Introduction to Mobile Communications TCOM 552, Lecture #10 Hung Nguyen, Ph.D. 13 November, 2006

Outline Cordless Systems and Wireless Local Loop (Chapter 11) GMU - TCOM 552, Fall 2006 Outline 11/13/2006 Cordless Systems and Wireless Local Loop (Chapter 11) Mobile IP and Wireless Application Protocol (Chapter 12) Hung Nguyen, TCOM 552, Fall 2006 11/13/2006 (C) Hung Nguyen, 2006

Cordless System Operating Environments 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. Hung Nguyen, TCOM 552, Fall 2006 11/13/2006

Design Considerations for Cordless Standards 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 Hung Nguyen, TCOM 552, Fall 2006 11/13/2006

Digital Enhanced Cordless Telecom & Personal Wireless Telecom Hung Nguyen, TCOM 552, Fall 2006 11/13/2006

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 Hung Nguyen, TCOM 552, Fall 2006 11/13/2006

Simplex TDD Transmission Hung Nguyen, TCOM 552, Fall 2006 11/13/2006

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 Hung Nguyen, TCOM 552, Fall 2006 11/13/2006

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 Hung Nguyen, TCOM 552, Fall 2006 11/13/2006

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 Hung Nguyen, TCOM 552, Fall 2006 11/13/2006

DECT 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 Hung Nguyen, TCOM 552, Fall 2006 11/13/2006

DECT Protocol Architecture Hung Nguyen, TCOM 552, Fall 2006 11/13/2006

Differential 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 Hung Nguyen, TCOM 552, Fall 2006 11/13/2006

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 Hung Nguyen, TCOM 552, Fall 2006 11/13/2006

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 Hung Nguyen, TCOM 552, Fall 2006 11/13/2006

ADPCM Encoder & Decoder GMU - TCOM 552, Fall 2006 ADPCM Encoder & Decoder 11/13/2006 Hung Nguyen, TCOM 552, Fall 2006 11/13/2006 (C) Hung Nguyen, 2006

Subject Measurement of Coder Performance 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 Hung Nguyen, TCOM 552, Fall 2006 11/13/2006

Wireless Local Loop (WLL)

Wireless 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 Hung Nguyen, TCOM 552, Fall 2006 11/13/2006

WLL Configuration Hung Nguyen, TCOM 552, Fall 2006 11/13/2006

Advantages of WLL over Wired Approach 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 Hung Nguyen, TCOM 552, Fall 2006 11/13/2006

Propagation 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 Hung Nguyen, TCOM 552, Fall 2006 11/13/2006

Propagation 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 Hung Nguyen, TCOM 552, Fall 2006 11/13/2006

Fresnel 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: Hung Nguyen, TCOM 552, Fall 2006 11/13/2006

Atmospheric 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 Hung Nguyen, TCOM 552, Fall 2006 11/13/2006

Effect 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 Hung Nguyen, TCOM 552, Fall 2006 11/13/2006

Effects 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 Hung Nguyen, TCOM 552, Fall 2006 11/13/2006

MMDS & LMDS

Hung Nguyen, TCOM 552, Fall 2006 11/13/2006

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 Hung Nguyen, TCOM 552, Fall 2006 11/13/2006

Advantages & 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 Hung Nguyen, TCOM 552, Fall 2006 11/13/2006

Advantages & 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 Hung Nguyen, TCOM 552, Fall 2006 11/13/2006

802.16 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) Are capable of broadband transmissions (>2 Mbps) Hung Nguyen, TCOM 552, Fall 2006 11/13/2006

802.16 Standards WiMAX (World-wide Interoperability for Microwave Access) Industry Group formed to promote 802.16 standards Hung Nguyen, TCOM 552, Fall 2006 11/13/2006

IEEE 802.16 Protocol Architecture Hung Nguyen, TCOM 552, Fall 2006 11/13/2006

Protocol 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 Hung Nguyen, TCOM 552, Fall 2006 11/13/2006

Protocol 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 Hung Nguyen, TCOM 552, Fall 2006 11/13/2006

802.16 Protocols in Context Hung Nguyen, TCOM 552, Fall 2006 11/13/2006

IEEE 802.16.1 Bearer Services Digital audio/video multicast Digital telephony ATM Internet protocol Bridged LAN Back-haul Frame relay Hung Nguyen, TCOM 552, Fall 2006 11/13/2006

IEEE 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 Hung Nguyen, TCOM 552, Fall 2006 11/13/2006

MAC 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 Hung Nguyen, TCOM 552, Fall 2006 11/13/2006

802.16 Physical Layer Upstream Transmission Continuous downstream mode 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) Hung Nguyen, TCOM 552, Fall 2006 11/13/2006

802-16 Data Rates in Mbps Hung Nguyen, TCOM 552, Fall 2006 11/13/2006

Mobile IP and Wireless Application Protocol Chapter 12

Mobile 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 Hung Nguyen, TCOM 552, Fall 2006 11/13/2006

Operation 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 Hung Nguyen, TCOM 552, Fall 2006 11/13/2006

Mobile IP Scenario Hung Nguyen, TCOM 552, Fall 2006 11/13/2006

Three 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 Hung Nguyen, TCOM 552, Fall 2006 11/13/2006

Discovery 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 Hung Nguyen, TCOM 552, Fall 2006 11/13/2006

Agent 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 Hung Nguyen, TCOM 552, Fall 2006 11/13/2006

Move 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 Hung Nguyen, TCOM 552, Fall 2006 11/13/2006

Co-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 Hung Nguyen, TCOM 552, Fall 2006 11/13/2006

Registration 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 Hung Nguyen, TCOM 552, Fall 2006 11/13/2006

Tunneling 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 Hung Nguyen, TCOM 552, Fall 2006 11/13/2006

Mobile IP Encapsulation Hung Nguyen, TCOM 552, Fall 2006 11/13/2006

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 Hung Nguyen, TCOM 552, Fall 2006 11/13/2006

WAP Infrastructure Hung Nguyen, TCOM 552, Fall 2006 11/13/2006

WAP Protocol Stack Hung Nguyen, TCOM 552, Fall 2006 11/13/2006

WAP Programming Model Hung Nguyen, TCOM 552, Fall 2006 11/13/2006

Wireless Markup Language (WML) Features 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 Hung Nguyen, TCOM 552, Fall 2006 11/13/2006

WMLScript 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 Hung Nguyen, TCOM 552, Fall 2006 11/13/2006

Wireless Application Environment (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 Hung Nguyen, TCOM 552, Fall 2006 11/13/2006

WAE Client Components Hung Nguyen, TCOM 552, Fall 2006 11/13/2006

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 Hung Nguyen, TCOM 552, Fall 2006 11/13/2006

Connection-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 Hung Nguyen, TCOM 552, Fall 2006 11/13/2006

WSP 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 Hung Nguyen, TCOM 552, Fall 2006 11/13/2006

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 Hung Nguyen, TCOM 552, Fall 2006 11/13/2006

Examples of WTP Operations Hung Nguyen, TCOM 552, Fall 2006 11/13/2006

Wireless Transport Layer Security (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 Hung Nguyen, TCOM 552, Fall 2006 11/13/2006

WTLS 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 Hung Nguyen, TCOM 552, Fall 2006 11/13/2006

WTLS Record Protocol Operation Hung Nguyen, TCOM 552, Fall 2006 11/13/2006

Phases of the Handshake Protocol Exchange 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 Hung Nguyen, TCOM 552, Fall 2006 11/13/2006

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 Hung Nguyen, TCOM 552, Fall 2006 11/13/2006

Wireless Control Message Protocol (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 Hung Nguyen, TCOM 552, Fall 2006 11/13/2006