Recently I took the train from Linz to Vienna and I was quite surprised that Mobilkom Austria (A1) must have put a more or less dedicated 3G coverage alongside the railway track even in very rural areas. I've had 3G coverage for most parts of the trip and in the few places 3G coverage was lost, their EDGE network kicked in. I've reported on my experiences with non-optimized 3G HSDPA coverage on board of trains before (here and here), but this time, the experience was even better. The connection I established was maintained throughout the trip and high speed data transfers taking several minutes were performing very well as shown on the image on the left. I even dared to launch my IM client as connectivity was simply always there. I stepped out of the train very impressed by what is possible when operators decide to do a proper network planing and deployment.
Over the past 2 years I've written a number of blog entries on Evolved EDGE (here, here, here and here). Now that the feature set is mostly specified, vendors are moving into the implementation phase. A recent whitepaper of '3G Americas' is giving an interesting overview of the different features (without going to much into the implementation details), their potential, and different likely implementation phases. I quite like the paper as it takes a look at EEDGE not only from a technical but also from a deployment point of view.
From a technical point of view the paper mentions one thing in particular which I have not thought about before, and that is that there are two improvements brought by the dual carrier feature. The first improvement is that it improves throughput because timeslots can be assigned simultaneously on two carriers. That's quite obvious.
The second improvement is that even if some timeslots are busy on one carrier for voice calls, the same timeslots on the second carrier might be free and can thus be assigned. This doesn't result in the full theoretical speed but at least compensates for the fact that it is difficult in many situations to have 5 timeslots in sequence available on one carrier. In effect this statistically increases the number of timeslots available for a dual carrier mobile compared to a current single carrier mobile and thus increases the overall speed experienced by a subscriber by using timeslots that could otherwise not be used.
In the past I've reported on activities in 3GPP on Evolved EDGE (here and here). Looks like standards are well on their way now and a number of network vendors and terminal manufacturers are working on the implementation.
According to analyst resources, especially China and India could be countries in which operators are interested in the new features, especially in the dual carrier functionality that promises to further increase data rates per device. In these countries, no or only little 3G has been deployed to date so it might well happen that operators in these countries will go directly to LTE, WiMAX and beyond and try to fill the gap in the meantime by evolving their GSM networks.
What I am wondering though is if networks in these countries really have enough capacity to assign timeslots on several carriers to a single mobile device? I would assume their network density and capacity is pretty well adapted to current traffic levels which doesn't leave much room for this. When looking at it from a different perspective the question is if they would be prepared to increase capacity (and thus CAPEX and OPEX) in their networks for the dual carrier feature?
If you have an opinion on this, please consider leaving a comment below.
Some years ago, when I tested how long the battery of a mobile phone would last when a mobile device was connected to a 2G or 3G network (PDP context established) but not transferring any data for most of the time. At the time, the result was quite clear: I could almost watch almost in real time how the battery level decreased. Looks like things have changed pretty much in the meantime.
When repeating the test these days with a Nokia N95 and a Nokia N82, one being connected to an EDGE network and the other to a UMTS network over the course of the day while transferring almost no data, there seems no difference anymore to the device not being connected throughout the day. The picture on the left shows a screenshot of my N95 that was connected to an EDGE network throughout the day. Note that at the time the screenshot was taken, the mobile was also connected to a Wireless LAN network (i.e. some applications used the EDGE connection, others the Wifi connection). The same test with the N82 that was connected to a 3G network showed the same result.
Very good, one thing less to be concerned about! No more advice about disconnecting from the network due to the fear of running the battery into the ground quickly.
I still remember that in the early days of GPRS, the main problem was to get mobile devices that could actually make use of the new network service. The story repeated itself with UMTS where where things became even worse. When UMTS first started, there were lots of networks around but no or only clunky mobile phones available for at least a year or so.
In the meantime it looks like the situation has reversed. Quite a number of 7.2 MBit/s HSPA devices are available, but only few networks yet support ten simultaneous downlink spreading codes and have the required backhaul capacity to the base station. With HSUPA it is quite similar. A number of devices, mainly USB sticks, are available on the market today, but most networks still lack support. And it’s not only in UMTS, where devices are far more capable then most networks today.
Even 2G mobiles now support features that most networks are lacking. The AMR (Adaptive Multi Rate) speech codec is a good example. Widely supported in handsets today, but only used in few networks today, despite the potential capacity increases the feature offers to operators. Or take DTM (Dual Transfer Mode), which enables simultaneous voice calls and Internet connectivity for GSM/GPRS/EDGE devices. Again, many mobiles support this today and it could be put into good use especially with feature phones. However, I haven’t seen a single network that supports it in practice.
A worrying trend. Are the standards bodies specifying too much?
Last week, Nokia Siemens Networks (NSN) press department did a good job announcing that they will support Evolved EDGE and double data speeds in GSM/EDGE based networks. Speculations started to go wild and the word iPhone was sometimes heard as well.
Well, by the time evolved EDGE hits the street the 2G iPhone will (hopefully) long be history. NSN says they will have it ready for operators by the end of this year. Which means that at best, we will see this available in some networks by mid- to end of 2009 at the earliest. Apple should have a 3G version of their phone by then, no? And besides, for those still having a 2G iPhone when evolved EDGE is available, they won’t benefit as it requires more than a simple software update in the mobile.
Anyway, it’s good to see that NSN is not the only vendor standing behind evolved EDGE. Others such as Ericsson and Nortel have announced their support (here and here) for about the same time frame long before.
Next, I am waiting for a word from mobile device vendors when they will support it. In the past they have supported features much earlier than they were available in life networks. DTM (Dual Transfer Mode, voice + packet data simultaneously) is a good example which Nokia already seems to support for ages now. I haven’t seen a network yet, however, that supports it.
As a frequent traveler I often use Vodafone Germany’s Websession offer which lets me connect wirelessly to the Internet in most countries in Europe and also in some countries overseas using 3G UMTS or 3.5G HSDPA. I’ve first reported about the details of the offer here and also posted reports of how well it performs in Italy, France and Switzerland in the meantime. This blog entry takes a look at how the offer performs in Austria:
A1’s 3G network (Mobilikom) coverage area throughout Austria is excellent and even in areas without 3G coverage, EDGE capable GSM base stations deliver throughput good enough for work and play. While in 3.5G HSDPA coverage, I reached top speeds of about 2 MBit/s when downloading three files simultaneously.
Single file download top speeds where at about 800 kbit/s. As in previous cases I am still a bit puzzled to why that happens as round trip delay time for the file download was around 230 ms. Together with a TCP window size of 65k, the throughput of a single TCP session should be 2.2 MBit/s. Note: For background information on the effect of the TCP window size and round trip delay times on throughput see here.
Nevertheless, 800 kbit/s per file is more than what I observed in Italy and France where bandwidth is throttled to around 500 kbit/s overall, independently of how many files are downloaded at the same time. Looks like Vodafone A1 does something differently with Vodafone Germany then the roaming partners in Italy (Vodafone Italy) and France (SFR).
So all things taken together the Websession performance in Austria is quite convincing, too.
I’ve already reported back in November 2006 that a number of companies in 3GPP are seeking to once again increase the data rates for GPRS beyond what is available with EDGE today. The feature is commonly called evolved-EDGE. At this point in time there seem to be a number of working groups inside 3GPP dealing with the nitty gritty details and they’ve called themselves RED-HOT and HUGE. Here’s what the abbreviations stand for:
- RED-HOT: REduced Symbol Duration – higher Order modulation and Turbo coding
- HUGE: Higher order Uplink performance for GERAN Evolution
Totally obvious… Here’s more on the 3GPP server.
The upload and download speeds that can be reached with a GPRS and EDGE mobile phones depends on a number of factors. First, the capacity available in the cell. Usually, voice calls take precedence over GPRS traffic and in case not enough time slots are available for both, some GPRS timeslots are sacrificed for voice calls. Second, the capability of the mobile, or it’s multislot class. Third, the network has to match the abilities of the mobile device. And fourth, the reception conditions experienced by the mobile.
The most comment GPRS/EDGE mobile station class today seems to be multislot class 10. Mobiles of this class can use 4 timeslots in downlink direction and 2 timeslots in uplink direction with a maximum number of 5 simultaneous timeslots. Depending on the amount of data to be transfered in the uplink the network will automatically configure the ongoing data stream for either 3+2 or 4+1 operation.
Some high end mobile, usually also supporting UMTS also support GPRS/EDGE multislot class 32. According to 3GPP TS 45.002 (Release 6), Table B.2, mobile stations of this class support 5 timeslots in downlink and 3 timeslots in uplink with a maximum number of 6 simultaneously used timeslots. If data traffic is concentrated in downlink direction the network will configure the connection for 5+1 operation. When more data is transferred in the uplink the network can at any time change the constellation to 4+2 or 3+3. Under the best reception conditions, i.e. when the best EDGE modulation and coding scheme can be used, 5 timeslots can carry a bandwidth of 5*59.2 kbit/s = 296 kbit/s. In uplink direction, 3 timeslots can carry a bandwidth of 3*59.2 kbit/s = 177.6 kbit/s.
While the numbers are quite impressive it should not be forgotten that a single carrier has 8 timeslots of which two are reserved for signaling on the first carrier. Using 6 timeslots for a single mobile means almost the complete carrier is used for the data transfer of a single mobile. Under realistic conditions it’s unlikely a cell has that much free capacity to offer next to voice calls.
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.