these slides are based on the slides formatted by dr sunilkumar s. manvi and dr mahabaleshwar s....

These slides are based on the slides formatted by Dr Sunilkumar S. manvi and Dr Mahabaleshwar S. Kakkasageri, theauthors of the textbook: Wireless and Mobile Networks, concepts and protocols. See slide number one.

Chapter 5Wireless Wide AreaNetworks


Learning objectives

– To understand Wireless Wide Area Networks(WWANs)– To study the WWAN standards– To know the architectures of WWANs– To study the protocols used in WWANS– To illustrate the applications of WWANs


Wireless wide area networks

technologies such as GlobalSystem

forMobileCommunications (GSM), General Packet Radio

Service (GPRS), UniversalMobile Telecommunications System (UMTS), Code Division Multiple Access (CDMA), etc., to transfer data.•WWAN can also use Local Multipoint Distribution Service (LMDS) and Wi-Fi to connect to the Internet.•WWAN connectivity allows a user with a laptop and a WWAN card to surf the web, check email, or connect to a Virtual Private Network (VPN) from anywhere within the regional boundaries of cellular service.

• WWAN is a form ofwireless

network which uses

mobile telecommunication cellular network


Cellular networks

• A cellular network uses a large number of low-power wireless transmitters to create cells - the basic geographic service area of a wireless communications system.

• Mobile users travel from cell to cell, their conversations are handed of between cells to maintain seamless service.

• Channels (frequencies) used in one cellcan be reused in

another cell some distance away.• Cells can be added to accommodate growth, creating new cells

in unserved areas or overlaying cells in existing areas.• Examples of this type of networks are GSM, PCS

(Personal communication systems) and UMTS/IMT 2000 (Universal Mobile Telecommunications System /International Mobile Telecommunications).


Principles of cellular networks• The cellular architecture consists of a backbone network

with fixed base stations (BSs) interconnected through a fixed network (usually wired), and of mobile stations (MSs) that communicate with the base stations via wireless links.

• The geographic area within which mobile stations (MSs) can communicate with a particular base station (BS) is referred to a cell.

• Neighboring cells overlap with each other, thus ensuring continuity of communications when the users move from one cell to another.

• The MSs communicate with each other, and with other networks, through the base stations and the backbone network.

• A set of channels (frequencies) are allocated to each base

station.


Principles of cellular networks (Contd..)

• Communication area is divided into hexagonal cells. Cell dimensions range from hundreds of meters till tens of kilometers.

• Each cell is served by a BS formed by a transceiver and a control unit. Each cell is allocated a frequency band for communication.

• Communication from MS to BS usesreverse link and

communication from BS to MS uses forward link.• Frequency reuse is a technique of reusing frequencies and

channels within a cellular network to improve the network capacity.

• Cells that reuse the same frequency must bedistant

enough for avoiding interference.

Principles of cellular networks (Contd..)

Cellular network Handoff in cellular networks



Handoff

• The procedure of moving from one cell to another, while a call is in progress, is called handoff.

• While performing handoff, the MS requires that the BS in the cell where it has moved allocates a channel.

– If channel is not available in the new cell, the handoff call is blocked and blocking is called handoff blocking.


Handoff (Contd..)• The QoS (Quality of Service) of a cellular network is

determined by new call and handoff blocking probabilities.

• Blocking probabilities can be reduced by increasing the capacity of the cellular networks.

• Capacity of Cellular networks can be increased– by applying efficient power control algorithms or– by reducing the size of the cells or– by increasing the number of channels in each cell.

• High cost solution– Reduced cells size– Adding supplementary channels


Other methods to increase capacityin cellular networks

• Frequency borrowing: congested cells use frequencies taken from adjacent cells where less traffic is observed.

• Cell sectoring: cells are divided into sectors and each sector is allocated its own set of frequencies. BSs use directional antennas to cover sectors.

• Microcells and picocells: a microcell covers a range of about 500 m and a picocell covers a range of about 10 m.


ExampleA cellular network has a total bandwidth 56 MHz. If two 35 KHz simplex channels are used to provide full duplex voice and control channels, compute the number of channels available per cell if a system uses (a) 4-cell reuse, (b) 7-cell reuse, (c) 12-cell reuse.Solution:•Given that the total available bandwidth is 56 MHz = 56,000 KHz.•Channel bandwidth = 35 KHz x 2 simplex channels = 70 KHz/duplex channels.•Total available channels = 56,000/70 = 800 channels.•let N denotes cell reuse.•(a) For N = 4, Total number of channels available per cell = 800/4 = 200 channels.•(b) For N = 7, Total number of channels available per cell = 800/7 = 115 channels.•(c) For N = 12, Total number of channels available per cell =800/12 = 67 channels.

ExampleIn a cellular network with hexagonal cells, it is forbidden to reuse a frequency band in an adjacent cell. If 915 frequencies are available, howmany frequencies can be used in a given cell?Solution:Given that the cell shape is hexagonal, hence it has six neighbors. If the central cell uses frequency group A, its six neighbors can use B, C, B, C B, and C respectively. In other words, only 3 unique cells are needed. Therefore each cell can have (915/3) or 305 frequencies.

Example scenario



ExampleConsider a cellular network with 64 cells. Each hexagonal cell has an approximate area 10 km2. The total number of radio channels allotted for the network is 336.•What is the total area covered by the cellular network.•Find the total number of channels of the network, if (a) N = 4, (b) N = 7, (c)N = 12, where N denotes cell reuse.Solution:•Total number of cells = 64. Each cell area = 10 km2.•The total area covered by the cellular network is, 64 X 10 = 640km2.•It is given that the total available channels in the network = 336.•(a) For N = 4, the available channels in a cell = 336/4 = 84

– Total channels = 84 X 64 = 5,376 channels.•(b) For N = 7 , the available channels in a cell = 336/7 = 48

– Total channels = 48 X 64 = 3,072 channels.•(c) For N = 12, the available channels in a cell = 336/12 = 28

– Total channels = 28 X 64 = 1,792 channels.


GSM•Salient features of GSM (Global System for Mobile Communications)•Frequency band: originally designed for 900 MHz band, later for 1800 MHz•Channels: 200 full-duplex channels per cell.

– Each channel consists of a downlink frequency and an uplink frequency.•Circuit switched

– suffers from high error rate, CDPD (Cellular Digital Packet Data) can beused to over come this problem.•Speed: see Chapter 1.•Hybrid frequency-division/time-division multiple access (FDMA/TDMA):

– FDMA divides 25 MHz allocated bandwidth into 125 carrier frequenciesthat are spaced 200 kHz apart.

– Eight burst periods (slots) are grouped into a TDMA frame (approx.4.615 ms, i.e., 0.577 ms for one slot).–A physical channel is one burst period per TDMA frame. Slow frequency hopping at up to 217 times per second.–Services: Supports value added services such as SMS (Short Message Service), access to Internet, Wireless Application Protocol, call forwarding, etc.

GSM Architecture• GSM

networksoperateatvarious

differentradio

and/orfrequencies: 900MHz1800MHz.

• USA and Canada operateat 850MHz and/or

1900MHz.• Major components of

a GSM network are:– MS (Mobile Station),– BSS (Base Station System),– Operation and Maintenance

Center (OMC), and– Network andSwitchingSubsystem (NSS). GSM network architecture


GSM Architecture (Contd..)

Station(MS):phone,PDA or

a

• Mobile Mobile laptop.

• It consists of a subscriber identity module (SIM) and a mobile equipment (ME).

– The ME (thephone itself), isidentified by

Mobile Identity

International Equipment (IMEI).


Base Station System (BSS)• Consists of

– One or more base transceiver station (BTS). A BTS (or BS), is a radio access point that defines a single cell: it includes a radio antenna, and a radio transceiver. Itperforms channel coding/decoding and encryption/ decryption.

– A base station controller (BSC): BSs are connected to a BSC which manages the radio resources. BSC is responsible for handovers to other cells based on BS transmitter power.These slides are based on the slides formatted by Dr Sunilkumar S. manvi and Dr Mahabaleshwar S. Kakkasageri,

theauthors of the textbook: Wireless and Mobile Networks, concepts and protocols. See slide number one.

OMC• Operation and Maintenance

Center (OMC):managesthe GSM functional blocks:

Mobile Switching Center (MSC) and the BSC (and indirectly the BS).•Maintains satisfactory operation of the GSM network based on observing the system load, blocking rates, handovers, etc.


NSS

• Network and SwitchingSubsystem (NSS): it contains

– Mobile Switching Center (MSC): used to facilitate communication between different MSs connected to different BSs.


NSS (Contd..)

– Interworking Functional Unit (IFU): allows the mobile stations (MSs) connected to a mobile switching center (MSC) to connect to public switched data network (PSDN), to public switched telephone network (PSTN) or the Internet.


NSS (Contd..)

– Equipment IdentityRegister (EIR):

It contains a list of valid MS equipment within the network, where each MS is identified by its International Mobile Equipment Identity (IMEI).


NSS (Contd..)– Home Location Register

(HLR): Database for management of mobile subscribers. Billing: must identify that every call is being made by either a home or a roaming user.

– Visitor Location Register (VLR): Manages roaming


NSS (Contd..)

– Authentication Center(AuC):

• It is a protected database that has a copy of the secret key stored in each subscriber’s SIM card.

• This key is used for authentication and encryption over the radio channel.



GSM as a cellular network standard• GSM was the European standard for voice services; later

data services were introduced.• Some of the standards developed for WWANs are IS-41,

IS-54, IS-88, IS-91, IS-93, IS-95, IS-124, IS-637, IS-756, and IS-2000.

• IS stands for Inter-Systems operation• Four different cell sizes in a GSM network

– macro, micro, pico and umbrella cells.• macro cells: cells where the BS antenna is installed in a mast

or a building above average roof top level.• micro cells: Antenna height is under average roof top level;

they are typically used in urban areas.• picocells: they are mainly used indoors.• umbrella cells : To cover shadowed regions of smaller cells

and fill gaps in coverage between those cells.


GPRS• General Packet Radio Service (GPRS) is a non-voice

value-added service that allows information to be sent and received across a mobile telephone network.

• It supplements today’s circuit-switched data and SMS.

• GPRS is not related to the global positioning system (GPS), a similar acronym that is often used in mobile contexts.


GPRS Architecture

• General Packet Radio Service (GPRS) is an enhancement over the GSM and adds some nodes in the network to provide the packet switched services.

• These network nodes are called GPRS support nodes (GSNs) and are responsible for the routing and delivery of the data packets to and from the MS and external packet data network (PDN)

GPRS Architecture (Contd..)



GPRS mobile station (MS)

• GPRS mobile station (MS) includes two components: MT (Mobile Terminal) and TE (Terminal Equipment).– MT is typically a handset used to access the radio interface.

It consists of• ME,• SIM, and• Terminal Adaptation Function (TAF)

– TAF helps GPRS TE merely to use theradio system at hotspots.– TE is typically a laptop or a

Personal Digital Assistant(PDA).


GPRS mobile station (Contd..)• Three different classes of MS have been

defined:– Class-A: supports simultaneous monitoring and operation

of both GPRS (packet-switched) and GSM (circuit- switched) services.

– Class-B: supports simultaneous monitoring but not simultaneous operation of GSM (circuit-switched) and GPRS (packet-switched) services.

– Class-C: supports either GSM (circuit-switched) or GPRS (packet-switched) monitoring and operation at a given time.

SGSN• SGSN (Serving

GPRS support nodes): It is responsible for the delivery of data packets from and to the mobile stations within its geographical service area.

• SGSN performs the following functions: authentication and authorization.


GGSN• GGSN (Gateway

GPRS support nodes). It acts as interface between the GPRS backbone and the external PLMN (Public Land Mobile Network) or Internet

• It interfaces to external data networks (basically it is a network router)These slides are based on the slides formatted by Dr Sunilkumar S. manvi and Dr Mahabaleshwar S. Kakkasageri, theauthors of the textbook: Wireless and Mobile Networks, concepts and protocols. See slide number one.


CGF (The Charging Gateway Function)• It provides the mechanism of transfer of charging

information from the GPRS Support Nodes (GSNs) the billing system

• The CGF can be a separate centralized element or itcan be distributed among GPRS Support Nodes• GPRS networks derive charging information for each

user transaction into Call Detail Records (CDRs) from SGSNs and GGSNs.

• Billing is typically based on the amount of data transferred


Functioning of GPRS• GPRS is a packet-switched protocol

for applications such as World Wide Web (WWW).

• SGSN receives andtransmits packetsbetween

the MSs and their counterparts in the PSDN• GGSN interworks with

the PSDN usingconnectionless network protocols• SGSN and GGSN interact with the GSM location

databases


Functioning of GPRS (Contd..)• The GPRS data units are routed to the destination

MSs based on location information.• Both SGSN and GGSN may be equipped with cache

memories containing location information to speed up the routing procedure.

• GPRS air interface requires a new radio link protocol to guarantee fast call setup procedure and low bit error rate for data transfer between the MSs and the BSs.


CDMA

• Code division multiple access (CDMA) is a channel access method utilized by various radio communication technologies.

• CDMA consistently provides better capacity for voice and data communications than other commercial mobile technologies.


CDMA (Contd..)

• When implemented in a cellular telephonesystem,

CDMA technology offers following benefits:– Capacity increases of 8 to 10 times that of an AMPS analog

system and 4 to 5 times that of a GSM system.– Improved call quality– Simplified system planning through

the use of the samefrequency in every sector of every cell.

– Improved coverage characteristics


CDMA (Contd..)

• CDMA One describes a complete wireless system based on the IS-95 CDMA standard, including IS-95A and IS-95B revisions.

• IS-95A describes the structure of the wideband 1.25 MHz CDMA channels, power control, call processing, hand-offs, and registration techniques for system operation.

• CDMA 2000 represents a family of International Telecommunication Union (ITU).

• WCDMA (or W-CDMA) stands for Wideband Code DivisionMultiple Access.

CDMA2000 network architecture



The Mobile Station (MS)

• In a CDMA2000 1X network, the mobile station-thesubscriber's handset-functions as a mobile-IP client.

• Upon power-up, the mobile stationautomatically registers with the HLR in order to– Authenticate the mobile for the environment

of the accessed network– Provide the HLR with the mobile's current location– Provide the Serving MobileSwitching

Centre (MSC-S)with the mobile's permitted feature set


Base Station Transceiver Subsystem (BTS)

• BTS controls the activities of the air link and acts asthe interface between the network and the mobile.• RF resources such as frequency assignments,

sector separation and transmit power control are managed at the BTS.

• In addition, the BTS manages the back-haul from the cell site to the Base Station Controller (BSC) to minimize any delays between these two elements.


Base Station Controller (BSC)• BSC routes voice- and circuit-switched data messagesbetween the cell sites and the MSC.

• It also bears responsibility for mobility management : it controls and directs handoffs from one cell site to another as needed.


Packet data serving node

• The PDSN does the following activities:– Manage the radio-packet interface between the

BSS (Base Station Subsystem = BTS + BSC) and the IP network by establishing, maintaining and terminating link layer to the mobile client

– Terminate the Point-to-Point Protocol (PPP) session initiated by the subscriber

– Provide an IP address for the subscriber (either from an internal pool or through a DHCP server or through an AAA server)


Packet data serving node (Contd..)

– Perform packet routing to external packet data networks or packet routing to the HA which optionally can be via secure tunnels

– Collect and forward packet billing data– Actively manage subscriber services based on the

profile information received from the SCS server of the AAA server

– Authenticate users locally, or forward authentication requests to the AAA server


Packet data serving node (Contd..)

• Accounting, Authentication, and Authorization (AAA) server: AAA server is used to authenticate and authorize users for network access and to store subscriber usage statistics for billing and invoicing.

• Home Agent (HA) server: HA supports seamless data roaming into other networks.

Call set-up scenario in CDMA2000



Call set-up scenario in CDMA2000 (Contd..)

• The sequence of operations during call set up arementioned below:

1. To register for packet data services, the mobile sends an Origination Message over the access channel to the BSS.

2. The BS acknowledges the receipt of the OriginationMessage, returning a BS ACK to the mobile.

3. The BS constructs a Service Request message and sends the message to the MSC.



4. The MSC sends an Assignment Request message to the BSS requesting assignment of radio resources. No terrestrial circuit between the MSC and the BS is assigned to the packet data call.

5. The BS and the mobile perform radioresource set-up

procedures.

6. The PCF sends Registration Request message to the selected PDSN.

7. The Registration Request is validated and the PDSN acceptsthe connection by returning an Registration Reply message.

8. After the radio link and connection are set-up, the BS sends an Assignment Complete message to the MSC.



9. The mobile and the PDSN establish the link layer (PPP) connection and then perform the registration procedures over the link layer (PPP) connection.

10.After completion of registration, the mobile can send/receive data.

11.The PCF periodically sends Registration Request messagefor refreshing registration for the connection.

12.For a validated Registration Request, the PDSN returns Registration Reply message.

GSM Vs. CDMA


Handover in cellular networks



The operation sequence for handover is as follows1.When a Mobile Station moves to a new MSC, it requests for location update.

2.New MSC enters subscribers details in associated (new) VLR by requesting update location area.

3.New VLR forwards location update to HLR.

4.HLR requests old VLR to delete subscribers entry. At the same time it also sends the subscriber's details to new VLR.

Handover in cellular networks (Contd..)


5. Deletion of the entry is acknowledged.

6. From new VLR, the subscriber details is acknowledged tothe HLR.

7. In HLR also the handover of MS is updated and it is acknowledged to the new VLR.

8. New VLR acknowledges the message to the new MSC.

9. New MSC updates the MS location.

Handover in cellular networks (Contd..)

Public Switched Telephone Network (PSTN)


Call set-up scenario from PSTN to the MS

1. From PSTN, the call is requested to the GMSC for the mobile station.

2. GMSC transfers the call to the HLR for verification and possible location of the mobile station.

3. HLR searches the assigned mobile station in MSC/VLR, where currently it is located.

4. VLR gives the requested mobile station current location (base station) to the HLR.

5. HLR transfers that message to the

GMSC for possible connectionwith where

the current basestation the mobile

station islocated.

GMSC (Gateway Mobile Switching Center) is aspecial kind of MSC that is used to route calls outside the mobile network


Call set-up scenario from PSTN to the MS (Contd..)

6. GMSC connects to the MSC.

7. MSC in-turn connects to thebase station.

8. Base station establishes the connection with the mobile station until the end of the call.

9. When the call is completed, the mobile station releases the channel by informing to the base station.

10.Base station releases the channel and updates in HLR and VLR.



Satellite networks

• A satellite is an object that orbits or revolves aroundanother object.• Satellite communication systems differ

from terrestrial systems in that the transmitter is not based on the ground but in the sky.

• A satellite system consisting of one or more satellites and the cooperating earth stations is referred as a satellite network.

Satellite and Orbits• An orbit is the path that

a satellite follows as it revolves around Earth.

• Basically there are three


categories ofLow

main orbits, Earth

They areOrbit (LEO),

OrbitandEarth

MediumEarth (MEO),GeostationaryOrbit (GEO)


Salient features• A satellite network communicates using earth stations and

satellites• Communication from earth station to satellite is called uplink

channel whereas communication from earth station to satellite is called downlink channel.

• Some of the features of satellite networks are as follows– Coverage– Speed– Security– Service types– Usage– Repeater– Packet switched– Frequency band

Architecture



Architecture (Contd..)

• Satellite– A satellite is a type of satellite network component that orbits the earth

in space as a wireless receiver/transmitter.

• Ground stations– Many satellites are moving in their respective orbits over the earth, thus

it is idealistic that we can freely communicate with a satellite by a radio frequency whenever we want to monitor its status or send a command.

• Users– A satellite network user may be a satellite telephone (sat phone), or a

communication unit in the ship is a type of mobile phone that connects to orbiting satellites instead of terrestrial cell sites.


WLAN Vs. WWAN

• Coverage– Wireless local area networks by definition operate over

asmall, local coverage area, normally about 100 m in range.

– Wireless wide area networks cover a much wider area, such as wherever the cellular network provider has wireless coverage.


• Speed– Wireless WAN speeds differ depending on the technology

used• GPRS networks offer a maximum user data rate of over 115 kbps if

all eight timeslots in a cell are allocated for data transmission.• Data speeds on CDMA networks were initially available at speeds

of 14.4 kbps, but have increased to a maximum throughput of 153 kbps as carriers have implemented CDMA2000 1X (1xRTT) networks

WLAN Vs. WWAN (Contd..)


• Data Security– In contrast to the security weaknesses in 802.11 networks,

cellular wireless WAN networks are extremely secure.– These networks incorporate military

technology and sophisticated encryption and authentication methods.

– Hotspots are wireless LANs availableto the public in a

location like an airport, coffee shop, or city neighborhood.



• Cost– Since wireless LANs operate in the unlicensed

frequency range, there is no service cost for using a private wireless LAN.

– The main cost involved is the cost of purchasing and installing the wireless LAN equipment and devices, and the cost of maintaining the network and the users.



Interworking of WLAN and WWAN

• Although WLANs and WWANs may appear to be competing technologies, they are far more useful as complementary technologies.

• These are used together, a user would have the best of both technologies, offering high-speed wireless access in a campus area, and access to all their data and applications with high-speed cellular access from anywhere with wireless WAN network coverage.


WWAN applications

• Wireless Internet– Internet can be accessed through the following:

IEEE 802.11, 802.11a,

• Global Satellite Networks.

• Cellular Networks: GSM, CDPD, GPRS.

• WCDMA/cdma2000 WirelessLANs:

802.11b.• Personal Area Networks: IEEE 802.15,

Bluetooth.

Wireless Internet access


– Fixed– Portable– Mobile– Terminal/User Mobility

• Service types forInternet access are asfollows:

Other applications of WWAN


these slides are based on the slides formatted by dr sunilkumar s. manvi and dr mahabaleshwar s....

Documents

dr mahabaleshwar

dr sunilkumar

mobile networks

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wireless communications

power wireless transmitters

type of networks