ScholarBank@NUShttps://scholarbank.nus.edu.sgThe DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material.Tue, 08 Oct 2024 06:57:24 GMT2024-10-08T06:57:24Z5051- Linear parallel interference cancellation in long-code CDMA multiuser detectionhttps://scholarbank.nus.edu.sg/handle/10635/112261Title: Linear parallel interference cancellation in long-code CDMA multiuser detection
Authors: Guo, D.; Rasmussen, L.K.; Lim, T.J.
Abstract: Parallel interference cancellation (PIC) is a promising detection technique for code division multiple access (CDMA) systems. It has previously been shown that the weighted multistage PIC can be seen as an implementation of the steepest descent algorithm used to minimize the mean squared error (MSE). Following this interpretation, a unique set of weights, based on the eigenvalues of the correlation matrix, was found to lead to the minimum achievable MSE for a given number of stages in a short-code system. In this paper, we introduce a method for finding an appropriate set of time-invariant weights for systems using long codes. The weights are dependent on moments of the eigenvalues of the correlation matrix, exact expressions of which can be derived. This set of weights is optimal in the sense that it minimizes the ensemble averaged MSE over all code-sets. The loss incurred by averaging rather than using the optimal, time-varying weights is practically negligible, since the eigenvalues of sample correlation matrices are tightly clustered in most cases of interest. The complexity required for computing the weights increases linearly with the number of users but is independent of the processing gain, hence on-line weight updating is possible in a dynamic system. Simulation results show that a few stages is usually sufficient for near-MMSE performance.
Wed, 01 Dec 1999 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1122611999-12-01T00:00:00Z
- Performance evaluation of an OFDM-based LMDS using measured channel modelshttps://scholarbank.nus.edu.sg/handle/10635/112363Title: Performance evaluation of an OFDM-based LMDS using measured channel models
Authors: Ravi, K.V.; Guo, D.; Cheah, K.L.
Abstract: In this paper, the use of orthogonal frequency division multiplexing (OFDM) for LMDS is proposed and investigated. The studies here utilise statistical channel models derived from our earlier field measurements in Singapore and present more realistic assessment of the proposed system performance. The simulation model considers RS/CC coding, convolutional interleaving and multilevel QPSK/QAM signaling. Robust performance is demonstrated under realistic SNRs for a wide range of system conditions. Recommendations on the choice of a suitable set of OFDM parameters like FFT length and cyclic prefix are presented. The performance of the proposed scheme is also compared with that of an LMS equaliser-based system and shown to be superior under similar channel conditions.
Sat, 01 Jan 2000 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1123632000-01-01T00:00:00Z
- MMSE-based linear parallel interference cancellation in CDMAhttps://scholarbank.nus.edu.sg/handle/10635/112348Title: MMSE-based linear parallel interference cancellation in CDMA
Authors: Guo, Dongning; Rasmussen, Lars K.; Sun, Sumei; Lim, Teng J.; Cheah, Christopher
Abstract: In this paper we mathematically describe the linear parallel interference canceller (PIC) using matrix algebra. It is shown that the linear PIC, whether conventional or weighted, can be seen as a linear matrix filter applied directly to the received chip-matched filtered signal vector. It is then possible to get an analytical expression for the exact bit error rate and to derive necessary conditions on the eigenvalues of the code correlation matrix and the weighting factors to ensure convergence. The close relationship between the steepest descent method for minimizing the mean squared error (MSE) and linear PIC is demonstrated and a modified PIC structure is suggested which converges to the MMSE detector rather than the decorrelator. Following the principles of the steepest descent method techniques are devised for optimizing the choice of weighting factors with respect to the mean squared error. It is shown that only K (the number of users) PIC stages are required for the equivalent matrix filter to be identical to the MMSE filter. For fewer stages, m
Thu, 01 Jan 1998 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1123481998-01-01T00:00:00Z
- A matrix-algebraic approach to linear parallel interference cancellation in CDMAhttps://scholarbank.nus.edu.sg/handle/10635/112207Title: A matrix-algebraic approach to linear parallel interference cancellation in CDMA
Authors: Guo, D.; Rasmussen, L.K.; Sun, S.; Lim, T.J.
Abstract: In this paper, linear parallel interference cancellation (PIC) schemes are described and analyzed using matrix algebra. It is shown that the linear PIC, whether conventional or weighted, can be seen as a linear matrix filter applied directly to the chip-matched filtered received signal vector. An expression for the exact bit-error rate (BER) is obtained, and conditions on the eigenvalues of the code correlation matrix and the weighting factors to ensure convergence are derived. The close relationship between the linear multistage PIC and the steepest descent method (SDM) for minimizing the mean squared error (MSE) is demonstrated. A modified weighted PIC structure that resembles the SDM is suggested which approaches the minimum MSE (MMSE) detector rather than the decorrelator. It is shown that for a K -user system, only K PIC stages are required for the equivalent matrix filter to be identical to the the MMSE filter. For fewer stages, techniques are devised for optimizing the choice of weights with respect to the MSE. One unique optimal choice of weights is found, which will lead to the minimum achievable MSE at the final stage. Simulation results show that a few stages are sufficient for near-MMSE performance. © 2000 IEEE.
Sat, 01 Jan 2000 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1122072000-01-01T00:00:00Z
- Aspects on linear parallel interference cancellation in CDMAhttps://scholarbank.nus.edu.sg/handle/10635/112314Title: Aspects on linear parallel interference cancellation in CDMA
Authors: Rasmussen, L.K.; Guo, D.; Lim, T.J.; Ma, Y.
Abstract: In this paper we devise a matrix-algebraic approach to analysing linear parallel interference cancellation. We show that linear parallel interference cancellation schemes correspond to linear matrix filtering. © 1998 IEEE.
Thu, 01 Jan 1998 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1123141998-01-01T00:00:00Z