Lecture 1: Introduction

illnurturedtownvilleMobile - sans fil

21 nov. 2013 (il y a 4 années et 1 mois)

83 vue(s)

Lecture 1: Introduction

Chapter 1


Introduction to Wireless
Communication Systems

2

Introduction


“It is dangerous to put limits on wireless.”
-

Guglielmo Marconi, 1932


There has been tremendous growth in wireless
in the past 10 years. Even more in Europe and
Asia than North America



Driven by technological advances



digital and
RF circuit fabrication improvements, large scale
circuit integration, miniaturization technologies,
digital switching

3


Driven by business investment



although
overinvestment has created bad profitability
recently.


Driven by consumer demand



Regardless of
current business profitability, the growth rate in
terms of numbers of customers is substantial. The
ability to communicate wirelessly is of obvious
benefit to many. What are some of the benefits?


4

I. History


Wired Communications


1834
-

Gauss and Weber build telegraph system in
Germany


1844
-

Morse connects Baltimore and Washington by
telegraph


1858
-

First transatlantic telegraph cable laid


1876
-

Alexander Bell demonstrates telephone


1911
-

New York can telephone Denver


Wireless Communications
--
Not so “new”


Had slow growth at first compared to other inventions.


But now is growing very rapidly.


5

6


1899

-

Marconi sends first radio message across Atlantic


1905
-

Hulsmeyer detects ships with radar


1927
-

US & Europe telephones linked by HF radio


1934
-

AM mobile police radios for public safety widely
used


1935
-

Edwin Armstrong demonstrates FM radio system,
became the primary modulation technique.


1940
-

First microwave radar


1965

-

First commercial communication satellite


1968
-

AT&T proposes cellular phone system to Federal
Communications Commission (FCC)


7


1983

-

FCC allocates spectrum for analog cellular service
(
AMPS
)


1990

-

GSM
digital cellular service introduced in Europe


1995
-

FCC auctions new Personal Communication Service
(PCS) licenses in U.S. for digital services


1998
-

40 million cellular phone users in U.S.


2000
-

In some countries, mobile users outnumber
conventional wireline customers.

8


2001
-

630 million subscribers worldwide (as compared
to 1 billion wired phone lines.


2001
-

Over 1% of worldwide wireless subscribers have
abandoned wired telephone service for home use.


2005 − Over 130 million cellular phone users in U.S.
(out of population of 300 million including children).

9

II. Frequencies


RF
-

Radio Frequency


1 MHz to 1 GHz
-

general classification, not absolute


100 MHz to 1 GHz
-

more widely used definition


Microwave


1 GHz to 300 GHz
-

general


1 GHz to 100 GHz
-

more widely used


Trends towards use of higher frequencies


greater signal bandwidth (BW) per channel


more users and/or higher data rates


but more difficult to design
-

more $$, more
engineering required

10

III. Wireless Applications


Mature


Home Appliances
-

What devices are used that are
wireless?



Communications


fixed microwave (point
-
to
-
point or Line Of Sight)
-

nearly 20,000 in U.S


satellite to
fixed
ground stations (TV, phone, defense,
etc.)


analog cellular : AMPS (FM) since 1980's


paging

11


Emerging


WLAN: Wireless Local Area Networks


Mobile computers/email


Wireless Local Loop (WLL)


local phone service via wireless connection


prominent in non
-
industrialized nations


cheaper to install than wired lines


new IEEE 802.16 standard has been developed for WLL.


Wireless
-
enabled Personal Digital Assistants (PDAs)


12


Wireless Device Connectivity between computer
peripherals (printers, monitors, keyboards, etc.)
-

Bluetooth


Satellite to
mobile
ground units
-

Land Mobile
Satellite (LMS)


Motorola/Iridium


Digital Cellular/PCS


PCS = Personal Communication Services


Several types of services and capabilities are
offered


13


Radio Frequency Identification Tags (RFID’s) on
merchandize in warehouses and stores.


Sensor networks


small devices wirelessly
communicating among themselves to monitor
environments using a variety of sensors.


14


FCC controls all usable Radio Spectrum
-

allocates specific frequency bands for specific
uses


Military


Public safety and public service
-

Police, fire,
utilities, medical


Commercial
-

To customers, between commercial
mobiles


Unlicensed


Amateur


Etc.

15

16


SMR Bands
-

Specialized Mobile Radio


Three 20 MHz bands from 800
-
900 MHz


Large number of
radio system
licenses nationwide


paging/messaging


voice dispatch
-

taxi, Police/Fire/Ambulance


data (UPS/Fedex)


Extended SMR


Nextel/Motorola partnership


Nationwide coverage providing digital cellular/data
service


Created by buying SMR licenses from a large
number of private radio service providers


17


ISM Bands
-

Industrial/Scientific/Medical


902
-
928 MHz, 2400
-
2484 MHz, & 5725
-
5850 MHz



“Garbage” bands


spread spectrum modulation


Transmit (Tx) power level < 1 W


Remote meter reading


Wireless medical monitors


Digital cordless telephones


Big new application: Wireless Local Area Networks
(WLAN’s)


18


Cellular Phone


AMPS:
A
dvanced
M
obile
P
hone
S
ystem


824
-
849 MHz


Reverse Channel: Transmit from mobile to fixed
base station


869
-
894 MHz


Forward Channel: Transmit from base station to
mobile


FCC mandated duopoly in Major Trading Areas (MTAs)


MTA = 51 largest U.S. cities


two providers per MTA


19


PCS Band


1.8
-
1.9 GHz


FCC Spectrum Auctions
-

$10 Billion!!


1st time spectrum sold for $$ in U.S.


It is has been hard for companies to recover this investment


A & B blocks for Major Trading Areas (MTAs)


duopoly like AMPS


C, D, E, & F blocks
-

Basic Trading Areas (BTAs)


BTA = 492 large rural areas (includes MTAs)


Digital cellular phone service + PCS


PCS = special services like messaging, caller ID, voice mail,
FAX, data, etc.


Compete with analog cellular and SMR services combined

20

V. Mobile Radiotelephony



The focus of this course: mobile wireless
communications.


Our predominant focus will be on mobile cellular
communications


Historically voice communications, but also
incorporating data into newer generation systems.

21


But we will also take a substantial look at Wireless LAN’s


Have grown quickly over the past couple of years.


Are an important replacement opportunity for traditional
wiring in buildings.


Some are trying to make them a competitor to cellular for
data communications.


Cellular can or will provide 10’s to 100’s of kilobits
per second.


But if one can connect to a Wireless LAN (either at
home/office or in public “hot spot” areas), 10’s of
Megabits per second are readily available

22


And below all of these technologies are important
radio transmission issues we need to study


Radio signal propagation


signal strengths varies with
distance from the transmitter, but may also vary by large
amounts over a few centimeters


Digital modulation


putting data on analog wireless signals.


Compensation for fading


making channels more reliable


Frequency reuse and sharing (multiple access techniques)

making best use of spectrum to support multiple users.


Sharing in the time, frequency, and code domains.


23


Early mobile phone systems used a

high power
Tx to cover a large spatial area (R = 50 km)


Half
-
duplex (HDX) operation


two
-
way communication using
same
radio channel


transmit or receive only at a given time (HDX)


“push
-
to
-
talk” system
-

CB radio

24


Allocated spectrum determines maximum # of
simultaneous
users


e.g., 10 MHz allocated BW with 100 kHz channels
= 100 simultaneous users/market


Demand was great in large cities and this led to
poor service (many blocked calls)


Spectrally inefficient system


allocated spectrum supports small # of users

25


In 1976, Bell Mobile Phone Service only had
12 channels for all of New York City (10
million people), which could acceptably only
support 543 customers.


Acceptable service
-

Certain probability of not
being able to make a call (i.e., be "blocked")


Given the # of customers, average calling load per
customer, # of channels → can compute blocking


26


Cellular Concept
-

break coverage area (market) into
many small cell

(many transmitters) where each non
-
adjacent cell will reuse different portions (not all) of
allocated spectrum


Increase spectrum efficiency


many users share same channels


Increase in required system infrastructure (base stations)


more capital costs to provide adequate coverage

27



BASE

STATION

28


Advanced Mobile Phone System (AMPS) spectrum
allocated by FCC in 1983


Full duplex (FDX) operation : simultaneous two
-
way
communication


two 30 kHz channels (forward & reverse)


Two providers for each market
-

duopoly


limited competition


Analog frequency modulation (FM) used exclusively


Frequency Division Multiple Access (FDMA)


one channel per pair of users

29


USDC: U.S. Digital Cellular proposed in 1991
(D
-
AMPS or IS
-
54)


Replace single user analog channel with digital
channels that support 3 users/30 kHz channel BW


User capacity is 3 times greater than AMPS
-

more
provider revenue ($$)


Digital modulation & speech coding allow Time
Division Multiple Access (TDMA)


3 users share one channel by using different time slots


This service is provided under the title "Digital
Cellular"

30

VI. Mobile Radio Terminology



Table 1.4, pg. 10

-

everyone is responsible for these
definitions




Mobile: high speed motion (e.g. cell phone in car)


Portable: low speed motion (cordless phone in home,
walking)


Mobile Unit = subscriber unit = user communication device


Transmitter (Tx) and Receiver (Rx)


Base Station: Tx/Rx on tower at center of cell that provides
service to group of mobile users

31


Forward/Reverse Channels (a.k.a. downlink/uplink)


Forward: From base station to mobile


Reverse: From mobile to base station


Simplex (SX), Half Duplex (HDX), & Full Duplex
(FDX)


Frequency Division Duplexing (FDD)
-

Using two
separate frequency bands to provide both sides of the
duplex operation


Example: AMPS uses 824
-
849 MHz for reverse channel
and 869
-
894MHz for forward channel


PSTN: Public Switched Telephone Network

32

33


VII. Paging Systems



One
-
way communication (SX)


Send short message to mobile unit (pager)


Wide area coverage


Page broadcast from many base stations
simultaneously
to remote units


no information as to user location


Reliable communication
everywhere
(need good
Signal to Noise performance)


Requires large Tx power and
low data rate
(~ 2
-
8 kbps)


Noise has less of an effect when the data rate is lower.


Coverage needed even inside buildings w/ 20
-
30 dB signal
attenuation


Needs an extensive network of transmitters to transmit the
signal everywhere

34

35

VIII. Cordless Telephone Systems


Primarily in
-
home use


Use ISM bands


900 MHz most popular for a while, now
2.4 GHz is common and 5.8 GHz is available.


Low power, limited range (~ 100 m) and coverage, and
limited mobility


36

IX. Cellular Telephone Systems



37


Large geographic coverage


Limited frequency spectrum


a surprisingly
low amount of spectrum has been allocated for
a service with such popularity.


High user mobility


High system capacity
-

Large # of simultaneous
users


obtained by limiting coverage of each base station
to small area (cell)


frequency spectrum can be reused by other non
-
adjacent cells in network

38


Base station


serves mobile users in each cell


bridge between mobile unit and MSC


connected to MSC via phone line (for example,
T1 of 24 channels or T3 of 672 channels) or
Line of Sight microwave link


39


MSC: Mobile Switching Center


controls base stations, call initiation & routing, handoffs, etc.


connects cellular system to Public Switched Telephone
Network (PSTN)


cellular network brains:



call initiation/setup



base station handoffs



controlling power levels in mobile units



billing information



roaming user ID and verification


Typically handles 5000 simultaneous calls supporting
100,000 cellular subscribers (at most 5% of subscribers are
assumed to be active at anyone time)

40


Common Air Interface (CAI)


Standard mechanism used by all mobiles.


Defines 4 different channels to be used by a mobile
unit


Forward/reverse voice channels
-

FVC/RVC


Full Duplex communication


Forward/reverse control channels
-

FCC/RCC


call initiation & setup


makes up 5% of total # of available channels


One cell contains 10 to 60 voice channels and only
1 to 3 control channel pairs (F+R)


MSC broadcasts call request from PSTN over all
FCC's of
all
base stations


to find the mobile user

41


There are two ways to keep mobiles “connected” to the
best base station


1. Mobile unit monitors FCC's looking for strongest base
station (closest) and incoming call


if FCC signal < acceptable level
-

mobile looks for
another base station


neighboring
base stations must use
same
frequencies for
FCC/RCC


handoff
from one base station to another occurs when
FCC signal is less than an acceptable level

42

2.

Base stations (current server + adjacent stations) monitor
RCC and report mobile unit signal strength to MSC
(analog AMPS system)


if RCC signal < acceptable level
-

MSC initiates handoff
to one of neighboring base stations


neighboring
base stations must use
different
frequencies
for FCC/RCC

43


Cellular Phone Call Timing


Mobile Identification Number (MIN) is the
subscriber's telephone number


Electronic Serial Number (ESN) is device identifier.


Station Class Mark (SCM) identifies the class of the
device, based on its maximum transmit power level.


44

45