As Meg takes the turn to her street in her SUV, she pushes the button on her garage door opener and her garage door opens, the main hallway light comes on, the central alternating current (AC) kicks in to her desired level, the plasma TV comes on to her favorite channel and her automatic blinds come down to provide comfortable viewing. This may sound far fetched, but with today's wireless technologies this scenario is easily within the realm of possibility.

Wireless is a broad technology encompassing everything from extremely low-power, low-cost radio frequency identification (RFID) tags to wireless metropolitan area networks using WiMax and ultra-wideband (UWB) as illustrated in Figure 1. This article will focus on the integration of Bluetooth, wirelessUSB and Zigbee radios into eight-bit microcontrollers and mixed-signal arrays to create low-power, low-cost single-chip wireless solutions that enable interdevice communication without the need for cables.

While 802.11 has made its mark in wireless local area networking, the next revolution is occurring in the areas of wire replacement and sensor networks. Wire replacement covers short-range wireless applications such as keyboard, mouse, presenter tools, in-home light management systems, simple sensor networks, garage door openers, car key fobs, and personal computer (PC) headsets. The heart of these systems consists of a wireless radio (usually Bluetooth or wirelessUSB) and a microcontroller (usually eight bit) along with various external components on the board.

Sensor networks are becoming popular with the recent creation of Zigbee, which has been designed as a standardized solution for sensor and control networks. Zigbee has been optimized for mesh and cluster-tree networks that allow peer-to-peer communication. Most Zigbee devices are extremely power sensitive (thermostats, security sensors, etc.) with target battery life being measured in years. The focus of Bluetooth is ad-hoc interoperability between cell phones, headsets and personal digital assistants (PDAs). Bluetooth is also used as a cable replacement solution for wireless computer peripherals. Most PDAs and high-end cell phones today contain an integrated Bluetooth solution. WirelessUSB is built upon the premise that a complex networking protocol is not required for simple point-to-point applications like PC mice, keyboards, and basic sensor networks.

Bluetooth, wirelessUSB, and Zigbee all operate in the 2.4 GHz industrial scientific and medical (ISM) band. (Zigbee can also operate in the 900 MHz band.) There are several benefits to the 2.4 GHz ISM band compared to other license-free bands:

1. 2.4 GHz is an ISM band and is available worldwide; many other license-free bands are not consistent worldwide. While the end consumer may not care, it is a big advantage to consolidate supply chain logistics for manufacturers.

2. High bandwidth — 27 MHz systems suffer from bandwidth limitation and co-location issues. 2.4 GHz has several channels and combined with intelligent coding schemes can offer virtually unlimited co-location properties.

3. Spread spectrum — Devices using the 2.4 GHz band have to use a spread spectrum technique, either frequency-hopping spread spectrum (FHSS) similar to Bluetooth or direct-sequence spread spectrum (DSSS) similar to Wi-Fi, to enable high interference immunity and rejection. This results in highly robust solutions.

4. Low cost — With the mass adoption and ability of semiconductors to move down the technology curve, we are almost reaching a point where the cost delta between a 27 MHz system and 2.4 GHz system is negligible and the benefits far outweigh the slightly higher cost for designers and marketing groups.

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