Frequency-Hopped Single-Sideband Modulation for Mobile Radio

Mobile radio telephone systems are required to operate in a hostile environment compared to radio systems using terrestrial and satellite links. The transmission channel is time varying in a manner dependent on the vehicle speed and location, distribution of buildings and terrain, siting of fixed antennas relative to the mobile, the effect of other mobiles, to mention but a few. Paramount of the design objectives is a high user density with good uninterrupted communication at a reasonable cost. To achieve these goals, a number of system concepts have been advocated,1,2 and a developmental system to provide Advanced Mobile Phone Service (AMPS) is currently being operated by Illinois Bell Telephone Company in the Chicago Area.3 Unlike conventional telephony where extra demand on communication capacity can be accommodated by additional links, the mobile 1389 radio spectrum is limited. To increase capacity, the area must be divided into cells and the RF band must be reused. Although mobiles in adjacent cells can be arranged not to interfere, co-channel interference caused by frequency reuse must be controlled in these systems. Thus, the mobile radio engineer increases capacity, not by using extra frequency assignments but by re-using the spectrum and taking care to reduce co-channel interference by adequate spacing between cells using the same frequencies. For urban mobile radio, the hexagonal cell structure giving complete coverage of an area has been extensively studied and is the one currently in vogue.