In the multiuser systems, after signal is received in the antenna, users will be detected by complicated processing of signals. Thus, not to waste the processing power, we prefer the signal convey information on its whole time. Meanwhile, we know that the transmitted signals do not contain information all the time. The Internet traffic is non-real time traffic and owns a statistical behavior. We have utilized the packet payload information in this paper and tried to enhance the capacity through a new view on the traffic model by a new Traffic Activity Factor (TAF). In line with that in this paper we used two methods: we proved a theorem indicating TAF effect on the capacity and also we used a signal to noise relation with TAF parameter. We used the popular traffic services such as www, ftp, email, telnet in the multiuser systems. Both methods proved our vision.

In this paper we present an in-depth review on the trends and the directions taken by the researchers worldwide in Optical Code Division Multiple Access (OCDMA) systems. We highlight those trends and features that are believed to be essential to the successful introduction of various OCDMA techniques in communication. Systems and data networks in near future. In particular we begin by giving a comprehensive review on the constructions of optical orthogonal codes (OOC). In our system study we first focus and discuss on various OCDMA techniques such as 1-D, 2-D and spectrally-encoded ultra short light pulse CDMA, and discuss their pros and cons. A comprehensive discussion takes place on all important aspects of each OCDMA technique. In particular, we elaborate on enabling technologies that are needed prior to full scale consideration of OCDMA in communication systems. We extend our discussion to various data networks, including fiber-based and wireless to indicate the directions and the applications that OCDMA systems are considered for. It is believed that OCDMA once fully developed and matured will be an inseparable part of advanced optical communication systems and networks due to its various desirable features and functionalities, in not so distant future.

In this paper, two multiple access methods in time and code domains are compared for Additive White Gaussian Noise (AWGN) channels. Time Division Multiple Access (TDMA) has been used for many years and its features are well-known. Characteristics of Code Division Multiple Access (CDMA) and its advantages over TDMA are studied in this paper. The burstiness nature of voice traffic and unequal bit transmission time in TDMA and CDMA are used to compare the performance of the two techniques. Delay, throughput and packet loss, as performance parameters, are evaluated and computed for data and voice traffics. Capability of CDMA in accommodating sources with different bit rates is also considered. The results represent a noticeable improvement in the performance of CDMA over TDMA when features of the spread spectrum techniques are taken into consideration.

Multiple access interference and near-far effect cause the performance of the conventional single user detector in DS/CDMA systems to degrade. Due to high complexity of the optimum multiuser detector, suboptimal multiuser detectors with less complexity and reasonable performance have received considerable attention. In this paper, we analyze and examine the performance of multilayer perceptron neural networks using back-propagation algorithm as multiuser detectors of CDMA signals in A WGN and multipath fading channels. Our results show significant improvement over the previous research. We compare the performance of neural network with the other detectors used in CDMA system. We also apply different neural networks and criterions such as the decision based, fuzzy decision, discriminative learning, minimum classification, and cross entropy neural nets and compare their performance. Further, we propose modified decision based network which improves the performance of decision based network

The capacity and the interference statistics of the sectors of the shaped W-CDMA cell are studied for the general form of microcell (Cigar-shaped, T-shaped and Crossshaped). A model of 5 cells is used to analyze the uplink, which limits the capacity. The cells are assumed to exist in rural zones. Results that show the capacity and the interference statistics of the cell are given for different breakpoint distances, different propagation exponent and different antenna side lobe levels when the microcell is of cigar-shaped form.

Cell planning is a complex problem. In this project we take advantage of Genetic Algorithms to find the optimum location of a cellular network base station, and to optimally determine other parameters such as power, height and tilt of each base station antenna, as well.The main goal is to maximize the network coverage and simultaneously to minimize the downlink interference in the Azadshahr region of Mashhad. In order to study the performance of the proposed method in a realistic way, the Urban Signal Propagation Simulator computer software (USPS) is used. The results indicate that our method has a very good performance in real situations.

This paper presents a multiobjective power control algorithm that updates the transmitted power based on local information. The proposed algorithm is expanded by using multiobjective optimization schemes. The objectives to be optimized in this paper are determined so as to reduce the SINR fluctuations as well as maintaining the SINR to an acceptable level with minimizing an average transmitted power. The convergence properties of the proposed algorithm are studied theoretically and with numerical simulations. The results indicate that the algorithm converges more rapidly and has lower average transmitted power than other existing algorithms. The current study also suggests a practical version of the proposed algorithm and compares it to the existing totally distributed bang-bang power control (B-BPC) or fixed step power control (FSPC) and multiobjective totally distributed power control (MOTDPC) algorithms. Numerical results show that the proposed algorithm is potentially much more efficient in terms of convergence speed and average consumption power than the other two algorithms.