Similarity based pattern recognition is concerned with the analysis of patterns that are specified in terms of object dissimilarity or proximity rather than ordinal values. For many types of data and measures, these dissimilarities are not Euclidean. This hinders the use of many machine-learning techniques. In this paper, we provide a means of correcting or rectifying the similarities so that the non-Euclidean artifacts are minimized. We consider the data to be embedded as points on a curved manifold and then evolve the manifold so as to increase its flatness. Our work uses the idea of Ricci flow on the constant curvature Riemannian manifold to modify the Gaussian curvatures on the edges of a graph representing the non-Euclidean data. We demonstrate the utility of our method on the standard ``Chicken pieces'' dataset and show that we can transform the non-Euclidean distances into Euclidean space.

This paper presents a coded multicarrier direct-sequence code-division multiple-access (DS-CDMA) system that, by the use of a minimum mean-squared-error receiver, achieves frequency diversity (instead of path diversity as in a conventional single-carrier RAKE DS-CDMA) and has the ability to suppress the intermodulation distortion and partially compensate for the signal distortion introduced by a nonlinear amplifier at the transmitter. A frequency-selective Rayleigh fading channel is decomposed into M frequency-nonselective channels, based on the channel coherence bandwidth. A rate 1/M convolutional code, after being interleaved, is used to modulate M different DS-CDMA waveforms. The new system is shown to effectively combat intermodulation distortion in the presence of multiple-access interference.

In this paper, we integrate the multicarrier signaling technique and the RAKE receiver to design a DS-CDMA system with the capability to increase the data rate, mitigate the effect of correlation among the various subcarriers, and suppress partial-band interference. In the proposed system, a data sequence is serial-to-parallel converted, and multicarrier DS-CDMA is used on each of the parallel data streams. The receiver provides a RAKE for each subcarrier, and the outputs of the RAKEs are combined by a maximal-ratio combiner. We employ a correlated subcarrier and frequency-selective fading channel model to derive the average probability of error of the system and compare the results with those of both a single carrier RAKE system and a multicarrier DS-CDMA system in a frequency selective Rayleigh fading channel with an exponential multipath intensity profile, when multiple access interference and partial-band interference are present.

This paper presents a coded multicarrier (MC) DS-CDMA system which, by the use of a linear convolutional code (CC) and minimum mean-squared error (MMSE) receiver, achieves frequency diversity instead of path diversity as in a conventional single carrier RAKE DS-CDMA, and has the ability to partially compensate for the distortion introduced by a nonlinear amplifier at the transmitter. A frequency selective Rayleigh fading channel is decomposed into M frequency non-selective channels, based on the channel coherence bandwidth. A rate 1/M convolutional code, after being interleaved, is used to modulate M different DS-CDMA waveforms. The new system is shown to effectively suppress multiple access interference in the presence of intermodulation distortion.

When user terminals powered by a finite battery source are used for wireless communications, energy constraints are likely to influence the design/choice of media access protocols. We analyze the energy efficiency of a multichannel wireless access protocol using a finite energy source in a mobile radio environment. The average number of correctly transmitted packets for a given amount of allocated energy is used as the appropriate energy efficiency metric. The mobile radio channel itself is characterized by a correlated Rayleigh fading process, whose memory parameters depend on the speed of the user terminal, the data rate, and the physics of the channel. We show that the protocol which recovers erroneous data packets through retransmission is more energy efficient at low channel correlations.