Ehsan Nourbakhsh’s Blog » wireless

Phone Carriers: Main Threat to The Future of 4G Devices?

Ehsan — Wed, 16 Dec 2009 00:27:01 +0000

Yesterday a Swedish cell phone provider announced they would offer the first 4G/LTE plan available to the public. Initial pricing of the plans offered by TeliaSonera will be $83 per month in Sweden and $120 in Norway. This price covers up to 30GB of data transfer, but does not include the price of the device itself.

This announcement comes few days after AT&T made public they are considering cutting back amount of data users can transfer on their iPhones. AT&T has been criticized for network problems due to higher data usage, and now seems to be projecting the problem to their customers. You might be wondering how much data on average an iPhone user transfers per month? This article puts that number close to 100MB in 2008, although the source did not mention if that amount is per month or per day. Even if we assume it is per day, a very unlikely assumption, the total would be close to 3GB per month. Again, very unlikely, but let us assume that is the case.

The question that popped up in my mind after reading about the 4G mobile finally coming to the market, was how will the providers handle this new rates? If AT&T cannot handle current small number of iPhone owners, estimated to be around 6.4 million by Nielsen, how will they be able to persuade users to upgrade to 4G cell phones once they are available? The technology of the cell phone devices and the BTSs will make transfers quicker, but still the back bone that is required to carry this amount of data needs to be upgraded. And if they are more interested in “managing” how their customers use their cell phones rather than making that upgrade right now, there is no guarantee they will be willing to do perform those upgrades once customers start using the faster 4G devices.

I hope the major cell phone providers understand that when a customer pays higher price in terms of mandatory data plan and a longer contract, they expect to use the device they received as an incentive. And I hope while researchers and developers in hardware manufacturing companies are working on the technical aspects of the 4G devices, the business people in carrier companies are also working on understanding customer data usage trends and plan to upgrade their networks accordingly.

UPDATE, three months later: March 12 2010, AT&T CEO unsure if LTE will trigger pricing changes but “reiterated his position that such a move would happen.”

TinyOS/nesC tip: ActiveMessage

Ehsan — Tue, 15 Dec 2009 20:37:20 +0000

Just a quick note for those who are looking on the web for the reason that their nesC code is not working:

calling AMSend.setSource( *amsg, addr) may change the source address locally, but when you are sending the packet it will be reset to ActiveMessageAddressC$addr.

After almost two days of wondering why I couldn’t forge messages on a base station, a friend more familiar with TinyOS gave me this warning. I couldn’t find it on the web, so .. here it is!

One other note: if you are using a bash script to do the TOS_NODE_ID assignment for you, you should call tos-set-symbol with ActiveMessageAddressC__addr. Using $ would -obviously- cause bash to consider it a variable and replace it with empty string.

Home eNB: Great Oppotunity for 3GPP LTE

Ehsan — Sat, 11 Apr 2009 02:38:01 +0000

In the recent years more and more wireless providers have started to provide femtocells to their customers. The customer can deploy the femtocell in any location that the coverage of normal towers are weak or absent. Consider a product like Samsung’s Ubicell. The user can plug this femtocell in their home internet switch, and use their regular cell phone to connect to the final service provider, e.g. Sprint.

E-UTRAN architecture from 3GPP document 36.300-880

As of December 2008, 3GPP documentation for Long Term Evolution networks has started to mention Home eNB as part of the Evolved UTRAN. This move can be a significant advantage for the final users, only if service providers fully recognize the extent of service this final addition can offer. This recognition might require a careful study of 802.11a/b/g Access Points, considering the similarities of the two products. Both these products are the front end of a network to final customers. While these final points are accessible to the customers, the actual network is not controlled by them.

Most APs initially were merely wireless transmitters, but they soon started evolving into more sophisticated equipments. The need to provide more functionality for the end user to adjust settings, e.g. channel or user access rules, resulted in simple interfaces to configure the AP. Currently wireless APs are commonly acting as firewalls, switches, DSL modems. But the true revolution for the APs happened when vendors such as Linksys started to provide open source firmware for their products. Because of the delay in this revolution, many golden opportunities are gone and we do not see as many diverse applications.

Given how larger organization such as universities might consider deploying a number of Home eNBs throughout their campus, there is a high level of interaction that would be only limited to these eNBs. As an example, in a university campus many calls and data interactions would be between students on the same area. Or consider an event like SXSW. While this year AT&T added enough resources to guarantee good coverage, smaller scale events do not motivate service provider to make such adjustments. Instead the organizing institute is well aware of the scale and the available resources and would be able to allocate more eNBs to the event area. One other aspect is access control: if I am paying for a Home eNB, I may not want my neighbor to user it for free unless it is an emergency call.

By providing good configuration options to the deploying organization, all sides of such scenario would benefit: the organization would enjoy faster service on their campus, the service provider would not have to worry about resource management and the manufacturer would ensure better sale of its products.

There are many challenges in providing such control to the final user. However, I believe the designers of 3GPP LTE have started taking initial steps and now the manufacturers need to move forward.

26 Channels, 26 Years

Ehsan — Tue, 01 Apr 2008 23:49:03 +0000

One of my lab-colleague friends Ryan created 15 images for our Ember Zigbee devices to run on all the channels up to 26. We jokingly attributed it to my 26^th birthday today, as well as an April 1^st joke. Anyways, I prefer to regard it as my birthday cake and its candles

Here is a screenshot of the Wi-Spy readings inside our Faraday cage.

Google Maps Mobile “My Location” feature, how does it work

Ehsan — Sun, 06 Jan 2008 06:13:32 +0000

Google Maps mobile has been one of my favorite applications from Google. Recently they added one beta feature to it which is a milestone for the Google Maps Mobile (GMM). They have added the ability to find your approximate geographical location solely based on the data that your cell phone receives from base stations. This is really nice since once you know the approximate location, you can guess the details yourself. Also, each time you don’t need to enter your own address before searching for the destination address.

It has been an interesting case to find out how they do it, and by how I mean the general implementation idea and not the theoretical foundations. I post here my current understanding of the implementation, which may be lacking some parts. I hope I can update this as I gather more information.

Federal Communications Commission (FCC) requires that antenna structures with height over 200ft, or close to airport or with some specific slope requirements, register themselves. FCC publishes information gathered from these registrations on their website here. One can search these based on file number, location, address or many other criteria. For instance the tower inside UTD is shown here. The FCC File Registration Number (FRN) shown here is posted in front of the facility too.

Still one problem remains unsolved. FCC only registers the antenna structures, and not the Cell ID broadcasted by the radis on the tower. The only thing that your cell phone receives when it is connected to the radio is the Cell ID (CID) and Location Area Code (LAC), and not the FRN of tower. Although the LAC indicates an area location, the exact location and its boundaries are not broadcasted. If users wish to map the LAC to latitude and longtitude, they should find the mapping themselves. And to make things worse, phone companies do not publish these datasets of CID/LAC.

There have been multiple attempts by different parties to collect information from users of how a CID/LAC pair is related to geographical location. For instance the GSMLoc.org , CellSpotting.com and many similar projects try to gather this information from their users. Unfortunately I have not been able to find such project with enough data for users inside United States, while most of these projects cover good pars of Europe.

Google seem to have a database of the to location mapping, and seems to be completing it based on the data it receives from users. When you press the 0 button, your cell phone sends the pair(s) that it sees to Google’s server. The server comes up with an approximate location(the blue dot) and the possible error (the blue circular area). Obviously you need a data connection for the location info and the map images being sent and received. I don’t know if they have been able to buy parts of the database from phone companies, or how they use user queries to update the database, but whatever it is their final software rocks.

One final note, there are some software that can show the Cell ID and Location Area Code on your cell phone. I am using NiceTrack on Windows Mobile 2005 on my HTC Wizard. It also shows the signal strength as a graph. There are also similar software for different platforms. If you want to try the GSMLoc and CellSpotting projects, these can give you the pair.

Links for more information and resources:

mininetstumbler on PDA device

Ehsan — Fri, 10 Aug 2007 00:49:32 +0000

I am using a set of iPaq devices for some of my experiments here in UTD Distributed Systems lab. One of the devices is running WindowsCE 2003, the rest are running Familiar Distribution Linux. The WinCE one is collecting data about available wireless networks using mini-Netstumbler. The data gathered is not precise, but at the moment I only need only a general idea.

There have been a couple of problems about using the devices, which I will try to document here from now on. The first thing to note is about mini-Netstumbler. Netstumbler is “a tool for Windows that facilitates detection of Wireless LANs using the 802.11b, 802.11a and 802.11g WLAN standards”. In general Netstumbler needs a compatible device to be able to report noise levels. I was lucky to have an old SanDisk CompactFlash WiFi card which is able to report noise level.

I used a converter to connect the CompactFlash WiFi card to my notebook using the PCMCIA slot. Netstumbler under Windows XP was able to use this card without any other change. Below is a screenshot of Netstumbler.

Running miniNetstumbler needed one extra step. If you do not know this you may easily waste some hours. I had to to go to network settings, and add a wireless network setting with ESSID “ANY“, without encryption. Then connected to this “network” and ran miniNetstumbler. If you do not use the “ANY” network, you will see only statistics of the network you are connected to and not other networks.

I will try to post more about these later.

UPDATE: The list of compatible devices provided by NetStumbler is *not* updated. I got a Linksys WUSBGV4 through the link in www.stumbler.com/compat but it does not work with NetStumbler.