Author: Martin

The recent podcast by Glen Fleishman with Matthew Gast, author of "802.11 Wireless Networks: The Definite Guide", published by O’Reilly is one of those rare tech podcast jewels which are both entertaining and interesting. Having read Matthew’s book a while ago it was also interesting to learn a bit more about the author behind it.

With lots of more or less compatible Pre-N Wifi and Mimo products coming out these days and less encouraging news about the state of discussions in the 802.11n standards group, it was also good to hear an update from somebody involved in the process.

Here are my thoughts triggered by the podcast:

State of Discussions (September 2006):

The current version of the IEEE 802.11n standard is called Draft 1 and was released earlier this year. Draft 2 will be out in the middle of 2007 and should resemble the final standard with only minor modifications before final acceptance.

The Wifi standard is driven by two bodies: The IEEE standards group which is consensus driven and the Wifi Alliance which is market driven. The Wifi Alliance is an industry group which ensures interoperability of devices of different manufacturers with a certification program. You might have seen their "Wifi" certification label on various products before. While deliberations on the standard are still ongoing a number of different companies, however, have already started to ship "Pre-N" products, many of them not compatible with each other. As this hurts the overall Wifi eco system, the Wifi Alliance has decided to launch a "Pre-N" certification program shortly to tackle the situation.

802.11n for power and size constrained devices

The main goal of 802.11n is to increase the data rate from todays 54 MBit/s (on the physical layer) to 100, 200, 400 MBit/s and beyond. Matthew states in the podcast that first devices will probably achieve about 200 MBit/s with higher speeds to be seen in the future. Faster speeds, however, increase power consumption due to increased signal processing requirements and requires multiple antennas. While this is less of a problem for devices like notebooks, meeting these requirements with small devices like PDAs and mobile phones is more difficult. Thus, the 11n working group is defining the standard in a way to allow mobile phones and other small devices to implement fewer options and thus optimize power consumption and size requirements. While such devices are slower, the standard is designed in a way to allow them to still be compatible and interoperable with chipsets for devices like notebooks that include additional options to push the speed limit. To me this makes a lot of sense. While applications like video streaming between PCs, notebooks , TV screens and other devices demand a lot of bandwidth, mobile devices with small screens usually require much less. Even if there are some mobile phone devices one day which act as Wifi Access Points to share a 3G or 4G Internet connection, even rudimentary Wifi speeds are still much higher than the speed of the wide area network.

Dimensions of Speed:

Like the current 802.11a and g standards, 802.11n uses Orthogonal Frequency Division Multiplexing (OFDM) on the physical layer. With this method, data is sent over many narrow band channels simultaneously. While current standards use a bandwidth of 20 MHz, 802.11n also uses 20 MHz and optionally 40 MHz. Using twice as much bandwidth in effect also doubles the speed available to users.

To further increase throughput,  802.11n uses a technique called Multiple Input Multiple Output (MIMO). MIMO uses 2, 3 or  4 antennas to send data simultaneously on the same frequency but over different spatial paths. This method is also called spacial multiplexing and exploits the fact that radio waves bounce off objects in the transmission path and thus create several independent paths from sender to receiver.

It’s interesting to note that WiMAX and the 3G Long Term Evolution (LTE) project also use MIMO to increase speed. Wireless "Pre-N" Wifi devices, however, will be the first on the using this new technology.

Backwards Compatibility

Backwards compatability is a difficult issue for 802.11n but absolutely necessary as it shares the 2.4 and 5 GHz bands with older 802.11b, g and a networks. In the 2.4 GHz frequency range 802.11n has to share the available bandwidth with 802.11b and g networks. While three non overlapping 20 MHz channels exist, only a single
40 MHz channel fits into this space. As a consequence, 40 MHz networks can not coexist at the
same place. This is quite difficult in today’s crowded Wifi environment. In the
5 GHz range, which is only used by few 802.11a devices today, things
look somewhat brighter.

In addition, new 802.11n networks must be able to handle both new 802.11n and older 802.11b, g and a devices. This is possible, but the overall speed in the network decreases. This is because of older stations not being able to use the the bandwidth as efficiently as new devices and because of additional precautions that have to be taken to prevent older stations from trampling over ongoing data transfers of new devices which they are unable to detect.

For situations in which no legacy devices have to be supported and no other networks use the same band, a "greenfield" mode is currently under discussion which throws all precautions overboard in order to increase transmission speeds. Such a mode is similar to the "g only" mode of current 802.11g access points which can be activated if no legacy devices are used.

Summary

The 802.11n standards group currently has to walk a fine line to ensure on the one hand that the standard is detailed enough, that it is designed in a way to allow power and size constrained devices to use it as well and on the other hand to finish their work as quickly as possible in order to prevent a further fractioning of the Pre-N market which has already begun. Not easy, but land is in sight.

Another week, another Carnival of the Mobilists, this time at "Communities Dominate Brands" a website of Tomi Ahonnen and Alan Moore. Again, a very interesting round up of this weeks best posts from the mobile community. So head over and check it out!

For some time now I’ve been experimenting with podcasts together with Debi Jones and Rudy DeWaele. I’ve recorded and edited both podcasts from home so they were not very mobile, despite mobility as their main topic. For people who would like to produce mobile podcasts while on the go, Cellcast the "One Call to All" might be quite interesting (for the English version click on the little English flag on the upper right of their web page). All you need is a mobile phone, no special software required. A pocast is simply recorded by calling a fixed line phone number. Once done, the podcast is immediately available on the Cellcast portal, at your personal URL and via your personal RSS feed. The web site has a cool modern design with AJAX functionality, tags, tag clouds and is pure social media. In short: Web 2.0 at it’s best!

Ever heard of Augmented Reality? No? Well, me neither but it looks like this might change soon. One flavour of Augmented Reality is the addition of artificial elements to a real time video stream. As a mobile enthusiast I found this video of augmented reality applications on a Nokia S60 camera phone quite fascinating: A multiplayer tennis game that uses the phone’s camera in real time. Its fascinating how the software reacts to user movements and adapts the artificial elements (ball, tennis court) accordingly.

Here are some additional links if I have aroused your interest:

• More videos about the topic from at Hitlab (source of the video and picture above)
• ARToolkit
• NVIS: Ubiquitous Augmented Mobile Reality
• Augmented Reality on Wikipedia

News of the new Nokia N95 have taken the blogsphere by storm. People like Justin who usually have long blog entries are simply left speechless. Incredible, incredible, incredible. A good intro with technical details can be found on AllAboutSymbian. And, likewise incredible: It took less than a day for at least half a dozen videos from the Open Studio Event in New York and from Nokia to show up on YouTube. Take a look here. I am amazed.

This will be my next phone, definitely! Things that stand out for me:

• It’s small size compared to other phones such as the N93.
• 5 mega pixel camera with Carl Zeiss lens.
• WLAN (o.k. already introduced in the N80, N91, N93…) but this is a must for my next phone. Let’s hope they’ve got a solid VoIP/SIP client in it this time.
• GPS inside. I’ve been waiting for this for a while. Endless possibilities. Also, see the N95 GPS video on YouTube.
• Category 6 3G UMTS HSDPA inside (according to AllAboutSymbian). That’s 3.6 MBit/s in downlink.
• Bluetooth Advanced Audio Distribution Profile (A2DP) inside. Cool for wireless stereo headsets.
• All the usual multimedia features from previous models improved.

This one’s going to crush the competition!

I like Bluetooth very much as it lets me connect my notebook with
my mobile phone to access the Internet via 3G networks. I also like Bluetooth because I can quickly exchange small chunks of data between different devices. Current 3G technologies like HSDPA and EVDO, however, pretty much challenge the bandwidth Bluetooth offers today and soon enough the last few centimeters of an Internet connection will become the bottle neck rather than the cellular connection. Also, using Bluetooth to transfer pictures and videos from my phone to the PC has become quite slow due to the ever increasing image resolution and frame rate. But rescue is in sight: Ultra Wideband (UWB) thechnology. Here’s a short overview of it’s capabilites, standards bodies and technical parameters:

Speed, Speed, Speed:

With speeds of up to 480 MBit/s (!!!) it will take a while before 3G, 4G and 5G networks catch up. Also, such speeds will make a whole new range of applications feasible such as fast picture and video transfers from mobile devices such as mobile phones and cameras to PCs. Let’s take a 3 mega pixel image with a file size of 2 megabytes as an example. UWB will transfer 30 of these per second. Video clips are transfered with lightning speed as well. A 2 minute video clip in an excellent resolution and frame rate takes 20MB on your phone’s memory card (MPEG4). UWB will transfer 3 of those clips or 6 minutes worth of video per second.

Standards Bodies:

As always there’s competition. That’s usually good as it drives innovation. At the beginning UWB standardization was started in the IEEE working group 802.15.3. Opinions diverged over time and some vendors including Intel decided to go their own ways and created the WiMedia Alliance. Since then they compete against the UWB Forum which backs the IEEE 802.15.3 efforts. The following technical details are from the WiMedia standard and you can find a more detailed introduction in "The MBOA-WiMedia Specification for Ultra Wideband Distributed Networks" from Javier del Prado Pavón et. al in the June 2006 Edition of the IEEE Communications Magazine.

The Tech Specs:

• Speed Again: The top speed of 480 MBit/s mentioned above can be reached at a distance of up to 2-3 meters. At a range of 10 meters speeds of 53 MBit/s and more will still be possible.

• Physical Layer: UWB uses OFDM (Orthogonal Frequency Division Multiplexing) technology with 128 subchannels, which is already used by other well known wireless technologies such as Wifi (802.11g) and WiMAX. The big difference to these technologies is the ultra wide bandwidth used by UWB. Instead of 20 MHz like Wifi, UWB uses a bandwidth of 528 MHz. This also explains why the maximum range is so limited. The maximum transmission power is the same as for other license free wireless technologies such as Wifi. For UWB, however, the signal energy is spread over a much wider channel, thus limiting the range.

• Frequency Hopping: UWB uses a frequency hopping scheme over a very large frequency band, 3.1 to 10.6 GHz, hence 14 channels. Only a single symbol is transmitted per channel before the frequency is changed. The symbol time is 312.5 ns.

• Self organization: While Bluetooth and cellular networks have a master device that controls access to the network, UWB networks are self organizing. Devices close to each other automatically form a temporary network even if they don’t want to exchange data with all devices that they can see. This way collisions are avoided when several devices want to exchange data at the same time in the same physical space. If a single device comes into contact with an already established network, it simply joins the already existing network if it wants to exchange data with another device. If several devices which have already formed a network come in contact with another network, the two networks automatically merge to form a single network. Again this is done to avoid collisions that would occur if data was sent in two or more separate networks in the same physical space.

• Beacon slots: As in other systems, UWB transfers data in frames. Each frame starts with a number of beacon slots. Each device of the network uses a different beacon slot to announce its presence and to announce that it would like to transfer its data to another device in the network. This way all devices of a network are aware of all other devices. Collisions can only occur when two devices would like to join a network at the same time using the same beacon frame. This can only happen once and only before the actual data transfer starts.

UWB standards today only seem to cover the lower layers of the protocol stack. What’s still missing is the application layer above. Here’s where the Bluetooth Special Interest Group (SIG) could come into play. The Bluetooth ecosystem specifies all layers of the protocol stack and also offers profiles such as the headset profile, the Dial Up Profile, OBEX profile and many many more that specify how applications on top shall use the radio link. This ensures interoperability between different devices which in turn generates widespread acceptance of the technology. Currently the Bluetooth SIG is thinking about selecting a UWB technology for the next major version of their standard. Still, nothing seems decided so I am looking forward to see who’s going to make the race, WiMedia or the UWB forum.

As things stand we are still a couple of years away from having a UWB ecosystem as mature and feature rich as Bluetooth. But I have no doubt that it will come.

Update: Just found a podcast on the topic over at Wifi Networking News.

I’ve dedicated well over 15 months of my quality time into my latest project and now it’s finally done and available in book stores around the world: Therefore, I am proud to announce general availability of the book to this blog "Communication Systems for the Mobile Information Society", published by John Wiley & Sons.

If you are looking for a solid introduction to GSM, GPRS including EDGE, UMTS with HDSPA and HSUPA, Wireless LAN, fixed and mobile WiMAX 802.16, as well as Bluetooth, this book is for you! My intention behind the book is to give a well balanced overview with a good level of detail for each technology rather than to go into the deepest details a book dedicated on a single technology would do. Here’s the link to the book on Amazon.com to find out more. If you have an Amazon.com account you can even browse through the book with their "look inside" functionality.

I felt it was time to write something like this as most students certainly do not read six individual books of 300 – 400 pages each for a college course on wireless. I’ve also seen that many wireless experts working in a particular field covered by the book would like to find out more about other technologies but simply do not have the time to read a 400 page book dedicated on a single wireless technology.

Each chapter contains a questionnaire at the end so you can test how
well you have understood the system explained in each chapter. The
answers to the questions are right here on this blog, take a look on
the left side.

If you come to this web site regularly you might have noticed that I do not only express my visions for the wireless future in my entries but usually also give them quite a technical spin. The book is similar in this regard as it contains my enthusiasm for wireless technologies, my knowledge on how they work, and explanations on why the systems were designed the way they are, their differences and their commonalities. The advantage of a book compared to a blog: You have more time and space to develop thoughts and explain.

Feedback and questions are always welcome! You can reach me at gsmumts (AT) gmx.de. Enjoy the book!

This blog entry is the fourth in a row about my thoughts on the current development of 4G wireless standards. You might want to take a look at the introduction before reading on. Previously, I’ve discussed why 4G networks are necessary and what to generally expect of 4G wireless networks. Three different standards are currently emerging and have already started to compete with each other for global dominance:

• WiMAX aka IEEE 802.16e
• UMTS Long Term Evolution (LTE)
• CDMA EVDO Rev. C (also dubbed DORC)

All of the contenders are still paper ware only and widespread adoption of 4G technologies is still several years away. So how can they already compete with each other? From my point of view there are three axis of competition today:

Time to Market

As all three types of networks have similar properties, time to market will be an essential component of the overall competitiveness of a standard.

• WiMAX is set to enter the market first as the air interface part of the standard, which is called IEEE 802.16e-2005, has already been approved by the members of the IEEE standards body back in February 2006. For those of you how like to read standards documents, you can find it here. Standards for the network infrastructure are specified by the WiMAX forum and you can download the latest drafts from this location. Here, work seems to be quite advanced but the standard has not been approved yet.

• The 3GPP has also started its activities around 4G and the UMTS Long Term Evolution (LTE) standardization is well on track. First fruits of their work can be downloaded from www.3gpp.org. The most interesting documents are 25.913 on requirements, the 25.912 feasibility study and 23.882, a report on different implementation options. To me, it looks like the work on the WiMAX standards is 12 to 24 months ahead of the LTE work.

• The work on CDMA EVDO Rev. C seems to be even further behind WiMAX which might be because the CDMA Development Group is still working on EVDO Rev. B, the multi carrier extension for current EVDO Rev. A networks.

User Base of 3G Predecessor Technology

Having a predecessor technology already in place is a great help in introducing a new technology especially if new devices are backwards compatible to existing networks. Here, LTE has a big advantage as the standard will most likely be defined in such a way. Thus, handsets and other mobile devices will not only work in LTE networks but also in 3G UMTS networks and most likely also in 2G GSM/GPRS/EDGE networks. This is especially important in the first few years of network deployments when coverage is still limited to big cities. EVDO Rev C. is likely to follow a similar path.

WiMAX on the other hand is not backwards compatible to any previous wireless network standard. Thus, it remains to be seen if devices will also include a 3G UMTS or EVDO chip. This is not only a question of technology but also a question of strategy. If a company with a previously installed 2G/3G network deploys WiMAX then they will surely be keen on offering such handsets. New alternative operators without an already existing network on the other hand might be reluctant to offer such handsets as they would have to partner with an already existing network operator. They might not have much of a choice though if they want to reach a wider target audience.

Migration Path

At some point current 2G and 3G network operators will migrate to a 4G network technology. As 4G network technology is based on IP only and includes no backwards compatibility for circuit switched services, current operators do not necessarily have to select the evolution path of the standard they are currently using.

For current UMTS network operators the most likely evolution path will be to LTE. Devices will most likely be backwards compatible to their existing 3G and 3.5G networks. Also, connectivity of the new LTE radio network to their existing core network infrastructure, billing systems and services will be seamless. Also, current 3.5G networks offer enough capacity for a number of years to come. Thus, UMTS operators are currently in no hurry with 4G technologies. Nevertheless, I think that WiMAX might have a chance with some operators trying a different game to see if they can gain a competitive advantage. In my opinion, the availability of dual mode handsets will be crucial for such a decision. In theory, UMTS operators might also choose EVDO Rev. C. I don’t think this is likely though due to the standard being nowhere on the horizon yet and the fact that the current EVDO market share is on the decline.

For EVDO operators the picture is a bit different. For them, EVDO Rev. C is still far out. Some of them especially in Taiwan and Australia have decided to make a radical move even sooner and are in the process of migrating from the current 3.5G EVDO networks to 3.5G UMTS/HSDPA. Recently, Sprint in the U.S. has made another early decision and announced that they have chosen WiMAX as their 4G technology instead of Rev. C and will start with the rollout of the network in 2007.

Summary

In the end I am quite convinced that at least two technologies will gain global traction. If WiMAX is one of them, and I am quite convinced that it will be, there will be even more competition in the wireless domain than today. The disadvantage of WiMAX of not having a network legacy could in the end be a major advantage. It will allow new companies to enter the market more easily and thus increase competition, network coverage, services and hopefully decrease prices.

It seems that creating podcasts has drawn me into its ban. After producing my first podcast back in July with Debi Jones on the US Wireless Carrier landscape, I’ve virtually ventured out to Spain this time and had a discussion with Rudy de Waele of m-trends.org. In the podcast we chat about his thoughts on the wireless operator landscape in Spain and how things are changing. I hope operators see it as constructive criticism.

Topics of the podcast:

• Wireless Internet prices in Spain and recent changes
• Usage scenarios
• On portal / off portal strategies
• Block mobile Internet access for your kids?
• Nokia’s new web browser in N-series phones
• Topics for the next Mobile Mondays in Barcelona

Podcast with Rudy de Waele.mp3 – 33 mins.

Another week another Carnival. This time, the carnival has stopped at MobileCrunch and Oliver has taken his time to come up with yet another extraordinary edtion. So for the best on wireless writing of the past week go, head over and enjoy!