RF intro telecoms

1. 1
GSM900
DCS1800
Introduction to Telecommunication Systems

2. 2
•Describe the major components of the network and
their interrelationships.
•Describe how your voice is converted to electrical
signals and transmitted over the network.
Objectives
Network Overview

3. 3
• A system of interconnected elements
• A system of various departments to
support these elements
• Traffic is the flow of information or
messages throughout the network
Definition of a network:

4. 4
• A system of interconnected elements
linked by facilities (i.e., physical
connections) over which traffic will
flow.
• The traffic may be conversations,
information, or complex video or audio
services. The telecommunications
network must also be able to control
the interconnected elements
What is a telecommunications network?

5. 5
• Physical components required for
telecommunication network
– Transmission Facilities
– Local Loop
– IOF - Interoffice facilities
– Switching Systems
– Customer Premise Equipment (CPE)
Network Components and Architecture

6. 6
•In its simplest form, a transmission facility is a
communication between two end points. This
communication path can also be referred to as:
•Channel
•Circuit
•Trunk
•For telephony purposes, the communication path (also
known as network facilities) can be classified into two
broad categories:
•Local Loop
•Interoffice Facilities (IOF)/Trunk
Transmission Facilities

7. 7
• The local loop:
– is a circuit that connects a
customer to the telephone
network.
– provides the customer with
access to the switching system.
• The term "loop" is derived from the
pair of wires that forms the electrical
path between the customer and the
central office.
• The local loop is also referred to as
the subscriber loop.
• A simple local loop architecture is
depicted in Figure
Transmission Facilities………..

8. 8
•The primary functions of switching systems
are to provide:
•Call setup and routing
•Call supervision
•Customer I.D. and phone numbers
•These are accomplished by interconnecting
facilities
Switching systems located at the central
office (CO) that are used to provide dial tone
and ringing are referred to as end offices or
local switches. These switches can also be
interconnected with other switches.
•Another type of switch, tandem, is used as a
hub to connect switches and provide routing.
(No dial tone is provided to the customer.)
Switching Systems

9. 9
•Three components of any transmission
system are the
•The transmitter
•The receiver
•The communication path
•In its simplest form, the CPE or customer
premises equipment, is the transmitter and
receiver. The media (twisted pair copper,
coaxial cable, optical fiber, radio waves) that
connects the CPE is the path.
Components for Transmission

10. 10
•Many customers' telephones are connected
to the central office by a pair of wires within a
cable
•Why two wires?
•Because your telephone is an electro-
mechanical instrument, it requires a
battery source and a ground source.
•The battery source is supplied from the
central office equipment to your telephone
set by a wire called the ring lead. The ground
source is transmitted from the central office
by a wire called the tip lead. Together, the tip
and ring of the telephone set are commonly
referred to as a cable pair.
Telephone Connection to the Central Office

11. 11
Analog and Digital Transmission

12. 12
•Describe a carrier system.
•Describe the major differences between analog and digital
signals.
•Describe the analog to digital and digital to analog conversion
process.
•Compare and contrast Frequency Division Multiplexing and Time
Division Multiplexing.
Objectives
Analog and Digital Transmission

13. 13
•The telecommunications network can transmit a variety of
information, in two basic forms, analog and digital. In this lesson we
will examine both. This information may be transmitted over a
circuit/channel or over a carrier system.
•Where: A circuit/channel is a transmission path for a single type of
transmission service (voice or data) and is generally referred to as the
smallest subdivision of the network. A carrier, on the other hand, is a
transmission path in which one or more channels of information are
processed, converted to a suitable format and transported to the
proper destination.
The two types of carrier systems we will be discussing in this lesson
are:
1. FDM (Frequency Division Multiplexing) -- analog
2. TDM (Time Division Multiplexing) - digital
Introduction

14. 14
• Multiplexing is the process of transmitting two or more individual
signals over a common path. In effect, it increases the amount of
information transmitted, while decreasing the requirement for the
physical media (no longer a 1:1 ratio).
• Frequency Division Multiplexing
• The first type of multiplexing was an analog multiplexing
technique. Frequency Division Multiplexing (FDM). In FDM, the
bandwidth of the transmission path serves as the frame of
reference for all of the information being transmitted. The total
bandwidth is divided into subchannels consisting of smaller
segments of the available bandwidth Each subchannel is capable
of carrying a separate signal. Signals are transmitted
simultaneously. Thus, with FDM each channel is:
• Assigned a different frequency
• Separated into channels 4000 Hz. wide.
• The different channels are then stacked and transported over a
common path. In other words, each channel occupies a portion of
the total frequency bandwidth.
Multiplexing

15. 15
• Digital Transmission, demanded by our customers, has continually
increased since its introduction in 1962. This is due, in large part, to the
fact that more of our customers require a high degree of accuracy in the
information they are transmitting over our network. And with a digital
transmission (as opposed to analog) system we are able to manage the
quality of the signal by managing the previously discussed transmission
impairments. Thus, digital systems: 1). are a better switching interface 2.)
are easier to multiplex 3.)produce clearer signals
• Digital Signals A digital signal is a discrete signal. It is depicted as
discontinuous -- Discretely variable (on/off) as opposed to an analog signal
which is continuously variable (sine wave) A digital signal has the following
characteristics:
1.) Holds a fixed value for a specific length of time
2.) Has sharp, abrupt changes
3.) A preset number of values allowed
Why Digital Transmission?

16. 16
• Pulse Code Modulation (PCM) converts analog signals to a digital format (signal). This process
has four steps
The Pulse Code Modulation (PCM) Process

17. 17
•Frequencies below 300 Hz and above 3400
Hz (Voice Frequency range) are filtered from
the analog signal
•The lower frequencies are filtered out to
remove electrical noise induced from the
power lines.
•The upper frequencies are filtered out
because they require additional bits and add
to the cost of a digital transmission system.
•The actual bandwidth of the filtered signal is
3100 Hz (3400 - 300). It is often referred to
as 4 kHz.
Step One: Filtering

18. 18
•The analog signal is sampled 8000 times
per second. The rate at which the analog
signal is sampled is related to the highest
frequency present in the signal. This is
based on the Nyquist sampling theorem. In
his calculations, Nyquist used a voice
frequency range of 4000 Hz (which
represents the voice frequency range that
contains "intelligent" speech). Thus, the
standard became a sampling rate of 8000
Hz, or twice the bandwidth. The signal that is
the result of the sampling process contains
sufficient information to accurately represent
the information contained in the original
signal. The output of this sampling procedure
is a Pulse Amplitude Modulated, or PAM,
signal.
Step Two: Sampling

19. 19
•In the third step of the A/D conversion
process, we quantize the amplitude of the
incoming samples to one of 255 amplitudes
on a quantizing scale
•Thus, in this step the sampled signal is
matched to a segmented scale. The purpose
of step three is to measure the amplitude (or
height) of the PAM signal and assign a
decimal value that defines the amplitude.
Based on the quantizing scale, each
sampled signal is assigned a number
between 0 and +127 to define its amplitude.
Step Three and Four: Quantizing and Encoding
•In the fourth step of the A/D conversion process, the quantized samples are
encoded into a digital bit stream (series of electrical pulses).

20. 20
• Time division multiplexing (TDM) is a digital multiplexing
technique. In TDM, a number of low rate channels are fed into a
multiplexer (e.g., D Bank), which combines them into one high rate
digital signal. Each of the 24 VF(voice frequency)/DS0 channels is
assigned a specific time slot by the TDM(Time Division
Multiplexer). Thus, TDM is a process by which several digital
signals are combined onto a single path and sent sequentially.
Relating this back to the PAM process: The analog signal is
sampled 8000 times a second. There will be 8,000 eight-bit words
transmitted per second. These words will be 1/8000 second (or
125 microseconds) apart.
Time division multiplexing (TDM)

21. 21
•The digital hierarchy represents the
standard rates by which digital
communications are sent in North America.
•The basic building block of the digital
hierarchy is the DS0 rate at 64 Kbps.
Remember that multiplying 8-bit words by
the sampling rate of 8000 times/second
produces the 64,000 bps rate. With Time
Division Multiplexing, multiplexing by an
additional 24 time slots and including 8000
framing bits for timing information produces
the 1,544,000 bps or 1.544 Mbs. DS1 is
considered the beginning of high capacity
digital transmission rates.
Digital Hierarchy

22. 22
Introduction to Switching

23. 23
Identify the major functions of switching.
State the meaning of electronic switching systems (ESS) and
stored program control (SPC) switching systems.
Describe how this family of switches differs from earlier switches.
Describe the major components of a digital switch and the main
functions of those components.
Identify and describe the basic traffic measurements.
Objectives
Fundamentals of Switching

24. 24
The purpose of a switch is to provide a path for the call. To process a
call the switch performs three main functions:
1) Identifies the customer
2) Sets up the communication path
3) Supervises the call
Functions of a Switch

25. 25
Initially customers were identified by the jack
position they occupied on the switchboard. With
the introduction of electromechanical switches,
customers were as signed telephone numbers.
(Also called line or station numbers.) The
customer's cable pair is terminated and cross-
connected to the office equipment at the main
distributing frame. Office equipment terminated
on the MDF represents a physical location in the
switch and a specific telephone number. With the
introduction of electronic switches, a telephone
number is no longer wired to a specific
component of the switch. The telephone number
is now associated with a customer record which
exists in the translations (or memory) of the
switch.
Identify the Customers

26. 26
Early in the processing of a call, the switch
needs to determine what type of a call is
being made. By analyzing either the first digit
(is it a 0 or a 1?) or the first three digits
(prefix), the switch will determine whether the
call is intraswitch or inter-switch. If the call
being processed is an intra-switch call, the
path that the switch will allocate is called a
line (i.e., "on the line side of the network"). If
the call is an inter-switch call, the path that
the switch will allocate is a trunk.
Set Up the Path

27. 27
The supervision functions of the switch tend
to be overlooked because they are
transparent to the customer. They are,
however, extremely important because they
directly impact the efficient functioning of the
switch itself.
Supervise the Call

28. 28
Wireless Fundamentals

29. 29
•Off Hook
•Dial Tone
•Dialing Digits
•RBT
•Conversation
•Ring
•Off Hook &
Conversation
•Signaling
•Traffic
SWITCH / EXCHANGE
BASIC Telephony

30. 30
BSC
BTS BTS
Mobile
Subscriber...
MSC
Wireless Telephony

31. 31
• Till 1982 Cellular Systems were exclusively Analog Radio Technology.
• Advanced Mobile Phone Service (AMPS)
– U.S. standard on the 800 MHz Band
• Total Access Communication System (TACS)
– U.K. standard on 900 MHz band
• Nordic Mobile Telephone System (NMT)
– Scandinavian standard on the 450 & 900 MHz band
Different Standards Worldwide

32. 32
Different Standards Worldwide

33. 33
• End of 1980’s Analog Systems unable to meet continuing demands
– Severely confined spectrum allocations
– Interference in multipath fading environment
– Incompatibility among various analog systems
– Inability to substantially reduce the cost of mobile terminals and infrastructure
required
Analog Mobile Telephony

34. 34
• Spectrum space - most limited and precious resource
• Solution - further multiplex traffic (time domain)
• Can be realized with Digital Techniques only
Digital Mobile Telephony

35. 35
• A cellular system links Mobile subscribers to Public
Telephone System or to another Mobile subscribers.
• It removes the fixed wiring used in a traditional telephone installation.
• Mobile subscriber is able to move around, perhaps can travel
in a vehicle or on foot & still make & receive call.
Cellular Communication

36. 36
• Mobility
• Flexibility
• Convergence
• Greater QOS
• Network Expansion
• Revenue/Profit
Advantage of Cellular Communication

37. 37
Courtesy of Rich Howard
First Mobile Radio Telephone (1924)

38. 38
• Advanced Mobile Phone Service (AMPS)
– US trials 1978; deployed in Japan (’79) & US (’83)
– 800 MHz band — two 20 MHz bands
– TIA-553
– Still widely used in US and many parts of the world
• Nordic Mobile Telephony (NMT)
– Sweden, Norway, Demark & Finland
– Launched 1981; now largely retired
– 450 MHz; later at 900 MHz (NMT900)
• Total Access Communications System (TACS)
– British design; similar to AMPS; deployed 1985
– Some TACS-900 systems still in use in Europe
First Generation

39. 39
• Digital systems
• Leverage technology to increase capacity
– Speech compression; digital signal processing
• Utilize/extend “Intelligent Network” concepts
• Improve fraud prevention
• Add new services
• There are a wide diversity of 2G systems
– IS-54/ IS-136 North American TDMA; PDC (Japan)
– iDEN
– DECT and PHS
– IS-95 CDMA (cdmaOne)
– GSM
Second Generation — 2G

40. 40
• Speech coded as digital bit stream
– Compression plus error protection bits
– Aggressive compression limits voice quality
• Time division multiple access (TDMA)
– 3 calls per radio channel using repeating time slices
• Deployed 1993 (PDC 1994)
– Development through 1980s; bakeoff 1987
• IS-54 / IS-136 standards in US TIA
• ATT Wireless & Cingular use IS-136 today
– Plan to migrate to GSM and then to W-CDMA
• PDC dominant cellular system in Japan today
– NTT DoCoMo has largest PDC network
D-AMPS/ TDMA & PDC

41. 41
• Used by Nextel
• Motorola proprietary system
– Time division multiple access technology
– Based on GSM architecture
• 800 MHz private mobile radio (PMR) spectrum
– Just below 800 MHz cellular band
• Special protocol supports fast “Push-to-Talk”
– Digital replacement for old PMR services
• Nextel has highest APRU in US market due to “Direct Connect” push-to-
talk service
iDEN

42. 42
• Also based on time division multiple access
• Digital European Cordless Telephony
– Focus on business use, i.e. wireless PBX
– Very small cells; In building propagation issues
– Wide bandwidth (32 kbps channels)
– High-quality voice and/or ISDN data
• Personal Handiphone Service
– Similar performance (32 kbps channels)
– Deployed across Japanese cities (high pop. density)
– 4 channel base station uses one ISDN BRI line
– Base stations on top of phone booths
– Legacy in Japan; new deployments in China today
DECT and PHS

43. 43
• Code Division Multiple Access
– All users share same frequency band
– Discussed in detail later as CDMA is basis for 3G
• Qualcomm demo in 1989
– Claimed improved capacity & simplified planning
• First deployment in Hong Kong late 1994
• Major success in Korea (1M subs by 1996)
• Used by Verizon and Sprint in US
• Simplest 3G migration story today
North American CDMA (cdmaOne)

44. 44
• TIA standard IS-95 (ANSI-95) in 1993
• IS-95 deployed in the 800 MHz cellular band
– J-STD-08 variant deployed in 1900 MHz US “PCS” band
• Evolution fixes bugs and adds data
– IS-95A provides data rates up to 14.4 kbps
– IS-95B provides rates up to 64 kbps (2.5G)
– Both A and B are compatible with J-STD-08
• All variants designed for TIA IS-41 core networks (ANSI 41)
cdmaOne — IS-95

45. 45
• « Groupe Special Mobile », later changed to
« Global System for Mobile »
– Joint European effort beginning in 1982
– Focus on seamless roaming across Europe
• Services launched 1991
– Time division multiple access (8 users per 200KHz)
– 900 MHz band; later extended to 1800MHz
– Added 1900 MHz (US PCS bands)
• GSM is dominant world standard today
– Well defined interfaces; many competitors
– Network effect (Metcalfe’s law) took hold in late 1990s
– Tri-band GSM phone can roam the world today
GSM

46. 46
Multiple Access Technologies

47. 47
30 KHz
30 KHz
30 KHz
30 KHz
30 KHz
30 KHz
30 KHz
30 KHz
Frequency FDMA — Frequency Division Multiple Access
1G — Separate Frequencies

48. 48
Frequency
Time
200 KHz
200 KHz
200 KHz
200 KHz
One timeslot = 0.577 ms One TDMA frame = 8 timeslots
2G — TDMA Time Division Multiple Access

49. 49
• Spread spectrum modulation
– Originally developed for the military
– Resists jamming and many kinds of interference
– Coded modulation hidden from those w/o the code
• All users share same (large) block of spectrum
– One for one frequency reuse
– Soft handoffs possible
• Almost all accepted 3G radio standards are based on CDMA
– CDMA2000, W-CDMA and TD-SCDMA
2G & 3G — CDMA Code Division Multiple Access

50. 50
Courtesy of Petri Possi, UMTS World
Multi-Access Radio Techniques

51. 51
• Universal global roaming
• Multimedia (voice, data & video)
• Increased data rates
– 384 kbps while moving
– 2 Mbps when stationary at specific locations
• Increased capacity (more spectrally efficient)
• IP architecture
• Problems
– No killer application for wireless data as yet
– Vendor-driven
3G Vision

52. 52
• ITU (International Telecommunication Union)
– Radio standards and spectrum
• IMT-2000
– ITU’s umbrella name for 3G which stands for International Mobile
Telecommunications 2000
• National and regional standards bodies are collaborating in 3G
partnership projects
– ARIB, TIA, TTA, TTC, CWTS. T1, ETSI - refer to reference slides at
the end for names and links
• 3G Partnership Projects (3GPP & 3GPP2)
– Focused on evolution of access and core networks
International Standardization

53. 53
Satellite
Macrocell
Microcell
Urban
In-Building
Picocell
Global
Suburban
Basic Terminal
PDA Terminal
Audio/Visual Terminal
IMT-2000 Vision

54. 54
• IMT-SC* Single Carrier (UWC-136): EDGE
– GSM evolution (TDMA); 200 KHz channels; sometimes called “2.75G”
• IMT-MC* Multi Carrier CDMA: CDMA2000
– Evolution of IS-95 CDMA, i.e. cdmaOne
• IMT-DS* Direct Spread CDMA: W-CDMA
– New from 3GPP; UTRAN FDD
• IMT-TC** Time Code CDMA
– New from 3GPP; UTRAN TDD
– New from China; TD-SCDMA
• IMT-FT** FDMA/TDMA (DECT legacy)
* Paired spectrum; ** Unpaired spectrum
IMT-2000 Radio Standards

55. 55
• Evolution from original Qualcomm CDMA
– Now known as cdmaOne or IS-95
• Better migration story from 2G to 3G
– cdmaOne operators don’t need additional spectrum
– 1xEVD0 promises higher data rates than UMTS, i.e. W-CDMA
• Better spectral efficiency than W-CDMA(?)
– Arguable (and argued!)
• CDMA2000 core network less mature
– cmdaOne interfaces were vendor-specific
– Hopefully CDMA2000 vendors will comply w/ 3GPP2
CDMA2000 Pros and Cons

56. 56
• Wideband CDMA
– Standard for Universal Mobile Telephone Service (UMTS)
• Committed standard for Europe and likely migration path for other GSM
operators
– Leverages GSM’s dominant position
• Requires substantial new spectrum
– 5 MHz each way (symmetric)
• Legally mandated in Europe and elsewhere
• Sales of new spectrum completed in Europe
– At prices that now seem exorbitant
W-CDMA (UMTS) Pros and Cons

57. 57
• Time division duplex (TDD)
• Chinese development
– Will be deployed in China
• Good match for asymmetrical traffic!
• Single spectral band (1.6 MHz) possible
• Costs relatively low
– Handset smaller and may cost less
– Power consumption lower
– TDD has the highest spectrum efficiency
• Power amplifiers must be very linear
– Relatively hard to meet specifications
TD-SCDMA

58. 58
CDMA
GSM
TDMA
PHS
(IP-Based)
64 Kbps
GPRS
115 Kbps
CDMA 1xRTT
144 Kbps
EDGE
384 Kbps
cdma2000
1X-EV-DV
Over 2.4 Mbps
W-CDMA
(UMTS)
Up to 2 Mbps
2G
2.5G
2.75G 3G
1992 - 2000+
2001+
2003+
1G
1984 - 1996+
2003 - 2004+
TACS
NMT
AMPS
GSM/
GPRS
(Overlay)
115 Kbps
9.6 Kbps
9.6 Kbps
14.4 Kbps
/ 64 Kbps
9.6 Kbps
PDC
Analog Voice
Digital Voice
Packet Data
Intermediate
Multimedia
Multimedia
PHS
TD-SCDMA
2 Mbps?
9.6 Kbps
iDEN
(Overlay)
iDEN
Source: U.S. Bancorp Piper Jaffray
Migration To 3G

59. 59
ARIB
(Japan)
T1
(USA)
ETSI
(Europe)
TTA
(Korea)
CWTS
(China)
TTC
(Japan)
TIA
(USA)
Third Generation
Patnership Project
(3GPP)
Third Generation
Partnership Project II
(3GPP2)
ITU
Mobile
Operators
ITU Members
IS-95), IS-41, IS-
2000, IS-835
GSM, W-CDMA,
UMTS
Mobile Standard Organizations