Wireless LAN QOS Bandwidth Computer Science Essay

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Providing an access network which is distinguished by high bandwidth requirements capable of providing excellent levels in the quality of service (QoS) to train passengers that offers a diverse spectrum of multimedia services that include video on demand, online gaming, voice over IP etc is needed. Assessing the required bandwidth needed to ensure a quality of service to the commuters is indeed a challenge for telecom operators. In the present scenario, the usage of cellular and satellite technologies cannot be regarded as the right solution since their limited bandwidth and improper delay are major constraints. Hence we propose a cellular wireless network all through the length of rail tracks. However, an important limitation for fast network users such as the train passengers with the majority of cellular networks is that the passengers encounter repeated handovers whilst moving from one base station (BS) to the other which results in numerous packet losses that greatly decrease the bandwidth. To resolve this shortcoming, an optical access network using Radio-over Fiber (RoF) can be fed to the base stations that are installed all along the rail tracks and this can be termed as the "moving cell" concept. This is a part of FAMOUS (Fast moving users) architecture which provides broadband connection to moving users. This new network architecture must be encouraged and the disadvantages of the current system would be addressed. The optical access network and the moving cell concept will be discussed correspondingly. The simulation results which reveal the exact working of the moving cell concept are shown. This is the first optical switching architecture used to understand the the moving cells in the optical realm.

In the broadband communication network that includes voice combining, data, video, multimedia services and any value added services, the wireless coverage of end user both indoors and outdoors becomes an important part. To provide integrated broadband services, these systems need to offer high capacities to transmit data which is way higher than what is currently given by the wireless systems. Wireless LAN (IEEE802.11a/b/g) offering up-to 54 Mbps and operating at 2.4 GHz and 5 GHz, and 3G mobile networks (IMT2000/UMTS) offering up-to 2 Mbps and operating around 2 GHz, are some of today's main wireless standards. IEEE802.16 or WiMAX is another recent standard aiming to bridge the last mile through mobile and fixed wireless access to the end user at frequencies between 2 - 66 GHz. High operating frequencies (above 6Hz) and smaller radio cells are required due to increased capacity per unit area especially in interior applications since high operating frequencies come across tremendous loss through building walls. The system installation and maintenance charges can be effectively reduced by making the radio antenna units uncomplicated. This can be done by combining signal processing functions at the centralized head end, through radio over fiber technology. The research aims to focus on the viability of using both single-mode and multimode fibers to distribute high-frequency microwave signals to simplified remote radio antenna units. Alternatively, radio over fiber technique known as Optical Frequency Multiplication (OFM) is being examined. OFM entails the periodic filtering of a swept optical signal at the head end followed by photo detection at the radio access unit. A low sweep frequency (e.g. 3 GHz) is used. After photo detection at the remote radio access unit, high-frequency (>21 GHz) harmonic components of the sweep signal are generated. The desired microwave signal is selected by means of band pass filtering, amplified, and radiated by the antenna. Modulated microwave carriers are generated by intensity modulating the frequency-swept optical signal. Through modelling, simulations, and extensive experiments, the behaviour and performance of a radio-over-fiber downlink employing OFM was investigated. Simulation and comprehensive experimental results showed that OFM can be used to generate pure high-frequency microwave signals with very narrow line width and low SSB phase noise. This is because in the OFM process laser phase noise is inherently suppressed. The low-phase noise capability of OFM enables it to support the delivery i.e, Summary of carriers modulated not only by the simple ASK data format, but also by complex multilevel modulation formats such as BPSK, QPSK, and x-level QAM. Multicarrier signals such as Subcarrier Multiplexed signals and OFDM signals used in wireless LANs are also supported. Low Error Vector Magnitudes (below 5%) were obtained for x-QAM modulation formats, including 64-QAM. BER measurements showed a modal dispersion penalty of about 1 dB for a 4.4 km MMF link under restricted launch condition.

It is found that OFM is tolerant to chromatic dispersion and is capable of supporting more than ten times longer single mode fiber transmission links which exceed 50 km than IMDD systems which endure the chromatic dispersion induced amplitude suppression. OFM facilitates the release of microwave carriers that exceed the modal bandwidth of MMF's using the higher transmission pass bands of the fiber response. Silica glass MMF links which are of four km are feasible. Due to its higher attenuation values, the maximum link length that can be bridged with Polymer Optical Fiber (POF) is considerably short. Hence POF are useful in in-building applications since link lengths of 500m are adequate. Several different implementations of the Mach Zehnder Interferometer, and the Fabry Perot Interferometer filters were considered to determine their simplicity, performance, and applicability within the end-user environment. The characteristics of the periodic optical fiber must be aligned with the wavelength of the optical FM source needs. Hence both the source and filter are collocated. This makes it simple to use electronic tuning control of the filter (e.g. a fiber Fabry Perot Interferometer), to track the alignment with the optical source automatically thereby greatly improving the stability of OFM. The capability to achieve high frequency multiplication factors, good phase noise performance, the support for all modulation formats, the ability to operate on both single mode and MMF's make OFM ideal for use in high frequency(>5 GHz) broadband wireless system applications.

Broadband Multimedia Services

The main aim of this study is to implore the modern approaches and technical solutions of network technologies in the promising broadband multimedia services.Tremendous proliferation of the multimedia data including audio, image, video and graphics and advances of multimedia technologies such as JPEG and MPEG standards, network based multimedia applications such as IPTV, VoD, VoIP became known and are an integral part of our life. Increasing demand of multimedia service has indeed made the access to broadband internet a common setup for internet users across modern cities globally. In the USA, broadband penetration has reached 89.3% amongst the active internet users in the year 2008.

However, in spite of the high data rate, broadband multimedia services are not satisfactory. For instance, the data rate connection to the internet of a computer may be 100 Mbps. But, even streaming of 500 Kbps of a video clip may still suffer playback interactions at times. This could be mainly due to lack of QoS support in the internet. This demonstrates the challenge of providing good quality broadband multimedia services. The scenario worsens when the number of variety of networks increases, diverse end users, notorious wireless channels, mobility, inter-networking, coexistence of different types of traffic etc.

Existing System

The existing system may use one of the modulation techniques to carry the data from the transmitter to the receiver.

Limitations

Using merely a single technique is not suitable to different ranges, as they may have certain limitations and hence a single technique cannot be used to carryout higher range. This would lead to high ber and low psnr thereafter decreasing the QOS.

Planned System

By designing a planned system that can apply diverse modulation techniques depending on the mobility of the device from its system, helps in easing the purpose of the system and reduces the BER which in turn enhances the QOS of the system.

Advantages

Unlike the existing system, the planned system does not depend on different systems for different mobility ranges of the devices from the station.

Literature Survey

FAMOUS: A Network Architecture for Delivering Multimedia Services to Fast Moving Users.

Access to the internet users today who commute regularly may be just surfing the web or email which is a serious constraint. Accessing interactive multimedia services like online gaming, video conferencing are unavailable despite the advent of new technologies like UMTS or WiMAX. Impact of high rate of multimedia traffic on the access network and the aggregation network is crucial subject that has not been addressed earlier. Network architecture has been designed to offer fast moving users with multimedia services. The network architecture is referred to as the FAMOUS network architecture and it consists of two parts-

An access network that deals with large number of users seeking high bandwidth whilst experiencing high handoff frequency.

an aggregation network that deals with dynamic tunnels of high bandwidth that experience low handoff frequency.

This study will assess the FAMOUS architecture elaborately with lucid presentation about optimized hands-off strategies, an optical switching architecture, design and methodology about dimensioning aggregation networks; and automatic tunnel reconfiguration and activation.

Performance characteristics of 60 GHz communication systems

The viability of long haul radio frequency wireless communication was revealed a century ago, radio waves are used to broadcast information over long distances, the number of satellites orbiting the earth, the number of microwave dishes and broadcast towers are multiplying each day. The available radio frequency spectrum is limited and the ever increasing demand for bandwidth (i.e increased data throughput) is leading to the development of sophisticated equipment due to this rapid growth. Due to this, satellite and land based microwave systems were reinstated by fiber and the continued expansion of the physical fiber backbone is an ideal solution to substitute inadequate long haul microwave segments.

Majority of the urban areas have installed fiber trunks carry large amounts of digital voice, video and data traffic; this infrastructure supports broadband connection to the users. This could be due to expensive installation charges, lead times are significant, and necessary right of way is often unavailable- issues referred to as last mile problem. Over the last few years, there has been a change in the wireless communication and number of wireless point to point technologies offers fiber data rates which are capable of supporting dense deployment architectures. This new technology can be relegated as satisfactory due to short links, high data rates, low cost, high densities, high security, low transmit power, small profile. Terabeam Corporation develops and manufactures two wiresless communication systems that meet the above mentioned criteria- the Elliptica, a free space optics (FSO) communication system; and the Gigalink, a millimeter wave (MMW) communication system. Infrared and millimeter portions of the electromagnetic spectrum are used in this technology which provides point-to-point and line of sight connectivity. Both FSO and MMW have their own strengths and weaknesses that define their suitability in any given application.

"Impact of Radio-over-Fiber Links on Wireless Access Protocols,"

In order to support the existing wireless system in a radio over fiber distribution network, wireless system characteristics must be evaluated to compile the requirements for the wireless system functionality and operation. The insertion of an optical path within the wireless system protocol stack is a crucial issue in addition to the generation and transport of the microwave signals from the central site (CS) to the antenna site(AS) and vice versa. The medium access control (MAC), duplexing schemes and multiple access methods of the different wireless systems set timing boundaries for the design of radio-over-fiber distribution networks, since the extra propagation delay inserted by the optical path has to be considered from the CS for the support of such systems. This study will assess the impact of any delay in the mobile and wireless radio networks and evaluates the centrally scheduled MAC schemes when compared to distributed MAC are far more flexible for the insertion of a fiber link between CS and AS.

"Optical Switching: Switch Fabrics, Techniques, and Architectures,"

The transmission capacity of the optics cannot be controlled by the switching speeds of electronics. The optical switch fabrics play an important role in switching functions to the optical layer. Optical packet switching provides an almost arbitrary fine granularity but faces significant challenges in the processing and buffering of bits at high speeds. Generalized multiprotocol label switching seeks to eliminate the asynchronous transfer mode and synchronous optical network layers, thus implementing Internet protocol over wavelength-division multiplexing. Optical burst switching attempts to minimize the need of processing and buffering by aggregating flows of data packets into bursts. In this paper, we present an extensive overview of the current technologies and techniques concerning optical switching.

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