Radio communications receivers commonly receive and decode messages which contain information. A part of this information may be an identity for the intended recipient or recipients of a given call. A radio, upon decoding valid identity information, will receive a call. For example a radio may unsquelch its receiver and pass audio signals to a loudspeaker upon receipt of a valid identity. Conversely, radios commonly transmit a message having identity information so that other radios intended to receive a given call can receive and decode the transmitted identity information.
Modern radios transmit and receive messages in the form of digital data. Such dale is modulated onto a radio frequency carrier which is used to accomplish radio communications. A portion of any given message may he the aforementioned identity information. This information is commonly called an ID code. A transmit ID code is transmitted by the transmitting radio, which is received as a receive ID code by the receiving radio. A single given radio may or may not use different transmit ID codes and received ID codes, depending on what other radios the given radio is attempting communications with.
A radio that is capable of both transmitting and receiving is known as a two-way radio. Such radios may operate in the simplex, half-duplex, and full-duplex modes of operation. These modes of operation are well known in the art. A simplex radio transmits and receives on one frequency during a call and is not capable of simultaneously transmitting and receiving. Rather, transmissions and receptions must be multiplexed in time in order to have a conversation.
A half-duplex radio is capable of transmitting and receiving on a pair of two different frequencies, and, like a simplex radio is not capable of simultaneously transmitting and receiving. A full-duplex radio operates on a pair of two different frequencies and is capable of simultaneously transmitting and receiving.
Both half-duplex and full-duplex radios are capable of operating through a radio repeater. A repeater is a radio transmitter and receiver pair which receive signals from radios and retransmit them to other radios. Radio repeaters, or repeaters, typically include a control unit for controlling their operation. One benefit of a repeater is that it can be located at a high elevation and operated at high power. This serves to extend the radio coverage range to a greater geographic area than would be available if two radios were to communicate directly with each other. For example, radios are typically deployed in the form of mobile radios for use in motor vehicles and the like or in the form of hand-held portable radios. In either case, size, power and elevation limitations would prevent these radios from communicating over long ranges or large geographic areas.
Often times, repeaters are shared between a large number of radio users. Many times, radios users are grouped together so that users with common communications needs can effectively communicate with each other. In some situations two radios are grouped together to provide for one to one communications. Alternatively, several radios may be grouped together. In situations where several radios are grouped together, a single radio will transmit messages to the remainder of the group. These radio groupings are called radio fleets. The one to one calls are called private calls and the one to many calls are called dispatch calls. A single radio may be a member of more than one group. For example, a single radio user may desire to have private calls in some instances and dispatch calls in other instances. Furthermore, any given radio may be a member of several private groups and/or dispatch groups. Another application of radios and repeaters is to interconnect a repeater to the Public Switched Telephone Network, (PSTN). With an interconnected repeater, a radio may communicate with the repeater via radio signals and further communicate with a telephone user via wires in the PSTN. Radios operating in the interconnected environment can place call into the PSTN or receive calls that originate in the PSTN. These calls are commonly known as interconnect calls.
In radio environments where there are a very large number of individual radio users, a single repeater may not be sufficient to provide an adequate degree of service. The Federal Communications Commission rules allow for the trunking of two or more repeaters together to form a trunked groups of repeaters, also called a repeater system. These repeater systems employ a trunking signaling protocol which allow the management of individual repeaters in real time. This trunking information is often times a part of the radio messages transmitted between radios and repeaters.
Transmit ID codes and receive ID codes are used to identify the transmitting and receiving radios in the various groupings as described above. Transmit and receive ID codes are usually transmitted as binary numbers and they are sometimes represented as base ten numbers. System operators who program ID codes, sell radios, and service radios become technically experienced with ID code usage and their limitations. However, to end users of radios, these ID codes can be confusing and difficult to work with. Yet it is still important for the end user to identify which dispatch fleet or private group the end user is calling or is to be called. Radios usually have a selection means, such as a push button or rotary knob for selecting a communications group which is specified by a group ID code. An association is often made between group ID codes and transmit ID codes and receive ID codes so that end users can simply select a familiar, simple group ID code which is ultimately linked to the appropriate transmit ID and receive ID needed to accomplish the desired communications.
In one example, a simple system has been devised that links group ID codes one through ten to pairs of a transmit ID's and a receive ID's. The radio user simply remembers, for example, that group 1 places a certain private call, group 2 places a telephone interconnect call, group 3 places a dispatch call, and etc. While receiving calls, the users radio may be enabled to scan all of the aforementioned receive ID's so that receipt of any one of them in a data message will cause the call to be received. When a call is received, the radio may display the familiar group ID code so that the radio user can identify the calling group. 0f course, other transmit ID codes and receive ID codes could be used, such as alpha-numeric characters, for example, that identify radio groups with words, numbers or mnemonics.
In partial summary, group ID codes are used to specify and identify specific transmit ID's and receive ID's for the purpose of controlling what group or fleet is being communicated with.
A described earlier, repeaters offer radio coverage over a larger geographic area than is possible with direct radio to radio communications. However, this does not mean that the coverage area is without limits. For various reasons that are well know in the art, repeaters also have finite coverage area. To offer even larger coverage area, operators of radio repeater systems may operate two or more repeater systems and offer service to individual radios on more that one repeater system.
Multiple repeater systems are often located in separate geographic areas. As a user of a radio moves from area to area, it is necessary to select the repeater system on which to initiate calls. Conversely, the radio must be tuned to a frequency of one of the repeaters in the local system in order to receive a call. Radios have been devised with a system scan feature which causes the radio to scan several frequencies of repeaters that are located in different repeater systems. While monitoring any particular repeater frequency, the radio also scans for particular receive ID codes which would indicate that a desired call is to be received.
In a similar fashion to the identification of particular transmit and receive ID codes with a group ID code, repeater systems are identified with a simple system ID code. For example, system ID codes may be numbered from one through ten to identify up to ten separate repeater systems, each of which may have one or more repeaters. Again, the radio user simply need remember, for example, that system 1 is used downtown, system 2 is used north of town, system 3 east of town, and etc.
It is now understood that a user of a radio selects a system to identify the repeater system, or geographic area, to communicate in, and a group to identify with whom the communications is to be had. Likewise when a call is received, a radio may display the system and group numbers which will identify the repeater system being used and which particular radio or group of radios is calling.
Modern radios have controllers which allow them to function with very little user intervention. Calls can be received automatically and the response to a call usually only requires the press of a single button. Such an automated system functions well if the radio user is present at the radio to communicate in a conversation. However, often times, the radio user is away from the radio while a call is received. Even while the user is away from the radio, the radio will scan systems and groups, received and decode data messages into ID codes, unsquelch the receiver, receive the call, and etc. However, all this information is meaningless if the users does not listen to, interpret, and/or respond to it. Upon the user's return to the radio, the user is unaware of the missed call, and therefore, communications is not completed. Since the main benefit of two-way radios is to improve the accessibility to communications for the end user, and since a missed called reduces the desired accessibility, clearly there is a need to provide a greater amount of call history detail to users of two-way radios, thus improving the accessibility to communications for the end user.