.

Recently, Peter Rysavy has also written a good column about this subject. Take a look here, his articles on wireless network technologies are among the best to be found on the web!

For the details take a look at the 500 pages of the 3GPP Technical Report TR 45.912.

Some wireless operators like Vodafone and O2 are now getting into selling  DSL access besides their wireless core business. I wonder if this might open up opportunities for devices like the Nokia N-series phones with Wifi capabilities (N80, N93 and N95)!?

With such devices, operators could offer data services for mobile devices that use the 3G network while away and the DSL line over Wifi while at home. Such applications could be eMail, web browsing, and social media applications like picture sharing and video services such as  YouTube adapted for mobile. A crucial factor for such an offer from the technical side is that the phone automatically uses the Wifi AP at home instead of the 3G connection. Nokia has done a first step in this direction with the Wifi configuration client that shows Wifi networks on the idle screen. The next step to automatically select a preconfigured Wifi Access Point instead of a 3G connection is simple.

Operators who can combine fixed+mobile access could also use their assets to offer advanced convergence services like access to the home network which is connected to the net via the DSL connection from a mobile phone or a notebook with a 3G card while the user is away from home. There is a huge potential here. The mobile could be used to access files, pictures and videos and to monitor and control appliances at home while underway. All these services require both the fixed and the mobile network plus an operator that is willing to integrate the service, i.e. to offer monitoring and control boxes like network connected power switches, household appliances, web cameras, video recorders, etc. as part of the fixed/mobile Internet package.

I think that such offers could be an ideal way for fix+wireless operators to distinguish themselves from fixed only or wireless only operators. At the same time they could sell services, which is their dream scenario anyway, and thus increase their (average) revenue per user (ARPU). BUT: this requires partnerships with external content and services providers such as YouTube for example. Internally developed applications just don’t stand much of a chance with the speed applications are developed by the larger Internet community.

So seen from a different perspective DSL helps to promote 3G and 3G helps to sell DSL. Sounds like a great combination to me. And while we are at it: Don’t forget to offer attractive 3G data roaming as part of such a package!

17 stories have been included in this weeks Carnival of the Mobilists, this time hosted by C. Enrique Ortiz at his Mobility Weblog. So for the best people around the world have written about the mobile ecosystem in the past week head over and enjoy!