I love ZigBee. I have written several long reports on it, covered numerous product announcements, gone to the conferences, and even played around with some of the many development kits. ZigBee is that short-range wireless technology based on the IEEE's 802.15.4 standard. It is being widely adopted for wireless mesh sensor networks and other short-range applications such as monitoring and control in home, building, and industrial environments.
With lots of vendors of ZigBee chips, modules, and kits, it is pretty easy to set up a system for whatever your needs may be. But you know what? As good as ZigBee is, it is overkill for many applications. Sometimes you just do not need all that complexity and overhead baggage that ZigBee carries to do its mesh thing. So while ZigBee is very capable and visible, you do have options. Here is a quick comparison to make you aware of some of the alternatives to help you select an optimum solution for your design problem.
Basis For Comparison
Let's use ZigBee as the basis for comparison here. Table 1 below sums up all the most critical ZigBee characteristics. The figures are typical and vary some with the specific vendor. These are the bottom line you need to define in a wireless link.
The main thing to note here is that there are really three versions of ZigBee. The most common and widely used is the version operating in the 2.4-GHz microwave band along with Wi-Fi, Bluetooth, and a few other services. It has the greatest data rate even though in most cases it is rarely used. The other versions operate in the UHF bands. The 868 MHz assignment and the low 20 kbits/s is required for Europe. The 915 MHz assignment is for the U.S. The 40 kbits/s rate is more than enough for most applications. The biggest advantage of the lower-frequency ZigBee versions is that typically they can cover a longer range.
Remember that ZigBee is more than just a wireless transceiver. The basic physical layer and media access control (MAC) layers are defined by the IEEE under the 802.15.4 standard. ZigBee adds the network, security, and application framework layers. Your application or one of ZigBee's application profiles lies on the top layer. So ZigBee is a full blown protocol with different profiles for a variety of applications supplied by the ZigBee Alliance. The ZigBee Alliance also provides testing and certification for ZigBee-enabled products to ensure full interoperability. That is a great benefit, but many applications just do not require it so simpler systems can be used.
Some of the bigger ZigBee chip suppliers are Atmel, Ember, Freescale Semiconductor, and Texas Instruments (Chipcon).
Some Interesting Short-Range Options
Table 2 sums up a few of the viable options to ZigBee especially if you are implementing simpler monitor and control projects and do not need a fancy protocol or mesh capability. These bear some explanation.
The WirelessUSB option is from Cypress Semiconductor. It is useful in point-to-point (P2P) and multipoint-to-point (M2P) applications. It was designed mainly for PC peripherals like the mouse and keyboard, but it is also good for games, toys, remote controls, and stuff like that. Its main advantage is that it acts as a human interface device (HID) so the wireless connectivity is completely transparent to the designer at the operating-system level. No special drivers are needed. Other potential applications are consumer electronics, home automation, automatic meter reading, personal health and entertainment systems, and wireless headsets.
The basic device described in Table 2 is the Wireless USB LS version, which has a limited range of about 10 meters. A longer-range version WirelessUSB LR boosts that to 50+ meters. A newer WirelessUSB LP version is a very low-power version with a 10-meter range but also runs at a higher data rate if you need it, 250 kbits/s with DSSS and up to 1 Mbit/s with GFSK. The neat thing about these devices is that they do provide a basic protocol so you do not have to invent one for your application. But it is pretty simple and flexible. The M2P capability lets you make a system that collects data from multiple sources. These single-chip devices come in a 48-pin QFN package and Cypress also sells some finished modules and a complete development kit.
One of the newer alternatives is Z-Wave from Zensys. This wireless system targets home automation specifically monitoring and control like turning lights off and on, dimming them or setting a thermostat. It is perhaps not as flexible as ZigBee but that makes it simpler and lower in cost for home automation.
The Z-Wave chips operate in the high UHF bands giving them good range. The data rate is limited to 9.6 kbits/s but that is usually more than enough in home automation. The chips have an on-board 8051 controller and some flash memory. They also run DES and 3DES encryption if you need that kind of security. Z-Wave has good momentum in their niche and they have the funding of Intel and Cisco behind them. The Z-Wave Alliance provides the backing of over 125 members.
Finally in Table 2 I listed the basic generic characteristics of a simple ISM (industrial scientific medical) band transceiver. The specs you see here I took from a recent Analog Devices brochure on wireless devices. However, several other manufacturers make these great low-cost devices. Micrel and Maxim come to mind. In the U.S., these devices come under the regulations of Part 15 of the CFR Part 47. The most commonly used frequencies are 315, 492, and 915 MHz.
These devices use mostly simple ASK/OOK for low speed (
Yes, I probably missed an option here. Some of you are probably saying, where is Bluetooth? Bluetooth is a great wireless system and in fact it has the greatest volume of any wireless technology including Wi-Fi. Some of you will also object to my leaving out Wi-Fi. But these technologies are not targeted to generic wireless applications where monitoring and control is the main goal. Both are pretty much overkill for these simpler applications. Yes, you could say that they are options but they come with a higher cost and overhead of complexity. If you just need short-range and cheap, stick with the ones I described here.
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