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With the rapid progress in telecommunications, more and more services are provided on the basis of broadband communications, such as video services and high-speed Internet. With worldwide fundamental construction of a backbone network based on optical fiber providing almost unlimited communications capability, the limited throughput of the subscriber loop becomes one of the most stringent bottlenecks.Compared to the capacity of the backbone network, which is measured by tens of gigabits per second, the throughput of the subscriber loop is much lower, only up to hundreds of megabits
per second for wired systems (including fixed wireless access). However, for mobile access the throughput is even lower, and depends on the mobility of the terminal. For example, the peak data rate is only 2 Mb/s for 3G systems.

Since there will be more and more need for mobile services, the poor throughput of mobile access not only limits user applications based on interconnection, but also wastes the capability of the backbone network. This case is quite similar to the traffic conditions shown in Fig. a, which is an image of an ultra-wide expressway with a few narrow entrances.

Since the little paths are rough,narrow, and crowded, the problems in Fig. a are:
Terminals are far away from the expressway, which will consume much power.
Too many cars converge into the same narrow paths.
Little paths converge several times before going into the expressway.
The expressway is used insufficiently, since few cars are running on it.

In telecommunications, the optical fiber network (expressway) is relatively much cheaper than the wireless spectrum (little paths), while the capability of the former is much greater than that of the later. As shown in Fig. b, besides the backbone expressway, there are some dedicated subexpressways used to provide direct entrance for distributed subscribers.The above example implies that the high-capacity wired network, being so cheap, can help us solve the problem of wireless access(too many users crowded in a very narrow bandwidth). The key issue is to provide each mobile user a direct or one-hop connection to an optical network.This structure also follows the trend in network evolution: the hierarchical or tree-like structure of traditional networks will be gradually flattened to simple single-layer ones.


The basic problem of wireless access is that the available spectrum is too limited compared to the almost unlimited service requirement, just like cars jammed in crowded narrow paths. Another basic problem is that there is great attenuation of energy. For example, the transmitter power may be 300 mW in order to transmit 2 Mb/s in a 2 GHz frequency band. Correspondingly, for a future system working on a 5 GHz band at a data rate of 100 Mb/s, we may need 30 W transmission with the same technique. This is impossible for a handset, considering the battery life and the radiation effect on the human body.


It seems that the only solution for the first problem is to explore the space resource. The cellular system is a successful example. With a cellular structure, the frequency can be reused as many times as needed. Also, the cellular structure reduces the maximum distance from the terminal to the nearest base station, which is also a clue to solve the second problem.

However, in a traditional cellular system, when the cell size gets smaller, capacity can be increased linearly with cell density. But this is based on the assumption of a large path loss exponent. Pathloss is the amount of loss introduced by the propagation environment between transmitter and receiver. When the cell size is small enough, the exponent gets small, which may be approximately 2; thus, the interference may be so large that the system may not work, as seen in Fig. 2.The above phenomenon indicates that the system capacity cannot be increased anymore when the density of cells reaches a certain level.

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Post: #3
the file we put on a file-hodting sute was accidentally deleted. This link has a pdf:
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please send me the full abstrac with word document and ppt to my email id within today as it is very urgent
Post: #5
This article is presented by:Prasenjit Pal
Electronics & Communication Engineering Department
Asansol Engineering College

The visible optical carrier waves or light has been commonly used for communication purpose for many years. Alexander Graham Bell transmitted a speech information using a light beam for the first time in 1880. Just after four years of the invention of the telephone Bell proposed his photophone which was capable of providing a speech transmission over a distance of 200m. In the year 1910 Hondros and Debye carried out a theoretical study and in 1920 Schriever reported an experimental work. Although in the early part of twentieth century optical communication was going through some research work but it was being used only in the low capacity communication links due to severe affect of disturbances in the atmosphere and lack of suitable optical sources. However, low frequency (longer wavelength) electromagnetic waves like radio and microwaves proved to be much more useful for information transfer in atmosphere, being far less affected by the atmospheric disturbances. The relative frequencies and their corresponding wavelengths can be known from the electromagnetic spectrum and it is understandable that optical frequencies offer an increase in the potential usable bandwidth by a factor of around 10000 over high frequency microwave transmission. With the LASER coming into the picture the research interest of optical communication got a stimulation. A powerful coherent light beam together with the possibility of modulation at high frequencies was the key feature of LASER. Kao and Hockham proposed the transmission of information via dielectric waveguides or optical fiber cables fabricated from glass almost simultaneously in 1966. In the earlier stage optical fibers exhibited very high attenuation (almost 1000 dB/km)which was incomparable with coaxial cables having attenuation of around 5 to 10dB/km. Nevertheless, within ten years optical fiber losses were reduced to below 5dB/km and suitable low loss jointing techniques were perfected as well. Parallely with the development of the optical fibers other essential optical components like semiconductor optical sources (i.e. injection LASERs and LEDs) and detectors (i.e. photodiodes and phototransistors) were also going through rigorous research process. Primarily the semiconductor LASERs exhibited very short lifetime of at most a few hours but by 1973 and 1977 lifetimes greater than 1000 hr and 7000 hr respectively were obtained through advanced device structure.
The first generation optical fiber links operated at around 850 nm range. Existing GaAs based optical sources, silicon photo detectors, and multimode fibers were used in these links and quiet understandably they suffered from intermodal dispersion and fiber losses. With the advent of optical sources and photo detectors capable of operating at 1300 nm, a shift in transmission wavelength from 850nm to 1300nm was possible which inturn resulted in a substantial increase in the repeaterless transmission distance for long haul telephone trunks. Systems operating at 1550nm provided lowest attenuation and these links routinely carry traffic at around 2.5Gb/s over 90 km repeaterless distance. The introduction of optical amplifiers like Erbium-doped fiber amplifiers (EDFA) and Praseodymium-doped fiber amplifiers (PDFA) had a major thrust to fiber transmission capacity. The use of Wavelength Division Multiplexing along with EDFA proved to be a real boost in fiber capacity. Hence developments in fiber technology have been carried out rapidly over recent years. Glass material for even longer wavelength operation in the mid-infrared (2000 to 5000nm) and far-infrared (8000 to 12000nm) regions have been developed. Furthermore, the implementation of active optoelectronic devices and associated fiber components (i.e. splices, connectors, couplers etc.) has also accelerated ahead with such speed that optical fiber communication technology would seem to have reached a stage of maturity within its developmental path.

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Please send me full report and absract on DISTRIBUED WIRELESS COMMUNICATION
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please send me the ppt of this topic urgently
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pls send me abstract on wireless plsssssssssss
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to get information about the topic"DISTRIBUTED WIRELESS COMMUNICATION SYSTEM" please refer link bellow

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