A description of the Bell system HCMTS cell-site radio and control hardware

Final planning and development is underway for a High Capacity Mobile Telecommunications System (HCMTS), a nationwide, compatible, cellular system that will permit a dramatic increase in the quantity of available mobile telephone service in the United States. In this cellular system the total coverage area is divided into a grid of small hexagonal cells. The radius of each cell is planned to be eight miles for startup systems, but might eventually shrink to one mile (by cell splitting) as traffic density increases. Mobiles located within the cells are serviced by low-power 850 MHz FM transceivers contained within cell-sites which are situated at alternate corners of each hexagonal cell. Two types of antennas may be used at a cell site. A startup system would employ omnidirectional antennas, since for this case traffic density is low and it is important to minimize first cost. Mature, high density systems, would employ three sets of directional antennas at alternate corners of each cell site, arranged such that the 120deg; beam from each antenna set would illuminate the interior of the corresponding cell. All cell sites are interfaced with one central control and switching center, the Mobile Telephone Switching Office (MTSO), by means of four-wire voice and data trunks. A call from the DDD telephone network is first routed to the MTSO, then over a voice trunk to the cell site which is to serve the mobile, and finally over an available radio channel to the called mobile. At call setup the mobile is located by measuring its received signal strength and range. During the call the mobile may be relocated several times a minute. If the mobile enters a new cell it is "handed-off" to a new cell site and radio channel by digital commands from the MTSO.