1. Introduction

2. It all started like this First telephone (photophone) – Alexander Bell, 1880 The first car mounted radio telephone – 1921

3. Going further 1946 – First commercial mobile radio-telephone service by Bell and AT&T in Saint Louis, USA. Half duplex(PTT) 1973 – First handheld cellular phone – Motorola. First cellular net Bahrein 1978

4. Wireless Comes of Age Galileo Marconi invented the wireless telegraph in 1896 Communication by encoding alphanumeric characters in analog signal Sent telegraphic signals across the Atlantic Ocean Communications satellites launched in 1960s Advances in wireless technology Radio, television, mobile telephone, communication satellites More recently Satellite communications, wireless networking, cellular technology

5. Broadband Wireless Technology Higher data rates obtainable with broadband wireless technology Graphics, video, audio Shares same advantages of all wireless services: convenience and reduced cost Service can be deployed faster than fixed service No cost of cable plant Service is mobile, deployed almost anywhere

6. Today’s Wireless Networks Radio Controller Gateway Telephone Network Internet Radio Edge Router Internet Telephone network

7. 3G: ITU-Developed IMT-2000 Satellite Macrocell Microcell Urban In-Building Picocell Global Suburban Basic Terminal PDA Terminal Audio/Visual Terminal

8. Future of Networks

9. Limitations and Difficulties of Wireless Technologies Wireless is convenient and less expensive Limitations and political and technical difficulties inhibit wireless technologies Lack of an industry-wide standard Device limitations E.g., small LCD on a mobile telephone can only displaying a few lines of text E.g., browsers of most mobile wireless devices use wireless markup language (WML) instead of HTML

10. Part One: Background Provides preview and context for rest of book Covers basic topics Data Communications TCP/IP

11. Band nameAbbrITU band Frequency Wavelengt h Example uses 100,000 kmHzkm Extremely low frequency ELF13–30 Hz 100,000 km – 10,000 kmHz Communication with submarines Super low frequencySLF230–300 Hz 10,000 km – 1000 kmHz Communication with submarines Ultra low frequencyULF3300–3000 Hz 1000 km – 100 kmHz Communication within mines Very low frequencyVLF43–30 kHz 100 km – 10 kmkHz Submarine communication, avalanche beacons, wireless heart rate monitorsavalanche beaconsheart rate monitors Low frequencyLF530–300 kHz 10 km – 1 kmkHz NavigationNavigation, time signals, AM longwave broadcastingtime signalslongwave Medium frequencyMF6300–3000 kHz 1 km – 100 m kHzm AMAM (Medium-wave) broadcasts High frequencyHF73–30 MHz 100 m – 10 mMHz ShortwaveShortwave broadcasts and amateur radioamateur radio Very high frequencyVHF830–300 MHz 10 m – 1 mMHz FMFM and television broadcaststelevision Ultra high frequencyUHF9300–3000 MHz 1 m – 100 mm MHz mm televisiontelevision broadcasts, mobile phones, wireless LAN, ground-to- air and air-to-air communicationsmobile phoneswireless LAN

12. Super high frequency SHF 10 3–30 GHz 100 mm – 10 mm GHz microwavemicrowave devices, mobile phones (W-CDMA), WLAN, most modern RadarsW-CDMAWLAN Radars Extremely high frequency EHF1130–300 GHz 10 mm – 1 mm GHz Radio astronomyRadio astronomy, high-speed microwave radio relay microwave radio relay Above 300 GHz < 1 mm GHz Night vision

13. Advantages It would save time and money due to the fact that you would spare the expense of installing a lot of cables A wireless networking system would rid of the downtime you would normally have in a wired network due to cable problems client computer needs to relocate to another part of the office then all you need to do is move the machine with the wireless network card.

14. Characteristics of Wireless Networks High bit error rate Low bandwidth (Data Rate) Variable delay Inconsistent performance Mobility

15. Switched Network

16. Switching Terms Switching Nodes: Intermediate switching device that moves data Not concerned with content of data Stations: End devices that wish to communicate Each station is connected to a switching node Communications Network: A collection of switching nodes

17. Observations of Figure 3.3 Some nodes connect only to other nodes (e.g., 5 and 7) Some nodes connect to one or more stations Node-station links usually dedicated point-to-point links Node-node links usually multiplexed links Frequency-division multiplexing (FDM) Time-division multiplexing (TDM) Not a direct link between every node pair

18. Techniques Used in Switched Networks Circuit switching Dedicated communications path between two stations E.g., public telephone network Packet switching Message is broken into a series of packets Each node determines next leg of transmission for each packet

19. Phases of Circuit Switching Circuit establishment An end to end circuit is established through switching nodes Information Transfer Information transmitted through the network Data may be analog voice, digitized voice, or binary data Circuit disconnect Circuit is terminated Each node de-allocates dedicated resources

20. Characteristics of Circuit Switching Can be inefficient Channel capacity dedicated for duration of connection Utilization not 100% Delay prior to signal transfer for establishment Once established, network is transparent to users Information transmitted at fixed data rate with only propagation delay

21. How Packet Switching Works Data is transmitted in blocks, called packets Before sending, the message is broken into a series of packets Typical packet length is 1000 octets (bytes) Packets consists of a portion of data plus a packet header that includes control information At each node en route, packet is received, stored briefly and passed to the next node

22. Packet Switching

24. Packet Switching Advantages Line efficiency is greater Many packets over time can dynamically share the same node to node link Packet-switching networks can carry out data-rate conversion Two stations with different data rates can exchange information Unlike circuit-switching networks that block calls when traffic is heavy, packet-switching still accepts packets, but with increased delivery delay Priorities can be used

25. Disadvantages of Packet Switching Each packet switching node introduces a delay Overall packet delay can vary substantially This is referred to as jitter Caused by differing packet sizes, routes taken and varying delay in the switches Each packet requires overhead information Includes destination and sequencing information Reduces communication capacity More processing required at each node

26. Packet Switching Networks - Datagram Each packet treated independently, without reference to previous packets Each node chooses next node on packet’s path Packets don’t necessarily follow same route and may arrive out of sequence Exit node restores packets to original order Responsibility of exit node or destination to detect loss of packet and how to recover

27. Packet Switching Networks – Datagram Advantages: Call setup phase is avoided Because it’s more primitive, it’s more flexible Datagram delivery is more reliable

28. Packet Switching Networks – Virtual Circuit Preplanned route established before packets sent All packets between source and destination follow this route Routing decision not required by nodes for each packet Emulates a circuit in a circuit switching network but is not a dedicated path Packets still buffered at each node and queued for output over a line

29. Packet Switching Networks – Virtual Circuit Advantages: Packets arrive in original order Packets arrive correctly Packets transmitted more rapidly without routing decisions made at each node

30. Wireless Enhancements Application Layer Middleware and OS Transport Layer Network Layer Link Layer & Below (Scheduling, MAC) (Mobility, routing, QoS) (Wireless TCP) (Content adaptation, Consistency, File system) Wireless Web, Location Services, etc

31. Physical Layer Communications infrastructure is the air/ frequency band limited bandwidth shared, public media often regulated re-use of resources is key to providing sufficient capacity to users

32. Multiple Access Techniques Multiple access schemes are used to allow many mobile users to simultaneously share a finite amount of radio spectrum Sharing should be done in such a way that over all performance of system should not be effected

33. Duplexing In conventional telephone systems it is possible to talk and listen simultaneously Frequency division duplexing(FDD) use two frequency bands for forward and reverse traffic. Time division duplexing(TDD) uses time instead of frequency for forward and reverse traffic

34. Multiple Access Techniques Three major access techniques Frequency Division Multiple Access (FDMA) Time Division Multiple Access(TDMA) Code Division Multiple Access(CDMA)

35. Frequency Division Multiple Access FDMA assigns individual channels to individual users. Each user is allocated a unique frequency channel which can not be shared by other users For duplexing pair of channels is provided to user

36. Frequency Division Multiple Access 30 KHz Frequency FDMA — Frequency Division Multiple Access

37. Features of FDMA The FDMA channel caries only one phone circuit at a time If FDMA channel is not in use it sits idle and thus a wasted resource FDMA is usually implemented for narrow band systems like (AMPS) Due to large symbol time in Narrowband systems no equalization is required Since FDMA is a continuous transmission scheme fewer over head bits are used as header and framing bits As FDMA systems use duplexers thus expensive in implementation Tight RF Filtering to minimize adjacent channel interference

38. Time Division Multiple Access Time division multiple access system divide radio spectrum into time slots and allocate these slots to individual user. Slots are repeated in cyclic manner and N time slots make a frame Each frame is made up of preamble (address and synchronization info) and tail bit TDD use half of time slots for forward and half for reverse traffic

39. Time Division Multiple Access Frequency Time 200 KHz One timeslot = 0.577 msOne TDMA frame = 8 timeslots

41. Features of TDMA TDMA shares a single carrier frequency with many users so maximum sharing No of slots vary in frame depending upon available bandwidth, modulation techniques and other factors Low battery consumption as transmitter can be shutdown between slot intervals TDMA uses different time slots for TX and RX so no duplexer needed thus lower module cost Wastage due to guard and other control bits High synchronization over head as compared to FDMA Different number of slots can be allocated to a user depending upon data requirements

42. Code Division Multiple Access All users in CDMA use same carrier frequency and transmit simultaneously Each user has its own codeword which is orthogonal to all other users codeword The receiver uses specific user codeword to decode that user signal other code words appear as noise to receiver Near far problem occurs and power control is used to minimize it in CDMA

46. Feature of CDMA Many users of CDMA system use same frequency No limitation for number of users but as number of users increases performance degraded due to increase in noise floor Multipath fading may be substantially reduced due to large spectrum Self jamming problem occurs if two users code are not orthogonal Near far problem occurs if no power control method is used

47. Channel Partitioning (CDMA) CDMA (Code Division Multiple Access) unique “code” assigned to each user; ie, code set partitioning used mostly in wireless broadcast channels (cellular, satellite,etc) all users share same frequency, but each user has own “chipping” sequence (ie, code) to encode data encoded signal = (original data) X (chipping sequence) decoding: inner-product of encoded signal and chipping sequence allows multiple users to “coexist” and transmit simultaneously with minimal interference (if codes are “orthogonal”)

48. CDMA Encode/Decode

49. CDMA: two-sender interference

50. Packet Radio In packet radio access technique many subscribers attempt to access a single channel in an uncoordinated manner. Transmission is done by using burst of data Collision due to transmission from multiple stations is detected at base station ACK and NACK used to provide feed back about received data burst

51. Frequency Hoping

52. Signal is broadcast over seemingly random series of radio frequencies A number of channels allocated for the FH signal Width of each channel corresponds to bandwidth of input signal Signal hops from frequency to frequency at fixed intervals Transmitter operates in one channel at a time Bits are transmitted using some encoding scheme At each successive interval, a new carrier frequency is selected

53. Frequency Hoping Spread Spectrum Channel sequence dictated by spreading code Receiver, hopping between frequencies in synchronization with transmitter, picks up message Advantages Eavesdroppers hear only unintelligible blips Attempts to jam signal on one frequency succeed only at knocking out a few bits

55. Migration to 3G

56. Wireless Transmission Impairments Attenuation and attenuation distortion Free space loss Noise Atmospheric absorption Multipath

57. Attenuation Strength of signal falls off with distance over transmission medium Attenuation factors for unguided media: Received signal must have sufficient strength so that circuitry in the receiver can interpret the signal Signal must maintain a level sufficiently higher than noise to be received without error Attenuation is greater at higher frequencies, causing distortion

58. Free Space Loss Free space loss, ideal isotropic antenna P t = signal power at transmitting antenna P r = signal power at receiving antenna = carrier wavelength d = propagation distance between antennas c = speed of light (» 3 ´ 10 8 m/s) where d and are in the same units (e.g., meters)

59. Free Space Loss Free space loss equation can be recast:

60. Free Space Loss Free space loss accounting for gain of other antennas G t = gain of transmitting antenna G r = gain of receiving antenna A t = effective area of transmitting antenna A r = effective area of receiving antenna

61. Free Space Loss Free space loss accounting for gain of other antennas can be recast as

62. Physical Impairments: Noise Unwanted signals added to the message signal May be due to signals generated by natural phenomena such as lightning or man-made sources, including transmitting and receiving equipment as well as spark plugs in passing cars, wiring in thermostats, etc. Sometimes modeled in the aggregate as a random signal in which power is distributed uniformly across all frequencies (white noise) Signal-to-noise ratio (SNR) often used as a metric in the assessment of channel quality

63. Categories of Noise Thermal Noise Intermodulation noise Crosstalk Impulse Noise

64. Thermal Noise Thermal noise due to agitation of electrons Present in all electronic devices and transmission media Cannot be eliminated Function of temperature Particularly significant for satellite communication

65. Thermal Noise Amount of thermal noise to be found in a bandwidth of 1Hz in any device or conductor is: N 0 = noise power density in watts per 1 Hz of bandwidth k = Boltzmann's constant = 1.3803 ´ 10 -23 J/K T = temperature, in kelvins (absolute temperature)

66. Thermal Noise Noise is assumed to be independent of frequency Thermal noise present in a bandwidth of B Hertz (in watts): or, in decibel-watts

67. Noise Terminology Intermodulation noise – occurs if signals with different frequencies share the same medium Interference caused by a signal produced at a frequency that is the sum or difference of original frequencies Crosstalk – unwanted coupling between signal paths Impulse noise – irregular pulses or noise spikes Short duration and of relatively high amplitude Caused by external electromagnetic disturbances, or faults and flaws in the communications system

68. Other Impairments Atmospheric absorption – water vapor and oxygen contribute to attenuation Multipath – obstacles reflect signals so that multiple copies with varying delays are received Refraction – bending of radio waves as they propagate through the atmosphere

69. Signal degradation Multi-path: Signal can get severely distorted due to reflection (objects larger than wavelength), Scattering (objects smaller than wavelength) diffraction (shadow fading)

70. Multipath Propagation Reflection - occurs when signal encounters a surface that is large relative to the wavelength of the signal Diffraction - occurs at the edge of an impenetrable body that is large compared to wavelength of radio wave Scattering – occurs when incoming signal hits an object whose size in the order of the wavelength of the signal or less

71. The Effects of Multipath Propagation Multiple copies of a signal may arrive at different phases If phases add destructively, the signal level relative to noise declines, making detection more difficult Intersymbol interference (ISI) One or more delayed copies of a pulse may arrive at the same time as the primary pulse for a subsequent bit

72. Improving Wireless System Performance Wireless Communication systems require signal processing techniques that improve the link performance in hostile mobile radio environment. Mobile radio channel impairments cause the signal at receiver to distort or fade significantly.

73. Techniques used to Improve system performance Equalization: Equalization is term used in signal processing operation that minimizes ISI. Equalizer works by tracking and training.

74. Equalizer First a fixed length training sequence is sent by the transmitter so that a receiver equalizer properly analyze the Bit Error Rate, and use recursive algorithm evaluate the channel and estimate filter coefficients to compensate for distortion due to multi path in channel. Immediately after training sequence data is send When equalizer has been properly trained it said to have converged

75. Channel Coding Channel coding is used to improve link performance by adding redundant bits in the transmitted signal. At the receiver end these redundant bits are used to detect and/or correct errors introduced during transmission. Turbo codes,Convolution codes, block codes etc

76. Security Safeguards for physical security must be even greater in wireless communications Encryption: intercepted communications must not be easily interpreted Authentication: is the node who it claims to be?

77. Sine Wave Parameters General sine wave s(t ) = A sin(2  ft +  ) The effect of varying each of the three parameters (a) A = 1, f = 1 Hz,  = 0; thus T = 1s (b) Reduced peak amplitude; A=0.5 (c) Increased frequency; f = 2, thus T = ½ (d) Phase shift;  =  /4 radians (45 degrees) note: 2  radians = 360° = 1 period

78. Sine Wave Parameters

79. Basic Encoding Techniques

80. Amplitude-Shift Keying One binary digit represented by presence of carrier, at constant amplitude Other binary digit represented by absence of carrier where the carrier signal is Acos(2πf c t)

81. Binary Frequency-Shift Keying (BFSK) Two binary digits represented by two different frequencies near the carrier frequency where f 1 and f 2 are offset from carrier frequency f c by equal but opposite amounts

82. Phase-Shift Keying (PSK) Two-level PSK (BPSK) Uses two phases to represent binary digits

83. Phase-Shift Keying (PSK) Four-level PSK (QPSK) Each element represents more than one bit

84. Effect of Packet Size on Transmission

85. Breaking up packets decreases transmission time because transmission is allowed to overlap Figure 3.9a Entire message (40 octets) + header information (3 octets) sent at once Transmission time: 129 octet-times Figure 3.9b Message broken into 2 packets (20 octets) + header (3 octets) Transmission time: 92 octet-times

86. Effect of Packet Size on Transmission Figure 3.9c Message broken into 5 packets (8 octets) + header (3 octets) Transmission time: 77 octet-times. Figure 3.9d Making the packets too small, transmission time starts increases Each packet requires a fixed header; the more packets, the more headers

87. Asynchronous Transfer Mode (ATM) Also known as cell relay Operates at high data rates Resembles packet switching Involves transfer of data in discrete chunks, like packet switching Allows multiple logical connections to be multiplexed over a single physical interface Minimal error and flow control capabilities reduces overhead processing and size Fixed-size cells simplify processing at ATM nodes

88. ATM Terminology Virtual channel connection (VCC) Logical connection in ATM Basic unit of switching in ATM network Analogous to a virtual circuit in packet switching networks Exchanges variable-rate, full-duplex flow of fixed-size cells Virtual path connection (VPC) Bundle of VCCs that have the same end points

89. Advantages of Virtual Paths Simplified network architecture Increased network performance and reliability Reduced processing and short connection setup time Enhanced network services

90. Call Establishment

91. Virtual Channel Connection Uses Between end users Can carry end-to-end user data or control signaling between two users Between an end user and a network entity Used for user-to-network control signaling Between two network entities Used for network traffic management and routing functions

92. Virtual Path/Virtual Channel Characteristics Quality of service Specified by parameters such as cell loss ratio and cell delay variation Switched and semi permanent virtual channel connections Cell sequence integrity Traffic parameter negotiation and usage monitoring Virtual channel identifier restriction within a VPC

93. ATM Cell Header Format Generic flow control (GFC) – 4 bits, used only in user- network interface Used to alleviate short-term overload conditions in network Virtual path identifier (VPI) – 8 bits at the user-network interface, 12 bits at network-network interface Routing field Virtual channel identifier (VCI) – 8 bits Used for routing to and from end user

94. ATM Cell Header Format Payload type (PT) – 3 bits Indicates type of information in information field Cell loss priority (CLP) – 1 bit Provides guidance to network in the event of congestion Header error control (HEC) – 8 bit Error code

95. ATM Service Categories Real-time service Constant bit rate (CBR) Real-time variable bit rate (rt-VBR) Non-real-time service Non-real-time variable bit rate (nrt-VBR) Available bit rate (ABR) Unspecified bit rate (UBR)

96. Examples of CBR Applications Videoconferencing Interactive audio (e.g., telephony) Audio/video distribution (e.g., television, distance learning, pay-per-view) Audio/video retrieval (e.g., video-on-demand, audio library)

97. Examples of UBR applications Text/data/image transfer, messaging, distribution, retrieval Remote terminal (e.g., telecommuting)