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Introduction to Mobile Communications TCOM 552, Lecture #10 Hung Nguyen, Ph.D. 13 November, 2006.
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Transcript of Introduction to Mobile Communications TCOM 552, Lecture #10 Hung Nguyen, Ph.D. 13 November, 2006.
Introduction to Mobile Introduction to Mobile CommunicationsCommunications
TCOM 552, Lecture #10Hung Nguyen, Ph.D.13 November, 2006
11/13/2006Hung Nguyen, TCOM 552, Fall 20062
OutlineOutline
Cordless Systems and Wireless Local Loop (Chapter 11)
Mobile IP and Wireless Application Protocol (Chapter 12)
11/13/2006Hung Nguyen, TCOM 552, Fall 20063
Cordless System Operating Cordless System Operating EnvironmentsEnvironments
Residential – a single base station can provide in-house voice and data support
Office– A single base station can support a small office– Multiple base stations in a cellular configuration
can support a larger office Telepoint – a base station set up in a public
place, such as an airport. Has not succeeded in the market.
11/13/2006Hung Nguyen, TCOM 552, Fall 20064
Design Considerations for Cordless Design Considerations for Cordless StandardsStandards
Modest range of handset from base station (up to 200 m), so low-power designs are used
Inexpensive handset and base station, dictating simple technical approaches
Frequency flexibility is limited, so the system needs to be able to seek a low-interference channel whenever used
11/13/2006Hung Nguyen, TCOM 552, Fall 20065
Digital Enhanced Cordless Telecom & Digital Enhanced Cordless Telecom & Personal Wireless TelecomPersonal Wireless Telecom
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Time Division Duplex (TDD)Time Division Duplex (TDD)
TDD also known as time-compression multiplexing (TCM)
Data transmitted in one direction at a time, with transmission between the two directions– Simple TDD (Simplex)– TDMA TDD
11/13/2006Hung Nguyen, TCOM 552, Fall 20067
Simplex TDD TransmissionSimplex TDD Transmission
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Simple TDD (Simplex)Simple TDD (Simplex)
Bit stream is divided into equal segments, compressed in time to a higher transmission rate, and transmitted in bursts
Effective bits transmitted per second:
R = effective data rate B = size of block in bits Tp = propagation delay Tb = burst transmission time Tg = guard time
gbp TTTB
R 2
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Simple TDD (Simplex)Simple TDD (Simplex)
Actual data rate, A:
Combined with previous equation:
The actual data rate is more than double the effective data rate seen by the two sides
b
gp
b
gp
T
TT
R
A
T
TTRA
12
12
bT
BA
11/13/2006Hung Nguyen, TCOM 552, Fall 200610
TDMA TDD (Time Slots)TDMA TDD (Time Slots)
Wireless TDD typically used with TDMA– A number of users receive forward channel
signals in turn and then transmit reverse channel signals in turn, all on same carrier frequency
Advantages of TDMA/TDD:– Improved ability to cope with fast fading– Improved capacity allocation
11/13/2006Hung Nguyen, TCOM 552, Fall 200611
DECT Protocol ArchitectureDECT Protocol Architecture
Physical layer – data transmitted in TDMA-TDD frames over one of 10 RF carriers
Medium access control (MAC) layer – selects/ establishes/releases connections on physical channels; supports three services:– Broadcast– Connection oriented– Connectionless
Data link control layer – provides for the reliable transmission of messages using traditional data link control procedures
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DECT Protocol ArchitectureDECT Protocol Architecture
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Differential QuantizationDifferential Quantization
Speech signals tend not to change much between two samples– Transmitted PCM values contain considerable
redundancy Transmit difference value between adjacent
samples rather than actual value If difference value between two samples
exceeds transmitted bits, receiver output will drift from the true value– Encoder could replicate receiver output and
additionally transmit that difference
11/13/2006Hung Nguyen, TCOM 552, Fall 200614
Differential PCM (DPCM)Differential PCM (DPCM)
Since voice signals change relatively slowly, value of k-th sample can be estimated by preceding samples
Transmit difference between sample and estimated sample– Difference value should be less than difference
between successive samples At the receiver, incoming difference value is
added to the estimate of the current sample– Same estimation function is used
11/13/2006Hung Nguyen, TCOM 552, Fall 200615
Adaptive Differential PCM (ADPCM)Adaptive Differential PCM (ADPCM)
Improve DPCM performance using adaptive prediction and quantization– Predictor and difference quantizer adapt to the
changing characteristics of the speech Modules
– Adaptive quantizer– Inverse adaptive quantizer– Adaptive predictor
11/13/2006Hung Nguyen, TCOM 552, Fall 200616
ADPCM Encoder & DecoderADPCM Encoder & Decoder
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Subject Measurement of Coder Subject Measurement of Coder PerformancePerformance
Subjective measurements of quality are more relevant than objective measures
Mean opinion score (MOS) – group of subjects listen to a sample of coded speech; classify output on a 5-point scale
MOS scale is used in a number of specifications as a standard for quality
Wireless Local Loop (WLL)Wireless Local Loop (WLL)
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Wireless Local LoopWireless Local Loop
Wired technologies responding to need for reliable, high-speed access by residential, business, and government subscribers– ISDN, xDSL, cable modems
Increasing interest shown in competing wireless technologies for subscriber access
Wireless local loop (WLL)– Narrowband – offers a replacement for existing
telephony services– Broadband – provides high-speed two-way voice
and data service
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WLL ConfigurationWLL Configuration
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Advantages of WLL over Wired Advantages of WLL over Wired ApproachApproach
Cost – wireless systems are less expensive due to cost of cable installation
Installation time – WLL systems can be installed in a small fraction of the time required for a new wired system
Selective installation – radio units installed for subscribers who want service at a given time– With a wired system, cable is laid out in
anticipation of serving every subscriber in a given area
11/13/2006Hung Nguyen, TCOM 552, Fall 200622
Propagation Considerations for WLLPropagation Considerations for WLL
Most high-speed WLL schemes use millimeter wave frequencies (10 GHz to about 300 GHz)– There are wide unused frequency bands
available above 25 GHz– At these high frequencies, wide channel
bandwidths can be used, providing high data rates
– Small size transceivers and adaptive antenna arrays can be used
11/13/2006Hung Nguyen, TCOM 552, Fall 200623
Propagation Considerations for WLLPropagation Considerations for WLL
Millimeter wave systems have some undesirable propagation characteristics– Free space loss increases with the square of the
frequency; losses are much higher in millimeter wave range
– Above 10 GHz, attenuation effects due to rainfall and atmospheric or gaseous absorption are large
– Multipath losses can be quite high
11/13/2006Hung Nguyen, TCOM 552, Fall 200624
Fresnel ZoneFresnel Zone
How much space around direct path between transmitter and receiver should be clear of obstacles?– Objects within a series of concentric circles around the line of
sight between transceivers have constructive/destructive effects on communication
For point along the direct path, radius of first Fresnel zone:
DS
SDR
11/13/2006Hung Nguyen, TCOM 552, Fall 200625
Atmospheric AbsorptionAtmospheric Absorption
Radio waves at frequencies above 10 GHz are subject to molecular absorption– Peak of water vapor
absorption at 22 GHz– Peak of oxygen
absorption near 60 GHz
Favorable windows for communication:– 28 GHz to 42 GHz– 75 GHz to 95 GHz
11/13/2006Hung Nguyen, TCOM 552, Fall 200626
Effect of RainEffect of Rain
Attenuation due to rain– Presence of raindrops can severely degrade the
reliability and performance of communication links
– The effect of rain depends on drop shape, drop size, rain rate, and frequency
Estimated attenuation due to rain:
A = attenuation (dB/km) R = rain rate (mm/hr) a and b depend on drop sizes and frequency
baRA
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Effects of VegetationEffects of Vegetation
Trees near subscriber sites can lead to multipath fading
Multipath effects from the tree canopy are diffraction and scattering
Measurements in orchards found considerable attenuation values when the foliage is within 60% of the first Fresnel zone
Multipath effects highly variable due to wind
MMDS & LMDSMMDS & LMDS
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Multipoint Distribution Service (MDS)Multipoint Distribution Service (MDS)
Multichannel multipoint distribution service (MMDS)– Also referred to as wireless cable– Used mainly by residential subscribers and small
businesses Local multipoint distribution service (LMDS)
– Appeals to larger companies with greater bandwidth demands
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Advantages & Disadvantages of MMDSAdvantages & Disadvantages of MMDS
MMDS signals have larger wavelengths and can travel farther without losing significant power
Equipment at lower frequencies is less expensive
MMDS signals don't get blocked as easily by objects and are less susceptible to rain absorption
Low frequency results in less bandwidth
11/13/2006Hung Nguyen, TCOM 552, Fall 200632
Advantages & Disadvantages of LMDSAdvantages & Disadvantages of LMDS
Relatively high data rates (Mbps range) Capable of providing video, telephony, and
data Relatively low cost in comparison with cable
alternatives Short range from base station requires a
large number to service a given area
11/13/2006Hung Nguyen, TCOM 552, Fall 200633
802.16 Standards Development802.16 Standards Development
Use wireless links with microwave or millimeter wave radios
Use licensed spectrum Are metropolitan in scale Provide public network service to fee-paying
customers Use point-to-multipoint architecture with stationary
rooftop or tower-mounted antennas Provide efficient transport of heterogeneous traffic
supporting quality of service (QoS) Use wireless links with microwave or millimeter
wave radios Are capable of broadband transmissions (>2 Mbps)
11/13/2006Hung Nguyen, TCOM 552, Fall 200634
802.16 Standards802.16 Standards
WiMAX (World-wide Interoperability for WiMAX (World-wide Interoperability for Microwave Access) Industry Group formed to Microwave Access) Industry Group formed to promote 802.16 standardspromote 802.16 standards
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IEEE 802.16 Protocol ArchitectureIEEE 802.16 Protocol Architecture
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Protocol ArchitectureProtocol Architecture
Physical and transmission layer functions:– Encoding/decoding of signals– Preamble generation/removal– Bit transmission/reception
Medium access control layer functions:– On transmission, assemble data into a frame
with address and error detection fields– On reception, disassemble frame, and perform
address recognition and error detection– Govern access to the wireless transmission
medium
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Protocol ArchitectureProtocol Architecture
Convergence layer functions:– Encapsulate PDU (protocol data unit) framing of
upper layers into native 802.16 MAC/PHY frames
– Map upper layer’s addresses into 802.16 addresses
– Translate upper layer QoS parameters into native 802.16 MAC format
– Adapt time dependencies of upper layer traffic into equivalent MAC service
11/13/2006Hung Nguyen, TCOM 552, Fall 200638
802.16 Protocols in Context802.16 Protocols in Context
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IEEE 802.16.1 Bearer ServicesIEEE 802.16.1 Bearer Services
Digital audio/video multicast Digital telephony ATM Internet protocol Bridged LAN Back-haul Frame relay
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IEEE 802.16.1 Frame FormatIEEE 802.16.1 Frame Format
Header - protocol control information– Downlink header – used by the base station– Uplink header – used by the subscriber to convey
bandwidth management needs to base station– Bandwidth request header – used by subscriber to request
additional bandwidth Payload – either higher-level data or a MAC control
message CRC – error-detecting code
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MAC Management MessagesMAC Management Messages
Uplink and downlink channel descriptor Uplink and downlink access definition Ranging request and response Registration request, response and acknowledge Privacy key management request and response Dynamic service addition request, response and
acknowledge Dynamic service change request, response, and
acknowledge Dynamic service deletion request and response Multicast polling assignment request and response Downlink data grant type request ARQ acknowledgment
11/13/2006Hung Nguyen, TCOM 552, Fall 200642
802.16 Physical Layer802.16 Physical Layer
Upstream Transmission– Uses a DAMA-TDMA (Demand Assignment Multiple
Access-Time Division Multiple Access) technique– Error correction uses Reed-Solomon code– Modulation scheme based on QPSK
Continuous downstream mode – For continuous transmission stream (audio, video)– Simple TDM scheme is used for channel access– Duplexing technique is frequency division duplex (FDD)
Burst downstream mode– Targets burst transmission stream (IP-based traffic)– DAMA-TDMA scheme is used for channel access– Duplexing techniques are FDD with adaptive modulation,
frequency shift division duplexing (FSDD), time division duplexing (TDD)
11/13/2006Hung Nguyen, TCOM 552, Fall 200643
802-16 Data Rates in Mbps802-16 Data Rates in Mbps
Mobile IP and Wireless Mobile IP and Wireless Application ProtocolApplication Protocol
Chapter 12
11/13/2006Hung Nguyen, TCOM 552, Fall 200645
Mobile IP UsesMobile IP Uses
Enable computers to maintain Internet connectivity while moving from one Internet attachment point to another
Mobile – user's point of attachment changes dynamically and all connections are automatically maintained despite the change
Nomadic - user's Internet connection is terminated each time the user moves and a new connection is initiated when the user dials back in– New, temporary IP address is assigned
11/13/2006Hung Nguyen, TCOM 552, Fall 200646
Operation of Mobile IPOperation of Mobile IP
Mobil node is assigned to a particular network – home network
IP address on home network is static – home address
Mobile node can move to another network – foreign network
Mobile node registers with network node on foreign network – foreign agent
Mobile node gives care-of address to agent on home network – home agent
11/13/2006Hung Nguyen, TCOM 552, Fall 200647
Mobile IP ScenarioMobile IP Scenario
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Three Basic Capabilities of Mobile IPThree Basic Capabilities of Mobile IP
Discovery – mobile node uses discovery procedure to identify prospective home and foreign agents
Registration – mobile node uses an authenticated registration procedure to inform home agent of its care-of address
Tunneling – used to forward IP datagrams from a home address to a care-of address
11/13/2006Hung Nguyen, TCOM 552, Fall 200649
Discovery ProcessDiscovery Process
Mobile node is responsible for ongoing discovery process– Must determine if it is attached to its home
network or a foreign network Transition from home network to foreign
network can occur at any time without notification to the network layer
Mobile node listens for agent advertisement messages issued by foreign agents– Compares network portion of the router's IP
address with the network portion of home address
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Agent SolicitationAgent Solicitation
Foreign agents are expected to issue agent advertisement messages periodically
If a mobile node needs agent information immediately, it can issue ICMP router solicitation message– Any agent receiving this message will then issue
an agent advertisement
11/13/2006Hung Nguyen, TCOM 552, Fall 200651
Move DetectionMove Detection
Mobile node may move from one network to another due to some handoff mechanism without IP level being aware– Agent discovery process is intended to enable
the agent to detect such a move Algorithms to detect move:
– Use of lifetime field – mobile node uses lifetime field as a timer for agent advertisements
– Use of network prefix – mobile node checks if any newly received agent advertisement messages are on the same network as the node's current care-of address
11/13/2006Hung Nguyen, TCOM 552, Fall 200652
Co-Located AddressesCo-Located Addresses
If mobile node moves to a network that has no foreign agents, or all foreign agents are busy, it can act as its own foreign agent
Mobile agent uses co-located care-of address– IP address obtained by mobile node associated with
mobile node's current network interface Means to acquire co-located address:
– Temporary IP address through an Internet service, such as DHCP
– May be owned by the mobile node as a long-term address for use while visiting a given foreign network
11/13/2006Hung Nguyen, TCOM 552, Fall 200653
Registration ProcessRegistration Process
Mobile node sends registration request to foreign agent requesting forwarding service
Foreign agent relays request to home agent Home agent accepts or denies request and
sends registration reply to foreign agent Foreign agent relays reply to mobile node Registration Security
– Mobile IP designed to resist attacks– For message authentication, registration request
and reply contain authentication extension for mobile-home, mobile-foreign and foreign-home
11/13/2006Hung Nguyen, TCOM 552, Fall 200654
TunnelingTunneling
Home agent intercepts IP datagrams sent to mobile node's home address– Home agent informs other nodes on home network that
datagrams to mobile node should be delivered to home agent
Datagrams forwarded to care-of address via tunneling. Encapsulated in outer IP datagram– IP-within-IP – entire IP datagram becomes payload in new
IP datagram– Minimal encapsulation – new header is inserted between
original IP header and original IP payload– Generic routing encapsulation (GRE) – developed prior to
development of Mobile IP
11/13/2006Hung Nguyen, TCOM 552, Fall 200655
Mobile IP EncapsulationMobile IP Encapsulation
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Wireless Application Protocol (WAP)Wireless Application Protocol (WAP)
Open standard providing mobile users of wireless terminals access to telephony and information services– Wireless terminals include wireless phones,
pagers and personal digital assistants (PDAs)– Designed to work with all wireless network
technologies such as GSM, CDMA, and TDMA– Based on existing Internet standards such as IP,
XML, HTML, and HTTP– Includes security facilities
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WAP InfrastructureWAP Infrastructure
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WAP Protocol StackWAP Protocol Stack
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WAP Programming ModelWAP Programming Model
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Wireless Markup Language (WML) Wireless Markup Language (WML) FeaturesFeatures
Text and image support – formatting and layout commands
Deck/card organizational metaphor – WML documents subdivided into cards, which specify one or more units of interaction
Support for navigation among cards and decks – includes provisions for event handling; used for navigation or executing scripts
11/13/2006Hung Nguyen, TCOM 552, Fall 200661
WMLScriptWMLScript
Scripting language (similar to HTML) for defining script-type programs in a user device with limited processing power and memory
WMLScript capabilities:– Check validity of user input before it’s sent– Access device facilities and peripherals– Interact with user without introducing round trips to origin
server WMLScript features:
– JavaScript-based scripting language– Procedural logic– Event-based– Compiled implementation– Integrated into WAE
11/13/2006Hung Nguyen, TCOM 552, Fall 200662
Wireless Application Environment Wireless Application Environment (WAE)(WAE)
WAE specifies an application framework for wireless devices
WAE elements:– WAE User agents – software that executes in
the wireless device– Content generators – applications that produce
standard content formats in response to requests from user agents in the mobile terminal
– Standard content encoding – defined to allow a WAE user agent to navigate Web content
– Wireless telephony applications (WTA) – collection of telephony-specific extensions for call and feature control mechanisms
11/13/2006Hung Nguyen, TCOM 552, Fall 200663
WAE Client ComponentsWAE Client Components
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Wireless Session Protocol (WSP)Wireless Session Protocol (WSP)
Transaction-oriented protocol based on the concept of a request and a reply
Provides applications with interface for two session services:– Connection-oriented session service – operates
above reliable transport protocol WTP– Connectionless session service – operates
above unreliable transport protocol WDP
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Connection-mode WSP ServicesConnection-mode WSP Services
Establish reliable session from client to server and release
Agree on common level of protocol functionality using capability negotiation
Exchange content between client and server using compact encoding
Suspend and resume a session Push content from server to client in an
unsynchronized manner
11/13/2006Hung Nguyen, TCOM 552, Fall 200666
WSP Transaction TypesWSP Transaction Types
Session establishment – client WSP user requests session with server WSP user
Session termination – client WSP user initiates termination
Session suspend and resume – initiated with suspend and resume requests
Transaction – exchange of data between a client and server
Nonconfirmed data push – used to send unsolicited information from server to client
Confirmed data push – server receives delivery confirmation from client
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Wireless Transaction Protocol (WTP)Wireless Transaction Protocol (WTP)
Lightweight protocol suitable for "thin" clients and over low-bandwidth wireless links
WTP features– Three classes of transaction service
Class 0 provides unreliable datagram service Class 1 provides reliable datagram service Class 2: provides request/response service
– Optional user-to-user reliability: WTP user triggers confirmation of each received message
– Optional out-of-band data on acknowledgments– PDU concatenation and delayed acknowledgment to
reduce the number of messages sent– Asynchronous transactions
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Examples of WTP OperationsExamples of WTP Operations
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Wireless Transport Layer Security Wireless Transport Layer Security (WTLS) Features(WTLS) Features
Data integrity – ensures that data sent between client and gateway are not modified, using message authentication
Privacy – ensures that the data cannot be read by a third party, using encryption
Authentication – establishes authentication of the two parties, using digital certificates
Denial-of-service protection – detects and rejects messages that are replayed or not successfully verified
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WTLS Protocol StackWTLS Protocol Stack
WTLS consists of two layers of protocols– WTLS Record Protocol – provides basic security services to
various higher-layer protocols– Higher-layer protocols:
The Handshake Protocol The Change Cipher Spec (encryption & hash algorithm, crypto
attributes, etc…) Protocol The Alert Protocol
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WTLS Record Protocol OperationWTLS Record Protocol Operation
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Phases of the Handshake Protocol Phases of the Handshake Protocol ExchangeExchange
First phase – used to initiate a logical connection and establish security capabilities
Second phase – used for server authentication and key exchange
Third phase – used for client authentication and key exchange
Forth phase – completes the setting up of a secure connection
11/13/2006Hung Nguyen, TCOM 552, Fall 200673
Wireless Datagram Protocol (WDP)Wireless Datagram Protocol (WDP)
Used to adapt higher-layer WAP protocol to the communication mechanism used between mobile node and WAP gateway
WDP hides details of the various bearer networks from the other layers of WAP
Adaptation may include:– Partitioning data into
segments of appropriate size for the bearer
– Interfacing with the bearer network
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Wireless Control Message Protocol Wireless Control Message Protocol (WCMP)(WCMP)
Performs the same support function for WDP as ICMP does for IP
Used in environments that don’t provide IP bearer and don’t lend themselves to the use of ICMP
Used by wireless nodes and WAP gateways to report errors encountered in processing WDP datagrams
Can also be used for informational and diagnostic purposes