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.
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.