Abstract: Multi-user interference (MUI) is the main reason of system deterioration in the Spectral Amplitude Coding Optical Code Division Multiple Access (SAC-OCDMA) system. MUI increases with the number of simultaneous users, resulting into higher probability bit rate and limits the maximum number of simultaneous users. On the other hand, Phase induced intensity noise (PIIN) problem which is originated from spontaneous emission of broad band source from MUI severely limits the system performance should be addressed as well. Since the MUI is caused by the interference of simultaneous users, reducing the MUI value as small as possible is desirable. In this paper, an extensive study for the system performance specified by MUI and PIIN reducing is examined. Vectors Combinatorial (VC) codes families are adopted as a signature sequence for the performance analysis and a comparison with reported codes is performed. The results show that, when the received power increases, the PIIN noise for all the codes increases linearly. The results also show that the effect of PIIN can be minimized by increasing the code weight leads to preserve adequate signal to noise ratio over bit error probability. A comparison study between the proposed code and the existing codes such as Modified frequency hopping (MFH), Modified Quadratic- Congruence (MQC) has been carried out.
Abstract: In this paper, with the purpose of further reducing the
complexity of the system, while keeping its temporal and spatial
focusing performance, we investigate the possibility of using optimal
one bit time reversal (TR) system for impulse radio ultra wideband
multi-user wireless communications. The results show that, by optimally
selecting the number of used taps in the pre-filter the optimal
one bit TR system can outperform the full one bit TR system. In
some cases, the temporal and spatial focusing performance of the
optimal one bit TR system appears to be compatible with that of the
original TR system. This is a significant result as the overhead cost
is much lower than it is required in the original TR system.