LTE vs WiMax

LTE vs. WiMAX: the battle continues

Parikshit Tiwari

Table of ContentsAbstract.......................................................................................................................................................5

1. Introduction.........................................................................................................................................7

2. General Aspects of WiMAX and LTE....................................................................................................8

2.1. WiMAX Overview.............................................................................................................................8

2.2. LTE Overview...................................................................................................................................9

3. Standards Development and Status..................................................................................................11

3.1. WiMAX...........................................................................................................................................12

3.2. LTE.................................................................................................................................................12

4. Technical Specifications.....................................................................................................................13

4.1. Physical Layer................................................................................................................................14

4.2. Latency..........................................................................................................................................14

4.3. Quality of Service in WiMAX and LTE Networks............................................................................14

4.3.1. QOS IN IEEE 802.16E..................................................................................................................15

4.3.2. Service Flow Types in IEEE 802.16E and Associated Parameters...............................................16

4.3.3. Air Interface Scheduler..............................................................................................................17

4.3.4. IEEE 802.16E Bandwidth Request and Grant Mechanism..........................................................17

4.4. IEEE 802.16M QOS Framework......................................................................................................19

4.4.1. AGP SERVICE..............................................................................................................................19

4.4.2. Quick Access..............................................................................................................................20

4.4.3. Delayed BR for BE......................................................................................................................21

4.4.4. Priority Controlled Access..........................................................................................................21

4.5. LTE QOS Framework......................................................................................................................21

4.5.1. LTE Air Interface Scheduler........................................................................................................23

4.5.2. Buffer Status Reporting..............................................................................................................23

4.5.3. 802.16M and LTE Comparison: QoS Aspect...............................................................................24

5. Power Conservation..........................................................................................................................24

6. Security..............................................................................................................................................25

6.1. WiMAX Security Models for the Enterprise...................................................................................25

7. Outlook..............................................................................................................................................27

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7.1. Industry Support............................................................................................................................28

7.2. Niche Applications.........................................................................................................................28

7.3. Support for Relay Stations.............................................................................................................28

7.4. A Standardized Interface...............................................................................................................28

7.5. Patent Management......................................................................................................................29

8. Conclusion.........................................................................................................................................29

9. References.........................................................................................................................................30

Acronyms...................................................................................................................................................30

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Table of FiguresFigure 1: Change Consumer Behavior..........................................................................................................7Figure 2: IEEE 802.16e WiMAX Deployment................................................................................................8Figure 3: Network Reference Model for WiMAX.........................................................................................9Figure 4: LTE Overall Architecture.............................................................................................................11Figure 5: The Long-Term Evolution (LTE) and WiMAX standards’ development.......................................12Figure 6: Main Technical Specifications for WiMAX and LTE.....................................................................13Figure 7: Service Flows in the WiMAX QoS Framework.............................................................................15Figure 8: QoS Attributes in the IEEE 802.16e.............................................................................................16Figure 9: Three-step random access BR procedure...................................................................................20Figure 10: Default and Dedicated Bearers of a Terminal (MS) in the LTE QoS Framework........................22Figure 11: LTE standardized QCI characteristics........................................................................................22Figure 12: WiMAX Authentication Process................................................................................................26Figure 13: Enhanced LTE Authentication Process......................................................................................27Figure 14: WiMAX vs. LTE..........................................................................................................................29

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AbstractIn the last few years, we have witnessed an explosion of IP connectivity demand, translated into a rapid development of the corresponding technologies in the wireless access network domain. IP services provision anytime and anywhere becomes very challenging and is seen by the mobile operators as a major opportunity for boosting the average revenue per unit. The further success of IP services deployment requires true mobile broadband IP connectivity on a global scale. For accomplishing this request, two technologies emerged with the aim of providing voice, data, video and multimedia services on mobile devices at high speeds and cheap rates: WiMAX (Worldwide Interoperability for Microwave Access) and LTE (3GPP Long Term Evolution). This report investigates LTE and WiMAX technologies in terms of architectural benefits, user and operator acceptance and first two layers performances. It is concluded that these technologies will play an equally important role in the future of wireless networks.

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AudienceThis report is a review of new developing technologies i.e. LTE and WiMAX. These technologies are currently getting deployed throughout the world. As the demands of the end user are increasing exponentially so is the need of higher bandwidth and data rate.

This report is meant for technically sound readers. The report consists of concepts of advance networking level and in some cases requires extensive knowledge of computer networks.

This report can play an important role for the person who is working in the field of wireless networks and is in the process of deploying LTE or WiMAX on a network. It will provide a broad prospectus of both the technologies and will illustrate both the advantages and disadvantages depending on need of end user.

I am confident that this report will appeal to all network administrators/person (interested in wireless) as they can learn a lot about wireless technologies and the way they work (authentication, QoS etcetera).

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1. IntroductionMobile communication technology evolved rapidly due to the increasing demands for higher data rates and higher quality mobile communication services. Fulfilling these demands was done by defining a new air interface for mobile communications which enhances the overall system performance and increases the capacity of the system. The conflict of rapidly growing users and limited bandwidth resources requires that the spectrum efficiency of mobile communication systems be improved by adopting some advanced technologies. It has been proved, in both theory and in practice that some novel key technologies such as MIMO (multiple inputs, multiple outputs) and OFDM (orthogonal frequency division multiplexing) improve the performance of current mobile communication systems. WiMAX and LTE are the two leading standards as the results of above efforts.

Figure 1: Change Consumer Behavior.

The economical aspects regarding these two technologies are comparable, considering that both are new and still under development. Important companies are developing new equipments, with improved performances that are starting to be available in the open market. Both technologies are already deployed, with a major advantage for WiMAX, considering that it is a more mature technology. WiMAX it is present now in more than 140 countries all over the globe, for testing purposes or for commercial use. LTE is currently being deployed in Nordic countries where it is the world’s first and largest LTE service (Stockholm, 14 December 2009). LTE is also expected to be deployed on large scale in 2010 in Japan. The expectations from these technologies are great, the most important aspect being the VoIP service which is supposed to offload a lot of congested 2G or 3G networks because the voice can now be delivered very efficiently over IP, as timing and synchronization over packet networks are mature

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enough. This paper proposes a comparative study between WiMAX and 3GPP LTE by focusing on their first two layers, i.e. Physical and MAC layer. The comparison specifically includes system architecture, radio aspects of the air interface such as frequency band, radio access mode, multiple access technologies, multiple antenna technologies and modulation, and protocol aspects of the air interface in terms of protocol architecture, mobility and Quality of Service (QoS).

2. General Aspects of WiMAX and LTE

2.1. WiMAX Overview

Figure 2: IEEE 802.16e WiMAX Deployment

WiMAX (Worldwide Interoperability for Microwave Access), is a wireless communication system that can provide broadband access on a large-scale coverage. It enhances the WLAN (IEEE 802.11) by extending the wireless access to Wide Area Networks and Metropolitan Area Networks. The initial version of WiMAX, IEEE 802.16-2004, was designed to provide broadband wireless connectivity to fixed and nomadic users for the last mile. The coverage can go up to 50 km, allowing users to get broadband connectivity in NLOS conditions. IEEE 802.16-2005 (Mobile WiMAX) comes with enhanced QoS and mobility up to 120 km/h. Mobile WiMAX is designed to fill the gap between wireless local area networks and high mobility cellular wide area networks. In order to obtain downlink peak data rates up to 75 Mbps in mobile scenarios, the standard uses scalable OFDMA to dynamically modify FFT size, depending on the channel conditions.The figure illustrates the Network Reference Model (NRM) in WiMAX, consisting of the following logical entities: Subscriber Station (SS), Access Service Network (ASN) and Connectivity Service Network (CSN) together with the reference points for interconnecting the logical entities (R1-R5).

The ASN holds one or more ASN Gateways (ASN GWs) and one or more Base Stations (BSs). The BS provides and manages resources over the air interface and is responsible for handover triggering.

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ASN-GW performs AAA client functionality, establish and manage mobility tunnel with BSs and connections towards selected Connectivity Service Network (CSN). CSN is defined as a set of network functions that provide IP connectivity to the WiMAX subscribers. The typical CSN comprises AAA proxy/servers, user databases, routers and Interworking gateway devices. CSN is responsible of IP address Management, mobility, roaming and location management between ASN’s and roaming between NSPs by Inter-CSN tunneling.

Figure 3: Network Reference Model for WiMAX

2.2. LTE OverviewLTE technology evolved from UMTS/HSDPA cellular technology to meet current used demands of high data rates and increased mobility. The LTE radio access is based on OFDM technique and supports different carrier frequency bandwidths (1.4-20 MHz) in both frequency-division duplex (FDD) and time-division duplex (TDD) modes [7]. The use of SC-FDMA in the uplink reduces Peak-to-

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Average Power Ratio compared to OFDMA, increasing the battery life and the usage time on the UEs. In downlink peak data rates go from 100 Mbps to 326.4 Mbps, depending on the modulation type and antenna configuration used. LTE aims at providing IP backbone services, flexible spectrum, lower power consumption and simple network architecture with open interfaces. LTE architecture can be seen as two-node architecture because only two nodes are involved between the user equipment and the core network. These two nodes are the base station (eNodeB) and the serving gateway (S-GW) in the user plane and the mobility management entity (MME) in the control plane, respectively [9]. Through this architecture, LTE offers smooth integration and handover to and from existing 3GPP and 3GPP2 networks, ensuring that operators can deploy LTE in a gradual manner using their existing legacy networks for service continuity [5]. LTE architecture is composed of Core Network (CN) and Access Network (AN), where CN corresponds to the Evolved Packet Core (EPC) and AN refers to E-UTRAN.

The CN and AN together correspond to Evolved Packet System (EPS). EPS connects the users to Packet Data Network (PDN) by IP address in order to access the internet and services like Voice over IP (VoIP). The overall network architecture is shown in Figure. MME is the control plane entity within EPS supporting the following functions: inter CN node signaling for mobility between 3GPP access networks, S-GW selection, roaming, authentication, bearer management functions and NAS (Non Access Stratum) signaling. Serving Gateway is the gateway which terminates the interface towards E-UTRAN. For each user associated with the EPS, at a given point in time, there is a single Serving GW that is responsible for transferring user IP packets, lawful interception and mobility anchor for intereNodeB handover and for inter-3GPP mobility.

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Figure 4: LTE Overall Architecture

Even if both technologies rely on OFDM modulation, allowing them to support very high peak rates and their performances are comparable, the architecture differs and the question arising from this difference is what technology should be used for upgrade based on CAPEX (Capital expenditures) and OPEX (Operating expenditure). LTE architecture was designed in such way that the operators interested in it, will be able to deploy it over their existing infrastructure with a minimum of changes and investments, and this may qualify it as the first choice based on deploying and day-to-day costs.

3. Standards Development and StatusFigure 1 shows the evolution of the WiMAX and LTE standards. All of the standards in Figure were developed by either 3GPP or IEEE.

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3.1. WiMAXIEEE developed the IEEE 802.16 standards, which include notably IEEE 802.16-2004, the first major WiMAX standard for fixed access. This was superseded by IEEE 802.16e-2005, known as Mobile WiMAX, which provides both fixed and mobile access.3 In October 2009; the IEEE 802.16 Working Group submitted its proposal for IMT-Advanced based on IEEE 802.16m, which enhances IEEE 802.16e-2005 to meet the IMT-Advanced requirements. The WiMAX Forum, which comprises more than 300 companies from the computer and telecommunications industries (www.wimaxforum.org), certifies interoperability of WiMAX products from various vendors and has been working to secure spectrum around the globe for WiMAX deployment. Furthermore, hundreds of WiMAX networks have been commercially deployed around the world. In the US, Clearwire has large operations with service offerings in cities such as Chicago, Philadelphia, and Las Vegas. Xanadoo offers service on a smaller scale to a few markets in the US.

Figure 5: The Long-Term Evolution (LTE) and WiMAX standards’ development.

3.2. LTE3GPP’s LTE standard evolved from the High-Speed Packet Access cellular standards (www.3gpp.org/ftp/Specs/html-info/21101.htm). 3GPP comprises several international standardizations bodies from the US, Europe, Japan, South Korea, and China. The 3GPP partner

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from the US is the Alliance for Telecommunications Industry Solutions. ATIS members include leading telecommunications companies such as AT&T, Cisco, and Verizon. The LTE standard is officially known as “document 3GPP Release 8.” LTE Release 8 almost achieves full compliance with IMT-Advanced requirements, so some call it 3.9G. In September 2009, 3GPP submitted its LTE-Advanced proposal for IMT-Advanced, officially called “document 3GPP Release 10.”

In December 2009, Swedish telecom operator TeliaSonera launched the first commercial deployments of LTE in Stockholm, Sweden and Oslo, Norway. Stockholm’s network was supplied by Ericsson while Oslo’s network was supplied by Huawei. The modems were supplied by Samsung.

4. Technical SpecificationsTable 1 shows the main technical specifications for WiMAX and LTE.

For WiMAX, the designation of release (R1.0 or R2.0) indicates the system profile. When certifying various vendors’ equipment, the WiMAX Forum creates the system profile (such as R1.0), selecting features from the standard to test. The WiMAX Forum tests a subset of features in every system profile. (Because the standard contains a plethora of features, it’s nearly impossible to test them all at once.) Typically, later releases contain more features and mechanisms. Most of the WiMAX base stations and products on the market are based on 802.16e. The standard created for the IMT-Advanced proposal, 802.16m (see www.ieee802.org/16/tgm), hasn’t proliferated the market yet.

Figure 6: Main Technical Specifications for WiMAX and LTE.

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4.1. Physical LayerIt’s worth mentioning that both LTE and WiMAX use orthogonal frequency-division multiple access (OFDMA) in the downlink, but they differ in the uplink. WiMAX continues to use OFDMA, while LTE’s approach is more advanced. Using OFDMA is power inefficient, but it’s tolerable in the downlink because the power amplifier is placed at the base station (or at the e-Node-B in 3GPP terminology). At the base station, power is available, and the many mobile terminals share the extra complexity. However, in the uplink, the transmissions start from mobile devices, which are battery powered. The mobile devices are also constrained because they must be low cost to enable mass deployment. 3GPP specifications thus propose a reduced peak-to average- power ratio (PAPR) transmission scheme for the uplink signal. This scheme is called single carrier frequency-division multiple access (SCFDMA). This makes it easier for the mobile terminal to maintain a highly efficient signal transmission using its power amplifier. The LTE uplink signal achieves this property and saves power without degrading system flexibility or performance.

4.2. LatencyThe latency requirement in the WiMAX and LTE specifications is small enough to support real-time applications, such as voice applications. A voice application could tolerate a delay of between 50 and 200 ms without the user perceiving a decrease in quality. Low latency is thus essential in these mobile broadband standards. The low latency is also coupled with high data rates to satisfy bandwidth-intensive applications. Both standards support mobility in that users can carry the device travelling at speeds of up to 350 km/h. So, users on a high-speed train, for example, could connect to a 4G network.

4.3. Quality of Service in WiMAX and LTE NetworksAs the number of mobile broadband subscribers and the traffic volume per subscriber are rapidly increasing, quality of service (QoS) is becoming significant as operators move from single to multiservice offerings, and emerging rich devices capable of running multimedia and gaming applications. Fourth-generation (4G) broadband wireless technologies such as IEEE 802.16e, IEEE 802.16m, and Third Generation Partnership Project (3GPP) Long Term Evolution (LTE) have been designed with different QoS frameworks and means to enable delivery of the evolving Internet applications. As the Internet evolves, Internet applications and associated traffic patterns are also evolving over time. Web 2.0 supports rich media applications such as interactive voice and video services, web audio/video streaming services, and online gaming services, with smart optimization engines at both the client and server sides [1]. QoS specifically for evolving Internet applications is a fundamental requirement to provide satisfactory service delivery to end users and also to manage network resources. In other words, today’s popular Internet applications, including real-time and non-real-time traffic such as multimedia services and online gaming, have very different traffic patterns and distinct QoS requirements. The traffic patterns of these emerging Internet applications show non-periodic variable-sized packet arrivals. The traditional QoS framework is no longer efficient and/or sufficient to support these new mobile Internet applications with good or required user experience.

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4.3.1.QOS IN IEEE 802.16EThe QoS framework in IEEE 802.16e is based on service flows (SFs). An SF is a logical unidirectional flow of packets between the access service network gateway (ASN-GW) and a mobile station (MS) with a particular set of QoS attributes (e.g., packet latency/jitter and throughput) identified by a connection ID. Based on IEEE 802.16e, packets traversing the medium access control (MAC) interface are associated with SFs according to classifier rules. The Figure demonstrates SFs in IEEE 802.16e.

Figure 7: Service Flows in the WiMAX QoS Framework.

Traffic mapping to appropriate SFs is done at the ASN-GW for downlink (DL) and at the MS for uplink (UL) directions, respectively. Between the ASN-GW and the base station (BS), the QoS of the SFs is supported by backhaul transport QoS. On the air interface, a BS scheduler provides QoS for DL, and cooperation between the BS and MS schedulers provides QoS for UL. This air interface scheduler at the MAC sublayer determines how radio resources are assigned among multiple SFs based on QoS attributes. Resources assigned to an MS enable it to receive traffic over DL and transmit data over UL. Details of air interface scheduler operation are not specified by the standard; therefore, it is vendor-specific. Traffic classification and mapping from application packets onto SFs in WiMAX is done at the convergence sublayer (CS), based on protocol-specific packet matching criteria like a combination of five-tuple, such as source and destination IP addresses, source and destination port address, protocol, and differentiated services code point (DSCP).

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IEEE 802.16e supports both QoS control paradigms: network-initiated, where SF creation is initiated by the BS, and terminal-initiated, where SF creation is initiated by the MS. With network-initiated, an application function (AF) inside the network can trigger messaging signals to set up SFs with appropriate QoS attributes; consequently, the client application can be left access-agnostic, and there is no need for access specific information in application layer signaling. On the other hand, with terminal-initiated QoS control, the MS requests creation of SFs with appropriate QoS attributes; hence, the client application is aware of the specifications of the access QoS model. Network-initiated SF creation is a mandatory, but terminal-initiated SF creation is an optional capability of IEEE 802.16e. SFs may be created, changed, or deleted through a series of MAC management messages referred to as DSX (i.e., DSA, DSC, and DSD).

4.3.2.Service Flow Types in IEEE 802.16E and Associated Parameters

IEEE 802.16e supports five SF types:

Unsolicited grant service (UGS): Supports real-time traffic with fixed-size data packets on a periodic basis.

Real-time polling service (rtPS): Supports real-time traffic with variable-size data packets on a periodic basis.

Extended rtPS (ertPS): Supports real-time traffic that generates variable-size data packets on a periodic basis with a sequence of active and silence intervals.

Non-real-time polling service (nrtPS): Supports delay-tolerant traffic that requires a minimum reserved rate.

Best effort (BE) service: Supports regular data services

The following figure summarize some key SF QoS attributes in the IEEE 802.16e standard and provide some targeted traffic types for each SF:

Figure 8: QoS Attributes in the IEEE 802.16e.

Maximum sustained traffic rate (MSTR): Defines capping rate level of an SF. Maximum traffic burst: Defines the maximum continuous burst a system should accommodate

for a service Minimum reserved traffic rate (MRTR): Specifies the minimum rate guaranteed to an SF

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Maximum latency: Specifies maximum packet delay over the air interface Tolerated jitter: Specifies maximum packet delay variation (jitter) for an SF Traffic priority: Can be exploited to adjust the priority of packets of different SFs based on a

combination of subscribers’ profiles and services mapped to SFs. Unsolicited grant interval (UGI): Defines the time interval between successive data grant

opportunities for an SF over DL. Unsolicited polling interval (UPI): Defines the maximal interval between successive polling grant

opportunities for an SF over UL.

WiMAX uses a BE SF, referred as the initial SF (ISF), to establish IP connectivity during network entry before any packet transmission and reception.

4.3.3.Air Interface SchedulerThe SF framework provides QoS granularity and inter-SF isolation over the air interface. The air interface scheduler is responsible for enforcing QoS by assigning DL and UL physical (PHY) layer resource blocks among SFs. This mechanism is called bandwidth allocation. A scheduling decision is determined based on appropriate SFs’ QoS state variables, like buffer lengths, elapsed packet delay, SFs’ QoS requirements such as MRTR and maximum latency, and radio frequency (RF) conditions of different MSs. In general:

• SFs with shorter maximum latency or SFs with higher MRTR receive higher priorities in the scheduling decision.

• SFs with late packets or long buffer lengths also, receive higher priorities in the scheduling decision.• MSs with better RF conditions receive higher priorities by the scheduler in order to improve overall

sector throughput. However, an operator can adjust fairness to ensure MSs in poor RF conditions receive reasonable QoS.

The air interface scheduler may differentiate between traffic flows within an SF by packet priority levels such as DSCP values (intra-SF). Also, it may further utilize the traffic priority attribute of SFs to differentiate between traffic associated with SFs of the same type (inter-SF).

4.3.4.IEEE 802.16E Bandwidth Request and Grant MechanismIn the UL direction, all SF types except UGS involve some form of bandwidth request/grant mechanism for bandwidth allocation. In the DL, the BS scheduler has all the information about DL SF status for making the best scheduling decision. However, UL SF status information is distributed in MSs. Additionally; an MS may need to be assigned some small bandwidth to send UL SF status information to the BS. Therefore, some mechanisms (i.e., bandwidth request [BR]) are required to inform the BS scheduler of UL SF status (i.e., BR message). Basically, BR refers to a mechanism MSs use to indicate to the BS their bandwidth needs.

In IEEE 802.16e there are a number of methods for sending a BR message to BS:

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• UL bandwidth requests: An MS indicates to a BS that one of its UL SFs need bandwidth that may be carried through a bandwidth request header or a grant management subheader for a piggyback request, or a BR indicator on the channel quality indication channel (CQICH) feedback. UL BR messages are per SF in order to inform the BS about MS’ traffic composition. There are two types of BR messages:

o Incremental: The BS adds the new request to the current perception of bandwidth needs of an SF.

o Aggregate: The BS replaces the perception of bandwidth it needs for an SF with a new request.

In order to avoid error accumulation in the BR mechanism, MS periodically uses aggregate BR message. Thus, BR mechanism in IEEE 802.16e is self-correcting and no acknowledgment is required for the BR message. There are several ways of requesting bandwidth:

o In contention-based (random access) BR, there is no reserved dedicated resource for an MS to transmit data, and the MS uses a code-division multiple access (CDMA)- based mechanism; so the BS allocates enough bandwidth for the BR message before sending the BR header.

o In contention-free BR, a signaling header or a piggybacked bandwidth request is used by appending it to UL data transmission when there is available UL resource or when BS polls MSs. In this case the MS is allocated sufficient bandwidth to send a BR message. Although the UPI is an SF parameter, the polling is always on a per MS basis. An MS with an active UGS connection is not polled, but the MS uses the poll me (PM) bit in the header of a UGS SF packet instead. Once the BS detects this request, it individually polls the MS to satisfy its request. The piggyback request mechanism allows an MS to perform incremental BR per SF using the piggyback field in the grant management subheader (GMSH). This mechanism avoids the BS allocating for the BR header. However, the capability of piggyback request is optional.

• UL bandwidth grants: After the BS is informed of a UL SF status; it makes a scheduling decision and allocates some bandwidth to the SF. However, by this time the status of the UL SF might have changed due to new packet arrivals. Therefore, the bandwidth grant mechanism in IEEE 802.16e is on a per MS basis. In other words, the BS assigns a UL burst to the MS for all of its SFs. This allows real-time reaction of the MS to QoS needs for any redistribution of bandwidth among the SFs. Also, this simplifies the system by sending only one grant (UL MAP IE) per MS instead of a number of grants per each SF. An intelligent MS scheduler distributes the allocated bandwidth among its SFs.

A voice service can be served using a UGS type SF with no need for BR during a talk spurt period; it does not need any BR during a silence period, either. However, there is a need for BR for a silence to talk spurt. IEEE 802.16e has provisioned ertPS for this purpose.

• Request/Grant for ertPS: The ertPS SF type is designed to reduce the complexity of the BR mechanism for some services such as VoIP with silence suppression. With ertPS and during a talk spurt, a BS provides unicast grants in an unsolicited manner as in UGS, but packet sizes with ertPS allocations are not fixed. An MS uses its periodic allocation for both data transfer and bandwidth

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request adjustments (e.g., using an extended piggyback request field of the GMSH). During a silence period, the allocation is taken from the ertPS SF, and with a silence to-talk-spurt transition, the MS sends a BR message to the BS to establish the periodic allocation during this talk spurt.

4.4. IEEE 802.16M QOS FrameworkThe next-generation WiMAX air interface, IEEE 802.16m advanced air interface (AAI), provides a more flexible and efficient QoS framework to support emerging and evolving mobile Internet applications. The new features introduced in the AAI QoS framework include a new scheduling service, adaptive granting and polling (aGP) service, quick access, delayed BR, and priority controlled access.

4.4.1.AGP SERVICEIn IEEE 802.16e the scheduling services UGS, ertPS, and rtPS are not efficient for applications such as online games, VoIP with adaptive multirate (AMR), and delay-sensitive TCPbased services that show ON-OFF traffic patterns with variable packet rates . Furthermore, applications such as Skype show variable rate traffic patterns not only with variable packet size, but also with variable periodical intervals. Therefore, it is desirable to have a more flexible QoS scheduling service to support the adaptation of both the allocation size and inter arrival.

A new scheduling service, aGP service, has been introduced in AAI to support not only granting and polling-based services, but also the adaptation of the QoS parameters to serve the dynamic traffic characteristics of applications with better efficiency.

The new QoS parameters introduced in the aGP service are mandatory: primary grant polling interval (GPI) and primary grant size; and optional ones: secondary GPI, secondary grant size, and adaptation method. Advanced BS (ABS) may grant advanced MS (AMS) UL allocation GPI with grant size, or poll AMS for BR periodically every GPI. During a service, the traffic characteristics and QoS requirements may change; for example silence-suppression enabled VoIP alternates between talk-spurt and silence period, which triggers adaptation of the scheduling service state machine as described below. Adaptation of scheduling state includes switching between using primary and secondary SF QoS parameters or changing the GPI and/or grant size to values within the QoS flexibility range (i.e., without exceeding the maximal QoS requirement or violating the minimal QoS guarantee).

Depending on the three adaptation methods specified during SF negotiation, the grant size and/or GPI can be changed by an ABS automatically upon detecting a certain traffic condition if the adaptation method is implicit, or triggered by explicit signaling from an AMS if the adaptation method is explicit sustained or explicit and one time only. Explicit signaling from an AMS includes a piggybacked BR, service-specific BR header, quick access message in the BR channel, or an ertPS/aGP service BR codeword in the primary fast feedback channel (P-FBCH). For explicit adaptation, if GPI_secondary and Grant_Size_secondary are defined, GPI and grant size switch between primary GPI/ Grant_Size_primary and GPI_secondary and Grant_Size_secondary as requested by the explicit signaling; otherwise, GPI and

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grant size changes as indicated by QoS requirements carried in the explicit signaling, as in the mechanisms mentioned above.

It is important to have appropriate support when a mix of IEEE 802.16m and legacy IEEE 802.16e BSs and devices are around. An IEEE 802.16m aGP SF can be mapped to an SF of legacy IEEE 802.16e scheduling type, during AMS handover from an IEEE 802.16m network to an IEEE 802.16e network. If primary grant size value is equal to the BR header size, it means this aGP SF is primarily polling-based SF, and hence should be mapped to an rtPS SF. Otherwise, this aGP SF is primarily a granting based service, and thus should be mapped to an ertPS SF.

Figure 9: Three-step random access BR procedure.

4.4.2.Quick AccessAMS performs random-access-based BR when it has UL traffic to send but with no allocation. Random access delay is a significant part of UL access delay, which has a big impact on the end user experience. In the legacy system, the BR message is communicated from MS to BS only after random access is successful. To shorten the random access delay, the IEEE 802.16m AAI introduces a quick access message to be carried in the first step of the random access BR procedure (e.g., contention) in order to simplify the procedure from five steps in the legacy system to three steps (Figure). The 12-bit station ID and 4-bit predefined BR index, which are carried in the quick access message, enable a quick exchange of BR information between ABS and AMS. The shorter random access delay can significantly improve the quality of experience (QoE) of delay-sensitive and interactive applications.

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4.4.3.Delayed BR for BEQuick access in IEEE 802.16m helps reduce the random access delay. The idea of delayed BR is to request bandwidth proactively in order to avoid random access and thus reduce the access delay. The service-specific BR header specifies a minimum grant delay to indicate the minimum delay of the requested grant for BE scheduling service. When an AMS is cleaning out its buffers, in one UL transmission it can send a delayed BR asking for future packet(s) with minimum expected grant delay if AMS can predict the future packet(s) arrival time. Hence, when the future packets do arrive, they do not need to use the lengthy random access BR procedure; instead, they can just use the dedicated UL allocation as a response to the previous delayed BR.

4.4.4.Priority Controlled AccessA new term, access class, is introduced to prioritize the contention-based random access. An operator can assign AMS with different access classes and block random access from certain AMSs by assigning a minimum access class of the network higher than the access class of those AMSs. The BR timer and random backoff parameters can also use different values to support differentiated random access in IEEE 802.16m.

4.5. LTE QOS FrameworkThe QoS level of granularity in the LTE evolved packet system (EPS) is bearer, which is a packet flow established between the packet data network gateway (PDN-GW) and the user terminal (UE or MS). The traffic running between a particular client application and a service can be differentiated into separate service data flows (SDFs). SDFs mapped to the same bearer receive a common QoS treatment (e.g., scheduling policy, queue management policy, rate shaping policy, and radio link control (RLC) configuration). A bearer is assigned a scalar value referred to as a QoS class identifier (QCI), which specifies the class to which the bearer belongs. QCI refers to a set of packet forwarding treatments (e.g., scheduling weights, admission thresholds, queue management thresholds, and link layer protocol configuration) preconfigured by the operator for each network element [9]. The class-based method improves the scalability of the LTE QoS framework.

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Figure 10: Default and Dedicated Bearers of a Terminal (MS) in the LTE QoS Framework.

The bearer management and control in LTE follows the network-initiated QoS control paradigm, and the network initiated establishment, modification, and deletion of the bearers. LTE offers two types of bearers:

• Guaranteed bit rate (GBR): Dedicated network resources related to a GBR value associated with the bearer are permanently allocated when a bearer becomes established or modified.

• Non-guaranteed bit rate (non-GBR): A service utilizing a non-GBR bearer may experience congestion-related packet loss.

A non-GBR bearer is referred to as the default bearer, which is also used to establish IP connectivity, similar to the initial SF in WiMAX. Any additional bearer(s) is referred to as a dedicated bearer and can be GBR or non-GBR.

In LTE the mapping of SDFs to a dedicated bearer is classified by IP five-tuple based packet filter either provisioned in PCRF or defined by the application layer signaling. However, the default bearer typically uses a match all packet filter; any SDF that does not match any of the existing dedicated bearer packet filters is mapped onto the default bearer. Therefore, if a dedicated bearer is dropped, its traffic is rerouted to the default bearer. LTE specifies a number of standardized QCI values with standardized characteristics, which are preconfigured for the network elements. This ensures multivendor deployments and roaming. The mapping of standardized QCI values to standardized characteristics is captured in the figure.

Figure 11: LTE standardized QCI characteristics.

Besides QCI, the following are QoS attributes associated with the LTE bearer:• QCI: A scalar representing a set of packet forwarding treatments (e.g., scheduling weights,

admission thresholds, queue management thresholds, and link layer protocol configuration).

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• Allocation and retention priority (ARP): A parameter used by call admission control and overload control for control plane treatment of a bearer. The call admission control uses the ARP to decide whether a bearer establishment or modification request is to be accepted or rejected. Also, the overload control uses the ARP to decide which bearer to release during overload situations [9].

• Maximum bit rate (MBR): The maximum sustained traffic rate the bearer may not exceed; only valid for GBR bearers

• GBR: The minimum reserved traffic rate the network guarantees; only valid for GBR bearers• Aggregate MBR (AMBR): The total amount of bit rate of a group of non-GBR bearers in 3GPP Release

8 the MBR must be equal to the GBR, but for future 3GPP releases an MBR can be greater than a GBR.

The AMBR can help an operator to differentiate between its subscribers by assigning higher values of AMBR to its higher-priority customers compared to lower-priority ones.

4.5.1.LTE Air Interface SchedulerThe LTE air interface scheduler is responsible for dynamically allocating DL and UL air interface resources among the bearers appropriately while maintaining their desired QoS level in both DL and UL directions. In order to make a scheduling decision, the LTE air interface scheduler uses the following information as input:

• Radio conditions at the UE identified through measurements made at the eNB and/or reported by the UE.

• The state of different bearers, such as uplink buffer status reports (BSR) that are packet scheduling, elapsed time.

• The QoS attributes of bearers and packet forwarding parameters associated with the QCIs.• The interference situation in the neighboring cells. The LTE scheduler can try to control intercell

interference on a slow basis. This improves the QoE associated with the MSs at the cell edge.

4.5.2.Buffer Status ReportingSimilar to the bandwidth request mechanism in WiMAX, LTE also has buffer status reporting mechanism. The buffer status reporting mechanism informs the UL packet scheduler about the amount of buffered data at the UE. This mechanism consists of triggering and reporting events. The triggering event can be periodic or regular. A periodic BSR trigger does not cause a service request (SR) transmission from the UE. When a BSR event is triggered and UE has resources allocated in the physical uplink shared channel (PUSCH), then BSR is transmitted. When a regular BSR event is triggered, an SR needs to be transmitted. If SR allocation is available in the physical uplink control channel (PUCCH), the SR is transmitted at the next opportunity; otherwise, the SR is transmitted via a random access procedure. Buffer status is reported per radio bearer group. There are two BSR formats: Short and Long. Short format can be used to report on one radio bearer group whereas the long one can be used for four groups.

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4.5.3.802.16M and LTE Comparison: QoS AspectThere are more components and functionalities in an end-to-end network providing QoS than the air interface QoS features discussed above, such as policy control and charging (PCC) functions in QoS provisioning. Here, we focus on a comparison of the QoS framework between LTE and IEEE 802.16e/IEEE 802.16m at the air interface:

• QoS transport unit: The basic QoS transport unit in the IEEE 802.16e/IEEE 802.16m system is an SF, which is a unidirectional flow of packets either UL from the MS/AMS or DL packets from the BS/ABS. The basic QoS transport in LTE is a bearer between UE and the PDNGW. All packets mapped to the same bearer receive the same treatment.

• QoS scheduling types: There are six scheduling service types in IEEE 802.16m including UGS, ertPS, rtPS, nrtPS, and BE from IEEE 802.16e and the newly defined aGP service. LTE supports GBR and non-GBR bearers. The GBR bearer will be provided by the network with a guaranteed service rate, and its mechanism is like rtPS; the non-GBR has no such requirement and performs like BE in IEEE 802.16e/IEEE 802.16m.

• QoS parameters per transport unit: Depending on the SF type, IEEE 802.16e/ IEEE 802.16m can control maximum packet delay and jitter, maximum sustained traffic rate (MSTR), and minimum reserved traffic rate (MRTR), and traffic priority. LTE MBR and GBR are similar to IEEE 802.16e/IEEE 802.16m MSTR and MRTR, respectively. However, MBR and GBR are only attributes of GBR bearers, while in IEEE 802.16e/IEEE 802.16m even a BE SF can be rate limited using its MSTR. Also, with 3GPP Release 8, GBR and MBR are set equal, while IEEE 802.16e/IEEE 802.16m allows the operator to select independent values for MSTR and MRTR. On the other hand, LTE AMBR allows the operator to rate cap the total non-GBR bearers of a subscriber.

• QoS handling in the control plane: The SF QoS parameters are signaled in IEEE 802.16e/IEEE 802.16m via DSx/AAI-DSx messages. In LTE the QCI and associated nine standardized characteristics are not signaled on any interface. Network initiated or client initiated QoS are both supported in IEEE 802.16e/IEEE 802.16m systems. Therefore, both operator managed service and unmanaged service can be supported. The flexible architecture gives the mobile client opportunities for differentiation. LTE only supports network initiated QoS control.

• QoS user plane treatment: The ARP parameter in LTE provides the following flexibilities to the operator:

o Accept or reject establishment or modification of bearers during the call admission control decision based on not only the requested bandwidth, available bandwidth, or number of established bearers, but also the priority of the bearer

o Selectively tear down bearers based on their priorities during an overload situation.

5. Power ConservationPower-saving mechanisms are essential in any standard that supports devices running on batteries. This is especially true for mobile devices. Because WiMAX and LTE aim to increase transmission rates by tenfold over their respective previous standards, they require power conservation both in the hardware circuit and protocols. A classic power-saving mechanism in battery operated communication devices is

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to turn off the transceiver when there’s no data to transmit or receive. LTE used this concept to introduce Discontinued Reception (DRX) and Discontinued Transmission (DTX). The DRX mode has an on/off cycle for the user’s radio. In the “on” mode, the radio can transmit and receive data. In the “off” mode, it doesn’t communicate with other equipment and thus saves power. Even in the middle of a voice conversation, the radio can be turned off during long pauses, such as when no packets are arriving or awaiting transmission.

WiMAX also has provisions for a sleep mode. It lets a device negotiate with the base station concerning when the device will turn off its radio. The base station won’t schedule the user for transmission or reception when the radio is off. The WiMAX standard specifies three power saving classes (Type I, II and III). These classes have varying on/off cycles and other parameters related to the type of data being transmitted. For example, best-effort traffic (such as a file download) can have an elongated off period; the download will resume once the radio is on again. However, for a real-time conversation, the radio must be on when new traffic arrives.

6. SecurityBoth WiMAX and LTE also provide security mechanisms, which are fundamental for wireless networks. WiMAX provides privacy so that eavesdroppers can’t read the data transmitted over the network. It also provides authentication so that unauthorized users can’t use the network’s services. IEEE 802.16 defines a security sublayer at the bottom of the Medium Access Control (MAC) layer. This sublayer has two protocols: a Privacy and Key Management (PKM) protocol and an encapsulation protocol. The PKM protocol distributes security keys between the base station and the subscriber or mobile station, and the encapsulation protocol encrypts the transmitted data. WiMAX also features a Multicast and Broadcast Rekeying Algorithm to refresh traffic-keying material to ensure secured multicast and broadcast services. LTE provides similar security mechanisms, using security keys between the mobile devices and the base station to encrypt the communication. The LTE standard presents a key derivation protocol n addition to other mechanisms, such as resetting the connection if it detects a corrupt key.

In an enterprise environment, the security is very important, and the security requirements contain two main aspects: 1. the device that will be connected to IT network must be authenticated; 2. the users that want to use IT service must be authenticated. To meet these two main requirements enterprise security credentials usually include identity certificates username and password are required to be authenticated. To authenticate these credentials security infrastructures such as AD server and CA, are usually deployed as IT services. I am comparing WiMAX and LTE with each other in two aspects: 1. how enterprise security credentials are authenticated in them 2. How the enterprise security infrastructure are integrated to them.

6.1. WiMAX Security Models for the EnterpriseThe WiMAX can use both EAP_TLS and EAP_TTLS protocol to do authentication. In our test bed, the EAP_TTLS protocol is used. And in EAP_TTLS protocol, the enterprise security credentials that introduced above can be integrated into seamlessly. Figure illustrates the details of the authentication processes. In

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mobile station side, the enterprise security credentials are provisioned, and in AAA server side, the AAA server is integrated to Intel AD server and CA, so that the AAA server can verify the real enterprise credentials. In our test bed, the EAP_TTLS protocol is standard protocol, and no any change to the software and protocols.

Figure 12: WiMAX Authentication Process.

Proposed LTE Security Models for the Enterprise

The mechanism that LTE has is called AKA. In this authentication mechanism, only a provisioned and pre-shared key is authenticated. This is not enough secure in enterprise environment. As mentioned before, the enterprise security credentials should be authenticated to meet the enterprise security requirements, but these security credentials cannot be authenticated in AKA protocol. This caused the LTE cannot meet enterprise security requirement. In this paper we introduced an enhanced-AKA authentication method, which ca authenticates all enterprise credentials. More specifically the LTE UE was provisioned with the identity (IMSI), password (key), server’s certificate and UE’s private kept for its own certificate. In this authentication method, the interactive messages are not changed, but some of the messages are encrypted by public key. The detail processes are shown in the figure. There are 9 steps in this authentication method including:

1. The authentication process starts by the authentication server sending EAP-Request / Identity message to supplicant (UE).

2. The supplicant responses by replying the EAP-Response/Identity message containing the identity and NAI.

3. Upon receipt of the EAP-Response/Identity message, the authentication server retrieves the supplicant’s certificate from the certificate repository.

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4. The authentication server generates the EAP-Request/AKA-Challenge message using the standard AKA way. Then it encrypts the whole package using the supplicant’s public key derived from the supplicant’s certificate.

5. The authentication server sends the EAP-Request/AKA-Challenge message encrypted by supplicant’s public key to the supplicant.

6. The supplicant decrypts the EAP-Request/AKA-Challenge message using its own private key. After that the supplicant runs the AKA algorithm and generated the EAP-Response/AKA-Challenge EAP message. It then encrypts the EAP-Response/AKA_Challenge message with the authentication Server’s public key.

7. The supplicant sends the EAP-response/AKA-Challenge message to the authentication server.8. The authentication server decrypts the information using server’s private key. After that it use the

AKA algorithm verifies the EAP-Response/AKA-challenge message.9. If the message is correct, the EAP server sends the EAP-Success message to the supplicant.

Figure 13: Enhanced LTE Authentication Process.

7. OutlookIn the battle between WiMAX and LTE for adoption as 4G technologies, there are several issues to consider.

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7.1. Industry SupportThe main difference between WiMAX and LTE is that WiMAX benefits from its earlier development

and deployment, while LTE has the advantage of being developed by telecommunications companies who get to choose which technology to deploy. WiMAX jumpstarted the mobile broadband market. According to the WiMAX Forum, WiMAX has about 519 deployments worldwide with more than 10 million subscribers. Also, WiMAX has spectrum allocated for it in 178 countries, and many telecommunications companies are involved in WiMAX activities. However, now that LTE’s development has picked up, some telecommunications companies have backed away from WiMAX. Recently, Cisco announced that it will discontinue offering WiMAX base stations and will focus on radio agnostic IP core solutions. Alcatel-Lucent made a similar announcement. However, companies such as Clearwire that have invested in WiMAX don’t have to discontinue their offerings. WiMAX could coexist in the broadband arena with LTE. We expect the ITU to make its recommendations for IMT-Advanced this summer. However, this doesn’t necessarily mean that WiMAX or LTE will prevail at that time, as we’ve learned from previous ITU recommendations. The IMT-2000 (3G) recommended several independent technologies that meet the same goals. For example, in 2007, ITU added OFDM as part of 3G at the request of IEEE. Thus, ITU can include multiple standards in its recommendation, which means the real battle between WiMAX and LTE will be how successfully they’re deployed and used.

7.2. Niche ApplicationsIn terms of deployment, some niche applications might favor one technology over the other. For

example, WiMAX has been targeting emerging markets that have little infrastructure, because WiMAX deployment would be faster and more cost-effective than laying a wired infrastructure. Besides, many people in these markets don’t even have computers. Thus, as Intel starts embedding WiMAX chips in its popular Centrino 2 platform for notebook computers, these markets will have an incentive to adopt WiMAX.

7.3. Support for Relay StationsWiMAX has also developed the IEEE 802.16j- 2009 standard, which supports relay stations. This

architecture can have a base station that’s connected to the Internet, and several relays without Internet connectivity can relay wireless data back to the base station to extend its range. Relays would be cheaper than a base station and easier to install at any site, because they don’t need the wired network. This could prove rewarding for WiMAX in markets that require this type of architecture.

7.4. A Standardized InterfaceWiMAX, however, needs to solve the issue of providing an open standard for the interface that

connects WiMAX base stations to the Access Service Network (ASN) gateway, which is linked to the IP’s core network. This interface is called R6 and is out of scope for the WiMAX standard, which focuses on the physical and MAC layers. The WiMAX Forum has established a Network Working Group to develop standardized specifications for R6. Without an open standard for R6, service providers would have to

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match one brand of base stations with an ASN gateway, which would limit the choices for operators or force them to use multiple ASN gateways where one would usually suffice.

7.5. Patent ManagementManagement of the patents covered in LTE might also play an important role. The royalty costs

incurred by patents must be manageable; a high royalty rate can doom a technology. The limited use of 3G networks has partly been blamed on high royalty rates. For LTE, there have been calls for patent pooling by several licensing management companies - notably, Sisvel, Via Licensing, and MPEG LA. Patent pooling lets several companies use each other’s patents pertaining to a certain technology, leading to lower royalty rates for the products. Then, when the market grows, all of the companies will benefit from increased sales.

Figure 14: WiMAX vs. LTE

WiMAX and LTE have several similarities, yet they differ in their evolution, industry support, and deployment models (see Figure). It will be interesting to see what role these two technologies play in the 4G market, which aims to achieve mass deployment of broadband mobile services.

8. ConclusionThe new trend can clearly be seen in the market. With the development of technology people require more functionalty on the move. Where it is just a simple text message to a video confrence over the globe the requirments are ever increasing. We also have seen a constant development in the cellular since a decade; it started with 2G technology to 3G technology which includes GSM, GPRS, EDGE, CDMA etc. While 2G only supported the voice communicate and 2.5G supports voice and data communication, 3G introduced a new speed for the end devicese. But now with the introduction of technologies like LTE WiMAX that are developed and implemented to keep in mind

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the high demand of multimedia applications like web browsing, video conferencing and much more. Also these technologies are capalbe to implement quality of service (QoS) and device mobility from one network to network at high speed. We have indeed come a long way from the start when we had a fixed phone line. I feel that by introducing 4G in the market was one of the most important role in the history and it will even for a limited time period will satisfy the needs of the users.The dominance of video content over wireless networks in the future creates a unique opportunity to optimize WiMAX and LTE networks for video applications.

After stduies and wroting this report it can b said that current WiMAX and LTE technologies have similar video service capabilities and face similar limitations in capacity, which can be overcome to a significant extent with the availability of more spectrum (i.e., through carrier aggregation) and projected growth in spectral efficiency with the adoption of more advanced air interface solutions. In conclusion, while capacities delivered by the available WiMAX and LTE technologies may be adequate for supporting the current deployment plans of operators, further video capacity enhancements will be essential for meeting the anticipated growth of mobile video traffic in wireless networks.

9. References1. Quality of Service in WiMAX and LTE Networks by Mehdi Alasti and Behnam Neekzad, Clearwire

Jie Hui and Rath Vannithamby, Intel Labs2. WiMAX vs. LTE: Who Will Lead the Broadband Mobile Internet?, Zakhia Abichar and J. Morris

Chang, Iowa State University Chau-Yun Hsu, Tatung University, Taiwan3. Z. Abichar, Y. Peng, and J.M. Chang, “WiMAX: The Emergence of Wireless Broadband,” IT

Professional, July/Aug. 20064. Toward Enhanced Mobile Video Services over WiMAX and LTE, Ozgur Oyman and Jeffrey

Foerster, Intel Corporation Yong-joo Tcha and Seong-Choon Lee, KT Corporation5. LTE vs WiMax:The battle continues6. Comparison of MAC Protocols between WiMAX and LTE, Zhongmin Li'， Lu Ga02， and Min

Liu'

Acronyms

AASN Access Service NetworkASN GWs ASN GatewaysAN Access NetworkATIS Alliance for Telecommunications Industry SolutionsAF Application FunctionAAI advanced air interfaceAMR adaptive multirateAMS advanced MSABS Advanced BS

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AMBR Aggregate MBRASN Access Service NetworkARP Allocation and retention priority

BBSs Base StationsBS base stationBE Best effortBSR Buffer Status Reports

CCSN Connectivity Service NetworkCN Core NetworkCAPEX Capital ExpendituresCS Convergence SublayerCQICH Channel Quality Indication ChannelCDMA Code-Division Multiple Access

DDL DownlinkDSCP Differentiated Services Code PointDRX Discontinued ReceptionDTX Discontinued Transmission

EEPC Evolved Packet CoreE-UTRAN Evolved Universal Mobile Telecommunications System Terrestrial Radio Access NetworkEPS Evolved Packet SystemertPS Extended rtPS

FFDD Frequency-Division Duplex

GGMSH Grant Management SubheaderGBR Guaranteed Bit Rate

IIP Internet ProtocolIEEE Institute of Electrical and Electronics EngineersIMT-Advanced International Mobile Telecommunications Advanced

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LTE Long Term Evolution

MMIMO Multiple Inputs, Multiple OutputsMME Mobility Management EntityMS Mobile StationMAC Medium Access ControlMSTR Maximum Sustained Traffic RateMRTR Minimum Reserved Traffic RateMBR Maximum Bit RateMPEG Moving Picture Experts Group

NNRM Network Reference ModelNAS Non Access StratumnrtPS Non-real-time Polling Servicenon-GBR Non-guaranteed Bit Rate

OOFDM Orthogonal Frequency Division MultiplexingOPEX Operating ExpenditureOFDMA Orthogonal Frequency-Division Multiple Access

PPDN Packet Data NetworkPAPR Peak-to Average- Power RatioPHY Physical layerP-FBCH Primary Fast Feedback ChannelPDN-GW Packet Data Network GatewayPUCCH Physical Uplink Control ChannelPUSCH Physical Uplink Shared ChannelPCC Policy Control and ChargingPKM Privacy and Key Management

QQCI QoS class identifier

RrtPS Real-time polling serviceRF Radio FrequencyRLC Radio Link Control

S

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SR Service RequestSS Subscriber StationS-GW Serving GatewaySCFDMA Single Carrier Frequency-Division Multiple Access

TTDD Time-Division Duplex

UUMTS/HSDPA High Speed Downlink Packet AccessUGS Unsolicited Grant ServiceUGI Unsolicited Grant IntervalUPI Unsolicited Polling IntervalUE User TerminalUL Uplink

WWiMAX Worldwide Interoperability for Microwave AccessWLAN Wide Area Network

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