Computer Engineering A.A. 2014-15:
Electronics and Communications Systems
Introduction to Wireless Communications
Giacomo Bacci
giacomo.bacci@iet.unipi.it
Dip. Ingegneria dell’Informazione, Univ. Pisa, Pisa, Italy
Dept. Electrical Engineering, Princeton Univ., Princeton, NJ
2
Electronics and Communications Systems
Computer Eng. 2014-15
Outline of this part of the course
• Introduction to wireless communications
• Basics of wireless propagation:
o Large-scale and small-scale fading
o Time and frequency selectivity
o Methods to combat channel impairments
• Fundamentals of cellular standards
o 3G communications
o 4G communications
o 5G communications
• Discussion and perspectives
Dip. Ingegneria dell’Informazione
University of Pisa, Pisa, Italy
Giacomo Bacci
Introduction to Wireless Communications
3
Electronics and Communications Systems
Computer Eng. 2014-15
Schedule (1/2)
• Week 1 (October 6-9, 2014 – 4 hours)
o Historical overview from 0G to 5G
o Basic concepts of radio cellular networks
o Basics of multiple access technologies, duplexing, and
switching
o Planning of a cellular network
• Week 2 (October 13-17, 2014 – 4 hours)
o Basic concepts of the wireless propagation channel
o Large-scale and small-scale fading
o Main small-scale propagation phenomena and the
multipath channel
o The concepts of frequency and time selectivity
o Methods to combat frequency and time selectivity: The
case study of 2G communications
Dip. Ingegneria dell’Informazione
University of Pisa, Pisa, Italy
Giacomo Bacci
Introduction to Wireless Communications
4
Electronics and Communications Systems
Computer Eng. 2014-15
Schedule (2/2)
• Week 3 (4 hours)
o Frequency hopping, CDMA, and UWB
o 3G standards: main system highlights, including signal
model and network architecture
o OFDM, OFDMA, and MC-CDMA
• Week 4 (4 hours)
o 4G standards: main system highlights, including signal
model and network architecture
o Basics of beyond-4G technologies: MIMO, cognitive radio
technologies, heterogeneous networks, and advanced
channel coding techniques
o Summary and conclusions
Dip. Ingegneria dell’Informazione
University of Pisa, Pisa, Italy
Giacomo Bacci
Introduction to Wireless Communications
Electronics and Communications Systems
Computer Eng. 2014-15
5
Introduction to modern
wireless communications
systems
Dip. Ingegneria dell’Informazione
University of Pisa, Pisa, Italy
Giacomo Bacci
Introduction to Wireless Communications
Introduction to modern wireless communications systems
6
Electronics and Communications Systems
Computer Eng. 2014-15
Some (whopping) facts (1/2)
o In 2014, the number of mobile users reach around 7 billion users
worldwide!
o In Italy, there are 88,580,000 mobile phones for a population of 60,090,400
inhabitants (December 2013): 147.4% penetration
Dip. Ingegneria dell’Informazione
University of Pisa, Pisa, Italy
Giacomo Bacci
Introduction to Wireless Communications
Introduction to modern wireless communications systems
7
Electronics and Communications Systems
Computer Eng. 2014-15
Some (whopping) facts (2/2)
o The number of people with access to
mobile communications is higher than
those with access to working toilets
(around 4.5 billions)
o The number of people that owns a mobile
phone is larger than the one that
owns/uses a toothbrush (around 4 billion)
o Every second, more than an hour of
videos is uploaded to Youtube
Dip. Ingegneria dell’Informazione
University of Pisa, Pisa, Italy
Giacomo Bacci
Introduction to Wireless Communications
Introduction to modern wireless communications systems
8
fixed (wired) subscriptions
mobile subscriptions
Electronics and Communications Systems
Computer Eng. 2014-15
Fixed vs. mobile broadband subscriptions
Dip. Ingegneria dell’Informazione
University of Pisa, Pisa, Italy
Giacomo Bacci
Introduction to Wireless Communications
Introduction to modern wireless communications systems
9
Electronics and Communications Systems
Computer Eng. 2014-15
A brief history of wireless communications (1/3)
•
1864: Maxwell proves the existence of electromagnetic waves
•
1887: Hertz sends and receives wireless waves, using a spark transmitter and a
resonator receiver
•
1895: Guglielmo Marconi sends a radio signal over more than a mile, from the Isle
of Wight to a tugboat 18 miles away
•
1904: Fleming patents the diode
•
1906: DeForest patents the triode amplifier; first speech wireless transmission, by
Fessenden
•
WW I: Rapid development of communications intelligence, intercept technology,
cryptography
•
1920: Marconi discovers short-wave radio, with wavelengths between 10 and 100
meters
•
1935: Armstrong invents the frequency modulation (FM)
Dip. Ingegneria dell’Informazione
University of Pisa, Pisa, Italy
Giacomo Bacci
Introduction to Wireless Communications
Introduction to modern wireless communications systems
10
Electronics and Communications Systems
Computer Eng. 2014-15
A brief history of wireless communications (2/3)
Mobile wireless systems ensure the communications between mobile nodes
In the last eighty years, wireless technology has evolved over many aspects:
• increased coverage distance
• increased quality (throughput, error rate performance, spectral
efficiency)
• improved availability of services (broadband communications)
• decreased energy consumption (energy efficiency)
• reduced costs (for both service providers and subscribers/users)
• reduced device sizes and costs
Dip. Ingegneria dell’Informazione
University of Pisa, Pisa, Italy
Giacomo Bacci
Introduction to Wireless Communications
Introduction to modern wireless communications systems
11
Electronics and Communications Systems
Computer Eng. 2014-15
A brief history of wireless communications (3/3)
Dip. Ingegneria dell’Informazione
University of Pisa, Pisa, Italy
Giacomo Bacci
Introduction to Wireless Communications
Introduction to modern wireless communications systems
12
Electronics and Communications Systems
Computer Eng. 2014-15
Basics of wireless communication systems
ad-hoc networks
infrastructure networks
•
•
higher rates
lower latencies
•
•
lower deployment costs
useful in impaired
environments
Examples:
• cellular networks
• WLANs
• paging systems
Dip. Ingegneria dell’Informazione
University of Pisa, Pisa, Italy
Giacomo Bacci
Introduction to Wireless Communications
Introduction to modern wireless communications systems
13
Electronics and Communications Systems
Computer Eng. 2014-15
An elementary wireless system
base transceiver
station (BTS)
mobile station
(MS)
coverage area
Note: This is not a cellular system, it can be labeled as a 0G system (1940s)
Constraints:
o limited frequency range (due to licensed spectrum)
o limited coverage area (due to power masks)
Features:
o low density of users (per unit of area)
o discontinued service when exiting the coverage area
Dip. Ingegneria dell’Informazione
University of Pisa, Pisa, Italy
Giacomo Bacci
Introduction to Wireless Communications
Introduction to modern wireless communications systems
14
End of 1950s/beginning of 1960s: introducing cells to provide seamless coverage
Electronics and Communications Systems
Computer Eng. 2014-15
The concept of cellular networks (1/2)
handover
co-channel
(intercell)
interference
cluster with size
(reuse factor) K=4
available channels
Dip. Ingegneria dell’Informazione
University of Pisa, Pisa, Italy
Giacomo Bacci
Introduction to Wireless Communications
Introduction to modern wireless communications systems
15
With the advent of 4G systems, we also have fractional frequency reuse (FFR)
Electronics and Communications Systems
Computer Eng. 2014-15
The concept of cellular networks (2/2)
available channels
Dip. Ingegneria dell’Informazione
University of Pisa, Pisa, Italy
Giacomo Bacci
Introduction to Wireless Communications
Introduction to modern wireless communications systems
16
Electronics and Communications Systems
Computer Eng. 2014-15
Medium access techniques
o radio transceiver configuration (duplexing)
o multiple access scheduling
Dip. Ingegneria dell’Informazione
University of Pisa, Pisa, Italy
Giacomo Bacci
Introduction to Wireless Communications
Introduction to modern wireless communications systems
17
Electronics and Communications Systems
Computer Eng. 2014-15
Duplexing
o frequency division duplexing (FDD): uplink and
downlink take place at the same time on different
frequencies
1G, 2G
o time division duplexing (TDD): uplink and downlink
take place on the same frequency at different times
3G, 4G
o full duplex (FD): uplink and downlink take place at
the same time on the same frequency
5G
Dip. Ingegneria dell’Informazione
University of Pisa, Pisa, Italy
Giacomo Bacci
Introduction to Wireless Communications
Introduction to modern wireless communications systems
18
Electronics and Communications Systems
Computer Eng. 2014-15
Multiple access techniques
Since the wireless channel is a shared
medium, some multiple access
techniques are needed to schedule
multiple users over a dedicated channel
We can exploit several
degrees of freedom:
frequency, time, space,
codes, etc.
Dip. Ingegneria dell’Informazione
University of Pisa, Pisa, Italy
Giacomo Bacci
Introduction to Wireless Communications
Introduction to modern wireless communications systems
19
Electronics and Communications Systems
Computer Eng. 2014-15
Frequency division multiple access (FDMA)
The available bandwidth B is subdivided into MF non-overlapping
subchannels (in the frequency domain):
FDMA is suitable to both analog and digital systems (used since the early
days of analog radios)
Dip. Ingegneria dell’Informazione
University of Pisa, Pisa, Italy
Giacomo Bacci
Introduction to Wireless Communications
Introduction to modern wireless communications systems
20
Electronics and Communications Systems
Computer Eng. 2014-15
Time division multiple access (TDMA)
The bandwidth B is assigned to the MT users using a round-robin
scheduling: each user makes use of the whole bandwidth for its
assigned time slot:
TDMA can be used only in digital systems
Dip. Ingegneria dell’Informazione
University of Pisa, Pisa, Italy
Giacomo Bacci
Introduction to Wireless Communications
Introduction to modern wireless communications systems
21
To accommodate more users in the same cell, we can assign each
user a different spreading code:
Electronics and Communications Systems
Computer Eng. 2014-15
Code division multiple access (CDMA) (1/2)
Dip. Ingegneria dell’Informazione
University of Pisa, Pisa, Italy
Giacomo Bacci
Introduction to Wireless Communications
Introduction to modern wireless communications systems
22
Electronics and Communications Systems
Computer Eng. 2014-15
Code division multiple access (CDMA) (2/2)
There exist different techniques to implement CDMA for spread
spcetrum (SS) communications:
o frequency hopping (FH)
o direct sequence (DS):
•
orthogonal codes
•
non-orthogonal codes (causing intercell interference)
Dip. Ingegneria dell’Informazione
University of Pisa, Pisa, Italy
Giacomo Bacci
Introduction to Wireless Communications
Introduction to modern wireless communications systems
23
Multiple antennas at both the transmit and the receive sides can
generate independent signals, thus achieving spatial multiplexing:
Electronics and Communications Systems
Computer Eng. 2014-15
Space division multiple access (SDMA)
Dip. Ingegneria dell’Informazione
University of Pisa, Pisa, Italy
Giacomo Bacci
Introduction to Wireless Communications
Introduction to modern wireless communications systems
24
As an example, the global system for mobile communications
(GSM) makes use of a combination of FDMA and TDMA:
Electronics and Communications Systems
Computer Eng. 2014-15
Mixed multiple access techniques
Dip. Ingegneria dell’Informazione
University of Pisa, Pisa, Italy
Giacomo Bacci
Introduction to Wireless Communications
Introduction to modern wireless communications systems
25
Electronics and Communications Systems
Computer Eng. 2014-15
Planning of a cellular network
Some key performance indicators:
o spectral efficiency [b/s/Hz]
o energy efficiency [b/J]
o area spectral efficiency [b/s/Hz/m2]
o handover frequency
o capital expenditure (CapEx) and
operating expenditure (OpEx) costs
o …
Dip. Ingegneria dell’Informazione
University of Pisa, Pisa, Italy
Giacomo Bacci
Introduction to Wireless Communications
Introduction to modern wireless communications systems
26
Electronics and Communications Systems
Computer Eng. 2014-15
Area spectral efficiency (1/4)
For the sake of simplicity, let us neglect considerations about
modulations and other PHY details, and let us focus on the density of
users (per unit area):
number of channels
coverage area
In the case of a 0G system, u is upper-bounded by:
o
a limited number of subchannels M, due to a finite licensed spectrum
o
a minimum area A, that ensures a sufficient coverage region for the users
Dip. Ingegneria dell’Informazione
University of Pisa, Pisa, Italy
Giacomo Bacci
Introduction to Wireless Communications
Introduction to modern wireless communications systems
27
Electronics and Communications Systems
Computer Eng. 2014-15
Area spectral efficiency (2/4)
To address a continuous coverage across the bidimensional space,
we make use of a cellular network, in which:
Using a cluster with reuse factor K,
Dip. Ingegneria dell’Informazione
University of Pisa, Pisa, Italy
Giacomo Bacci
Introduction to Wireless Communications
Introduction to modern wireless communications systems
28
Electronics and Communications Systems
Computer Eng. 2014-15
Area spectral efficiency (3/4)
Let us consider a hexagonal cell with radius R:
R
Using simple geometrical notions,
Dip. Ingegneria dell’Informazione
University of Pisa, Pisa, Italy
Giacomo Bacci
Introduction to Wireless Communications
Introduction to modern wireless communications systems
29
Electronics and Communications Systems
Computer Eng. 2014-15
Area spectral efficiency (4/4)
As a consequence,
The radius R represents a tradeoff between:
o
CapEx and OpEx costs (R as high as possible, to reduce the number of BTSs)
o
power consumption budget (R as low as possible, to save the energy
expenditure at the cell edge)
R ranges from a hundred meters (highly-populated urban
scenarios) to some kilometers (poorly-populated rural areas)
The minimum K must be chosen according to the selected technology
Dip. Ingegneria dell’Informazione
University of Pisa, Pisa, Italy
Giacomo Bacci
Introduction to Wireless Communications
Introduction to modern wireless communications systems
30
Electronics and Communications Systems
Computer Eng. 2014-15
Choosing the reuse factor K (1/6)
Although a low K is desirable to increase u, good system performance is
guaranteed by a minimum signal-to-interference-plus-noise ratio (SINR), with
the SINR defined as
useful signal
power
cellular systems are usually
interference-limited
multiple-access additive noise
interference (both
inter- and intra-cell)
To provide a good signal quality, we must ensure
SINR
, where the minimum
depends on the system parameters, such as:
o
modulation
o
bandwidth
o
channel coding
o
multiple access technique
Dip. Ingegneria dell’Informazione
University of Pisa, Pisa, Italy
Giacomo Bacci
Introduction to Wireless Communications
Introduction to modern wireless communications systems
31
Electronics and Communications Systems
Computer Eng. 2014-15
Choosing the reuse factor K (2/6)
How is
impacted by the network parameters?
Let us focus on the downlink, and let us
make some simplifying assumptions:
o
Each BTS is placed in the cell center
o
Both the BTSs and the MSs have
omnidirectional antenna patterns
o
Only the first interfering tier is considered
o
All BTSs use the same transmit power PT
o
All received powers can be computed using
where d is the distance between the transmitter and the receiver, n is the path-loss exponent,
and
is a scaling factor
Dip. Ingegneria dell’Informazione
University of Pisa, Pisa, Italy
Giacomo Bacci
Introduction to Wireless Communications
Introduction to modern wireless communications systems
32
Electronics and Communications Systems
Computer Eng. 2014-15
Choosing the reuse factor K (3/6)
The useful signal power received at the MS is
The interfering power caused by the k-th cochannel BTS is
where dk is the distance between the k-th
BTS and the MS
Dip. Ingegneria dell’Informazione
University of Pisa, Pisa, Italy
Giacomo Bacci
Introduction to Wireless Communications
Introduction to modern wireless communications systems
33
Electronics and Communications Systems
Computer Eng. 2014-15
Choosing the reuse factor K (4/6)
To determine dk, we need to compute the reuse distance D:
D
Using the Carnot theorem, we get
Dip. Ingegneria dell’Informazione
University of Pisa, Pisa, Italy
Giacomo Bacci
Introduction to Wireless Communications
Introduction to modern wireless communications systems
34
Electronics and Communications Systems
Computer Eng. 2014-15
Choosing the reuse factor K (5/6)
In practice, when
, we can make the approximation
and thus
In the worst-case scenario (when all interfering BTSs are active),
To sum up,
Dip. Ingegneria dell’Informazione
University of Pisa, Pisa, Italy
Giacomo Bacci
Introduction to Wireless Communications
Introduction to modern wireless communications systems
35
Electronics and Communications Systems
Computer Eng. 2014-15
Choosing the reuse factor K (6/6)
As an example, let’s consider n=4 (urban scenario):
We can then plug this value back to
of users
Dip. Ingegneria dell’Informazione
University of Pisa, Pisa, Italy
to compute the density
Giacomo Bacci
Introduction to Wireless Communications
Introduction to modern wireless communications systems
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Electronics and Communications Systems
Computer Eng. 2014-15
More on area spectral efficiency
Since the user density is given by
the service providers can fix K and u, so that the actual cell size (i.e., R)
depends on the density of population.
A more realistic BTS
deployment on an actual
urban scenarios can look like
the picture on your right side
Dip. Ingegneria dell’Informazione
University of Pisa, Pisa, Italy
Giacomo Bacci
Introduction to Wireless Communications
Introduction to modern wireless communications systems
37
Electronics and Communications Systems
Computer Eng. 2014-15
Interference reduction methods
There exist some additional techniques to increase the SINR. Just to mention a few
examples, we can use:
o
cell sectoring
o
frequency hopping
o
multiuser detection
Dip. Ingegneria dell’Informazione
University of Pisa, Pisa, Italy
Giacomo Bacci
Introduction to Wireless Communications
Introduction to modern wireless communications systems
38
Electronics and Communications Systems
Computer Eng. 2014-15
The wireless standards across time
GSM:
9.6 kb/s
EDGE:
384 kb/s
GPRS:
171.2 kb/s
UMTS:
2 Mb/s
300 ms
Dip. Ingegneria dell’Informazione
University of Pisa, Pisa, Italy
HSPA:
LTE-A:
5.76/14.4
100 Mb/s /
Mb/s
1 Gb/s
HSPA+:
22/168
Mb/s
150ms
15ms
Giacomo Bacci
Introduction to Wireless Communications
Introduction to modern wireless communications systems
39
Electronics and Communications Systems
Computer Eng. 2014-15
0G systems
o analog single-cell systems
o frequency modulation (FM)
o FDMA
o FDD
o channel spacing:
•
1940s: 120 kHz
•
1960s: 60 kHz
•
1970s: 25 kHz
Dip. Ingegneria dell’Informazione
University of Pisa, Pisa, Italy
Giacomo Bacci
Introduction to Wireless Communications
Introduction to modern wireless communications systems
40
Electronics and Communications Systems
Computer Eng. 2014-15
1G systems
1981:
Nordic
Mobile
1983: NMT
Telephone
TotalTACS
Access (NMT)
Communication
SystemRC2000
(TACS)
RTMS
C-450 TACS
TACS
1983:
AMPS
Advanced
Mobile Phone
System (AMPS)
1979:
NTT
Nippon Telegraph
and Telephone
(NTT)
AMPS
AMPS
AMPS
Dip. Ingegneria dell’Informazione
University of Pisa, Pisa, Italy
o
analog cellular systems
o
FM + FDMA + FDD
o
carrier frequencies: 450 MHz, 900 MHz
o
channel spacing: 12.5 ÷ 30 kHz
Giacomo Bacci
Introduction to Wireless Communications
Introduction to modern wireless communications systems
41
Electronics and Communications Systems
Computer Eng. 2014-15
2G systems
GSM
1991:
Global System for
GSM
Mobile
communications(
GSM)
1994:
IS-54
Interim
Standard
54cdmaOne
(IS-54,
1995:a.k.a.
DAMPS)
Interim Standard
95 (IS-95, a.k.a.
cdmaOne)
1993:
Pacific
PDCDigital
Cellular
(PDC)
GSM
GSM
GSM
GSM
GSM
o
digital cellular systems
o
GMSK+ FDMA/TDMA + FDD (GSM)
o
1997: GPRS (2.5G), to support packet switching
o
carrier frequencies: 900 MHz, 1800 MHz
o
2003: EDGE (2.75G), to support higher rates
o
channel spacing: 200 kHz (GSM)
Dip. Ingegneria dell’Informazione
University of Pisa, Pisa, Italy
Giacomo Bacci
Introduction to Wireless Communications
Introduction to modern wireless communications systems
42
Electronics and Communications Systems
Computer Eng. 2014-15
3G systems
2002:
Universal
UMTS Mobile
Telecommunications
System (UMTS)
2002:
3Gcdma2000
IS-95 (a.k.a.
cdma2000)
UMTS
2002:
FOMA
Freedom
Of Mobile
multimedia Access
(FOMA)
UMTS
UMTS
UMTS
o
digital cellular systems
o
QPSK+ CDMA + FDD/TDD
o
2006: HSPA (3.5G), to support asymmetric rates
o
carrier frequencies: 2 GHz
o
2008: HSPA+ (3.75G), to support higher rates
o
channel spacing: 5 MHz (UMTS/FOMA)
Dip. Ingegneria dell’Informazione
University of Pisa, Pisa, Italy
Giacomo Bacci
Introduction to Wireless Communications
Introduction to modern wireless communications systems
43
Electronics and Communications Systems
Computer Eng. 2014-15
4G systems
Dip. Ingegneria dell’Informazione
University of Pisa, Pisa, Italy
o
digital cellular systems
o
QAM + OFDMA + FDD/TDD
o
carrier frequencies: 2.5, 3.5, 5.8 GHz
o
channel spacing: 3.5 ÷ 20 MHz
Giacomo Bacci
Introduction to Wireless Communications
Introduction to modern wireless communications systems
44
Electronics and Communications Systems
Computer Eng. 2014-15
5G systems
The challenging requirements set by the IMT-2020 for 5G systems include:
o data rates:
•
1000× aggregate data rate increase
with respect to (wrt) 4G
•
100 Mb/s edge rate (100× wrt 4G)
o latency: 1 ms (10× wrt 4G)
o energy efficiency: 100× wrt 4G
Dip. Ingegneria dell’Informazione
University of Pisa, Pisa, Italy
Giacomo Bacci
Introduction to Wireless Communications
Introduction to modern wireless communications systems
45
Electronics and Communications Systems
Computer Eng. 2014-15
Generation shift highlights
o 0G  1G:
cellular deployment
o 1G  2G:
digital systems
o 2G  3G:
wideband signals (using CDMA)
o 3G  4G:
even wider bandwidths (using OFDMA)
o 4G  5G:
network densification, mmWave, massive
MIMO, full duplex?
Dip. Ingegneria dell’Informazione
University of Pisa, Pisa, Italy
Giacomo Bacci
Introduction to Wireless Communications
46
Electronics and Communications Systems
Computer Eng. 2014-15
Questions???
Thank you!
Giacomo Bacci
giacomo.bacci@iet.unipi.it
gbacci@princeton.edu
Dip. Ingegneria dell’Informazione
University of Pisa, Pisa, Italy
Giacomo Bacci
Introduction to Wireless Communications
Bibliography
47
Electronics and Communications Systems
Computer Eng. 2014-15
Bibliography
[01] T.S. Rappaport, Wireless Communications: Principles and Practice, 2nd ed.
Upper Saddle River, NJ: Prentice-Hall, 2002.
[02] A.J. Goldsmith, Wireless Communications. Cambridge, UK: Cambridge Univ.
Press, 2005.
[03] J.G. Proakis and M. Salehi, Digital Communications, 5th ed. New York, NY:
McGraw-Hill, 2007.
[04] A.F. Molisch, Wireless Communications. West Sussex, UK: J. Wiley & Sons,
2005.
[05] A. Mehrotra, GSM System Engineering. Boston, MA – London, UK: Artech
House, 1996.
[06] H. Holma and A. Toskala, WCDMA for UMTS, 2nd ed. West Sussex, UK: J. Wiley
& Sons, 2002.
[07] H. Holma and A. Toskala, HSDPA/HSUPA for UMTS. West Sussex, UK: J. Wiley &
Sons, 2006.
[08] H. Holma and A. Toskala, WCDMA for UMTS: HSPA Evolution and LTE. West
Sussex, UK: J. Wiley & Sons, 2010.
[09] International Telecommunications Union (ITU), ICT Facts and Figures, 2014.
Dip. Ingegneria dell’Informazione
University of Pisa, Pisa, Italy
Giacomo Bacci
Introduction to Wireless Communications