Piscataway, N.J. – The Institute of Electrical and Electronics Engineers (IEEE) adopted a dual-use standard positioned both as a high-speed Bluetooth competitor and as a more efficient, more reliable alternative to WiFi for distributing standard-definition (SD) and high-definition (HD) digital video.
The new 2.4GHz standard, dubbed 802.15.3, is designed to coexist with 2.4GHz WiFi and Bluetooth devices, so the standard’s authors expect networked homes to use WiFi for data networking and 802.15.3 for a separate AV network.
The standard features a top raw data rate of 55Mbps at 50 meters (165 feet) but offers 22Mbps speed at 100 meters (330 feet). It automatically changes channels if a channel is already in use by another wireless device. All told, it links up to 245 wireless consumer devices in a home.
By the end of 2004, adapters could be available to convert USB2 and 1394 connections into wireless 802.15.3 connections, said Robert Heile, chairman of the IEEE’s 802.15 working group.
Like Bluetooth, the standard is ‘battery-friendly,’ so it can be built into PDAs and other portable devices, Heile said. Unlike Bluetooth with its 1Mbps data rate, the new standard will support quick transfers of large files, including multimedia files, and be able to replace wired 1394 connections on digital camcorders. To extend battery life, the standard’s power output steps down from a maximum 125mW at 100 meters as devices get closer.
As a WiFi alternative, the new standard’s bandwidth efficiency and inherent quality of service (QoS) solution makes it possible to simultaneously stream seven broadcast-definition digital programs at 6Mbps each, Heile said. Alternately, the standard supports two simultaneous 19.2Mbps high-definition video streams or one HD stream combined with multiple video and uncompressed-audio streams, he said.
Heile admitted the standard’s data rate is comparable to that of 54Mbps WiFi products (based either on the 2.4GHz 802.11g standard or the 5GHz 802.11a standard). However, he called the new standard ‘very efficient,’ allowing for net throughput exceeding 45 Mbps. The two WiFi standard’s throughput drops to 29Mbps because of ‘ethernet overhead,’ he said.
On top of that, the effective throughput of 802.11 networks drops further in homes equipped with an 802.11-family access point, often built into a broadband Internet gateway, Heile explained. In those homes, all 802.11 devices usually communicate indirectly through the access point, effectively turning one stream into two and doubling the amount of bandwidth needed to deliver the stream. This type of ‘star configuration, like the Ethernet’s, is designed for ‘collision avoidance,’ he explained.
Although ‘techno-geeks’ can ‘force-reconfigure’ 802.11 devices to do peer-to-peer streaming, the task is complicated, ‘and you lose the collision-avoidance mechanisms,’ he said.
QoS advantages are, besides its bandwidth advantage over WiFi, the new standard features ‘inherent quality of service,’ making it suitable for video streaming, he said. Advocates of the 802.11 family ‘have been trying for three years to deliver QoS for video, but the video still suffers,’ he contended.
The 802.15.3 standard uses Time Division Multiple Access (TDMA) technology to dedicate time slots for a specific audio or video stream between two devices. If someone tries to add an AV stream while the network is at capacity, the user will get a ‘busy signal’ to prevent degradation of the existing AV streams, Heile said.
Although the IEEE has, after three years of deliberations, finally put to ballot a QoS enhancement for the 802.11 family, the enhancement only prioritizes AV streams over data streams, Heile said. As a result, users who initiate data streams on a loaded network won’t cause an existing video stream to drop out, but the video quality will degrade.
The 802.11 enhancement simply promises ‘a best effort,’ Heile said. The 802.15.3 standard, on the other hand, ‘guarantees quality of service always.’