Motorola Corporation

Lee T Gusler

Richard Lee Goodson

Mickey C Rushing

Gary D Hunt

Orlyn C Hall, Jr

An apparatus and method are provided for a data communications device, such as a modem (100, 101) or facsimile machine, to detect and discriminate various amplitude modulated signals, such as an ANS signal of the ITU V.25 protocol and an ANSam signal of the ITU V.8 protocol, which may be subject to impulse distortions (FIG. 5B). The apparatus and method embodiments band pass filter (204) an incoming signal at a first frequency, and dynamically limit (208) any impulse distortions of the incoming signal to a limit threshold (211). The limit thresholds may be dynamically determined by rectifying (209) and low pass filtering (210) the band pass filtered signal to determine a low frequency average magnitude level of the incoming signal, with the limit thresholds set as a predetermined variance from this low frequency average magnitude level. The various frequency components of the amplitude modulated signal may then be discriminated by rectifying (215) and band pass filtering (217) at a second frequency, such as the frequency of the amplitude modulating component. Various detectors (205, 206) then determine the type of information present in the incoming signal, such as whether the signal is an ANS signal or an ANSam signal.

Apparatus and method for detecting and discriminating various signal

An apparatus and method are provided for a data communications device (100), such as a modem, to detect the loss of a telecommunications channel connection, in the absence of other notification signals. The apparatus and method embodiments of the invention utilize a near end echo in full duplex transmission, and compare (630) periodically sampled transmit data (610), preferably composed of an n-bit sequence, with sampled values of received data (620), to determine the occurrence of a match between the data received and the data transmitted (640). If a predetermined number of consecutive matches have occurred (670), then a loss of a telecommunications channel connection has occurred and is detected (680). Preferrably, the apparatus is embodied in a processor (108) or a processor (107) coupled with a digital signal processor (106), which are within the data communications device (100).

Apparatus and method for detecting a loss of a telecommunications

An apparatus and method for a data communications device, such as a modem (100, 101), to determine a symbol rate and carrier frequency combination, from a received probe signal, for optimizing a bit rate for data transmission and reception. The various embodiments utilizing a processor (108) or a digital signal processor (106) receive a probe signal, which also typically contains noise and other distortions. The various method and apparatus embodiments then determine signal to distortion ratios for a plurality of symbol rate and carrier frequency combinations (820), and other optimization parameters, such as channel characteristics and attenuation distortion parameters (830). These optimization parameters are then utilized to determine an optimal symbol rate and carrier frequency (840).

Apparatus and method for determining a symbol rate and a carrier

An apparatus and method for a data communications device such as a modem (100, 101) to determine carrier frequency offset and timing frequency offset, from a received probe signal. The various embodiments utilizing a processor (108) or digital signal processor (106) receive first and second sets of a transmitted probe signal having known characteristics, and determine a set of phase differences for the tones comprising the probe signal (702, 703, 704, 705). The various method and apparatus embodiments then form a linear approximation from the set of phase differences to determine the carrier frequency offset and the timing frequency offset (706). In the preferred embodiments, the linear approximation is formed from a minimization of a least square error estimate proportionally weighted by either signal to noise ratios or normalized, average amplitudes of the set of tones of the received probe signal.

Apparatus and method for determining carrier frequency offset and timing

An apparatus and method for a data communications device such as a modem (100) to generate initial coefficient values for an equalizer (440) from a transmitted training signal received via a channel, in which the transmitted training signal has predetermined characteristics. The apparatus and method embodiments of the invention determine a finite impulse response characteristic of the inverse frequency response of the channel based on a received training signal and the transmitted training signal (610). In the various embodiments, an energy index, a magnitude index, and an offset index are generated and combined with an equalizer length index to select a sequence of initial coefficient values for the equalizer (630, 640, 650).

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Huntsville, AL, United States of America

Lee T Gusler