Abstract: A method for clock recovery comprises a series of steps to be performed in a decoder to adaptively estimate the ratio P/S of the frequency of an encoder system time clock and the frequency of a decoder. The steps include performing a series of overlapping trials N which calculate time differentials dP(n), dS(n), respectively) between selected pairs of temporally separated clock references CRs and arrival times STCs. Each trial concludes by calculating an estimated ratio X according to the formula: X(N)=(&Sgr;dP(n))/(&Sgr;dS(n)) A preferred embodiment of the present invention also includes the step of adjusting the decoder clock in accordance with a damped version of the estimate, thereby “recovering” the encoder STC in the decoder.

Abstract: A shaping filter for a PAM mapper is provided which manipulates incoming PAM code level signals to produce outgoing PAM code level signals whose frequency spectrum is shaped to meet desired criteria. In manipulating input code level values in(t), the shaping filter preferably utilizes previous output signal values without using previous incoming signal values. In a preferred embodiment, the output code level values out(t) are constrained to an output alphabet which is a predefined subset of code levels within the .mu.-law constellation, and are obtained by manipulating the input signals according to an integer-valued shifting function such that out(t) are code level values within the output alphabet. The preferred shifting function S "shifts" in(t) by a number of places in the output alphabet in the direction opposite the sign of ##EQU1## to provide out(t), where out(t) are .mu.-law code output level values at times t, and a.sub.i are weighting factors chosen to shape the frequency spectrum of out(t).

Abstract: A spectral and power shaping mapper for high data rate signaling modem functions in a first mode having spectral and power shaping and using convolutional encoding, a second mode having power shaping, a third mode having power shaping using convolutional encoding, and a fourth mode having straight-forward mapping. Based on data rates and other criteria, incoming bits are grouped together, with a first subgroup of bits used in the first mode to generate two sign vectors (and in the other modes a single vector), a second subgroup of bits used in conjunction with an appended bit in the first, second and third modes to generate at least two magnitude manipulation vectors, and a third subgroup of bits used in a modulus converter to generate a plurality of quotients. The quotients and magnitude manipulation vector(s) are used to select one, two or four sequences of constellation points from a multidimensional constellation depending on mode.

Abstract: A spectral and power shaping mapper for high data rate signaling modem is provided. Based on data rates and other criteria, groups of incoming bits are grouped together, with a first subgroup of bits being used to generate two sign vectors, a second subgroup of bits being used in conjunction with an appended bit to generate two magnitude manipulation vectors, and a third subgroup of bits being used in a modulus converter to generate a plurality of quotients (r.sub.k). The quotients and magnitude manipulation vectors are used to select two or more sequences of constellation points from a multidimensional constellation. The sequences of selected points are combined with the sign vectors to generate four sequences of octets for a shaping selector. The shaping selector, preferably in the form of a convolutional encoder state machine uses criteria such as lowest cost paths and/or lowest average power in order to select which sequence of octets to output.