Wireless communication description , introduction. basic concepts

1. 1
Introduction to Wireless
Communications and Networks
https://drive.google.com/drive/folders/1MOT1_zHe
7TB_DuvFWoh-ywZkN6QaYwat?usp=sharing

2. Outline
2
■ Overview of a Communication System
■ Digital vs. Analog Communications
■ Examples of Wireless Communication Systems
■ Why Wireless is Different ?
■ Wireless System Architecture
■ Multiple Access Techniques
■ Evolution of Cellular Networks (1G ~ 3G)
■ Wireless Local Area Networks (WLANs), Bluetooth and
Personal Area Networks (PANs)
■ Topics to be covered in the course

3. Wireless History
 Ancient Systems: Smoke Signals, Carrier Pigeons, …
 Radio invented in the 1880s by Marconi
 Many sophisticated military radio systems were
developed during and after WW2
 Cellular has enjoyed exponential growth since 1988
 Ignited the wireless revolution
 Voice, data, and multimedia becoming ubiquitous
 Use in third world countries growing rapidly
 Wifi also enjoying tremendous success and growth
 Wide area networks (e.g. Wimax)
 Short-range systems: Bluetooth, UWB, …

4. Components of a Communication System (1)
Figure 1: Communication Systems
4

5. Components of a Communication System (2)
5
■ The source originates a message, which could be a human voice, a
television picture or data. The source is converted by an input transducer
into an electrical waveform referred to as the baseband signal or message
signal.
■ The transmitter modifies the baseband signal for efficient transmission.
The transmitter generally consists of one or more of the following
subsystems: a pre-emphasizer, a sampler, a quantizer, a coder and a
modulator.
■ The channel is a medium through which the transmitter output is sent,
which could be a wire, a coaxial cable, an optical fiber, or a radio link, etc.
Based on the channel type, modern communication systems are divided
into two categories: wireline communication systems and wireless
communication systems.

6. Components of a Communication System (3)
6
■ The receiver reprocessed the signal received from the channel by
undoing the signal modifications made at the transmitter and the
channel. The task of the receiver is to extract the message from the
distorted and noisy signal at the channel output. The receiver may
consist of a demodulator, a decoder, a filter, and a de-emphasizer.
■ The receiver output is fed to the output transducer, which
converts the electrical signal to its original form.
■ Transmitters and receivers are carefully designed to overcome the
distortion and noise. The Goal of Physical layer Communication
System is to transmit information accurately and efficiently
(power and spectrum).

7. Wireless System Definitions(1)
 Mobile Station
 A station in the cellular radio service intended for use while
in motion at unspecified locations. They can be either
hand- held personal units (portables) or installed on
vehicles (mobiles)
 Base station
 A fixed station in a mobile radio system used for radio
communication with the mobile stations. Base stations
are located at the center or edge of a coverage region.
They consists of radio channels and transmitter and
receiver antennas mounted on top of a tower.

8. Wireless System Definitions (2)
 Mobile Switching Center
 Switching center which coordinates the routing of calls in
a large service area. In a cellular radio system, the MSC
connections the cellular base stations and the mobiles to
the PSTN (telephone network). It is also called Mobile
Telephone Switching Office (MTSO)
 Subscriber
 A user who pays subscription charges for using a
mobile communication system
 Transceiver
 A device capable of simultaneously transmitting
and receiving radio signals

9. Wireless System Definitions (3)
 Control Channel
 Radio channel used for transmission of call setup,
call request, call initiation and other beacon and
control purposes.
 Forward Channel
 Radio channel used for transmission of information from
the base station to the mobile
 Reverse Channel
 Radio channel used for transmission of information
from mobile to base station

10. Wireless System Definitions (4)
 Simplex Systems
 Communication systems which provide only one-
way communication
 Half Duplex Systems
 Communication Systems which allow two-way
communication by using the same radio channel for both
transmission and reception. At any given time, the user
can either transmit or receive information.
 Full Duplex Systems
 Communication systems which allow simultaneous two-
way communication. Transmission and reception is
typically on two different channels (FDD).

11. Wireless System Definitions (5)
 Handoff
 The process of transferring a mobile station from
one channel or base station to an other.
 Roamer
 A mobile station which operates in a service area
(market) other than that from which service has been
subscribed.
 Page
 A brief message which is broadcast over the entire
service area, usually in simulcast fashion by many base
stations at the same time.

12. Digital vs. Analog Communications (1)
1
2
■ Analog and Digital Signals
■ Messages are digital or analog.
■ Digital messages are constructed with a finite number of
symbols. For example, a text file is a digital message
constructed from 50 symbols, consists of 26 letters, 10
numbers, a space and several punctuation marks. Similarly,
a Morse-coded telegraph is a binary message, implying only
two symbols – mark and space.
■ Analog messages are characterized by data whose values
vary over a continuous range. For example, a speech
waveform has amplitudes that vary over a continuous range.
A picture is also an analog message.

13. Noise immunity of digital signals
1
3

14. Digital vs. Analog Communications (2)
1
4
■ Noise immunity of digital signals – digital data can be recovered without
any error as long as the distortion and noise are within limits. On the other
hand, for an analog message, even a slight distortion or interference in the
waveform will cause an error in the received signal.
■ Regenerative repeaters––Based on this “noise immunity”, when
transporting a bit stream over a long distance, regenerative repeaters or
repeater stations are placed along the path of a digital system at distances
short enough to ensure that noise and distortion remain within a limit. The
viability of regenerative repeaters is the main reason for the superiority of
digital systems over analog ones.
■ Every possible communication can be carried on with a minimum of
two symbols, i.e., by using a proper binary sequence. In the last 20 years,
digital communication gradually replace its analog competitors, and the
revolution is now nearly complete.

15. Interface of Analog and Digital Systems
-- A/D and D/A Conversion
1
5
■ Sampling Theorem A meeting ground exists for analog and digital signals:
conversion of analog signals to digital signals. The backbone that supports
the interface is Shannon's Sampling Theorem, which states that if the
highest frequency in the signal spectrum is B (in hertz), then the signal can
be recovered from its samples, taken at a rate not less than 2B samples
per second.
■ Quantization each sample is approximated, or round off to the nearest
quantized level, the information is thus digitalized. The quantized signal is
an approximation of the original one. We can improve the accuracy of the
quantized signal to any desired degree by increasing the number of levels.
■ Coding
■ Source coding Convert the quantized signal into binary sequences.
■ Channel coding Introduce redundancy in a controlled manner to
overcome the effects of noise and interferences.
■ Mapping Map binary sequence into symbols.
■ Transmission Symbols are applied to a transmitter filter, which produces a
continuous signal for transmission over a continuous channel.

16. Examples of Wireless Communication Systems
10
■ Codeless telephones --- use radio to connect a portable handset to
a dedicated base station over a distance of a few tens of meters.
■ Paging systems --- Communication systems that broadcast a page
from every base station in the network and send brief messages to
a subscriber.
■ Cellular telephone systems --- provide a wireless connection to the
PSTN (Public Switched Telephone Network) for any user location
within the radio range of a system.
■ Garage car opener
■ Remote controllers for home entertainment equipment
■ Hand-held walkie-talkies
■ Wireless keyboard and mouse
■ Wireless Lan router and adapter
■ …..

17. Wireless Vs. Wireline Communications
---- Challenges in Wireless Communication Systems
17
■ Wireless channel
■ Have time varying and multipath propagation properties.
■ Communicate over a medium significantly less reliable than wired
physical layer.
■ Are unprotected from outside signals and interceptions. Multiuser
interference (MUI) is a significant problem in wireless communications.
■ Has neither absolute nor readily observable boundaries outside of
which stations are known to be unable to receive network frames.
■ User Mobility
■ Destination address does not equal to a fixed destination location.
■ Power management --- performance, interference lever and power
consumption.
■ Hand-off --- A mobile switches its serving base station while moving
from cell to cell.
■ Location management --- tracks the user’s movement, support users
roaming delivers calls to the user at its current location.

18. Trends on Wireless Communications
■ Rapid growth In the last few
decades, new and cheaper
wireless services are emerging
continuously, due to advances in:
■ Digital signal processing
■ Digital and RF circuit fabrication
■ Large scale circuit integration
■ Digital switching techniques ->
large scale deployment of radio
communication networks
■ Convergence of wireless and
Internet ---- Broadband
communications
■ 3G cellular and PCS networks
■ WLAN networks
■ Ad-hoc Networks (military)
18

19. Cellular System Architecture
Core
Network
Core Network Backbone
Emergency
Service
Internet
PSTN
Mobile
RNC
Node B
Mobile
RadioAccess
19
Node B

20. Cellular System Architecture
20
■ Radio Access: RF related signal processing and radio resource
management. Mobile => base station => BSC or RNC => MSC.
■ Core Network: Main part is MSC (mobile switching center),
performs user authentication, admission control, traffic control,
roaming, billing, network support and maintenance etc.
■ Backbone networks: Providing voice services (PSTN, Public
Switched Telephone Network), data services (through Internet),
and emergency services. Wireless networks need to be connected
to backbone networks to extend its service capabilities and
geographic coverage.

21. Multiple Access Techniques
21

22. Multiple Access Techniques
22
■ FDMA (Frequency Division Multiple Access) each user is allocated a
unique frequency band or channel, no other user can share the same
frequency band.
■ TDMA (Time Division Multiple Access) divides the radio spectrum into time
slots, and in each slot, only one user is allowed to either transmit or
receive.
■ CDMA (Code Division Multiple Access) each user is assigned a special
code sequence (signature) to modulate its message signal, all users are
allowed to transmit over the same channel simultaneously and
asynchronously.
■ SDMA (Space Division Multiple Access) controls the radiated energy for
each user in space. SDMA serves different users by using spot beam
antennas.

23. How a cellular telephone call is made?
23
■ Receiving a call
■ Turn on a cellular phone
■ The cellular phone scan the control channels to determine the one with the
strongest signal, it then monitors the signal drops below a usable level. At
his point, it starts to search of strongest base station again.
■ If a phone call is placed to a mobile user, the MSC dispatches the request to
all the base stations in the system, the MIN (mobile identification number, i.e.
the mobile’s phone number) is broadcast as a paging message through the
forward control channel.
■ The mobile receives the signal through the base station it monitors
and responds by identifying itself through the reverse control channel.
■ The base station informs the MSC of the handshake.
■ The MSC instructs the base station to move the call to an unused voice
channel within the cell.
■ The base station signals the mobile to change frequencies to the
unused unused forward and reverse voice channel pair.
■ The base station instructs the mobile phone to ring, thereby to instruct the
user to answer the phone.

24. How a cellular phone call is made (continued)
24
■ Initiating a call
■ The mobile sends a call initiation request through the reverse control channel,
with this the unit transmits its MIN, ESN (electronic serial number) and the
phone number of the called party.
■ Base station receives the request and sends it to the MSC.
■ The MSC validates the request, making connection to the called party through
PSTN.
■ The MSC instructs the base station and mobile user to move to an unused
forward and reverse voice channel pair.
■ Roaming
■ All cellular systems provide a service called roaming. This allows subscribers to
operate in service areas other than the one from which the service is
subscribed.
■ The MSC issues a global command every several minutes, asking all
unregistered mobiles to report their subscription information.
■ Mobiles report back upon receiving the request.
■ If the mobile has roaming authorization for billing purpose, the MSC registers
the subscriber as a roamer.

25. 25
The third generation cellular networks were developed with the
aim of offering high speed data and multimedia connectivity to
subscribers. The International Telecommunication Union (ITU)
provides the standard known as, IMT-2000 (International Mobile
Telecommmunications-2000). IMT-2000 is intended to form the
basis for 3G systems.
The aim of IMT-2000 is to harmonize worldwide 3G systems to
provide Global Roaming.
3G System

26. 26
A few technologies are able to fulfill the International Mobile
Telecommunications (IMT) standards, such as CDMA, UMTS and
some variation of GSM such as EDGE.

27. 27
For IMT-2000 intended Data Rates Low 144 kbits/s satellite and rural outdoor,
Medium 384 kbits/s urban outdoor, High 2048 kbits/s indoor and low range
outdoor. The speed of the MS above 10 Kmph will loose data rate.

28. 28
Common Spectrum worldwide (1.8-2.2GHz band)
Multiple radio environments (cellular, cordless, satellite, LANs)
Wide range of telecommunication services (voice, data,
multimedia, Internet)
Global seamless roaming
Enhance security and performance
Integration of satellite and terrestrial system.
IMT-2000 Vision

29. 29
After trying to establish a single 3G standard, ITU finally approved a
family of 3G standards, which are part of the 3G framework known
as IMT-2000:
W-CDMA
CDMA2000
TD-SCDMA (Time Division-High Speed Circuit Switched Data)

30. 30
IS-95 IS-136 & PDCGSM-
EDGE
GPRS
HSCSD
IS-95B
Cdma2000-1xRTT
Cdma2000-1xEV,DV,DO
Cdma2000-3xRTT
W-CDMA
EDGE
TD-SCDMA
2G
3G
2.5G
3GPP3GPP2
Evolution to 3G
AMPSIS-41 ETACS
Advanced Mobile Phone System
European Total Access Communication
System
United States Digital Cellular
Global Systems for Mobile
Cellular Digital Packet Data
AMPS
ETACS
USDC
GSM
CDPD
GPRS
EDGE
General Packet Radio Service
Enhanced Data Rates for GSM Evolution
UMTS
3GPP
Universal Mobile Telecommunications System
3rd
Generation Partnership Project

31. 1G Wireless Systems
20
■ Appeared in late 1970s and deployed in early 1980s.
■ All based on analog techniques, all used FDMA and FM
modulation.
■ System capacity is low. Data rate: 8~10 kbps
■ Representative Standards:
■ AMPS: Advanced Mobile Phone System, developed by AT&T Bell
Labs in late 1970s. First deployed in 1983. The first AMPS system
used large cells and omni-directional base station
antennas, therefore, the number of users that can be
supported was quite limited. AMPS is used all over the world and
is esp. popular in US, South America, China and Australia.
■ ETACS: European Total Access Communication Systems. Almost
identical to AMPS except that the channel bandwidth is scaled to
25kHz instead of 30 kHz as in AMPS.

32. 2G Wireless Systems: Characteristics
32
■ Deployed in mid 1990s, 2G wireless systems all use
digital voice coding and digital modulation.
■ Can provide advanced call capabilities and at least a 3-
times increase in overall system capacity.
■ Was designed before the widespread of the Internet,
mainly supported voice-centric services and limited
date-service, like short messages, FAX,etc.
■ Date rate: on the order of 10 kbps

33. 33
GSM evolution to 3G
GSM
9.6kbps (one timeslot)
GSM Data
Also called CSD
GSM
General Packet Radio Services
Data rates up to ~ 115 kbps
Max: 8 timeslots used as any one time
Packet switched; resources not tied up all the time
GSM / GPRS core network re-used by WCDMA (3G)
GPRS
HSCSD
High Speed Circuit Switched Data
Dedicate up to 4 timeslots for data connection ~ 50 kbps
Good for real-time applications (better than GPRS)
Inefficient in a sense that ties up resources, even when
nothing is sent
Not as popular as GPRS (many skipping HSCSD)
EDGE
Enhanced Data Rates for Global Evolution
Uses 8PSK modulation
3x improvement in data rate on short distances
Can fall back to GMSK for greater distances
Combine with GPRS (EGPRS) ~ 384 kbps
Can also be combined with HSCSD
WCDMA

34. 2G Wireless Systems: Representative Standards
34
■ GSM (Global Systems for Mobile communications)
■ A TDMA system, serves as the pan-European cellular service, provides
a wide range of network service, including phone service, FAX, short
message service. Support 24.7kbps data rate.
■ USDC IS-136 (United States Digital Cellular)
■ A TDMA system which is compatible with AMPS, it supports more
users (6 times) with improved performance. It shares the same
frequencies, frequency reuse plan and base stations as AMPS.
Provides access to VPN, supports short messages. Support 48.6kbps
data rate.
■ IS-95 (United States Digital Cellular Standard )
■ A CDMA standard also designed to be compatible with AMPS through
using of CDMA/AMPS dual mode phones and base stations. Capacity
is 8~10 times that of AMPS. Support 14.4kbps data rate.

35. 2.5G Wireless System
35
Compared to 2G systems, 2.5G systems enables high speed data communications,
provides continuous connection to internet.
■ CDPD (Cellular Digital Packet Data), a data service for 1st and 2nd generation US cellular
systems without additional bandwidth requirement, packet channels are dynamically assigned to
idle voice channels. Support 48.6kbps data rate as in IS-136.
■ GPRS (General Packet Radio Service), based on GSM by allowing multiple slots of a GSM
radio channel be dedicated to an individual user, promises data rate from 56 kbps to 114kbps---
continuous connection to the Internet for mobile phone and computer users, easy access to VPN
(Virtual Private Network).
■ EDGE (Enhanced Data Rates for GSM Evolution), providing 384kbps rate by using improved
modulation (8-PSK instead of GMSK in GSM) and relaxed error control. Also referred to as
EGPRS.
■ CDMA one (IS-95B): Providing high speed data access on a common CDMA radio channel
by dedicating multiple orthogonal user channels for specific users or specific purposes. Support
115.2kbps.

36. 36
UMTS
UMTS is the European vision of 3G.
UMTS is an upgrade from GSM via GPRS or EDGE.
The standardization work for UMTS is carried out by Third
Generation Partnership Project (3GPP).
Data rates of UMTS are:
144 kbps for rural
384 kbps for urban outdoor
2048 kbps for indoor and low range outdoor
Virtual Home Environment (VHE)

37. 37
A UMTS network consists of three interacting domains: Core
Network (CN), UMTS Terrestrial Radio Access Network (UTRAN)
and User Equipment (UE) or ME.
The 3G system terminal is called ‘‘UE’’ and it contains two
separate parts, Mobile Equipment (ME) and the UMTS Service
Identity Module (USIM). USIM contains member specific data and
enables the authenticated entry of the subscriber into the network.
UMTS System Architecture

38. 38
UMTS network architecture
Circuit switch domain
Packet switch domain
GERAN: GSM EDGE Radio Access Network
The GERAN air interface is Um, whereas
the UTRAN air interface is Uu

39. 39
This UMTS UE is capable of working in three modes: CS (circuit
switched) mode, PS (packet switched) mode and CS/PS mode.
SD
Mobile Station
MSC/
VLR
Base Station
Subsystem
GMSC
Network Subsystem
AUCEIR HLR
Other Networks
Note: Interfaces have been omitted for clarity purposes.
GGSN
SGSN
BTS
BSC
Node
B
RNC
RNS
UTRAN
SIM
ME
USIM
ME
+
PSTN
PLMN
Internet

40. 40
Base Station is referred as Node-B and control
equipment for Node-B's is called Radio Network
Controller (RNC) as if the BSC of GSM.
The functions of Node-B are:
Air interface Transmission / Reception
Modulation / Demodulation
CDMA Physical Channel coding
Micro Diversity
Error Handing
Closed loop power control
The functions of RNC are:
Radio Resource Control
Admission Control
Channel Allocation
Power Control Settings
Handover Control
Macro Diversity
Ciphering
Segmentation / Reassembly
Broadcast Signaling
Open Loop Power Control

41. 41
Core Network (CN) :
The Core Network is divided in circuit
switched and packet switched domains.
Some of the circuit switched elements are
Mobile services Switching Centre (MSC),
Visitor location register (VLR) and Gateway
MSC.
Packet switched elements are Serving
GPRS Support Node (SGSN) and Gateway
GPRS Support Node (GGSN). Some network
elements, like EIR, HLR, VLR and AUC are
shared by both domains.
To provide switching, routing and transit
for user traffic. The basic CN architecture for
UMTS is based on the GSM network with
GPRS.

42. 42
 Serving GPRS Support Node (SGSN) interfaces the access
network of MS and the Gateway GPRS Support Node (GGSN)
connects UMTS core network with external packet network like
Internet, X.25 or similar.
The Asynchronous Transfer Mode (ATM) is defined for UMTS core
transmission. The ATM Adaptation Layer type 2 (AAL2) handles the
circuit switched connection and the packet connection protocol
AAL5 is designed for data delivery.

43. 43
UMTS Network Architecture
SD
Mobile Station
MSC/
VLR
Base Station
Subsystem
GMSC
Network Subsystem
AUCEIR HLR
Other Networks
Note: Interfaces have been omitted for clarity purposes.
GGSN
SGSN
BTS
BSC
Node
B
RNC
RNS
UTRAN
SIM
ME
USIM
ME
+
PSTN
PLMN
Internet

44. 44

45. 45
Two international bodies are established.
Third Generation Partnership Project (3GPP)
The Japanese standardization body ARIB (Association of Radio
Industries and Business), Telecommunications Industry Association
(TIA) of Korea, ESTI (European Telecommunication Standards
Institute) of Europe proposed for WCDMA is based on DS-CDMA
(direct sequence code division multiple access) technology.
Third Generation Partnership Project 2 (3GPP2),
A partnership consisting of five telecommunications standards
bodies: CWTS in China, ARIB and TTC in Japan, TTA in Korea and
TIA in North America proposed for CDMA-2000.
Bodies Give Proposal for 3G

46. 46
3GPP
North
America
T1
Europe
ESTI
China
CWTS
Japan
ARIB/
TTC
Korea
TTA
T1→ANSI Committee
CWTS→ China Wireless Telecommunications Standard

47. 47
3GPP2
North
America
TIA
China
CWTS
Japan
ARIB/
TTC
Korea
TTA

48. 48
TIA of USA and TTA of Korea proposed 3G CDMA-2000. Code
division multiple access 2000 is the natural evolution of IS-95
(cdmaOne).
It includes additional functionality that increases its spectral
efficiency and data rate capability. CDMA (code division multiple
access) is a mobile digital radio technology where channels are
defined with codes (PN sequences).
CDMA permits many simultaneous transmitters on the same
frequency channel.
3G CDMA-2000

49. 49
IS-95B
IS-95B
Uses multiple code channels
Data rates up to 64kbps
Many operators gone direct to 1xRTT
CDMA
IS-95A
IS-95A
14.4 kbps
Core network
re-used in
CDMA2000
1xRTT
CDMA2000 1xRTT(Radio Transmission
Technologies): single carrier RTT
First phase in CDMA2000 evolution
Easy co-existence with IS-95A air interface
Release 0 - max 144 kbps
Release A – max 384 kbps
Same core network as IS-95
1xEV-DO
CDMA2000 1xEV-DO: (Evolution-Data Only)
1XEV-DO, also called 1XEV Phase One, is an enhancement
that puts voice and data on separate channels in order to
provide data delivery at 2.4 Mbps.
1xEV-DV
CDMA2000
3xRTT
EV-DV, or 1XEV Phase Two promises data
speeds ranging from 3 Mbps to 5 Mbps.
CDMA20003X evolution: speeds to 5Mbps
(more than 3xRTT i.e. 3 times the standard
1.25 MHz )
CDMA2000 evolution to 3G

50. 50
Evolution to 3G – The Carrier’s Choice
1995 1999 2000 2001 2002
Nearly Doubles Voice, 307k, RF backward compatible
Data only 2.4 Mbps
RF backward compatible
Voice, 14.4k Voice, 64k
CDMA
CDMA2000 1xIS-95A
CDMA2000 1xEV-DO
IS-95B
2003 2004
Evolution of CDMA Networks

51. 51
Time Division-Synchronous Code Division Multiple Access, or
TD-SCDMA, is a 3G mobile telecommunications standard, being
pursued in the People's Republic of China by the Chinese Academy
of Telecommunications Technology (CATT).
This proposal was adopted by ITU as one of the 3G options in
late 1999. TD-SCDMA is based on spread spectrum technology.
3G TD-SCDMA

52. 52

53. 53
Three system parameters coverage area of a cell, quality of voice
and capacity of physical channel are interlinked. Enhancement of
any parameter will degrade another two parameters. For example if
coverage area of a cell is increased then delay difference of
multipath propagation will also increase hence BER will be high. To
keep the BER within tolerable range chip rate i.e. capacity of the
channel has to be reduced or size of the cell must be lowered to
reduce the delay difference of mulipath propagation.
Capacity
Coverage
Quality
Three system parameters

54. CDMA
54

55. 55
CDMA physical channels are defined by RF frequency and code
sequence.
The logical channels in CDMA are the control and traffic channels
Physical and Logical channel
The Forward CDMA channel is the cell-to-mobile direction of
communication or the downlink path. The Reverse CDMA
channel is the mobile-to-cell direction of communication or the
uplink path.
Forward and Reverse Channel

57. 57
Logical
Channels
Forward
Link
Pilot Channel
Sync Channel
Paging Channel
Traffic Channel
Variable-Bit-Rate
User Information
Power Control
Signaling
Messages
Reverse
Link
Access Channel Traffic Channel
Variable-Bit-Rate
User Information
Signaling
Messages

58. 58
Each Walsh code identifies one of the 64 forward channels. After
the channel symbols are spread using orthogonal codes, they are
further scrambled in the in-phase and quadrature phase lines by
what are called the short PN-spreading codes.
The PN-spreading codes (period of 32,768 chips) are orthogonal
but possesses excellent autocorrelation and cross correlation
properties to minimize interference among different channels.
Orthogonal codes are used to isolate the transmission between
different channels within a cell and the PN spreading codes are used
to separate the transmission between different cells. In effect the
PN sequences are used to differentiate between several BSs in the
areas that are all employing the same frequency.
CDMA Forward Channel

59. 59
It is a pseudo-noise code sequence
Each user has a unique PN code orthogonal to all other
users.
Orthogonal Walsh codes are generated from Hadamard
matrices.
PN Sequence
  NnnSk  01)(







NN
NN
N
HH
HH
H
22
22
2 1
The forward link (base station to mobile station) uses Walsh codes,
while the reverse link (mobile station to base station) uses pseudo-
random noice (PN) codes for channelization.

60. 60
a a
a a
1 1
1 0
0 0
0 1
OR
=

61. 61
0 0
0 1
0 0
0 1
0 0
0 1
1 1
1 0
1 1
1 0
1 1
1 0
1 1
1 0
0 0
0 1
4×4 matrix (4-bits Walsh codes)

62. 62
Pilot Channel
The pilot channel is intended to provide a reference signal for all MSs within a
cell that provides the phase reference for coherent demodulation.
Its data content is a sequence of zero contains no information except the RF
carrier. It is about 4-6dB stronger than all other channels.
It is also spread using PN-spreading code to identify the BS. The way to identify
the BS is to offset (shift of chip sequence) the PN sequence by some number of
chips.
To QPSK
modulation
BPF
BPF
All 0s
I pilot PN at
1.2288 Mcps
Q pilot PN at
1.2288 Mcps
Walsh W0
1.2288
Mcps
BBF- Baseband Filter

63. 63
Each pilot channel transmits the same spreading sequence at different
time offset (in IS-95 offset of 64 chips is used), which can be used to
distinguish signals of different pilots. There are 512 offset values
available i.e. 512 possible spreading sequences that can be reused
elsewhere in the same system.
The pilot channel consists of an un-coded direct sequence spread
spectrum signal with its own identifying spreading code and is shared
among all users in a sector or cell.
To QPSK
modulation
BPF
BPF
All 0s
I pilot PN at
1.2288 Mcps
Q pilot PN at
1.2288 Mcps
Walsh W0
1.2288
Mcps
BBF- Baseband Filter

64. 64
Uniquely identifying sector/cell
Providing phase/time/signal strength reference
Rescanning or periodically checking for better sector/cell
4-6dB stronger than other channels
No power control in pilot channel
A summery of pilot channel

65. 65
Sync Channel
The synchronization channel is used to acquire initial time synchronization.
It provides a mobile with the system and network identification parameters
required to synchronize with the network and obtain a paging channel.
Sync channel
message
1.2 kbps
Convolutional
encoder
Symbol
repetition
Block
interleaver
Rate ½ Code
Symbol
2.4
ksps
4.8
ksps
Modulated
Symbol
To QPSK
modulation
BBF
BBF
4.8
ksps
I pilot PN at
1.2288 Mcps
Q pilot PN at
1.2288 Mcps
Walsh W32
1.2288
Mcps

66. 66
System identification number (SID)
Network identification number (NID)
Verion of radio interface being supported
Precise time-of-day information
PN offset of the associated pilot channel
Uses W32 for spreading
Operates at 1200bps
Provides paging channel data rate
A summery of synchronization channel

67. 67
Paging Channel
Paging channel
message
4.8 or 9.6 kbps
Convolutional
encoder
Symbol
repetition
Block
interleaver
Rate ½ Code
Symbol
9.6 or 19.2
ksps
19.2
ksps
Modulated
Symbol
To QPSK
modulation
BBF
BBF
I pilot PN at
1.2288 Mcps
Q pilot PN at
1.2288 Mcps
Walsh W1-7
1.2288
Mcps
19.2
ksps
Long code
mask for
paging
channel
Long code
generator
Long code
decimator
1.2288
Mcps
19.2 ksps
64:1

68. 68
Used to page the MS (like GSM) in case of an incoming call, or to carry the control
messages for call set up.
Provides notification of incoming call.
Paging channel can be used to broadcast messages.
Uses W1-W7
There is no power control
Additionally scrambled by PN long code, which is generated by LFSR (Linear
Feedback Shift Register) of length 42
The rate 4.8 Kbps or 9Kbps
Provides list of CDMA carriers.

69. 69
This channel is used for voice communication and signaling to a specific
mobile during a call. Traffic (channels 8 to 31 and 33 to 63) – the forward
channel supports 55 traffic channels. Supported data rates are up to 9600bps
in the first proposal and 14400bps in the revision.
Forward Traffic Channel
Gain
Control
Baseband
Filter
Baseband
Filter
I PN
Q PN
1.2288
Mcps
Walsh
Function
Block
Interleaving
symbol
Repetition
19.2
Ksps
Decimator
Long PN Code
Generator
Scrambling
Long Code Mask
1.2288
Mcps
19.2
Ksps
Voice traffic
Power
Control
Bits 800
bps
Decimator
800 Hz
M
U
X
Puncture 2
of every
6 input
28.8
Ksps
bits chips
CHANNEL ELEMENT
R = 1/2,
Convolutional
Encoding
64:1
24:1
19.2
Ksps

70. 70
Scrambler
Used for Data Encryption. Make call more secure.
Randomizes data. Prevents the transition of a long series of
1’s or 0’s
Decimator
Under samples pulses

71. 71
Forward Traffic Channel Processing
Steps
• Speech is encoded at a rate of 8550 bps
• Additional bits added for error detection
• Data transmitted in 2-ms blocks with forward error correction.
• Data interleaved in blocks to reduce effects of errors
• Data bits are scrambled, serving as a privacy mask
• Power control information inserted into traffic channel
• Digital bit stream modulated onto the carrier using QPSK
modulation scheme

72. 72
The CDMA reverse channel (MS to BS) is fundamentally
different from forward channel. It employs OQPSK (Offset QPSK)
rather than OPSK since OQPSK is more power efficient for MS as
a transmitter.
Compared with the forward channel, there is no spreading of
data symbol using orthogonal codes but uses waveform
encoding (orthogonal modulation scheme) that consume BW
but reduces BER (Bit Error Rate).
CDMA Reverse Channels

73. 73
Logical
Channels
Forward
Link
Pilot Channel
Sync Channel
Paging Channel
Traffic Channel
Variable-Bit-Rate
User Information
Power Control
Signaling
Messages
Reverse
Link
Access Channel Traffic Channel
Variable-Bit-Rate
User Information
Signaling
Messages

74. 74
The reversed access channel is one-third rate convolutionally
encoded, interleaved spread-spectrum channel. It is used by a
mobile to initiate a call with base station and to response to
paging channel message. The reverse channel is spread by one
of 242-1 PN code. The encoded spread-spectrum data are then
MOD2 added with the I and Q PN sequence and finally
modulated.
Access Channel

75. 75
Access message
4.8 kbps
Convolutional
encoder
Symbol
repetition
Block
interleaver
Rate ½ Code
Symbol
14.4
ksps
28.8
ksps
Modulated
Symbol
To QPSK
modulation
BBF
BBF
I pilot PN at
1.2288 Mcps
Q pilot PN at
1.2288 Mcps
1.2288
Mcps
64-ary
orthogonal
modulator
28.8 ksps
Long code
generator
Long code mask for
access channel
Reverse Access Channel

76. 76
Bit rate 9600 and 4800bps
System access
Traffic channel request
Call originations
Page response
System registration
Summary of Reverse Access Channel

77. 3G Wireless Systems: Features
77
■ Features:
■ High transmission rate and the support of multimedia
services.
■ Multiple-megabit internet services, and simultaneous voice and
data access with multiple parties at the same time using a single
mobile handset.
■ Date rate: around 2Mbps. Bandwidth: in the order of MHz
■ Seamless global roaming: wireless access from anywhere on
the earth. Obviously, it will include the satellite networks.
■ 3GPP and 3GPP2
■ Worldwide standardization organizations established to gather
global expertise, participated by almost all the big companies.
■ 3GPP: based on backward compatibility to GSM, IS-136, GPRS, EDGE
etc.
■ 3GPP2: based on backward compatibility to IS-95, and CDMAone.

78. 3G Wireless Systems: Challenges
78
■ Impact of high transmission rate --- frequency selective fading
■ High transmission rate implies that the signal bandwidth is much wider
than the coherence bandwidth of the channel, different frequency
components in the signal will experience different fading characteristic.
■ Solution: Modulate each signal components onto a different subcarrier
and send them over the channel in parallel, so that each component
will experience flat fading. => multicarrier systems.
■ System capacity and user mobility
■ Enlarged capacity and higher transmission rate requires more efficient
deployment of the available bandwidth, which implies that the system
needs to be reused more often.
■ Higher degree of frequency reuse implies more complex mobile
management.
■ How to increase spectrum efficiency is the ultimate goal of
communication research.

79. 79
SvMBN
S
R
B
I
E
fw
w
t
b
.).1(
.
0 







Where It is the total interference and thermal noise psd and Eb is energy per bit.
Signal strength in dB,
S=Pm+Gm+Gb+Mfade+Lp+Lcable+Lbody+Lpent
R = transmission rate of MS in bps
Bw= bandwidth
Gb= receive antenna gain of the BS in dB
Gm= transmit antenna gain of MS in dB
Lbody= body loss (dB)
Mfade=log-normal shadow margin (dB)
Lcable= cable connection loss (dB)
Lpent= building/vehicle penetration loss (dB)
Lp= path loss in dB
Pm= transmit power of MS in dB
vf = Voice activity factor
Eb/It of Reversed Link:

80. 80
)1.(.)1.()./(
.1 0
fvS
BN
fvIE
GM
f
cw
ftb
c
p













The number of mobiles, are transmitting at a given time in a cell,
The pole point or asymptotic cell capacity,










)1.()./(
.1max
fvIE
GM
ftb
c
p

Neglecting 1 we can rewrite the equation,










)1.()./(
.max
fvIE
GM
ftb
c
p


81. 81
Where c = power control factor
f = interference factor from the neighboring cells.
maxM
M
 is called the loading factor.

82. Thanks