Constrained-envelope digital-communications transmission system and method therefor

Abstract

A constrained-envelope digital-communications transmitter circuit (22) in which a binary data source (32) provides an input signal stream (34), a phase mapper (44) maps the input signal stream (34) into a quadrature phase-point signal stream (50) having a predetermined number of symbols per unit baud interval (64) and defining a phase point (54) in a phase-point constellation (46), a pulse-spreading filter (76) filters the phase-point signal stream (50) into a filtered signal stream (74), a constrained-envelope generator (106) generates a constrained-bandwidth error signal stream (108) from the filtered signal stream (74), a delay element (138) delays the filtered signal stream (74) into a delayed signal stream (140) synchronized with the constrained-bandwidth error signal stream (108), a complex summing circuit (110) sums the delayed signal stream (140) and the constrained-bandwidth error signal stream (108) into a constrained-envelope signal stream (112), and a substantially linear amplifier (146) amplifies the constrained-envelope signal stream (112) and transmits it as a radio-frequency broadcast signal (26).

Description

[0001]Notice: More than one reissue application has been filed for the reissue of U.S. Pat. No. 6,104,761. This Reissue Application is a continuation of Reissue application Ser. No. 10 / 718,507 filed Nov. 19, 2003 (U.S. Reissue Pat. No. Re. 41,380) which is a reissue of application Ser. No. 09 / 143,230 (U.S. Pat. No. 6,104,761). Both of these reissues applications are reissues of the same U.S. Pat. No. 6,104,761.TECHNICAL FIELD OF THE INVENTION[0002]The present invention relates generally to the field of digital communications. More specifically, the present invention relates to the field of constrained-envelope digital transmitter circuits.BACKGROUND OF THE INVENTION[0003]A wireless digital communications system should ideally refrain from using any portion of the frequency spectrum beyond that actually required for communications. Such a maximally efficient use of the frequency spectrum would allow the greatest number of communications channels per given spectrum. In the real-world,...

AI Technical Summary

Benefits of technology

The present invention provides a circuit and method for biasing a transmitter output amplifier to ensure that a spectrally unconstrained waveform is at the top of the amplifier's linear region without causing clipping of a spectrally constrained waveform. This allows for efficient use of the transmitter output amplifier, resulting in higher power output for a given bandwidth and cost-effectiveness. The invention also allows for the efficient use of a lower-power amplifier to achieve the same bandwidth requirements, resulting in significant savings in cost. Overall, the invention provides improved performance and cost-effectiveness for digital communications transmitters.

Problems solved by technology

In the real-world, however, some spectral regrowth (i.e., increase in spectral bandwidth) is inevitable due to imperfect signal amplification.

This is because the low throughput rate allows sufficient time between symbols for the processor to perform extensive and often repetitive calculations to effect the required signal modification.

Unfortunately, high-throughput applications, i.e., those greater than 0.5 Mbps, such as the transmission of high-speed video data, cannot use complex processing algorithms because the processing power required to process the higher data rate is impractical.

This methodology is not practical when continuous (as opposed to burst) transmission is used.

This poses several problems.

Such clipping causes a marked increase in spectral regrowth, obviating the use of Nyquist-type filtration.

This results in an inefficient use of the output amplifier.

Such a higher-power amplifier is inherently more costly than its lower-power counterparts.

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