Fractional rate modulation is accomplished by separating incoming data into frames of bits. Each frame is partitioned into bit words of unequal lengths. The words are divided by a modulus to obtain remainders. The remainders are transmitted using for example QAM modulation. At the receiving end the process is reversed. The ratio of the baud rate of the system to the incoming bit rate defines the modulus as well as the number of QAM modulation points.
5926507 - Quotient coding modem - Owned by The United States of America as represented by the Secretary of the Navy (Washington, DC)
A quotient coding modem comprises a modulator that encodes transmitted symbols by the equation ##EQU1## and a demodulator that decodes received symbols by the equation ##EQU2## where q(t) and q.sub.r (t) are functions of time for transmitted and received symbols s(t) and s.sub.r (t) respectively at time t, P.sub.r (t)=.vertline.q.sub.r (t).vertline..sup.2 is instantaneous received baseband power at time t, .eta. is a function of the two smallest symbol amplitudes, and P.sub.max is peak transmitted power.
An improved multiple modulus conversion (MMC) procedure is provided that employs an alternate scheme for obtaining the MMC outputs in response to a binary input of a number of bits. The alternate MMC procedure utilizes short-word division operations such that a practical digital processor may efficiently perform the required binary divisions. An exemplary short-word division process partitions the original long-word binary input into a plurality of short binary words, each having an equal number of bits. Individual short words or a combination of two short words are then divided by the appropriate modulus in a systematic manner to obtain the quotient and remainder associated with the particular division operation. The short-word divisions technique may be employed throughout the entire MMC procedure to suitably obtain the output values associated with each modulus.
The present invention relates to multiple modulus conversion (MMC) techniques for mapping data in a pulse code modulation (PCM) modem system. In accordance with the present invention, signal point constellations are arranged to receive the output indices generated by the MMC procedure such that the probability of transmission of higher power codewords is relatively low compared to the probability of transmission of lower power codewords, while maintaining the same or larger minimum distance between signal points. In addition, the present invention provides techniques for obtaining the probability of occurrence for each constellation or signal point associated with a given data communication session and for determining the theoretical average transmit power associated with a given set of signal point constellations and MMC parameters. In addition, the present invention provides a method for estimating a reasonable upper bound for the average transmit power associated with a given set of signal point constellations and MMC parameters. The present invention is also capable of transmitting the codewords defined by an MMC procedure in a specific order that may be optimized in accordance with a particular cost function associated with the modem system.
A device of dynamic communication of information allows, on the average, non-integer bits per symbol transmission, using a compact code set or a partial response decoding receiver. A stream of selectable predetermined integer bits, e.g., k or k+1 data bits, is grouped into a selectable integer number of bit vectors which then are mapped onto corresponding signal constellations forming transmission symbols. Two or more symbols can be grouped and further encoded, so that a symbol is spread across the two or more symbols being communicated. Sequence estimation using, for example, maximum likelihood techniques, as informed by noise estimates relative to the received signal. Each branch metric in computing the path metric of a considered sequence at the receiver is weighted by the inverse of the noise power. It is desirable that the constellation selection, sequence estimation and noise estimation be performed continuously and dynamically.
A combined frame mapping technique that uses aspects of Minimum Modulus Conversion (MMC) and Shell Mapping (SM) to map data bits to a sequence of data symbols, or points. The apparatus includes a shell mapper to generate ring indices from K data bits and a modulus converter to select the signal points from within the ring based on B data bits. The apparatus and method permits the use of constellations having any integer number of points per ring. Variations in the constellations from time-slot to time-slot within a frame are also accommodated. The number of rings in each constellation remains constant, but the moduli vary. MMSM produces d.sub.min equal to the best of MMC and SM, and in some cases d.sub.min, may be better than that for either MMC or SM.
