GSM Phaseout Architectures

Back in 2000, most of us in the industry thought that by 2012 or so, GSM would be on a good way to become history in Europe and elsewhere, having been replaced by 3G and whatever came afterward. Now in 2008, it's clear that this won't be the case. About a year ago, I published an article to look at the reasons why this has not happened. With LTE now at the doorstep, however, it has to be asked how mobile operators especially in Europe can support three radio technologies (GSM, UMTS/HSPA and LTE) into the foreseeable future.

While over the next few years, many network operators will transition their customer base to 3G handsets and thus might be able to switch off GSM from that point of view, there are a number of factors that will make them think twice:

  • There might still be a sizable market for customers who are not willing to spend a great deal on handsets. Fact is that additional hardware and licenses for combined GSM/UMTS prevent such handsets for becoming as cheap as very basic GSM only handsets.
  • Operators are keen on roaming charges from subscribers with 2G only handsets, this is a very profitable business.
  • Current 3G networks are transmitting on 2.1 GHz and as a result the inhouse coverage of 3G networks is much inferior to current GSM networks. Putting more base stations in place could help to some degree but it's unlikely to be a cost effective solution.

In other words, in order to switch GSM off (whenever that might be) a number of things need to fall in place first, i.e. needs to be part of an operator's strategy:

  • 3G must be used on a wide scale in the 900 MHz band (or 850 MHz respectively in the US and elsewhere). This, however, requires new mobile devices as only few models currently support this band. At this point in time it is not clear if national regulators will allow the use of 3G networks in the 900 MHz band in all European countries because it has significant implications on the competition with other technologies. Note: 4G deployment in 900/850 MHz is unlikely to help due to the voice gap discussed here.
  • An alternative could be that combined DSL/Wi-Fi/3G Femtos become very successful in the market, which could compensate for missing 900 MHz coverage. But I am a bit skeptical if they can become that successful.
  • Most roamers would suddenly pop-up with 3G capable handsets. I don't see that happening in the near- to mid-term either due to many countries not going down the 3G route and even for 900 MHz. Also, roamers with mobiles from places such as North America use different 3G frequencies and thus would not work in Europe and elsewhere and of course vice versa. Maybe this will change over the next couple of years two, but except for data cards, I haven't seen a big push for putting 3G on 850/900/1700/1900/2100 into handhelds.

At some point, however, it might become less and less economical to run a full blown GSM network alongside UMTS/HSPA and LTE networks despite lucrative 2G roamers and better inhouse coverage on 900 MHz. I see several solutions to this:

  • Since GSM traffic declines in favor of 3G it will be possible at some point to reduce the capacity of the GSM network. At this point, separate GSM, UMTS and LTE base station cabinets could be combined into a single box. Base station equipment keeps shrinking so it is conceivable that at some point the GSM portion of a base station will only take little space. By using a single antenna casing with several wideband antennas inside could keep the status quo in the number of antennas required to run three network technologies alongside each other. Cabling could also be kept fairly constant with techniques that combine the signal to/from the different antennas over a single feeder link. For details have a look at my post on the discussion I recently had with Kathrein.
  • Maybe advances in software defined radio (SDR) will lift the separation in base station cabinets between the different radio technologies. Should this happen, one could keep GSM alive indefinitely. SDR is discussed in the industry for many years now. Since I am not a hardware/radio expert I can't judge if and when this might become part of mainstream base stations.
  • And yet another interesting idea I heard recently is that at some point two or more operators in a country might think about combining their GSM activities and instead of running several networks, only a single GSM network is maintained by all parties involved . As this network is just in place to deal with the roamers and the super low ARPU users (and maybe still lacking inhouse coverage), it is unlikely that this network will be upgraded with new features over time, so it could be pretty much static. So running such a combined network might be a lot easier than running a combined 3G network to save costs.

So what is your opinion, which scenario is the likeliest?

Does RAN Sharing Make Sense As Usage Grows?

In the UK Vodafone and Orange on the one hand and T-Mobile and 3 on the other are trying to find ways to decrease their CAPEX and OPEX of running their 2G and 3G radio access networks (RANs). Early announcements said that they intended to share not only the base station sites, antennas and feeders but also the base stations and the radio network controllers. Looks like in the meantime, Orange and Vodafone are likely to only share base station sites. This is not a particularly new approach, as in many countries sites and masts are often used by two or even more network operators.

With the quickly growing use of 3G networks for Internet access I even wonder if base station sharing makes sense at all!? After all, sharing a base station instead of using two individual ones decreases overall capacity. Sure, a single base station could be upgraded to have an individual transmitter for each operator, but not much beyond. Also, the backhaul link would have to be upgraded to support this. With usage increasing significantly these days I wonder if that wouldn't create a bottleneck rather sooner than later as operators can probably not add any additional hardware to such base stations to increase capacity later on.

So even if there should be some cost savings from this scheme, I wonder if the inflexibility this creates negates the effect. Cost for software and hardware upgrades to achieve higher speeds for example would have to be shared between the two companies. So if one is happy with the current performance of the network but the other is not, that would pose a serious issue for the party who's network is close to overload.

Maybe a better way to save costs is to open the radio networks for national roaming in areas which do not require a lot of bandwidth such as on the countryside for example. Operators could then agree who builds the RAN in which area and invites others to share the infrastructure. Not sure if national telecom regulators would be happy about such deals as it surely has an impact on competition, just as the original plans for RAN sharing.

Mobile Web Megatrends Conference in Berkeley

Mobile Web Megatrends
Do you know Ajit Jaokar and Michael Mace? If not I suggest to head over and check out their blogs (here and here) for great insight into the mobile domain. Or, even better, use the opportunity to meet them in person on the 8th of September at the University of Berkeley, California at the Mobile Web Megatrends Conference on September 8th, 2008. Topics of the conference range from mobile browser evolution, browser offline capabilites, advertising models, the iPhone (of course…), mass market impact with Nokia's S40 6th edition, cloud computing, etc. etc.

Lots of other great speakers, I let the conference's web site speak for itself.

Definitely a conference not to miss if you can make it. Unfortunately my calender is already booked for that date so I won't be able to make it. But good for you since I have one free ticket to give away! First come first served.

1st Anniversary of the Prepaid Wireless Internet Wiki

A year ago, I decided to share my knowledge about how to stay connected to the Internet while on the move with prepaid SIM cards. A Wiki looked like the best solution for the info I had on about four or five different countries. Pages can easily be changed because offers are changing frequently and I was speculating that others might put there info in there as well. Now a year later, I have to say the result is stunning!

  • My initial 4 or 5 pages have expanded to 85, most supplied by others.
  • Entries now range from North and South America, Europe and Asia to Australia.
  • In July 2008, the Wiki had 12.000 page hits from 6.000 different visitors, that's about 200 visitors a day.

I am very happy because my willingness to share has actually brought me great new tips I was not aware about. Especially the following have been invaluable to me personally:


So thanks to all of you how have added your information to the Wiki and to those who that keep the pages up to date in this quickly changing market. Together we have created an invaluable source of information for travelers!

How To Extend SIP For Mobile Networks

In the fixed line world, the basic Session Initiation Protocol (SIP) has become quite popular for offering voice telephony service. Lots of companies such as Vonage, Siptel and DSL providers are making use of it today. So why are we not using SIP in 3.5G and 4G networks as well? I guess there are both policital and technical answers to this question. From a technical point of view there are a few features missing that are essential in wireless networks:

– Voice codecs: Current SIP implementations usually use G.711 voice encoding which produces a 64 kbit/s data stream. Transported over IP the total bandwith requirement per direction is 80 kbit/s. Compared to the effient codecs used in wireless networks today such as 12.2 kbit/s AMR with a similar voice quality this is quite a lot and significantly reduces the number of simultaneous voice calls per cell. The current voice architecture uses a transcoder between the radio network and the core network to restore G.711 compatability. So from a capacity point of view, using G.711 in the radio network is probably not a good idea and would meet the resentment of most operators. So from my point of view we need AMR capable mobile SIP clients and transcoders in the network to reach non AMR capabale (fixed) SIP clients and circuit switched networks. Note that such transcoders are already present in the SIP networks today, usually as media gateways between the SIP world and the classic circuit switched world to which most people are still connected to with their fixed line and mobile phones.

– We need to get rid of NAT and STUN: Most mobile operators use private IP addresses for their customers. This requires Network Address Translation (NAT) which in turn unfortunately requires frequent polling packets to the SIP and STUN (Simple Traversal of UDP through NAT) server. These packets keep the connection to the network open continuously but drain the battery of a mobile device very quickly. The solution to this issue is to use public IP addresses and to ensure that keep alive messages are removed from the SIP implementation as much as possible. With the lack of sufficient public IPv4 addresses this will require IPv6 at some point.

– End to End – Encryption: All SIP clients I use today do not encrypt signalling or the voice call itself. With freely available tools such as Wireshark, calls can easily be traced and recorded. While circuit switched networks are reasonably secured it is difficult to ensure there are no unwanted listeners in the route in public IP networks.

– The missing link: Handover to 2G circuit switched connections when running out of coverage. This one is very difficult to do. Sure there is VCC (Voice Call Countinuity) for IMS but the complexity both in the network and the mobile device is significant. I have to admit I have no easy solution for that.

Are there other essential SIP extensions that you, fellow readers, can think of to enable SIP for mobile networks without going to a full blown IMS implementation?

Linksys launches a simulatenous 2.4 and 5 GHz Wi-Fi Access Point

Good news on the Wi-Fi front: Linksys has launched the WRT610N access point, which simultaneously operates in the 2.4 GHz band for current 802.11b/g devices and in the 5 GHz band for new 802.11n devices that support the so far little used frequency band. Should make the transition to the new frequency band much easier, especially if more vendors do the same in the future and integrate it with DSL modems!

From a technical point of view it's interesting to note that the data sheet says each band has it's own set of three antennas (I guess to support MIMO).

Have You Heard of WIPI?

In a report I read today I learnt that WIPI (Wireless Internet Platform for Interoperability), a mobile device runtime environment for applications similar to BREW and JAVA, is mandated by the Korean government to be included on any mobile phone sold in Korea that allows Internet access.

An interesting way to prevent companies such as Nokia, SE, Apple and others to sell their devices in Korea. In the past there were only CDMA based 3G networks available in Korea so this technology dispute was mainly between Korea and the US (hello Qualcomm…). As some Korean operators have now transitioned from CDMA to UMTS the issue now gains a more global dimension.

While these UMTS networks now theoretically enable Nokia, Sony Ericsson, Apple and others to sell their devices in Korea, the WIPI ruling prevents that from happening. But it looks like some operators have become rather unhappy and are asking for lifting the WIPI ruling. Lots of questions poping up here:

  • I wonder if there is a black market in Korea for such phones today?
  • Not sure if such phones would even be desired at the moment due to the probably missing Korean language integration and also due to the sophistication of LG/Samsung phones.
  • Also, I wonder how widely WIPI is used at the moment, is it seen as an integral part by a large user base?
  • In case the application environment is very popular I wonder if lifting the WIPI ruling would have an immediate effect if people would not buy devices without it.

Fellow readers in Korea, what do you think?

Do you have a wireless BHAG?

Recently a friend made me aware that companies should have a BHAG, a Big Hairy Audacious Goal to be successful and to motivate employees! I found this a rather intriguing way of looking at things and this article on Wikipedia gives some details and also some good examples of BHAGs.

BHAGs in the wireless domain I can see today are for example:

  • David Wood’s vision of Symbian to become the most widely used operating system in the world.
  • Nokia’s mission to become an Internet company.

What about your company? Do you have a BHAG?

IMT-Advanced (4G) Submission and Evaluation Process

News from the ITU (International Telecommunication Union) on 4G, aka IMT-Advanced: In a recent meeting it was decided that technology has now moved sufficiently beyond enhanced 3G systems (such as UMTS HSPA, WiMAX, CDMA1xEvDo also called ‘enhanced IMT-2000 systems’ in ITU terms) that the selection process of suitable technologies for 4G can now begin. In a paper, the ITU describes the steps that will now follow and the time frame they see for the process:

  • 2008 – beginning of 2009: Companies can submit proposal for candidate technologies. I guess 3GPP’s LTE Advanced and IEEE’s WiMAX 802.16m are hot candidates. Let’s see who else will come up with something.
  • Up to 2010: Evaluation of the proposed technologies
  • Mid-2010: Decision will be made which systems will get the IMT-Advanced stamp

A further interesting note is that the new documents now published by the ITU do not specify any new technical details concerning the properties of future 4G systems. Instead, they just reference ITU-R M.1465, which has been around for some time now, which calls for data rates of 100 MBit/s while moving and 1 GBit/s while stationary.

Via LTE Watch