This document provides an overview of wireless communications and mobile computing. It begins with definitions of communication, telecommunications, and the basic components and models of communication systems. It then discusses wireless transmission media like radio waves, microwaves, and infrared. The document outlines the history of wireless technologies from early systems like radio to modern cellular standards. It also describes different types of wireless services including broadcast, paging, cellular telephony, trunking radio, cordless telephony, and wireless local area networks.

1. Chapter one
Introduction to Communication Systems
and Wireless Communications

2. Outline
Part I
 Communication systems
Part II: wireless communications and mobile computing
 Introduction to wireless communications
 History wireless communications
 Types of services
 wireless vs mobile
 Strength and weaknesses
 Applications

3. Definition
Communication
 Process that allows information to pass between a
sender and receiver
 Transfer of meaningful information between two
locations
Telecommunications
 Tele means far off or distant
 Telecommunications today means communication by
electrical or electromagnetic means, usually over a
distance

4. Component of a Communication
 Source of Information (Sender)
 Meaning full Information or message
 Communication channel
 Communication Protocol
 Destination (Receiver)

5. Simplified Model of Communications

6. Main task of a Communication System
 Transmission system
utilization
 Addressing
 Interfacing
 Routing
 Signal generation
 Recovery
 Synchronization
 Message formatting
 Exchange management
 Security
 Error detection and
correction
 Network management
 Flow control

7. Communication System Requirements
 Availability
 System ready and operating when needed
 Reliability
 System trouble free and error free
 Real time or real-enough time
 Response time
 System does not hinder user by introducing too much
delay
 Ease of use
 Flexibility and scalability
 System easy to change to meet future needs

8. Data Representation
 Every data in Computer communication is
represented by a binary number.
 A binary digit or bit has only two states, “0” and “1”
 A digital data are represented by this two states.
 There are several code sets, some are used for specific
applications while others are the proprietary code sets
of computer manufacturers
 The Following two code sets are very common
1. ANSI’s 7 bit American Standard Code for Information
Interchange (ASCII)
2. IBM’s 8 bit Extended Binary Coded Decimal Interchange Code
(EBCDIC)

9. Digital Transmission Format
 Data transmission refers to movement of the bits over some
physical medium connecting two or more digital devices.
 There are two options of transmitting the bits.
1. Parallel Transmission: all the bits are transmitted
simultaneously on separate wires. Multiple circuits
interconnecting the two devices are required.
2. Serial Transmission: In serial transmission bits are
transmitted serially one after the other.

10. Modes of Data Transmission
 There are two methods of timing control for reception
of bits.
 The transmission modes corresponding to these two
timing methods are:
 Asynchronous Transmission: in this transmission signal timing is not required;
signals are sent in an agreed pattern of bits and if both ends are agreed on the pattern then
communication can take place.
 Bits are grouped together and consist of both data and control bits. If the
signal is not synchronized the receiver will not be able to distinguish when the
next group of bits will arrive.
 To overcome this the data is preceded by a start bit, usually binary 0, the byte
is then sent and a stop bit or bits are added to the end. Each byte to be sent
now incorporates extra control data. In addition to the control data small gaps
are inserted between each chunk to distinguish each group

11.  In asynchronous transmission each bit remains timed in the usual way.
Therefore, at bit level the transmission is still synchronous (timed).
However, the asynchronous transmission is applied at byte level, once the
receiver realizes that there is a chunk of incoming data timing
(synchronization) takes place for the chunk of data.
 Asynchronous transmission is relatively slow due to:
 the increased number of bits and gaps.
 It is a cheap and effective form of serial transmission and it is particularly
suited for low speed connections such as keyboard and mouse.
 One example of asynchronous transfer is Asynchronous Transfer Mode
(ATM) switching. ATM allows voice, data and video to be transmitted in
fixed length cells of 53 bytes.

12.  Synchronous Transmission: sends data as one long bit stream or block
of data. There are no gaps in transmission; each bit is sent one after the
other. The receiver counts the bits and reconstructs bytes. It is essential
that timing is maintained as there are no start and stop bits and no gaps.
Accuracy is dependent on the receiver keeping an accurate count of the
bits as they come in.
 Synchronous transmission is faster than asynchronous because fewer bits
have to be transmitted; ie: only data bits and no extra control bits. For this
reason it is the choice for network communications links.

13. Modes of Data Communication
1. Simplex
 Data in a simplex mode is always one way. Simplex channels
are not often used because it is not possible to send back error
or control signals to the transmit end. An example of simplex
is Television, or Radio.
2. Half Duplex
• A half-duplex channel can send and receive, but not at the
same time. Only one end transmits at a time, the other end
receives. In addition, it is possible to perform error detection
and request the sender to retransmit information that arrived
corrupted.
3. Full Duplex
 Data can travel in both directions simultaneously. There is no
need to switch from transmit to receive mode like in half
duplex.

14. Communication Channels
 A channel is a path between two communication devices
 Channel capacity: How much data can be passed
through the channel (bit/sec)
 Also called channel bandwidth
 The smaller the pipe the slower data transfer!
 Consists of one or more transmission media
 Materials carrying the signal
 Two types:
 Physical: wire cable
 Wireless: Air
destination
network server
T1 lines
T1 lines
T1 lines
T3 lines

15. Physical Transmission Media
 A tangible media
 Examples: Twisted-pair cable, coaxial cable, Fiber-optics, etc.
 Twisted-pair cable:
 One or more twisted wires bundled together (why?)
 Made of copper
 Coax-Cable:
 Consists of single copper wire surrounded by three
layers of insulating and metal materials
 Typically used for cable TV
 Fiber-optics:
 Strands of glass or plastic used to transmit light
 Very high capacity, low noise, small size, less suitable to
natural disturbances

16. Wireless Translation Media
 Broadcast Radio
 Distribute signals through the air over long distance
 Uses an antenna
 Typically for stationary locations
 Can be short range
 Cellular Radio
 A form of broadcast radio used for mobile communication
 High frequency radio waves to transmit voice or data
 Utilizes frequency-reuse
 Microwaves
 Radio waves providing high speed transmission
 They are point-to-point (can’t be obstructed)
 Used for satellite communication
 Infrared (IR)
 Wireless transmission media that sends signals using infrared
light- waves

17. Part II
 wireless communication and mobile
computing

18. Introduction
 Mobile computing systems are computing
systems that may be easily moved physically
and whose computing capabilities may be
used while they are being moved.
 Examples are laptops, personal digital
assistants (PDAs), and mobile phones

19. Introduction…
 Wireless communication involves the
process of sending/reciving information
through invisible waves in the air.
Information such as text, voice, and video
are carried through the radio frequency of
the electromagnetic spectrum.

20. Introduction…
 Wireless communications is one of the
biggest engineering success
 market size dominating the whole economy
 e.g + 4 billion GSM subscribers of the world
 Working habits, have been changed
“anywhere, anytime.”
 mobility of workers have increased

21. Introduction …
 large number of applications have been
developed,
 Wireless sensor networks monitor factories,
 wireless links replace the cables between computers
and keyboards, mouse and other peripheral devices
 wireless positioning systems monitor the location of
trucks
 This variety of new applications causes the
technical challenges for the wireless engineers
to become bigger with each day.

22. History : How it all started
 Ancient Systems – shouts and jungle drums ,smoke
signals, light ,Carrier Pigeons,…….
 Marconi invented the wireless telegraph in 1896.
 By encoding alphanumeric characters in analog signals,
he sent telegraphic signals across the Atlantic Ocean.
 This led to a great many developments in wireless
communication networks that support radio, television,
mobile telephone, and satellite systems that have changed
our lives.

23. History : The First Systems
 Unidirectional information transmission
 was done for entertainment broadcasting. By the
late 1930s,
 the need for bidirectional mobile
communications emerged.
 Military ,police departments ,fire station….
 Many sophisticated military radio systems
were developed during and after WW2

24. History :The First Systems…
 1946, the first mobile telephone system
 have an interface to the Public Switched
Telephone Network (PSTN),
 this interface was not automated, but rather
consisted of human telephone operators.
 Has a total of six speech channels for the whole
city, the system soon met its limits.
 Led to investigations of how the number
of users could be increased.

25. History :The First Systems…
 Researchers at AT&T’s Bell Labs found the
answer:
 the cellular principle, where the geographical
area is divided into cells; different cells might use
the same frequencies.
 To this day, this principle forms the basis for
the majority of wireless communications
 In 1957, the Soviet Union launched the first
satellite (Sputnik) and the U.S.A. soon followed.

26. Cellular Systems
BASE
STATION

27. History: Analog Cellular Systems
 1970s saw a revived interest in cellular communications
 Device miniaturization made the vision of “portable”
devices more realistic.
 Motorola, AT&T, Ericson
 Nordic Mobile Telephone (NMT) system
 use digital switching technology that allowed them to
combine different cells in a large area into a single network
 Advanced Mobile Phone System (AMPS).
 analog phone standards in the U.S.A

28.  1980s, the phones were “portable,” but definitely not
handheld.
 In most languages, they were just called “carphones,”.
 But at the end of the 1980s, handheld phones with
good speech quality and quite acceptable battery
lifetime flourish.
 The quality had become so good that in some markets
digital phones had difficulty establishing themselves.

29. History: GSM and the Worldwide Cellular
Revolution
 Analog phones have a bad spectral efficiency and
due to the rapid growth of the cellular market,
operators had a high interest in making room for more
customers
 In 1990s, the European Telecommunications
Standards Institute (ETSI) group came up with a
digital cellular standard that would become
mandatory throughout Europe and was later adopted
in most parts of the world:
 Global System for Mobile communications (GSM).

30. History: GSM and the Worldwide Cellular
Revolution
 GSM got wide acceptance with short
period
 better speech quality, and the possibility for
secure communications.
 By the year 2000, market penetration in
Western Europe and Japan had exceeded 50%
growth rates were spectacular

31. Overview of
Cellular communication Systems
 1G: Basic mobile telephony service
 Based on analog cellular technology
 American Mobile Phone (AMPS) and NMT in Europe
 2G: mobile telephony services for mass users with
encryption and efficient utilization of the radio spectrum
 Digital cellular technology……… GSM and CDMA
 2.5G: Mobile Internet/data services together with voice
services
 Packet switching technology adding into 2G
 Providing mobile data services over 2G networks
 GPRS (General Packet Radio Service) and EDGE
 3G: enhanced 2.5G services with improved mobile
internet services and emerging new applications
 CDMA2000 and UMTS (Universal Mobile Telecommunication System)

32. History :New wireless systems
 a whole range of new services was introduced in the 1990s.
 Cordless started to replace the “normal” telephones
 The first versions of these phones used analog
technology; however, digital technology proved to be
superior. Among other aspects, the possibility of
listening into analog conversations, and the possibility
for neighbors to “highjack” an analog cordless Base
Station (BS) and make calls at other people’s expense,
led to a shift to digital communications.
 While cordless phones never achieved the spectacular
market size of cell phones, they constitute a solid
market.

33. History :New wireless systems
 Fixed wireless access and Wireless Local
Loop (WLL) –
 Wireless local loop (WLL) service refers to the distribution of telephone
service from the nearest telephone central office to individual
customers via a wireless link. In some cases, it is referred to as “the last
mile” in a telephone network. This term is a bit misleading, though,
because the coverage area of a WLL system may extend many miles
from the central office. This is especially popular in developing
countries.
• Fiber optic cable
• Radio transmitter

34. Types of Services
 Broadcast
 The first wireless service was broadcast radio.
 Properties
 information is only sent in one direction
 transmitted information is the same for all users.
 information is transmitted continuously.
 Simple
 Transmitter does not need to have any knowledge or
consideration about the receivers
 Simplex
 No. of users does not matter

35.  Paging
 unidirectional wireless communications systems.
 Properties
 user can only receive information, but cannot transmit.
 The information is intended for, and received by, only a
single user.
 The amount of transmitted information is very small.
 used by..doctors , police allowing them to react to
emergencies in shorter time.
 better area coverage

36.  Cellular Telephony
 most important form of wireless
communications.
 Properties
 information flow is bidirectional.(full duplex)
 E.g. cellphone

38.  Trunking radio
 trunking is a method for a system to provide network access to many clients by
sharing a set of lines or frequencies instead of providing them individually.
 there is no connection between the wireless system and the PSTN;
 it allows the communications of closed user groups.
 Obvious applications include police departments, fire departments, taxis, and similar
 Services
 Group calls: several users simultaneously, or several conference call between multiple
users of the system.
 Call priorities: enable the prioritization of calls and allow dropping a low-priority call
in favor of a high-priority one.
 Relay networks: the range of the network can be extended by using each Mobile
Station (MS) as a relay station for other MSs .

39.  Cordless telephony
 describes a wireless link between a handset and a BS that is directly connected
to the public telephone system.
 main difference from a cellphone
 is associated with, and can communicate with, only a single BS
 thus no mobile switching center; rather, the BS is directly connected to the
PSTN.
 Properties
 no need to find out the location of the MS. Similarly, there is no need to provide
for handover between different BSs.
 There is no central system, there is no need for (and no possibility for)
frequency planning.
 there are no network operators that can charge fees for connections from the MS
to the BS; rather, the only occurring fees are the fees from the BS into the PSTN.

40.  Wireless Local Area Networks (WLANs)
 very similar to that of cordless phones
 connecting a single mobile user device to a public
landline system. Laptop -to-Internet.
 main advantage is convenience for the user, allowing
mobility.
 WLANs can even be used for connecting fixed-
location computers (desktops)
 A major difference between wireless LANs and
cordless phones is the required data rate

41.  Cordless 64kbps more than 700kbps for WLAN
 a number of standards have been developed for WLAN, all of which
carry the identifier IEEE 802.11.
 The original IEEE 802.11 standard 1Mbit/s,
 the very popular 802.11b standard (also known under the name
WiFi) allows up to 11Mbit/s and the 802.11a standard extends that
to 55Mbit/s.
 Even higher rates are realized by the 802.11n standard that was
introduced in 2008/2009.
 WLAN devices can, in principle, connect to any BS (access point)
that uses the same standard.

42.  Personal area network(PAN)
 coverage area even smaller than that of WLANs,
 number of standards for PANs have been developed by
the IEEE 802.15 group
 intended for simple “cable replacement” duties.
 For example, Bluetooth standard allow to connect a
hands-free headset to a phone without requiring a cable;
in that case, the distance between the two devices is less
than a meter.
 In such applications, data rates are fairly low (<1Mbit/s).

43. PAN…
 Recently, wireless communications between (DVD
player to TV), between computer and peripheral devices
(printer, mouse), and similar applications have gained
importance . data rates in excess of 100Mbit/s are used.
 Networks for even smaller distances like Body Area
Networks (BANs), which enable communications
between devices located on various parts of a user’s
body. monitoring of patients’ health and of medical
devices(e.g., pacemakers).

44. Services…
 Fixed Wireless Access
 essentially replacing a dedicated cable connection
between the user and the public landline system.
 no mobility of the user devices
 the distances bridged by fixed wireless access devices
are much larger (between 100m and several tens of
kilometers).
 its main market for covering rural areas, and for
establishing connections in developing countries that do
not have any wired infrastructure in place.

45. Services..
 Ad hoc Networks and Sensor Networks
 we have dealt with “infrastructure-based” wireless communications,
 where certain components (base stations, TV transmitters, etc.) are
intended by design to be in a fixed location, to control over the network
and interface with other networks.
 an alternative in which there is only one type of equipment, and
those devices, all of which may be mobile, organize themselves into
a network according to their location and according to necessity.
Such networks are called ad hoc networks
 There can still be “controllers” in an ad hoc network, but the choice
of which device acts as master and which as slave is done
opportunistically whenever a network is formed.

46.  The advantages of ad hoc networks
 low costs (because no infrastructure is required), high flexibility.
 The drawbacks
 reduced efficiency, smaller communication range, and restrictions on
the number of devices that can be included in a network.
 Ad hoc networks play a major role in the recent abundance of
sensor networks, which allow communications between machines
for the purpose of building control (controlling air conditioning,
lighting, etc., based on sensor data), factory automation,
surveillance, etc.

47. Satellite Systems
 Cover very large areas
 Distance several hundred kilometers
 the transmit powers need to be larger,
 high-gain antennas need to be used
 communications from within buildings is almost impossible
 costs of setting up a satellite – are much higher
 Global Positioning System (GPS) use growing
 Satellite signals used to pinpoint location
 Popular in cell phones, PDAs, and navigation devices

48. Is wireless mobile?
or
Is mobile wireless?

49.  A communication device can exhibit any one of the following
characteristics:
 Fixed and wired
 Example the typical desktop computer in an office. Neither
weight nor power consumption of the devices allow for mobile
usage. The devices use fixed networks for performance reasons.
 Mobile and wired:
 Many of yesterday’s laptops fall into this category; users carry
the laptop from one hotel to the next, reconnecting to the
company’s network via the telephone network and a modem.

50.  Fixed and wireless:
 This mode is used for installing networks, e.g., in
historical buildings to avoid damage by installing wires, or
at trade shows to ensure fast network setup.
 Mobile and wireless:
 This is the most interesting case. No cable restricts the
user, who can roam between different wireless networks.
Most technologies discussed in this course deal with this
type of device and the networks supporting them.
 Today’s most successful example for this category is GSM
with more than 4 Billion users.

51.  Today
Revise different types of services
Requirements for the services
Economic and social aspects
Applications

52. Service ?
 What are the different
types of wireless
services that we have
seen in this class?
 Broadcast
 Paging
 Cellular Telephony
 Trunking Radio
 Cordless Telephony
 Wireless LAN,PAN,BAN
 Fixed wireless access
 Ad hoc and sensor Nets
 Satellite services

53. Revise different types of services
Requirements for the services
Economic and social aspects
Applications

54. Requirements..
 Different applications
have different
requirements
 Data rate
 Range & no of users
 Mobility
 Energy consumption
 Use of spectrum
 Direction of transmissions
 Service Quality

55. Requirements…
 Data rate : fewer bits/sec upto gigabits/sec
 Sensor networks: ~ 1kbits/s
 Temperature, speed ….
 Speech communications: 5- 64kbits/s
 Cordless, Cellular telephony
 Elementary data service : 10-100kbits/s
 2G2.5G cellular data service.
 Communication between computer peripherals
 1Mbits/sec, mouse, key board…..
 High speed data: 0.5-100Mbits/s
 WLAN , 3G cellular
 PAN : 100Mbits/s
 Entertainment systems TV, DVD,Game, PC

56. Requirements…
 Range & no of users
 BAN ~1M
 PAN ~10M
 WLAN : few hundred Meter
 Cellular : 10-50Km
 Fixed wirless:5-10km
 Satellite systems: 1000km- 36,000km

57. Data rate Vs Range

58. Requirements…
 Mobility
 Fixed devices
 Nomadic: Certain place for certain time(min/hrs)
 Laptops
 Low mobility: Pedestrian speed
 Cordless telephone
 High Mobility :30-150km/h
 Vehicle
 Extreme high mobility:300-1000km/hr
 High speed trains, planes

59. Data rate Vs Mobility

60. Requirements…
 Energy consumptions: critical aspect
 Rechargeable batteries
 Nomadic & mobile devices
 Standby time and operating time are critical
 Cellphone: Min 48hr standby 2hr talk time .
 One way batteries
 Sensors
 Power mains
 Base stations(BSs) and fixed devices.
 Weight of MS is determined (70-80%) by its
battery. Weight & size are critical for sales.

61. Requirements...
 Use of spectrum
 Spectrum dedicated to service/operator
 Frequency controlled by operator
 Free spectrums
 Used by different service & diff operators
 ISM band 2.4GHz: Micro oven , wifi, Bluetooth,…
 Interference is managed by users

62. Requirements…
 Direction of transmission
 Simplex
 Half-duplex
 Full duplex
 Asymmetric duplex
 Data rate depends on the direction
 Satellite uplink & downlink

63. Requirements…
 Service Quality
 Speech quality
 Mean opinion score (MOS)
 Subjective to human judgments
 Data transmission speed : bit/s
 Service quality
 Fraction of blocked calls + 10 * fraction of
dropped calls (cellular)
 Admissible delay(latency)
 Voice less than 100ms
 Security & safety (sensors ) – latency is vital

64. Revise different types of services
Requirements for the services
Economic and social aspects
Applications

65. Economic and social aspects
 Strength
 Social & cultural factor
 Mobile life style (Anytime Anywhere)
 Increase of social communication
 Increase revenue & productivity
 Ease of setup
 Less expensive
 Development in mobile devices(dynamic)

66.  Weakness and issues
 Social issue
 Privacy
 Security (easy to tap)
 Health issues (Brain cancer)
 Noise pollution ,(irritation in classroom)
 Accident (use of cellphone while driving)

67.  Weakness…
 Technology issues
 Lack of standards
 High cost of technology
 Quality of service
 Device limitation
 Low data rates

68. Revise different types of services
Requirements for the services
Economic and social aspects
Applications

69.  List some wireless system applications in
different areas of our life?

70. 70
At Home
WiFi
WiFi
WiFi
cellular
bluetooth
UWB
satellite WiFi 802.11g/n

71. 71
On the Move
Source: http://www.ece.uah.edu/~jovanov/whrms/

72. 72
On the Move: Context-Aware
Source: http://www.cs.cmu.edu/~aura/docdir/sensay_iswc.pdf

73. 73
GSM/UMTS,
cdmaOne/cdma2000,
WLAN, GPS
DAB, TETRA, ...
road condition,
weather,
location-based services,
emergency
On the Road
road condition,
weather,
location-based services,
emergency

74. Applications
 Vehicles
 Emergencies
 Business
 Agriculture
 Replacement of wired networks
 Infotainment and more
 Location dependent services

75.  Vehicles
 Navigation , tracking(GPS)
 Music, news, weather report (DAB)
 Collision avoidance(wireless sensors)
 Accident reporting , Traffic reporting (Ad-
hoc)

76. 76
Collision Avoidance : V2V Networks
 stalled vehicle
warning
 bland spots

77.  Emergencies
 Wireless networks are the only means of
communication in the case of natural
disasters such as hurricanes or earthquakes.
(wireless ad-hoc networks)
 Accident reporting (wireless sensors)
 Ambulance high-quality wireless connection

78.  Business
 Traveling salesman/employee
 having instant access to the company’s
database: to ensure that files on his or her
laptop reflect the current situation,
 Business anytime anywhere mobile office,

79.  Agriculture and Natural Resources
 Animal tracking and identification.
 Monitoring water or flood levels.
 Monitor crop health, rainfall, temperature and
other meterological data.
 Track shipments of perishable crops and crop
inputs

80.  Replacement of wired networks
 remote sensors for weather forecasts,
earthquake detection, or to provide
environmental information
 for tradeshows, or in historic buildings.

81.  Infotainment
 provide up-to-date information at any
appropriate location.
 Internet everywhere? Not without wireless
networks!
 entertainment and games to enable, e.g., ad-
hoc gaming networks as soon as people meet
to play together.

82.  Location dependent services
 Follow-on services: Wherever you are, service
and information will follow you
 Location aware services:

83. Future Wireless Networks
Ubiquitous Communication Among People and Devices
Next-generation Cellular
Wireless Internet Access
Wireless Multimedia
Sensor Networks
Smart Homes/Spaces
Automated Highways
In-Body Networks
All this and more …

84. Home work
 Read the article:
“The computer for the 21st century”
by Mark weiser

85. Reading Assignment two
 Common Wireless Technologies
 Wireless ATM (WATM)
 Wi-Fi (Wireless Fidelity)
 Mobile Ad-hoc Networks (MANET)
 Microwave links
 MMDS (Multichannel Multipoint Distribution Service)
 LMDS (Local Multipoint Distribution Service)
 The reading work includes the following:
 Defining and its purpose
 The architecture
 Components
 How it works

86.  Mobile computing

87. 87
Example: IntelliDrive (Vehicle
Infrastructure Integration)
 Traffic crashes resulted in
more than 41,000 lives lost in
2007
 Establishing vehicle-to-vehicle
(V2V), vehicle-to-infrastructure
(V2I) and vehicle-to-hand-
held-devices (V2D)
communications
 safety: e.g., intersection collision
avoidance/violation warning/turn
conflict warning, curve warning
 mobility: e.g., crash data,
weather/road surface data,
construction zones, emergency
vehicle signal pre-emption
More info: http://www.its.dot.gov/intellidrive/index.htm

88. 88
Collision Avoidance at Intersections
 Two million
accidents at
intersections
per year in US
Source: http://www.fhwa.dot.gov/tfhrc/safety/pubs/its/ruralitsandrd/tb-intercollision.pdf

89. 89
Disaster Recovery/Military
 9/11, Tsunami, Hurricane Katrina,
South Asian earthquake …
 Wireless communication and
mobile computing capability
can make a difference
between life and death !
 rapid deployment
 efficient resource and energy usage
 flexible: unicast, broadcast, multicast, anycast
 resilient: survive in unfavorable and untrusted
http://www.att.com/ndr/

90. 90
Habitat Monitoring: Example on
Great Duck Island
Patch
Network
Transit Network
Basestation
Gateway
A 15-minute human visit leads to 20%
offspring mortality