module 4: wireless metropolitan and wide area networks · smd161 wireless mobile networks ......

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Module 4: Wireless Metropolitan and Wide Area Networks

Kaustubh S. PhanseDepartment of Computer Science and Electrical Engineering

Luleå University of Technology

SMD161 Wireless Mobile Networks

SMD161 Wireless Mobile Networks 2

Lecture objectivesDefine wireless metropolitan and wide area networks

Cellular networksSome background and historySystem architectureSystem design issuesMobility management

IEEE 802.16 WiMaxMotivationPhysical and MAC layers

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ReferencesT. Rappaport, Wireless Communications: Principles and Practice, Prentice Hall, 1996.

W. C. Y. Lee, Mobile Cellular Telecommunications: Analog and Digital Systems, McGraw-Hill Publications, 2nd ed., 1995.

C. Eklund, R. B. Marks, K. Stanwood and S. Wang, ”IEEE Standard 802.16: A Technical Overview of the WirelessMAN™ Air Interface for Broadband Wireless Access,” IEEE Communications Magazine, June 2002.

S. J. Vaughan-Nichols, ”Achieving Wireless Broadband with WiMax,” IEEE Computer, June 2004.


Metropolitan area wireless networksBroadband wireless connectivity (for the last-mile)

Mostly fixed and low mobilityIEEE 802.16

Infrastructure Residential broadband(DSL/cable alternative)

High speed enterprise wide networkBackhaul for local

hotspots

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Wide area wireless networksEnable connectivity over national, continental or global level

Seamless connectivity at high speed mobilityRelatively low bandwidth (for now, higher bandwidth is expensive)GSM/UMTS, satellite systems

Mobile cellular systems

Satellite systemsInfrastructure


Cellular systems have come a long way...Mobile Telephone Service (MTS) in New York (1976)

Total of 33 channels covering an area of 50 miles in diameterDivided into three systems: MTS, MJ and MK systems

MJ system served 225 customers with another 2400 on waiting list

MK system served 225 customers with another 1300 on waiting list

Overall, poor performance, but high demand and high blocking probability during busy hours

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Evolution of mobile telecommunications systems

1G 2G 3G2.5G

IS-95cdmaOne

IS-136TDMAD-AMPSGSMPDC

GPRS

IMT-DSUTRA FDD / W-CDMA

EDGE

IMT-TCUTRA TDD / TD-CDMA

cdma2000 1X

1X EV-DV(3X)

AMPSNMT

IMT-SCIS-136HSUWC-136

IMT-TCTD-SCDMA

CT0/1

CT2IMT-FTDECT

CD

MA

TDM

AFD

MA

IMT-MCcdma2000 1X EV-DO

HSDPA


Cellular subscribers

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System architecture of a cellular network

Radio sub-system

MS: Mobile station

BS: Base-station

BSC: Base-station controller

Network switching sub-system

MSC: Mobile switching centre

HLR: Home location resgiter

VLR: Vistor location register

GMSC: Gateway MSC

BSCBSC

MSC MSC VLRVLR

GMSC

HLR

Another network

Internet

MS MSBS

BS

BSCBSC

MSC MSC VLRVLR

GMSC

HLR

Another network

Internet

MS MSBS

BS


Radio sub-system (radio access network)

MSC MSC VLRVLR

GMSC

HLR

Another network

Internet

BSCBSC

Connectivity between mobile stations and base-stations

Radio resource managementSetup, maintenance and release of channelsCall admission control

Micro-mobility managementCall/session handover between base-stations

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Network and switching sub-system (core network)

MSC MSC VLRVLR

Gateway MSC

HLR

Another network

Internet

BSCBSCConnectivity between radio access networks and other

infrastructure networksMobile switching centre (MSC)

Storage of user data and macro-mobility managementHome location register (HLR)Visiting location register (VLR)

Service provisioning


Subscriber identitySubscriber identity module (SIM)

Personalized chip card to be inserted in the mobile station

Stores specific user dataTelephone number, called Mobile subscriber ISDN number (MSISDN)User identity, called International mobile subscriber Identity (IMSI)Secret keys for encryption

Service supportAddress and phone bookInbox (for storing SMS)Recently called and received phone numbers, etc.

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Routing call to mobile user

MSC HLR

VLR

GMSC

Public switched telephone

network (PSTN)

BSC

1MSISDN

2 MSISDN

3MSRN

MSRN 4

6TMSI

7TMSI

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8TMSI TMSI

TMSI9

5MSRN

BSC

MSISDN: Mobile Subscriber ISDN Number

MSRN: Mobile Station Roaming Number

TMSI: Temporary Mobile Subscriber Identity


Handover (or handoff)Transfer of an ongoing call or session from one base-station to another

When user moves from coverage of the old base-station into the coverage of a new oneShould be transparent to the userNew resources (channel) should be allocated by the new base-station

Proper design of handover algorithm crucialfor seamless mobility

Generally not standardized; up to the network operator

BSC

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Handover strategiesControlled by the MSC

Based on the received signal strength indicator (RSSI) at the base-station∆ = Prhandoff – Prminimum usable

If ∆ is too small, may not allow enough time for handover resulting in a dropped callIf ∆ is too large, it may cause unnecessary handovers

Mobile assisted handover (MAHO)Mobile station makes handover decision based on received signal strength of its current base-station and neighboring base-stations


Handover strategiesMobile assisted handover (MAHO)

Received powerBSold

Received powerBSnew

MS MS

HO_MARGIN

BSold BSnew

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Types of handover

BSC

BSC

Intra BSC handover Intra MSC

handover

BSC

MSC MSC

Inter MSC handover

BSC

MSC

Inter technology handover, e.g., GSM to UMTS


System design issuesCell shape

Why hexagonal?

Approximation to simplify modeling and analysis

Ideal omni-directional isotropic propagation

Real non-isotropic propagation

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Frequency reuseSpace division multiple access (SDMA)

Efficient use of limited spectrum bandwidth

f4

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f1f3

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f1

f4

f5

f1f3

f2

f6

f7

f3f2

f4

f5

f1


Frequency reuseCellular system with:

Total number of duplex channels = SDivided into a group of N cellsk of these channels are allocated to each cellSo, total number of duplex channels can be expressed as

The N cells which collectively use the complete set of available frequencies is called a cluster

The factor N is called the cluster size

S = k x N

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Frequency reuseIf a cluster is replicated M times, then the total number of duplex channels C represents the system capacity and is given by

Based on hexagonal geometry, N can only have values which satisfy the following equation

where i and j are non-negative integers

C = M x k x N = M x S

N = + ij + 2i 2j


Frequency reuse distance calculationGiven the total area to be covered, the frequency reuse distance Dis a function of the cluster size (and the cell size)

Co-channel reuse factor is expressed as

f4

f5

f1f3

f2

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f3f2

f4

f5

f1

f4

f5

f1f3

f2

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f7

f3f2

f4

f5

f1

D/R = = Q3N

D

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Frequency reuse patterns

f1

f3

f2

f4

f2

f3

f1

f4

f5

f7

f6

f1

f3

f2

f3

f1

f4

f5

f7

f6

f2

f3

f1

f4

f5

f7

f6

f2

f4

f2f4

N = 4 (i = 2, j = 0)

N = 7 (i = 2, j = 1)


Co-channel interferenceIf io is the number of co-channel (i.e., using the same frequency) interfering cells, then signal-to-interference ratio (SIR) is expressed as

If distance D to all interfering cells is equal, then

where n is the path loss exponent

S/I = S / (sum of received power from iointerfering cells)

S/I = / ion)3N(

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System capacityTrunking (also known as oversubscription)

Accomodate large number of subscribers in a limited radio spectrumExploit statistical behavior of users (i.e., not all users are expected to use the network simultaneously)

Grade of service (GOS)Metric to measure performance of a trunked systemAbility of a user to access a trunked system during busiest hoursExpressed in Erlangs (one Erlang is the traffic intensity carried by channel that is completely busy, e.g., one call-hour per hour)


System capacityAverage duration of a call = HAverage number of calls per unit time = µ

Traffic intensity of a user Au is expressed as

For a system containing U users, the total traffic intensity is

Assuming the traffic is equally distributed over C channels, the traffic intensity per channel is

Au = µ x H

A = U x Au

Ac = (U x Au) / C

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Blocking probabilityErlang B

Blocked Calls Clear system

Erlang CBlocked Calls Delayed system


Improving system capacityCell splitting

Improve utilization of spectrum efficiencySubdividing a congested cell into smaller cells (called microcell) Each microcell has its own base-station (smaller tranmission range)

Permanent cell splitting

Dynamic cell splitting

Microcells Picocells

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Improving system capacitySectorization

Base-stations use directional antennas to transmit in a specified sector

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1

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12

34

5

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12

34

5

6

120 deg. sectoring 60 deg. sectoring


802.16: BackgroundIEEE 802.16 standard (aka 802.16-2001)

Approved in 2001 (published in April 2002)WirelessMAN™ air interface for wireless metropolitan area networks (MANs)

Market potential and usage scenariosProvide broadband wireless access to businesses and homesAlternative to wired access technologies like fibre optics, cable and DSLCover broad geographical areas at low cost

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802.16: BackgroundCommunication between a central base station and a receiver installed on a building with exterior antenna

The receiver will connect to individual users through in-building LANs, e.g., Ethernet, WiFi, …Future standards may allow direct communication between base-station and user device (e.g., laptop, PDA)

© IEEESource: S. J. Vaughan-Nichols, ”Achieving Wireless Broadband with WiMax,” IEEE Computer, June 2004.


802.16: BackgroundSome initial products and deployments starting 2003

Forecasts predict exponential growth

WiMax forumCertification of 802.16 compliant productsWiMax: Worldwide interoperability for microwave access

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802.16: Protocol layer structure

Service Specific Convergence Sublayer

MAC Common Part Sublayer

Security Sublayer

Transmission Convergence Sublayer

Physical Layer

MAC Layer

Physical Layer


802.16: Physical layerSupport for multiple frequency bands and hence multiple transmission ranges and bandwidth

10 to 66 GHz802.16-2001Direct line of sight between transmitter and receiverSingle carrier modulationUp to 75 Mbps per channel (on both uplink and downlink)

2-11 GHz802.16a (2001)No line-of-sight required (better penetration of barriers)Single and multiple carrier modulation (OFDM)More flexibility with point-to-multipoint transmissionsSupport for mesh deployment

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802.16: Enhancements802.16b

Use of spectrum in the 5 and 6 GHz frequeny rangeEnhancements for supporting quality of service (QoS)

802.16cDetails added to 802.16-2001 (10 to 66 GHz)Encourage more consistent implementation and interoperability

802.16dMinor enhancements to 802.16aCreates system profiles for compliance testing

802.16eSupport (e.g., fast handover) for communication between base-station and mobile users moving at vehicular speeds


802.16: Physical layerFrequency Division Duplexing (FDD)

Uplink and downlink use different frequencies

Time Division Duplexing (TDD)Both uplink and downlink share the same frequency

Standard supports both full duplex and half duplex transceivers

Time Division Multiplexing (TDM)Allow base-station (BS) to communicate simultaneously with multiple subscriber stations (SS)

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802.16: Physical layerBurst single carrier modulation

QPSK16-QAM64-QAM

WirelessMAN-OFDM 256-carrier OFDMTDMA for multiple access

WirelessMAN-OFDMA2048-carrier OFDMMultiple access provided by assigning a set of carriers to each receiver


802.16: Physical layerAdaptive burst profiles

Transmission parameters such as modulation and FEC settings can be modified for each SS on a frame-to-frame basisDownlink Interval Usage Code (DIUC)Uplink Interval Usage Code (UIUC)

Radio link control (RLC)Controls power control, ranging and transition from one burst profile to another

Ranging request (RNG-REQ)Initial power leveling and ranging request made by the SS

Ranging response (RNG-RSP)Power, ranging and timing adjustments recommended by BS

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TDD frame structure

Frame j-1… …

… …

Frame j Frame j+1

Downlink Subframe Uplink Subframe


FDD frame structure

Frame j-1… …Frame j Frame j+1

Downlink (frequency m)

Frame j-1… …Frame j Frame j+1

Uplink (frequency n)

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802.16: MAC layerConnection-oriented

All traffic including inherently connectionless traffic is mapped into a connectionEach connection is identified by a connection identifier (CID)Reserved CIDs for management, broadcasts, …

Provides ability to map QoS and transmission parameters for every connection

Each connection is associated with a service flow


802.16: MAC layer

Each SS has a unique 48-bit MAC addressMainly serves as equipment identifierPrimary addresses used during operation are the CIDs

Upon initialization, SS is assigned three management connectionsin each direction

Transfer of short time-critical MAC and radio link control messagesTransfer longer, more delay-tolerant messages, e.g., used for authentication and connection set-upTransfer management related messages, e.g., SNMP, DHCP, TFTP

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802.16: Channel accessAt the beginning of every frame, the BS transmits the downlink map (DL-MAP) and uplink map (UL-MAP) messages

UL-MAP defines uplink channel access and UIUC for the uplink subframeDL-MAP defines the DIUC for the downlink subframe


802.16: Downlink subframe structure

Used only in FDD systems

© IEEESource: C. Eklund, R. B. Marks, K. Stanwood and S. Wang, ”IEEE Standard 802.16: A Technical Overview of the WirelessMAN™ Air Interface for Broadband Wireless Access,” IEEE Communications Magazine, June 2002.

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802.16: Uplink subframe structure

© IEEESource: C. Eklund, R. B. Marks, K. Stanwood and S. Wang, ”IEEE Standard 802.16: A Technical Overview of the WirelessMAN™ Air Interface for Broadband Wireless Access,” IEEE Communications Magazine, June 2002.


802.16: QoS supportQoS support defined in the form of four service flows

Unsolicited grant service (UGS) for CBR real-time traffic such as voice over IPReal-time polling service (rtPS) for VBR real-time traffic such as audio/video streamingNon-real-time polling service (nrtPS) for VBR non-real-time traffic that expects better than best effort service, e.g., highbandwidth FTPBest effort (BE) for traffic that does not require QoS support

Bandwidth allocationGrant per connection (GPC)Grant per SS (GPSS)

module 4: wireless metropolitan and wide area networks · smd161 wireless mobile networks ......

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