Why do we need 4G? To answer this question we need to understand some of the major limitations of 3G. Some of the reasons for a new generation of mobile communication are listed below
- Difficulty of CDMA to provide higher data rates
- Need for continuously increasing data rate and bandwidth to meet the multimedia requirements
- Limitation of spectrum and it's allocation
- Inability to roam between different services
- To provide a seamless transport end-to-end mechanism
- To introduce a better system with reduces cost
C. Some main desired Features of 4G:
High usability and global roaming: The end user terminals should be compatible with any technology, at any time, anywhere in the world. The basic idea is that the user should be able to take his mobile to any place, for example, from a place that uses CDMA to another place that employs GSM.
Multimedia support: The user should be able to receive high data rate multimedia services. This demands higher bandwidth and higher data rate.
Personalization: This means that any type of person should be able to access the service. The service providers should be able to provide customized services to different type of users.
D. Main Challenges
To achieve the desired features listed above researches have to solve some of the main challenges that 4G is facing. The main challenges are described below Multimode user terminals: In order to access different kinds of services and technologies, the user terminals should be able to configure themselves in different modes. This eliminates the need of multiple terminals. Adaptive techniques like smart antennas and software radio have been proposed for achieving terminal mobility.
Wireless system discovery and selection: The main idea behind this is the user terminal should be able to select the desired wireless system. The system could be LAN, GPS, GSM etc. One proposed solution for this is to use software radio approach where the terminal scans for the best available network and then it downloads the required software and configure themselves o access the particular network.
Terminal Mobility: This is one of the biggest issues the researchers are facing. Terminal mobility allows the user to roam across different geographical areas that uses different technologies. There are two important issues related to terminal mobility. One is location management where the system has to locate the position of the mobile for providing service. Another important issue is hand off management. In the traditional mobile systems only horizontal hand off has to be performed where as in 4G systems both horizontal and vertical hand off should be performed. As shown in figure 1, horizontal hand off is performed when a mobile movies from on cell to another and vertical handoff is performed when a mobile moves between two wireless systems. Some solutions for achieving vertical hand off have been discussed in section IV.
Hand off mechanisms
Personal mobility: Personal mobility deals with the mobility of the user rather than the user terminals. The idea behind this is, no matter where the user is located and what device he is using, he should be able to access his messages.
Security and privacy: The existing security measures for wireless systems are inadequate for 4G systems. The existing security systems are designed for specific services. This does not provide flexibility for the users and as flexibility is one of the main concerns for 4G, new security systems has to be introduced.
Fault tolerance: As we all know, fault tolerant systems are becoming more popular throughout the world. The existing wireless system structure has a tree like topology and hence if one of the components suffers damage the whole system goes down. This is not desirable in case of 4G. Hence one of the main issues is to design a fault tolerant system for 4G.
Billing System: 3G mostly follows a flat rate billing system based where the user is charged just by a single operator for his usage according to call duration, transferred data etc. But in 4G wireless systems, the user might switch between different service providers and may use different services. In this case, it is hard for both the users and service providers to deal with separate bills. Hence the operators have to design a billing architecture that provides a single bill to the user for all the services he has used. Moreover the bill should be fair to all kinds of users.