Method and apparatus for detecting control signals

3

FIG. 3 presents a portion of the control function presented in FIG. 2 concerned with receiving and detecting control signals.

FIG. 4 presents the eight lowest-order discrete prolate spheroidal sequences determined for NW=4. 5

FIG. 5 presents the eigenvalues of discrete prolate spheroidal sequences determined for NW=4.

FIG. 6 presents an illustrative DTMF receiver according to the present invention.

FIG. 7 presents a time progression of signal segments 10 provided by an illustrative embodiment of the present invention.

FIG. 8 presents the embodiment presented in FIG. 6 illustratively augmented to provide a maximum frequency variation check, a maximum amplitude varia- 15 tion check, a maximum phase variation check, and a twist check.

FIG. 9 presents an illustrative embodiment of the present invention which performs a simultaneous estimation of signal amplitude and frequency. 20

FIG. 10 presents an illustrative embodiment of the present invention which provides for the simultaneous estimation of the amplitudes of two component tones of a DTMF signal.

DETAILED DESCRIPTION 25

A. Introduction to the Illustrative Embodiments A communication system comprises a multiplicity of devices or systems which need to communicate with each other, and a set of one or more channels, coupled 30 to the devices or systems, which facilitate communication. Perhaps the most well-known and widespread of all communication systems are the telecommunication systems, such as telephone networks. These include, for example, local- and long-distance telephone networks 35 (e.g., the AT&T long-distance telephone network), and private branch exchange networks (PBXs) (e.g., the AT&T DEFINITY ® PBXs) used to provide special services to many businesses and institutions. A communication system device which transmits or receives 40 information over the system is referred to as a system station.

FIG. 1 presents an illustrative communication system comprising a plurality of individual telephone networks and a collection of stations. The individual telephone 45 networks include PBXs 3, providing features such as a central answering position, station-to-station intercom calling, and connectivity to local and long distance telephone networks; a local-telephone network 5, providing not only services associated with completing 50 local telephone calls and connecting local stations to a long-distance network 6, but also integral services such as, voice-messaging, three-way calling, call-waiting, etc.; and a long-distance network 6, linking individual local networks 5 together and also providing integral 55 services. Stations may include telephones 1, facsimile machines 2, and personal computers 4 (PCs), among other things. The illustrative telecommunication system of FIG. 1 may further comprise, e.g., network switching systems (e.g., the AT&T 4ESS TM and 5ESS ® 60 switches) network-based teleconferencing (e.g., AT&T Alliance ® Teleconferencing) and messaging (e.g., AT&T Message Service), PBX-based messaging and switching systems, voice transaction systems, etc. Components (or parts thereof) of a communication system 65 may be referred to generically as system elements.

In order for one system element to communicate with another, a system element referred to as a channel must

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be established. A channel may take the form of a dedicated coupling between elements, or a shared coupling used by several pairs or groups of elements simultaneously. A channel may comprise an electrical coupling, a radio link, a fiber-optic element, an acoustic coupling, etc.

To establish and maintain communication channels (among other things), communication systems (such as telephone networks) may comprise one or more elements referred to as system control functions. A system control function provides control of a communication system element in response to control signals communicated over a channel by another system element. For example, a system control function may control system switching capability directing information flow through a telephone network. That is, a communication channel may be established when a station desiring to initiate communication (a source station) with another station (a target station) transmits control signals over the network identifying the target to one or more system control functions. A system control function, in response, directs the coupling (or switching) of channels to facilitate the desired communication between source and target stations.

In addition to, or instead of, controlling a switching capability, a system control function may control special functions, services, devices, and systems ("systems") which augment or enhance a communication system's basic switching and communication functions. Like a switching capability, these special systems are controlled by a control function in response to control signals. In telephone networks, these special systems might include call-forwarding and -transfer systems, voice-messaging, teleconferencing, transaction systems, etc. (in effect, any function, service, device or system which may be initiated or directed by control signals).

FIG. 2 presents an illustrative system control function for the telecommunication system of FIG. 1. This control function could be resident anywhere in the telecommunication system where control of switching or special systems is needed (e.g., at a station, at a PBX, in a channel, in a local telephone network, or in a longdistance network). Input to the system control function (CF) are a plurality of network communication channels 7, from a plurality of system elements (not shown). These input channels are also coupled to, e.g., a network switch 8. Switch 8, in turn, is coupled to other (output) channels 9 leading to other system elements (also not shown). Switch 8 may perform the coupling of any of the input channels 7 to any of output channels 9, and may provide special functions, all under the direction of control processor 10 of the system control function.

Control processor 10 of the system control function receives control signals from a system element via input channel 7 and input control signal interface 13. Control signals may comprise, e.g., electrical or Optical signals representative of a telephone number of a target station or a code for a special function desired by a station. Control signals, when detected by control signal interface 13, are passed to control processor 10 to be used as input information for software executed by the processor 10. This software, stored in program memory 11, provides the functionality associated with the system control function. As a result of executing the software, control processor 10 determines other signals necessary to, e.g., facilitate connection of source and target stations, or to provide desired special functions. (To per