RAN – Page 5 – WirelessMoves

Femtospots

These days I was wondering if in the mid-term, femtocells might replace public Wi-Fi hotspots!?

With the rise of 3G USB keys and notebooks with built in 3G connectivity, the popularity of Wi-Fi hotspots, especially paid ones, is likely to degrade over time. Once people have a 3G card anyway and have instantaneous connectivity anywhere, people just won't bother anymore to search for a public Wi-Fi hotspot and go through the manual login process. In addition, femtos remove another shortcoming of public Wi-Fi, the missing air interface encryption which today leaves the door wide open for all kinds of attacks.

With rising demand for Internet access in hotspot areas such as hotels, airports, train stations, etc., HSPA or LTE femtocells might be the ideal replacement for aging Wi-Fi access points which at some point have to be replaced by new equipment anyway. So mobile operators such as T-Mobile, Orange and others, who have a dual 3G / Wi-Fi strategy today could at some point just make such a move if they see that use of their Wi-Fi systems is decreasing and use of their 3G/4G macro base stations in the neighborhoods of their Wi-Fi installations is significantly increasing.

Some 'dual-mode' operators might even have a database with the geographical location of their base stations and their Wi-Fi installations. Together with traffic statistics of both systems an automated system could document changes over time and could be used to help predict when and if a replacement of the Wi-Fi access points for femto cells might make financial sense. After all, femto cells are just as easily connected to a DSL line than a Wi-Fi installation.

Maybe some femto manufacturers even come up with integrated Wi-Fi/Femto boxes for public installations with the Wi-Fi being used to create a wireless mesh between several nodes in locations with only a single backhaul line and for access for those people not yet having 3G connectivity. Agreed, femto vendors today mainly position themselves around the femto base station for home networks but public femtos might be an interesting opportunity as well.

Dongle Upgrade Incentives

Here's a thought experiment about whether and how operators should encourage users to upgrade their 3G dongles to a newer model:

Most HSPA dongles currently 'in the wild' are are HSDPA category 6, i.e. they are capable of theoretical speeds of up to 3.6 MBit/s. Category 7 dongles with a maximum theoretical speed of 7.2 MBit/s are now also available and currently going over the counter. The speed increase between the two is mainly due to an increase of the number of spreading codes the device can handle simultaneously. In other words, from an overall network capacity point of view it does not matter a lot whether most of the devices used for high speed Internet access are category 6 or 7. In the future however, this is going to change.

Pretty soon, higher speeds in HSPA networks will be mainly achieved by more sophisticated 3G devices and networks. Receive diversity with several antennas helps during weak signal conditions (this Ericsson paper is a good starting point for further research) and MIMO while reception is good. In addition, more sophisticated mathematical approaches to separate noise from useful data will also help to increase data speeds. From a network point of view, this means that the more of those newer devices are in the network compared to the number of older devices, the higher the overall throughput of the network.

So should it be in the opreators interest to encourage users to upgrade to newer devices? And if so, how could that be done best? Is the higher speed achived with those devices incentive enough or should the base station scheduler also take the UE category into account to further boost data rates of newer devices? I could also imagine to offer a reduced rate to users with newer hardware as they use the air interface more economically than users with older hardware. Kind of a similar approach to taxing older cars with higher emissions higher than new cars (don't take the analogy too far…). Or maybe this is all overkill and the normal equipment replacement cycle of 2-4 years will do the job anyway!?

Virtual GSM in the Future?

While HSPA+ and LTE drive data rates higher and higher and have network operators and vendors discussing which is the right way to go, GSM for voice and low bandwidth data applications is unlikely to go away anytime soon. I've speculated in the past about when GSM would be switched off in Europe and elsewhere and wondered if maybe at some point Software Defined Radio (SDR) technology would allow to fold all radio access technologies into the same hardware and into a single digital and a single radio module in the base station.The more I think about it the more interesting such a combined option looks like to me.

With backhaul already converging to IP for GSM, HSPA and LTE, there will be nothing standing in the way from that side of the network in just a couple of years from now. From a handset perspective, GSM might also be the least costly and best technology for the foreseeable future for voice only devices. When I look at my 3.5G mobile stuffed with the latest technology and compare it to the simple GSM phone I use for voice calls only I can not only see a significant difference in size but also in price. After all, a 3G handset does not only have to contain more hardware but the license/patent fees are much higher than for 3G phones. And LTE will further increase the hardware and royalty costs, so there is no break from this perspective, either.

And while LTE and HSPA+ might be optimized for speed, they are definitely not optimized for voice and power consumption when compared to GSM.

A single digital / radio module in the base station would also have another interesting benefit: When only little capacity for GSM voice and GPRS/EDGE data is required in a region the base station could automatically reconfigure itself and use more of the bandwidth for LTE. During busy hour, when voice calls over GSM come close to the capacity of the current configuration, the LTE carrier bandwidth could be reduced and additional narrow band GSM carriers could be fired up within a few seconds. Currently, LTE bandwidths are defined at 1.25, 2.5, 5, 10, 15 and 20 MHz. Maybe not yet fine grained enough but that could be changed in future versions of the standard.

In the backhaul, everything will have converged on IP right up to the MSC Media Gateway and from there the phone call is also sent through the network over IP connections. The H.248 protocol between the Media Gateway and the MSC Call Server is also based on IP, as well as the link to the Home Location Register and all other equipment in the core network. In effect, the once circuit switched GSM network has become fully IP based and only higher layer protocols such as DTAP and MAP are still remaining from the original protocol stack to preserve the super efficient GSM air interface technology for voice.

Unconventional ideas, but who knows what the future holds.

3G Coverage on a Train Ride to Vienna

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.

HSPA State Change Measurements

Last week I did some measurements to get an idea of the time required when switching between different HSPA air interface states. While data is transferred, the mobile is usually in Cell-DCH state on a High Speed Shared Channel. When only little or no data is transferred, the connection transferred to the Forward Access Channel, which is slow but has little overhead for both the network and the mobile device in terms of control measurements and power adjustments commands. If no data is transmitted for a longer duration (e.g. 30 seconds) the connection is put into Idle state. While the IP address is retained, the physical connection between the mobile and the network is severed.

As can be seen in the picture on the left, the round trip time to the first hop in the network of a ping packet is around 100 to 120 milliseconds while the mobile is using a high speed shared channel. While on the slower forward access channel, round trip time increases to 240 to 260 milliseconds. Moving from the high speed shared channel to the forward access channel is relatively quick, it takes around 550 to 600 ms (minus the actual round trip time of the packet itself). Going back to the high speed shared channel takes a little bit more time, around 1000 to 1500 milliseconds.

When using a 3G dongle with a notebook, a connection is rarely set into idle state as there is always one program or another such as an instant messenger, VoIP client, etc., that feels it needs to send a keep alive message to a server in the network before the idle time can expire. Therefore I haven't measured it this time. In the past, I've seen values around 2500 to 2800 milliseconds.

Some say that the effect of this state switching is that web browsing feels a bit more sluggish over HSPA than over a DSL line, which always offers Internet connectivity at full speed without the need of state switching. I use 3G connectivity a lot and quite frankly, while I can feel a difference, it's absolutely no problem to work and live with it.

And here's a quick overview of the test setup: Mobilkom Austria 3.5G HSPA network, a notebook connected via Wi-Fi to a D100 Wi-Fi/3G gateway, connected to a Huawei E220 3G USB stick, HSDPA category 6, no HSUPA.

Uplink Downlink Ratios Revisited

I've been traveling for two weeks now in Austria and Italy and have been online throughout that time 'only' via 3G to do my daily business thanks to prepaid 3G Internet access. Wherever I went, 3G HSPA access has been available so using the Internet with a 2 MBit/s downlink on average didn't feel much different from using DSL at home. I've reset the data counters on my N95, which I used as my 3G modem during the trip, to get an idea on how much data I exchanged. In the past seven days, I used about 750 MB in total for e-mail, web browsing, company Intranet access, VoIP, IM, etc.

As can be seen on the picture on the left, my uplink to downlink ratio is around 1:2 and not 1:10 as I observed during a previous trip. That's probably got something to do with the fact that this time, I received and sent many e-mails with massive file attachments (those 5 MB PDF or PPT files everybody likes…) and have been using VoIP extensively for lengthy conference calls. With VoIP, the uplink / downlink ratio is 1:1 and generates around 20 MB per hour in each direction.

From a network point of view a 1:2 ratio means that I used about as much resources in the uplink as I did in downlink, since uplink transmissions are less efficient than those in downlink due to the smaller antenna and little transmission power compared to a base station. While in most situations, I could get uplink speeds of around 400 kbit/s, which is almost as fast as the uplink of my DSL line at home, I nevertheless wished I would have had a High-Speed Uplink Packet Access (HSUPA) capable device and network. Those 5 MB Power Point presentations do take quite a while to get transmitted.

Yes, one can never have enough bandwidth 🙂

Telstra to Upgrate to HSPA+

A tip from a reader brought me to this article on Telstra in Australia saying that they intend to upgrade their 3.5G network in Australia first to 21 MBit/s in 2009 and later on to 42 MBit/s. The step to 21 MBit/s seems logical. According to the 3GPP standards, that's an upgrade to 64QAM modulation. If they have the latest base stations from Ericsson, they might be able to do this without a hardware upgrade.

Concerning the 42 MBit/s, that sounds like the 28 MBit/s one gets with MIMO plus 64QAM modulation on top. When I last had a look at the standards document referenced above, there was not yet a terminal class for this maximum speed.

A note of caution: Such speeds can only be reached under very special circumstances, i.e. no other subscribers in the cell and the base station antenna very close by.

First ‘One Tunnel’ Network Sighted in the Wild

While LTE is in development, loads in 3G networks are increasing and network operators are looking for ways to reduce their costs. One such move seems to be moving to a 'One Tunnel' architecture in which the user data packets bypass one of the packet core nodes, the SGSN.

Instead of tunneling the packets between the mobile device and the Internet through the base station, the RNC, the SGSN and the GGSN, this approach directly connects the RNC and the GGSN. As a consequence, fewer resources are required on the SGSN since it doesn't have to 're-package' the frames from one tunnel into another (hence the feature's name 'One Tunnel'). For details see this blog entry.

Nokia Siemens Networks now reports that network operator '3' in Austria is their first customer for the One Tunnel feature in this podcast that can be found here. I can imagine that they are quite keen to use the feature since Austria is a very competitive market and SIM cards and USB data sticks for 3G Internet access can be bought in every supermarket for next to nothing.

HSDPA Alongside A CS Voice Call

Back a year ago I noticed that an incoming circuit-switched voice call during a 3.5G HSDPA packet-switched data session forced the packet connection to go back to 64 kbit/s dedicated bearer while the call was ongoing. After the call the bearer was upgraded to 384 kbit/s but was only put back on the High Speed Shared Channels once the download was finished. Looks like the software on the network side has advanced a bit in the meantime as I recently noticed that even during a phone call an ongoing download continued at HSDPA speeds. Very nice!

Note: The test a year earlier was performed in the German Vodafone network while my latest observation is from the Orange France network. The RAN vendors might not necessarily be the same and it's even likely that they are not.

T-Mobile USA and the HTC G1 Google Phone – An Interesting Couple

O.k. the HTC G1, or the first Google Android phone, is about to launch and everybody is looking at the Google side of things. But have a look on the other side of the equation: That phone has to use a network. And this network is going to be T-Mobile USA. The interesting thing about this is that this is one of the two networks on this planet that is using 1700 MHz UMTS. For the moment, they only have three very low end 3G phones (according to Wikipedia, see here, here and here) which must sell very well against insignificant competition such as the iPhone.

The HTC G1 will be even more than a quantum leap for T-Mobile USA, it will be the first phone which will use their 3G network in a meaningful way. The HTC page doesn't yet list a lot of network specifications on the device yet. I wonder if it will be dual band 3G, 1700 MHz for T-Mobile USA and 2100 MHz for the rest of the world or if the version announced for the UK will be a different hardware. But then, how about positively surprising me and delivering a Quad band UMTS device with 850, 1700, 1900 and 2100 MHz UMTS built in? Now that would be something, but I'd be really surprised.

I just had a look around which other phones do/will support 1700 MHz. Interestingly the Sony Ericsson X1 came up as 1700 Mhz + quad-band 3G capable. I wonder if T-Mobile USA will pick it up sooner or later!? Also interesting is the Wikipedia link on UMTS quad-band and UMTS tri-band. They give a pretty interesting overview which 3G phones work on more than one continent on speeds faster then EDGE. Nice to see that the list is growing. But what would really be nice for true world roamers are 5 bands. How would that be called? Quinband?