| Apparatus and method for monitoring a trunked radio communications system -> Monitor Keywords |
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Apparatus and method for monitoring a trunked radio communications systemRelated Patent Categories: Telecommunications, Transmitter And Receiver At Separate Stations, Having Measuring, Testing, Or Monitoring Of System Or PartApparatus and method for monitoring a trunked radio communications system description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070149130, Apparatus and method for monitoring a trunked radio communications system. Brief Patent Description - Full Patent Description - Patent Application Claims
BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The invention relates generally to the field of radio systems, and more specifically to methods and apparatus for monitoring trunked radio communications, decoding the digital data from trunked radio control channels, and to methods and apparatus for determining the type of trunked radio system by observing the characteristics of the digital data transmitted on a control channel. [0003] 2. Description of the Related Art [0004] Modernly, the two types of mobile radio communication systems. The first is a conventional radio communication system. Here, mobile radio units are assigned a single radio frequency channel. All subscribers to the system share the same channel, and cooperate by monitoring the channel for activity. Most conventional radio communication systems work well when there is a small number of subscribers and the usage patterns for all the subscribers is similar. [0005] To overcome the limitations of the conventional radio communications system, an implementation of a trunked communications system is employed. In the trunked communication system, a central controller allocates a number of channels among many subscribers. Generally, the subscribers are organized into fleets, sub-fleets or groups, and individuals. Accordingly, each subscriber has a fleet, group, and an individual identification code. A mobile radio initiates communications by transmitting a digital request message to a system central controller via a predetermined inbound frequency. Here, the mobile unit generates a channel request that includes the necessary information to identify it to the central controller. The central controller responds to the mobile unit with a digital message via a separate and distinct predetermined outbound frequency that, in turn, authorizes the mobile unit to operate on an n another channel. This outbound digital message is often referred to as an outbound signaling word (OSW) or a channel assignment message or a channel grant message. Both the inbound and outbound channel is often referred to as a "system control channel". In addition, the mobile unit also responds to other commands that are received from the central controller. [0006] There are a number of trunked radio systems that are currently use in the United States. One of these trunked radio systems is described in U.S. Pat. Nos. 4,692,945 and 4,723,264 issued to Motorola. These two patents disclose an improved dispatch trunked radio system having an expanded unifying signaling protocol used to implement several enhanced system features. Here, the subscriber or mobile units are capable of generating and receiving signaling information in a single word or concatenated in a dual-word signaling scheme. The central control unit is able to decode and generate signaling information in either a single or concatenated dual-word signaling scheme, as well as generates channel controlling information in accordance with either signaling scheme. [0007] In addition, U.S. Pat. Nos. 4,055,832 and 4,312,070 also issued to Motorola describes the method used to encoding data transmitted over the control channel of a trunked radio system implemented by Motorola. Here, En and Coombes, et al. discloses an encoding and decoding system suited for use in a mobile trunked dispatch communication system capable of error correction, error detection, and detection of loss of synchronization. More specifically, the system disclosed in En and Coombes, et al., respectfully, provides an error correction system that can correct one random error out of every four bits transmitted with a minimum of time delay in transmission and a minimum number of components for system implementation. [0008] In U.S. Pat. No. 4,905,302 issued to Childress, et al. discloses another trunked radio communications system, known as EDACS, that provides substantial improvements in channel acquisition and channel drop, and in reliability of critical control signaling. The system uses a much higher digital signaling rate than is typically found in prior art systems, and uses a control channel to convey digital channel request and assignment messages between the central site and mobile transceivers. The mobile radio systems transmit channel requests on the inbound control channel (if no response is received, the mobile retries during a retry time window which increases in duration in dependence on the number of retries). The mobile transceiver switches to a working channel in response to an assignment message received on the control channel. Digital signals transmitted on the control channel and subaudible digital signal transmitted on active working channels allow late entry, shifting to higher priority calls, and other advanced functions. Message and transmission trunking capabilities are both present so as to maximize working channel usage without compromising channel access for high priority communications. During transmission, the calling as well as the calling transceivers return to the control channel after each transmission (and called transceivers may be inhibited from transmitting) but grant higher priority to calls from the other transceivers being communicated with to ensure continuity over an entire conversation. [0009] It is desirable to monitor various users of a communication system, but without any capability of transmitting. Conventional communication systems are easily monitored with a variety of radio communication receivers. One example of this type of radio communication receiver is a scanner. Scanners are radio receivers that typically cover a range of frequencies between approximately 30 MHz and 1 GHz. The scanning receiver is sequentially tuned through a set of predetermined, user selected frequencies. If a signal is detected, the scanner stops scanning and remains tuned to that frequency until the signal ceases, whereupon the scanner resumes searching for another frequency. The typical scanner is comprised of a receive-only radio without any capability of transmitting a signal. Such scanning receivers are inexpensive and enable a user to hear transmissions on a conventional radio system with little effort on the part of the user, and little or no effort on the part of the communications systems operator. A conventional scanner is not able to correctly follow a sequence of transmissions on a trunked radio system because the scanner has no ability to understand the outbound channel assignment messages sent by the trunking system controller. [0010] U.S. Pat. No. 5,784,388 issued to Knox discloses several significant improvements to a conventional scanner and improves the ability to decode the messages from a Motorola trunked system control channel. The system disclosed in Knox decodes encoded data from the control channel of a trunked radio communications system. The decoder includes a de-interleave, an auto synchronization sequence combiner, and a table lookup error detector to recover the transmitted information and also indicates whether any errors are present in the recovered information. However, the advancement disclosed by Knox requires that the scanner be specifically designed and manufactured to operate for use with Motorola trunked radio communications systems. Additionally, the system disclosed by Knox requires that the operator of the scanner be able to identify the various types and characteristics of a trunked system, the particular radio frequencies of the system as well as to program these details into the scanner or computer. [0011] In the case of the EDACS trunking system, the data messages transmitted by the system controller do not contain frequency information. EDACS messages only contain logical channel numbers. EDACS mobile units are pre-programmed with a frequency table that allows the mobile unit to associate a specific radio frequency with logical channel numbers. To properly tune a scanning radio to an EDACS working channel, the user must know which frequencies are assigned to the system. [0012] Therefore, there is a need for providing a method and apparatus for monitoring trunked radio communications system that automatically determines the characteristics and frequencies of trunked radio communications systems, thus, eliminating the need for a user to program these details. SUMMARY OF THE PRESENT INVENTION [0013] A preferred embodiment of the present invention provides a method and apparatus for monitoring a trunked radio communications system by using some type of radio scanning receiver that is not designed for that purpose. [0014] In accordance with the purpose of the invention, as embodied and broadly described herein, the invention relates to provide a method for automatically determining the polarity of the received control channel data. [0015] Further in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides a method for automatically determining the type of trunked radio communications system. In addition the invention provides a method for automatically determining the bit rate of transmitted digital signals over a control channel of a trunked radio communications system. [0016] Further in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides a method for automatically determining the frequencies used in a trunked radio communications system. [0017] The preferred embodiment of the present invention for monitoring communications in a trunked radio communication system includes a personal computer with a sound card for sampling the baseband, a frequency tunable receiver, a zero crossing detector to convert PCM samples to NRZ equivalent, a plurality of preamble correlators to detect the phase, bit rate, polarity and type of trunked radio communication system, a bit phase compensator to recover the transmitted data from the sampled data stream, decoding means to decode transmitted digital control channel messages and respond to channel assignment messages from a decoded working channel. [0018] An alternative of the preferred embodiment uses a micro-controller such as the one used to control a receiver scanner. In this embodiment, the pre-calculation steps are carried out once, during the programming of the micro-controller. Additionally, the incoming data bits are sampled directly using an input port on the micro-controller, rather than using a sound card. Here, the sample rate is selected from a possible set of values for a given the micro-controller architecture and its associated clock rate. [0019] Advantages of the invention will be set forth, in part, in the description that follows and, in part, will be understood by those skilled in the art from the description herein. The advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims and equivalents. BRIEF DESCRIPTION OF THE DRAWINGS [0020] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate several embodiments of the invention and, together with the description, sever to explain the principles of the invention. [0021] FIG. 1 is a block diagram that illustrates how the embodiment of the present invention can be implemented. Continue reading about Apparatus and method for monitoring a trunked radio communications system... Full patent description for Apparatus and method for monitoring a trunked radio communications system Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Apparatus and method for monitoring a trunked radio communications system patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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