1. Technical Field
This invention relates to cordless telephones and, more particularly, to a cordless telephone having a plurality of portable units arranged for communicating with a base unit in a frequency hopping system.
2. Description of the Prior Art
Recent rulings promulgated by the FCC in the utilization of spread spectrum systems, including a frequency hopping system, now allow suppliers to produce improved cordless telephones which provide users much greater freedom and mobility than is available with conventional cordless telephones. Frequency hopping systems spread their energy by changing, or hopping the center frequency of the transmission many times a second in accordance with a pseudo-randomly generated list of communication channels. The result is a significantly higher signal to noise ratio than may be achieved by conventional techniques such as amplitude modulation that uses no bandwidth spreading.
These improved cordless telephones provide security naturally from an eavesdropper listening in on a conversation simply because of the spread spectrum/frequency hopping transmission technique employed by these telephones. Examples of such improved cordless telephones are described in U.S. Pat. No. 5,323,447 which issued to M. E. Gillis et al. on Jun. 21, 1994 and U.S. Pat. No. 5,353,341 which issued to M. E. Gillis et al. on Oct. 4, 1994. Although these improved cordless telephones give users much more freedom and mobility than conventional cordless telephones, they do not readily permit communications between multiple portable units and a single base unit and also between multiple portable units. As a result, each of multiple cordless telephone portable units are unable to share a common telephone line without having a respectively associated base unit.