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

2. 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

3. 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

4. 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

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

6. 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

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

8. 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

9. 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

10. 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

11. 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

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

13. 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

14. 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

15. 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

16. 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

17. 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

18. Wireless Local Loop (WLL)

19. 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

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

21. 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

22. 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

23. 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

24. 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

25. 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

26. 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

27. 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

28. MMDS & LMDS

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

30. 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

31. 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

32. 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

33. 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

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

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

36. 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

37. Protocol Architecture
Convergence layer functions:
Encapsulate PDU (protocol data unit) framing of upper layers into native MAC/PHY frames
Map upper layer’s addresses into addresses
Translate upper layer QoS parameters into native MAC format
Adapt time dependencies of upper layer traffic into equivalent MAC service
Hung Nguyen, TCOM 552, Fall 2006
11/13/2006

38. 802.16 Protocols in Context Hung Nguyen, TCOM 552, Fall 2006
11/13/2006

39. 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

40. 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

41. 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

42. 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

43. Data Rates in Mbps
Hung Nguyen, TCOM 552, Fall 2006
11/13/2006

44. Mobile IP and Wireless Application Protocol
Chapter 12

45. 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

46. 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

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

48. 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

49. 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

50. 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

51. 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

52. 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

53. 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

54. 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

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

56. 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

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

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

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

60. 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

61. 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

62. 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

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

64. 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

65. 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

66. 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

67. 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

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

69. 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

70. 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

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

72. 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

73. 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

74. 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