PSK digital echo modulator with reduced memory capacity required

Claim 2

In a modulator for producing a composite transmission signal corresponding to a plurality of overlapping signal elements, each signal element corresponding to an element of data, and having a permanent memory for storing a multiplicity of digital representations of instantaneous values of amplitudes of each said signal element at a plurality of positions corresponding to sampling time intervals along said signal elements, the improvement comprising; temporary memory means for storing a selected plurality of said multiplicity of digital representations of instantaneous signal element values, each of said selected plurality corresponding to a separate one of said signal elements during a single sampling time interval; and means for adding said selected plurality of values from said temporary memory to produce a digital representation of the instantaneous value of said composite signal in a single add operation during said single sampling time interval.

Claim 3

The apparatus of claim 1 wherein said modulator is a digital echo modulator.

Claim 4

The modulator of claim 1 wherein a zero amplitude level of a first one of said signal elements is represented by a digital value at the midpoint of the range of values of said digital values stored in said permanent memory and wherein said modulator further includes means for generating a second signal element having a phase shift of 180° relative to said first signal element by calculating the two's complement of each digital representation of an instantaneous value of said first signal element.

Claim 5

The modulator of claim 3 further comprising multiplexer means, coupled to said permanent memory and said two's complement signal generating means, for alternatively coupling a digital representation of an instantaneous value of said first and second signal elements to an output of said multiplexer means, said temporary memory means including at least two latch means, coupled to said output of said multiplexer means, for storing digital representations of an instantaneous value of said first and second signal elements.

Claim 6

The modulator of claim 4 wherein digital representations of the instantaneous value of four signal elements are generated during each sampling interval, said four signal elements being selected from a first two signal elements stored in said permanent memory and a second two signal elements generated from said first two signal elements by said two's complement signal generating means.

Claim 7

The modulator of claim 5 wherein each signal element extends for a specified time period and each succeeding signal element commences at a time 1/4 of said time period after a preceding signal element commences.

Claim 8

The modulator of claim 1 wherein each of said digital representations of an instantaneous value of a signal element consists of six binary bits.

Claim 9

A digital echo modulator for producing a composite transmission signal corresponding to a plurality of overlapping signal elements, each signal element corresponding to an element of data, comprising: a permanent memory for storing a multiplicity of digital representations of instantaneous values of amplitudes of at least a first one of said signal elements at a plurality of positions corresponding to sampling time intervals along said signal elements, a zero amplitude level of said first signal element being represented by a digital value at the midpoint of the range of values of said digital values stored in said permanent memory; means for generating a second signal element having a phase shift of 180° relative to said first signal element by calculating the two's complement of each digital representation of an instantaneous value of said first signal element; multiplexer means, coupled to said permanent memory and said two's complement signal generating means, for alternatively coupling a digital representation of an instantaneous value of said first and second signal elements to an output of said multiplexer means during a single sampling time interval; at least two latch means, coupled to said multiplexer output, for storing said digital representations of an instantaneous value of said first and second signal elements; and means for adding said digital representations from said latch means to produce a digital representation of the instantaneous value of said composite signal in a single add operation during said single sampling time interval.

Claim 10

A digital echo modulator for producing a composite transmission signal corresponding to a plurality of overlapping signal elements, each signal element corresponding to an element of data, comprising: a permanent memory for storing a multiplicity of digital representations of instantaneous values of amplitudes of at least a first one of said signal elements at a plurality of positions corresponding to sampling time intervals along said signal elements, a zero amplitude level of said first signal element being represented by a digital value at the midpoint of the range of values of said digital values stored in said permanent memory; means for generating a second signal element having a phase shift of 180° relative to said first signal element by calculating the two's complement of each digital representation of an instantaneous value of said first signal element; multiplexer means, coupled to said permanent memory and said two's complement signal generating means, for alternatively coupling a digital representation of an instantaneous value of said first and second signal elements to an output of said multiplexer means during a single sampling time interval; at least two latch means, coupled to said multiplexer output, for storing said digital representations of an instantaneous value of said first and second signal elements; and means for adding said digital representations from said latch means to produce a digital representation of the instantaneous value of said composite signal in a single add operation during said single sampling time interval.

Claim 11

The modulator of claim 8 further comprising differential encoder means for generating an address of said permanent memory corresponding to a phase of one of said signal elements, said phase being determined from a phase change corresponding to the difference between one of said elements of data and a preceding element of data.

Claim 12

The modulator of claim 8 further comprising address generating means for producing addresses of said permanent memory corresponding to a stored signal element and for producing a signal to control said multiplexer means.

Claim 15

The method of claim 11 wherein said signal elements are used for digital echo modulation.

Claim 16

The method of claim 11 wherein a zero amplitude level of a first one of said signal elements is represented by a digital value at the midpoint of the range of values of said digital values stored in said permanent memory and further including the step of generating a second signal element having a phase shift of 180° relative to said first signal element by calculating the two's complement of each digital representation of an instantaneous value of said first signal element.

Claim 17

The method of claim 13 wherein said temporary memory comprises at least two latches and further including the step of alternatively coupling a digital representation of an instantaneous value of said first and second signal elements to an output of a multiplexer.

Claim 18

The method of claim 13 further including the step of generating digital representations of the instantaneous value of a third and a fourth signal elements during said single sampling time interval, said third signal elements being selected from said permanent memory and said fourth signal element being generated from said third signal element by said two's complement signal generating step.

Claim 19

The method of claim 15 wherein each signal element extends for a specified time period and each succeeding signal element commences at a time 1/4 of said time period after a preceding signal element commences.