1. Advance Computer Networks Lecture#12
Instructor:
Engr. Muhammad Mateen Yaqoob

2. Mateen Yaqoob Department of Computer Science
Introduction
IEEE i.e. WiMAX latest technology for Broadband wireless access
Evolved from to d for fixed wireless access and the new e for mobility support
The standard specifies the air interface, including the medium access control (MAC) and physical (PHY) layers.
Key development in the PHY layer includes orthogonal frequency-division multiplexing (OFDM), in which multiple access is achieved by assigning a subset of subcarriers to each individual user.
OFDM system, the data is divided into multiple parallel substreams at a reduced data rate, and each is modulated and transmitted on a separate orthogonal subcarrier.
IEEE standard specified a frequency range of 10–66 GHz with a theoretical maximum bandwidth of 120 Mb/s and maximum transmission range of 50 km. However, the initial standard only supports line-of-sight (LOS) transmission and thus does not seem to favor deployment in urban areas.
IEEE a-2003, can support NLOS (non line of sight transmission)
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Features
Added Mobility support is an advantage like in latest IEEE e (Mobile WiMAX)
It uses adaptive antenna system (AAS) and multiple input multiple output (MIMO) technologies to improve coverage.
It improves NLOS coverage by utilizing advanced antenna diversity schemes and hybrid automatic repeat request (hARQ).
IEEE provides the capability to offer new wireless services such as multimedia streaming, real-time surveillance, voice over IP (VoIP), and multimedia conferencing.
Due to its long-range and high-bandwidth transmission, IEEE has also been considered in areas where it can serve as the backbone network with long separation among the infrastructure nodes.
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4. Comparisons between WiMAX and WiFi
Comparisons and confusion between WiMAX and Wi-Fi are frequent because both are related to wireless connectivity and Internet access.
WiMAX is a long range system, covering many kilometers, that uses licensed or unlicensed spectrum to deliver connection to a network, in most cases the Internet.
Wi-Fi uses unlicensed spectrum to provide access to a local network.
Wi-Fi is more popular in end user devices.
Wi-Fi runs on the Media Access Control's CSMA/CA protocol, which is connectionless and contention based, whereas WiMAX runs a connection-oriented MAC.
WiMAX and Wi-Fi have quite different quality of service (QoS) mechanisms:
WiMAX uses a QoS mechanism based on connections between the base station and the user device. Each connection is based on specific scheduling algorithms.
Wi-Fi uses contention access - all subscriber stations that wish to pass data through a wireless access point (AP) are competing for the AP's attention on a random interrupt basis. This can cause subscriber stations distant from the AP to be repeatedly interrupted by closer stations, greatly reducing their throughput.
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ITU Definitions
Fixed wireless access (FWA)
Wireless access application in which the location of the end-user termination and the network access point to be connected to the end-user are fixed.
Mobile wireless access (MWA)
Wireless access application in which the location of the end-user termination is mobile.
Nomadic wireless access (NWA)
Wireless access application in which the location of the end-user termination may be in different places but it must be stationary while in use.
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Standards
World Interoperability for Microwave Access
There are two main applications of WiMAX:
Fixed WiMAX (IEEE ) - Fixed WiMAX applications are point-to-multipoint enabling the delivery of last mile wireless broadband access as an alternative to cable and DSL for homes and businesses.
Mobile WiMAX (IEEE e-2005) - Mobile WiMAX offers the full mobility of cellular networks at true broadband speeds.
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7. Mateen Yaqoob Department of Computer Science
WiMAX
Fixed WiMAX Architecture
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8. Fixed and Mobile WiMAX Adoption
Fixed WiMAX Adoption Fixed WiMAX is currently available however the adoption rate is impacted by the high cost of equipment in comparison to cable or DSL. Fixed WiMAX provides greater benefits for developing countries that do not already have physical infrastructure to support wired broadband access.
Mobile WiMAX Adoption Mobile equipment testing typically takes between 12 to 18 months before the equipment is introduced to the consumer market.
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9. Mateen Yaqoob Department of Computer Science
MAC layer in WiMAX
MAC layer consists of three sublayers: the service-specific convergence sublayer (CS), MAC common part sublayer (MAC CPS), and security sublayer.
Main functionality of the CS is to transform or map external data from the upper layers into appropriate MAC service data units (SDUs) for the MAC CPS.
MAC CPS provides the core functionality for system access, allocation of bandwidth, and connection establishment and maintenance.
For the PHY layer, the standard supports multiple PHY specifications, each handling a particular frequency range.
IEEE d MAC provides two modes of operation: point-to-multipoint (PMP) and multipoint- to-multipoint (mesh).
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10. Point to Multipoint mode
PMP operational mode fits a typical fixed access scenario, where multiple service subscribers are served by a centralized service provider.
uplink transmissions from a subscriber station (SS) to a base station (BS) occur in separate timeframes.
In the downlink subframe, the BS can transmit a burst of MAC protocol data units (PDUs).
SS listening to the data transmitted by the BS is only required to process PDUs addressed to itself.
Subscriber stations share the uplink to the BS on a demand basis.
Downlink and uplink subframes are duplexed either using frequency-division duplex (FDD) or time-division duplex (TDD).
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11. MULTIPOINT-TO-MULTIPOINT
Mesh mode nodes are organized in an ad hoc fashion.
Each station is able to establish direct communication to a number of other stations
Some certain nodes could provide BS function of connecting mesh network to backhaul links
The key difference is that in mesh mode all SSs may have direct links with other SSs.
IEEE defines two mechanisms to schedule data transmission in mesh mode.
In centralized scheduling the BS works like a clusterhead and determines how SSs share the channel in different time slots.
In distributed scheduling every node competes for channel access using a pseudo-random election algorithm based on the scheduling information of its two-hop neighbors.
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P2P & P2MP Architecture
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Additional features
Flexible spectrum allocation in that it is scaled to work in different channelization from 1.25 to 20 MHz complying with diverse requirement in different countries
High data rate with the MIMO antenna techniques and flexible sub-channelization schemes, which can support peak rates of 63 Mb/s in downlink and 28 Mb/s uplink per sector
There are many issues that must be carefully examined, including the deployment of infrastructure, data transmission, service guarantee, and scheduling.
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14. Bandwidth allocation and scheduling for enhanced QoS
In downlink transmissions a BS has sufficient information to perform scheduling, but in uplink transmissions a BS performs the scheduling of various service transmissions based on information gathered from SSs.
SS will request uplink bandwidth from the BS, and the BS will allocate bandwidth on an as needed basis.
Unsolicited grant service (UGS) is designed to support real-time constant bit rate (CBR) traffic such as VoIP; this provides fixed size transmission opportunities at regular time interval without the need for requests or polls.
Real-time polling service (rtPS) is designed to support variable bit rate (VBR) traffic such as MPEG video. In this service the BS offers the SS periodic request opportunities to indicate the required bandwidth.
Non-real-time polling service (nrtPS) is for delay-tolerant data service with a minimum data rate, such as FTP. This service allows an SS to use contention request and unicast request opportunities for bandwidth request. Unicast request opportunities are offered regularly in order to ensure that the SS has a chance to request bandwidth even in a congested network environment.
Best effort (BE) service does not specify any service related requirements. Similar to nrtPS, it provides contention request and unicast request opportunities, but it does not provide bandwidth reservation or regular unicast polls.
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Hindrance Factors
WiMAX BSs to provide wide coverage for an entire region can still be economically infeasible due to the high cost of setup and maintenance of infrastructure.
With the existing 3G or/and other cellular infrastructure available, cost issues will always remain a major concern hindering the deployment of WiMAX.
The IEEE j Working Group aims to solve these issues through the use of multihop relay stations in an attempt to extend the coverage area and improve throughput at a feasible economical level.
It is well known that an increase in the number of hops in transmission adversely affects overall throughput; this is further challenged by the potential QoS degradation and scheduling complexity.
DSL Digital subscriber line
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16. Mateen Yaqoob Department of Computer Science
WiMAX Deployment
Alternative to cable and DSL
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17. INTEROPERABILITY OF IEEE 802.16 AND IEEE 802.11
Interoperability between IEEE and other wireless technologies is one area that warrants much research interest.
IEEE builds on a completely different design at the MAC level.
IEEE the MAC protocol uses contention access, in which each SS has to compete against one another for accessing a wireless access point (AP).
subscriber distant from an AP can suffer performance degradation which makes it difficult to maintain the service requirements for applications like VoIP and streaming video.
one possible IEEE deployment is to combine IEEE and IEEE to form a wireless network for both outdoors and indoors.
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18. INTEROPERABILITY OF IEEE 802.16 AND IEEE 802.11
not be practical or economically feasible to use WiMAX for providing full coverage of an indoor environment as obstruction and building materials can attenuate outdoor signals to a large extent.
To provide more complete coverage of indoor and outdoor
environments, it seems natural to use a mix of IEEE and IEEE
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19. Integrated IEEE 802.16e and IEEE 802.11e scenario
An end user performs a handover from an IEEE e network to an IEEE e network.
The core network represents the backbone of the overall network, which provides connectivity for BSs and APs.
The network must be able to recognize the handover and reroute packets appropriately such that there is minimum disruption to the traffic routing.
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20. Mateen Yaqoob Department of Computer Science
Applications of WiMAX
Last mile connectivity : It is cost effective to provide high speed last mile connectivity to areas (remote, isolated & sparsely populated) that are too expensive to serve with wired technology. Hence, alternative to ADSL, DSL, ISDN, cable modems & fiber optics.
Flexibility to accommodate a variety of applications through a scheduling algorithm that assigns data allocations to various SS based on their needs.
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21. Mateen Yaqoob Department of Computer Science
Applications of WiMAX
Class Description
Real Time
Application Type
Bandwidth
Interactive Gaming
Yes
50-85 kbps
VOIP, Video Conference
VOIP
kbps
Video Phone
kbps
Streaming Media
Music/Speech
kbps
Video Clips
kbps
Movies Streaming
>2Mbps
Information Technology No
Instant Messaging
<250 byte messages
Web Browsing
>500 kbps
(with attachments)
Media Content Download (store & Forward)
Bulk data, Movie Download
>1Mbps
Peer-to-peer
>500kbps
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22. WiMAX System Components
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23. Mateen Yaqoob Department of Computer Science
WiMax Success Factors
It is crucial that WiMax becomes an important building block to enable fixed/mobile convergence and to ensure its success.
Ability to offer ease of use is crucial to the success of WiMAX service providers
Success of WiMAX may depend on the ability to combine fixed and mobile access over the same infrastructure
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Conclusions
It is expected that WiMax becomes the dominant standard for Wireless MAN in the world market, at least, in fixed broadband networks.
WiMax products will have to be delivered to the market needs and those for the end-users will have to be extremely easy to install.
Focus is too often on technologies
Subscribers pay for services, not technologies
Broadband capabilities are important, but bandwidth is not the only meter to assess service
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25. Mateen Yaqoob Department of Computer Science
What is mobility?
spectrum of mobility, from the network perspective:
no mobility
high mobility
mobile wireless user,
using same access
point
mobile user, connecting/ disconnecting from network using DHCP.
mobile user, passing through multiple access point while maintaining ongoing connections (like cell phone)
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26. Mateen Yaqoob Department of Computer Science
Mobility: vocabulary
home network: permanent “home” of mobile
(e.g., /24)
home agent: entity that will perform mobility functions on behalf of mobile, when mobile is remote
wide area network
permanent address: address in home network, can always be used to reach mobile
e.g.,
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27. Mobility: more vocabulary
visited network: network in which mobile currently resides (e.g., /24)
permanent address: remains constant (e.g., )
care-of-address: address in visited network.
(e.g., 79, )
wide area network
foreign agent: entity in visited network that performs mobility functions on behalf of mobile.
correspondent: wants to communicate with mobile
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28. Mateen Yaqoob Department of Computer Science
Mobility: approaches
let routing handle it: routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange.
routing tables indicate where each mobile located
no changes to end-systems
let end-systems handle it:
indirect routing: communication from correspondent to mobile goes through home agent, then forwarded to remote
direct routing: correspondent gets foreign address of mobile, sends directly to mobile
not
scalable
to millions of
mobiles
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29. Mateen Yaqoob Department of Computer Science
Components of cellular network architecture
correspondent
wired public telephone
network
MSC
MSC
MSC
MSC
MSC
different cellular networks,
operated by different providers
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30. Handling mobility in cellular networks
home network: network of cellular provider you subscribe to (e.g., Sprint PCS, Verizon)
home location register (HLR): database in home network containing permanent cell phone #, profile information (services, preferences, billing), information about current location (could be in another network)
visited network: network in which mobile currently resides
visitor location register (VLR): database with entry for each user currently in network
could be home network
Mateen Yaqoob Department of Computer Science