Wireless communications is, by any measure, the fastest growing segment of the communications industry. As

such, it has captured the attention of the media and the imagination of the public. Cellular systems have experienced

exponential growth over the last decade and there are currently around two billion users worldwide. Indeed,

cellular phones have become a critical business tool and part of everyday life in most developed countries, and

are rapidly supplanting antiquated wireline systems in many developing countries. In addition, wireless local area

networks currently supplement or replace wired networks in many homes, businesses, and campuses. Many new

applications, including wireless sensor networks, automated highways and factories, smart homes and appliances,

and remote telemedicine, are emerging from research ideas to concrete systems.