In recent years, wireless communication systems have emerged as an important alternative to wireline communications in the United States. These systems offer users the convenience of mobility and personal services, as well as significant cost savings over traditional wireline systems in the installation and relocation of telecommunications equipment. The use of wireless systems is also proliferating in remote areas of the world due to the ease of installation of such systems as compared to wired communications.
One type of wireless communications system, cellular telephone systems, uses radio communications between a plurality of subscriber units with in the wireless system and between subscriber units and the Public Switched Telephone Network ("PSTN") for calls to or from outside the wireless system.
In cellular systems, as illustrated in FIG. 1, a geographical area is divided into cells covered by the radio system at the base station. The cells are connected via a respective base station (B1-B7) to a Mobile Services Switching Center ("MSC"). The MSC, in turn, is connected to the PSTN. The telephone users (mobile units) communicate with the MSC through the base stations. The MSC switches calls between wireline and mobile subscribers, controls signaling to the mobile stations, compiles billing statistics, and controls the overall operation of the system.
Cellular systems overcome many of the problems associated with traditional wireline communications. These systems, however, still require the installation of expensive infrastructure equipment (i.e., base stations B1-B7, and MSC's) to provide system functionality and the necessary switching capabilities.
Other wireless communications systems overcome the need for expensive infrastructure equipment by using point-to-point radio communications. However, these systems do not provide the extensive switching capabilities provided in cellular and PCS systems. For example, multiple-user radio transceiver communication systems exist in which squelching circuits are used to limit communications between selected radio transceivers within a group of transceivers. In one such system described in U.S. Pat. No. 4,646,358, a first transceiver sends an origination address and a destination address. The transceivers within the broadcast area receive these addresses. When the received destination address corresponds to the address of the second transceiver, the second transceiver turns off its squelch circuit in order to receive the communications from the first transceiver. Any transceiver that receives the radio broadcast and does not have a corresponding destination address leaves its squelch circuit on so that the received signal cannot be heard by the user.
The second transceiver then communicates with the first transceiver by sending its address and the origination address of the first transceiver with a broadcast communication. When the first transceiver receives the broadcast communication with its address, the first transceiver turns off its squelching circuit in order to receive the communications. Thus, two transceivers may establish communications in a broadcast radio communications system. In operation, the system requires that all signaling between transceivers include both the address code of the originating station and the address code of the destination station. However, this system suffers from several disadvantages. For example, because origination and destination addresses must be sent with all communications, the likelihood of coding and transmission errors increases. Therefore, if an origination address is incorrectly received, stored, or retransmitted, the intended transceiver may not receive the communication.
In another system using squelching circuits, as described in U.S. Pat. No. 5,058,205, the origination transceiver only transmits the address with the initial message transmission. Once communication is established between two transceivers, a responding transceiver does not send its own address nor does the originating transceiver send its own address again during two-way communications between the two transceivers. Instead, the only address information required to be sent between the transceivers is the destination address of the communications.
These point-to-point radio communication systems, however, do not provide the capabilities associated with traditional wireless systems. In particular, these systems do not permit these transceivers to send and receive calls via the PSTN, maintain billing information, or provide switching capabilities associated with cellular telephone systems.
Thus, a need has arisen for an improved wireless communication system that eliminates the problems of existing systems, while maintaining the convenience of mobility and personal services provided by traditional wireless systems.