The number of mobile user's increases day by day and their demands like having good speed whether fixed or mobile terminal, global connectivity, high security, better internet resources access. 3G which is the existing wireless system lacks such characteristics. It has speed up to 2Mb/s which cannot be improved further because of the complexity in CDMA.3G is the combination of circuit switched and packet switched with a limited access schemes like CDMA, WCDMA which makes 3G difficult to roam globally and across different networks. Moreover, 3G has weak algorithms for security which can easily be attacked. Thus, a system for future wireless communication has been modeled and has given name 4G. 4G will cope the problems faced by 3G.It will be completely IP Packet based so; it will be roamed globally by using IPv6. The key techniques that 4G will be using are OFDM, MIMO, Smart Antenna, Software Defined Ratio (SDR) and IPv6.Pre 4G has been launched in two Scandinavian countries Sweden and Norway in 2009. However, it could not satisfy the target of IMT Advanced (International Mobile Telecommunications Advanced). Thus, full 4G is supposed to be deployed in 2011. However, it has some challenging problems as well such as Multimode user Terminal, Terminal and Personal Mobility, Security, Privacy and Billing System.
EVOLUTION OF 4G
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It is the need and demand of the people behind the development of the Technology. There was no telecommunication source among people before the invention of telephone. The invention of telephone was thought to be great invention in communication field and it has named 1G which is the basis for all the next mobile generations .1G was totally analogue, circuit switched, and basic voice telephony and had regional coverage. In order to send text messages along with voice, GSM introduced in 1991 which is digital, circuit switched and low data speed. It has named 2G and it uses TDMA scheme which can connect up to 8 people at a time. It has speed is 9.6kbps which is very low data rate. After the invention of Internet, research started how to connect mobile phone to internet. As a result GPRS is introduced with the existing GSM which is based on packet switching to connect to the internet resources where data transfers on best effort basis. It charges per Megabyte of the traffic sent .The problem with GPRS, it has very low speed and very expensive as well. One can check out his email address or view a website but there is no room to watch a video on mobile phone while using GPRS.EDGE introduced to enhance the performance of GPRS which improved three times of that of GPRS.EDGE utilizes high bandwidth efficiency, by this it can support video applications as well, however, it is not that much effective. In 2001, first 3G launched in Japan which is packet and circuit switched like EDGE, supporting multimedia applications, fast data access and global coverage. It has improved the speed up to 2Mbit/s by using WCDMA. Because of the complexity of WCDMA, 3G has difficulty to enhance the speed further. Furthermore, it has some security problems. Thus, it is a need of the day to have such generic system which is all IP based, support more advanced multimedia applications, improved Qos and having global roaming and coverage. It has named 4G.Pre 4G has been launched in some European countries; however, full 4G will be launched in 2011.
THE KEY FEATURES OF 4G
As 4G is the successor of 3G, the main focus of 4G is to remove the problems of 3G network and enhance the QoS of the communication system and make good use of bandwidth.4G will not only further develop 3G applications but also add new applications like HDTV data ,minimal services which can better utilize the bandwidth. The 4G working group defines the following key features of 4G system
- It will be completely based on IP network.IPv6 will be using in 4G instead of IPv4 because 4G needs more addresses and security.
- For static users it will have speed of 1Gbps while mobile users it will be having speed up to 100Mbps which is much better than 3G
- It will have variable Qos depending on dynamic bandwidth allocation and transmission power
- It will achieve seamless roaming .No matter what kind of media ,communication host and network, it will make seamless connectivity
- It will be having unique id which will work anywhere in the World
- It will be much cheaper as far as communication charge is concerned
- It will have good use of bandwidth because of OFDMA technique which will use bandwidth 20 times of that of WCDMA in 3G.
- It will be smarter network than previous generation networks.4G will have intelligent signal processing technology and will have self-adaptive network.
- It will have good coordination with existing wireless standards.
COMPARISON BETWEEN 3G AND 4G
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Data speed, services, ways of transmission, access to the Internet, the compatibility to interface with wire-line network, QoS and security will be distinctive factors between 3G and 4G. As far as speed is concerned, 3G has maximum speed up to 2Mbps which is much slower while 4G will provide at least 100 Mbps rates in full-mobility mode and 1Gbps in static mode by using sophisticated access scheme OFDMA which efficiently utilizes the bandwidth. It is very difficult for 3G to roam globally and have coordination across networks, on the other side,4G will be a global standard that support global mobility and service portability so that service provider will no longer be limited by single-system . In other words, smooth global roaming will be the necessary part of 4G. Moreover, 3G will rely on a wide-area concept applying circuit and packet switching for transmission having limited access scheme, like WCDMA, CDMA and TD-SDMA which cannot bring further improvement in the performance. However, the 4G system will depend on broadband IP-based which is entirely packet switching method having transmission seamlessly access convergence. It shows that 4G incorporated all access technologies, services and applications can unlimitedly be used through wireless system over wire-line system using IP address. Furthermore, 4G is considered to be having more security and privacy than 3G.
ARCHITECTURE OF 4G
- Core Architecture of 4G
4G wireless systems is projected to be built on an IP- based core network architecture as shown in figure 1, for large-scale routing having more modified Access Points (Radio Access Routers) that supports dynamic hand off mechanism
And Ad-Hoc routing.3G network will also be connected with IP core network, it means that everything has to go through IP core network. Mobile IPv6 is the uniform IP- based mobility protocol for IPv6. 4G AP will be installed everywhere like in Parks, vehicles etc which will be having specific region to cover .In 4G mobile systems, each user will be given a home agent, which will have a permanent home IP address. When user will go to another place it will get a new short-term address which will call the care-of address. The user terminal regularly will inform the home agent with its updated address. If the user will be at his permanent location and someone will want to have communication then it will be quite simple just using its home IP address. Let us suppose user will move to some other place then communication will be carried out by using some other procedure. In that case the calling part first will send setup message to the called party's home agent. As the home agent will know the care of address of the called party so, home agent will forward the setup message to the called party and will also forward the care of address of the user to the calling party for future use so that they would communicate directly with each other.
- Layered Architecture of 4G
The OSI layered model as shown figure 2, for 4G wireless systems will be the same as computer network OSI layers. It will have Physical interface (air interface), Data link, and Network, Transport and application layers. The application and transport layers of 4G will be similar to computer networks application and transport layers. The criteria for 4G to be successful are that it will provide good QoS, cheaper and moreover, it will be more flexible than 3G. The network layer of 4G be more flexible and support different networks like Personal Networks, Hot Spots, Cellular, and to the Distribution Networks etc. In 4G the physical layer and the data link control layer are layer 1 and 2 of the OSI model respectively. 4G will provide a new transmission technique and a new error correction technique for physical layer and data link layers. Unlike 3G, the overhead will be shifted to access point from end terminal.
4G KEY COMPONENTS
- Orthogonal Frequency Multiple Access (OFDMA) Scheme
Orthogonal Frequency Multiple Access is the key technique will be used in 4G wireless networks which will fully utilize the bandwidth of the channel and there will be inter symbol interfaces between sub-channels due to orthogonality of sub-channels
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In OFDM, at the transmitter side as shown in figure 3, a stream of symbol binary digits are first demultiplexed, formed sets of particular number of data and then each set is modulated by using quadrature amplitude modulation or phase-shift keying an. Each modulated set is then passed through FFT inverse. The real and imaginary part of the resulted digital signal is passed through DAC (Digital to Analogue) and the resulted analog signals are modulated with sine and cousin waves of frequency fc .The signals are then combined together and are transmitted.
At receiver side signalr(t) as shown in figure 4, is received by the antenna, which is demodulated to baseband by using cosine and sine waves at the carrier frequency. The demodulated signals are then sampled and digitized usingADCs which are given to FFT to convert those signals back to the frequency domain. After getting\scriptstyle Nparallel sets, each of which is then demodulated into a binary stream? Finally, these parallel binary streams are combined into a serial stream, s[n] which is the estimate of the original binary stream.
As 4G will be completely packet switched and will be used globally so, there is a need of internet protocol to have enough addresses to support more devices.IPv6 is the main addressing protocol for 4G networks which is 128 bits address, 4 times more than IPv4 address. IPv6 will have 4 portions ,each one will be 32 bits. The first part of the address will be used for home address which will be like normal address like internet address. The second part of IPv6 will spared for care of address. That is the address to identify the network which will be visited by the user. The third part of the IPv6 address will be signed as a tunnel (mobile IP address) which will be the link between wire-line network and wireless network. This mobile IP address will be used by an agent to establish a channel between the cell phones and PC. The last part of IPv6 address will be local network address for virtual private network (VPN).
- Multiple Input Multiple Output (MIMO)
Multiple-input and multiple-output, or MIMO, will be the key component of 4G networks. In MIMO multiple antennas are used at both the transmitter and receiver to improve communication efficiency. It has been one of the forms of intelligent antenna technology.
In wireless communications, MIMO technology is one of the best attracted attention component because of its significant increases in data rate and link range without any need of extra bandwidth or transmit power. It has been attracted by international wireless research due to its higher spectral efficiency and link reliability or diversity.
There are three main categories of MIMO, precoding, spatial multiplexing or SM, and diversity coding.
Multi-layer beamforming is formed in a narrow sense at the transmitter in a wide-sense. In beamforming, from each of the transmit antennas the same signal is transmitted having appropriate phase, weighting such that the signal power is maximized at the receiver input. The main advantages of beamforming are to enhance the signal gain from constructive combining and to minimize the multipath fading effect.
MIMO antenna configuration is required for spatial multiplexing. In this kind of antenna, a high rate signal is divided into larger number of lower rate streams and each stream is emitted from a different transmit antenna in the same frequency channel. Once these signals reach at the receiver antenna having different spatial signatures, these streams are separated by the receiver, making parallel channels free. This technique is a very powerful for the enhancement of channel capacity at higher Signal to Noise Ratio (SNR).
When there is no way to know about channel at the transmitter then Diversity Coding techniques are used. In this technique a single stream is transmitted, however, the signal is using techniques for coding which is called space-time coding. The signal which is transmitted from each of the transmit antennas using certain principles of full or near orthogonal coding. This technique is used to enhance signal diversity
- Software Defined Radio (SDR)
A software-defined radio, or SDR, will be the key component of 4G system. Instead of implementing components in hardware (e.g. mixers, filters, amplifiers, modulators/demodulators, detectors, etc.), will be implemented in software by using personal computer or embedded computing devices. A basic SDR system would have a personal computer, or other analog-to-digital converter, added by some form of RF front end. Significant amounts of signal processing will be given to the general-purpose processor, instead of special-purpose hardware. This technique will produce a radio that can receive and transmit widely different radio protocols completely based on software
MAIN CHALLENGES FACING 4G
In order to get the preferred results for 4G, there are some challenges 4G are facing need to be solved. Researches have to think about it and give solutions to those problems. Some of the main challenges that 4G is facing are described below
Multimode user terminals: To get access to different kinds of services and technologies, the 4G user terminal must be able to work its in different modes. The proposed solution which has been given by researchers to cope this challenge is to use smart antennas and software radio, by which terminal mobility can be achieved.
- Wireless system discovery and selection: As we know 4 G will be the combination of multiple wireless systems like GSM, GPS etc, thus, the user terminal should be more intelligent in order to access the most suitable wireless system. The system could be LAN, GPS, and GSM etc. The solution which has been given to solve this challenge is to use software radio approach. By using this software the terminal will scan for the best available network. The only thing which will be needed is to download the software and configure in the user terminal.
- Terminal Mobility: It is one of the biggest problems of 4G is facing. Terminal mobility means to get access the user to roam across different geographical areas that have different technologies. Terminal mobility has two important issues. One is location management where the system must know the exact location of the mobile in order to provide service. Second important issue of terminal mobility is handover management. Previous mobile systems have just horizontal handover which has to be performed; however, 4G system will have both horizontal and vertical handovers as shown in figure, need to be performed. Horizontal handover occurs whenever, a mobile terminal goes from on cell to another while vertical handover is occurs when a mobile moves between two different wireless systems.
- Personal mobility: It is another important issue of 4G, such kind of mobility deals with the mobility of the user instead of user terminals. No matter, wherever the user is and what kind of user terminal device he is using, he must have access to his profiles and the messages just like we have the same profile of computer user in a network.
- Security and privacy: 3G network has a lot of security which need to cope in 4G systems and some extra security measures will be need in 4G systems because of its heterogeneous nature. 3G security systems are made for particular services which does not show flexibility for the users .However,4G systems main concern will be to provide more flexibility as far as security is concerned
- Billing System: 3G has a very flat rate billing system which is totally based on call duration. Another word, a user is charged just by a single operator for how long he uses the service. However in 4G wireless systems, the user will deal with different service providers and will be using different services. In this case, it is not difficult for the users but also for service providers to deal with separate bills. Thus, it is a big challenge for researchers and operators to design such a billing system that will provide a single bill to the user for all kind of services he will have used.