Browse Prior Art Database

Digital Four Phase PSK Modulator

IP.com Disclosure Number: IPCOM000087232D
Original Publication Date: 1976-Nov-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 2 page(s) / 48K

Publishing Venue

IBM

Related People

Lautier, A: AUTHOR [+2]

Abstract

The figure shows a digital modulator capable of generating a 50 Mbps SK signal. The data stream to be transmitted is divided into groups of two consecutive bits (dibits). Each is encoded as a carrier phase change, and the modulated carrier is sent over the channel.

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Digital Four Phase PSK Modulator

The figure shows a digital modulator capable of generating a 50 Mbps SK signal. The data stream to be transmitted is divided into groups of two consecutive bits (dibits). Each is encoded as a carrier phase change, and the modulated carrier is sent over the channel.

Assuming a signalling rate 1/T, the four-phase PSK signal can be expressed in the form:

(Image Omitted)

Signal s(t) can be obtained by generating at each signalling instant the two signals:

(Image Omitted)

In the modulator shown in Fig. 1, signals a(t) and a'(t) are derived from weighted pulse trains SE1 and SE2 (Fig. 2), respectively, assuming f(c) = 1/T. Weighted pulse trains SE1 and SE2 extend over four and three signalling periods, respectively, and the amplitude levels of the pulses are determined so that the frequency spectrums of SE1 and SE2 match the frequency characteristics of the channel. The pulse train corresponding to SE1 is generated by four-stage shift register SR1 and AND gates A-G. The pulse train corresponding to SE2 is generated by three-stage shift register SR2 and AND gates H-N. These two pulse trains are weighted in digital-to-analog converters D/A I and D/A II, respectively, and summed. A low-pass filter (LPF) provides the PSK signal to be transmitted. Shift register SR1 and SR2 are shifted at rate 1/T under the control of signals SRC and SRS, respectively. Signal SRS is a 1/4 T delayed version of SRC. Assuming a PSK signal corresponding to p(k)...