Presence Of AWGN Research Articles

Low SNR approximation to phase PDF for PSK signals

For the original article see ibid., vol. 30, no. 16, p. 1279-80 (1994). In the afore-mentioned paper the authors, P.C. Sapiano et al., derived a Fourier series expansion of the probability density function of the signal phase in the presence of AWGN. The commenter shows how Fourier series coefficients may be obtained directly from this expansion. In reply, the authors agree with this but maintain that their alternative route for deriving the Fourier series coefficients, based on series expansions of special functions, is still valid. However, they consider that this does not detract from the main thrust of their argument which was based on the low SNR approximation of a multilevel PSK phase PDF and an efficient method for generating the Fourier series coefficients. >

Performance of pi /4 SQAM in a hard-limited channel in the presence of AWGN

A strategy that reduces the spectral spreading when an ideal hard-limiter is used as a first approximation to a fully saturated power amplifier is presented. This strategy combines superposed quadrature amplitude modulation (SQAM) filtering with the pi /4-shift quadrature phase-shift keying (QPSK) digital transmission format adopted for the first generation of US digital cellular systems. Simulation results showed that this pi /4 SQAM filtering strategy increased capacity by 35% in comparison to hard-limited pi /4 QPSK. Using computer-aided design, a receive filter that would limit the degradation of E/sub b//N/sub 0/ to less than 1.4 dB at a bit error rate of P/sub e/=10/sup -4/ was selected.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A new 3-dimensional modulation-coding system

The classic problem of transmitting digital information with minimum probability of error in the presence of noise, fading and various interferences is investigated. The multi-gap shift keying MGSK technique is introduced and used in conjunction with the classic MFSK and MPSK techniques to increase the signal's immunity to noise and interferences. The same bits of information will control the phase, frequency and gap location of a composite MGSK/MPSK/MFSK signal (word) and, at the composite receiver, maximum likelihood decisions will minimize the probability of word errors. Modest amount of convolution error correction is needed so that the total effective rate is not sacrificed. The average performance of the new 3-dimensional signaling scheme was analysed and the average probability of bit errors with and without coding in the presence of AWGN and Raleigh fading was determined.