Mehmet V. Tazebay

Adaptive subband transforms in time-frequency excisers for DSSS communications systems

A smart time-frequency exciser for DS-SS communications is proposed in this correspondence. This technique utilizes the concept of uncertainty in time-frequency analysis of signals. It brings the novel concept of domain switchable signal processing. Hence, the adaptive time-frequency (ATF) exciser has the capability of deciding the domain of the interference cancellation. Additionally, adaptive subband transforms are utilized for frequency domain excision. For time-domain excision, the ATF excision algorithm utilizes a sliding time window to reject the nonstationary, pulsed (time-localized) interference. It is shown that the proposed adaptive time-frequency exciser-based DS-SS communications receiver drastically outperforms the existing systems. Its performance is nearly optimal and very robust to the inter and intradomain variations of the undesired signal.

Wavelet and subband transforms: fundamentals and communication applications

Subband and wavelet transforms have been a subject of great interest, especially in the fields of signal processing and applied mathematics. This article presents a tutorial on this subject, emphasizing the fundamentals and the reason for its success, importance, and potential. Subband and wavelet transform applications in communications are also reviewed. These application areas include interference excision, spread spectrum codes based on subband transform bases, CDMA, and discrete multitone transceivers.

A new look at digital orthogonal transmultiplexers for CDMA communications

Orthogonal transmultiplexers have been successfully utilized for multiuser communications. They are of the FDMA type in their most common version. The transmultiplexers using frequency selective PR-QMFs as their user codes were reported in the literature. This approach conflicts with the requirements of a CDMA communications system. We introduce novel spread spectrum PR-QMF codes, wherein the orthogonality is distributed over both time and frequency domains. It is shown that the proposed multivalued spread spectrum PR-QMF codes with minimized auto and cross-correlation properties outperform the conventional binary Gold codes in CDMA communication scenarios considered in the article.

A performance analysis of interference excision techniques in direct sequence spread spectrum communications

It is well known that a proper interference exciser enhances the performance of a spread spectrum communications system. There have been several competing excision techniques reported in the literature. This article presents a performance evaluation of those excision techniques via the analytical and computer simulation tools. It is found that the analytical performance tools presented match up with the computer simulation results. It is also shown that a previously proposed adaptive time-frequency exciser consistently outperforms the existing interference excision techniques in the literature.

A smart time-frequency exciser for spread spectrum communications

A smart adaptive time-frequency (ATF) excision algorithm is proposed to perform interference suppression in spread spectrum communications. The ATF exciser has the intelligence of deciding the domain of the excision. Additionally, adaptive subband transforms are utilized for frequency domain excision in order to track the spectral variations of the incoming signal. This adaptive transform approach brings significant performance improvements in spectral resolution. Bit error rate (EER) performance of the novel ATF exciser-based direct sequence spread spectrum (DSSS) system receiver is compared with other existing transform domain-based DSSS receivers. Time localized or frequency-localized interferer types and additive white Gaussian noise (AWGN) channels are considered in the study. In all cases, the smart ATF exciser-based DSSS receiver drastically outperforms the existing competitors. Its robust performance against the variations of the interferers is verified.

Progressive optimality in hierarchical filter banks

The concept of progressive optimization is proposed for the design of hierarchical subband transforms. The time and frequency properties of the product filters in subband trees are discussed and evaluated. It is shown that the performance improvements in image coding are possible by using different PR-QMF banks at different nodes of a subband tree.<<ETX>>

Adaptive time-frequency analysis of autonomic nervous system

Spectral analysis of heart rate variability (HRV) provides a noninvasive estimate of sympathetic and parasympathetic influences on heart rate. The Time-Frequency analysis was utilized to expand the concept of spectral analysis of HRV to describe changes in vagal tone as a function of time. A new adaptive methodology is now proposed to uncover the region of true parasympathetic activity. It is known that parasympathetic activity is highly correlated with the respiration frequency. This technique traces the respiration frequency and extracts the corresponding parasympathetic activity from the HRV signal by adaptive filtering.

Spread spectrum PR-QMF transmultiplexer codes for CDMA communications

Orthogonal transmultiplexers have been successfully utilized for multiple access communications. They are of FDMA type in their most common version. The frequency selective PR-QMFs were used in transmultiplexers for CDMA communications reported in the literature. This conflicts with the fundamentals of CDMA theory. We introduce novel spread spectrum PR-QMF codes. It is shown that the spread spectrum PR-QMF codes with minimized auto- and cross-correlation properties drastically outperform the conventional Gold (1967) codes in CDMA communication scenarios considered.

Performance analysis of direct sequence spread spectrum communications system employing interference excision

It is well known that a proper interference exciser enhances the performance of a spread spectrum communications system. There have been several competing excision techniques reported in the literature. This paper presents a performance evaluation of those excision techniques via the analytical and computer simulation tools. It is found that the analytical performance tools presented are in match with the computer simulation results. It is also shown that a previously proposed adaptive time-frequency exciser consistently outperforms the existing interference excision techniques in the literature.

A sliding and variable window based multitone excision for digital audio broadcasting

This study considers the transmission of digital signals in-band on-channel for application in digital audio broadcasting (DAB). In the FM-channel used for analog transmission, two different DAB scenarios are simulated. In the first approach, the digital data is spread in form of a weak direct sequence spread spectrum (DSSS) signal underneath the FM. Since the FM signal is a multitone interference to the DSSS signal, it is to be excised. In this paper, a new adaptive frequency domain technique is proposed for excising multitone interference in DAB, The second scenario performs an amplitude modulation on the FM signal. This technique assures no interference in-between the new, digital, and the already existing analog service,.