ies within non-adjacent cells was a creative innovation that added capacity to cellular networks. AT&T's Bell Laboratories (now part of Nokia) created this first generation of cellular service. At that time, Bell Labs was owned by AT&T, which in turn owned all of the local telephone companies in the United States. Bell Labs provided the research and development for all the AT&T-owned telephone companies at that time. See the section "The Breakup of AT&T" in Chapter The Division of Airwaves into Frequencies All wireless services operate over spectrum. Spectrum is divided into and allocated by frequencies. A frequency is the number of times per second that a radio wave completes a cycle. A cycle can be imagined as a letter S lying on its back, such that it appears similar to looking at a cross-section of an ocean swell. A cycle is complete when energy passes through an entire radio wave from the highest to the lowest portions of the wave. For a visual depiction of a complete wavelength cycle, see Figure 7-1. Frequency is measured in hertz, which refers to the number of complete cycles per second. Thus, for a frequency of 30 million hertz-or megahertz (MHz), as it is called-energy passes through 30 million resting S's in one second. Wavelengths www.TechnicalPDF.com Long wavelength, low frequency Short wavelength, Light www.TechnicalPDF.com nigh frequency Figure 7-1 A comparison of short, high-frequency wavelengths and long, low-frequency wavelengths. The Characteristics of Short and Long Wavelengths Spectrum is divided into frequency ranges from low ranges of frequencies of about 30MHz to 300MHz allocated to government agencies, local police, highway, and state police to high frequencies such as 24 to 50 gigahertz (GHz) for fixed, point-to-point wireless service and for 5G networks. Each range of frequencies is measured by the wavelength in the range. Wavelengths in low frequencies, such as AM radio at 100Khz, measure 9,000 feet (3,000 meters) long. Higher-frequency 10Ghz wavelengths measure 1.78 inches (3 centimete