Slashdot Mirror
Ultrawideband Signal Passes Data Through Walls
writertype writes "You may already be familiar with ultrawideband; UWB technology has been specifically talked about and designed to replace wired USB connections for over a year. Due to its high bandwidth, it's also been considered as an A/V cable replacement. The problem is that UWB radio performance degrades precipitously, effectively confining it to a single room. Until now, that is. Startup TZero says its UWB implementation provides high throughput through walls. Will this be an effective competitor to 802.11n?"
Um, no. 802.11n has significantly greater range (as a spec, at least). Plus, if this company is claiming to have developed it, I don't think they will just give it up for free. 802.11n is a public standard.
So, no. ;-)
Stiny! Get me a danish!
Not when UWB's output power is limited so that its range is only 30 feet.
Ultrawideband is being developed as a WPAN standard for IEEE 802.15.3a, which aims to provide a high (~20Mbps) alternative to Bluetooth. .15.3a is being called "WiMedia" and is intended for use in the Wireless USB (WUSB) standard. This is clearly the market this company is trying to address.
WPAN (Personal Area Networks), like Bluetooth or ZigBee, aim at a different market than WLAN (WiFi). For a WPAN, it may be advantageous to have a shorter range to reduce interference.
Extending the range to blur the line between WPAN and WLAN is an interesting business plan. There are numberous competing technolgies in the WPAN arena, and history tells that not all will survive. Time will tell if this one is viable.
One major issue with UWB is the antenna design. Its proving very hard to built antennas that have constant gain over the whole BW. As a result, the antenna essentially induces a transfer function on the transmitted (or recieved) signal. It could be possible to compensate using DSP in the Tx or Rx circuits, however the transfer function is different for differing RF environments. That is, move the metal legged table in your living room and the compensation algorithms are no longer valid. There are a few new antenna designs being proposed that focus on ensuring the s21 values are constant over the whole UWB spectrum, but its still early days with those.
The 'going through walls' part is a bit of a tempest in a teapot. That will come when the RF aspects of UWB are better designed.
I recently built a 400m (a quarter mile) link using 802.11a pointtopoint equipment (1W ERP, max legal power here).
It is line-of-sight w.r.t. buildings, but there was a group of trees inbetween. The signal had to pass trough maybe 20 meters of foilage.
The link barely worked. Sometimes 6 Mbps, sometimes 12 Mbps.
Relocating one of the endpoints so that those trees were out of the way (actual position lower than it was, now just skimming a building) improved the signal by about 20dB.
Result: 54Mbps link and power output decreased by 5-6dB (by TPC). Could probably gain another 6dB by having more clearance above the building.
I really did not expect this, comparing with results on 2.4 GHz.
You are right that allowed ERP on 2.4 is lower, but I think there would have been a big difference in path loss in this case.
It's a common myth that MIMO - sticking on multiple antennas - is for redundancy purposes.
If you actually crunch through the math, increasing the number of antennas basically increases the theoretical capacity of the wireless channel, meaning faster transmission speeds over the same distance/attenuation/power. So the extra antennas aren't in case one antenna fails, it's to increase transmission speeds.