DASH7 was recently the subject of an article in IEEE Spectrum entitled “DASH7 Networking Gains Momentum” … compares DASH7 to Zigbee. Readers of this blog know my views on the comparison, but two points were made by the author that I want to clarify:
1. The zigbee rep implies that zigbee might be better at penetrating a window “if the only way for a radio signal to pass into or out of a room is through a window, a shorter wavelength may, in fact, work better.” Zigbee developers deal with this every day since their technology perpetually frustrated with its inability to reliably penetrate walls, ceilings, and floors, thus this kind of argument is not surprising given the source. But the argument is sort of a red herring. DASH7 penetrates all of the above, including glass, reliably and with great range so the comment is pretty misleading. In an extremely niche case where the only exit out of a room were a 70cm window, the claim might be true, but only marginally so.
2. The comment in the article about an alleged difficulty designing antennas for DASH7 is, frankly, baffling. (ha!) There are plenty of 433 MHz and DASH7 antennas today that are super small and getting smaller. No idea where this came from — oh — wait a minute – scratch that.
Finally, the zigbee rep tries to argue that DASH7 is engaging in “market positioning”, which when I read it, it sounds like he’s saying we’re hyping the technology or making claims we can’t support. Neither is true – any good product manager “positions” his product vis-a-vis substitutes or competitors every day, DASH7 is no different. In our case, the strengths of DASH7 position starkly with those of zigbee and in many cases, it’s simple physics and nothing to do per se with DASH7. 433 Mhz is superior to 2.45 MHz for wireless sensor networking in nearly every case we’ve studied. Exceptions are a) high bandwidth video or audio file sharing or internet backhaul, or b) instances where mesh networking is truly an end user requirement, which in our experience rarely if ever occurs. Were it not for the signal propagation limitations of 2.45GHz, much of the “meshing” going on out there would not be necessary. More than one zigbee developer has said this to me. More support on us vs. them here.
I also know more than one zigbee developer understands this and is beginning the move from 2.45 GHz, where most zigbee implementations occur, to 900 MHz, but this just creates further interoperability problems, increases the cost of ownership to customers, and fundamentally doesn’t solve zigbee’s many challenges. 900 MHz also has global frequency allocation issues, unlike 433 MHz.
Perhaps the zigbee folks can respond below with their ripostes?
Just curious why you indicate 433 MHz is globally open frequency, when it appears to be allocated to the 70cm amateur radio band in the US?
As the designer that you mentioned that seems to be moving to 900 mhz, I think you might be misunderstanding something. Since I’m designing open source 802.15.4 software, I’m trying to support all the bands that 802.15.4 runs in. Hence, since 868/915 MHz is one of the bands specified for 802.15.4, then I’m starting to play with it.
In regards to 433 MHz, you often mention how much better it is in range, but I rarely hear you make the power argument. Since Dash7 at 433 runs roughly 10x slower than 802.15.4, then the amount of power consumed for transferring the same amount of data is roughly 10x as well due to the time that the transceiver needs to stay on. In wireless sensor networks, power is often more important than range, since we’re dealing with localized nodes that need to stay alive for long periods of time.
Chris,
First of all, thanks for commenting. Great to have the de-facto leader of the ZB movement weighing in.
The vast majority of the power consumed by a DASH7 (or ZigBee) device is devoted to waiting around (listening) and waiting for data to arrive, independent of the data rate for transmitting a message. So your argument really doesn’t stand up.
Separately, unless your sensor network is moving lots of video or audio around —- the exception in most cases we see — the idea that somehow a sensor network needs a big pipe for transmitting lots of data quickly is really “old school” thinking. DASH7 is ideal for sending sensor messages because the average message size is so small. No need for a firehose when a syringe will do just fine.
The fact is, DASH7 draws 10% of the power of ZigBee. You don’t need as many DASH7 nodes as ZigBee nodes in a given area given the range advantage, so total cost ownership is far lower both from the standpoint of a device investment but also from the maintenance costs of replacing or recharging batteries.
Gotta jump on a plane but can respond more later …
OK, I buy in to all the Dash 7 advantages. I’m a systems integrator and need to get data from 25 devices spread over a half a mile. Where are the Dash 7 products. I need gateway or bridges to connect these 25 devices to a master system for data collection. I want to replace Ethernet wiring with Dash 7 wireless. Whatproducts will let me do that?
Vito,
I would recommend the following DASH7 vendors that have been actively participating in the DASH7 Alliance test and certification process:
http://www.evigia.com
http://www.identecsolutions.com
http://www.savi.com
Each may have a slightly different prescription for your needs depending on the exact use case. More vendors are on the way or others reading this post may want to chime in …
Cheers,
Pat
Thanks for your quick response Pat. I had looked at these these manufacture’s sites already and took another look on your suggestion. Their products are all RFID related.
I’m looking for essentially an Ethernet replacement to wirelessly transmit and receive data from 25 remote devices to a master system. The distance is 2500 ft. Preferably the device would have an Ethernet or USB interface. If you or anyone knows of a manufacturer of such a device using DASH 7 technology, I would appreciate a response.
Vito,
What type of data? If video or other heavy streaming, then DASH7 may not be the best fit.
DASH7 is an active RFID standard, but increasingly we’re veering away from using the term “RFID” to represent the more dynamic characteristics of DASH7 — longer range, sensor net support, security, etc. So regardless of the term used, the equipment from the above vendors should suit your application fine provided the throughput requirement is not > 28kbps.
Hi Pat,
Thanks for your reply. We are gathering sensor data from strain gages. Not fast at all. 4 or 5 16-bit readings ever 30 minutes.
I still don’t see any thing that would work for me from these vendors. They seem to be RFID specific.