802.15.4 and Zigbee
15/04/09 13:59 Filed in: wireless technology
I’ve been waiting to talk about ZigBee and its underlying PHY IEEE 802.15.4. Waiting until I felt more sure of the opinions I’ve given for some time, since the birth of the technology. More correctly, it is the cloning of the original HomeRF to suit industrial needs.
In my next blog, I’ll talk specifically about the technology as it applies to healthcare. My general concerns remain just that: general. 802.15.4 has the underlying Direct Sequence Spread Spectrum techniques of using its frequency bands as does WiFi (802.11 b/g). Although ZigBee/802.15.4 specify several frequency bands, the majority of the deployment to date is in the 2.4 GHz ISM band.
That means it is just begging for interference issues when it is in the same crowded space as, for example, a high density enterprise environment like a modern hospital.
The technology gets its power savings from being a very low duty cycle transmitter/receiver. Ideally, it spends most of its time in sleep modes that use little or no power. It gets its robustness not through coding or agility, but with brute-force retransmission. What this means is that in the presence of interference (like WiFi), the battery life is going to be poor to dismal.
I recall having this discussion at CES with a ZigBee company almost 5 years ago. It wasn’t until last year that I found out I was indeed correct and that there were non-standard implementations of a frequency agile version to resolve this issue. I’ve heard more recently that the standard group responsible is considering that as well, but for now any implementation that addresses the issue is non-standard.
In the January issue (OK, so I’m a little behind in my reading) of Product Design and Development magazine, there was an interesting article with a surprising interview contribution by a great guy at CSR, Rogin Heydon. Roibin’s contribution is definitely not what the author was originally looking for, I’d expect. See the article including Robin’s accurate comments; click here.
In my next blog, I’ll talk specifically about the technology as it applies to healthcare. My general concerns remain just that: general. 802.15.4 has the underlying Direct Sequence Spread Spectrum techniques of using its frequency bands as does WiFi (802.11 b/g). Although ZigBee/802.15.4 specify several frequency bands, the majority of the deployment to date is in the 2.4 GHz ISM band.
That means it is just begging for interference issues when it is in the same crowded space as, for example, a high density enterprise environment like a modern hospital.
The technology gets its power savings from being a very low duty cycle transmitter/receiver. Ideally, it spends most of its time in sleep modes that use little or no power. It gets its robustness not through coding or agility, but with brute-force retransmission. What this means is that in the presence of interference (like WiFi), the battery life is going to be poor to dismal.
I recall having this discussion at CES with a ZigBee company almost 5 years ago. It wasn’t until last year that I found out I was indeed correct and that there were non-standard implementations of a frequency agile version to resolve this issue. I’ve heard more recently that the standard group responsible is considering that as well, but for now any implementation that addresses the issue is non-standard.
In the January issue (OK, so I’m a little behind in my reading) of Product Design and Development magazine, there was an interesting article with a surprising interview contribution by a great guy at CSR, Rogin Heydon. Roibin’s contribution is definitely not what the author was originally looking for, I’d expect. See the article including Robin’s accurate comments; click here.