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MOBILE COMMUNICATIONS
M . PRAVEEN KUMAR M.RAJESHWARI V.GOWTHAMI 2nd Btech ECE
ABSTRACT: At the start of the 21-century the wireless mobile communications are going to witness unprecedented growth fuelled by an information explosion and a technology revolution in the form of Third Generation (3G) mobile wireless communications. The first generation wireless mobile systems were analog and insecured. The present second generation systems are digital, secured but limited to a certain geographical area due to different technology standards by different countries. While these proposed 3G systems are sophisticated, Globally compatible and offer significant improvement of data and multimedia capabilities. 03+Global roaming with a single system provided with large bandwidth, guaranteed by quality of services, ease of deployment coupled with recent advancements in semiconductor technologies for wireless applications make 3G wireless systems very attractive than that of first and second generation systems. Many enabling technologies including wideband code division multiple access, software defined radio, packet switched programmable intelligent networks, Please send your feedback to projectsworld@live.com and send more projects to us and we upload it to www.projectsworld.co.cc and you can share the projects and help other to participate.
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www.projectsworld.co.cc provides all projects for All Students networks with distributed data storage offer a variety of services like wireless mobile internet, mobile multimedia Applications, mobile video telephony along with voice communications while roaming through different network standards. The concept (3G)initiated by International Telecommunications Union(ITU)and fuel by projects like International Mobile Telecommunications(IMT2000)and 3 Generation Partnership Projects(3GPP-1 and 3GPP-2),presently these systems are under vigorous development and are going to be deployed within a short period in various regions round the people. In this paper we discussed the motivating factors and technological trends that are going to be used in these expected future systems and also project a scope for the systems beyond 3G.
HARMONISATION OF 3G MOBILE SYSTEMS: Most of the second generation systems were individually developed by different countries and are incompatible with each other. Some of the second generation systems and their relative occupation in the present worldwide mobile industry can be seen from the following data Global System for Mobile GSM)----------------58% Code Division Multiple Access (CDMA)---------14% Time Division Multiple Access(TDMA)---------9% Other 2G Systems-------------------------------10% Analog Systems----------------------------------9% The International Telecommunication Union (ITU) launched third-generation project in 1986 with the aim to provide personal communication using an expensive mobile terminal that can truly facilitate communication anywhere anytime By June 1998,a total of 15 proposals from around the world had been submitted to the
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www.projectsworld.co.cc provides all projects for All Students ITU, and it launched a project known as International Mobile Telecommunications2000(IMT-2000) As the European Union sought a need for the rapid evolution towards 3G,the European Telecommunications Standards Institute(ETSI) initiated the concept of a concept of Third Generation partnership project (3GPP) at the beginning of 1998.In December 1998 five standards development organizations ARIB(JAPAN),ETSI (EUROPE), TI (USA), TTA (KOREA) and TTC( JAPAN) launched the 3GPP.The project is also known as (3GPPI) was spearheaded by ETSI . The purpose of 3GPP is to prepare approve and maintain globally applicable technical specifications and 3GPP initiative, the American technical reports for 3G systems based on GSM(Global System for Mobile) and UTRA (Universal Terrestrial Radio Access).Parallel to National Standards Institute(ANSI) spearheaded the creation of 3GPP2 after ETSI declined to expand its proposal to include other non-GSM technologists, so that 3G partnership project could accommodate all industry participants. It is expected that the 3GPP also form the basis of ITU members contributions in accordance with the existing procedures and will support internetworking between IMT-2000 family members. EVOLUTION TOWARDS 3G: At the start of the projects it was initially hoped that a unique air interface standard would be desirable worldwide and a 2200 MHz band. But reality soon led to the realization that 3G systems need to evolve from existing to the systems since a lot was already expended on these systems and the proposed frequency band is allotted for other systems in many countries. Also it is undesirable to abandon all present expansion of network activities for one or two years so that these can be replaced by the new systems which are incompatible to existing systems. Hence it is proposed that the numerous 2G standards will converge to a few different standards, which meet the 3G standards. project was launched known as Universal Mobile Telephone Services(UMTS), which is proposed to operate in 1800-
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www.projectsworld.co.cc provides all projects for All Students For most 2G systems based on GSM or TDMA (Time Division Multiple Access) standards, the evolution of 3G is planned through the Enhanced Data for GSM Evolution (EDGE) standard. For new green field service providers, the UMTS systems will likely be used and for systems based on IS-95CDMA systems, the evolution is based on the CDMA-2000. TECHNICAL ASPECTS: Three main aspects drive the proposal, evolution, harmonization and technical activities of these 3G systems: operators, manufacturer and subscribers requirements. OPERATORS REQUIREMENTS: From operators point of view the important requirement is to minimize their 3G investment risk by ensuring smooth and compatible evolution path from existing infrastructure, without abandoning current infrastructure, replacing it with new incompatible system. MANUFACTURERS REQUIREMENTS: From manufacturer view point the convergence of the global standard is attractive because it eliminates costly duplication of R&D efforts associated with multiple standards and reduces the development cost. SUBSCRIBERS REQUIREMENTS: From subscriber stand point, the general consensus is that a harmonized standard will maximize the customers ability to roam with their services across the regions, countries and systems. As these 3G systems created much interest in all, a large number of proposals came from different countries and technical groups round the globe. A few these proposals are listed down here, which are under vigorous development .A brief discussion is provided about each topic separately. Wideband Code Division Multiple Access (W-CDMA) Software Defined Radio (SDR) Intelligent Antennas Quality of Services (QoS) Radio Resource Allocation (RRA) the
W-CDMA: The classical method of providing multiple communication channels is by using Frequency Division Multiple Access (FDMA) and Time Division Multiple Access Please send your feedback to projectsworld@live.com and send more projects to us and we upload it to www.projectsworld.co.cc and you can share the projects and help other to participate.
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www.projectsworld.co.cc provides all projects for All Students (TDMA). Figures at the end of the paper shows diagrammatically how the channel is subdivided in frequency and time in TDMA and FDMA. Instead of these two conventional techniques an entirely new multiple access method is proposed for the 3G systems known as Code Division Multiple Access (CDMA). CDMA allows all users to send simultaneously using the same frequency. At first glance it may be doubled that if everyone is transmitting on the same frequency how it is possible to select just one transmitted signal at the receiver? This concept may be difficult to grasp at once but as an analogy imagine that you having a conversation with a friend in a lift. The lift stops and two people enter conversing in Japanese, next two people enter conversing in Russian. If we assume that every one in the lift can only their own language. Then you can see that these three conversations can occur simultaneously without any mix-up of information. A similar technique is used in CDMA. Every transmitted signal is coded with a unique code sequence called Pseudo Noise (PN) sequence, which appears to all other users as noise expect but to the intended receiver.
FDMA: t P
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CDMA:
TDMA
Initially CDMA was used in military environment and in a few 2G systems and employed a narrow signalf bandwidth of 100KHz. An enhanced Wideband CDMA F1 F2 F2 f (W-CDMA)technique is used by these 3G F1 systems which requires 5 MHz bandwidth in order to support a high data rate of 2Mbits/sec. A typical W-CDMA systems is shown in Fig4.
W-CDMA SYSTEM : TRANSMITTER Data in 1.024 Mbps Encoder & Interleaver RF Signal
Chip code 12.288 Mbps
RF plus Noise
RECEIVER
Digital circulator
Decoder & Deinterleaver
Data Out
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SOFTWARE DEFINED RADIO: Given the selection of possible 3 Gair standards such as EDGE, UMTS and CDMA 2000, using different bitrates ,frequency bands ,depending on the service providers and the problem is a single system compatible and support all these standards. One technique thought to have the potential to solve this problem is Software Defined Radio(SDR). With this technique ,only one infrastructure hardware system would need to be developed. The difference in frequency bands and technology standards would be implemented by loading different software into the system .In addition to the advantage of being able to support different standards with a unified platform and hardware ,SDR has the following benefits: Many commercial digital architecture and software protocol stacks are already available and can be used to further reduce the cost and the time to market. It will be much easier to introduce new services and features with software upgrades. The implemented system can easily be tailored to specific customer needs for both mass and niche markets. It provides flexibility to optimize the system performance over time amd reduce new deployment risk. Since the software radio terminals must be able to process many various communication standards ,based on different master clock rates and bit/chip rates , a number of master clock hardware circuits must be provided which has impact on Digital run power consumption of the system and size. The solution for this is toO/P the system on a fixed clock rate and perform digital sample rate conversion controlled by DSP Soft ware RF/ANALOG software as shown in FIG. A/D & A/D SIGNAL Compute Engine A SDR TRANSCEIVER WITH A SINGLE MASTER CLOCK:
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It is of paramount importance to keep in mind that software radio concept is a process of re-sampling. Hence rate conversion turns out to be main problem with fundamental effects such as sampling ,imaging and aliasing .Different rate change factors ,pass band width and stop band attenuation are the main characteristics which must be variable , and call for the reconfigurability of the hardware platform for sample rate conversion in radio transceivers. INTELLIGENT ANTENNAS: The continuous moving of the user in the cell puts stringent requirements on the antennas used in the mobile environment especially at base stations. Similarity continued rapid growth of wireless mobile applications, more system capacity is needed that can be met by Intelligent Antenna concept. Current proposals include two techniques. The steered beam and Switched beam approaches. The steered been array approach utilizes phased array antennas. The phased array elements are used in the antenna to create a narrow beam directed only to the intended mobile on the forward link This beam is then steered with the mobile as it moves. The Switched beam approach differs Switched beam approach in atleast two ways.First the aperture of the antenna in the Switched beam approach is fixed to a fraction of a sector and second, instead of adaptively steered with the mobile user as it moves, the system simply switches from one antenna beam to the another .Another important issue in mobile environment is the Reverse link ,i.e. the signal from the mobile to the base station, which is limited by the maximum mobile system transmit power. Consequently, the reduction the system noise figure becomes important for coverage improvement. Utilizing a Super conductor device or low noise amplifier on top of the tower at the antenna, the noise figure can be reduced by a few dB,resulting Please send your feedback to projectsworld@live.com and send more projects to us and we upload it to www.projectsworld.co.cc and you can share the projects and help other to participate.
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www.projectsworld.co.cc provides all projects for All Students in a larger coverage radius. The Super conductor technology is limited by its cost and reliability the device. QUALITY OF SERVICES (QOS):The QoS users with same quality of services in mobile environment as they enjoy in their environment. As the channel conditions change according to mobile environment continuosly,the QoS is the one of the important issue to be addressed. To satisfy the growing demand for accessing the internet anywhere anytime, Internet services need to be extend to these 3G systems.This would require a precisely defined QoS mechanism on 3G air interface that is optimized to support Internet services. In addition,3G wireless networks need to support a variety of services including those that are well defined as well as those that emerge in the future. In order to have a QoS framework is proposed.The framework is based on the paradigm of service classes. To illustrate, consider a system with three classes premium, gold and silver. Each class offers a characteristic performance to its customers, defined as group behavior. For example premium service can offer a negotiated bandwidth at all times, regardless of congestion, interference or degradation in the channel quality on the air interface. Each of the remaining two service classes has a certain elasticity associated with it. Incase of congestion, bandwidths offered to the users are adjusted in accordance with the elasticities of their classes, so that congestion is mitigated. RADIO RESOURCE ALLOCATION: Resource Allocation is one of the main problems faced by the system designers because the QoS places complicated issues on the scarce resource. As the mobile user moves from one cell to the other a soft handoff is needed to ensure QoS. Hence radio resources on the neighboring cells should be reserved a mobile user, which decreases system capacity. As the services offered vary from low data rates to very high data rates, as in paging services to the multimedia applications, connection blocking limitations and currently the Tower Top Low Amplifier (TTLNA) is beginning to be widely accepted with increased improvement in reliability and size or
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www.projectsworld.co.cc provides all projects for All Students schemes should identify properly the services required to ensure optimum through put. To meet these problems a probabilistic resource estimation and semi reservation scheme is proposed for flow oriented multimedia wireless networks, which improve the connection blocking probability, connection dropping probability and bandwidth utilization. This scheme uses a flexible resource reservation approach to replace the conventional full reservation method and a soft-reject approach is used to replace the hard-reject if there is insufficient bandwidth. A VISION FOR SYSTEMS BEYOND THIRD GENERATION: Third generation mobile radio systems are expected to be deployed within a short period in different regions. Due to the long necessary time frame for the definition, development and standardization of new systems beyond third generation mobile radio systems, discussions are already starting today. For example Bluetooth technology based systems, which offer enormous bandwidth, are under rigorous development and form the basis for such future generation systems. Systems beyond third generation will not just be wideband access systems to provide high data rates to users. Those systems will follow the general concept of many combined optimized access systems for special purposes on a common network platform, which complement each other in an efficient and optimized way. Depending on the selected services, available access systems and bearer capabilities, these systems will select the most appropriate access system. In addition , the concept will use algorithms for reconfigurability , self-optimizing networks, and automatic network configuration, so that new network entities and access systems can easily be added. This requires extensive international research activities in the areas of access systems improvement, optimization of IP for radio transmission and mobility management and implementation of multimode and multiband terminals. CONCLUSION: With less than 50 years of commercial history, wireless mobile communications have already changed the way people communicate with each other. Whole the progress has been impressive , much more is yet to come that will revolutionize communications , as
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www.projectsworld.co.cc provides all projects for All Students we know it, leading eventually to communicating with anyone or any device at any place and any time. BIBLIOGRAPHY: Computer Networks- Tanenbaum IEEE Communications Magazine- 2000-2001 Editions IEEE Spectrum-1995 Elektor Electronics-June 2001
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