Junhui Zhao and Xuexue Zhang
Over the last decade, wireless communications has expanded significantly, with an annual increase of cellular subscribers averaging about 40% worldwide. Currently, it is estimated that there are between 36 and 46 million cellular users in the United States alone, representing over 20% of the U.S. population. In the next few years, it is expected that a total of about 200 million wireless telephones will be in use worldwide, and that in the next 10 years, the demand for mobility will make wireless technology the main source for voice communication, with a total market penetration of 50%–60% .
Meanwhile, depending on wireless positioning, ...