An adjunct lecture to EE undergrad students in Universiti Teknologi Petronas in 2014 on Signals and Systems. The mission was to bridge the theory they have learnt with its applications in mobile telecommunications.

1. Lecture
Signals and Systems
Adjunct Lecture by
Ir Amir Hamzah Mohd Amir (P.Eng, MIEM)
Telekom Malaysia Berhad
Universiti Teknologi Petronas
Tronoh, Perak
11 August 2014
ABOUT MOBILE
COMMUNICATION

2. Lecture
Executive Summary
2
Content
Overview
• The evolution of Mobile Technology
• Concepts in action
1
2
This lecture relates the concepts of
Signals and Systems in simplified analogy
to the Mobile Technology.
3
2

3. LectureLecture
Section1
3
Overview
1.0 Signals and Systems
1.1 Recall: Convolution
1.2 Recall: Fourier Analysis
Before we start let’s do some revision on
Signals and Systems

4. Lecture
Recall: Signals and Systems1.0
4
Source: Oppenheim MIT Marker board Lectures

5. Lecture
Recall: Convolution1.1
5
Source:
•Oppenheim MIT Marker board Lectures
•http://cnx.org
A system defined by its impulse response h(t)
Shifted impulse = Shifted response
Scaling the input = scaling the response Output of infinite number of possible f(τ) = Convolution Integral

6. Lecture
Recall: Fourier Analysis1.2
6
Fourier Series
Fourier Transformation

7. LectureLecture
Section2
7
The evolution of mobile technology
2.0 Building Blocks in a Mobile Network
2.1 2G in a nutshell
2.2 3G in a nutshell
2.3 4G in a nutshell
2.4 Evolution in mobile technology
services
2.5 Evolution in mobile technology
architecture
Overview of your lifestyle technology

8. Lecture
Building blocks in a mobile network2.0 Confidential
8
Core
Network
Internet
Other
Networks
RANDevice
BSS/
OSS
RAN: Radio Access Network
BSS: Business Support Systems
OSS: Operation Support Systems
Air interface

9. Lecture
2G in a nutshell2.1
9
https://lteconference.files.wordpress.com/2014/03/5g-mobile-comms_infographic.jpg

10. Lecture
3G in a nutshell2.2
10
https://lteconference.files.wordpress.com/2014/03/5g-mobile-comms_infographic.jpg

11. Lecture
4G in a nutshell2.3
11
https://lteconference.files.wordpress.com/2014/03/5g-mobile-comms_infographic.jpg

12. Lecture
Evolution in mobile technology services2.4
12
technology
services
standard
CDMA
voice
SMS
*USSD#
Data (Faster) <~42Mbps>
3G (UMTS), HSDPA
OFDM+MIMO
Data (Faster and Better)
<~150Mbps>
Voice
Towards 4G (LTE)
TDMA/FDMA
Voice
SMS
*USSD#
Data (Slow) <~300kbps>
2G (GSM), GPRS, Edge
IP + MOBILITY +
SPEED =
ENDLESS
APPLICATIONS

13. Lecture
Evolution in mobile technology architecture2.5 Confidential
13
2G/3G
Circuit Switch
Network
voice
sms
ussd
Packet Switch
Network
data
IMS
voice /
unified comm.
Policy
Control &
Charging
(PCC)
Technology
TDMA
CDMA
42Mbps
LTE
Packet Switch
Network (EPC)
dataOFDM
+MIMO
150Mbps

14. LectureLecture
Section3
14
Concepts in action
3.1 Sig & Sys in Mobile Communication
Design
3.2 Case: Modeling of a Multipath
Propagation Channel
How Sig & Sys is applied in telecom

15. Lecture
Sis & Sys in mobile communication design3.1 Confidential
15
Core
Network
Internet
Other
Networks
RANDevice
BSS/
OSS
Air interface
h(t)x(t) y(t)
channel
• The wireless channel modeled as an LTI system
• Received signal y(t) can be predicted from convolution

16. Lecture
Example: Modeling of a Multipath Propagation Channel3.2 Confidential
16
h(t)s(t) r(t)
channel
A wireless channel can be modeled to
predict the impact it creates on an input
signal x(t) why does a signal experience
distortion?
• delayed replicas of signal arrival at receiver
• fading: constructive and destructive adding
of signals
• impact: poor signal quality, high error bit
rates
Case example: The effects of a multipath
channel Transmitted signal
Complex symbol
Pulse waveform
Path Attenuation Path Phase Path Delay

Line of Sight
Path
Channel impulse response
Delay Spread (Tm)
Received signal

17. Lecture
Sig & Sys applied3.2 Confidential
17
h(t)s(t) r(t)
channel
The received multipath signal r(t) is the sum of L attenuated, phase shifted and delayed
replicas of the transmitted signal s(t).
Normalized Delay Spread D = (Tm/T) where T is the width of an s(t) pulse.
• When D << 1 (coherence bandwidth bigger than signal bandwidth):
the channel is narrowband / frequency non-selective / flat fading  There is no inter
symbol interference, all frequency components experience same magnitude of fading
• When D approaches or exceeds 1:
the channel is wideband / frequency selective fading  different frequency
components of signal experience uncorrelated fading
f
S(f)
f
R(f)
f
S(f)
f
R(f)

18. Lecture
Sig & Sys applied3.2 Confidential
18
How so we solve multipath fading for a wideband system (selected examples)
TDMA Systems (e.g. GSM):
Equalization
• Find out how a known transmitted signal is modified by
multipath fading
• Construct an inverse filter to extract the rest of the
desired signal
• Introduction of a 26-bit training sequence transmitted
in the middle of every time-burst slot
CDMA Systems (e.g. 3G):
Rake Receiver
• combine multiple copies of transmitted signal to
produce the best estimation of the original signal
OFDM Systems (e.g. LTE):
Multi-Carrier Modulation
• Transport information in multiple sub-carriers in flat
fading zone  signal bandwidth smaller than coherence
bandwidth
• Complex equalizer not needed
h(t)s(t) req(t)
channel
1/h(t)
equalizer
h(t)s(t)
channel Correlator τ1
Rake receiver
Correlator τ2
Correlator τn
Combiner
req(t)
h(t)s(t)
req(t)
channel
Serialtoparallel
InverseFFT
ParalleltoSerial
Serialtoparallel
InverseFFT
ParalleltoSerial

19. Lecture
Voila3.3 Confidential
19
• How the mobile technology has evolved to
meet the lifestyle demands of the society
• Signals and Systems played a crucial role in
the development of the technology that today
we all rely on

20. Lecture 20
Thank You