WIRELESS GRIDS FOR 4G MOBILE COMMUNICATION SYSTEMS

Grid computing lets devices connected to the Internet, overlay peer-to-peer networks, and the nascent wired computational grid dynamically share network connected resources in 4G kind of scenario. The wireless grid extends this sharing potential to mobile, nomadic, or fixed-location devices temporarily connected via ad hoc wireless networks. As fig. 1 shows, users and devices can come and go in a dynamic wireless grid, interacting with a changing landscape of information resources. Following Metcalfe's law, grid-based resources become more valuable as the number of devices and users increases. The wireless grid makes it easier to extend grid computing to large numbers of devices that would otherwise be unable to participate and share resources. While grid computing attracts much research, resource sharing across small, ad hoc, mobile, and nomadic grids draws much less

 
Figure 1: Dynamic and fixed wireless grids

Wireless grids, a new type of resource-sharing network, connect sensors, mobile phones, and other edge devices with each other and with wired grids (Figure 1). Ad hoc distributed resource sharing allows these devices to offer new resources and locations of use for grid computing. In some ways, wireless grids resemble networks already found in connection with agricultural, military, transportation, air-quality, environmental, health, emergency, and security systems.

A range of institutions, from the largest governments to very small enterprises, will own and at least partially control wireless grids. To make things still more complex for researchers and business strategists, users and producers could sometimes be one and the same. Devices on the wireless grid will be not only mobile but nomadic—shifting across institutional boundaries. Just as real-world nomads cross institutional boundaries and frequently move from one location to another, so do wireless devices. The following classification offers one way to classify wireless grid applications.

• Class 1: Applications aggregating information from the range of input/output interfaces found in nomadic devices.
• Class 2: Applications leveraging the locations and contexts in which the devices exist.
• Class 3: Applications leveraging the mesh network capabilities of groups of nomadic devices.

The three classes of wireless grid applications conceptualized here are not mutually exclusive. Understanding more about the shareable resources, the places of use, and ownership and control patterns within which wireless grids will operate might assist us in visualizing these future patterns of wireless grid use.

The Grid, is a promising emerging technology that enables the simple "connect and share" approach analogously to the internet search engines that apply the "connect and acquire information" concept. Thus, mobile/wireless grids are an ideal solution for large scale applications which are the pith of 4G mobile communication systems. Besides, this grid-based-approach will potentially increase the performance of the involved applications and utilization rate of resources by employing efficient mechanisms for resource management in the majority of its resources, that is, by allowing the seamless integration of resources, data, services and ontologies. Figure 2 places wireless grids in context, illustrating how they span the technical approaches and issues of Web services, grid computing, P2P systems, mobile commerce, ad hoc networking, and spectrum management. How sensor and mesh networks will ultimately interact with software radio and other technologies to solve wireless grid problems requires a great deal of further research.

 
Figure 2: Wireless grid issues and standard chart demonstrating their complex needs

MOBILE GRIDS FOR 4G MOBILE COMMUNICATION SYSTEMS

Mobile computing is an aspect that plays seminal role in the implementation of 4G Mobile Communication Systems since it primarily centers upon the requirement of providing access to various communications and services every where, any time and by any available means. Presently, the technical solutions for achieving mobile computing are hard to implement since they require the creation of communication infrastructures and the modification of operating systems, application programs and computer networks on account of limitations on the capability of a moving resource in contrast to a fixed one.

In the purview of Grid and Mobile Computing, Mobile Grid is a heir of Grid, that addresses mobility issues, with the added elements of supporting mobile users and resources in a seamless, transparent, secure and efficient way. It has the facility to organize underlying ad-hoc networks and offer a self-configuring Grid system of mobile resources (hosts and users) connected by wireless links and forming random and changeable topologies.

The mobile Grid needs to be upgraded from general Grid concept to make full use of all the capabilities that will be available; these functionalities will involve end-to-end solutions with emphasis on Quality of Service (QoS) and security, as well as interoperability issues between the diverse technologies involved. Further, enhanced security policies and approaches to address large scale and heterogeneous environments will be needed. Additionally, the volatile, mobile and poor networked environments have to be addressed with adaptable QoS aspects which have to be contextualized with respect to users and their profiles.

Enhancements to IPv6 Mobility Management Protocols Required by 4G Networks

Although the features mentioned are suited for 4G networks, recently, there has been almost universal recognition that IPv6 needs to be enhanced to meet the need for future 4G cellular environments. In particular, the absence of a location management hierarchy (IPv6 uses only simple location updates for location management) leads to concerns about the signalling scalability and handoff latency. This is especially significant when we consider that 4G aims at providing mobility support to potentially billions of mobile devices, within the stringent performance bounds associated with real time multimedia traffic.

There are three main areas where IPv6 needs to be enhanced before being used as the core networking protocol in 4G networks:

1. Paging Support: The base IPv6 specification does not provide any form of paging support. Hence to maintain connectivity with the backbone infrastructure, the mobile node needs to generate location updates every time it changes its point of attachment, even if it is currently in dormant or standby mode. Excessive signaling caused by frequent motion leads to a significant wastage of the mobile node's battery power, especially in environments with smaller cell areas (such as 802.11 based cellular topologies). It is thus impractical to rely completely on location updates and is essential to define some sort of flexible paging support in the intra-domain mobility management scheme.
2. Scalability: IPv6 allows nodes to move within the Internet topology while maintaining reachability and on-going connections between mobile and correspondent nodes. To do this a mobile node (MN) sends Binding Updates (BUs) to its Home Agent (HA) and all Correspondent Nodes (CNs) it communicates with, every time it moves. Authenticating binding updates requires approximately 1.5 round trip times between the mobile node and each correspondent node (for the entire return routability procedure in a best case scenario, i.e. no packet losses). In addition one round trip time is needed to update the HA; this can be done simultaneously while updating CNs. These round trip delays will disrupt active connections every time a handoff to a new radio access technology is performed. Elimination of this additional delay element from the time-critical handover period will significantly improve the performance of IPv6. Moreover, in the case of wireless links, such a solution reduces the number of messages sent over the air interface to all CNs and the HA. A local anchor point will allow Mobile IPv6 to benefit from reduced mobility signaling with external networks. For these reasons a new Mobile IPv6 node, called the Mobility Anchor Point (MAP) is being suggested, that can be located at any level in a hierarchical network of routers. Unlike Foreign Agents in IPv4, a MAP is not required on each subnet. The MAP will limit the amount of Mobile IPv6 signaling outside the local domain. The introduction of the MAP provides a solution to the aforementioned problems in the following way:
   1. The MN sends binding updates to the local MAP rather than the HA (which is typically further away) and CNs.
   2. Only one binding update message needs to be transmitted by the MN before traffic from the HA and all CNs is re-routed to its new location. This is independent of the number of CNs that the MN is communicating with. Thus by decreasing signaling traffic by having an intermediate level in the hierarchy helps accommodate a larger number of mobile nodes in the system.
3. Technologies: A mobile node switches from one network to another network in one of two cases: (a) when the signal from the network it is currently in starts to become weak or (b) when the mobile host detects another network which is better suited to its application compared to its current network.

The decision of the mobile device on the suitability of the network can be based on signal strength, network bandwidth or certain policies which the user might have stored in his profile based on which subsequent switching between networks of different access technologies may occur. For example, when a user is streaming a video, he/she may use WLAN and when he/she is listening to highly compressed audio, she might switch to GPRS.

Further, another issue that needs to be resolved is that of informing the source (HA/CN) when the MN has moved. In such a situation, the MN does a location update to its HA, which then takes charge of sending IP datagrams to the MN's new location using standard Mobile-IP mechanisms.

In line with the 4G vision of bringing together wide-area networks and local-area packet-based technologies, mobile terminals are being designed with multiple physical or software-defined interfaces. This is expected to allow users to seamlessly switch between different access technologies, often, with overlapping areas of coverage and dramatically different cell sizes. Mobility management protocols should then be capable of handling vertical handoffs.

Mobility Management in 4G

The 4G mobility management includes mobility related features, absent in previous generation networks, such as: Moving Networks, Seamless Roaming and Vertical Handover.

Mobility Management Operations

The operation of mobility management is divided into two related parts, location management and handoff management.

Location Management

Location management involves two operations; location registration and call delivery as shown in figure 10. Location registration involves the mobile terminal periodically updating the network about its new location (access point). This allows the network to keep a track of the mobile terminal. In the second operation the network is queried for the user location profile and the current position of the mobile host is retrieved. Current techniques for location management involve database architecture design and the transmission of signaling messages between various components of a signaling network. Since location management deals with database and signaling issues, many of the issues are not protocol dependent and can be applied to various networks such as PLMN (Public Land Mobile Network) based networks, PSTN (Public Switched Telephone Network). ISDN (Integrated Services Digital Network). IP, Frame Relay, X.25, or ATM (Asynchronous Transfer Mode) Networks depending on the requirements.

 

Figure 1: Location management operations

Some key research issues for location management include:

• Addressing, i.e. how to represent and assign address information to mobile nodes. The problem is becoming more severe since the 4G mobile communication systems will be based on the internetworking and interoperability of diverse and heterogeneous networks of different operators and/or technologies. A global addressing scheme is needed, e.g. IPv6 address, to locate the roaming nodes.
• Database Structure, i.e. how to organize the storage and distribution of the location information of mobile nodes. Database structure can be either centralized or distributed, or the hybrid of these two schemes. Tradeoff is needed between access speed, storage overhead, and traffic overhead due to the access to the related databases. Caching is also an important technique for the improvement of access performance.
• Location Update Time, i.e. when a mobile node should update its location information by renewing its entries in corresponding databases. Schemes for location update can be either static or dynamic. In a static scheme location update is triggered by some fixed conditions like time period or network topology change. A dynamic scheme is more personalized and adaptive, and based on some situations such as counter, distance, timer, personal profile, or even predicted factors.
• Paging Scheme, i.e. how to determine the exact location of a mobile node within a limited time. Obviously an adequate tradeoff is needed between time overhead and bandwidth overhead. There are also both static and dynamic schemes for location paging. In static cases paging is simply done to the whole certain area where the mobile node must be in. For a dynamic method, the main problem is to firstly organize the paging areas into groups and then recognize the best sequence of the separated areas for paging, based on information like distance, probability, moving velocity, etc.

Handoff Management

Handoff management equals controlling the change of a mobile node's attachment point to a network in order to maintain connection with the moving node during active data transmission.

Operations of handoff management include (Figure 2):

• Handoff Triggering, i.e. to initiate handoff process according to some conditions. Possible conditions may include e.g. signal strength deterioration, workload overload, bandwidth decrease or insufficiency, new better connection available, cost and quality tradeoff, flow stream characteristic, network topology change, etc. Triggering may even happen according to a user's explicit control or heuristic advice from local monitor software.
• Connection Re-establishing, i.e. the process to generate new connection between the mobile node and the new attachment point and/or link channel. The main task of the operation relates to the discovery and assignment of new connection resource. This behaviour may be based on either network-active or mobile-active procedure, depending on which is needed to find the new resource essential to the new establishment of connection.
• Packet Routing, i.e. to change the delivering route of the succeeding data to the new connection path after the new connection has been successfully established.
  
  

 

Figure 2: Handoff of management operations

Wireless networks vary widely in both service capabilities and technological aspects, so no single wireless network technology can fulfill the different requirements on latency, coverage, data rate, and cost. An efficient strategy is necessary for the management of such a wireless overlay architecture and mobility within the framework. In homogeneous environments, traditional horizontal handoff can be employed for intra-technology mobility. In heterogeneous environments, vertical handoff should be used for inter-technology mobility. Vertical handoff may be occur either upward (i.e. to a larger cell size and lower bandwidth) or downward (i.e. to a smaller cell size and higher bandwidth); and the mobile device does not necessarily move out of the coverage area of the original cell. Some packet-level QoS parameters become more important to real-time multimedia services, including packet latency, packet loss rate, throughput, signalling bandwidth overhead, and device power consumption.

Besides the basic functions that implement the goal of handoff management, there are many other requirements on performance and packet-level QoS that should be carefully taken into account when trying to design or select a handoff management scheme, including

• Fast Handoff, i.e. the handoff operations should be quick enough in order to ensure that the mobile node can receive data packets at its new location within a reasonable time interval and so reduce the packet delay as much as possible. This is extremely important to real-time services.
• Seamless Handoff, i.e. the handoff algorithm should minimize the packet loss rate into zero or near zero. Fast handoff and seamless handoff together are sometimes referred to as smooth handoff. While the former concerns mainly packet delay, the latter focuses more on packet loss.
• Routing Efficiency, i.e. the routing path between corresponding node and mobile node should be optimized in order to exclude possible redundant transfer or bypass path as triangle routing. Some distinct but complementary techniques exist for handoff management to achieve its performance and QoS requirements above, including:
• Buffering and Forwarding, i.e. the old attachment point can cache packets during the MN in handoff procedure, and then forward to the new attachment point after the operation of connection re-establishing of mobile node's handoff.
• Movement Detection and Prediction, i.e. mobile node's movement between different access points can be detected and predicted so that the next network that will soon be visited is able to prepare in advance and packets can even be delivered there before and/or during handoff simultaneously to the old attachment point.
• Handoff Control, i.e. to adopt different mechanisms for the handoff control. Typical examples include e.g. layer two or layer three triggered handoff, hard or soft handoff, mobile-controlled or network-controlled handoff, etc.
• Domain-Based Mobility Management, i.e. to divide the mobility into intra-domain mobility and inter-domain mobility according to whether the mobile host's movement happens within one domain or between different domains

Technological solutions for 4G

Adaptable Capability - Aware Service Provision	Different wireless access networks differ significantly in terms of coverage area and supported bandwidth, mobile network, their capabilities should be considered so as to refine the list of applicable services.
Transparent Mobility and Universal Roaming Capability	Seamless user mobility across different wireless access technologies (e.g. WLAN, UMTS etc.) with minimal or zero user intervention must be supported by efficient inter-system mobility management and hand over procedures. Roaming should build on cross industries standard protocols and architecture, such as hierarchical Mobile IPv6. As different systems may entail different charges, it should include QoS and pricing information as part of mobility management signaling.
Automated Protocol Configuration Mechanisms	The multiple options capable of accommodated the same set of services will result in accruing different charges in 4G mobile environments, thus users to be informed regarding the pricing preferences
Policy Based Management and Information Models	Policy based management demarcates between enforcer entities and decision entities in the infrastructure which results in realization of flexible management architecture that spans across multiple administrative domains. Policy protocols also support both outsourcing and provisioning modes of operation, making policy based management an ideal approach for 4G mobile environments.
Flexible Pricing and Billing Mechanisms	Network related pricing models must be completely independent from service related ones, with regarding to formulation as well as application matters.
Application and Mobile Execution Environment Aspects	As million mobile terminals and different manufacturers with different characteristics and applications will use 4G environment so there is a need to develop universal hardware platform with hassle free application with interpreted languages. The independent service provider will be relieved from the burden of developing, supporting and maintaining multiple versions of their applications for each possible client.

4G Heterogeneous Networks General Architecture

The 4G Mobile communications will be based on the Open Wireless Architecture (OWA) to ensure that the single terminal can seamlessly and automatically connect to the local high-speed wireless access systems when the users are in the offices, homes, airports or shopping centers where the wireless access networks (i.e. Wireless LAN, Broadband Wireless Access, Wireless Local Loop, HomeRF, Wireless ATM, etc) are available. When the users move to the mobile zone, the same terminal can automatically switch to the wireless mobile networks (i.e. GPRS, W-CDMA, cdma2000, TD-SCDMA, etc.).

The advantages of this converged wireless communications are:

1. Spectrum efficiency is greatly increased.
2. Highest Data rate to the wireless is mostly ensured.
3. Best sharing of the network resources and channel terminal utilization.
4. Optimally manage the service quality and multimedia applications.

The modules within the architectural framework should be able to incorporate the following high-level mobility issues (Figure 1):

• Users: This focuses on the movement of user, and allows user access to his/her home network while on the move, which involve the provision of personal communication.
• Terminals: This allows the provision of services at any time and anywhere. Terminal mobility allows mobile clients to roam across geographic boundaries of wireless networks. The greatest challenge in providing terminal mobility within a 4G Infrastructure is to locate and update the locations of the terminals in various systems.
• Networks: Network mobility is the ability of the network to support roaming of an entire subnet work, structured or ad hoc.
• Applications: Mobile application should refer to a user's profile so that it can be delivered in a way most preferred by the subscriber, such as context based personalized services.

 

Figure 1: Mobility dimensions

The incorporation of new functions into existing mobility protocols and mechanisms does not appropriately solve the demands of future communication scenarios. Therefore a new‘Mobility Architecture’ needs to be defined, based on the following principles: Diversity, Harmonization among layers, Legacy Awareness, Concept of mobile entities and Naming and name management.

With the acceleration of technology, there is competition among commercial houses to create significant growth and they are looking for various technological solutions for Fourth Generation Mobile Communication Systems

CHALLENGES TO 4G VISION

Simplicity and security are the main challenges for the consumers of wireless devices. All consumers have different needs but they all want simplicity i.e. use of their wireless device at any place any time. Corporate houses also want to ensure that their employees are accessing confidential data in a secure way. 4G technology will require massive innovation and substantial investment. It requires multiple changes in technology and network infrastructure, in handsets and software. A huge amount of innovation is necessary to deliver this kind of promise. As discussed the 4G network will be fully Internet protocol (IP) wireless infrastructure and thus this will give the ability to exploit the capabilities of Internet. The major challenges in realizing the 4G visions are:

1. Power consumption: Multiple processing and communication elements will increase the current drain. Managing power use in the infrastructure will play a vital role in achieving 4G technology. Additional hardware acceleration technology is required to manage power. OFDM based technology is crucial to manage some of the process streams and power challenges in such kinds of applications and devices. Some form of management of current drain and reduced battery drain is required for better battery life.
2. Spectrum efficiency: More spectrum is required to be made available. For this we have to refurbish existing spectrum. Use of cognitive radio can improve the spectral efficiency. Even with these steps, the 4G radio access network will need to provide significantly better spectral efficiency.
3. Cost: This is not only about infrastructure, operating or handset costs but also the cost of deployed services too. To deliver the spectral efficiency, the coverage is required. And for coverage there will be a dramatic growth in the number of base stations. Three times more base stations will be required to deliver a ten fold increase in data rate. Deployment of advanced antenna techniques such as MIMO and Space-Time Coding (STC) can improve spectrum efficiency, as well as reduction in growth rate of base stations; thus the capital cost will be reduced. On the handset side, there are significant challenges in continuing to drive down the cost of integrating greater and greater processing capability in multi mode RF technology.
4. Miniaturization and Processing Challenges: Miniaturization challenges include power reduction, cost, size and product development cycle. Multimode technology in 4G means availability of different types of radio access technologies in a seamless way. There are significant software, billing, carrier interoperability and enterprise carrier interoperability challenges. For bulk CMOS (Complementary Metal Oxide Semiconductor) process technologies, various companies are trying to provide higher performance at lower power as the semiconductor industry migrates from 90nm to 65nm to 45nm to 32nm technology. It is expected that in next five to ten years the evolving bulk CMOS technologies will completely resolved these complications. RF CMOS are continuing to scale for high-speed high-resolution A/D converters, and isolation techniques are being developed in the industry for multiple radio operation and single-chip die integration.
5. Advanced Architectures for 4G: In WCDMA, there are two variables -coding and time. With OFDM-based 4G, frequency, space and time are being used as variables to extract the data. With OFDM, information is separated into small sub-bands, and the information in each of these bands can be signal-processed independently in a parallel fashion. As consumers expect continuous service, so parallel processing is being increased so that the net result is that a high-speed, low-power drain OFDM engine architecture which can be developed to support 4G data throughput requirements. OFDM is typically discussed as being a WiMAX technology. WiMAX is an important technology as base business model behind broadband wireless access.
6. Business Challenges: 4G is not going to be driven by a single entity or organisation. It will require a tremendous number of partnerships and a robust ecosystem which can exploit the capabilities that are available in wireless technologies. Multiple standards bodies, corporations and government entities are required to come together to drive standards-based interoperability and the opportunity to deliver 4G networks. Governments will have to manage the spectrum in different parts of the world, and this will have a dramatic impact on how we can exploit the capabilities available to us in wireless technologies. To enable triple-play merged services delivered over wired and wireless networks, the issue of equipment has also to be taken into account for affordability, simplicity, interoperability and reliability.
7. Miscellaneous challenges: As we move from circuit-switched networks to IP networks, some of the challenges include packet acceleration, traffic management, data integrity, security and quality of service, which all represent different challenges for us on the infrastructure side compared to the traditional network infrastructure. This notion of high performance in a very constrained power envelope continues to be a significant challenge open standards continue to be another issue.
8. Challenges in IP Network Security and Traffic Control: Wireline internet access is increasingly being challenged to improve security. Security has multiple elements, much more than just moving encrypted traffic at faster and faster rates across the network. Security is also about denial of service attacks and digital rights management. These are all becoming carrier problems. Improved security and quality of service require providers to be able to identify video packets and prioritize them so that viewers get an uninterrupted stream of video content, if they are watching a movie or TV show on demand. These security / quality of service capabilities are the key elements of managing the network in both wireless and wireline infrastructure. From the processor perspective, the network processor has been exceptionally efficient at driving performance at layers 2 and 3, but suffers a significant drop-off in performance in layer 4-7 protocols. A general-purpose microprocessor does not deliver the kind of performance networks require at layer 2, and does little better at layers 4-7. Today's communications processors use hardware acceleration techniques to achieve better performance in the lower levels and do slightly better in the higher levels. But there is still a significant content processing gap in terms of microprocessor, network processor and communications processor technologies. Clearly one of the requirements is the ability to provide a solution that does not just forward headers and IP packets. We need to inspect those packets; connect those packets and carry out stream processing instead of packet processing. In terms of base station size and cost constraints, there is a trend towards more base stations covering smaller areas while managing multiple power output limits, frequencies and standards.
9. Financial Challenges: There are various financial challenges in reducing the cost of power amplifier in the base station which manifests as a largest expense. Other financial challenges are cost of components, software or services providers or carriers; significant investment is required to enable the next generation 4G network