FireWire Goes Wireless

[Gregg Lengling]

You may have seen news last week of WiMedia's endorsement of the Multi-band OFDM Alliance (MBOA) UWB PHY and MAC technical specifications, paving the way for wireless USB, wireless 1394 ("FireWire") and IP. Also last week, the 1394 Trade Association approved a protocol adaptation layer (PAL) for running IEEE 1394 (FireWire) over IEEE 802.15.3a UWB links. The IEEE 802.15.3a process has been stormy, with competing proposals based on OFDM from MBOA and proposals from Motorola and others based on impulse UWB. The WiMedia endorsement gives the OFDM UWB a boost and it appears to be the closest to being implemented. The 1394 PAL will work with either system.


The impact of this technology is clear -- video and files can be transferred without wires from camcorders to computer editors, TVs or other devices equipped with wireless FireWire (another oxymoron to join the ranks of "wireless cable"). However, don't expect this technology to deliver full data rate FireWire connectivity at any significant distance. The best document I could find describing the MBOA system was an IEEE submission Multi-band OFDM Physical Layer Proposal Update. The Multi-band OFDM System Parameters in this document specify a multipath tolerance of 60.6 nanoseconds at all data rates and information data rates up to 200 Mbps (mandatory) and 480 Mbps (optional). All of these information data rates use the same channel bit rate of 640 Mbps with 100 tone OFDM/QPSK modulation. The only difference is the forward error correction coding rate and the spreading rate. The link budget in the proposal uses distances of 10 meters for 110 Mbps, 4 meters for 200 Mbps and only 2 meters for 480 Mbps. Note that these data rates are bits per second, not bytes per second, so the range for a standard DV camcorder data rate would be around 3 meters using the optional 320 Mbps information data rate.


According to the Proposal Update, the FCC is still working to resolve this interpretation of its rules to determine if this system complies with Part 15 rules.


Note that Ultra-wideband, or UWB, does, as its name implies, use a large chunk of spectrum. FCC UWB rules require a minimum 500 MHz bandwidth! For more information on this interesting technology, refer to the Multi-band OFDM Alliance web site and the IEEE 802.15 WPAN High Rate Alternative PHY Task Group 3a. For many more links with information on both the technology and the competing UWB standards, do a Google search on "IEEE 802.15.3a".
Doug Lung's RF Report