NASHRIYYAH -I MUHANDISI -I BARQ VA MUHANDISI -I KAMPYUTAR -I IRAN, A- MUHANDISI -I BARQ
Year:2004 | Volume:2 | Issue:1|Papers Count:6

For location updating of mobile users, two compression algorithms, namely, LZ78 and proposed compression algorithm (modified LZ78) are introduced in this paper to be used in PCS networks. Some problems related to using these algorithm are the usage of memory of dictionary in mobile users and HLR data base as well as the ambiguity about the last location of mobile users due to delay in location updating caused by the compression algorithm. The advantage of these algorithms is reduction at the number of location updating for a mobile user. With some modifications in the LZ78 algorithm, its problems in implementation are reduced and its usage for PCS networks is enhanced. These changes result from combining this algorithm with distance based location updating algorithm and sending symbols corresponding to some limited neighborhoods identity instead of cell number by compression algorithm For comparison between LZ78 and proposed modified algorithm, we use simulation technique. The simulation program has two structures for PCS network, namely, square cells and hexagon cell networks. For mobile users, we considered two movement patterns: one is directional and the other is omnidirectional movement pattern. The outputs of the simulation program are the number of location updating, the maximum ambiguity of user location and size of dictionary for compression algorithms. Comparing the two algorithms by simulation, we observe that in the modified LZ78 algorithm the parameters of location updating number, maximum user ambiguity and size of dictionary are lower than those in the LZ78 algorithm. At the end of the article, cost of location management of mobile user versus call to mobility ratio (the average number of call toward user to the average number of its movement) is calculated. By comparing location management for LZ78 algorithm, modified LZ78 and distance based location updating algorithm, we observe that the cost of location management is reduced for modified LZ78 compression algorithm.

In order to guaranty the quality of real time services on IP based networks, robust survivability with fast fault recovery and path restoration are the main goals. Many recent restoration methods spend much time for fault recovery and path restoration.MPLS based networks with connection –oriented ability can guaranty QoS by useful restoration method in short time.In this paper we proposed a new restoration mechanism base on pre-assigned end to end protection path .We apply self similar and Poisson process separately for modeling the traffic arrivals time.The comparative analysis between two models reveals the reliability growth gained through applying the proposed algorithm.

Using some simplifying assumptions in a separate absorption and multiplication avalanche photodiode (SAM-APD), in this paper we develop a circuit model. Then, using this circuit model, we calculate the gain and the quantum efficiency of the device. To examine the accuracy of the device, we compare the results obtained from the model with the experimental results. A fairly good correspondence between the model an the experimental results, shows that this model is capable of predicting the device behavior, while varying different parameters such as applied bias, device size, and hence the light wavelength.

In this paper a new kind of coupled lines called circular symmetric coupled microstrip transmission lines is introduced. At first the capacitance C and inductance L matrices of this kind of microstrip lines are determined by solving the laplace’s equation using fourier series method. Then by some examples the capacitance C and inductance L matrices of this kind of microstrip lines are discussed.

One of the most important topics in designing the microwave circuits is the topic of noise and “noise parameter extraction of the circuits”. In this paper a new method is introduced for noise parameter extraction. The results of the new method are then compared with the results of one of the commonly used methods using the measured noise parameters of a microwave transistor

The frequency multipliers are widely used in microwave and wireless transceivers. This paper introduces an accurate technique to model and to design a microwave frequency multiplier using HEMT transistors. Based upon this technique, a frequency doubler in C band and a frequency Tripler in Ku band are designed and implemented. The excellent agreement between simulation and measurement results shows the validity and the accuracy of the technique.