Method and apparatus for signal transmission and reception

Abstract

A method and modem for communicating serial input data over a transmission link. Serial input data is partitioned into parallel data elements prior to rotation by an invertible linear mapping. Resulting frames of parallel signal elements sequentially modulate a carrier, which is then transmitted over the link. After receipt of the modulated carrier from the link, the signal is demodulated and assembled into frames of parallel signal elements which are de-rotated by an inverse linear mapping. Thresholding the result of the inverse mapping recovers the parallel data elements, which are then re-assembled into serial output data. The linear mapping employs: 1) commuting rotation matrices for convolutionally rotating data vectors into signal vectors and vice-versa; 2) filter bank polyphase rotation matrices; or 3) computationally efficient multi-rate wavelet filter banks. Transmitter pre-emphasis places most of the information in lower baseband frequencies; complimentary de-emphasis occurs in the receiver. Logarithmic amplification of the baseband signal prior to carrier modulation improves modulation gain and transmit channel noise attenuation. Coefficients of the rotation matrix of the receiver are adaptively equalized to correct for transmission path distortion. FM double-side band is employed in systems requiring minimized cost and complexity. FM single-side band is employed in systems in which bandwidth reduction is desirable. AM is also employable.

Description

RELATED APPLICATIONS [0001] This application is a continuation-in-part of application Ser. No. 08 / 342,259, filed Nov. 18, 1994 (Attorney Docket MILL-001 AX), which is a continuation of U.S. Pat. No. 5,367,516, filed Mar. 17, 1993, issued Nov. 22, 1994 (Attorney Docket MILL-001XX).FIELD OF THE INVENTION [0002] This invention relates to signal transmitting and receiving systems and more particularly to modems employing polyphase filtering techniques. BACKGROUND OF THE INVENTION [0003] As is known in the art, a modulator-demodulator (modem) is an electronic device that modulates transmitted signals and demodulates received signals. The modem generally provides an interface between digital devices and an analog communications system to thus make possible analog transmission of digital information between two terminals or stations. Such transmissions may be over a transmission link such as a telephone line, cellular communication link, satellite link, and cable TV, each of which being ge...

AI Technical Summary

Benefits of technology

[0013] The polyphase filtration of these methods and this modem enables FM modulation of the transmitted symbols since only a real component of the original symbols is generated. FM, whether achieved using frequency modulation or phase modulation of the input signal, provides enhanced immunity to non-Guassian noise, provides high bandwidth efficiency, utilizes non-coherent IF and thus requires no carrier recovery, is of lower cost than conventional modems in part due to the absence of A / D converters, provides low co-interference due to the FM capture effect, and is compatible with analog signals, owing to the use of commuting operators. More power efficient, but potentially less linear amplifiers such as Class B and Class C can be employed since zero crossings are used to determine data content; carrier recovery is not required. Prior art modems employing modulation schemes such as QAM cannot employ such non-linear amplification. Further, satellite modems employing the presently disclosed method and modem save on TWT backoff power and thus are more energy efficient since intermodulation is not a problem, while personal computers achieve higher data rates without sacrificing bit error rate.

[0018] FM double-side band is employed in systems requiring minimal cost and complexity. FM single-side band is easily implemented in systems in which the bandwidth reduction is desired. AM modulation of a carrier is also implemented in a further embodiment.

Problems solved by technology

Prior art modems employing modulation schemes such as QAM cannot employ such non-linear amplification.

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