Routing Optimization | COMPARING INNOVATION ROUTING AND 4G REQUIREMENTS

At the early days of the Internet, routing took into account the number of hops an as important metric for path selection. This was a wise decision at the time as most of the Internet was still homogenous in terms of its links, router capacity and traffic. Soon later, weights were associated to links giving autonomous systems a new criterion to decide on the best routes and a mean to engineer their traffic and balance this. The creation of labels by MPLS provided a similar traffic engineering mechanism capable of controlling and improving the routing and service delivery through path selection.

In the new context of 4G networks, routers must deal with different dynamic link stability levels, security and QoS levels and network handoff It is for such reasons that the 4G networks will certainly need to also consider new routing metrics and change these according to their environment or context. Under some scenarios, reachability could be more important than performance whereas QoS may become the metric of choice in other circumstances. This may also be service and application driven. Electronic mail transfer is a store and forward application that requires information integrity mainly whereas video conferencing considers low delay and bandwidth as primordial network resources.

Future 4G will certainly embrace disruptive connections and delay tolerant networks, high mobility users resulting in a challenging mix with different routing metaphors and techniques thriving within a single 4G unifying architectures. A simple, "one hat fits all" approach to routing cannot be the way forward. Therefore 4G needs to consider multi-metric optimization following different innovative routing approaches instead of merely reusing traditional strategies. It is believed that new routing and resource management insights borrowed from areas as diverse as biology, social phenomena, random and probabilistic diffusion models are expected to lead the way ahead.

But this is nonetheless not a complete breakaway from routing as we know it. In fact one expects to continue making use of useful traditional concepts such as clustering and hierarchical structures to simplify, organize and improve 4G routing. Following a dynamic approach, social algorithms exchange messages to find popular nodes and establish similarity among them in order to create clusters and hierarchical structures. Similarly to traditional routing algorithms from fixed networks, messages can be forwarded from any social node to a popular one judged to be in a better position to disseminate the information and capable of increasing the probability of a message reaching its destination. This offers ways to increase the delivery rate, but differently from the flooding algorithm, the social strategy reduce s the number of message replication as these messages only are forwarding among a restricted number of nodes. Moreover, approaches such as SOLAR and (Leguay, Friedman & Conan, 2006) work by extracting location information to identify mobility patterns in order to improve their routing efficiency. They rely therefore on the understanding of user's behaviors in terms of mobility patterns 4G networks are expected to collaborate with each other independently of their underlying technologies. For example, a user with Bluetooth and GPRS devices can choose one or another technology to disseminate a given type of information according to application level criteria such as urgency and destination distance. One could use an epidemic algorithm to send a simple message to a friend through a Bluetooth interface while selecting a GPRS interface to transfer credit (possible future money) to a distant family member.

ANALYSES OF UNTRADITIONAL ROUTING | Improve Routing and Future 4G Networks

The restrictions imposed by traditional network technologies were presented and we showed how new ways for thinking about routing have emerged to overcome these. They include insights and parallels made from observing a number of biological, social and epidemic behaviors. A number of proposals, associated to these metaphors, make use of mobility patterns, pheromone levels, user habits and profiles, relationships and other types of stimulus to offer self-organization, load balancing, adaptability and advanced technology dependent routing. This section is going to perform some concrete evaluations to show and determine the impact of some of network and other important parameters and examine their configuration. To achieve this, the reader is invited to review some optimization and evaluation techniques that are very much relevant to the context of routing in future networks,

Percolation

The percolation theory is inspired from the observation that there is a limit value for a physical material to make a transition between two states called by "critical phenomenon". For instance, water (a fluid) has two states: liquid and gas. A bottle of water may transition from the state liquid to gas when submitted to a higher temperature, namely, at 100°C at sea level. Another example is that of a filter where there is a given alpha number of porous in a stone. When the number of porous reaches a threshold, water, then, passes to the other side of this stone. These probabilistic changes of states are defined according to a percolation model that uses a threshold to determine such transitions. Hence, such strategy would help determining which routing parameter values would cause percolation, or successful knowledge sharing in the context of future 4G networks.

Some works set up a static percolation coefficient value in order to improve routing. The spatial gossip is an example of a routing algorithm that used this to select the forwarding node. Other works chose to evaluate the environment to discover when such algorithm percolates. For instance, one could seek the relation between buffer size and the success delivery rate. Otherwise, one could check if there is a limit buffer size that determines success or no delivery of messages. The analogy in this example associates messages to a fluid in a percolation scenario and nodes to the surface. Consequently, when all the messages start going from the source and reach their destination, one says that routing has percolated.

Diffusion and Chemotaxy

Adolph Fick was among the pioneering researchers who studied extensively the diffusion process. He observed that salt movement occurs from high to low concentration in liquids and defined an equation to express the proportionality between the flow and the spatial gradient of diffusion. Other researchers also studied the diffusion observing a spontaneous particles movement from low to high concentration. However, there is a common concept among these equations: they expressed the movement of cell or substance to obtain equilibrium, considering, in general, the position as a variable or both time and position.

Similarly, Chemotaxy is a movement behavior according to the gradient of concentration, but it is not a spontaneous event. Chemotaxy represents the attraction or retraction among cells due to some substance. It is commonly used in biology to analyze the behavior of human cell, virus or bacteria. However, such behavior has been analyzed and shown to also benefit the routing environment. Routing policies could be seen as the substance that modifies spontaneous movement.

Given that some message forwarding is based on a probabilistic mechanism set according to the encounter frequency of nodes (i.e. PRoPHET). We could evaluate the diffusion by modifying node movement in order to verify whether node mobility could be a stimulus to influence this behavior or not. In other words, we could check whether node mobility increases or not the message delivery rate.

Considering that PRoPHET could also be executed in sensor networks, policies are likely to move a node by several spaces in order to increase the encounter frequency and as a result may be used to improve the delivery ratio. Alternatively, one could set fake information altering encounter frequency, the message delivery decreases, because messages are removed from a buffer before actually finding their destination.

Stigmergy

Pierre-Paul Grassê introduced the Stigmergy concept after studying nest building. He observed that there is an indirect communication used by social individuals in order to coordinate their efforts towards some objective. For example, Ants lay down more pheromone when they find food to enable other ants to detect and react to this stimulus. In summary, they indirectly interact and cooperate to feed (or finding a path in the routing analogy). Although it is a comprehensive behavior, there is lack of mathematical models or equations to describe Stigmergy. Typically, the stimulus is not reached by some well established known equation, one may consider a given variable as stimulus to Stigmergy behavior and verify whether only a node with a fake variable can modify the Stigmergy of all individuals of a group and consequently the environment

Given that the decision mechanism of PRoPHET routing evaluates the number of encounters of neighbors, we could setup the encounter frequency for a single given node with fake information and next observe the success ratio. The encounter frequencies are used by such node as a Stigmergy where the nodes collaborate with this information to route the information.

SOCIAL OVERLAY NETWORKS

The overlay network approach allows the creation of several virtual networks over physical ones. Here one hop in a virtual network may correspond to several hops from one or more physical networks (underlays). In turn, a virtual network may even be built over other virtual networks. However the overlay routing does not have direct control over how the underlay forwarding of packets is actually performed. As a result one may not classify solutions such as Buble and SimBet as mechanisms to build overlay networks, since their nodes have routing control over the physical layer. Other routing algorithms found in widely spread Peer-to-Peer (P2P) social networks such as Gnutella, Chord and Tapestry are examples of peer-to-peer protocols that can be used to create overlay networks. In order to improve these overlay networks, and other works applied social mechanisms and consequently we named these proposals as social overlay networks. They deal with security and optimization using social ideas extracted from the underlays.

DSL (Davis Social Links) is an example of a proposal that applied social approaches to deal with security. It has a social overlay mechanism that creates trust relationships of social networks based on the small-world phenomenon in order to control, trace and separate address and identity information. The idea is to allow communication between nodes with a direct link or a social path linking them. Messages in the DSL social network contain a set of keywords describing node properties. The social path is created by the exchange of keywords between nodes connected by direct links. The nodes can accept or drop messages from some social path or modify these along another one. There is consequently a recipient controllability being exerted. For example, nodes A and B have "red" and "yellow" as part of their keyword sets respectively. These strings are cryptographically exchanged prior to the exchange of data. A Node can propagate the keywords in order to increase routability.

Work is a bit similar to social routing while not applied at the physical layer however. SOLAR, seen earlier, imports a user's profile information to forward data. In SOLAR, the profile is defined by a node itself and describes node mobility and its likely locations. Differently from SOLAR, acts at the application layer where the profile manipulates the dissemination and routing of messages. An even greater difference is to do with the fact that the profile in  may be updated and created by friends and acquaintances of a given node instead of being the sole responsibility of the node as in SOLAR. When a node creates a link, the user must attribute one or more keywords to describe the new friend. This one, the friend, needs then to agree with such description to allow for the effective link creation. As described by an application in, it is important to find a best person to answer some questions about some given keywords. This idea for creating profiles by friends could be implemented at the network level in terms of performance and made available to view by other nodes. Consequently, a profile that describes the options and possibilities for other nodes could be an interesting mechanism to help the node decide if another encountered node is a good relay to forward its messages.

PeopleNet is another social mechanism that propagates information using overlay networks. It has only three types of messages: request propagation, request and response. The request and response messages are always forwarded over long range connectivity such as over a cellular infrastructure; the propagation messages are always broadcasted with shorter range connections until some node matches the request propagation with some response. Whenever a propagation message matching occurs, the user who placed the request message receives the response message via long range connectivity. Moreover, the users can pre-determine the type of queries to handle in some specific geographic context, called Bazaar. So, any person close or distant to a Bazaar can send requests through the cellular infrastructureto other users in a specific geographic (Bazaar). Information is spread around to users in a specific geographic location, but it does not benefit from the number of meetings among nodes in a specific geographic area as in SOLAR.

PeopleNet differs from the proposal defined in as it does not concern itself with any mobility pattern, similarity of mobility and the ability of nodes to learn about their own mobility. PeopleNet relies on the innovative idea of using the widely deployed cellular infrastructure and Bluetooth devices to propagate information search. A second peculiar contribution involves the overlay routing according to the meta-information (i.e. Bazzar and message type) to choose what connection must be used to forward the messages. So, one could extract the importance from high level information that could be used in routing.

SPROUT presents a social mechanism to route messages in overlay networks such as Distributed Hash Tables (DHT). It is based on the use of the knowledge of a trust relationship among social nodes to choose what node must receive a message and to associate message priority. SPROUT presents possible trust function according to the number of hops in a social overlay (the distance d_ij between social nodes n₁ and n_j). The relation in (46) is one of its trust functions used to choose the next hop, where f is a static probability for two nodes to be trusted friends. The reader may note that the probability of two nodes being friends is limited by the value r. For example, if f = 0.95 and r = 0.6, then the trust function assumes that the friends with high proximity of node n i are best friends (reflecting a high trust relationship) and consequently very likely to correctly route a message and when d_ij >8 the trust will be maintained as 0.6. The objective of this work is to reduce the number of several network attack types that may drop the packets or forward the data to any different node other than the correct destination. For instance, in a DHT structure, a malicious node may exchange messages in order to disseminate unwanted information. SPROUT locates the trustiest friend of a given node that has a closer identifier, but not greater than, a key value until finding the destination node for that given key. Should this fail, then the source node executes the traditional DHT process. Although this work has been implemented in overlays, it could also be applied at the network layer. A node should evaluate the trust relationship of its neighbor instead of choosing the shortest path, which may be an unsafe path in terms of optimization and integrity. Further, trust identification remains a hard undertaking.

On the other hand, the trust relationship is not immune to attacks completely. Malicious nodes may convince a small number of honest ones trough the creation of several and false identities to increase their influence and credibility in the network. Looking at this problem SybilGuard and Syb-ilLimit map users and nodes, separating the network in two groups: a honest region with nodes with only one identity and a Sybil region populated by malicious nodes with more than a single identity. They also established that the number of links between these regions (called attack edges) is independent of the number of malicious identities. Moreover, if a trust route contains only nodes into the honest region then all the routes that cross the same node or edge will converge. Therefore, one may observe that there are several works applying social approaches in order to improve information propagation in overlay networks, security and optimization.

Propagation in social overlay and underlay is very similar, but there is a little difference. Both the optimization and security are interlaced in the context of social networks. This may be the case when messages are dropped or wrongly forwarded. A number of security enhancements have been suggested in to improve underlay security. User's devices are used to route data in DTN scenarios, increasing the likelihood to disseminate worms and viruses, as their users are often inexperienced with regard to such security threats. Moreover, networks with high-degree nodes tend to connect to other high-degree node networks (the famous often move in the same circles) and are therefore more likely to be subject to epidemics. Indeed a single infected high degree node will quickly infect other high-degree ones. On the other hand, networks where high-degree nodes tend to connect to low-degree nodes show the opposite behavior; a single infected high-degree node will not spread an epidemic very far.

Challenges for Future 4G Networks

We have established that 4G convergence is expected to deal with several environments, including short range networks, which, in general, involve devices with capabilities subject to CPU, memory and disk limitations. Thus, with regard to routing, the next generation network should consider strategies that conserve battery power not only from a device survival point of view but more importantly in an attempt to use greener environment friendly solutions. These are also known as power-aware routing. For example, these devices should avoid the use of highly demanding table updates.

Routing mechanisms using location information have been proposed in order to improve energy consumption and data delivery. Note that the excessive use of location information from devices such as GPS for routing decisions can lead to a considerable increase in energy consumption when compared to location agnostic solutions. Moreover, vehicular networks are also expected to maintain location servers for vehicles to help in information routing.

In existing 2G and 3G networks, there is the horizontal cell connectivity handoff, one that involves cell changes by a terminal within the same type of network. 4G introduces also the vertical handoff. Here devices are expected to change networks they attach to. Hence, the challenge is to design routing protocols that are capable of handling vertical handoffs between pairs of different types of networks, while maintaining QoS requirements and optimizing common radio resources availability.

Under 4G networks, security is also seen as a paramount concern. Traditional attacks on existing IP networks will certainly migrate to 4G networks encouraged by both the heterogeneity and the open air interfaces of such networks. Routing information may be targeted in such attacks on system security, there is a need to design secure routing approaches to ensure the integrity of routing in 4G systems. This is not however the object of this chapter.

In summary, among the many routing-related challenges this work has identified, we mentioned QoS, security, energy and location information. The following section will present the details of new routing algorithms, with new network metrics and routing mechanisms, which motivate the extension of traditional classification to include epidemic, biological and social class of routing ideas, one expects to see in 4G networks.

Optimal or Shortest Path Routing | 4G Networks

In terms of route choices, the traditional routing may be classified as Optimal or Shortest Path routing. An algorithm is said to present optimal routing, only when it has a convex function f _routing. (X): X → D, where D is always the best routing for all X, the convex set of parameters for this function. Although seemingly highly desirable, it suffers from some design limitations. It is difficult to build an optimized routing function that accurately captures all the performance measures and balances all data flows in a network. This task could lead to the use of routing parameters with incorrect or insufficient information, generating a probable unbalanced environment.

In general, many works define a function f (x) which expresses how to measure the network performance using metrics such as delay, latency, packet loss, link throughput and so on. Next, f(x) is minimized over variable x by applying one or more derivatives and defining the inequality of the form g_i(x) ≤ α and/or equality of the form h_i(x) = ω asconstraints, where g_i is a convex function and h_i is an affine function (i.e. one that consists of a linear transformation then a translation). As a result, an optimal routing algorithm controls the traffic and load balancing according to constraints of the minimum global value. The formula (4) could be a generic optimal function defined to choose the best route r_i(one with minimal load among neighbors of node k expressed by N_k) in terms of network load (expressed using constraints over the total mean and variance flow over the network).

Although not strictly a routing protocol, acting between the link and network layers, the IETF multiprotocol label switching (MPLS) may be seen as one that falls into the optimal routing class. MPLS has emerged as a very promising traffic engineering tool used in the control of traffic within current broadband core networks.

The routing protocols, classified as Shortest Path Routing (SPF), are characterized as those where each network node k selects routes following a formula such as the one in (5): here node k chooses the neighbor that can route its message with the shortest metric between source (node k) and destination. The number of hops is the usually used metric, but others also may used in addition to the attribution of weight for each metric such delay, throughput and others. In this case, the shortest path is the route with lowest weight instead to be the one with smallest number of hops. Consequently, we could classify SPF as an optimal routing when the network traffic is always stable, where, for example, the user's network maintains   and σ² ≤ ω.

However, this scenario is not a common one. Given that each node leads with estimated costs of link and does not worry whether its choices will unbalance the network traffic, SPF nodes tend to generate points of congestion on the network on a shortest path, along which most traffic is directed. Consequently, this class of algorithms is not an interesting one when dealing with highly dynamic network and disconnections. Dynamicity may turn the environment unstable with some nodes underutilized and others overloaded.

Routing algorithms 4G Networks

Routing algorithms are mechanisms to build paths and forwarding messages by selecting one or more intermediary nodes between source and destination of data messages. At the early days of the Internet, theses algorithms were designed to often lead with a single routing metric: the number of hops between routers. This was primarily due to the homogenous nature of the early IP backbone of the ARPANET. A general rule of thumb was adopted: the fewer hops a packet goes through, the less time it stays in the network and the fewer resources it uses. With time, the Internet evolved to a heterogeneous melting pot where such simple hop routing could no longer be sufficient. Let us consider that a network, expressed by N, is constituted by a set of heterogeneous routers (n nodes), then N = {n_1′ n_2′…n_n-1, n_n}, where each node n_i can have a distinct total network capacity c_i and a set of known routes {r_1′ r_2′…r_n-1, r_n} that consumes the node's resources. Given that each router can have different capacities and routes known to it, its available capacity to forward messages can be represented by formula (1). Consequently, the network is constituted by a set of available capacities of nodes X= {x_1′ x_2′… x_n-1′x_n }, where the network balance can be measured by the average and variance according to formulas (2) and (3) respectively.

However, performance measurements itself generate overhead that should be known and controlled. Node and network measurement, as well as, the routing algorithms also consume resources. Overhead control may be subject to what is being evaluated, the operating capacities of each node, its dynamicity, mobility, constraints on the resources and the underlying network switching, transmission capabilities among other factors. As a result, several routing algorithms have emerged, where each one is better when executed in specific environment(s) according to some pre-established. On the other hand, there are some common characteristics among them, allowing their grouping and classification. The traditional classification of routing algorithms looks for similarity in terms of three routing aspects: the process of route selection, whether it concerns itself or not with network balancing and process of route building, when routes are announced, including also what is announced and to whom.

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

STANDARDIZATION MOVES

Before elaborating on standardization, let us study some of the existing wireless standards which are summarized in table 1.

Table 1: The existing wireless standards 

1G	NMT, AMPS, Hicap, CDPD, Mobitex, DataTAC
2G	GSM, iDEN, D-AMPS, IS-95/cdmaOne. PDC, CSD, PHS, 2.5G - GPRS, HSCSD, WiDEN, 2.75G - CDMA2000, IxRTT/IS-2000, EDGE (EGPRS)
3G	W-CDMA, UMTS (3GSM). FOMA, lxEV-DO/IS-856, TD-SCDMA, GAN/UMA, 3.5G - HSDPA, 3.75G - HSUPA
4G	WiMax, WiBro

The two groups within the International Telecommunication Union (ITU) are specifically engaged to define the next generation of mobile wireless. These two groups are:

• Working Party 8F (WP8F) in section ITU-R.
• Special Study Group (SSG) "IMT 2000 and Beyond" in section ITU-T.

WP8F is focused on the overall radio-system aspects of 4G, such as radio interfaces, Radio-Access Networks (RANs) spectrum issues, service and traffic characteristics, and market estimations as shown in figure 7. The SSG "IMT - 2000 and Beyond" is primarily responsible for the network or wireless aspects of future wireless systems including wireless Internet, convergence of mobile and fixed networks, mobility management, internetworking and interoperability.

 

Figure 1: Structure of WP 8F

The main deliverable of WP8F is Recommendation ITU-R M 1645. This recommendation contains the overall goals for the future development of wireless communications. The list of the suggestions that are contained in the recommendation are:(i) the framework for 4G systems should fuse elements of current cellular systems with nomadic wireless-access systems and personal-area networks in a seamless layered architecture that is transparent to the user; (ii) data rates of 100 Mbps for mobile applications and 1 Gbps for nomadic applications should be achievable by the year 2010; (iii) Worldwide common spectrum and open, global standardization should be pursued.

Not only above, but the process of developing a standard is a long one, carried out by other several groups, which include Standards Development Organizations (SDOs),industry forums, and companies, such as OEMs, that have a stake in the end product. Some of the major SDOs are nonprofit regional or governmental bodies, such as ETSI (European Telecommunications Standards Institute) in Europe, CCSA (China Communications Standards Association) in China, and the TTA (Telecommunications Technology Association) in Korea. 3GPP and 3GPP2 are examples of industry SDOs (Service Data Objects) that develop and maintain standards for current 2G and 3G technologies. In April 2007, the ITU convened a global congress to set a course for the 4G standards development process. China has expressed interest to submit the standard in 2010. Presently it is doubtful that standard will emerge 2012. Nor are standards necessarily the final word on the subject. In the meantime, there is nothing to stop the various SDOs and wireless operators from deploying so-called 4G systems without waiting for the completion of the formal standards process.

The World Radio Communication Conference (WRC) in October/November 2007 at Switzerland discussed on the spectrum assignment for 4G. The road map of the ITU-R (International Telecommunication Union Radio communication Sector) targets the availability of 4G standard proposals for the year 2012. As soon as frequency bands for 4G are defined, 4G standardization activities are expected to start.

4G Transition Components

Some of the 4G transition components in brief are:

• Multi-Antenna Systems: To foster the growing data rate needs of 4G, deploying multiple antennas at the transmitter and receiver.
• Software Defined Radio (SDR): SDR is one form of Open Wireless Architecture (OWA). Since 4G is the collection of wireless standards, the final form of the 4G device will constitute all standards. SDR Technology offers one possible realization.
• Smart antennas and beam forming: These offer a significantly improved solution to reduce interference levels and improve the system capacity. With this technology, each user's signal is transmitted and received by the base station only in the direction of that particular user. This drastically reduces the overall interference in the system.
• Adaptive Modulation and Coding Techniques: The modulation and coding techniques change according to the network resource, user requirement and physical channel conditions.
• Access Schemes: The scarce resource frequency and network infrastructure is accessed using the channel accessing schemes. The existing wireless standards use TDMA (Time Division Multiple Access). FDMA (Frequency Division Multiple Access). CDMA (Code Division Multiple Access) and combinations of these. Recently, new access schemes like OFDMA (Orthogonal Frequency-Division Multiple Access) and MC-CDMA (Multi Carrier CDMA System) gained more importance in 802.16e and 802.20 standards.
• IPv6: It is generally believed that 4th generation wireless networks would support great number of wireless devices that are addressable and routable. Therefore in the context of 4G, IPv6 is an important network layer technology and standard that can support great number of wireless enabled devices. In addition to increasing the number of IP addresses, IPv6 also removes the need for Network Address Translation (NAT)—atechnique used in 3G and other networks to make private IP addresses work with Internet applications. In the context of 4G, IPv6 also enables a number of applications with better multi-cast, security and route optimization capabilities. With the available address space and number of addressing bits in IPv6, many innovative coding schemes can be developed for 4G devices and applications that could aid deployment of 4G networks and services.
• Mesh Networks: A mesh network is reliable and offers redundancy. If one node can no longer operate, all the rest can still communicate with each other, directly or through one or more intermediate nodes. Mesh networks work well when the nodes are located at scattered points that do not lie near a common line 

4G Objective

Before studying the objectives of 4G, let us understand some of the characteristics of 4G, which are summarized here in table 1.

Table 1: Characteristics of 4G 

Achievable Data Rates	10 Mbps (wide coverage) to 1 Gbps (local area). These are design targets and represent cell overall throughput.
Networking	All-IP network (access and core networks). Plug & Access network architecture. An equal opportunity network of networks.
Ubiquitous	Mobile, seamless communications.
Cost Reduction	Cost per bit: 1/10-1/100 lower than 3G Infrastructure cost-1/10 lower than 3G.
Connected Abilities	Person to person communication Person to Machine communication/Machine to machine communication.

The objective of 4G is to cater the quality of service and rate requirements set by the forthcoming applications like wireless broadband access, Multimedia Messaging Service, video chat, mobile TV, High definition TV content, DVB and minimal service like voice and data at anytime and anywhere 4G is being developed, the 4G working groups have defined the following as the objectives of the 4G wireless communication standard.

• Spectrally efficient system (in bits/s/Hz and bit/s/Hz/site)
• High network capacity, 10 times higher than 3G
• Nominal data rate of 100 Mbps at high speeds and 1 Gbps at stationary conditions as defined by the ITU-R
• Data rate of at least 100 Mbps between any two points in the world
• Smooth handoff across heterogeneous network
• Seamless connectivity and global roaming across multiple networks i.e. seamless services with fixed NW (Net Work) and private
• High quality of service for next generation multimedia support (real time audio, high speed data, High-Definition Television (HDTV) video content, mobile TV, etc)
• Higher frequencies: Microwave: 3-10 GHz
• Interoperable with the existing wireless standards
• All IP system, packet switched network
• Next-generation Internet support: IPV6, QoS, MoIP (Mobile over IP)
• Lower system costs: 1/10 of IMT-2000

In summary, the 4G system should dynamically share and utilize the network resource to meet the minimal requirements of all the 4G enabled users. Figure 1 illustrates here a prospective view of physical layer of 4G.

Figure 1: Prospective physical layer of 4G

 

Key Parameters

The move to 4G is complicated by attempts to standardize on a single 3G protocol. Without a single standard on which to built, designers face significant additional challenges.

Table 2 compares some of the key parameters of 3G and 4G. Though 4G does not have any solid specification as of yet, it is clear that some standardization is in order.

Table 2: Comparison of key parameters of 3G and 4G 

Key Parameters	3G	4G
Frequency Band	1.8-2.5 GHz	2-8 Ghz
Bandwidth	5-20 MHz	5-20 MHz
Data Rate	Upto 2 Mbps	Upto 20 Mbps
Access	W-CDMA	MC-CDMA or OFDM (TDMA)
Forward Error Correction	Convolutional Rate	Concatenated coding scheme
Switching	Circuit/Packet	Packet
Mobile Top Speeds	200 km/h	200 km/h
Component Design	Optimized antenna design, multi-band adapters	Smarter Antennas, software multiband and wideband radios
IP	A number of air link protocols, including IP 5.0	All IP (IP6.0)

4G Network Requirement

From above it is clear that 4G is immensely complicated and hence there will be special requirement for future networks. Some of these tentative requirements are hereby summarized in table 3.

Table 3: Requirement for future networks (tentative) 

Media	Transmission speed	Delay	Connection Latency	Terminal capabilities
Speech/3D Audio	< 1 Mbps	< 50ms	< 1 sec	3D sound field control High efficiency loud speakers
Video/3D video	10 Mbps (2D video) - 30 Gbps (3D video)	< 50ms	< 1 sec	Real time hologram
Enhanced Reality	< 1 Mbps	≪ 50 ms Should be predictable	N/A	Eyeglass display 3D and multimodal UI
Five senses communications	< 1 Mbps	< 50ms	N/A	Five sense sensors
Tele-existence	< 10Mbps (Robotic I/F) < 1 Gbps (Virtual avatar) < 100 Mbps (Alter-ego existence)	< 10 ms < 30ms < 5 ms (Small and known jitter)	1 Sec	Alter-ego robot

Development of 4G

There are many phases of developing 4G mobile communication systems. Let us study here two phases, i.e. development period and maturity period, which are described in table 4.

Table 4: Stepwise development of 4G mobile communications 

4G Mobile Communications
	Phase 1 (2009-2010): Developmental Period	Phase 2 (2011): Maturity Period
Core cellular systems	3.5G 3.5G mobile-communications system enhancing IMT-2000 (HSDPA/1xEV-DV)	4G 4G Mobile-communications systems
Transmission speed	30 Mbps	50 Mbps-100 Mbps
Service level	High-level application service	Service with higher-level authentication and security
Main users	Advanced users	General users
Functions	Basic functions	Fully-fledged system
Seam-lessness with other systems	Flexible realization of seamlessness with other systems	Seamlessness with no awareness thereof
Social impact	Positioning with social functions	Positioning as a factor inducing changes in social structure.