Post on 30-Apr-2018
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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
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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.
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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D/R = = Q3N
D
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Frequency reuse patterns
f1
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f1
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N = 4 (i = 2, j = 0)
N = 7 (i = 2, j = 1)
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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)
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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
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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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120 deg. sectoring 60 deg. sectoring
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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.
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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
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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
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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
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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
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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
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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
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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.
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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)