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Friday, February 12, 2010

Compare the Comparison

It is said that if you know your enemies and know yourself, you will not be imperiled in a hundred battles; if you do not know your enemies but do know yourself, you will win one and lose one; if you do not know your enemies nor yourself, you will be imperiled in every single battle.                      - Sun Tzu

Once upon a time, comparing to Zigbee was a must-to-do for any emerging technologies doing wireless sensor network. Z-Wave did that; ANT did that; WirelessHart did that; Dash7 has done that and is continue doing that. All have proved to be successful to some extent, Z-wave in home area network, ANT in sports and fitness, WirelessHart in industrial control, Dash7 is active RFID. Isn't comparison to competitor an effective marketing activity?

Zigbee is the first open standard of wireless sensor network, initially targeting to all the possible use cases people can ever imagine. But one thing can not fit all. Each late comer has one focus and one point strong. They beaten or try to beat Zigbee at that point cared by a particular market.

Now Bluetooth Low Energy is the latest jumping into the wireless sensor battle field. Whom does BTLE chosen to compare to?

The recent Bluetooth SIGnature magazine published a comparison table. Bluetooth Low energy choses to compare with Zigbee and ANT. But it is a very disappointing comparison.

Akiba from Freaklabs, a Zigbee lover, posted "Whew...haven't seen a trashy comparison like this in a while. They seemed to have omitted a few details like multi-hop capability, security comparison, and device profile availability, etc... Basically, as I usually say, each protocol has its strengths and weaknesses and is a good fit for some markets, and totally sucks for others. Zigbee, ANT, and BTLE are no different"

Obviously the following in the comparison table are not true,

1. Distance/Range:
Many factors determine the achievable range of a radio, the output power, the receiver sensitivity, the data rate etc. Using similar GFSK radio for BTLE and ANT, there is no way that one is significantly better than the other. If one is better, the difference should not be user noticeable.

BTW, there is also a hilarious mistake that it reads as BTLE and Zigbee are not good for communication within 10 meters.

2. Frequency hopping:
BTLE uses just one frequency for one connection event. It does hop to another frequency for the next connection event, which will happen when CRC error is detected. But this is the kind of frequency hopping in broad definition and will not provide the same benefit as the frequency hopping used in classic Bluetooth. 

ANT is able to do this kind of frequency hopping too. ANT calls it frequency agility. Apparently this frequency agility has not been widely implemented in ANT devices, but it has it.

Also unfair for Zigbee, though it does not use FHSS (Frequency Hopping Spread Spectrum), it uses DSSS (Direct Sequence Spread Spectrum). There is pros and cons in between DSSS and FHSS.

3. Connection to mobile phone / computer / watch:
Large installation base on mobile phone and PC is the biggest strength of Bluetooth, but it is Bluetooth classic not Bluetooth Low Energy. It will take years to Bluetooth 4.0 to prevail, though this step seems a natural evolution.

But isn't ANT strong in sports watch? How many ANT watches are in the market today branded Garmin, Suunto, Timex etc.

4. Network nodes
The number of nodes in one given network or the number of uniquely addressable nodes in total (the capacity of unique network address), which is the definition here? No matter which, there is no way for a technology to have unlimited network nodes. Such an insane statement just reminds me how Bluetooth low energy gave themselves a full mark score in Continua Health Alliance. You can not do this in a serious technical writing.

Enough is enough. A comparison need to show where you are really strong at and where others are really weak. I do not see that in this comparison from Bluetooth SIG.

Interestingly, doing a search of any other comparisons among the three technologies, I found one provided by ANT. However, it is a bit outdated and only compares to Bluetooth. But it says, "Current data on the not-yet-released Bluetooth Low Energy indicates that it will cost 25%-35% more per sensor node and consume a minimum of 25% more power for the same data transmitted." This ANT comparison makes more sense to me. I still have question markers. but much smaller. Apparently it claims ANT is better on current consumption, cost and networking capability.

By all means, Bluetooth SIG should have done a better comparison job than what is published. At least as I know, BTLE is better at security and privacy, which may not be important in sports applications, but is concerned in health and home related use cases.

My last word to BTLE in this post, do not repeat the mistakes made by Zigbee. If the SIG thinks Bluetooth low energy fits almost every use cases, as listed in the comparison table (Health and fitness monitoring, wrist devices/watches, proximity applications, remote control (e.g., home entertainment), mobile phones, industrial automation, gaming, PCs, automotive) and put efforts on every direction, it will go no where.


  1. Nice post! I would partially disagree on the Zigbee Lover comment, as I'm becoming more and more partial towards IPv6 over 802.15.4 (6LoWPAN). But I do write open source Zigbee software so I guess I need to at least love it a little.

  2. I agree - nice post! From the standpoint of DASH7, there's too much to unpack in the BTLE comparison in this comment box, but one common thread for nearly all the above technologies is the use of "meshing" as an inherently important feature. Our argument is that the need to mesh is intrinsically tied to the weaknesses of 2.45Ghz and other signal propagation issues inherent in these "session" oriented technologies. So here's a question, let's just pretend for a moment that BTLE, ANT, or Zigbee had better signal propagation/range (say, 1 kilometer, and LF-like propagation through concrete walls, etc., what would be an example of an application that inherently requires meshing?



  3. Hi Pat,

    To comment on mesh. I think the major benefit of mesh is to increase of network robustness. Normally mesh mandates message hopping, so increased range would a good side effect. But with that being said, today's widely used mesh tech can not justify the cost burden except for a few applications like industrial control, the market for WirelessHart and ISA100.11a. I have not seen any good and suitable for personal and home use.


  4. What are the industrial control applicastions where mesh is inherently necessary? I see a few very niche applications in military apps, but otherwise, the need for mesh is a myth that is holding back WSN adoption globally.

  5. Regarding your last paragraph, Bluetooth SIG is famous for its desire to go in all directions at once. You can count on them to at best make the mistakes made by Zigbee, and at worst to go far beyond.

  6. so will dash 7 replace zig-bee? Is it too early to tell and a risk to start development with? I comparing different home automation options and it appears to be too young? any comments?