Spectrum consideration for wireless communications in the twenty first century

It is expected that wireless users will exceed one billion by the, year 2010. Besides voice, a new range of services such as multimedia, high-speed-data, etc. are being offered for delivery over wireless networks. Mobility will be seamless, realizing the concept of persons´ being in contact anywhere, at anytime. There are some fundamental aspects such as limited spectrum, propagation effects, and unknown and time varying access will result in a profound impact on the choice of technologies to provide future mobile communications. So that the challenges to the technologies imposed by the radio spectrum limitations, radio channel propagation induced distortions, are seriously concerned by manufactures, operators, and regulators. The International Telecommunications Union (ITU) is engaged in development of global standards for wireless communications, and is referred to as International Mobile Telecommunications 2000 (IMT-2000). Wireless ATM (WATM) is expected to provide significantly high bit-rate services to meet the demand for handing multimedia information, such as high definition still pictures, moving pictures, and large files. In addition, WATM is required to provide a variety of services like CBR, VER, ABR, and UBR, and flexible connection, including symmetric/asymmetric bandwidth to support multimedia services. This article gives an overview of the frequency considerations of IMT-2000. It is very important in order to effectively use the limited spectrum resource and in selecting suitable third generation wireless technologies