12-09-2014, 10:30 AM
4G TECHNOLOGY
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ABSTRACT
Third-generation (3G) mobile networks face a new rival: so-called 4G. And, astonishingly, the new networks may even be profitable. Alvin Toffler, an eminent futurologist, once said, “THE FUTURE ALWAYS COMES TOO FAST, BUT IN THE WRONG ORDER”. The state of wireless telecoms is a classic example. Even as 3G mobile networks are being switched on around the world, a couple of years later than planned, attention is shifting to what comes next: a group of newer technologies that are, inevitably, being called Fourth Generation Mobile Networks (4G). 4G is all about an integrated, global network that's based on an open systems approach.
The goal of 4G is to replace the current proliferation of core cellular networks with a single worldwide cellular core network standard based on IP for control, video, packet data, and VoIP. This integrated 4Gmobile system provides wireless users an affordable broadband mobile access solutions for the applications of secured wireless mobile Internet services with value-added QoS. This paper gives the reasons for the evolution of 4G, though 3G has not deployed completely. And then gives the information on the structure of the transceiver for 4G followed by the modulation techniques needed for the 4G. Later this gives the information about the 4G processing .Finally concludes with futuristic views for the quick emergence of this emerging technology. [1]
INTRODUCTION
While 3G hasn't quite arrived, designers are already thinking about 4G technology. With it comes challenging RF and baseband design headaches. Cellular service providers are slowly beginning to deploy third-generation (3G) cellular services. As access technology increases, voice, video, multimedia, and broadband data services are becoming integrated into the same network. The hope once envisioned for 3G as a true broadband service has all but dwindled away. It is apparent that 3G systems, while maintaining the possible 2-Mbps data rate in the standard, will realistically achieve 384-kbps rates. To achieve the goals of true broadband cellular service, the systems have to make the leap to a fourth-generation (4G) network.
This is not merely a numbers game. 4G is intended to provide high speed, high capacity, low cost per bit, IP based services. The goal is to have data rates up to 20 Mbps, even when used in such scenarios as a vehicle traveling 200 kilometers per hour. The move to 4G is complicated by attempts to standardize on a single 3G protocol. Without a single standard on which to build, designers face significant additional challenges [2].
What is 4G?
4G takes on a number of equally true definitions, depending on who you are talking to. In simplest terms, 4G is the next generation of wireless networks that will replace 3G networks sometimes in future. In another context, 4G is simply an initiative by academic R&D labs to move beyond the limitations and problems of 3G which is having trouble getting deployed and meeting its promised performance and throughput. In reality, as of first half of 2002, 4G is a conceptual framework for or a discussion point to address future needs of a universal high speed wireless network that will interface with wire line backbone network seamlessly.[2]
VISION OF 4G
This new generation of wireless is intended to complement and replace the 3G systems, perhaps in 5 to 10 years. Accessing information anywhere, anytime, with a seamless connection to a wide range of information and services, and receiving a large volume of information, data, pictures, video, and so on, are the keys of the 4G infrastructures. The future 4G infrastructures will consist of a set of various networks using IP (Internet protocol) as a common protocol so that users are in control because they will be able to choose every application and environment. Based on the developing trends of mobile communication, 4G will have broader bandwidth, higher data rate, and smoother and quicker handoff and will focus on ensuring seamless service across a multitude of wireless systems and networks. The key concept is integrating the 4G capabilities with all of the existing mobile technologies through advanced technologies. Application adaptability and being highly dynamic are the main features of 4G services of interest to users. These features mean services can be delivered and be available to the personal preference of different users and support the users' traffic, air interfaces, radio environment, and quality of service. Connection with the network applications can be transferred into various forms and levels correctly and efficiently. The dominant methods of access to this pool of information will be the mobile telephone, PDA, and laptop to seamlessly access the voice communication, high-speed information services, and entertainment broadcast services. Figure 1 illustrates elements and techniques to support the adaptability of the 4G domain. The fourth generation will encompass all systems from various networks, public to private; [2]
4G MOBILE COMMUNICATIONSYSTEMS
International Mobile Telecommunications’ - 2000(IMT-2000) and the Universal Mobile Telecommunications System (UMTS) will be among the first 3G mobile communication systems to offer wireless wideband multimedia services using the Internet protocol. Two important technological changes will facilitate this advancement. The first change is a shift from last-generation radio-access technologies such as the global system for mobile (GSM) communication, CDMA One (an IS-95 code division multiple access standard), and personal digital cellular (PDC) toward more sophisticated systems with higher data-transfer rates such as the enhanced data. fourth-generation mobile communication systems will combine standardized streaming with arrange unique services to provide high-quality content that meets the specific needs of the rapidly growing mobile market. GSM environment (EDGE), wideband CDMA (WCDMA), and cdma2000.As Figure 1 illustrates, the second important technology shift is from a vertically integrated to a horizontally layered service environment. A horizontally layered4G service network seamlessly integrates Internet protocol transport into a mobile service environment with a variety of access networks, opening up many new opportunities for IP-based mobile applications. For example, mobile terminals will be able to access existing Internet content through protocols and markup languages such as WAP and WML that are optimized for wireless application scenarios. 4Gmobile communications will have transmission rates up to 20 Mbps_ higher than of 3G. The technology is expected to be available by the year 2010. 4G is being developed with the following objectives: 1. Speeds up to 50 times higher than of 3G. However, the actual available bandwidth of 4G is expected to be about 10 Mbps.2. Three-dimensional virtual reality_imagine personal video avatars and realistic holograms, and the ability to feel as if you are present at an event even if you are not. People, places, and products will be able to interact as the cyber and real world’s merge.[3]
The fourth generation
4G mobile communications will have transmission rates up to 20 Mbps—higher than of 3G. The technology is expected to be available by the year2010. Presently, NTT Do Como and Hewlett-Packard are on their agenda to make it available by the year 2006.4G is being developed with the following objectives:1. Speeds up to 50 times higher than of 3G.However, the actual available bandwidth of 4G is expected to be about 10 Mbps.2. Three-dimensional virtual reality—imagine personal video avatars and realistic holograms, and the ability to feel as if you are present at an event even if you are not. People, places, and products will be able to interact as the cyber and real world’s merge.3. Increased interaction between corroborating technologies; the smart card in your phone will automatically pay for goods as you pass a linked payment kiosk, or will tell your car to warm-up in the morning as your phone has noted you leaving the house.Ericsson and the University of California are jointly researching CDMA wireless access technology, advanced antenna systems, next-generation mobile Internet, quality of service, power amplifier technology, and wireless access net works. Other 4G applications include high-performance streaming of multimedia content based on agent technology and scalable media coding methods
What is needed to Build 4G Networks of Future?
To achieve a 4G standard, a new approach is needed to avoid the divisiveness we've seen in the 3G realm. One promising underlying technology to accomplish this is multicarrier modulation (MCM), a derivative of frequency-division multiplexing. Forms of multicarrier systems are currently used in digital subscriber line (DSL) modems, and digital audio/video broadcast (DAB/DVB). MCM is a baseband process that uses parallel equal bandwidth sub channels to transmit information. Normally implemented with Fast Fourier transform (FFT) techniques, MCM's advantages include better performance in the inter symbol interference (ISI) environment, and avoidance of single-frequency interferers. However, MCM increases the peak-to-average ratio (PAVR) of the signal, and to overcome ISI a cyclic extension or guard band must be added to the data.
Why OFDM?
OFDM overcomes most of the problems with both FDMA and TDMA (ie ICI and ISI). OFDM splits the available bandwidth in to many narrow band channels. The carriers for each channel are orthogonal to one another allowing them to be spaced very close together, with no overhead as in the FDMA. Because of this there is no great need for users to be time multiplexed as in TDMA, thus there is no overhead associated with switching between the users. Each carrier in an OFDM signal has a very narrow bandwidth (i.e. 1 K Hz), thus the resulting symbol rate is low. This results in signal having a high tolerance to multipath delay spread, as a delay spread must be very long to cause ISI ( i.e. >500 μsec).[3]
THE 4G TRANSCEIVER
The structure of a 4G transceiver is similar to any other wideband wireless transceiver. Variances from a typical transceiver are mainly in the baseband processing. A multicarrier modulated signal appears to the RF/IF section of the transceiver as a broadband high PAVR signal. Base stations and mobiles are distinguished in that base stations transmit and receive/ decode more than one mobile, while a mobile is for a single user. A mobile may be a cell phone, a computer, or other personal communication device.
The line between RF and baseband will be closer for a 4G system. Data will be converted from analog to digital or vice versa at high data rates to increase the flexibility of the system. Also, typical RF components such as power amplifiers and antennas will require sophisticated signal processing techniques to create the capabilities needed for broadband high data rate signals. Figure 1 shows a typical RF/IF section for a transceiver. In the transmit path in phase and quadrature (I&Q) signals are unconverted to an IF, and then converted to RF and amplified for transmission. In the receive path the data is taken from the antenna at RF, filtered, amplified, and down converted for baseband processing. The transceiver provides power control, timing and synchronization, and frequency information. When multicarrier
4G PROCESSING
Figure 2 shows a high-level block diagram of the transceiver baseband processing section. Given that 4G is based on a multicarrier technique, key baseband components for the transmitter and receiver are the FFT and its inverse (IFFT). In the transmit path the data is generated, coded, modulated, transformed, cyclically extended, and then passed to the RF/IF section. In the receive path the cyclic extension is removed, the data is transformed, detected, and decoded. If the data is voice, it goes to a vocoder. The baseband subsystem will be implemented with a number of ICs, including digital signal processors (DSPs), microcontrollers, and ASICs. Software, an important part of the transceiver, implements the different algorithms, coding, and overall state machine of the transceiver. The base station could have numerous DSPs. For example, if smart antennas are used, each user needs access to a DSP to perform the needed adjustments to the antenna beam.
BASEBAND PROCESSING
The error correction coding of 4G has not yet been proposed, however, it is known that 4G will provide different levels of QoS, including data rates and bit error rates. It is likely that a form of concatenated coding will also be used, and this could be a turbo code as used in 3G, or a combination of a block code and a convolution code. This increases the complexity of the baseband processing in the receive section. 4G baseband signal-processing components will include ASICs, DSPs, microcontrollers, and FPGAs. Baseband processing techniques such as smart antennas and multi-user detection will be required to reduce interference.
MCM is a baseband process. The subcarriers are created using IFFT in the transmitter, and FFT is used in the receiver to recover the data. A fast DSP is needed for parsing and processing the data. Multi-user detection (MUD) is used to eliminate the multiple access interference (MAI) present in CDMA systems [3].
STREAMING STANDARDIZATION
4G multimedia applications. In addition to mobile addresses other applications such as are less complex than for conversational services, audio compression/decompression software in enduser common standardized format because it is unlikely equipment will help reduce terminal costs. Expensive than setting up content for several formatted text into mobile multimedia applications. Furthermore, preparing and providing content in one Future. Using standardized components such as Internet Streaming Media Alliance (ISMA) and the messaging services can include text, images, audio, Mobile streaming services in particular require a multimedia protocol stacks and codecs _video and proprietary Internet streaming formats in the near proprietary streaming solutions individually. We must receiving multimedia messages. Multimedia service. This service integrates simultaneously playing Several organization and industry groups including the short video clips, or video-stream URLs. standardized format is less time consuming and Streaming services as an important building block of streaming standardization, it is also require to that mobile terminals will be able to support all the need for standardization of streaming services. The protocols and terminals for streaming applications There are some standard specifies both protocols and to address mobile streaming standardization. Video, audio, images, and video conferencing and services for composing and We have to use the mobile packet-switched streaming which require media input devices and encoders. Wireless Multimedia Forum (WMF) have recognized
CONCLUSION
System designers and services providers are looking forward to a true wireless broadband cellular system, or 4G. To achieve the goals of 4G, technology will need to improve significantly in order to handle the intensive algorithms in the baseband processing and the wide bandwidth of a high PAVR signal. Novel techniques will also have to be employed to help the system achieve the desired capacity and throughput. High-performance signal processing will have to be used for the antenna systems, power amplifier, and detection of the signal. A number of spectrum allocation decisions, spectrum standardization decisions, spectrum availability decisions, technology innovations, component development, signal processing and switching enhancements and inter-vendor cooperation have to take place before the vision of 4G will materialize. We think that 3G experiences - good or bad, technological or business - will be useful in guiding the industry in this effort. To sketch out a world where mobile devices and services are ubiquitous and the promise of future fourth generation (4G) mobile networks enables things only dreamed of, we believe that 4G will probably become an IP-based network today.[4]