Variable-rate (pi)/4-APSK modulation
Date
1993
Authors
Schnorr von Carolsfeld, Rudolf
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Abstract
A new method of modulation for digital communication that supports variable data transfer rates over an additive white Gaussian noise communication channel is presented. The proposed modulation technique was developed for use in a non-mobile data telemetry system. Based on the π/4-QPSK modulation scheme adopted for the North American digital cellular system, the technique offers the increased spectral efficiency of APSK signaling and is called π/4-APSK signaling.
Amplitude scaling of the π/4-QPSK channel signal provides an additional dimension in the modulation domain. In this thesis, expressions for the theoretical error performance of the π/4-QPSK signaling technique are determined, and optimum receiver decision regions and signal constellations are derived. Results of computer simulation of the proposed system subject to an ideal A WGN channel are presented. It is shown that this new modulation technique may be used to increase the data transfer rate of the system, to support error correcting codes for improved data reliability, or to support an enhanced network protocol.
Using a π/4-QPSK signal with two optimally-spaced signal points per quadrant (3 bits per symbol) provides a symbol error probability of 10-5 at a signal-to-noise ratio of approximately 19 dB; the same probability is attained at about 25 dB using 4-level π/4-APSK signaling (4 bits per symbol), and at about 31 dB using 8-level π/4-QPSK (5 bits per symbol).
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UN SDG 7: Affordable and Clean Energy