Chapter1 Part1 FoundationOfCellularCommunications V1 ForProfessors
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Transcript of Chapter1 Part1 FoundationOfCellularCommunications V1 ForProfessors
Foundation of Cellular
CommunicationsDr. Nishith Tripathi
Dr. Jeffrey Reed
This presentation is based on Chapter 1 of our book, “Cellular Communications- A Comprehensive and Practical Guide” published by Wiley/IEEE.Visit our website, “The Wireless University,” for additional information: http://www.thewirelessuniversity.com.
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ObjectivesAt the end of this module, you will be able to Give examples of communications
milestones Illustrate the cellular network architecture List examples of frequency bands used on
the air interface Describe the concept of frequency reuse Discuss how duplexing enables
simultaneous transmission and reception Summarize how multiple access techniques
enable users to share the same air interface Distinguish between the types of
interference
© 2015 by Tripathi, Reed, and IEEE/Wiley.
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Cellular Communications:
Motivation Look around- who does not have a cell phone? (!)
Mobile communications using a terrestrial network without any wires connected to the user device
Integral part of our lives: Phone calls, Short Message Service (SMS), emails, news, weather reports and warnings, photos, videos, and the list goes on…
Cell Phone: Ranked 2nd in the list of inventions that have changed the world (Internet: 1st)
© 2015 by Tripathi, Reed, and IEEE/Wiley. Book Reading: Section 1.1
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Cellular Communications:
Selected Milestones- I
© 2015 by Tripathi, Reed, and IEEE/Wiley.
1876 The telephone is invented.1887 Hertz showed that electromagnetic waves exist.1895 Marconi proves the feasibility of radio communications.1947 The cellular concept is born at Bell Labs. 1958 Jack Kilby invents an integrated circuit.1972 Bell Labs patents its mobile communications system.1973 Motorola introduces a small mobile phone, DynaTAC.1974 Vinton Cerf & Robert Kahn use the term Internet for the first time.1977 Cellular systems are launched in Chicago, Washington, D.C., and Baltimore1979 A microwave telephone system is installed in Saudi Arabia.
The first commercial cellular system is installed by NTT in Tokyo.1983 Advanced Mobile Phone System (AMPS), the world’s first standardized & fully automated commercial cellular service, is deployed in Chicago.
YEAR EVENT
Book Reading: Section 1.2
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Cellular Communications:
Selected Milestones- II Just ask those around you, “Who invented the
telephone?” More than likely, you will get the answer
“Alexander Graham Bell.” Well, Alexander Graham Bell and Elisha Gray
independently invented the telephone in 1876. Bell was awarded priority because he filed for a
patent a few hours earlier than Gray. What a difference a few hours can make…we all
remember Bell but only some of us would remember Gray.
Next time you have an idea, run (and do not walk!) and file the patent at the speed of light!!!
The Value of Time: A Lesson from the Communications History
© 2015 by Tripathi, Reed, and IEEE/Wiley. Book Reading: Section 1.2
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Generic Network Architecture
© 2015 by Tripathi, Reed, and IEEE/Wiley. Book Reading: Section 1.3.1
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Air Interface between Device and Network
The mobile device and the radio network use the radio frequency (RF) spectrum for wireless communications.
© 2015 by Tripathi, Reed, and IEEE/Wiley. Book Reading: Sections 1.2.2 and 1.3.2
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Heart of Cellular Communications: Frequency Reuse Cellular communications reuse the same frequency
in multiple cells, which enables the cellular network to serve numerous users simultaneously using scarce and precious RF spectrum.
© 2015 by Tripathi, Reed, and IEEE/Wiley. Book Reading: Section 1.3.3
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“A Hexagonal Cell” in Cellular Communications
Bell Labs considered three shapes for geometric representation of the cell: triangle, square, and hexagon.
The hexagon shape was eventually chosen because it allows the maximum number of mobiles to be connected to the Base Station (BS) in the center at the farthest distance from the BS.
The hexagon shape closely mimics the circular signal energy pattern radiating from the BS using an omnidirectional antenna.
The choice of the circular shape would have led to either significant overlap (and hence more cells to cover a given area) or areas with no coverage.
The hexagonal shape helps achieve an efficient layout for system deployment and analysis.
© 2015 by Tripathi, Reed, and IEEE/Wiley. Book Reading: Section 1.3.3
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Cells and Clusters
© 2015 by Tripathi, Reed, and IEEE/Wiley.
Cluster: A set of cells covering a geographic area that uses the target amount of RF spectrum.Different clusters use the same RF spectrum.
Different cells in a given cluster use different parts of the target RF spectrum.
Book Reading: Section 1.3.3
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Classification of Cells
Example classification of cells is shown below, but there are no strict or universally-accepted definitions.
© 2015 by Tripathi, Reed, and IEEE/Wiley. Book Reading: Section 1.3.3
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Frequency Reuse Factor & Cluster Size
Cluster size (K): Number of cells in the cluster Frequency Reuse Factor (FRF): Inverse of the
cluster size (indicates how frequently we use a given amount of spectrum)
Early deployments of second-generation (2G) cellular system called GSM used K=7.
Deployments of 3G UMTS and 4G LTE use K=1. The case of K=FRF=1 is termed “universal
frequency reuse,” where every cell in the system uses the same RF spectrum.
A higher FRF implies that more users can be supported due to availability of more radio resources but the amount of interference would be high compared to the case of a lower FRF.
© 2015 by Tripathi, Reed, and IEEE/Wiley. Book Reading: Section 1.3.3
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Desired Signal vs. Interference Carrier-to-Interference power (C/I) ratio
quantifies the relative strengths of desired signal and interference.
© 2015 by Tripathi, Reed, and IEEE/Wiley. Book Reading: Section 1.3.3
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(C/I) Ratio and Cluster Size (K)
S is the signal power measured at the MS, Rk is the co-channel interference
measured at the MS from the co-channel BS k, Nco−ch is the total number of co-channel BSs, K is the cluster size, and n is the propagation path loss exponent. Different technologies operate satisfactorily at different (C/I)
levels. For K=7 and n=4, (C/I) is 73.5 or 18.66 dB, which is more than
adequate for systems such as GSM. Technological advancements later enabled GSM to operate well for K=4 too.
© 2015 by Tripathi, Reed, and IEEE/Wiley.
See Pages 18 & 19 of the book for details.
Six first-tier of co-channel BSs
Book Reading: Section 1.3.3
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Sectorization
Focusing of energy in a limited geographic area as opposed to all directions (“Omni-directional”)
© 2015 by Tripathi, Reed, and IEEE/Wiley.
You are looking at the most commonly deployed network configuration on the PLANET!
Book Reading: Section 1.3.4
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Sectorization and (C/I) Sectorization reduces interference for
systems with FRF < 1 (i.e., Cluster size K > 1)
© 2015 by Tripathi, Reed, and IEEE/Wiley.
No Sectorization 120° Sectorization
Book Reading: Section 1.3.4
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Impact of Sectorization Sectorization has different impacts on different
multiple access technologies. Sectorization reduces interference for TDMA
systems and improves the quality of communications. If the interference reduction is significant to allow higher FRF (and smaller cluster size), sectorization increases capacity of TDMA systems.
Sectorization increases both interference and capacity for FRF=1 systems such as CDMA systems due to more frequent reuse of the spectrum compared to an omnidirectional CDMA system. For example, resources are used 3 times in 3 sectors of a cell with 120° sectorization instead of just 1 time in an omnidirectional cell.
© 2015 by Tripathi, Reed, and IEEE/Wiley.
TDMA: Time Division Multiple Access CDMA: Code Division Multiple Access
Book Reading: Section 1.3.4
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Review Exercise- IMatch the column entries (1-to-1 Mapping)
Column I Column II
1. Existence of electromagnetic waves
2. Feasibility of radio communications
3. Telephone
4. Cellular Concept
5. Internet
A. Bell Labs
B. Hertz
C. Bell (and Gray)
D. Marconi
E. Vinton Cerf & Robert Kahn
© 2015 by Tripathi, Reed, and IEEE/Wiley.
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Answers for Review Exercise- I
Match the column entries (1-to-1 Mapping)
Column I Column II
1. Existence of electromagnetic waves
2. Feasibility of radio communications
3. Telephone
4. Cellular Concept
5. Internet
A. Bell Labs
B. Hertz
C. Bell (and Gray)
D. Marconi
E. Vinton Cerf & Robert Kahn
© 2015 by Tripathi, Reed, and IEEE/Wiley.
23
Review Exercise- II1. Explain the concept of frequency reuse.2. True or False? Two different clusters use the
same RF spectrum. 3. True or False? Two cells in a given cluster use
different RF spectrum.4. Assume cluster size of K=7. The Frequency
Reuse Factor (FRF) = _______.5. Assume the Frequency Reuse Factor (FRF) = ¼.
Calculate (C/I) in dB if the propagation path loss exponent is 3.5 and the number of first-tier co-channel BSs is 6.
© 2015 by Tripathi, Reed, and IEEE/Wiley.
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Answers to Review Exercise- II
1. Frequency reuse: reuse the same RF spectrum in different geographic areas.
2. True. Two different clusters use the same RF spectrum.
3. True. Two cells in a given cluster use different RF spectrum.
4. Assume cluster size of K=7. The Frequency Reuse Factor (FRF) = 1/K=1/7.
5. Assume the Frequency Reuse Factor (FRF) = ¼. K= 1/FRF=4. (C/I)= ( )n/6= ( )3.5/6 =12.9 or 10*log10(12.9)= 11.1 dB.
© 2015 by Tripathi, Reed, and IEEE/Wiley.
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Duplexing Duplexing: “Simultaneous” transmission and
reception of signals on two communication links (uplink and downlink)
Two methods Frequency Division Duplex/Duplexing (FDD) Time Division Duplex/Duplexing (TDD)
Majority of cellular deployments use FDD.
© 2015 by Tripathi, Reed, and IEEE/Wiley.
Downlink (Forward Link)
Uplink(Reverse Link)
Book Reading: Section 1.4.1
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FDD vs. TDD
© 2015 by Tripathi, Reed, and IEEE/Wiley.
Tx: TransmissionRx: Reception
FDD Benefits+: Easier network deployment+: Typical spectrum is paired (both links)
TDD Benefits+: Simpler design of transceiver (fewer components)+: Cheaper spectrum (less operator interest)
Book Reading: Section 1.4.1
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Multiple Access Multiple Access: Ability of multiple users to
receive services simultaneously in a given cell or sector
Three Generic Methods Frequency Division Multiple Access (FDMA) Time Division Multiple Access (TDMA) Code Division Multiple Access (CDMA)
FDMA is used in first-generation cellular systems TDMA is used in 2G GSM CDMA is used in 2G IS-95 and 3G UMTS A variant of FDMA, Orthogonal Frequency
Division Multiple Access (OFDMA) , is used in LTE. OFDMA is covered in Chapter 15.
© 2015 by Tripathi, Reed, and IEEE/Wiley. Book Reading: Section 1.4.2
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Interference in Cellular Networks The receiver’s job of properly detecting the
desired signal is hampered by thermal noise and interference.
Two main types of interference Adjacent Channel Interference (ACI) Co-channel Interference (CCI)
© 2015 by Tripathi, Reed, and IEEE/Wiley. Book Reading: Section 1.5
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Adjacent Channel Interference (ACI)
ACI is addressed by means such as suitable radio channel assignments, filters, and transmit power management.© 2015 by Tripathi, Reed, and IEEE/Wiley. Book Reading: Section 1.5
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Co-channel Interference (CCI)
CCI is addressed by means such as separation of the co-channel cells (i.e., large enough cluster size K) and transmit power management.
© 2015 by Tripathi, Reed, and IEEE/Wiley. Book Reading: Section 1.5
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Points to Remember- I Examples of communications milestones include
invention of the telephone by Bell (and Gray!), discovery of the existence of electromagnetic signals by Hertz, the use of radio signals by Marconi, and the development of the cellular concept at Bell Labs.
The cellular network includes the radio access network, the core network(s), and the services network. The radio network has nodes such as BSs and BSC/RNCs and communicates with the mobile devices over the air interface. The core networks interface with the PSTN and the Internet to enable the consumer to access these networks.
Popular frequency bands for cellular communications in the U.S. include 700 MHz, 850 MHz cellular band, 1900 MHz PCS band, and 1.7 GHz/2.1 GHz AWS band.
© 2015 by Tripathi, Reed, and IEEE/Wiley.
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Points to Remember- II Frequency reuse across the geographical
regions is at the heart of cellular communications.
FDD and TDD are main duplexing methods, which support simultaneous (bi-directional) transmission and reception
FDMA, TDMA, CDMA, OFDMA multiple access techniques that enable multiple users to share the same air interface simultaneously
ACI occurs between the communication links that use adjacent radio channels, and CCI occurs between the communication links that are using the same radio channel.
© 2015 by Tripathi, Reed, and IEEE/Wiley.
40
Review Exercise- IIIFill in the blanks.1) The _______ {radio access network, core network,
services network} directly communicates with the mobile device over the air interface.
2) _____________ {Duplexing, Multiple access, Frequency reuse} involves the use of the same RF spectrum in different geographic areas.
3) ___________ {Duplexing, Multiple access, Sectorization} facilitates simultaneous (i.e., bi-directional) transmission and reception using time or frequency domain.
4) _________ {Duplexing, Multiple access, Sectorization} enables multiple users to share the same RF spectrum.
5) _________ {Duplexing, Multiple access, Sectorization} focuses energy in a narrow geographic area, leading to higher quality and/or capacity.
© 2015 by Tripathi, Reed, and IEEE/Wiley.
41
Answers to Review Exercise- IIIFill in the blanks.
1) The radio access network directly communicates with the mobile device over the air interface.
2) Frequency reuse involves the use of the same RF spectrum in different geographic areas.
3) Duplexing facilitates simultaneous (i.e., bi-directional) transmission and reception using time or frequency domain.
4) Multiple access enables multiple users to share the same RF spectrum.
5) Sectorization focuses energy in a narrow geographic area, leading to higher quality and/or capacity.
© 2015 by Tripathi, Reed, and IEEE/Wiley.