Telecommunications – Transmitter and receiver at separate stations – Plural transmitters or receivers
Reexamination Certificate
1998-04-10
2002-04-16
Trost, William (Department: 2683)
Telecommunications
Transmitter and receiver at separate stations
Plural transmitters or receivers
C455S426100, C455S524000
Reexamination Certificate
active
06374115
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to trunked radio communications systems, and in particular to a method and apparatus for trunked radio repeater communications with new and existing protocols.
BACKGROUND OF THE INVENTION
Mobile radio communication systems provide for two way radio communications between a central control station and a fleet of cars, trucks, or other vehicles. Typical users of mobile radio communication systems include, for example, police departments, fire departments, taxi services, and delivery services. Present mobile radio communication systems can be configured to provide for radio communications between the control station and all vehicles in a fleet, between the control station and selected vehicles in the fleet, or between different individual vehicles or groups of vehicles within a fleet.
Conventional mobile radio communication systems are typically organized with a number of vehicles and a control station assigned to a single common channel for a given coverage zone. A user assigned to the common channel must wait until no one else is transmitting on that channel before sending a message, because only one transmission at a time can be processed by a single channel. Even when a transmission is addressed to only one user in a conventional system (and therefore not heard by other users), the other users in the system must wait until that transmission is completed before they can use the system to communicate.
Mobile radio communication systems using transmission trunking are an improvement over conventional mobile radio communication systems in that trunked systems enable two or more users to communicate on the system at the same time. For instance, the dispatch console in a transmission trunked communication system can be communicating with one of the vehicles in the fleet; while, at the same time, two other vehicles in the fleet can be using the same trunked system to communicate with each other. Transmission trunked communication systems group a number of channels for the same coverage zone together into a single audio communication system, with each channel accessible to each user in the system. Because each user will only need to communicate over the trunked system part of the time, and because it is unlikely that all users will need to communicate at precisely the same time, the number of channels assigned to a trunked system group can always be less than the number of users allocated to that trunked system group.
The United States Federal Communications Commission (FCC) has assigned 600 channels in the 800 MHZ band for trunked land mobile use. Each channel is comprised of a pair of assigned frequencies, a mobile transmit frequency and a repeater transmit frequencies. Mobile transmit frequencies are 806-821 MHZ, with the repeater transmit frequencies exactly 45 MHZ above the corresponding mobile transmit frequency, or 851-866 MHZ. Channel spacing is 25 KHz, with the maximum allowed deviation between channels being ±5 KHz. In September 1987, the FCC also allocated 399 channels in the 900 MHZ band for trunked land mobile use. Mobile transmit frequencies are 896-901 MHZ, with the repeater transmit frequencies exactly 39 MHZ above the corresponding mobile transmit frequency, or 935-940 MHZ. Channel spacing is 12.5 KHz, with the maximum allowed deviation between channels being ±2.5 KHz.
In transmission trunked communication systems, a signaling protocol is used to send and receive control signals among users on each channel in the trunked system and a switching protocol is used to establish which channels those users will be communicating over. The preferred conventional transmission trunked communication system uses a signaling protocol that transmits the control signals in the subaudio band simultaneously with the transmission of voice or data information signals. Signaling protocols that can communicate control signals within the constraints of the subaudio band are preferred, because use of the subaudio band precludes the need for using a dedicated channel for transmitting the control signals (thereby reducing the number of available channels in the trunked system for voice and data communications). A switching protocol is used by the trunked system to automatically find and engage an open channel when a user initiates a transmission. To maximize the trunking capabilities of such a system, the switching protocol must efficiently allocate channels in the trunked system and avoid channels that are already in use at the time the transmission is initiated. For further explanation of the preferred conventional transmission trunked communication systems, reference is made to the description of the operation of the ClearChannel LTR® system contained in the manual entitled “E. F. Johnson ClearChannel LTR Application Note”, Part No. 009-0001-020 (Rev. 5, October 1988), available from E. F. Johnson Company, Waseca, Minn., which is fully incorporated by reference herein.
A substantial amount of LTR-compatible equipment is currently in use, however, the LTR system does not provide modern network-based communication functionality. For example, the LTR protocol is limited and does not support new and special functions for network-based communications. Furthermore, the LTR protocol does not support advanced channel selection functions.
Another drawback of the LTR system is that LTR communications are conducted on a predetermined set of fixed transmission frequencies. Therefore, the number of communication channels available at any given time in an LTR system are fixed. Additionally, the receive and transmit channels in an LTR system are always at a predetermined offset frequency. Therefore, the LTR protocol does not provide flexible use of communications bandwidth.
Yet another drawback of the LTR system is that it was designed to accommodate a limited number of subscribers and a predetermined number of commands. Modem communication networks provide a number of new features which cannot be exercised using mature communication protocols, such as LTR.
New transmission trunked communications systems have been proposed which incorporate advances in network communications. For example, the E. F. Johnson MULTINET(tm) system, part of which is described in U.S. Pat. No. 5,159,701 to Barnes, et al., provides for, among other things, distributively interconnecting a plurality of land mobile trunked transmission communication systems into a wide area network. However, this system is not compatible with traditional LTR systems.
There is a need in the art for a trunked radio repeater communication system which provides sophisticated network-based communications. This system should provide flexibility to channel assignments for both reception and transmission frequencies. The system should also provide for a large number of subscribers. Also, the system should support a variety of new commands and features. Finally, the system should support and allow for LTR communications such that existing LTR subscribers can communicate in the system with minimal interference issues.
SUMMARY OF THE INVENTION
The present invention satisfies the aforementioned and other needs by providing a trunked radio communication repeater system including a protocol for communications by a large number of users. In one embodiment, the protocol includes a plurality of word formats for communications between one or more repeaters and the or more subscribers, each word format including a synchronization code for receiver synchronization, a type code indicating a first word format and a second word format and compatible with protocols using an area code to identify subscribership to a particular repeater site, and a checksum code to error check communicated words; where the first word format further includes a channel in use code to identify a channel in use, a home code identifying a home channel, a group code providing a code for one or more groups of subscribers, and a free code identifying a free channel; and wherein the second word format further includes fun
Barnes Keith W.
Grindahl Mervin L.
Smith Rory A.
Perez-Gutierrez Rafael
Schwegman Lundberg Woessner & Kluth P.A.
Transcrypt International/E.F. Johnson
Trost William
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