WirelessMoves

While my Wi-Fi access point / VDSL router at home was so far limited to a single 20 MHz channel in the 2.4 GHz band I was surprised that after a recent software update for getting better file sharing abilities has also resulted in a much improved throughput in the 2.4 GHz band. When copying a large file from one PC to another I noticed that the aggregate throughput was suddenly around 80 Mbit/s. A layer 1 Wi-Fi trace confirmed the assumptions as shown in the screenshot on the left. While my Wi-Fi card easily detects 20+ networks, the layer 1 trace reveals that they were not heavily used. Another thing that was fixed by the update was the interoperability I had for almost two years with my Nokia N8 and that Wi-Fi router. For some reason, the power save mode on the N8 slowed the Wi-Fi access point down to a trickle. The only solution so far was to disable the power save mode on the N8 or only running 802.11g on the access point. With this software update the issue has disappeared so they must have fixed it. Quite a long time for a fix but better late than never.

To predict 10 years into the future is a very long time in technology but perhaps a look back will help.

Let's zoom back to 2002. At the time there were only GSM and GPRS networks deployed in Europe. Mobile was was already ubiquitous but mobile data was just at the very beginning with a data rate of just a few kilobits per second over the air. UMTS was already standardized in Release 99, with efforts having started in the mid 1990's, but networks were not available yet. UMTS HSDPA was standardized in the 2002 timeframe when networks were not even launched and the uplink part HSUPA followed in 2004. In other words, the wireless technologies we are using today were first thought of about 12 years ago and then put into standards which were finalized around 10 years ago. Wikipedia has a good overview of which 3GPP Release was published when. LTE networks have launched in the meantime as well and their standardization started in 2004, even before I had my first UMTS phone, as described in further detail here.

With that in mind, let's have a look what's currently being standardized by 3GPP. Unlike 10 years ago, no move to a new revolutionary air interface technology is on the agenda like the move from GSM to UMTS previously. So the acronym LTE (Long Term Evolution) holds true to its name so far. The reason for that is that with LTE all angles of increasing data transfer rates are being explored. Ever higher modulation and coding schemes, MIMO, sectorization, beamforming and carrier aggregation across diffrent bands are possible from a standardization point of view and only the hardware implementation and physical nature of the radio channel are the limit. This is different to GSM with its focus on 200 kHz (0.2 MHz) channels and its voice centric timeslot design. Also, UMTS came to its limits in the frequency domain with its 5 MHz channels. The standard evolved over time to allow carrier aggregation and many networks and some device implement the dual-carrier variant by now. But several carriers was not in the mind of engineers from the beginning so aggregating more becomes cumbersome from a protocol point of view. As everyone is going to LTE anyway I doubt we'll see more than two carriers aggregated in the future.

So without any other air interface technology currently in the specification phase it's pretty certain that the networks we'll have in 10 years from now will still be based on LTE. LTE macro networks are still being expanded, however, so the LTE networks 10 years down the road will be much more ubiquitous than today and also much more dense in metro areas to satisfy the increasing demand. While in the US most networks use a 10 MHz LTE carrier today and 20 MHz carriers are used by many networks in Europe, most network operators have bought much more spectrum and will start using it once more capacity is needed. Whether channels will mostly be used independently and users are scheduled on different channels and bands depending on the channel load and local transmission conditions or whether mobiles will be able to aggregate channels beyond 20 MHz is, from my point of view, not quite clear. The standards exist to aggregate several 20 MHz channels but if this will happen in practice is another matter. But hardware evolves and when looking back 10 years and what radio interfaces of mobile devices were capable then (remember, there wasn't even UMTS at the time in practice) I guess one should never say never.

Except for using ever more spectrum, other angles of approach to increase the capacity of the network without increasing the highest data rate achievable by mobile devices is to use techniques such as using 6 instead of only 3 independent sectors per base station and to bring beamforming technologies to fruition that concentrates the available power during the transmission of data to a particular user into his direction.

What I think that we won't see is a further densification of the macro layer beyond what we have with 2G and 3G today. As described here, the range of one sector in a cell is typically already 300m or less today in densely populated areas. To get to a cell range of 50m or less such as in some parts of Seoul, new approaches are required. Small cells is the buzzword when further densification is required. Small refers to the size of the base station and the antenna which should be integrated and not much bigger than today's Wi-Fi access points so they can be deployed anywhere quickly and cheaply. Small also referrs to the power output and thus the range and area covered by that radio. The smaller the cell the higher the overall capacity of the network as the channel can be more often reused.

Apart from getting a backhaul link to small cells, another challenge is how to mitigate interference at the many cell edges as interference has a significant impact on data transfer rates at those cell borders. The straight forward approach is to have them work independently from each other and let them coordinate in the same loose fashion as today in the macro network by handing over ongoing connections and manage inter-cell interference by cooperation between the cells. Another, albeit more complicated approach, is Heterogeneous Networks (HetNets, eICIC) and Coordinated Multipoint (CoMP) in which the smaller cells are tightly coupled with a macro cell or are even remote radio heads controlled by a central scheduler. Which of these approaches will be dominant in 10 years from now is difficult to tell. Perhaps simplicity trumps over complexity. On the other hand, 10 years is a long time to perfect HetNet and CoMP.

Needless to say is that Wi-Fi will also be around in 10 years from now and will play an ever more important role at home and work. New standards such as the 802.11ac extension will further increase data rates in such places, which will certainly be needed as DSL, cable and fiber backhaul to homes are already today often exceeding the practical transfer speeds achievable with 802.11n through typical home environments with several rooms and walls between access point and devices. In theory, public Wi-Fi hotspots could also be more tightly integrated into cellular networks to offer higher localized transmission speeds. Standards exist for such a coupling but I am skeptical that they will really be implemented. On the one hand, Wi-Fi is a completely unmanaged component in mobile devices today and users have full control over it. Changing this might not be very desirable from a mobile device manufacturer, operating system and user point of view. Also, there are other alternatives such has HetNets and CoMP on the other hand that can be implemented mostly on the network side and as part of the baseband radio chip in mobile devices.

And finally, there's the voice gap in LTE networks today. Currently, all major networks still use either a dual radio approach (e.g. Verizon) or fallback to GSM or UMTS. Migrating to an operator based Voice over LTE service requires a lot to be put in place. First, network coverage must become much more ubiquitous than LTE and even 3G networks are today. While I can have an ongoing voice call on my daily train commute without any call drops, there are several data outages on the 3G layer that that would kill any Voice over LTE call. But since we won't get there anytime soon, a fallback to traditional GSM or UMTS circuit switched channels for IP voice calls needs to be put in place. This is called Single-Radio Voice Call Continuity (SR-VCC) and more details can be found here. The feature behind SR-VCC is IMS Centralized Services and the practical implementation of this in real networks is likely going to be a major pain. But I can imagine that in 10 years from now LTE networks are ubiquitous enough for true voice over LTE without many fallbacks required anymore. It won't come cheap, however, to get the same voice call quality and very low drop rates we have today in many networks.

Summary

In short, there are currently no plans to replace LTE with anything different in 10 years from now, unlike previously where UMTS was not even out of the tracks when a successor technology was already in the making. Instead, the LTE air interface will be refined as networks become denser and capacity requirements increase.

When I got my VDSL line installed at home about 3 years ago with a 25 Mbit/s downlink and a 5 Mbit/s uplink I wasn't actually quite sure for what I would use such high speeds. At the time, most servers could not deliver data at such high speeds anyway. This has changed in the meantime, however.

While for web surfing such speeds are still far beyond what is necessary today, there are a number of services that make good use of the available bandwidth by now. My online video recorder, save.tv, has been capable to send me the recorded videos at my full line speed for a while now. A full movie recorded from television at my home in just a few minutes. Also, downloading Linux distributions to experiment with are now usually also downloaded at full line speed.

The 5 Mbit/s in the uplink are also taken into good use in the meantime, for example for my private VPN at home to tunnel my mobile Internet connectivity from my PC for privacy and security reasons through my network at home. As all data goes through the uplink, the highest speed I can get over the VPN is not 25 Mbit/s but 5 Mbit/s. Still enough for most purposes but if it was any slower the solution would be far less usable for many purposes. Also, I sometimes have to share large files with other people and don't like cloud based solutions such as Dropbox for the purpose. Instead I store the files on my NAS at home and let the recipient access the files via https. Works perfectly and the 5 Mbit/s are put to good use for this service as well.

OS and program updates are now usually also delivered via content delivery networks and a 50 MB update is downloaded in a matter of seconds instead of saturating the line for many minutes. And finally, Skype video telephony also makes good use of a fast uplink, perhaps not the full 5 Mbit/s but at least 1-2 Mbit/s for very good video quality. With a 5 Mbit/s uplink, other services using the network simultaneously do not get in the way of the transmission.

And I've only talked about single use so far. When you have kids at home, each with a computer and other gadgets accessing the Internet, even such a link could become congested sometimes. Time to think about the next step and perhaps put some traffic shaping in place 🙂

Ever since Free has started as a forth mobile network operator in France, the three others are less than happy about it and are complaining about too much competition and too lower prices by their fourth competitor. But, I would argue, they are still far from the prices consumers enjoy in other countries. Here's a pretty interesting example:

When I'm in France I use a prepaid Internet access offer of Orange at the moment. 25 euros buys me 495 megabytes of data to be used within 2 months. In Austria, on the other hand, I get 1500 megabytes on a prepaid SIM valid for 12 months for only 20 euros. 495 megabytes in two months, vs. 1500 megabytes over 365 days for even less money. Quite a a difference I would say.

Every now and then I want to share large files with someone else and I am always a bit reluctant to use cloud based services such as Dropbox for privacy reasons. With a recent software update of my Fritz.Box VDSL router, I finally have all that is necessary to share files and directories right from that box with other people without the need for a dedicated device in my home network.

While my Fritz Box 7390 already contains half a gigabyte of Flash for user files I've decided to connect a USB flash drive via the USB port for extra storage. That doesn't take much extra power and provides a couple of gigabytes of extra storage. Sharing files is then as easy as copying the file from my PC to the the network drive via a Windows network share or via the web interface and then getting a unique download by simply clicking on a button in the web interface.

Links to files and directories individual, so I can share different files with different people. And for the other side, getting the file is as simple as clicking on the link. Just what I wanted for years without using a dedicated box for the purpose in my home network. And with the 5 Mbit/s uplink speed of my VDSL connection, even big files can be transferred over the Internet in a very reasonable amount of time.

Great, another cloud service replaced with my own infrastructure!

Already back in 2007 when I got my first HSDPA data card I was quite surprised how big the difference in terms of data transfer speed was when a mobile device's antenna was just moved by a few centimeters. In the meantime, better receivers and noise cancellation must surely have done away with this!? Turns out that this is not the case at all.

Recently, when being in the countryside with very weak network coverage, I managed to only get around 50 kbyte/s throughput with my 3G dongle and very unstable connections. But with some measurement equipment I finally found a spot in my room where I could get a sustainable and rock solid data rate of around 750 kbyte/s, i.e. around  6 Mbit/s (Dual Carrier 3G dongle…) in the downlink direction and around 3.5 Mbit/s in the uplink direction.

The screenshot on the left shows the remarkable difference (click on the picture to enlarge). The low throughput on the left half is in various spots in the room while the right throughput shows what is possible from one corner in the room. Just 15cm away and we are back at 50 kbyte/s. Remarkable!

Even with an old HSDPA category 8 dongle I could still get around 400 kbyte/s in the downlink direction. I did not quite expect that because that is more than half of what is possible with the dual carrier dongle, even though that category 8 stick does not have the same kind of interference cancellation techniques of the dual carrier stick. Again, something I did not expect.

Light Reading has recently posted an interesting article on how much power Voice over LTE calls draw compared to circuit switched calls today from a smartphone battery. In the report, Metrica Wireless is quoted with a power consumption measurement of a VoLTE call of 1358 mW compared to 680 mW of a circuit switched call over a CDMA network.

No further details are available so it's difficult to tell why the difference is quite significant in the device tested. It could be many factors such as a still non-optimized air interface use for voice over IP on both the network and the smartphone side. Also, there's an additional overhead in the smartphone itself for using the baseband processor for the radio transmission and the IP stack and voice compression on the application processor versus the standard circuit switched voice approach in which all processing is done in the baseband processor.

For people that mostly use their smartphones for non-voice related activities will probably not care very much. For those who make a lot of phone calls during the day, however, the difference will be quite notable.

The interesting thing to look out for now is by how much these initial values can be improved over time. And there is still some time left as there are only few VoLTE deployments and users so far and LTE network ubiquity in most countries is still far from GSM and UMTS.

While there is little incentive for European operators to think about LTE carrier aggregation at the moment, things might be different for US operators that have a couple of megahertz in one band and a couple of megahertz in another (relatively speaking to the large 20 MHz bands used in Europe). So I was a bit surprised when reading this whitepaper by Nomor research that points out that inter-band carrier aggregation is only introduced in 3GPP Release 11, which is not even yet out the door. In other words, we are at least 2 or 3 years away from mobile devices (and networks) that might actually be able to combine carriers in different bands. Very strange, I would have thought US carriers would have been more insisting to get this functionality sooner…

P.S.: The paper also contains interesting details on how a correct timing advance is ensured in inter-band carrier aggregations HetNet situations where antennas are distributed and connected via fiber links and timing advance to different component carriers can be different.

Femto cells have been a buzzword for many years in the industry. They might now have been renamed into small cells but in most countries they are not (yet) used. One way to use a femto cell is to patch coverage holes in private homes. Here, it may makes sense to restrict the use of the femto to family members. Other mobiles that see the femto and try to use it are then rejected and have to return to the macro network. There are several ways how that can be done and I always wondered which one is used in practice. Recently, I stumbled over this blog entry that describes an encounter with a femto in practice. This one used a Location Update Reject with Cause Code #13 (Roaming Not Allowed In This Location Area). This then triggers the return to the macro network. For further details, have a look at that post, it also contains other interesting thoughts about femtos in practice based on the authors observation.

When I watched a video on Youtube today I noticed that the page's URL was https://www.youtube.com…. Interesting, I thought, it's encrypted now! If the streams are encrytped too, that would have interesting implications for video caching and compression servers in some mobile networks as they would no longer be able to compress and scale videos.

So I ran a quick Wireshark trace to see if the streams themselves were encrypted, too. However, they were not. An interesting implication of this is that the user might get the impression that the session is secure. But as the videos are sent in the clear, it's actually not secure at all. From the outside, it is no longer possible to see what the user is searching for, but which videos are streamed are still visible and can be cached or modified or simply blocked.

As the unecrypted URL requests are requeted by the Flash player there's also no warning that there are "secure and non-secure elements on the web page", as browsers often display when web pages start mixing secure and non-secure content.

From this point of view, I am not sure that it is a good idea to use https for Youtube. It simply gives a wrong impression of security to the user…