CROSS LAYERED FUNCTIONALITY FOR WiMAX TECHNOLOGY
CROSS LAYERED FUNCTIONALITY FOR WiMAX TECHNOLOGY
Dr.Hari Ramakrishna
Professor, Department of CSE, Chaitanya Bharathi Institute of technology
Gandipet -500 075, Hyderabad,
dr.hariramakrishna@rediffmail.comK.Ravi
Asst. Professor, Informatics,
Alluri Institute of Management Sciences
Hunter Road, Warangal,
kolipakaravi@yahoo.comMohd.Nayeemuddin
Asst. Professor, Informatics,
Alluri Institute of Management Sciences
Hunter Road, Warangal,
mohd.nayeemuddin@gmail.comABSTRACT
Today the world is running on the wireless technology. WiMAX is one of the wireless technologies to provide services to the people. In wireless technology most important issue is the Quality of Service (QoS). To provide this QoS WiMAX is implemented on different aspects.
This paper focuses on each aspect of these mechanisms in cross-layer Quality of Service architecture, highlighting both PMP and Mesh topology aspects and their differences. Each kind of topology presents not only a different way to obtain QoS, but also other important aspects such as bandwidth allocation scheduling and call admission control algorithms, which are left to vendor implementation.
Keywords: cross layer, WiMAX, QoS, PMP,Mesh, MAC, control algorithm
1. INTRODUCTION
WiMAX appears to be one of the most promising technologies of recent years and especially in its most recent version which specifies user mobility support and allows wireless multimedia services to be provided to a wide area. The term wide' has many advantages, both economic and practical. For example, consider the possibility of installing a WiMAX wireless infrastructure in a low density population area such as a small town or rural area, instead of creating a new fixed and wired infrastructure from scratch. The real source of success will be to provide services that meet the user's needs, thus making the technology ever closer to the simplicity and quality that each generic user expects. To characterize the services provided with QoS (Quality of Service), the IEEE 802.16 protocol
Describes various mechanisms related to network topology.
The Cross-layer QoS architecture is implemented by both PMP and Mesh topology aspects and their differences. Each kind of topology presents not only a different way to obtain QoS, but also other important aspects such as bandwidth allocation scheduling and call admission control algorithms are implemented to provide to provide best QoS with WiMAX>
2. WHAT IS QoS?
In order to understand the concept of QoS, we must examine it from different points of view. The user's point of view is the most abstract: a generic user tags a service as a qualitative satisfactory service if it meets his abstract qualitative expectations. For example, with regard to a video on demand service, the user will be satisfied if the video is displayed with no visible slowdown problems or distorted images. The user does not know the details about video transmission and network protocols but he is satisfied if the video is received in the correct way. The user and the requested application are the most obvious aspects of a communication scenario, but they are not the only aspects. The components that have a role are:
User
Application
Network
Protocol
Each of these components provides different points of view and, excluding the user, each component is related to various technical aspects and provides a concrete definition of quality. The particular application defines its expectations in terms of well-defined constraints; the network affects the scenario with its particular architecture and physical constraints; and finally the protocol contributes with the definition of rules' and mechanisms available to ensure that the required quality levels can be achieved. An example of QoS constraints may be the following:
end-to-end delay: the average packet delay from source to destination;
delay jitter: end-to-end delay variation of packets;
packet error rate (PER)/Bit error rate (BER): percentage value of packets/ bits lost;
Throughput: the percentage of sent packets correctly received at destination.
3. QoS MECHANISMS OFFERED by IEEE 802.16
Each protocol defines its particular mechanisms and algorithms so as to achieve high levels of QoS. It is important to note and to bear in mind that QoS is not related to a particular layer of the protocol stack. A protocol does not define only one layer but illustrates the behavior of a series of layers. The coordination of all of these layers contributes to establishing the performance of the network based on a particular protocol. In this way QoS can be seen as a concept related to various layers which constitute the entire protocol stack.
WiMAX (Worldwide Interoperability for Microwave Access) is the commercial name which is used to indicate devices compatible with the IEEE 802.16 protocol. The IEEE 802.16 protocol defines guidelines for providing wireless broadband services in a wide area. The protocol defines the physical layer (PHY), the medium access control (MAC) layer and also each management aspect; the PHY layer defines five air interfaces and the MAC layer allows itself to be interfaced with the IP (Internet Protocol) or ATM (Asynchronous Transfer Mode) upper layer protocol.
3.1 CROSS-LAYER QoS ARCHITECTURE
Figure 1 depicts a simple scenario in which a generic user tries to use a service offered by a remote server; this service may be a streaming video, VoIP call or other types of service. In Figure 1 the path from user to server is represented and the first step of the path is a WiMAX connection; that is the user device is connected to an SS (Subscriber Station), which in turn is connected to a BS (Base Station).
Figure 1: WiMAX scenario: user server connection
The protocols define an SS not only as a device' capable of providing service to only one user but also to a set of users in a building. In a user device, in a server and in each entity which plays a role in the communication the protocol stack defining the communication rules is implemented. For greater clarity and simplicity the user device and the server are considered as SSs. In our particular case, the MAC and PHY layers are defined by the IEEE 802.16 protocol, while the internet cloud can be constituted by each kind of technology. When a user application requires, for example, the transmission of a video, the higher protocol layer on the server side signals to the lower layer the need to send data with well-defined QoS constraints.
Thus, the MAC and PHY layers of the 802.16 protocol begin a process to reach the common goal that is to send the real time data respecting the QoS constraints; PHY and MAC share a set of parameters passing information from one layer to the others, in this way they initialize a cross-layer paradigm that exploits inter-relations between network layers to improve efficiency and quality. The intrinsic nature of the algorithm which must guarantee a high QoS level can introduce a cross-layer aspect, this is because the QoS is not only related to one layer, but also involves all the stack protocol layers. Thus, to guarantee compliance with QoS constraints there is a need to create collaboration between the various layers.
Considering the inherent characteristics of wireless communication and networking, the traditional layered network architecture can be considered to be inadequate to realize the full potential of wireless networks. Cross-layer design approaches can be used to improve and optimize the network performance by breaking the layer boundaries and passing information explicitly from one layer to the others. In Figure 2 a set of possible collaborations between pairs of protocol layers is illustrated. The black arrows of Figure 2 represent the information flows exchanged in the cross-layer architecture.
Figure 2: Cross-Layer example
3.2 MAC LAYER POINT OF VIEW
The MAC layer supports two different operative modes: point to multipoint (PMP) and mesh mode. In Figure 3 the two modes are depicted: the user segment operates in PMP mode and the BS server side operates in mesh mode.
Figure 3: IEEE 802.16 PMP and mesh mode.
These two operative modes provide different mechanisms that affect the MAC's behavior is a different way. Overall, in a WiMAX network, we can identify three different entities: the base station (BS), the subscriber station (SS) and the mobile subscriber station (MSS). In PMP mode the BS has a central role and is the only entity that can manage the bandwidth allocation and schedule the bandwidth requests received from SSs. Only BS-SS links are admitted and the BS is the only station which can broadcast data and control messages without coordinating the transmissions or asking permission from other stations.
In mesh mode there is a novelty: the capability to create direct links between SSs, thus an SS which goes behind the BS coverage area can also reach BS using a multi-hop route constituted by SS-SS links. Bandwidth scheduling can take place in a distributed or centralized manner; in the latter case the BS maintains a central role, while in distributed scheduling all entities are defined as mesh nodes'; we can distinguish the BS only because it is the gateway to reach the rest of the world'. MSS, finally, represents the mobile user and can only create a connection with BS in a PMP mode.
Figure 4 shows the protocol stack as defined by the IEEE 802.16 protocol. It is also possible to note the three sub layers which make up the MAC layer.
Figure 4: IEEE 802.16 protocol stack
The Convergence Sublayer (CS), in PMP mode, performs the task of classification of SDU (Service Data Unit), mapping the various SDUs from higher layers in the proper connection. To do this mapping in an effective way, a set of classifiers is defined and each SDU must be submitted to it. This task is related only to the PMP mode, because in PMP mode it is possible to create more than one connection between BS and SS. Each connection is related to a particular QoS level and this is true both in data and management connections.
The task of the Privacy sublayer is to provide a strong protection to service providers against theft of service. Moreover, it protects the data flow from unauthorized access by strengthening the encryption of the flows passing through the network. The Privacy sublayer provides a client/server management protocol authentication key where the BS (server) monitors the key distribution to the clients. There are two main components in the Privacy sublayer: an encapsulation protocol for the encryption of data packets that are sent over the network and a key management protocol (Privacy Key Management: PKM).
3.3 OFFERING QoS IN PMP MODE
If the network operates in PMP mode, when the server receives the request for a video on demand service, to guarantee a well-defined QoS level, it may rely on three important concepts. These concepts are:
connection
service class;
service flow
In Figure 5 the four ellipses represent the components of protocol which are not defined in the IEEE 802.16 standard.
Figure 5 Basic mechanisms offered by protocol
Compliance with the service constraints and consequent user satisfaction is related to these three important mechanisms which are not supported in mesh mode. In order to satisfy the client request, the server needs bandwidth. To simplify, we consider the server as an SS. The SS must send a bandwidth request for a particular connection to BS. The MAC protocol is strongly connection oriented and the connection is identified by a 16 bit CID (Connection Identifier). Consequently, the service in our example must be mapped on a well-defined connection. This connection can group each data flow which is characterized by the same QoS requirements. In PMP mode the bandwidth request from an SS can be made in three different ways:
using a bandwidth request header
by making a piggyback request using the Poll Me bit (PM) present in grant management sub header
Depending on service class in which the application is mapped, an SS can be polled periodically to verify any requests. The polling can be made in a broadcast or unicast way.
3.4 QoS INTRODUCTION IN MESH MODE
The basic principle of transmission coordination in an 802.16 mesh network is that no one node, including the BS node, can transmit on its own initiative without coordinating its transmission within its extended neighborhood. In a network operating in mesh mode there are two different ways to manage bandwidth allocation: centralized or distributed mode. The distributed scheduling, in turn, can be either coordinated or uncoordinated. In the distributed coordinated scheduling, all mesh nodes have to coordinate their transmissions in their extended neighborhood and they use the same channel to transmit the scheduling information.
The uncoordinated distributed scheduling allows fast setup communications between two nodes and does not cause collisions with the messages and the traffic of coordinated scheduling. Both modes of distributed scheduling, coordinated or not, use a three-way-handshake protocol. Considering the example introduced in previous sections, if the server is a mesh node of the network, in order to transmit data it has to send a request to the next hop mesh node, indicating the requested number of minislots it needs. The destination node replies with the grant message that is acknowledged with a grant copy by the server.
One of the advantages of mesh mode is the capability to reach the destination using a multi-hop path. If the server does not fall within the BS coverage area it can still reach the destination. The mesh mode only supports the TDD (Time Division Duplexing) mode; thus, the frame is divided into two parts:
control subframe;
data subframe
3.5 QOS APPLICATION ON PACKET BY PACKET BASIS
In PMP mode the IEEE 802.16 protocol defines various mechanisms useful for providing QoS. In mesh mode, the protocol does not have the following concepts: connection, service class and service flow. The protocol guidelines, inherently the QoS issues in mesh mode, are that the quality of service must be guaranteed, in the link context, packet by packet. The mesh node has the task of managing the received packets in such a way as to guarantee compliance with the application QoS constraints.
The generic header of a MAC PDU contains a 16-bit CID field. In the mesh mode, in the case where the payload is constituted by a MAC management message, the CID field is split into two parts. The first portion, of eight bit length, is the logical network identifier and the second portion contains the link identifier. If the MAC PDU contains a data payload, the first 8-bit portion of the CID is redistributed over four fields used to implement the QoS policies. The four fields are:
Type: indicates if PDU transports a management message or an IP datagram; it is two bits long. Two configurations of this field are reserved for future developments;
Reliability: this field indicates the number of admitted retransmissions for the current MAC PDU. Two possible values are: no chance of retransmission or a maximum number of retransmissions equal to four;
Priority/Class: indicates the priorities associated with the membership class of the message;
Drop Precedence: a message with a high drop precedence value has a high probability of being eliminated in the case of network congestion.
4. IMPROVING WIMAX FEATURES?
4.1 SCHEDULING ALGORITHM
The scheduling algorithm decides when a station can forward data and how much bandwidth is granted from the BS or from another mesh node. The protocol defines QoS mechanisms, such as the service classes in PMP mode or the PDU classification by CID in mesh mode; the scheduler must exploit' these mechanisms in an efficient way to provide optimized bandwidth management.
4.2 PMP Mode
PMP has many mechanisms available to provide QoS, namely service flow, service class and connection concepts. Each PDU of a particular application is mapped on a well-defined service class characterized by the parameter of a service flow. A scheduling algorithm, in PMP mode as in mesh mode, has to guarantee to each service class the forwarding of PDU stored in data queues, respecting the QoS constraints. Another important concept is fairness among connections of the same class, however it is also important to avoid starvation of a service class with lower QoS constraints.
The protocol describes the concepts summarized previously but does not present a scheduling algorithm. Thus, in order to realize a realistic, complete and functioning BS, we can select a scheduling algorithm from amongst those presented in the literature. We mention some solutions as examples. To delineate BS behavior it is necessary to establish how the BS makes the grants to the various service classes.
In this model, which also involves a mathematical queue model, the amount of grants is established as a function of network traffic. Usually, in each solution, as in this one, the UGS class is considered in a privileged manner, and rtPS and nrtPS receive grants in a dynamic way.
In this way, by collecting various ideas from the literature it is possible to improve the 802.16 protocol. It is important to note that the research is always in progress; the protocol was standardized five years ago but researchers are still stimulated by the possibility of constructing ever more efficient solutions. Evidence of this research activity is to be found in and . The former selects a set of scheduling algorithms such as:
Earliest Deadline First (EDF)
Weighted Round Robin (WRR)
4.2 MESH MODE
In the previous subsection we have seen the difficulties in creating an efficient BS scheduler in PMP mode; instead, in the following subsections we will analyze the mesh mode case. The mesh mode introduces further complications owing to the nature of network architecture. In this case the bandwidth allocation can be made in a centralized or distributed way, but in both cases the network topology is more complicated than with PMP.
In the case of PMP the network has a star topology, while in mesh mode, also using centralized scheduling, the topology can be built randomly. The scheduling algorithm therefore proves to be more complicated; it must also take into account transmission coordination problems such as hidden terminal or exposed terminal. The scheduler has to unite the concepts of coordination in the extended neighborhood and bandwidth allocation.
4.3 DISTRIBUTED ALGORITHM
If a mesh network, in order to provide bandwidth allocation, utilizes distributed scheduling, it does not have a privileged entity taking the role of coordinator; the coordination takes place in a distributed manner between mesh nodes belonging to the extended neighborhood. In Figure 6 the extended neighborhood for several mesh nodes is represented. The scheduling algorithm, implemented in each mesh node, has to operate in order to comply with the QoS constraints. An important aspect is that each node must provide a classification of received PDU because the service class concept is not present. Summarizing the focus of scheduling algorithm in distributed modes we have:
To respect PDU QoS constraints applying a sort of PDU classification: QoS must be applied packet by packet;
To decide the instance of transmission trying to avoid collision in the two-hop neighborhood.
Figure 6: Extended neighborhood of server node.
4.4 CENTRALIZED ALGORITHM
In centralized scheduling the focus of the scheduler is the same as in the distributed case, but its task is facilitated by the presence of a coordinator. In the previous case the scheduler can be imagined as distributed on each mesh node; in this case however, the only coordinator is the BS. Each mesh node has to send its request toward the BS and consequently the BS replies, spreading the bandwidth grants. To allow message forwarding, a coverage tree is considered. As we may understand from the previous concept, in the centralized way the coverage tree and the routing are important topics.
Figure 7: Example of coverage tree.
4.5 CALL ADMISSION CONTROL ALGORITHM
With regard to a WiMAX scenario: when a user makes a request to a remote server to obtain a particular service, the server must execute the following steps:
To identify the next node in order to forward data
To forward to the next node a request for a new connection
When the next node (BS in PMP mode or a generic WiMAX node in mesh mode) receives the request, it has to decide whether or not to admit the new call. The call admission control has to make this decision on the basis of network condition and traffic behavior. This decision is very important because it influences not only the QoS for the new connection, but also the QoS of existing connections.
4.6 PMP MODE
In PMP mode the entity which takes decisions is always the base station. The BS, in a centralized way, can organize and decide each new call admission or preemption of an old connection with lower priority. The BS can take its decision following a specially selected set of QoS parameters. Some of the parameters that can be considered are:
End-to-end delay
Throughput
Number of refused calls
In the literature the lack of a call admission control algorithm is met with various types of solutions. If a call admission control algorithm is presented in which the concept of service preemption is introduced and the admission decision is based on traffic class and bandwidth utilization of each traffic class. Each traffic class has a bandwidth portion reserved for it and can also preempt the lower priority admitted services. In [42], however, the focus is on reducing the polling delay and a cost-based function for admission decision is proposed.
Another simple idea to create a CAC algorithm is to exploit the service class concepts defined by the protocol and the mechanism of bandwidth reservation for traffic class, such as that realized in. Another interesting solution, like a cross-layer scheme, can be found it is important to keep in mind that in order to implement a new CAC algorithm, the algorithm task has to be established and, then, each QoS support mechanism provided by the protocol must be taken into account.
4.7 MESH MODE
In mesh mode the call admission control process has the same tasks as the PMP mode The main difference is that the entity which takes decisions is not the base station but a generic mesh node. Another important difference is that the PMP mode has a set of mechanisms to provide QoS that are not present in mesh mode. Thus, to realize the CAC algorithm the first step is to create a sort of classification of requested services; after this, it is possible to create, for example, a simple CAC scheme using the priority values of services.
5. FUTURE CHALLENGES
We have considered the classic challenges related to QoS, explained how to build cross layer solutions and highlighted the things to keep in mind in constructing cross-layer solutions. From this point, however, we are going to consider the most complex challenges which arise when looking to the future. One of these concerns end-to-end communication in an IP world, which represents the application of the IP protocol above 802.16 MAC. In the Wireless WAN (WWAN) context or other scenarios where WiMAX has to be integrated with other existing technologies, end-to-end QoS support will become an interesting challenge.
It is very interesting to take a look at new ways of addressing the cited problems, using theories and tools which belong to other branches of research.
5.1 END-TO-END QOS IN THE IP WORLD
Considering, for example, the IPv6 protocol which represents the future of the IP world, we can say that some problems arise in a world in which IP meets WiMAX. The neighbor discovery of IPv6 supports various functions for the interaction between nodes of a single subnet, such as address resolution. IPv6 was designed with no ties, independent from the underlying levels of protocol; however, to optimize the operations it requires the presence of multi-cast technology. Protocol 802.16 in PMP mode does not support bidirectional multicast and therefore appears inappropriate for the IPv6 features listed below:
Address resolution
Router discovery
Auto configuration
Duplicated address detection.
The 802.16 protocol also enables encapsulation of an IP datagram in a MAC PDU, but does not define how it should be made. The PMP mode has a reluctance with regard to IPv6 features, unlike the mesh mode where the SS has the chance to distribute the messages in a multi-cast way; the problem remains with the MSS because it must connect itself with the BS in point-to-point mode. If we continue the analysis of the world built on the integration between IP and WiMAX, we can distinguish between two different access modes: fixed and mobile.
The first is a valid alternative to XDSL connections, while the second creates support for new mobile data services, voice and multimedia traffic. Diversification can also be made in the mobile access; an IPv6 link can be defined as a shared IPv6 prefix link model or as a point-to-point. In the first case, with reference to Figure 8, a subnet consists of a single AR (Access Router) interface and multiple SS units.
Figure 8: Example of shared IPv6 prefix link model
In the second case, a subnet consists of only single AR, BS and MSS; so each connection is treated individually. Obviously, each scenario and each type of link introduced can influence the quality of service of an end-to-end connection. There are many problems to solve, for example, the need to make a mapping between the service classes of IEEE 802.16 and the IP concept of DiffServ.
This is to answer the question: how can we continue to guarantee the QoS to a service that starts from a WiMAX node under a specific technology and is then mapped onto another service over a different technology? This is obviously true in the case of transition from different levels of the same protocol stack such as IP and MAC, as well as peer-level MAC 802.11 and MAC 802.16. It is necessary to note that every discontinuity that represents a transition from one protocol to another introduces the need to reconsider the quality of service. These concepts emphasize the importance of cross-layer solutions and this becomes more and more evident if we consider the possible handoff problems typical of mobile terminals.
5.2 NEW WAYS TO RESOLVE THE WIMAX QoS PROBLEM:
To create even more optimized and original solutions, the researcher analyzes the classical telecommunication problems, with the help of interesting theories developed for applications in other disciplines. Many of these theories allow one to achieve fascinating but also elegant and efficient solutions. Two examples of these theories are the interesting game theory and fuzzy logic.
5.2.1 GAME THEORY IN THE WIMAX SCENARIO
The game theory was founded primarily for economic applications, dealing with situations of strategic interaction between decision makers which are intelligent and rational. The term intelligent' means that decision makers understand the situation they are faced by and are able to reason logically. Rational' means that preferences are consistent with the final outcomes of the decision-making process and are intended to maximize these preferences. The maximization is carried out by trying to achieve a certain gain, which is expressed through a utility function.
A game is therefore an iteration between multiple entities. An initial classification of games is as follows:
Cooperative Games: studying the formation of coalitions with binding agreements that may be of benefit to the individual components.
Non-cooperative Games: the theory of non-cooperative games is concerned with mechanisms of individual decisions, based on individual reasoning, in the absence of mandatory alliances.
Game theory deals with situations where there are at least two entities that interact according to the rules of the game. As with roulette, it deals with situations where there are at least two entities that interact according to the rules of the game. A game is classifiable as a game with complete information if the rules of the game and the utility
functions of all players are common knowledge amongst all players. Also, a game is over when each player has a finite number of moves available and the game ends after a finite number of moves.
5.2.2 FUZZY LOGIC: WHAT IDEA TO GUARANTEE QOS?
Fuzzy logic allows us to resolve the issues we have introduced in a different way. Fuzzy logic was born in computer science and more specifically, arises in the application of artificial intelligence. It certainly looks different from the classical Boolean logic in which the only allowed values are true or false, identified as 0 and 1. Fuzzy logic introduces the concept of degree of belonging to a set. In fact, while for classical logic an element can belong to a given set or its complement in an exclusive way, in fuzzy logic an element can belong to both sets, and the concept of membership is accompanied by a degree of ownership that can take values between 0 and 1.
This level of membership can be interpreted as the degree of truth of the element belongs to'. For clarification, here is an example. To define the state of congestion of a network we consider a threshold that represents the current use of the bandwidth and we say: for a utilization value greater than 70% the network is congested, while if the current bandwidth utilization is less than or equal to 70% the network is not congested. At this point, according to classical logic, a network with utilization value equal to 71% is defined as congested while a network that has utilization of 70% is not congested even if the true condition of the two networks is almost identical.
Figure 9: Example of fuzzy logic based control.
5.2.3 DESIGNING MOBILITY MESH WIMAX
The IEEE 802.16 protocol presents very interesting features in both PMP and mesh mode. These two operating modes offer the opportunity to create a broad spectrum of scenarios that can meet the most disparate needs. Despite this, the research seeks to go beyond the limits imposed by the protocol and analyze, from different points of view. The opportunity to further enrich the WiMAX by having mobile stations that support the mesh mode. Currently, MSS stations are restricted by the presence of a BS, the MSS is able to establish a connection only with a BS and it is not possible to create links with other MSS or SS.
5.2.4 HOW TO EXTEND QOS MECHANISMS
The introduction of the mesh mode in mobile WiMAX makes it necessary to introduce changes at every level of the protocol stack in order to ensure a well-defined QoS and the proper working of the network. WiMAX has still not become part of everyday communication and in the literature there are many proposals to change the protocol so as
to support the mesh mode in the mobile version of WiMAX. Without doubt, to ensure high throughput it is appropriate to introduce a physical level using the SOFDMA-1024 (Scalable Orthogonal Frequency Division Multiple Access with 1024 sub carriers) technique that would increase the efficiency of available bandwidth.
Interesting changes also affect the MAC level; to support mobile mesh it is proposed to limit the scheduling to the distributed manner only, in order to remove the bottleneck formed by the presence of BS. The use of the distributed mode prevents the introduction of delays typical of the centralized mode; in this latter mode each bandwidth request and each bandwidth grant should always pass through the BS. The mechanism of registration of a new station and especially the mechanism of mesh election as presented in the mesh protocol should be changed. Currently the mechanism of mesh election is based on coordination in the two-hop neighborhood of a node, where the neighborhood is a fixed set of nodes. This constraint must be removed in the mobile mesh.
A cross-layer solution for updating the routes and the neighbors of a node would be interesting at this point. We must also mention the possible changes to the handoff process which at this point would not only be engaged with a BS but with any SS or other MSS. In the literature there is research that deals with the interesting possibility of the introduction of mobile mesh and which may also consider new WiMAX network architectures implemented in clusters .
6. SUMMARY
In this paper we have described briefly the IEEE 802.16 protocol, known as WiMAX. Besides introducing the basic mechanisms of the protocol, we have discussed how the various mechanisms of the protocol ensure well-defined quality of service levels. This has been done by highlighting the differences between the two modes supported by the protocol: PMP and mesh. Subsequently, we discussed all of the various gaps neglected deliberately by the developers of the protocol and which are relevant in the absence of algorithms for scheduling, call admission control and adaptive modulation and coding.
These shortcomings, as mentioned above, have been neglected deliberately so as to enable the implementers of WiMAX devices to create ad hoc solutions which are optimized according to certain objective functions. In discussing the various issues the importance of cross-layer solutions has been emphasized. We concluded the discussion by introducing exciting new challenges in the research, such as the introduction of mobile mesh. Another interesting aspect of the chapter is the introduction of games theory and fuzzy logic: two theories developed in other disciplines but used recently to resolve network problems such as bandwidth resource allocation or call admission control. This is very interesting from a didactic point of view because it is an example of the integration of different disciplines through an interdisciplinary way of thinking.
7. REFERENCES
[1] IEEE 802.16-2004. IEEE Standard for Local and Metropolitan Area Networks, Part 16: Air Interface for Fixed Broadband Wireless Access Systems.
[2] IEEE 802.16e-2005. IEEE Standard for Local and Metropolitan Area Networks, Part 16: Air Interface for Fixed and Mobile Broadband Wireless Access Systems Amendment 2: Physical and Medium Access Control Layers for Combined Fixed and Mobile Operation in Licensed Bands and Corrigendum 1.
[3] IEEE 802.16-2001. IEEE Standard for Local and Metropolitan Area Networks, Part 16: Air Interface for Fixed Broadband Wireless Access Systems.
[4] IEEE 802.16c-2002. IEEE Standard for Local and Metropolitan Area Networks, Part 16: Air Interface for Fixed Broadband Wireless Access Systems Amendment 1: detailed system profiles for 10-66 GHz.
[5] IEEE 802.16a-2003. IEEE Standard for Local and Metropolitan Area Networks, Part 16: Air Interface for Fixed Broadband Wireless Access Systems amendment 2: medium access control modification and additional physical layer specifications for 2-11 GHz.
[6] IEEE 802.16.2-2004. IEEE Recommended Practice for Local and Metropolitan Area Networks, Coexistence of fixed broadband wireless access systems.
[7] IEEE 802.16f-2005. IEEE Standard for Local and Metropolitan Area Networks, Part 16: Air Interface for Fixed Broadband Wireless Access Systems Amendment 1: Management Information Base.
[8] IEEE 802.16k-2007. IEEE Standard for Local and Metropolitan Area Networks: Media Access Control (MAC) Bridges, Amendment 2: Bridging of IEEE 802.16.
[9] IEEE 802.16g-2007. IEEE Standard for Local and Metropolitan Area Networks, Part 16: Air Interface for Fixed Broadband Wireless Access Systems Amendment 3:Management Plane Procedures and Services.
[10] IEEE 802.16 Conformance01-2003. IEEE Standard for Conformance to IEEE 802.16, Part 1: Protocol Implementation Conformance Statement (PICS) Proforma for 10-66 GHz WirelessMan-SC air interface.
[11] IEEE 802.16 Conformance02-2003. IEEE Standard for Conformance to IEEE 802.16, Part 2: Test Suite
Structure and Test Purpose for 10-66 GHz wirelessMan-SC air interface.
CROSS LAYERED FUNCTIONALITY FOR WiMAX TECHNOLOGY
By: K Ravi
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