Showing 3 results for Ds-Cdma
V. Vakil, H. Aghaeinia,
Volume 5, Issue 1 (3-2009)
Abstract
The throughput enhancement of Space-Time Spreading (STS)-based Multicarrier
Direct Sequence Code Division Multiple Access (MC DS-CDMA) system is investigated in
this paper. Variable Spreading Factor (VSF) is utilized to improve the data throughput of
the system. In this contribution, an analytical approach is proposed to compute a new
expression for the Bit Error Rate (BER) performance of the STS-based MC DS-CDMA
system against pre-dispreading Signal-to-Noise Ratio (SNR) for different values of
spreading factor (SF). The other contribution of the paper is deriving a new closed form
expression for computing the throughput enhancement and the BER performance of the
VSF STS-based MC DS-CDMA system over Rayleigh fading channel. It is demonstrated
that using VSF method in STS-based MC DS-CDMA system improves the throughput of
the system by keeping the BER performance at the target level.
M. Dosaranian Moghadam, H. Bakhshi, G. Dadashzadeh,
Volume 6, Issue 3 (9-2010)
Abstract
In this paper, we propose smart step closed-loop power control (SSPC)
algorithm and base station assignment based on minimizing the transmitter power (BSAMTP)
technique in a direct sequence-code division multiple access (DS-CDMA) receiver in
the presence of frequency-selective Rayleigh fading. This receiver consists of three stages.
In the first stage, with conjugate gradient (CG) adaptive beamforming algorithm, the
desired users’ signal in an arbitrary path is passed and the inter-path interference is
canceled in other paths in each RAKE finger. Also in this stage, the multiple access
interference (MAI) from other users is reduced. Thus, the matched filter (MF) can be used
for the MAI reduction in each RAKE finger in the second stage. Also in the third stage, the
output signals from the matched filters are combined according to the conventional
maximal ratio combining (MRC) principle and then are fed into the decision circuit of the
desired user. The simulation results indicate that the SSPC algorithm and the BSA-MTP
technique can significantly improve the network bit error rate (BER) in comparison with
other algorithms. Also, we observe that significant savings in total transmit power (TTP)
are possible with our proposed methods.
S. Shaerbaf, S. A. R. Seyedin,
Volume 7, Issue 3 (9-2011)
Abstract
Chaos based communications have drawn increasing attention over the past years. Chaotic signals are derived from non-linear dynamic systems. They are aperiodic, broadband and deterministic signals that appear random in the time domain. Because of these properties, chaotic signals have been proposed to generate spreading sequences for wide-band secure communication recently. Like conventional DS-CDMA systems, chaos-based CDMA systems suffer from multi-user interference (MUI) due to other users transmitting in the cell. In this paper, we propose a novel method based on radial basis function (RBF) for both blind and non-blind multiuser detection in chaos-based DS-CDMA systems. We also propose a new method for optimizing generation of binary chaotic sequences using Genetic Algorithm. Simulation results show that our proposed nonlinear receiver with optimized chaotic sequences outperforms in comparison to other conventional detectors such as a single-user detector, decorrelating detector and minimum mean square error detector, particularly for under-loaded CDMA condition, which the number of active users is less than processing gain.
