Wavelet packets have been found a promising candidate for user signature waveforms in code division multiple access communication systems due to their good orthogonality property. In this paper we investigate the use of wavelet packets in multicarrier CDMA. In conventional multicarrier CDMA systems, the multi channel signals are modulated on sub carriers of sinusoid waveforms, using FFT to achieve fast computation. To combat multipath channel effect, a guard interval is inserted between consecutive data symbols. On the other hand, wavelet packet waveforms have the property of localization in both time and frequency domains. This property enables the time domain diversity of the multi carrier signal so that the need for guard intervals is eliminated by time domain diversity combining. Simulations are shown to compare the performance of the wavelet packet receiver design with the DFT based multi carrier CDMA system.

In this paper, we propose a new nonstationary jammer suppression technique for DS/SS communications. This technique is based on combined operations of bilinear signal synthesis and projections. The time-frequency distributions (TFDs) is used to define the jammer time-frequency (t-f) signature. Multi-sensor array at the receiver allows both the spatial and temporal signatures of the signal arrivals to be utilized. To estimate the waveform of a jammer, a mask is constructed and applied such that the masked t-f region captures the jammer energy, but leaves out most of the DS/SS signals. The jammer signals are then synthesized from the masked TFDs that can be removed from the received signal by orthogonal projection.

One significant difference between CDMA systems and FDMA/TDMA systems is that the number of users supported in a CDMA system is not hard-limited by the number of frequency bands or time slots. Whenever a new user is added to a CDMA system, the existing users will suffer a slightly higher interference level. The interference level highly depends on the orthogonality of user waveforms. We present an algorithm to construct a set of wavelet packet based user waveforms for CDMA systems. This algorithm provides more signature waveforms than previously proposed wavelet packet based waveform division systems. The basic waveform set is constructed utilizing double orthogonality based on wavelet packets and binary Walsh codes. This double orthogonality produces auto- and cross-correlations that are much better than the conventional wavelet packet sets and are comparable to the pseudo random binary codes. Under system overload, the waveforms introduce a tolerable interference level to the users.

This paper presents the performance analysis of the interference excision techniques in direct sequence spread spectrum (DSSS) communications using orthogonal subspace projections. It is shown that this technique is sensitive to the errors in the instantaneous frequency (IF) estimate of the interference over segments of the bit period. This paper discusses the effect of two different types of errors on the receiver SINR and compares the performance of the block-wise processing to the single block projection approach.

A new method is introduced for interference excision in spread-spectrum communications that is conducive to software-radio applications. Spare processing capacity in the receiver permits the use of time-frequency techniques to synthesize a nonstationary interference from the time-frequency domain using least squares methods. The synthesized signal is then subtracted from the incoming data in the time domain, leading to jammer removal and increased signal-to-interference-and-noise ratio at the input of the correlator. The paper focuses on jammers with constant modulus that are uniquely described by their instantaneous frequency characteristics. With this a priori knowledge, the jammer signal amplitude is restored by projecting each sample of the synthesized signal to a circle representing its constant modulus. With the phase matching provided by the least squares synthesis method and amplitude matching underlying the projection operation, a significant improvement in receiver performance/bit-error rates is achieved over the case where no projection is performed. Software-radio aspects including computational complexity and processing modes are also discussed.

A new method is introduced for interference excision in spread spectrum communications. Time-frequency synthesis techniques are used to synthesize the nonstationary jammer from the time-frequency domain using least-squares methods. The synthesized jammer is then subtracted from the incoming data in the time domain, leading to increased signal to interference ratio at the input of the correlator. The paper focuses on jammers with constant modulus where the jamming signal is a polynomial phase. With this a priori knowledge, the jammer signal amplitude is restored by projecting each sample of the synthesized signal to a circle representing its constant modulus. With the phase matching provided by the least-squares synthesis method and amplitude matching underlying the projection operation, the paper shows a significant improvement in receiver performance/bit error rates over the case where no projection is performed.