This letter proposes an entropy-gradient adaptive feedback filter specially derived for the blind decision feedback equalizer with a self-optimized configuration. Using software simulations, the parametric nonlinearity of the feedback filter is aligned through two operation modes—blind acquisition and soft transition—to respond with a maximum entropy signal. As a result, a simple stochastic gradient algorithm is obtained, and it can be easily optimized for an applied signal constellation.

In this paper, uplink time division duplex (TDD) multi-carrier code-division multiple-access (MC-CDMA) systems applying pre-equalization to combat channel impairments are considered. Especially, the performance degradation caused by the Doppler induced frequency offsets among the different mobile users is analyzed in detail. Based on this analysis different frequency interleaving schemes are proposed and their potential to reduce the performance degradation is investigated. It turns out, that a frequency interleaver which is allowed to skip a few, well-defined subcarriers is capable of reducing the influence of Doppler induced frequency offsets significantly causing a very little loss in bandwidth efficiency.

In this paper the influence of the channel estimation error on the performance of the closed loop Tx diversity algorithms for WCDMA is studied for a high number of Tx antennas. The analysed algorithms are generalised closed loop Tx diversity, all-antenna Tx diversity and one-antenna selection Tx diversity. It was shown that generalised closed loop Tx diversity algorithm is more robust to channel estimation errors that all-antenna Tx diversity algorithm. This is valid for both uncorrelated fading and for correlated fading between Tx antennas. The one-antenna selection Tx diversity algorithm is also robust to the channel estimation errors, but its performance is worse than that of generalised closed loop Tx diversity algorithm.

A new method of pulse compression polyphase code synthesis based on the aperiodic autocorrelation function properties and the assumption of coherent processing in the radar receiver is presented. Properties of the proposed code, including spectrum, ambiguity function, precompression bandlimiting effects, and the noise/clutter influence are analyzed. The main features of the synthesized code are the absence of sidelobes in the compressed pulse and its tolerance of precompression bandlimiting limitations. A comparison to the known classes of pulse compression does is made.>

A direct-sequence spread-spectrum (DSSS) receiver using both decision feedback (DFB) and two-sided transversal filters for combatting narrowband interference (NBI) is proposed. The receiver is made up of two branches. In the first branch, the conventional demodulator is followed by a DFB filter, while in the second, auxiliary branch, a demodulator with the carrier in quadrature is followed by a two-sided adaptive transversal (AT) filter. Performance of this receiver was analyzed on the basis of the calculated mean-square error and the probability of error at the output of the receiver. Special attention was paid to the effects caused by the propagation of errors in the DFB filter. The results obtained show that NBI rejection is fairly high and practically does not depend upon the difference of frequencies of the desired and interfering carriers or upon the interfering carrier level.>

A new proposed robust FM demodulator (RFMD) is a simplified version of the recently reported demodulator (FMD) [1] which improves FM system interference immunity. The RFMD is applied to combat the adjacent channel interference and its improvement factor is only negligibly smaller than that of the FMD.

As a result of investigation of interference into FM systems, a new algorithm for the process of demodulation is proposed. When compared to the method using the conventional limiter-discriminator, it offers better immunity against the baseband interference noise. Desired signal processing is performed by the functional devices added to the conventional limiter-discriminator in such a way that this new demodulator can be optimized in the sense of the minimum baseband interference noise. The statistics of the wanted and interfering signals must be known. Several examples involving interference problems in FDM-FM radio-relay systems carrying multichannel telephone signals are elaborated to illustrate the performances of the proposed demodulator. FDM-FM, PSK, or FSK systems are considered the cause of the interference. The noise power ratio (NPR) at the output of the conventional limiter-discriminator and the improvement factor offered by the new demodulator, obtained on digital computer, are presented versus baseband frequency in the form of diagrams. Different IF filters in FDM-FM receiver and transmit filters in the interfering systems are taken into account. The improvement offered by the proposed demodulator is of such a degree that some of the important restrictions in planning different radio systems could be relaxed.