In this paper, we investigate a coded solution to compensate for the nonlinear distortion of TDMA satellite waveforms. Based on a Volterra-type channel model and the turbo principle, we present a turbo-like system that includes a simple rate-1 encoder at the transmit side in addition to a conventional channel encoder; the receive side iteratively equalizes the nonlinear channel effect and decodes the received symbols. Some other design alternatives are also explored and computer simulated performance is presented. Numerical results show that significant improvement over conventional approaches can be achieved by the proposed turbo system.

In this letter, the effect of distorted constellation shapes of 16-ary modulation due to the power saturation channel is analyzed. In particular, error bounds for 16-QAM and 16-APSK with distorted constellations are derived, and optimal operating points in terms of Es/N0 are presented. The result can be used to accurately predict the performance of these modulation schemes with a given level of the constellation distortion, as well as to determine the amount of input power to the saturation channel which minimizes the probability of modulation symbol error.

In this paper we present a 3D adaptive nonlinear filter, namely the 3D adaptive CPWLN, based on the Canonical Piece Wise-Linear Network with an LMS L-filter type of adaptation. This filter is used to equalize nonlinear channel effect and remove impulsive/or mixed impulsive and Additive White Gaussian noise from video sequences. First, motion compensation is performed by a robust estimator. Then, a 3-D CPWLN LMS L-filter is applied. The overall combination is able to adequately remove undesired effects of communication channel and noise. Computer simulations on real-world image sequences are included. The algorithm yields promising results in terms of both objective and subjective quality of the restored sequence.

An important area in visual communications is the restoration of image sequences degraded by channel and noise. Since a nonlinearity is commonly involved in image transmitting procedure, an adaptive nonlinear equalizer is required. In this paper we address this problem by proposing a 3D adaptive nonlinear filter, namely the 3D adaptive Volterra filter with an LMS type of adaptation algorithm. This adaptive filter is used for equalizing an unknown 2-D channel with some point-wise nonlinearity and restoring image sequences degraded by this channel. Prior to filtering, motion is estimated from the sequence and compensated for. For this purpose, a robust region-recursive Higher Order Statistics (HOS) based motion estimation method is employed. The overall combination is able to adequately remove undesired effects of communication channel and noise. The performance of this algorithm is examined using real image sequences demonstrated by experimental results.

A deterministic simulation method is investigated for rate 3/4 trellis-coded (TC) 16PSK, TC-16QAM and TC partially overlapped (PO) 12QAM schemes. The BER performance of these schemes are evaluated on realistic channels with the same transmisson parameters, and are compared with BER values obtained from a distance spectrum expression. The results of this study show that the BER values obtained by the deterministic simulation coincide well with those from the distance spectrum method, and that TC-16PSK is superior to both TC-16QAM and TC-PO-12QAM in terms of BER performance over linear and nonlinear channels. The BER degradation caused by a nonlinear amplifier and the BER difference between two mapping methods ( Gray code and natural binary code mapping) are also clarified.

This paper proposes a half-chip offset QPSK (Quadrature Phase Shift Keying) modulation CDMA (Code Division Multiple Access) scheme to allow the simple differential detection while realizing a compact spectrum in nonlinear channels for wireless LAN systems. The experimental results show the proposed scheme achieves excellent Pe (probability of error) performances in ACI (adjacent channel interference) and CCI (co-channel interference) environments. Moreover, by employing time diversity and high-coding-gain FEC (Forward Error Correction), the half-chip offset QPSK-CDMA scheme realizes an improvement of 3.0 dB (in terms of Eb/No at a Pe of 105) in Rician fading environments with a Doppler frequency fD of 10 Hz and a delay spread of 40 nsec.