Yong Up Lee

Analysis of quasi-ML multiuser detection of DS/CDMA systems in asynchronous channels

We consider the quasi-maximum-likelihood (quasi-ML) detectors of the reverse link system that uses antenna arrays in asynchronous channels when the channel vector is time-invariant and time-varying. A channel vector estimation method based on eigendecomposition for time-invariant channels and its adaptive version suitable for the time-varying channels are also proposed. It is shown that the proposed quasi-ML detector can be regarded as a beamformer followed by a decorrelating filter and that the proposed system performs better than the conventional decorrelator scheme. It is also observed that the performance gain of the proposed scheme over the conventional decorrelator system increases as the numbers of active users and antenna arrays increase.

Double-dwell serial-search PN code acquisition using a nonparametric detector in DS/CDMA systems

In this paper, we propose to use a nonparametric noncoherent detector for PN code acquisition in DS/CDMA systems. We compare two verification modes and show that type I performs better than type II. We also compare the type I double-dwell scheme using the proposed detector with that using the conventional detector. The PN code acquisition scheme with the proposed detector is robust and has better performance than that with the conventional detector when the estimation of the interference variance is not possible.

An analysis of DOA estimation method under a dispersive signal model

In direction of arrival estimation, the signal sources are usually assumed to be point sources. If the signal sources are dispersive, however, direction of arrival estimation methods based on the point source assumption may result in poor performance. In this paper, we consider direction of arrival estimation under a parametric dispersive signal modeling. An estimation method based on the well-known conditional maximum likelihood method in the parametric model are considered.

The DS/SSMA systems using trellis coding with asymmetric PSK signal constellation

Analyzes the performance of direct-sequence spread spectrum multiple access (DS/SSMA) systems using trellis coding with asymmetric phase shift keying (PSK) modulation. By designing the signal constellation to be asymmetric, the authors obtain a performance gain of DS/SSMA systems over the systems using the traditional symmetric signal constellation. Bit error probability analysis of the proposed system is carried out for some cases. A few examples are given to show the performance gain due to the asymmetry of the signal constellation.